Details of a Researcher - MURAI Motohiko

Papers - MURAI Motohiko

about 291

Things to Consider for the Era of Floating Offshore Wind Turbine Utilization

Motohiko Murai

The 31st Ocean Engineering Symposium OES31-A0012 2025.3

Authorship：Lead author,　Last author,　Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

A study on changes of underwater behavior of Power Transmission Cable linked a floating

Takehiro Ueda, Motohiko Murai, Jialin Han

The 31st Ocean Engineering Symposium OES31-A0032 2025.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Experiments for Power Generation Assessment of a Point-Absorber Wave Energy Converter Based on a Small Scaled Model -2nd Report: Investigation of Control Strategy

Tatsuki Kawagishi, Ryusei Anzai,Motohiko Murai, Jialin Han, Qiao Li

The 31st Ocean Engineering Symposium OES31-A0018 2025.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Experiments for Power Generation Assessment of a Point-Absorber Wave Energy Converter Based on a Small Scaled Model -1st Report: Proposal and Validation of Experimental Methodology

Ryusei Anzai, Tatsuki Kawagishi, Motohiko Murai, Jialin Han, Qiao Li

The 31st Ocean Engineering Symposium OES31-A017 2025.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Study on the characteristics of floating platform with suspended section in waves for floating offshore wind turbine

Sora Yoneda, Motohiko Murai, Jialin Han

The 31st Ocean Engineering Symposium OES31-A010 2025.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

A Fundamental Study on the Potential of AI Prediction in Control Force Estimation to Maximize Power Generation of PA-WECs in Irregular Waves

Kawagishi Tatsuki, Haruta Hideki, Murai Motohiko

Journal of the Japan Society of Naval Architects and Ocean Engineers 40 ( 0 ) 1 - 12 2024.12 [Reviewed]

DOI CiNii Research

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

The Japanese government has established the target for the proportion of renewable energy in the electricity supply to 36–38 % by 2030. One of the ocean renewable energy sources is wave energy. This study focuses on a point-absorber wave energy converter (PA-WEC). Let irregular waves be expressed as the sum of regular wave components whose periodic components are “known”, then the control force required to maximize the average generated power can be solved theoretically. However, in real sea, the optimal control force cannot be identified instantaneously. This is because the periodic components of the irregular waves are “unknown”. Therefore, we have investigated that the optimal control force could be estimated instantaneously using artificial intelligence (AI) with only instantaneous input data. In this study, time-domain simulation is conducted while the control force estimated by AI is included in the motion equation each time step. We investigated the appropriate explanatory variables for training to increase the average generated power in regular and irregular waves. The average generated power was less likely to be negative using the heave velocity of the float as the explanatory variable, and the heave displacement made a large contribution in wave periods of 7.0–10.0 [s].

Discussion on Controls Reducing the Non-Operating Time of a Point-Absorber Wave Energy Converter

Kawagishi Tatsuki, Kakimoto Shinnosuke, Murai Motohiko, Han Jialin

Journal of the Japan Society of Naval Architects and Ocean Engineers 40 ( 0 ) 13 - 22 2024.12 [Reviewed]

DOI CiNii Research

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

The Japanese government has set a target for renewable energy to account for 36–38 % of the electricity supply by 2030. Wave energy is one of the ocean renewable energy sources. This study aims to enhance the workability of a point-absorber wave energy converter (PA-WEC). A PAWEC float has a physical limitation in its heave motion, and exceeding this limitation necessitates operation suspension to avoid damage. This study proposes a control strategy designed to reduce the non-operating time of a PA-WEC by deriving control force coefficients to keep heave motion within the limitation. Additionally, investigation on the effectiveness of switching control scenarios is also conducted. The results indicate that the workability of the PA-WEC is improved, with validation performed through case studies involving the heave limitation up to 3 meters.

RESEARCH ON THE IMPACT OF INTERMEDIATE SINKERS ON THE COMPACTNESS OF MOORING CABLE DEPLOYMENT

Murai Motohiko, Kondo Shuto, Jialin Han

Proc. of 1st Asia Pacific Conference on Offshore Wind Technology ( P0028 ) 2024.11

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (international conference proceedings) Publisher：The American Society of Mechanical Engineers (ASME) Joint Work

Switching DNN Control Strategy for Three Arrayed Point Absorber Wave Energy Converters

Tatsuki Kawagishi, Motohiko Murai

( 39 ) 895 - 905 2024.11

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A Study on Practical Control Methods Using DNN for Multi-Point-Absorber Wave Energy Converter

MIyuki Homma, Tatsuki Kawagishi, Motohiko Murai

( 39 ) 921 - 932 2024.11

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Study on Behavioral Change Assuming Weight Change due to Attachment of Organisms to Power Transmission Cables

Takehiro Ueda, Motohiko Murai, Jialin Han

1 - 4 2024.7

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Numerical Study on Cause and Characteristics of Low-Frequency Yaw Motion of a Slack-Moored FOWT

Kawagishi Tatsuki, Ota Makoto, Murai Motohiko, Han Jialin, Otaka Isami

Proceedings of the Third World Conference on Floating Solutions : WCFS 2023; 28–29 August, Tokyo, Japan 683 - 704 2024.6 [Reviewed]

CiNii Research

Language：English Publishing type：Research paper (scientific journal) Publisher：Springer Singapore Joint Work

Slack-moored floating offshore wind turbines (FOWTs) may experience low-frequency motions. In fact, in the Fukushima demonstration FOWT project, low-frequency motions were observed not only in storms but also in relatively calm sea states. Low-frequency motions could cause damages to the slack-mooring system and the power cables that transmit electricity generated by the turbine. Furthermore, the low-frequency motion in yaw could cause damages to the connection part of the nacelle and the tower. Suppressing low-frequency yaw motion requires an accurate understanding of the cause and the characteristics of the motion. To do so, numerical simulation of a slack-moored 15 MW FOWT has been conducted in two or three wave components. The results indicate that the low-frequency yaw motion and resonance could occur at various frequencies.

STUDY ON PRACTICAL CONTROL FORCE DECISION TO IMPROVE FACILITY UTILIZATION OF PA-WEC

Murai, M; Kakimoto, S; Kawagishi, T; Han, JL

PROCEEDINGS OF ASME 2024 43RD INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING, OMAE2024, VOL 4 2024.6 [Reviewed]

DOI Web of Science

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Joint Work

ON THE APPLICABILITY OF DNN-BASED MODELS TRAINED UNDER THE FIXED SPAR CONDITION TO CONTROL FORCE ESTIMATION OF A TLP MOORED PA-WEC

Kawagishi, T; Murai, M; Han, JL

2024.6 [Reviewed]

DOI Web of Science

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Joint Work

2024S-GS18-4 Applicability of Switch Algorithm of DNN-Based Trained Models to Control Force Estimation of a PA-WEC according to Wave Conditions

Kawagishi Tatsuki, Haruta Hideki, Murai Motohiko

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 38 ( 0 ) 589 - 596 2024.5

DOI CiNii Research

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

2024S-GS9-1 Experimental Research on Waves Characteristics between Aquaculture Cages and Spar Type Floating Offshore Wind Turbine

Bai Shenyi, Dong Shuchuang, Zhou Jinxin, Kitazawa Daisuke, Li Qiao, Murai Motohiko

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 38 ( 0 ) 443 - 447 2024.5

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

Review of recent research on offshore floating wind turbine collaborated with aquaculture cages

Shenyi Bai, Shuchuang Dong, Jinxin Zhou, Daisuke Kitazawa, Qiao Li, Motohiko Murai

Proc.of EAWOMEN2023 2024.1

Language：English Publishing type：Research paper (research society, symposium materials, etc.) Single Work

Consideration of changes in the hydrodynamic behavior of power transmission cables caused by biological attachment in waves

Takehiro Ueda, Motohiko Murai, Jialin Han

Proc.of EAWOMEN2023 2024.1

Language：English Publishing type：Research paper (research society, symposium materials, etc.) Single Work

Numerical Study on Cause and Characteristics of Low-Frequency Yaw Motion of a Slack-Moored FOWT

Kawagishi, T; Ota, M; Murai, M; Han, JL; Otaka, I

PROCEEDINGS OF THE THIRD WORLD CONFERENCE ON FLOATING SOLUTIONS, WCFS 2023 465 683 - 704 2024.1

DOI Web of Science

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

TLP型PA-WECの制御力推定に対するDNNによるスパー固定条件下での学習モデルの適用可能性

河岸立起, 村井基彦

日本船舶海洋工学会　講演論文集 ( 37 ) 785 - 792 2023.11

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：日本船舶海洋工学会 Joint Work

A Numerical Assessment of the Motion Response of Gravity-Based Structure While Towing in Different Drafts

Aritra Kumar Saha, Motohiko Murai, Jialin Han

日本船舶海洋工学会　講演論文集 ( 37 ) 475 - 481 2023.11

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：日本船舶海洋工学会 Joint Work

2023A-GS7-4 A Numerical Assessment of the Motion Response of Gravity-Based Structure While Towing in Different Drafts

Kumar Saha Aritra, Murai Motohiko, Han Jialin

日本船舶海洋工学会講演会論文集 37 ( 0 ) 475 - 481 2023.11

DOI CiNii Research

Language：English Publishing type：Research paper (scientific journal) Publisher：公益社団法人日本船舶海洋工学会 Joint Work

2023A-GS24-3 Applicability of DNN-based Learning Models under the Fixed Spar Condition to TLP-type PA-WEC Control Force Estimation

Kawagishi Tatsuki, Murai Motohiko

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 37 ( 0 ) 785 - 792 2023.11

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

Parametric Study of the Motion Response of the Gravity Based structure while Towing in Irregular Wave

Aritra Kumar Saha, Motohiko Murai, Jialin Han

The 30th Ocean Engineering Symposium OES20-A0018 2023.9

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Comprehensive Assessment From Offshore Wind Farms Based on the Index Assessment of energy transport from offshore wind farms to shore based on the comprehensive assessment Index III

Motohiko Murai, Kouhei Watanabe

The 30th Ocean Engineering Symposium OES20-A0024 2023.9

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

A Study of the Hydrodynamic Force Acting on the Hull of a Quad-maran during Self-rotation Motion

Jialin Han, Yasunori Nihei, Motohiko Murai

The 30th Ocean Engineering Symposium OES20-A0054 2023.9

Language：English Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Discussion on the capacity factor improvement of a PA-WEC based on a second-best control strategy

Shinnosuke Kakimoto, Tatsuki Kawagishi, Motohiko Murai, Jialin Han

The 30th Ocean Engineering Symposium OES20-A0051 2023.9

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Numerical simulation and evaluation of a DNN control model aimed to maximize the power generation of a PA-WEC

Tatsuki Kawagishi, Hideki Haruta, Motohiko Murai

The 30th Ocean Engineering Symposium OES20-A0019 2023.9

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Numerical Study on Cause and Characteristics of Low-frequency Yaw Motion of a Slack-moored FOWT

T. Kawagishi, M.Ohta, M.Murai

World Conference on Floating Solutions WCFS2023 Japan 2023.8 [Reviewed]

Authorship：Corresponding author Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A PROBLEM OF LONG PERIOD YAW MOTION OF AN ULTRA-LARGE FLOATING OFFSHORE WIND TURBINE AND ITS REDUCTION COUNTERMEASURE

Ota Makoto, Murai Motohiko, Otaka Isami, Kondo Shuto

Proc. of ASME 2023 42nd International Conference on Ocean, Offshore and Arctic Engineering ( 102321 ) 2023.6 [Reviewed]

Authorship：Corresponding author Language：English Publishing type：Research paper (international conference proceedings) Publisher：The American Society of Mechanical Engineers (ASME) Joint Work

In June 2022, the New Energy and Industrial Technology Development Organization (NEDO) of Japan created a 2 trillion yen "Green Innovation Fund" in June 2022. The fund will "develop technologies for wind turbines and floating structures that are suited to Asian weather and ocean conditions for floating wind turbines, which are expected to expand in the medium to long term, and demonstrate the integrated design of wind turbines, floating structures, cables, and other components with a cost level that can compete globally, leading to their social implementation".
The demonstration of floating wind turbines in actual sea areas in Japan has been conducted off coast of Fukushima Prefecture, off coast of Goto in Nagasaki Prefecture, and in the Hibikinada Sea in Fukuoka Prefecture, where technological accumulation and investigation toward commercialization are being conducted.
While the rated power generation capacity of these demonstration wind turbines is 2-7 MW, the rated power generation capacity envisioned in the above-mentioned fund is 15 MW, and the specifications for the design of floating structures to accommodate ultra-large wind turbines have become more stringent.
As a new issue, it is a relative yaw motion between a nacelle and a tower. The characteristic of such yaw motion has a long period yaw motion, and it is relatively slower than pitch or heave motion but relatively faster as its nacelle tracking motion for catching the wind direction. The effects of reduction of yaw motion and yaw motion speed by a virtual propulsion system attached to the floating structure were qualitatively and quantitatively investigated as countermeasures against the yaw motion problem.

NUMERICAL SIMULATION OF MOTION RESPONSES OF A CABIN-SUSPENDED CATAMARAN IN HEAD WAVES

Han Jialin, KItazawa Daisuke, Murai Motohiko

Proc. of ASME 2023 42nd International Conference on Ocean, Offshore and Arctic Engineering ( 103284 ) 2023.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Publisher：The American Society of Mechanical Engineers (ASME) Joint Work

In this study, the motion responses of a suspension catamaran in head waves are presented using numerical calculation and
experimental validation. The cabin-suspended ship has 9 degreeof-freedom, as the heave, pitch, and roll motion of the cabin can
be separated from that of the twin-hull through a suspension unit.
The suspension unit consists of four compression springs and
linkages to guide the motion. The hydrodynamic coefficients and
the wave exciting force/moments of the twin-hull were calculated
using a potential flow solver named OrcaWave. A method was
proposed to approximate the wave exciting force/moments at an
advancing speed using the wave exciting force/moments at zero
speed. The study analyzed the motion response of the ship at
different damping coefficients and spring constants. The results
show that motion reduction of the cabin by tuning only the spring
constant and damping coefficient is limited, and different pairs of
spring constant and damping coefficient would be needed for different wave encounter frequencies. The study provides valuable
insights for the design of suspension ships to reduce motion responses in head waves

数値シミュレーション上で出現する複数の波周期の最⼩公倍周期で振動する長周期動揺

河岸立起, 村井基彦

日本船舶海洋工学会　講演論文集 2023.6

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：日本船舶海洋工学会 Joint Work

2023S-GS10-4 Low-frequency Motions Varying with Least Common Multiple Periods of Wave Periods Appearing in Numerical Simulation

Kawagishi Tatsuki, Murai Motohiko

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 36 ( 0 ) 495 - 501 2023.6

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

NUMERICAL SIMULATION OF MOTION RESPONSES OF A CABIN-SUSPENDED CATAMARAN IN HEAD WAVES

Han, JL; Kitazawa, D; Murai, M

PROCEEDINGS OF ASME 2023 42ND INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE & ARCTIC ENGINEERING, OMAE2023, VOL 7 2023 [Reviewed]

Web of Science

Language：English Publishing type：Research paper (scientific journal) Joint Work

単機 PA-WEC の発電量最大化を目的とした DNN 制御モデルを組み込んだ数値シミュレーションとその評価

村井基彦

第30回海洋工学シンポジウム 1 2023

CiNii Research

Authorship：Lead author Language：The in addition, foreign language Publishing type：Research paper (scientific journal) Single Work

PA-WEC の設備利用率の向上を目的としたセカンドベストな制御に関する検討

村井基彦, 韓佳琳

第30回海洋工学シンポジウム 1 2023

CiNii Research

Language：The in addition, foreign language Publishing type：Research paper (scientific journal) Joint Work

2方向2成分規則波中における緩係留FOWTの大振幅長周期動揺に対する波向の感度解析

河岸立起, 村井基彦

日本船舶海洋工学会　講演論文集 2022.11

Authorship：Last author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：日本船舶海洋工学会 Joint Work

浮体の大型化，特に鉛直方向への高さの伸張は，風車の発電機材が搭載されるナセル部分の高高度化を伴う。このとき，ナセル部やブレード部分に対する浮体運動の影響は，特にpitchやrollに伴う傾斜運動に連動する水平方向加速度が，大型化に比例して大きくなることから，数MW級の浮体よりも寧ろ，実傾斜角の抑制が求められる可能性がある。その実傾斜角の抑制には様々な手法が考えられるが，本研究では物体が軸に対して回転運動をするときに生じるジャイロ効果および軸心保持効果について着目し，その効果による抑制の可能性について検討をする。一般にコマの軸心保持効果などの例は剛体の回転運動を想定しているが，原理的には円環中を一様に流れる環状流でも生じるはずである。この場合，円環自体は回転する必要は無く，環状流の速度などを変更できる場合，浮体運動の抑制についての能動的制御力を得られる可能性も考えられる。そこで，本論文ではその基礎的な研究として，環状流によるジャイロ効果および軸心保持効果が浮体運動にどのような影響を与えるかについて数値的な検討を行う。

浮体式風力発電設備の長周期Yaw問題及び対策に関する一考察

太田真, 村井基彦, 大高武己, 近藤柊斗

日本船舶海洋工学会　講演論文集 2022.11

Authorship：Last author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：日本船舶海洋工学会 Joint Work

2022A-GS14-1 Sensitivity Analysis of Wave Direction for Large Slow Drift Motion of a Soft Moored FOWT in Bidirectional Bichromatic Wave

Kawagishi Tatsuki, Murai Motohiko

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 35 ( 0 ) 535 - 542 2022.11

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

2022A-GS14-2 A Study on Long-period Yaw Problem and Countermeasures for Floating Offshore Wind Turbine

Ota Makoto, Murai Motohiko, Otaka Isami, Kondo Shuto

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 35 ( 0 ) 543 - 547 2022.11

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

Committee V.6: Ocean Space Utilization

Sebastian Schreier; Felice Arena; Harry Bingham; Nuno Fonseca; Zhiqiang Hu; Debabrata Karmakar; Eka … Show more authors

Volume 2 380 - 444 2022.11

DOI

Language：English Publishing type：Research paper (international conference proceedings) Single Work

Engineering Possibility Studies of a Novel Cylinder-Type FOWT Using Torus Structure with Annular Flow

Liu Xiaolei, Murai Motohiko

ENERGIES 15 ( 13 ) 2022.7 [Reviewed]

DOI Web of Science

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A Basic Study on the Effect of Deep Learning to Determine the Control Force to Maximize the Power Generation of PA-WEC in Irregular Waves

Motohiko MURAI, Sho SAKAMOTO

Proc. of ASME 2022 41st International Conference on Ocean, Offshore and Arctic Engineering ( OMAE2022-785 ) 2022.6 [Reviewed]

DOI

Authorship：Lead author Language：English Publishing type：Research paper (international conference proceedings) Publisher：The American Society of Mechanical Engineers (ASME) Joint Work

Marine renewable energy is expected as an alternative energy source to fossil fuel. Wave energy is one of the marine renewable energy. The subject of this paper is maximizing power generation by a Point Absorber Wave Energy Converters (PA-WEC) in irregular waves. In the previous study on maximizing the power generation by one of the authors, it has been shown the theoretical solution of the time-domain control force in irregular waves which are defined by superposing regular waves components. That is, if the PA-WEC can simultaneously understand the irregular incident waves as multi certain regular wave components, it can be decided the control force for maximizing the power generation. On the other hand, it is quite difficult to predict precisely and simultaneously the component of coming irregular waves to a PA-WEC installed in the ocean.

In the recent, Artificial Intelligence (AI) and machine learning technology progress rapidly. In the machine learning system, because reading huge data with the relation among them, sometimes it finds out the path connecting A matter and B matter without visible theoretical or logical relations. In this case, the quality of a training data is quite important for accuracy or certainty of the efficient prediction.

In this paper, we examine the possibility of applying AI to predict and decide the control force for maximizing the power generation of the PA-WEC in irregular waves. Some of the results given by the AI has been quite close to the theoretical answer in irregular waves. Through the examination, we investigate and discuss the best or the effective combination of training data sets which are based on the theoretical situation in known waves.

A Fundamental Study on the Potential of AI Prediction in Control Force Estimation to Maximize Power Generation of PA-WECs in Irregular Waves

Murai Motohiko, Sakamoto Sho

Journal of the Japan Society of Naval Architects and Ocean Engineers 35 ( 0 ) 55 - 64 2022.6 [Reviewed]

DOI CiNii Research

Authorship：Lead author,　Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

Marine renewable energy is expected to replace fossil fuels as an energy source. Wave energy is one of these marine renewable energy sources. A floating point-absorber wave energy converter (PA-WEC) is a wave energy generation system that is expected to be utilized because of its low mechanical loss and lack of wave directionality. Many studies have been conducted to maximize the power generation of PA-WECs, and theoretical solutions have been presented for the maximum expected value of power generation and its control in regular waves and known irregular waves. However, the components of the incoming irregular waves are not known when the system is actually installed on the ocean. Therefore, in this study, a basic investigation of the possibility of applying AI to predict and determine the control power to maximize the power generation of PA-WEC is conducted. In this investigation, we have narrowed down the focus to the possibility of estimating the optimal control power from time to time, and investigated and discussed the effective combination of training data sets based on theoretical situations in known waves.

Other Link： https://www.jstage.jst.go.jp/article/jjasnaoe/35/0/35_55/_article/-char/ja/

Nurturing and Creating the Next Generation of Marine Industry, the Key to Realizing a Decarbonized Society

Motohiko MURAI

The 29th Ocean Engineering Symposium OES29-078 2022.3

Authorship：Lead author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Single Work

This paper introduces the second proposal of “Appeal for realizing integrated management of marine and coastal　areas: Policy proposal for the 4th Basic Plan of Ocean Policy”, which was published by the Japan Society of　Ocean Policy (JSOP) and Japanese Association for Coastal Zone Studies (JACZS). Of the five major recommendations contained in the report, this presentation will discuss the purpose of "Proposal 4: Nurture and Create Next-Generation Marine Industries as the Key to Realizing a Decarbonized Society" and the awareness of the issues that emerged during the discussion.

Basic Study on Offshore Connection of Rectangular Floating Structures in Block Method for Floating Wind Turbines

Shuto KONDO, Motohiko MURAI

The 29th Ocean Engineering Symposium OES29-062 2022.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Offshore wind power generation is expanding all over the world, especially in Europe, and is a method of power generation that will expand in Japan as we work toward becoming carbon neutral by 2050. In the construction of offshore wind turbines, the block construction method, rather than the conventional integrated construction method, allows for more efficient transportation and short-term assembly. In this study, I will investigate the possibility of constructing a floating structure consisting of several units, which are then jointed together at sea to form an offshore wind turbine.

Verification of Power Generation Variation of Twin-engine Vertical Axis Wind Turbine Considering Interference between Floating Motion and Wind

Natsumi SATO, Motohiko MURAI

The 29th Ocean Engineering Symposium OES29-037 2022.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Among floating wind turbines, vertical-axis turbines have a low center of gravity, which is considered to be a great advantage for floating wind turbines. In particular, the twin-engine type, in which two wind turbines rotate in opposite directions, has the advantage that the rotational reaction force of the wind turbines on the floating structure is canceled out and the power generation efficiency is increased due to wind interference under crosswind conditions. However, there have been few studies on the effect of the relative distance between two wind turbines, the wind direction, and the relative wind speed due to the motion in waves on the power generation efficiency of twin-engine wind turbines.
In this study, we propose a method of estimating the power generation by coupling the wind interference with the motion of a floating structure using OrcaFlex and QBlade, and investigate the effects of changes in wind speed and distance between the wind turbines on the floating structure.

Influence of internal resistance and thrust coefficient in a linear generator installed on a PA-WEC on power generation

Shinnosuke KAKIMOTO, Motohiko MURAI

The 29th Ocean Engineering Symposium OES29-031 2022.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

A point absorber wave energy converter (PA-WEC) with a linear generator can generate electricity efficiently because the motion of the floating body and the drive of the generator are integrated. In order to maximize the power generation, the optimum control force and the distance between the floats in the array arrangement have been studied, but there are few studies that focus on the internal resistance and thrust coefficient in the linear generator. In this study, the internal resistance and the thrust coefficient used in the calculation of the power generation are varied, and the value of them that maximizes the power generation of PA-WEC is investigated.

A studyon tilt angle control by changing the position of the center of gravity to make a large tilt state assuming a spar type floating wind turbine

Mitsuki Yamaguchi, Motohiko MURAI

The 29th Ocean Engineering Symposium OES29-081 2022.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Single Work

In recent years, offshore wind power is noticed at the growing demand for renewable energy. Then, "super-enlarged" is in progress of the ocean wind turbine. When we examined a large-sized spar type wind turbine that is easy to operate in the water depth, the maintenance of wind turbine has many problems. For example, when the maintenance is performed in the port, it is shallow for wind turbine’s floating body, and it is costly for towing. And, when the maintenance is performed offshore, the upper nacelle part is at a high elevation so working maintenance is requiring special devices such as large cranes. When focusing on maintenance work by local work, I thought that it could be easily maintained using conventional equipment without requiring high-place work if the wind turbine itself can be tilted on the sea level. In this study, we aim to control the center of gravity and intentionally change the stability of the floating body to control to any tilt angle with a constant spinning force, and we consider the feasibility by numerical calculation on the large tilt problem in that case.

Hydroelastic response of a floating airport with damping under severe sea conditions

Hideki Haruta, Motohiko MURAI

The 29th Ocean Engineering Symposium OES29-033 2022.3

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Floating airport are considered feasible from a technical point of view, but they have not been realized. In order to ensure the safety and function of the airport, it is necessary to consider ways to reduce the motion of the floating structure. In order to do this, we will add a damping effect to some of the partial floats that make up the floating structure, so that the motion can be suppressed even under severe marine conditions, and the energy can be used to generate electricity. In this paper, we investigate the difference of the response and the energy obtained by changing the arrangement of the damping effect floating part in a very large floating body.

A BASIC STUDY ON THE EFFECT OF DEEP LEARNING TO DETERMINE THE CONTROL FORCE TO MAXIMIZE THE POWER GENERATION OF PA-WEC IN IRREGULAR WAVES

Murai, M; Sakamoto, S

PROCEEDINGS OF ASME 2022 41ST INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE & ARCTIC ENGINEERING, OMAE2022, VOL 4 2022 [Reviewed]

Web of Science

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Joint Work

THE FUNDAMENTAL RESEARCH ON AI PREDICTION AND DETERMINATION OF CONTROL FORCE FOR MAXIMIZING THE POWER GENERATION OF PA-WEC IN IRREGULAR WAVES

Motohiko MURAI, Sho SAKAMOTO

Proc. of ASME 2021 40th International Conference on Ocean, Offshore and Arctic Engineering 5 2021.10 [Reviewed]

DOI

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：The American Society of Mechanical Engineers (ASME) Joint Work

Possibility of Reducing Spar-Type FOWT Hydrodynamic Response Using a Torus Structure With Annular Flow

Motohiko Murai, Xiaolei Liu

Proc. ASME. OMAE2021, Volume 5: Ocean Space Utilization V005T 2021.10 [Reviewed]

DOI

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：The American Society of Mechanical Engineers (ASME) Joint Work

Gyroscopic motion is considered as an appropriate approach to suppress the shaking motion of rigid bodies. Its spatial orientation is also used to make gyro compasses in the marine industry. In this paper, the floating offshore wind turbine (FOWT) was designed based on potential theory and gyroscopic effect and rotational axis retention effect were also considered, so that FOWT could obtain better hydrodynamic response. However, gyroscopic motion was generated through an annular flow in the internal torus instead of rigid body rotation. The scale of torus and the angular velocity of the annular flow were the design parameters that this article was eager to understand obviously. By vast quantity of calculations, the suitable range of design parameters was obtained.

Estimation of Maximum Bending Moment at FPSO Bow Considering Slamming in External Turret Mooring

Ishihara Yuki, Kato Shunji, Murai Motohiko, Nakajima Yasuharu

Journal of the Japan Society of Naval Architects and Ocean Engineers 33 ( 0 ) 87 - 96 2021.9 [Reviewed]

DOI CiNii Research

Authorship：Last author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

The external turret system is widely used for mooring of Floating Production, Storage and Offloading system (FPSO). Slamming is one of important issues which should be considered for designing FPSOs because FPSOs must stay in the same area even if those are under harsh conditions such as a storm. In response to cases of accidents caused by slamming, such as Schiehallion, a series of research projects were conducted in Europe, which proposed that the simplified estimation method of maximum slam force; however, it was too simplified to be used for detailed design.In this paper, we present the extreme value estimation of maximum bending moment including the slamming effect at the connection between the FPSO bow and the external turret lever. The foundation of the estimation method is based on the time-domain simulation by using the simulation model which was validated by comparing the results of the simulations with those of model tests. The simulation model was validated through comparison between model test results and the simulations. Two estimation methods for the expected value of 3 hour-maximum bending moment using the validated simulation model were investigated; one was the way of averaging maxima in multiple simulations, and another was due to extreme value analyses by four kinds of methods. As a result, the first method required more than 30 simulations; for the second method, the generalized Pareto distribution was the most suitable for extreme value analysis.

Other Link： https://ci.nii.ac.jp/naid/130008081001

A novel conceptual design of a dynamically positioned floating wind turbine

Xu Shengwen, Murai Motohiko, Wang Xuefeng, Takahashi Kensaku

OCEAN ENGINEERING 221 2021.2 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Joint Work

Currently, all floating wind turbines served on the sea are positioned by the mooring system. A novel conceptual design of using the dynamic positioning system (DPS) to position the floating wind turbine is proposed in this paper. Certain benefit aspects of the proposed conceptual design are elaborated. A time domain simulation for the designed floating wind turbine is conducted to demonstrate its effectiveness. It is obtained from the results that approximately 1/2 of the generated energy is utilized by the DPS to keep the floating wind turbine positioned if current forces are not considered, while the ratio becomes 4/5 if current load effects are taken into account. Thus, the proposed conceptual design is demonstrated to be feasible in the view of conservation of energy. The impact of several primary design variables, such as the diameter of the wind turbine rotor, the diameter of the thruster and the wind speed, on the power ratio is specifically investigated. To make the conceptual design more convincible, several representative operational situations of the floating wind turbine in its lifetime are analyzed. It can be found that the situations that the consumed power is larger than the generated power can be effectively tackled by the stored hydrogen converted in the far long period of operation of the wind turbine in rated wind speed. Considering the proposed concept has particular benefits that cannot be replaced by conventional moored floating wind turbines, further research on the novel concept is warranted.
(英訳):Currently, all floating wind turbines served on the sea are positioned by the mooring system. A novel conceptual design of using the dynamic positioning system (DPS) to position the floating wind turbine is proposed in this paper. Certain benefit aspects of the proposed conceptual design are elaborated. A time domain simulation for the designed floating wind turbine is conducted to demonstrate its effectiveness. It is obtained from the results that approximately 1/2 of the generated energy is utilized by the DPS to keep the floating wind turbine positioned if current forces are not considered, while the ratio becomes 4/5 if current load effects are taken into account. Thus, the proposed conceptual design is demonstrated to be feasible in the view of conservation of energy. The impact of several primary design variables, such as the diameter of the wind turbine rotor, the diameter of the thruster and the wind speed, on the power ratio is specifically investigated. To make the conceptual design more convincible, several representative operational situations of the floating wind turbine in its lifetime are analyzed. It can be found that the situations that the consumed power is larger than the generated power can be effectively tackled by the stored hydrogen converted in the far long period of operation of the wind turbine in rated wind speed. Considering the proposed concept has particular benefits that cannot be replaced by conventional moored floating wind turbines, further research on the novel concept is warranted.

Study on Power Generation of Single Point Absorber Wave Energy Converters (PA-WECs) and Arrays of PA-WECs

Motohiko Murai, Qiao Li, Junki Funada

Journal of Renewable Energy 164 1121 - 1132 2021.2 [Reviewed]

DOI Web of Science

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Joint Work

The effects of humanity's carbon footprint deserve attention and remediation. The ocean can provide an abundant source of renewable energy instead of fossil fuels in the form of wave energy. However, wave energy collection needs to be comparable in terms of cost and efficiency to be considered a viable alternative. Point Absorber Wave Energy Converter (PA-WEC) is one method of capitalizing on the ocean's wave energy. Past research provides methods for optimizing control force parameters for single PA-WECs. This paper provides methods for optimizing control force parameters for arrays of PA-WECs; optimization considers factors such as radiation hydrodynamic interactions, diffraction hydrodynamic interactions, array arrangements, and wave incident angles. In section 2, we outline the steps to determining optimal control forces. In section 3, we present numerical simulations of PA-WECs and compared the results between single PA-WEC systems and arrayed PA-WEC systems.

THE FUNDAMENTAL RESEARCH ON AI PREDICTION AND DETERMINATION OF CONTROL FORCE FOR MAXIMIZING THE POWER GENERATION OF PA-WEC IN IRREGULAR WAVES

Murai Motohiko, Sakamoto Sho

PROCEEDINGS OF ASME 2021 40TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING (OMAE2021), VOL 5 2021 [Reviewed]

Web of Science

Authorship：Lead author Language：English Publishing type：Research paper (international conference proceedings) Joint Work

POSSIBILITY OF REDUCING SPAR-TYPE FOWT HYDRODYNAMIC RESPONSE USING A TORUS STRUCTURE WITH ANNULAR FLOW

Murai Motohiko, Xiaolei Liu

PROCEEDINGS OF ASME 2021 40TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING (OMAE2021), VOL 5 2021 [Reviewed]

Web of Science

Authorship：Lead author Language：English Publishing type：Research paper (international conference proceedings) Joint Work

The Evaluation of Seakeeping of a Cylinder-shaped Floating Structure with Gyroscopic Motion Based on the Potential Fluid Theory

Motohiko Murai,Xiaolei Liu

2020.11

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

2020A-GS11-3 The Evaluation of Seakeeping of a Cylinder-shaped Floating Structure with Gyroscopic Motion Based on the Potential Fluid Theory

Murai Motohiko, Liu Xiaolei

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 31 ( 0 ) 295 - 301 2020.11

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

Short-Time Wave Force Prediction and Control Strategy for a Point-Absorber WEC

Qiao Li, Motohiko Murai, Daisuke Kitazawa

Journal of Ocean Engineering 218 2020.11 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Joint Work

There are several numerical analyses for solving the hydrodynamic responses of a floating body in the time domain. Most of these provide a theoretical solution in the given irregular waves. However, the solution can be obtained only if accurate irregular waves represented by the wave spectrum are provided. Because we consider actual operation, we know that it is difficult to detect accurate irregular waves instantaneously as accuracy is required in most time domain analyses for the control force feedback to the system. This paper proposes a new method to predict the practical wave force from the displacement of waves of a floating body in the time domain analysis almost instantaneously. This method, that can be applied to predict forces in the wave energy converter with a linear electric generator, helps us to select the control force for higher conversion of electric power. We confirm the algorithm and examine its effectiveness used statistical database of real sea waves. We showed the limits of the range of application by ACL control algorithm and hybrid control algorithm under ideal conditions when considering physical motion restrictions and output restrictions that are always present in actual equipment.

Study on scale effect of fluid force coefficient in water tank experiment simulating OWC type wave power generator

Motohiko MURAI, Masaki Fujioka, Takuya Nagashima

The 28th Ocean Engineering Symposium OES28 - 078 2020.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

In recent years, ocean renewable energy has attracted attention from the viewpoint of energy diversification.
Japan has one of the world's largest exclusive economic zones, and its effective utilization is expected. In this study, we conducted experiments on the effects of the nozzle opening ratio, internal air volume and internal water level fluctuation of the OWC type wave power generator. However, the influence of the hydrodynamic force coefficient on the scale change of the OWC wave power generator has not been confirmed. In this study, we focused on the scale effect of the OWC type wave power generator model, and performed a forced oscillation test in an experimental water tank. For the model, we used 1/30, 1/60, and 1/120 of the size compared to the actual model, and compared the results to examine the scale effect. As a result of the analysis, it was found that the hydrodynamic coefficient was different for each of the scales, and the knowledge about the scale effect of the hydrodynamic coefficient in the OWC type wave power generator was obtained.

Study on scale effect of fluid force coefficient in water tank experiment simulating OWC type wave power generator

Motohiko MURAI, Sho Sakamoto, Takumi Nakajima, Takero Yoshida, Qiao Li, Daisuke Kitazawa

The 28th Ocean Engineering Symposium OES28 - 056 2020.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

One of the major issues in the introduction of offshore wind power generation is coordination with fishermen
who use the ocean until now as so far. Currently, as a solution to the problem, there is an idea that the introduction of offshore wind turbines in cooperation with local fishermen will lead to the revitalization of local fisheries and aim to collaborate fishing. Here we treat "Floating offshore wind power generation cooperative with fisheries" and investigate the motion of a floating offshore wind turbine with a net of aquaculture cages. In this study, the dynamic characteristics of the net were examined by conducting experiments first, and based on the characteristics, a numerical analysis was performed on the motion of the floating body when the aquaculture net was attached to the floating offshore wind turbine.

HOW THE HYDRODYNAMIC RESPONSE OF PA-WECS' ARRAY UNDER MAXIMIZING THE POWER GENERATION BY ITS ARRANGEMENT AND CONTROL FORCE CHANGE?

Motohiko Murai, Junki Funada, Li. Qiao

OMAE2020 1 - 8 2020.8 [Reviewed]

DOI

Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

As for the maximization of the power generation of the array, the authors have proposed the arrangement concept of the array increasing the power generation potential and the way of the determination of the individual control force on each WEC for maximizing the power generation of the array. In the research, we also examined the sensitivity of the arrangement and control force. As a result, there is a best interval among the WECs for each number of the array of WECs and wave frequency.
In this paper, we examine how to change the whole hydrodynamic motion which is 6 times of the number of arrayed WECs by the hydrodynamic interaction among them under controlled for maximizing the arrayed WECs power generation.

EXPERIMENTAL STUDY OF SLAM FORCES ON EXTERNAL TURRETS WITH DIFFERENT TOP ANGLES

Yuki Ishihara , Motohiko Murai, So Nakanishi, Shunji Kato, Yasuharu Nakajima

OMAE2020 1 - 8 2020.8 [Reviewed]

DOI

Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

The Eexternal turret is widely used for mooring FPSOs. However, external turrets can be exposed to slamming and it leads to generate FPSO's whipping. To analyze the fatigue strength of the FPSOs, probability distributions of slam forces acting when slamming happens are necessary. In this study, we examined the probability distribution of peak slam forces, the effect of the top angle on slam forces, and the difference of two types (fixed and oscillator-mounted) tests. For three turret models with different top angle (180°, 160°, and 140°), two types of model tests were carried out.

Research on how the arrangement of arrayed PA-WECs influences to their electric power generation

Funada Junki, Murai Motohiko, Li Qiao

Journal of the Japan Society of Naval Architects and Ocean Engineers 31 ( 0 ) 59 - 71 2020.7 [Reviewed]

DOI CiNii Research

Authorship：Corresponding author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

This paper describes the relationship between an arrangement of Point Absorber Wave Energy Converter (PA-WEC) and power generation. In an array of PA-WECs, complex hydrodynamic interaction occurs. The interaction affects both increase and decrease of wave power density among PA-WECs. When aiming to maximize the generated electric power, it is necessary to appropriately select the control force of the generator in consideration of the positive effect of hydrodynamic interaction. This paper presents a numerical solution of the control force parameter for maximizing the generated electric power of the multi PA-WECs, taking into account the hydrodynamic interaction among PA-WECs in both diffraction and radiation problems. Then, numerical studies are carried based on the proposed method. From these results, the effects of the distance between PA-WECs and the number of PA-WECs in a linear arrangement on the generated electric power are discussed. In addition, the sensitivity of the arrangement of PA-WECs to the generated electric power is considered.

Other Link： https://ci.nii.ac.jp/naid/130007905617

Consideration on how to decide the optimal control force of a PA-WEC for maximizing its electric power generation in irregular waves

Murai Motohiko, Iikura Hibiki

Journal of the Japan Society of Naval Architects and Ocean Engineers 31 ( 0 ) 73 - 81 2020.7 [Reviewed]

DOI CiNii Research

Authorship：Lead author Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

This paper describes an analytical solution on the optimal control force for maximizing power generation of Point Absorber Wave Energy Converter (PA-WEC) in irregular waves. The response and optimum control force on a PA-WEC in regular waves achiving a maximum electric power generation has been already developed taking into account the energy loss in the electric circuit in frequency domain and in regular waves. On the other hand, in irregular waves, to obtain the best control force in timely has been difficult, because the control force act on the instantaneous power generation rate and the whole later heaving response of the PA-WEC. This means that whether the decided control force is the best or not is difficult to judge. Actually, in the previous researches, the researchers applied a lot of way to decide the control force. But the generated electric power in irregular waves ratio to the expected generated power obtained from the wave spectrum is up to almost from 0.3 to 0.7. This paper presents an analytical solution of the control force parameter for maximizing the generated electric power in irregular waves on a PA-WEC in time domain. Then, numerical studies are carried based on the proposed method. From these results, it is shown that the proposed method achieves the generated electric power to the expected generated power obtained from the wave spectrum

Other Link： https://ci.nii.ac.jp/naid/130007905611

The Study on the Optimal Control Force for a Point Absorber Wave Energy Converter in Irregular Waves

Motohiko Murai, Hibiki Iikura

Conference paper of the Japan Society of Naval Architects and Ocean Engineers 30 269 - 275 2020.6

Language：Japanese Publishing type：Research paper (scientific journal) Publisher： The Japan Society of Naval Architects and Ocean Engineers Single Work

This paper presents an analytical solution of the control force parameter for maximizing the generated electric power in irregular waves on a PA-WEC in time domain. Then, numerical studies are carried based on the proposed method. From these results, it is shown that the proposed method achieves the generated electric power to the expected generated power obtained from the wave spectrum.

第2章　海洋教育啓発活動の事例

村井基彦

日本船舶海洋工学会誌　KANRIN（咸臨） 89 ( 0 ) 17 - 20 2020.3

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：公益社団法人日本船舶海洋工学会 Single Work

2020S-GS4-1 The Study on the Optimal Control Force for a Point Absorber Wave Energy Converter in Irregular Waves

Murai Motohiko, Iikura Hibiki

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers 30 ( 0 ) 269 - 275 2020

DOI CiNii Research

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

HOW THE HYDRODYNAMIC RESPONSE OF PA-WECS' ARRAY UNDER MAXIMIZING THE POWER GENERATION BY ITS ARRANGEMENT AND CONTROL FORCE CHANGE?

Murai, M; Funada, J; Li, Q

PROCEEDINGS OF THE ASME 39TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING, OMAE2020, VOL 5 2020 [Reviewed]

Web of Science

Authorship：Lead author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Joint Work

EXPERIMENTAL STUDY OF SLAM FORCES ON EXTERNAL TURRETS WITH DIFFERENT TOP ANGLES

Ishihara, Y; Murai, M; Nakanishi, S; Kato, S; Nakajima, Y

PROCEEDINGS OF THE ASME 39TH INTERNATIONAL CONFERENCE ON OCEAN, OFFSHORE AND ARCTIC ENGINEERING, OMAE2020, VOL 6A 2020 [Reviewed]

Web of Science

Language：English Publishing type：Research paper (scientific journal) Joint Work

Trend and consideration on the changes in population density of short neck clam at “Umino-Kouen"

Motohiko Murai

Journal of Japanese Association for Coastal Zone Studies 32 ( 3 ) 2019.12 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japanese Association for Coastal Zone Studies Single Work

“Umino-Kouen" is an artificial beach park located south side of Yokohama city and faced to Tokyo-Bay. It is well known as a shio-higari (seashell digging) spot and a few 10 thousands people visit per day in the best season for enjoying shio-higari. The park doesn't control and manage directly the number of short neck clam (Ruditapes philippinarum, Japanese little neck) which is main target of shio-higari, even though the many other shio-higari sites control the number of shot neck clam with releasing juvenile shellfish. So, the number or density of short neck clam in the area is changed naturally. But it is easy to imagine that the “shio-higari" done by over than 10,000 visitors par day influences the number of the short neck clam living in the area.
We started a monthly observation of the existence amount of Japanese little neck in May 2003 for surveying the relation of the number of short neck clam and the shio-higari. In this paper, we introduce the observation data in these 15 years, then we analyze and discuss the trend and periodicity of the change based on the observed data. As a result, we confirmed the followings: From the macro view point the number of the short neck clam in Umino-Kouen keeps a certain level without radical decrease. There are periodical changes of some years in the number of the short neck clam. And the period is different by the size of the short neck clam.

The study on a trend of the appropriate control forces for maximizing the power generation on lined up multi PA-WECs

Junki Funada, Motohiko Murai, Qiao Li

EAWOMEN2 2019 2019.10

Language：English Publishing type：Research paper (scientific journal) Joint Work

Marine renewable energy is expected as an alternative energy source to fossil fuel. Wave energy is one of the marine renewable energy. The object of this paper is an array of Point Absorber Wave Energy Converters (PA-WECs). In the array, complex hydrodynamic interaction occurs among WECs. The interaction affects both increase and decrease of wave power density among WECs. When we aim to maximize the generated electric power, it is necessary to appropriately select the control force of the generator in consideration of the positive effect of hydrodynamic interaction. In the past research, as for a selection of the appropriate control force of a single PA-WEC, the analytical solution is shown within linear system. In this paper, we show the numerical solution of the control force parameter for maximizing the generated electric power of the multi WECs taking the hydrodynamic interaction among the WECs both in diffraction and radiation problem into account. Then we carried out the numerical examination based on proposed method and discussed the effect of the distance between WECs in the linear arrangement on the generated electric power. We also discussed the effect of the number of WEC.

A SIMPLE PREDICTION METHOD OF IRREGULAR WAVES FOR CHOOSING A CONTROL PARAMETER OF A WAVE ENERGY CONVERTER SYSTEM

Motohiko MURAI, Qiao Li

SNAK 2019 Annual Autumn Meeting 2019.10

Language：English Publishing type：Research paper (scientific journal) Publisher：Society of Naval Architects of Korea Joint Work

Study on Motion Response of a Floating Offshore Turbines' Unit with OWC

Motohiko Murai, Ryohei Mochiduki

PRADS2019 2019.9 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

Recently the problem of the global warming rises an importance of using the re-newable energy. Wind energy is recognized as one of the key sustainable energy source. In fact, there are rapidly increase the number of a wind power plant in land and now the power plant extends to offshore area. Therefore, a floating off-shore wind turbine (FOWT) system which can be applied to various sea area is attracted. One of the problem is that FOWT must oscillate in waves. Generally, the FOWT system is horizontal axis system as same as those in land, however, the motion of FOWT in waves causes relatively large acceleration at a nacelle. And it is concerned that the acceleration disturbs the maintenance work.
Because the vertical axis type FOWT has a nacelle, which many of the mechani-cal system is in, set near the water level though its efficiency in aerodynamics has disadvantage, it is possible that the maintenance work will be easier. The authors has proposed a concept of twin vertical axis type FOWT. In our past experiment we have confirmed that the twin system can cancel a gyro moments induced by each rotation and the suitable distance of the twin turbine increases the rotational speed of the turbine than the single turbine. On the other hand, the shape of the underwater structure making the needed buoyancy and reducing the passive ex-ternal hydrodynamic force has relatively small stability inducing acceptable but relatively large pitch motion in waves. So, to reduce the pitch motion while gen-erating the electrical energy, we propose a new concept of a floating offshore twin vertical axis turbines system with oscillated water columns (OWCs). The OWC is one of the type of wave energy converter (WEC).

海の公園に於けるアサリ資源量の経年変化について

村井基彦

日本沿岸域学会2019 年度全国大会 2019.7

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：日本沿岸域学会2019 年度全国大会 Single Work

2003年4月から海の公園を対象域として、二枚貝類の現存量をほぼ毎月調査してきた。その間、海の公園では，2003年に青潮の被害が発生し、2005年3月以降には横浜市により一人あたりアサリの採捕量の2kg制限等を含む新たな条例が施行されるなどの政策的な変化もあった。本論文では、この15年間の観測データの中から当該海域の殻長毎の平均個体数密度の変動について第1段階としての解析と検討の結果を示す。

STUDY ON THE GENERATED POWER CHANGES BY THE RELATION BETWEEN AN ARRANGEMENT OF AN ARRAY OF POINT ABSORBER TYPE WECS AND AN INCIDENT WAVE ANGLE

Motohiko Murai, Li. Qiao, Junki Funada

OMAE2019 1 - 8 2019.6 [Reviewed]

DOI Web of Science

Authorship：Lead author Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

Using marine renewable energy can contribute providing the energy instead of using fossil fuel. There are some types of marine renewable energy. Wave energy is one of these and no one doubts its vast potential once they glance the sea. The object of this paper is an array of Point Absorber Wave Energy Converters (PA-WECs). In the array, complex hydrodynamic interactions among the array will occur. The interaction influences the wave power density among the array both increase and decrease. When we consider the maximization of generated electric power of the array, the suitable choice of the control force of the generator taken into a positive effect of the hydrodynamic interactions is the key. In the past research, as for a detection of the suitable control force of a single PA-WEC it has been shown the analytical solution within linear system. In this paper, we show the numerical solution of the control force parameter for maximizing the generated electric power of the array taking the hydrodynamic interaction among the array both in diffraction and radiation problem into account. Then we carried out the numerical examination and discussed the good arrangement of an array in waves based on the proposed method and an effect of the choice of the best and better control force.

CONTROL STRATEGY FOR A POINT-ABSORBER WAVE ENERGY CONVERTER

Li. Qiao, M.Murai

OMAE2019 1 - 6 2019.6 [Reviewed]

DOI Web of Science

Authorship：Last author Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

Linear driving wave energy converter (WEC) system need to
control the electric generator to obtain more power generation. Electric power is consumed by control, but it is possible to control the natural period of the floating motion. By resonating the movement of the float part with wave, it is possible to obtain the power generation more than the control power consumption, the total power generation performance will be improved.
In this study, to ensure the WEC safety and performance for various wave condition, especially high wave height, the electrical control algorithms are changed for different wave condition. A control strategy is proposed for various wave condition considering the control force limitation and motion amplitude limitation. Basis on the control strategy, the range of operation by electric control is estimated. In addition, by estimating the expected value of power generation in the set sea,
the setting parameters of the WEC can be discussed according to the wave situation.

ENVIRONMENTAL REGENERATION FOR A SMALL-SCALE BEACH “HEDA-MIHAMA PROJECT"

Shigeru Tabeta, Ken Okamoto, Takayoshi Kato, Rikito Hisamatsu, Hiroaki Muto, Akinori Hino, Motohiko … Show more authors

OMAE2019 1 - 6 2019.6 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

In 1950's and 1960's, Mihama beach in Heda Bay located on western coast of Izu peninsular had been famous for the richness in shell fauna, for example, about 400 species including rare ones were collected. In 2000's, however, the impoverishment of ecosystem function has become considerable, which led us to project the investigation on the origin and restoration. The authors carried out field survey in 2007-2008 and found that the impoverishment of Mihama is derived not from surface water but from the benthic environment.
The suitability indices (SI) for each environmental factors were calculated by using the results of hydrodynamic and sediment transport simulations. By using the developed scheme, total habitat unit was evaluated for the proposed regeneration plans and compared to that without countermeasures. It was predicted that the removal of the piers will improve the habitat condition in the target site. Based on the proposal by the authors, a water pathway under the pier was built in 2009. The authors conducted field survey again in 2014 and confirmed that the benthic environment has been improved.

EXPERIMENTAL STUDY ON BUBBLE SIZE MEASUREMENT FOR DEVELOPMENT OF SEAFLOOR MASSIVE SULFIDES

S.Imai, Y. Nakajima, M.Murai

OMAE2019 ( 6 ) 1 - 6 2019.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

Seafloor Massive Sulfides have been expected to be future
mineral resources. To promote the development of Seafloor
Massive Sulfides, Seafloor Mineral Processing, a method of extracting valuable minerals from the ores on deep seafloor using flotation to reduce the lifting cost of ores from the seafloor to the sea surface, was proposed. Bubble size measurement by image analysis was carried out by the procedure established at the first phase. While the process of bubble generation at the high pressures was similar to that at the atmospheric pressure, the bubble size was decreased as the pressure rose. The result implies there is a strong correlation between the pressure and the bubble size.

SThe Basic Study oSlam Forces Acting on External Turrets -The Effect of Deadrise Angle-

Y. Ishihara, S. Kato, K.Yukawa, M.Murai

Proc. of annual conference of JASNAOE 28 351 - 356 2019.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Study on Electrical Power for Multiple Linear Wave Energy Converter Considering the Interaction Effect

Li Qiao, Murai Motohiko, Kuwada Syu

Journal of Energies 11 ( 11 ) 2964 2018.11 [Reviewed]

DOI Web of Science

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：MDPI, open access Journal Joint Work

A linear electrical generator can be used on wave energy converter for converting the kinetic energy of a floating structure to the electricity. A wave farm consists of multiple wave energy converters which equipped in a sea area. In the present paper, a numerical model is proposed considering not only the interference effect in the multiple floating structures, but also the controlling force of each linear electrical generator. In particular, the copper losses in the electrical generator is taken into account, when the electrical power is computed. In a case study, the heaving motions and electrical powers of the multiple wave energy converters are estimated in the straight arrangement and triangle arrangement. In addition, the average electrical power is analyzed in different distances of the floating structures. The aim of this paper is to clear the relationship between the interference effect and electric powers from wave energy converters. This will be useful for deciding the arrangement of multiple wave energy converters.

RESPONSE CHARACTERISTICS TO WINDS AND WAVES ABOUT FLOATING STRUCTURE SUPPORTING HIGH RISE BUILDING

HASEBE Masanobu, TAKEUCHI Masaki, ONO Shuhei, YOSHIDA Ikuo, SHIMADA Kenji, NAKASHIMA Hideo, MURAI M … Show more authors

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering) 74 ( 2 ) I_958 - I_963 2018.9 [Reviewed]

DOI

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：Japan Society of Civil Engineers Joint Work

 For this paper, hydraulic model experiments and numerical computations were conducted to perform a basic verification of the technology related to new conceptual floating structure supporting high rise building. It was confirmed that the mooring system could withstand winds and waves with a 200-year return period in Tokyo Bay. However, it was also found that resonance might occur at around 3.0 Hz between the building and the floating body. In particular, this resonance could amplify the horizontal oscillation at the top of the building. In addition, around this resonance frequency, there could be large spectral components of shear stress and bending moment at the base of the building. It is important to consider these phenomena carefully in the structural design. There is also the problem of establishing a way to evaluate the resonance effect for the structural design.

Other Link： https://ci.nii.ac.jp/naid/130007482524

海洋未来都市構想の技術検証 ― その１計画概要 ―

吉田郁夫, 三浦大作, 依田謙人, 内田加苗, 本島禎二, 嶋田健司, 中島秀雄, 小野秀平, 長谷部雅伸, 椚隆, 竹内真幸, 村井基彦

日本建築学会　学術講演梗概集 2018.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：日本建築学会 Joint Work

大都市沿岸部での浮体式高層建築技術の確立を目標とし, 湾内における浮体式高層建築の技術検証に必要なモデルプランの設計をおこない，社会インフラとしての共用期間・再現期間を設定し，環境条件を算出した．これを元に技術検証をおこない第三者による認証を得た．

海洋未来都市構想の技術検証 ― その５高層浮体建築の構造設計と居住性 ―

椚隆, 正藤倫宏, 平戸達朗, 中島秀雄, 小野秀平, 兼光知巳, 長谷部雅伸, 吉田郁夫, 竹内真幸, 村井基彦

日本建築学会　学術講演梗概集 2018.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：日本建築学会 Joint Work

本稿では筆者らがAIP認証を取得した下部構造の上に構築される高層部 24 階建の浮体構造物に関して，高層部の構造設計の概要とその居住性について検討を行い， O‛Hanlon の嘔吐率，日本建築学会の居住性能評価指針により実験結果を評価した上で，振動抑制の対策について述べた．さらに，今後の浮体建築の居住性評価について，そのあり方に付言した．

海洋未来都市構想の技術検証 ― その 4 浮体式人工地盤の構造設計 ―

小野秀平, 中島浩世, 内田加苗, 本島禎二, 長谷部雅伸, 吉田郁夫, 椚隆, 竹内真幸, 村井基彦

日本建築学会　学術講演梗概集 2018.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：日本建築学会 Joint Work

本稿では筆者らがAIP認証を取得した浮体構造物を対象とし、海洋未来都市構想の基本設計について，コンクリート製大型浮体構造物の設計例を示しつつ，動揺解析と連動した時刻歴応答解析や，コンクリートの非線形性を考慮した解析への発展が望まれること，全体動揺解析では，暴風や波浪の周波数応答のピークと，浮体構造物の固有振動数が近い場合は，大きな共振応答が生じること，固有振動数は，浮体の剛性および重量，係留ドルフィンのバネ値が大きく関わることから，部材の要求性能を満足するだけではなく，全体応答を低減する部材決定のフローを確立することが重要であることを示した。

海洋未来都市構想の技術検証 ― その３強風・波浪中の動揺に関する実験と解析 ―

長谷部雅伸, 兼光知巳, 小野秀平, 嶋田健司, 椚隆, 吉田郁夫, 竹内真幸, 村井基彦

日本建築学会　学術講演梗概集 2018.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：日本建築学会 Joint Work

本稿では筆者らがAIP認証を取得した浮体構造物1)を対象とし、東京湾での荒天時を想定した強風・波浪中における動揺応答特性について、水理模型実験と数値解析による検討を行う。水理模型実験では、タワー部分の弾性運動の効果を考慮しその影響を検討し、東京湾での強風・波浪を想定した実験と解析より浮体とタワーの共振影響を定量的に把握した上で構造安全性を確認した。

海洋未来都市構想の技術検証 ― その２汎用 3 次元 CAD を利用した復原力算定 ―

三浦大作, 依田謙人, 小野秀平, 長谷部雅伸, 吉田郁夫, 椚隆, 竹内真幸, 村井基彦

日本建築学会　学術講演梗概集 2018.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：日本建築学会 Joint Work

本稿では，今回認証を得た海洋都市未来構想 1）の基本設計における復原力算出と判定について検討を行い, ，初期平衡状態及び，非損傷時，損傷時の算定結果を示し，判定基準に適合することを説明した．

Development of a Practical Prediction Method of Wave Force for a Wave Energy Converter

Li Qiao, Murai Motohiko

Journal of the Japan Society of Naval Architects and Ocean Engineers 27 ( 0 ) 125 - 132 2018.8 [Reviewed]

DOI

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineers Joint Work

There are a lot of numerical analysis for solving hydrodynamic responses of a floating body in time domain. Most of them can give a theoretical solution in given irregular waves. It means, however, that the solution can be obtained only if the accurate irregular waves represented by the wave spectrum should be given. As we consider the actual operation, we know it is difficult to detect the accurate irregular wave's instantaneously as needed accuracy in the most of the time domain analysis for feed backing the control force to the system. This paper proposes a new method to predict the practical wave force from the displacement of waves at a floating body in time domain analysis almost instantaneously. The method, which can apply to predicting forces in wave energy converter with linear electric generator, helps us to choose the control force for convert more electric power in irregular waves. We confirm the algorithm and examine its effectiveness.

Other Link： https://ci.nii.ac.jp/naid/130007439666

Ocean Future City Concept GREEN FLOAT Part1, Outline of Plan

Ikuo YOSHIDA, Masaki TAKEUCHI, Takashi KUNUGI, Tomohiro BESSHO, Shuhei ONO, Masanobu HASEBE, Motohi … Show more authors

The 27th Ocean Engineering Symposium OES27 - 034 2018.8

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Since the Industrial Revolution, global population growth problems and problems of sea level rise accompanying the increase in CO2 emissions are occurring. As a solution to this, floating cities that use seas occupying 70% of the earth's surface are drawing attention. Housing with a floating structure has already been realized, but large-scale buildings and cities have not been realized. A high-rise building with a floating structure is planned. This aims for a new global environmental city. The location is on the Pacific Ocean just below the equator. A city is designed where 50,000 people can live. There are not only residences, but also cultivated land that can be self-sufficient. Furthermore, emphasis is placed on hydrophilicity and an artificial shallow is set. Concrete is used for this floating structure. Regarding high-rise buildings with floating structures, we will step down from small ones. Initially, we will conduct a technical verification of a high-rise building with a small floating structure that assumes the port of the suburbs of the big city as the planned site, and plan to obtain a review by a third party.

OWC 付き浮体式双発垂直軸型風車ユニットの浮体運動特性について

村井基彦, 望月良平

第２７回海洋工学シンポジウム OES27 - 082 2018.8

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：日本海洋工学会・日本船舶海洋工学会 Joint Work

本研究では浮体式双発垂直軸型風車と OWC 型発電装置の特徴を活かし、OWC を浮体式双発垂直軸型風車の浮体部に搭載する。具体的には OWC を浮体部に取り付け、OWC による復原力やダンパー効果を浮体部に働かせることによって浮体式双発垂直軸型風車の課題であった浮体のPitch 運動を抑制し、風車の安全性を高める狙いがある。またOWC を浮体に取り付けることによって、OWC の課題であった波の入射による内部水面の上下動ではなく浮体の Heaveと Pitch 運動による揺れで内部水面を相対的に上下動させることが出来るため、OWC による発電の効率化も狙えると考えた。

Ocean Future City Concept GREEN FLOAT PART2, A Study on Vibration of High-Rise Floating Building

Takashi KUNUGI, Ikuo YOSHIDA, Shuhei ONO, Tomohiro BESSHO, Masanobu HASEBE, Tatsuro HIRATO, Kenji S … Show more authors

The 27th Ocean Engineering Symposium OES27 - 035 2018.8

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Floating high-rise buildings have the characteristic of vibrating easily due to wave and wind. As an evaluation method, O'Hanlon proposed vomiting ratio to evaluate the vibration quantitatively, that is practically used.
Architectural Institute of Japan has established "Guidelines for the evaluation of habitability to building vibration". The purpose of the guideline is to evaluate the performance of habitability of buildings based on the sensing probability of usual vibration. In this paper, authors clarify the vibration characteristics of the floating high-rise building GREEN FLOAT2 based on the experimental result and make an observation on evaluation methods referring to the research findings until now.

SSTUDY ON A TIME DOMAIN PREDICTION METHOD FOR WAVE FORCE -APPLICATION FOR A POINT-ABSORBER WEC-

Li. Qiao, M.Murai

OMAE2018 ( 6 ) 1 - 8 2018.6 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (scientific journal) Publisher：ASME Joint Work

There are a lot of numerical analysis for solving hydrodynamic responses of a floating body in the time domain. Most of them can give a theoretical solution in given irregular waves. It means, however, that the solution can be obtained only if the accurate irregular waves represented by the wave spectrum should be given. As we consider the actual operation, we know it is difficult to detect the accurate irregular waves instantaneously as needed accuracy in the most of the time domain analysis for feed backing the control force to the system.
This paper proposes a new method to predict the practical
wave force from the displacement of waves at a floating body in time domain analysis almost instantaneously. The method, that can apply to predict forces in wave energy converter with linear electric generator, helps us to choose the control force for convert more electric power in irregular waves. We confirm the algorithm and examine its effectiveness.

On prediction method of optimized control parameters for an array of point absorber type Wave Energy Converters in waves

Murai Motohiko, Li Qiao, Funada Junki, Shigetome Hasuki

2018 OCEANS - MTS/IEEE KOBE TECHNO-OCEANS (OTO) 2018.5 [Reviewed]

DOI Web of Science

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：IEEE Oceanic Engineering Society Joint Work

Using marine renewable energy can contribute providing the energy instead of using fossil fuel. There are some types of marine renewable energy. Wave energy is one of these and no one doubts its vast potential once they glance the sea. The object of this paper is an array of Point Absorber Wave Energy Converters (PA-WECs). In the array, hydrodynamic interactions among the array will be increase. When we consider the maximization of generated electric power of the array, the suitable choice of the control force of the generator is the key. In the past research, as for the detection of the suitable control force of the single PA-WEC it has been shown the analytical solution within linear system. In this paper, we show the analytical solution of the control force parameter for maximizing the generated electric power of the array taking the hydrodynamic interaction among the array both in diffraction and radiation problem into account. Then we carried out the numerical examination and discussed the validation of the proposed formulation and the good arrangement of an array in waves based on the proposed formulation.

Study on Bubble Size Measurement for Development of Seafloor Massive Sulfides

Seira Imai, Shunji Kato, Yasuharu Nakajima, Motohiko Murai

Proc. of annual conference of JASNAOE 26 139 - 142 2018.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Study on Design and Safety Evaluation of Tower-Yoke Mooring Systems in the Use of FSRU

Yuko Ishida, Shunji Kato, Kazuhiro Yukawa, Motohiko Murai

Proc. of annual conference of JASNAOE 25 503 - 508 2017.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

Outline of the Brazil-Japan Collaborative Education Program on Naval Architecture and Offshore Engineering

Toru Sato, Georgios Fytianos,Murilo Augusto Vaz, Armand Hideki Shinohara, Tomoaki Ustunomiya,Motohi … Show more authors

Proc. of annual conference of JASNAOE 25 53 - 55 2017.11

Language：English Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Strategy of a Control Algorism for a Point Absorber Type WEC in Wave Conditions

Qiao LI, Motohiko Murai

Proc. of annual conference of JASNAOE 25 43 - 46 2017.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Study on Hydrodynamic Interaction of Arrayed Point Absorber WECs with Control Force

Haruyuki Ikemasu, Motohiko Murai, Qiao LI

Proc. of annual conference of JASNAOE 25 509 - 514 2017.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Propose of Prediction Method for Wave Force and its Application for Wave Energy Converter

Qiao Li, Motohiko Murai

17PR002/0000 - 0313 2017.11

DOI

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：SICE Joint Work

There are a lot of numerical analysis for solving hydrodynamic responses of a floating body in time domain. Most of them can give a theoretical solution in given irregular waves. It means, however, that the solution can be obtained only if the accurate irregular waves represented by the wave spectrum should be given. As we consider the actual operation, we know it is difficult to detect the accurate irregular waves instantaneously as needed ac-curacy in the most of the time domain analysis for feed backing the control force to the system.
This paper proposes a new method to predict the practical wave force from the displacement of waves at a float-ing body in time domain analysis almost instantaneously. The method, that can apply to predicting forces in wave energy converter with linear electric generator, helps us to choose the control force for convert more elec-tric power in irregular waves. We confirm the algorithm and examine its effectiveness.

Other Link： https://www.jstage.jst.go.jp/article/jacc/60/0/60_313/_article/-char/ja/

A Propose of Prediction Method for Wave Force and A strategy of a control algorithm for a point absorber type WEC

Qiao Li, Motohiko Murai

2017.9

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Joint Work

for efficiently transferring energy. The control force from PTO system is decided wave condition especially the wave force. In this paper, a new method is proposed for predicting the wave force from the displacement of a sea wave. The method that can be used to PTO system, help us to choose the control force for convert more electric power from wave. In addition, a control strategy of PTO system basic on the statistical database of waves are discussed considering the motion limitation of floating structure and the extreme limit of control force. Here, the target sea area is KAMAISHI bay in the northeast of Japan, and the target model is propose by "NEDO Linear Drive Wave Energy Converter".

The design of an unit-type floating disaster prevention base and the proposal of its usage along a timeline of the restoration

Anna Odake, Motohiko Murai

2017.7

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

THE INFLUENCE OF AN ARRANGEMENT OF AN ARRAY OF SEMI-SUBMERSIBLE TYPE FOWTS TO THEIR HYDRODYNAMIC RESPONSES

Motohiko Murai, Kensaku Takahashi

Proc.ASME 2017 36th International Conference on Ocean, Offshore and Arctic Engineering OMAE2017 ( 6 ) 1 - 8 2017.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

The progress of the global warming is one of our key issue should be overcome in the 21st century. We should balance the energy consumption and reduction of exhausting greenhouse effect gas. The wind energy is expected as one of the key technology for utilizing renewable energy. It is said that as for the efficiency of the electric generation, it is better the wider wind farm with larger wind mill. But, as the land space for the extensive wind farm is quite limited, it will be a candidate how to use the vast ocean space for human activity. So, the construction of an offshore wind farm is one of the solution now. To extend the wind farm widely in the ocean the floating wind turbine system becomes an essential technology. Under such background, there are many researches on the floating wind turbine in waves and in wind. And hydrodynamic response of them in waves is one of the major topics. Many of the researches on the hydrodynamic response, however, deal with the motion of a single floating wind turbine. This report deals with the hydrodynamic response of a wind farm which is consisted of semi-submersible wind turbines. In addition, the investigation of how does the arrangement of the array impact on the hydrodynamic response including the motion of the nacelle is also reported. In the last the example of the change of the expected efficiency of the generator by change of the array arrangement in each sea area around Japan are shown.

NUMERICAL STUDY ON EXPECTED ELECTRICAL POWER OF LINEAR WAVE ENERGY CONVERTER IN ARRANGEMENT CONDITION

Qiao Li, Motohiko Murai, Syu Kuwada

Proc.ASME2017, Int. Conf. OMAE2017 OMAE2017 ( 6 ) 1 - 8 2017.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

A linear electrical generator is a kind of device which can be used to wave energy converter, for directly converting mechanical energy of a floating structure into electrical energy. A wave farm consists of multiple wave energy converters which equipped in a sea area. In the present paper, a numerical model is proposed considering the interference effect in the multiple floating structures, and the controlling force of each linear electrical generator. Especially, the copper losses in the electrical generator is taken into account, when the electrical power is computed. At first, the controlling force coefficients are discussed to find their physical effects on heaving motion. In a case study, the heaving motions and electrical powers of the three floating structures are estimated in the straight arrangement and triangle arrangement. And the average electrical power is analyzed in different distances of the floating structures.

Viscous Drift Force on a Semisubmersible in Irregular Waves

Ryo Fukushima, Shunji Kato, Kazuhiro Yukawa, Motohiko Murai

Conf. Proc. The Japan Society of Naval Architects and Ocean Engineers ( 24 ) 665 - 668 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

Minimization of pivoting performance due to wave drift force for a single point mooring FOWT

Motohiko Murai, Naoki Makimura

Conf. Proc. The Japan Society of Naval Architects and Ocean Engineers ( 24 ) 775 - 779 2017.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

Experimental study on Interaction of Air Amount, Air Amount at Nozzle, Nozzle Opening Ratio and Water Surface Variation in Column with Semi-Submersible Nozzle

Hisaki Yoshioka, Motohiko Murai

Proc. of the 26th Ocean Engineering Symposium OES26 - 038 2017.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：J F O E S & J A S N A O E Joint Work

Oscillating water column(OWC) wave power devices is one of the most typical wave power generating system.
However, there are few studies on the influence of the nozzle opening ratio and the internal air amount on the water surface fluctuation with respect to the internal water surface fluctuation of the vibration water column type wave power generator.
In this research, we focus on the nozzle opening ratio and the internal air quantity, and we examined the influence of them on the basis of experiment and numerical calculation.

Survey Report on Trend of Marine Renewable Energy Tank Test

Motohiko Murai, Tokomi Ikoma, Yasutaka Imai, Shinichiro Hirabayashi, Yukitaka Yasuzawa

Proc. of the 26th Ocean Engineering Symposium OES26 - 055 2017.3

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：J F O E S & J A S N A O E Joint Work

To achieve the commercial operation in the actual sea the evaluation of the performance of the system through a tank test is an important step. However, using a conventional water tank constructed for evaluation of the ship performance sometimes face difficulty. For example, keeping the ratio of a draft of a model and a depth of a
water tank, generating the fluid velocity keeping the scale ratio, incorporating a tiny PTO system in a scale model and so on. Therefore it becomes important that to establish the procedure of the experiment in the tank by
accumulating the experience and the theoretical consideration.
This paper reports the recent trend of the tank test on the marine renewable energy focusing into wave energy and marine current energy through the literature research.

A Study on Electric Power for Multiple Linear Wave Energy Converter Considering the Controlling Force and Interaction Effect

Syu Kuwada, Motohiko Murai, Qiao LI

Conference Proceedings The Japan Society of Naval Architects and Ocean Engineers ( 23 ) 613 - 618 2016.11

Language：Japanese Publishing type：Research paper (scientific journal) Publisher： The Japan Society of Naval Architects and Ocean Engineers Joint Work

Recently years, a lot of renewable energy systems are being introduced positively in the developed countries. Of course, Japan surrounded by the vast ocean which has enormous energy potential expects to develop the system leading the energy potential. Linear type wave energy converter(WEC) is one of the strong candidates of WEC, because of its simple and efficient system arrangement.
In this paper, we describe how do the copper loss in the WEC and hydrodynamic interaction among multi-WECs influence the power generator.

Heave motion and Electric Power of Multiple Cylinders for Wave Energy Converter Considering the Controlling Force

Li Qiao, M. Murai, S. Kuwada

Techno-Ocean 2016 Proc. ( 1 ) 385 - 391 2016.10

DOI

Language：English Publishing type：Research paper (scientific journal) Publisher：IEEE Joint Work

A linear electrical generator is a kind of device which van be used to wave energy converter, for directly converting mechanical energy of a floating structure into electrical energy. A wave farm consists of multiple wave energy converters in a sea area. In the present paper, a numerical model is proposed considering the interference effect in the multiple floating structures, and the controlling force of each linear electrical generator. Especially, the copper losses in the electrical generator is taken into account, when the electrical power is computed.

EXPERIMENTAL STUDY ON A 3-DIMENSIONAL HYDRO-ELASTIC DEFORMATION OF "UNDERWATER PLATFORM" WITH MULTI-TOWERS IN WAVES

Ken Haneda, Motohiko Murai, Jun Yamanoi

Proc.ASME2016, Int. Conf. OMAE2016 OMAE2016 - 54744 2016.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

Underwater platform was proposed in OMAE 2015 for the purpose of enhancing productivity of various types of renewable energy converter on the sea and its feasibility study was carried out through 2 types of tank experiment [1]. The underwater platform which is a very large frame shape structure connects several floaters under the sea to share power cables and mooring lines and to keep relative distances between the floaters. In the experiment, 1/200 scale elastic model with three spar buoys was used. The buoys imitated spar type floating offshore wind turbines (FOWTs). From the experiment, it was shown that the platform with large draft can reduce its response in waves.

In this paper, we report new result and knowledge obtained by additional model experiments use the 1/200 model. In the experiment, we changed the arrangement and draft of the model and measured hydro-elastic deformation of the underwater platform in waves. From the last experiment, relationship between draft settings and response was shown. In the experiment, relationship between wave angles and response was surveyed.
From the experiment, we have confirmed followings: 1. Rigid-body motion is remarkable in beam waves, 2. Elastic response is remarkable in head waves, and 3. Remarkable torsional motion is occurred in 45 degrees' waves. The more important thing, however, is that the experimental result indicated that the platform of large draft decreases its motion in the all the wave angles.

A Study on Responses of Underwater Platform in Waves -2nd report-

M.Murai, K. Haneda, J. Yamanoi

Conf. Proc. The Japan Society of Naval Architects and Ocean Engineers ( 22 ) 603 - 608 2016.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

Changes in the opeimal shape of a floating body with wave energy absorption system

Naoki Okada, M. Murai

Journal of Naval Architecture and Ocean Engineerings ( 22 ) 45 - 54 2015.12 [Reviewed]

DOI

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：The Japan Society of Naval Architects and Ocean Engineerings Joint Work

Other Link： https://www.jstage.jst.go.jp/article/jjasnaoe/22/0/22_45/_article/-char/ja/

Hydrodynamic modelling of marine renewable energy devices: A state of the art review

A.H. Day, A. Babarit, A. Fontaine, Y.-P. He, M. Kraskowski, M. Murai, I. Penesis, F. Salvatore, H.- … Show more authors

Journal of Ocean Engineering 108 ( 1 ) 46–69 2015.9 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Joint Work

This paper reviews key issues in the physical and numerical modelling of marine renewable energy systems, including wave energy devices, current turbines, and offshore wind turbines. The paper starts with an overview of the types of devices considered, and introduces some key studies in marine renewable energy modelling research. The development of new International Towing Tank Conference (ITTC) guidelines for model testing these devices is placed in the context of guidelines developed or under development by other international bodies as well as via research projects. Some particular challenges are introduced in the experimental and numerical modelling and testing of these devices, including the simulation of Power-Take-Off systems (PTOs) for physical models of all devices, approaches for numerical modelling of devices, and the correct modelling of wind load on offshore wind turbines. Finally, issues related to the uncertainty in performance prediction from model test results are discussed.The paper is based on the report of the International Towing Tank Conference specialist committee on Hydrodynamic Modelling of Marine Renewable Energy Devices to the 27th ITTC held in Copenhagen, Denmark in 2014 (ITTC Specialist Committee on Hydrodynamic Modelling of Marine Renewable Energy Devices, 2014a.

A Study on Loll Floating Body for Improving Ability of Motion in Waves for a Floating Type Wave Power Generation

Shunya Nishizawa, Motohiko Murai

The 25th Ocean Engineering Symposium OES25 - 015 2015.8

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Ocean wave has variety of frequencies, and it is difficult to do stable power generation. In this study, we proposed a new type of floating body increasing the motion in waves. The point of the floating is utilizing a loll of the floating body which has negative GM in the calm sea and stable angles around a few degree. To confirm that the new type of floating body can improve the motion in waves, we carried out simulation and experiment of the loll body motion. As a result of the simulation, large motions with twice period of wave in shorter wave periods and longer wave periods are seen. Also, when the wave slope is increased, the estimated motion at the long wave period is greater than the estimated response of the usual floating body. And such a large motion was also observed in the experiment.

Tank test technology for floating offshore wind turbine

S.Ishida, S.Inoue, H. Imamura, M. Ohta, T. Chujo, R.Matsui, M. Murai, H. Yoshida

The 25th Ocean Engineering Symposium OES25 - 063 2015.8

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：J F O E S & J A S N A O E Joint Work

Floating offshore wind turbine is the promising power generation system from vast renewable energy at sea. To
start commercial operation in the near future, much study is underway in japan and foreign countries. For
promoting the research and development of floating offshore wind turbines, the Japan Society of Naval
Architects and Ocean Engineers (JASNAOE) formed the special committee of floating offshore wind turbines
from 2013 to 2014 FY. The working group on tank test technology, one of the working groups under the
committee, conducted review of published papers in OMAE, ISOPE, JASNAOE and so forth. The working
group analyzed the papers on the viewpoints of purpose, facility, model, external forces, measuring and scale
effect. This paper introduces the report of the working group.

Coupled Motion Response of a Moored Floating Body in Breaking a Mooring Line in Waves

Motohiko Murai, Nozomi Suyama

The Proceedings of The Twenty-fifth (2015) International OCEAN AND POLAR ENGINEERING CONFERENCE ( 4 ) 1453 - 1460 2015.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Publisher：International Society of Offshore and Polar Engineers Joint Work

A catenary mooring system has a feature point that is able to make a delay of a propagation of a damage on a mooring line to the other lines, on the other hand, it has been said that it is difficult to detect the damage in the system. In this paper, we introduce a hydrodynamic response of a floating body and mooring lines by numerical simulation results in case that a mooring line contacting the seabed has been broken. Then we discuss the difference of the hydrodynamic response before the breakage and after the breakage.

EXPERIMENTAL STUDY ON A MOTION OF "UNDERWATER PLATFORM" INCLUDING HYDRO-ELASTIC DEFORMATION IN WAVES

Motohiko Murai, Ken Haneda, Jun Yamanoi, Yuta Abe

Proceedings of the ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering OMAE2015 ( 6 ) V006T05A017 2015.5 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

A new type of floater for floating offshore wind turbine (FOWT) was proposed. The floater, named an "underwater platform", aims at high economic efficiency of energy generation of floating wind farm. The underwater platform is a large scale submerged structure which has small water plane area and can support several wind turbines. It is expected that the platform has small motion characteristics in waves because of its small water plane area, and it contributes for FOWT to generate energy safety.
In this study, the feasibility and usefulness study about the platform was carried out through experiments and numerical simulations. The first experiment was conducted with partial rigid model of the platform to verify the feasibility. From the experiment, it was confirmed that the model has small motion characteristics in waves. The experimental results were compared with numerical simulations of potential theory and they were well matched. Besides, the coupling analysis with aero-hydro dynamics was also carried out and it was confirmed that the stability of the platform was enough in steady wind condition.
The second experiment was conducted with elastic body model to study the elastic deformation of the platform in waves. From the experiment, it was confirmed that the deformation is small when the draft was 250mm (50m in the actual model).

Comparison of Weathervane Performance Between Two Types of FOWT Systems Moored to SPM

Kazuhiro Iijima, Yuiko Kuroda, Yasunori Nihei and Motohiko Murai

Proceedings of the ASME 2015 34th International Conference on Ocean, Offshore and Arctic Engineering OMAE2015 ( 6 ) V006T05A010 2015.5 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

This paper addresses the weathervane performance of Floating Offshore Wind Turbines (FOWTs) moored to single-point mooring (SPM) systems. A system of equations of motion to describe the motions in horizontal plane around the mooring point in the combined environmental conditions is derived. Wind, wave and current loads are considered. Two types of SPM-FOWT systems proposed by the present authors are considered for comparison. It is found out that the weathervane performance of the SPM-FOWT systems is acceptable in a point that the power generation efficiency does not reduce significantly. The stability is also checked based on the eigenvalue analysis for the linearized equations of motion around the equilibrium point. The stability and the responsivity are discussed in comparison between the two systems. Sensitivity of the stability and responsivity to design parameters such as length between the buoy and the main floater to the turning motion performance is discussed, too.

A Survey of Recent Trends on a New Concept of a Floating Offshore Wind Turbine Technology

Katsunari Fujioka, Kensaku Takahashi, Motohiko Murai

Proc. of JASNAOE Annual Conf. ( 20 ) 37 - 40 2015.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Basic Study on an Array Arrangement for Point Absorber Type of Ocean Wave Energy Converter

Syu Kuwada, Motohiko Murai, Naoki Okada

Proc. of JASNAOE Annual Conf. ( 20 ) 327 - 330 2015.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

A Basic Study on the Motion of a Twin-Floating Vertical Wind Turbines in Waves

Motohiko Murai, Goushi Hashimoto

Proc. of JASNAOE Annual Conf. ( 20 ) 41 - 44 2015.5

Language：English Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

Recent researches on the wind turbine on land show a possibility of keeping an efficiency despite the narrow distance arrangement of multi vertical axis wind turbines. When we apply the knowledge to the FOWT, it can be expected the material and mooring cost reduction by supporting two FOWT with one structure.
Furthermore, the reaction force and moment will be canceled each other when we let rotate the blades of the two FOWT on the one structure in opposite directions.
So, in this paper, we also propose a concept that one
floating structure supports twin vertical axis wind turbines with a certain narrow distance among them. The image of the new concept. And we carried out the water tank experiments on the twin-floating vertical wind turbine to confirm the feature points of the new concept.

A Study on Optimization Algorithm for Designing Internal Turret Mooring System in FLNG

Ryo Fukushima, Shunji Kato, Kazuhiro Yukawa, Motohiko Murai

Proc. of JASNAOE Annual Conf. ( 20 ) 345 - 348 2015.5

Language：Japanese Publishing type：Research paper (scientific journal) Publisher：JASNAOE Joint Work

Coupled response of floating body and mooring system in case of a mooring line break

Nozomi Suyam, Motohiko Murai

Journal of JASNAOE ( 19 ) 217 - 220 2014.11

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：JASNAOE Joint Work

Weathervane performance of a single point moored FOWT

Kazuhiro Iijima, Yuiko Kuroda, Chong Ma, Motohiko Murai, Yasunori Nihei

( 19 ) 129 - 132 2014.11

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：JASNAOE Joint Work

SPATIAL DISTRIBUTION OF HYDRODYNAMIC RESPONSE OF FLOATING OFFSHORE WIND FARM IN WAVES

2nd AWTEC 014 277 - 284 2014.7

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AWTEC Joint Work

In the 21st century, we face a progress of the global warming. We should balance energy consumption and make an effort to reduce the exhausting greenhouse effect gas. The expansion of wind farm is expected as one of the key technologies for utilizing renewable energy. The land space for the extensive wind farm is, however, quite limited. Therefore the extension of an offshore wind farm is important. Especially, the floating wind turbine system is essential technology to extend the wind farm widely in the ocean. Under such background, there are many researches on the floating wind turbine in waves and in wind. And hydrodynamic response of them is one of the major topics. Many of the researches on the hydrodynamic response, however, deal with the floating wind turbine existed alone. In this report, we deal with the hydrodynamic response of a wind farm which is consisted of a group of many floating wind turbines. Through the numerical prediction, the particular spatial distributions of the motion response in the wind farm are discussed.

A FUNDAMENTAL STUDY ON RESPONSES OF "UNDERWATER PLATFORM" IN WAVES

Motohiko Murai, Ken Haneda, Shinsaku Munakata, Jun Yamanoi

2nd AWTEC 014 285 - 291 2014.7

Language：English Publishing type：Research paper (international conference proceedings) Publisher：AWTEC Joint Work

An underwater platform for FOWT, which aims to increase productivity of large scale offshore wind farm, is proposed in this paper. The platform consists of several spar buoys and buoyancy frames. Though each technique has been already existed, we expect that the combination of the techniques reduce its response in waves. Its possibility and its efficacy verification were examined through water tank experiments and numerical simulations. The model experiment was carried out in 2D water tank, and the linear small response of the platform was confirmed. Numerical simulations of full scale model were also carried out. The numerical simulation considering aero-hydrodynamic problem indicates that the blade rotation effect is small to the response in the steady state. Then the numerical simulation considering hydro-elastic problem indicates that its elastic deformation becomes relatively small when the platform installed in deep draft.

Second-order resonance among an array of two rows of vertical circular cylinders

H. Kagemotoa, M. Murai and T. Fujii

Applied Ocean Research 47 192 - 198 2014.6 [Reviewed]

DOI Web of Science

Language：English Publishing type：Research paper (scientific journal) Publisher：Elsevier Joint Work

Experimental and theoretical works are conducted on the first-order and second-order wave interactionsamong an array of two rows of vertical circular cylinders.We show that both the first-order and the second-order resonance of dynamic free-surface displace-ment could in some cases be quite relevant among an array of two rows of vertical cylinders not onlyin theory but also in real phenomena. In some cases, on the other hand, we show that large free-surfacedisplacement predicted theoretically is quite attenuated in reality probably due to viscous dissipation.

A Comparative Study of Motion Performance of Four Different FOWT Designs in Combined Wind and Wave Loads

Yasunori Nihei, Kazuhiro Iijima, Motohiko Murai and Tomoki Ikoma

ASME 2014 33rd International Conference on Ocean, Offshore and Arctic Engineering OMAE2014 - 24643 2014.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

This paper summarizes our recent collaborative/competitive works on floating offshore wind turbines (FOWTs) among four universities including Osaka Prefecture Univ., Osaka Univ., Yokohama National Univ., and Nihon Univ. The tasks assigned to each member were to develop the respective FOWT designs which could support 5MW class wind turbine, then to fabricate a scale model based on their own concept, and finally to evaluate the performance by tank tests under prescribed environmental (wind and wave) conditions. Osaka Prefecture Univ. adopted TLP concept, Yokohama National Univ. semi-submersible concept, Nihon University SPAR concept while Osaka Univ. also adopted semi-submersible, however, with single-point mooring. All the measured data were collected and compared among the four designs. It turned out that: (1) All the proposed deigns suffice criteria in terms of motion performance which were assumed at the beginning of the study. (2) The TLP type shows the most favorable performance among the four while the SPAR type shows largest acceleration in almost all the range of environmental conditions. The large acceleration may pose a problem of maintainability. (3) The SPAR type suffers the gyration effects more than the other types. (4) The RAOs of motions under combined wind and wave loads are almost the same as those under only wave loads for all the concepts but the single-point moored semisubmersible. (5) The difference of the RAOs for the single-point moored semisubmersible may be ascribed to the larger coupling effects between the main floater and the mooring system under the combined loads.

A Study on Spatial Dynamic Response Distributions of Floating Structures Constituting an Offshore Wind Farm in Waves

Motohiko Murai, Miki Takei

Journai of JASNAOE ( 18 ) 303 - 306 2014.5

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：JASNAOE Joint Work

A study on responses of Underwater Platform in waves

Motohiko Murai, Ken Haneda, Shinsaku Munakata, Jun Yamanoi

Journai of JASNAOE ( 18 ) 113 - 116 2014.5

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：JASNAOE Joint Work

An experimental study on wind-following response of single-point mooring type offshore wind turbine

M.Murai, Y.Nihei, M. Matsuura, K. Takahashi

Journai of JASNAOE ( 18 ) 117 - 120 2014.5

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Publisher：JASNAOE Joint Work

Second-order resonance among an array of two rows of vertical circular cylinders - Comparisons of theoretical calculations and reality -

H. Kagemoto, M. Murai and T. Fujii

Proc. 29th International Workshop on Water Waves & Floating Bodies, 93 - 96 2014.3

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Hydrodynamic Time Response Analysis of Side-by-Side Vessels with Consideration of Fender and Mooring Lines Effect

Akmal Bin Ahamed, Motohiko Murai

Proc. of the 24th Ocean Engineering Symposium OES24 - 65 2014.3

Language：English Publishing type：Research paper (research society, symposium materials, etc.) Joint Work

A Feasibility Study of a Floating Offshore Wind Farm Project around Japan with Consideration of Construction Conditions and Motion Characteristics

Shoichiro Yabe, Motohiko Murai

Proc. of the 24th Ocean Engineering Symposium OES24 - 63 2014.3

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Joint Work

A study on a numerical simulation of motion responses of a floating offshore wind turbine by combination of the hydrodynamic force analysis by potential theory and the aerodynamic analysis by FAST

Masahiro Waki, Motohiko Murai

Proc. of the 24th Ocean Engineering Symposium OES24 - 71 2014.3

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Joint Work

A study on responses of Small Stability Underwater Platform in waves

Motohiko Murai, Ken Haneda, Shinsaku Munakata, Jun Yamanoi

Proc. of the 24th Ocean Engineering Symposium OES24 - 75 2014.3

Language：Japanese Publishing type：Research paper (research society, symposium materials, etc.) Joint Work

Experimental Investigations into the Motion Characteristics of a Single-Point-Moored FOWT

K. Iijima, M. Kawai, S. Sharath, C. Ma, Y. Nihei, M. Murai, T. Ikoma

International Symposium on Marine and Offshore Renewable Energy (More2013) S5 - 5 2013.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A new design concept of a semi-submersible type floating offshore wind turbine (FOWT) moored by a single-point mooring is proposed. The FOWT model supporting 5MW class wind turbine is designed. The motion characteristics of the FOWT are evaluated by a series of tank tests. To this end, a scaled model with a scale ratio 1/100 is fabricated. The scaled mode tests are performed under winds, waves, and combined winds and waves to check its fundamental feasibility. A series of simulations is performed to understand the fundamental behavior, too. It is observed that the motion characteristics under wind and waves are acceptable in general, and the combination of the single point mooring and the down-wind type rotor is effective in terms of weathervane. It is also shown that the difference between the two transfer functions to wave loads, one with and the other without wind loads, is small except pitch response at low frequencies.

Research about Motion Characteristics of SPAR Type Offshore Wind Turbines in Wind and Wave Coexisting Conditions

Y. Nihei, T. Ikoma, M. Kozen, M. Murai, K. Iijima

International Symposium on Marine and Offshore Renewable Energy (More2013) S4 - 2 2013.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

In this paper, we will discuss about the designing process and the motion characteristics of the spar type offshore wind turbines. When considering a spar type structure for offshore wind turbines, it is important to take a lot of elements into consideration which have not yet been considered in the case of oil and gas platforms. In this research, we used the following standards to conduct our tests. The limit of the heel angle was 5 degrees when the wind turbines are generating in the rated state. When designing the substructure for this research we have decided to go with a substructure that operates in depth of 100m or more. Following the conditions above we have designed the spar type offshore wind turbine used for this research. In order to compare the simulated result we have created a scale model and per formed tank tests under various conditions. Also we observed unexpected motion characteristics in certain mooring arrangement. So we will touch these subjects in this paper.

Experimental Study on a Hydrodynamic Behavior of a Semi-Submersible Type FOWT

M. Murai, M. Takei, H. Saeki, Y. Nihei, K. Iijima, T. Ikoma

International Symposium on Marine and Offshore Renewable Energy (More2013) S4 - 4 2013.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Many researches about various type of FOWT have been already carried out by many researchers including the authors of this paper. As a result, we know that each type has own advantages and own disadvantages. On the other hand, in general, because the floating type is different for each project, it has not compared its performance among those projects in the same condition. Therefore, the authors have examined the performance of the various types of FOWT under the same experimental conditions.
In this paper, the performance of the FOWT focusing on Semi-submersible type of multi-column type in particular is reported. First, we examined as design requirements the shape of a column with footing, the distance between the columns and the number and the arrangement of the multi-column. Within it, we investigated the combination of the variables for good performance in waves and winds. We manufactured a 1/100 experiment model which is based on the design requirements and carried out the experiment in waves and winds. Then we discuss the effectiveness of the model using the experimental results and the numerical results.

Comparisons of Hydrodynamic Behavior of Vertical Axis and Horizontal Axis FOWT

M. Murai, A. Nagamine

International Symposium on Marine and Offshore Renewable Energy (More2013) S5 - 3 2013.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

The sea around Japan has deep and complicated sea bottom, so the floating offshore wind turbine is more suitable than the fixed type wind turbine in the area.
The behavior of floating wind turbines in waves has been already investigated in many researches. And most of them deal with a horizontal axis wind turbine (HAWT) as the floating offshore wind turbine (FOWT).
It is generally said that three blades type HAWT produces best performance in the ideal condition. But the nacelle of HAWT is set at high position to get strong wind. Therefore component of the floating wind turbine becomes top heavy condition.
It decreases physical safety for a person who enters to the nacelle part to maintain the machine of the wind turbine. On the other hand, a gravity center of a vertical axis wind turbine (VAWT) is low, because the nacelle could be set in low position which is near the water level. In this report, we focus on the acceleration of the nacelle part of the FOWT and compare the condition between VAWT and HAWT for a person who maintains it in the FOWT.

A Research about Motion Characteristics of TLP Type Offshore Wind Turbines in Wind and Waves

Y. Nihei, M. Matsuura, M. Murai, K. Iijima, T. Ikoma

International Symposium on Marine and Offshore Renewable Energy (More2013) S5 - 4 2013.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

In this paper, we will show a new proposal to design a Tension Leg Platform (TLP) type offshore wind turbines. Generally, TLPs are used in deepwater oil and gas development fields due to their favorable motion characteristics. In this field, they have high set up costs. An upper structure of 5MW wind turbine, however, is only 450tons at its total weight, which is much lighter than that of oil and gas platforms. Therefore the displacement and water plane area of the platform might be smaller. As a result, wave forces could decrease and it could lead initial tensions to be lower. This idea that leads to low set up costs was discussed in our previous paper. Principal particulars of TLP prototypes was proposed and a tank test with both waves and wind that used 1/100 scale models was examined in the previous paper. Capsizing could be observed based on the conventional design method. So we reason why and how this capsizing occurred in this paper. Also we propose new design process and new TLP prototypes based on this process.

Studies on the floating body shape to maximize the kinetic energy that are intended to be small wave power generator

Shunya NISHIZAWA, Naoki OKADA, Motohiko MURAI

OTEC 2013.9

Language：Japanese Publishing type：Research paper (other science council materials etc.) Publisher：Saga Universicity Joint Work

Working Environment on a Floating Offshore Wind Turbine in the Perspective of Acceleration of the Nacelle Part

M.Murai, A Nagaimine

2013.9

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

On the trend of the requirements of offshore wind farm business

Shouichirou Yabe, Motohiko Murai

2013.7

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Study on coupling of mooring line moved non-linear and motion of moored floating body

Keiji Nonaka, Motohiko Murai

Proc. of the Conferece on Computational Engineering and Science ( 18 ) H - 4-4 2013.6

Language：Japanese Publishing type：Research paper (other science council materials etc.) Publisher：Proceedings of the Conference on Computational Engineering and Science Joint Work

New Design Proposal for the TLP Type Offshore Wind Turbines

Yasunori Nihei, Midori Matsuura, Motohiko Murai, Kazuhiro Iijima, Tomoki Ikoma

Proc. OMAE2013 OMAE2013 - 11263 2013.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A Study on Non-Linear Response of Moored Floating Body Considering Dynamic Motion of Mooring Lines

Keiji Nonaka, Motohiko Murai, Atsushi Nagamine

Proc. OMAE2013 OMAE2013 - 10612 2013.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Publisher：ASME Joint Work

Designing Process and Motion Characteristics of Spar Type Offshore Wind Turbines

Yasunori Nihei, Tomoki Ikoma, MInori Kouzen, Fumiya Sato, Motohiko Murai, Kazuhiro Iijima

Proc. OMAE2013 OMAE2013 - 11262 2013.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Investigations Into Motion Characteristics of a Multi-Column Type FOWT in Waves and Winds

Motohiko Murai, Miki Takei, Hotsuma Saeki, Yasunori Nihei Kazuhiro Iijima

Proc. OMAE2013 OMAE2013 - 11131 2013.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Conceptual Design of a Single-Point-Moored FOWT and Tank Test for Its Motion Characteristics

K. Iijima, M. Kawai, Y. Nihei, M. Murai, T. Ikoma

Proc. OMAE2013 OMAE2013 - 11259 2013.6 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Studies on the Floating Body Shape that Aims to Maximize the Kinetic Energy in Waves (2nd Report)

Naoki Okada, Shunya Nishizawa, Motohiko Murai

( 16 ) 297 - 300 2013.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Dynamic interaction of parallel moving ships in close proximity

M. Rafiql Islam, Motohiko Murai

( 12 ) 261 - 271 2013.5 [Reviewed]

DOI

Language：English Publishing type：Research paper (scientific journal) Single Work

A study on safety of SPAR type offshore horizontal axis wind turbine and vertical axis wind turbine

Motohiko Murai, Atsushi Nagamine

( 16 ) 477 - 480 2013.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A Study on 6 Free Degree Motions of a Semi-Submersible Type Offshore Wind Turbine

Motohiko Murai, Miki Takei, Hotsuma Saeki, Yasunori Nihei, Kazuhiro Iijima, Tomoki Ikoma,

( 16 ) 453 - 456 2013.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Designing Process and Motion Characteristics of Spar Type Offshore Wind Turbines

Yasunori Nihei, Tomoki Ikoma, Minori Kouzen, Fumiya Sato, Motohiko Murai, Kazuhiro Iijima

( 16 ) 449 - 452 2013.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A Designing Process and Motion Characteristics of TLP Type Offshore Wind Turbines

Yasunori Nihei, Midori Matsuura, Motohiko Murai, Kazuhiro Iijima, Tomoki Ikoma

( 16 ) 445 - 448 2013.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Second-order resonance among an array of two rows of vertical circular cylinders

H. Kagemoto, M. Murai and T. Fujii

Proc. 28th International Workshop on Water Waves and Floating Bodies 93 - 96 2013.4

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Studies on the floating body shape that aims to maximize the kinetic energy in waves

Naoki Okada, Motohiko Murai

( 15 ) 359 - 362 2012.11

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A study on nonlinear response of mooring lines considering dynamic motion of floating body

( 15 ) 377 - 380 2012.11

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Experiments on floating wave-power generation using piezoelectric elements in the water tan

2012.9

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A study on the Suitable Arrangement of the legs of a Semi-Submersible type offshore wind turbine in the sea around Japan

M. Takei, M.Murai

Proc. of 6th APhydro2012 60 - 63 2012.9

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

An Experimental Study on an Effect of Internal Flow of a U-shaped Flexible Tube

OES - 37 2012.8

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A basic study on floating wave-power generation using piezoelectric device and pendulums

OES - 028 2012.8

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Studies on the Efficiency of Utilization and Maintenance of Offshore Wind Power Generation Facility

OES - 032 2012.8

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A fundamental study of underwater platform the purpose of sharing facilities around the floating body response in wave

OES - 27 2012.8

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

海洋再生可能エネルギーの現状

村井基彦

第32回防錆防食技術発表予稿集 155 - 162 2012.7 [Invited]

Language：Japanese Publishing type：Research paper (other science council materials etc.) Single Work

海洋産業はそれだけの余地があるほど未開拓の分野である。この未開拓の分野の技術革新と発電容量の増加には、まだ未利用の海洋空間の開拓が不可欠である。また、そのためには水深によらない浮体式のシステムの導入が必須となってくる。本稿では海洋再生可能エネルギーの浮体式の再生可能エネルギーの動向について、最近の実証実験の例を紹介する。

EXPERIMENTAL ANALYSIS OF THE EFFECTS OF THE INTERNAL FLOW ON THE DYNAMIC OF A U-SHAPED FLEXIBLE PIPE

Marcio Yamamoto, Motohiko Murai, Shotaro Uto, Tomo Fujiwara

OMAE2012 - 83069, 47-56 2012.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Experimental validation for motion of SPAR-type floating wind turbine at inclination with effect of gyro moment of the rotating blade of windmills

Mostafa, N., Murai, M., Nishimura, R., Fujita, O., Nihei, Y

In Proc. of the 22nd International Offshore (Ocean) and Polar Engineering Conference, 292 - 299 2012.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

An experimental study on dynamic behavior of a flexible tube having curvature with internal flow

Motohiko Murai, Ken Haneda, Shotaro Uto, Tomo Fujiwara

( 14 ) 2012.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Experiments on floating wave-power generation using piezoelectric elements and pendulums in the water tank

Naoki Okada, Shoichiro Yabe, Hironori Fujimoto, M.Murai

Proc. of Oceans 2012 1 - 8 2012.5

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Study of Motion of SPAR-TYPE Floating Wind Turbines in Waves with Effect of Gyro Moment at Inclination

N. Mostafa, M. Murai, R. Nishimura, O. Fujita, Y. Nihei

Journal of Naval Architecture and Marine Engineering ( 9 ) 67 - 79 2012.5 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

Experimental Investigation of the Effect of the Internal Flow on Flexible Pipe in Jumper Configuration

Marcio Yamamoto, Motohiko Murai,Shotaro Uto, Tomo Fujiwara

( 13 ) 213 - 216 2011.11

Language：English Publishing type：Research paper (other science council materials etc.) Joint Work

The current situation of the renewable energy in the ocean

( 12 ) 131 - 134 2011.11

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

An experimental study on dynamic vibration behavior of a flexible tube in the water tank

Ken Haneda, Motohiko Murai, Syotaro Uto, Tomo Fujiwara, Marcio Yamamoto)

5th EAWOMEN 2011 2011.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Possibility of offshore wind power stations in Japan judging from III

Motohiko Murai, T. Aono

5th EAWOMEN 2011 2011.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A Study about the Dynamic Interaction between Submersed Hanging Tube and Internal Flow

Yamamoto Marcio, Motohiko Murai

219 - 230 2011.6 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

An Experimental Analysis of a Flexible Riser in Jumper Configuration

Motohiko Murai, Marcio Yamamoto, Shotaro Uto and Tomo Fujiwara

OMAE2011 - 49506, pp. 495-502 2011.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A Basic Study on the Motion of Mooring Line for Ultra Deep Water Using the Method of theLumped-Mass

Motohiko Murai, Keiji Nonaka

( 12 ) 59 - 62 2011.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

An example evaluation by Inclusive Impact Index 'Triple I' - Offshore airport -

Motohiko Murai

The 22nd Ocean Engineering Symposium OES22 - 060 2011.3

Language：Japanese Publishing type：Research paper (other science council materials etc.) Single Work

A fundamental study on reducing CO2 emission from ships by local production for local consumption of ocean renewable energy

Motohiko Murai, Atsushi Nagamine, Kenshiro Takahashi

The 22nd Ocean Engineering Symposium OES22 - 081 2011.3

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A study for the practical use of Vertical Weight Stabilizer

Naoki Okada, Koji Kakizoe, Yoshiaki Hirakawa, Takehiko Takayama, Motohiko Murai, Tsugukiyo Hirayama

The 22nd Ocean Engineering Symposium OES22 - 034 2011.3

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

An Experimental Study about the Effects of Internal Flow on the Dynamics of a Flexible Riser

The 22nd Ocean Engineering Symposium OES22 - 036 2011.3

Language：English Publishing type：Research paper (other science council materials etc.) Joint Work

A study on responses of a SPAR type offshore wind turbine in waves considering inertia moment of a windmill blades

Osamu Fujita, Motohiko Murai, Md. Nur-E-Mostafa, Ryuji Nishimura

The 22nd Ocean Engineering Symposium OES22 - 102 2011.3

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A basic study on floating wave-power generation using piezoelectric device

Hironori fujimoto, Motohiko Murai

The 22nd Ocean Engineering Symposium OES22 - 103 2011.3

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

AN EXPERIMENTAL ANALYSIS OF THE INTERNAL FLOW EFFECTS ON MARINE RISERS

Motohiko Murai, Marcio Yamamoto

Martec2010, Proceeding 159 - 165 2010.12

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A fundamental study on CO2 emission from ships by local production for local consumption of ocean renewable energy

Motohiko Murai, Atsushi Nagamine, Kenshiro Takahashi

( 11 ) 225 - 228 2010.11

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Numrical simulation of characteristics behavior of spar type offshore wind turbine and compare the result with experimental value

M.Murai, N. Mostafa, R.Nishimura

Techno Ocean2010 Proceedings N0.13 2010.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Experimental Study of Dynamic Vibration Flexible Riser

M.Murai, K.Haneda, M.Yamamoto, S.Uto, T.Fujiwara

Techno Ocean2010 Proceeding N0.17 2010.10

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A NUMERICAL ANALYSIS OF THE INTERNAL FLOW EFFECT ON THE RISER’S MECHANICAL BEHAVIOR

Marcio Yamamoto, Motohiko Murai

OMAE2010 OMAE2010 - 20316, 345-353 2010.6

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

AN EXPERIMENTAL ANALYSIS OF THE INTERACTION BETWEEN HANGED PIPE AND INTERNAL FLOW

Motohiko Murai, Marcio Yamamoto, Luis A. R. Quadrante, Ken Haneda, Shotaro Uto, Tomo Fujiwara, Shi … Show more authors

OMAE2010 OMAE2010 - 20312, 333-344 2010.6 [Reviewed]

Web of Science

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

The pipes are playing an important role in the offshore environment. Risers and pipelines are widely deployed by the petroleum industry for the well drilling and hydrocarbons production. Whereas during drilling, a mixture of drilling mud and solids in suspension (rock cuttings) flows through the drilling riser; during the production, mono or multiphase flow (comprising oil, water and gas) takes place within the production system. However up till now, most of investigations on offshore pipelines and risers have neglected the effects of the internal flow and have focused mainly on the interaction among pipe’s structure, hydro-dynamic forces and offshore platform’s motion. This paper deals with the interaction between the pipe structure and its internal flow. An experimental analysis was carried out, in the Deep Sea Basin of the National Maritime Research Institute (Japan), using a model of 10 m length. In this experiment, a mono-phase fluid of liquid and another bi-phase fluid of liquid and solids in suspension are used as the internal flow fluid and a parametric analysis using the internal flow rate and pipe’s oscillating frequency was carried out. Discussion about the experimental results is also included.

A STUDY ON THE OPTIMIZATION FOR THE ARRANGEMENT OF TWO TYPES OF SUPPORTING COLUMNS FOR VLFS USING GA

Tatsunori Nishi, Motohiko Murai

OMAE2010 OMAE2010 - 20255, 49-56 2010.6 [Reviewed]

Web of Science

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A study on an experiment of behavior of a SPAR type offshore wind turbine considering rotation of wind turbine blades

Motohiko Murai, Kyohei Ishikawa Ryuji Nishimura

Oceans2010 2010.5

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Can a single floating body be expressed as the sum of two bodies

H.Kagemoto, M.Kashiwagi, M. Murai

Journal Eng. Math ( 68 ) 153 - 164 2010 [Reviewed]

DOI

Language：English Publishing type：Research paper (scientific journal) Joint Work

INCLUSIVE IMPACT INDEX FOR CONSTRUCTION OF OFFSHORE AIRPORT IN TOKYO-BAY

EAWOMEN2009 2009.11

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Experiment in Small Water Tank about Wave Power Generation by Using Piezoelectric Elemen

Motohiko Murai, Hironori Fujimoto, Osamu Fujita

Conf. Proc. JASNAOE ( 9 ) 191 - 194 2009.11

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

戸田御浜周辺海域の流況の現地調査とシミュレーション

45.久松力人, 多部田茂, 加藤孝義, 村井基彦, 木下健, 日野明徳, 岡本研, 北澤大輔, 杉原奈央子, 伊藤翔

第21回海洋工学シンポジウム CD-ROM OES21 - 139 2009.8

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

An Experimental Analysis of the Internal Flow Effects on Vertical Pipes

Motohiko Murai, Marcio Yamamoto

21st Ocean Engineering Symposium CD-ROM 2009.8

Language：English Publishing type：Research paper (other science council materials etc.) Joint Work

A Study on an Environmental Assessment of Floating Offshore Wind Power Generation by III

Motohiko Murai

21st OCEAN ENGINEERING SYMPOSIUM CD-ROM OES21 - 184 2009.8

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Inclusive environmental assessment for offshore wind power stations

ISOPE2009 CD-ROM TPC - 393, 406-413 2009.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

An Experimental Study of the Interaction between Pipe Structure and Internal Flow

28th International Conference on Ocean, Offshore and Arctic Engineering CD-ROM OMAE2009 - 79312 2009.6 [Reviewed]

Web of Science

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A Study of the Internal Flow Effects on Vibrating Risers and Pipelines

Conf. Proc. JASNAOE ( 8 ) 65 - 68 2009.5

Language：English Publishing type：Research paper (other science council materials etc.) Joint Work

A Study on Inclusive Environmental Impact Assessment for Floating Offshore Wind Power Generation

Motohiko Murai

Conf. Proc. JASNAOE ( 8 ) 115 - 118 2009.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Study on Hydroelastic Responses of a VLFS with Local Elasticity Change in Waves

Motohiko Murai, Osamu Nakagawa

Conf. Proc. JASNAOE ( 8 ) 501 - 504 2009.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

Inclusive Environmental Impact Assessment for Construction of Offshore Airport

M.Murai, A.Yoan

Journal of Japan Society of Naval Architects and Ocean Engineers ( 8 ) 27 - 34 2008.12 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

海の公園のアサリの現状と潮干狩りのインパクトについて

村井基彦、舟木雄太

平成２０年度アサリ勉強会 2008.12

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A study on the numerical simulation of the seashell-digging human action in a seaside park by Multi-Agent Model - Model for UMINOKOUEN -

M.Murai, S. Fujiwara, R. Yamanaka, Y. Inoue

Jounal of The Society of Naval Architects of Japan ( 8 ) 1 - 8 2008.12 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

マルチエージェントアルゴリズムによる船舶からの避難シミュレーションに関する研究

村井基彦, 西崎大祐、大木義昭、仲田翔

日本船舶海洋工学会講演会論文集 ( 7 ) 419 - 422 2008.11

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

若手優秀講演賞受賞

The Latest Efforts to Promote the Naval Architecture and Ocean Engineering Education for young generation in Yokohama National University

PAAMES 2008 2008.9

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

外洋上プラットフォームの余寿命便益評価に基づく保守管理手法の検討

岩田亮治、川村恭己、村井基彦、浅友紀

日本船舶海洋工学会講演会論文集 ( 6 ) 71 - 74 2008.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A study on safety of a SPAR type offshore wind turbine in waves considering rotation of wind turbine blades

M.Murai, K. Ishikawa

5 pp.255 - 258 2008.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A study on the optimization for an arrangement ofsupporting floating shapes of VLFS by GA

M.Murai, T. Nishi

( 6 ) 249 - 252 2008.5

Language：Japanese Publishing type：Research paper (other science council materials etc.) Joint Work

A Study on an Analysis of an Annual Change of Distribution of Short-necked clam in a Tideland Considering Huge Human Impact

Oceans 2008 ( CD-ROM ) 2008.4 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A study on the optimization for an arrangement of two types of supporting columns of VLFS by GA

T. Nishi, M.Murai

20th Ocean Engineering Symposium 2008.3 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Inclusive Environmental Assessment for Construction of Offshore Airport

M. Murai, A. Yoan

20th OCEAN ENGINEERING SYMPOSIUM 2008.3 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A STUDY ON THE HYDROELASTIC RESPONSES OF A VLFS IN LARGE WAVES

PUL International Conffernce 2007.12

Language：English Publishing type：Research paper (international conference proceedings) Single Work

A study on relations between distribution of short-necked clam in a tideland and the flow fields in the tideland

EAWEMEN2007 2007.11

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A Prediction of Human Impacts of Seashell-digging on the Ecosystem in a Tideland Park

M.Murai, S. Fujiwara, R. Yamanaka Y. Inoue

ISOPE 2007 596 - 603 2007.7 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A study on the difference of Remaining Life Benefit of the bulk carrier between differnt ship routes

( 4 ) 419 - 422 2007.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A study on the numerical simulation of the seashell-digging human action in a seaside park, 2nd report

M. Murai, S. Fujiwara, R.Yamanaka, Y. Inoue

Conf. Proc. JASNAOE ( 4 ) 499 - 502 2007.5

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A study on responses of a SPAR type offshore wind turbine in waves considering rotation of wind turbine blades

M. Murai, Y. Yamaguchi, Y. Inoue

Conf. Proc. JASNAOE ( 4 ) 279 - 282 2007.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Field observation of human impacts on the clam resorce in "Umino-kouen"

( 4 ) 119 - 120 2007.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Direct Human Impacts on Benthic Organism (5th Report)

( 4 ) 503 - 506 2007.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

重合格子法による沿岸域の流動解析に関する研究

村井基彦、木下祐介、山中亮一、井上義行

第５６回応用力学連合会講演会 2007.3 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A study on the wave phenomena in a moon pool of a very large-scale floating structure

Proc. Techno-Ocean 2006 paper - 67 2006.10 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Spatio-temporal Variations of Visitors of Recreational Shellfish-Gathering at an Artificial Beach in Tokyo Bay

3rd conf. Monitoring and Management of Visitors Flows in Recreational and Protected Areas 1 356 - 359 2006.9 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A Prediction of a Human Action on Seashell-digging at a Seaside Park based on a Multi-Agent Simulation Model

3rd conf. Monitoring and Management of Visitors Flows in Recreational and Protected Areas 1 109 - 111 2006.9 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A study on an optimal arrangement of upper facilities on a very large floating structure considering with the hydroelastic response in waves

16th ISOPE 2006 1 108 - 115 2006.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

A study on the numerical simulation of the seashell-digging human action in a seaside park

M. Murai, T. Hirobayashi, R. Yamanaka, Y. Inoue

( 2 ) 101 - 104 2006.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

The applicability of Meso-scale model data in numerica simulation of coastal circulation.

( 2 ) 95 - 98 2006.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A study on the optimum design for decreasing hydroelastic responses of a VLFS by using a genetic algorithm

( 2 ) 79 - 83 2006.5

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Flow analysis around artificial structure on ocean space based on overset method

( 2 ) 91 - 94 2006.5

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Direct Human Impacts on Benthic Organism (4th report) - Environmental impact analysis of the new regulation for shellfish resource conservation at "Umino-Kouen" -

( 2 ) 99 - 100 2006.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

A study on the hydroelastic responses of a VLFS in large waves by using MPS method

( 2 ) 83 - 86 2006.5

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

造船系大学院に所属する大学院生の研究意識に関するアンケート調査

村井基彦

日本船舶海洋工学会講演会論文集 ( 1 ) 119 - 120 2005.11

Language：Japanese Publishing type：Research paper (scientific journal) Single Work

一般的に理工系の研究において、萌芽的な研究や革新的なアイデアの創出は20代が多いと言われている。船舶海洋系の大学院（東大、横国、阪府大、阪大、九大）に所属する大学院生を対象に研究意識や研究生活に関するアンケートを実施し、大学院生の研究意識に関する調査研究を行い、博士課程後期への進学を検討するに当たっては経済的な負担感がもっとも重要な要素となっていることなどを指摘している。

A study on techniques of visulaizaion and measurement of wave fields in a very small water tank (2nd report)

( 5 ) 119 - 120 2005.6 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Direct Human Impacts on Banthic Organism (3rd report)

( 5 ) 105 - 106 2005.6 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

The optimal arrangement of upper facilities on a very large floating structure

( 5 ) 113 - 114 2005.6 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

大規模洋上施設へのアクセス方法に関する検討

村井基彦、井上義行、佐藤直幸、小坂啓輔

第18回海洋工学シンポジウム ( Proc. ) 12 2005.1 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

大型洋上施設を沖合に設置した場合に不可欠なアクセスに関して、船舶によるアクセスと橋梁を設置し車によるアクセスに関して、経済的な観点および環境負荷の観点から比較検討を行っている。その結果、沿岸でも数km以内の沖合で１日数万人規模の利用が認められる場合には橋梁をかけた方が利点があるが、それ以外の場合には船舶の方が有利であった。

人為インパクトが海底生態系に及ぼす影響（第２報）－「海の公園」における貝類現存量の周年変化－

山中亮一、村井基彦、井上義行、藤原奨、桒山陽太郎

日本造船学会講演会論文集 ( 4 ) 131 - 132 2004.11 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

海の公園における二枚貝現存量の年間変動およびその要因に関して、実地調査をベースに議論している。海洋環境に人間活動が与える影響については様々な要因が考えられるが、短期間で集中的な潮干狩りが海底生態系に与える影響は無視できないものと考えられる。本研究ではその影響について海の公園を対象域として、周年の現存量の変化と人為インパクトの大きさについて実測データに基づいた検討を行った。

小型水槽実験に於ける波浪場の可視化および計測法に関する研究

村井基彦、井上義行、武居弘基、鴫原健、東原克成、山下真史

日本造船学会論文集 ( 195 ) 171 - 178 2004.10 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

長さや幅が数メートル、深さが10cm程度の小型の平面水槽を用い、大型浮体の1000分の１の縮尺模型による水槽実験を行うことの可能性を示すことは、実験コストも時間コストも大幅に抑制しつつ、実現象を予測や種々の数値解析結果の妥当性の検証に有効である。本研究では1mm未満の波浪場を光学的な陰陽を利用した可視化を広域的に行い、その陰陽の画像データから波の大きさを定量的に計測手法する手法を提案し、その有効性を示した。

WATER-SURFACE DYNAMICS AMONG A PERIODIC ARRAY OF FLOATING BODIES SUBJECT TO REGULAR INCIDENT WAVES

21st International Conference on Theoretical and Applied Mechanic Proc. 2004.8

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

人為インパクトが海底生態系に及ぼす影響（第１報）－潮干狩りと人工干潟の生物量－

山中亮一、村井基彦、井上義行、藤原奨、木下祐介

日本造船学会講演会論文集 ( 3 ) 169 - 170 2004.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

海の公園での潮干狩りが貝の現存量に及ぼす影響に関して、当該海域における二枚貝の現存量年間変動調査に基づいた報告

小型水槽実験を用いた大型浮体模型の流力弾性応答実験

村井基彦、井上義行、赤芝秀介、松本浩成

日本造船学会講演会論文集 ( 3 ) 131 - 132 2004.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

小型水槽を用いた大型浮体の模型実験手法の開発及びその実験精度に関する研究。１０００分１の縮尺模型による実験で定性的に数値計算結果と同等の知見を得ることが出来た。

Can a single floating body be expressed as the sum of two bodies?

18th Int. Workshop on Water Waves and Floating Bodies Proc. 2004.3 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Astudy on techniques of visualization and measurement of wave fieldsin a very small water tank

( 2 ) 135 - 136 2003.11

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Hydroelastic respsonse characteristics of a column-supported very large floating structure

Proc. of 3rd Int. Conf. on Hydroelasticity in Marine Technology Proc. 289 - 296 2003.9 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

画像処理を用いた波浪場の計測法に関する研究

村井基彦、井上義行、東原克成、山下真史

第１７回海洋工学シンポジウム Proc. .291 - 296 2003.7 [Reviewed]

Language：Japanese Publishing type：Research paper (international conference proceedings) Joint Work

超小型水槽を用いた大型浮体の大縮尺模型による水理実験では全ての現象が、1mmに満たない微小な現象となり、非接触で高精度な計測技術の確立が非常に重要となる。本研究では光学的な特性を活かした波浪場の傾斜と陰影との相関性を用いた可視化手法を提案すると共に、可視化された情報を定量化する手法を提案した。

Hydroelastic responses of a Very Large Floating Structure Supported by Footing-Columns in Waves

22nd OMAE2003 Proc. 701 - 708 2003.6 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

The prediction method of hydroelastic response of VLFS include sea bottom topographical effects

12th ISOPE 2003 Proc. 106 - 112 2003.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

多列円柱群に入射する規則波の共振現象

影本浩、村井基彦

九州大学応用力学研究所研究集会報告 14ME-S3 40 - 42 2003.3

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

Hydroelastic responses of a column-supported VLFS in waves of trapped-mode frequencies

4th International Workshop on Very Large Floating Structures Proc. 53 - 59 2003.1 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

On a study of the hydroelastic responses of a column-supportive VLFS in waves

4th International Workshop on Very Large Floating Structures, Proc. 92 - 97 2003.1 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

海底地形を考慮した超大型浮体の流力弾性応答の推定法に関する研究

村井基彦、井上義行、中村泰二郎

日本造船学会論文集 ( 192 ) 309 - 318 2002.11 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体を沿岸域に設置する場合、浮体の下部の海底地形は水平でなく水深が場所により変化することは容易に想像できる。こうした水深の変化は波浪場の変化をもたらし、その変化が大型浮体の弾性応答へ影響を与えると考えられる。本研究では、海底地形を考慮できる大型浮体の流力弾性応答の解析手法を示すと共に、その定式化に基づき大型浮体を緩斜面、すり鉢状、上げ底状の海底地形の上に設置したことを想定した解析を行い、その影響を示した。

The hydroelastic response of very large floating structure suppoted by footing-columns (2nd report)

M.Murai, Y.Inoue,T.Kibe

Jounal of The Society of Naval Architects of Japan ( 192 ) 299 - 308 2002.11 [Reviewed]

DOI

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

抄録
A Very Large Floating Structure (VLFS) is expected as a new utilization of the ocean space. Rigidity of VLFS is, however, relatively small, so that an hydroelastic response of VLFS in waves should be considered. Many researchers studied on the elastic response of a pontoon type VLFS, in addition, on that of column support type VLFS. The VLFS supported by columns shows the smaller elastic response than that of the pontoon type VLFS. In the 1st report of this paper, we have discussed about hydrodynamic responses of a column with footing which has a wave-free frequency on wave exciting force and also examined the hydroelastic responses of a VLFS supported by a large number of the columns in regular waves.
In this paper, we investigate on the charcteristics of hydroelastic behaviors of a VLFS supported by a large number of footing-columns which have two wave-free frequencies. And then, we disccuse about the hydroelastic behaviors of a VLFS in irregular seas based on spectral analyses. Furthermore we compare the hydroelastic responses of VLFSs among supported by columns without wave-free frequency, supported by columns with one wave-free frequency and supported by columns with two wave-free frequencies. In the analyses, the hydrodynamic forces of the single column are calculated by using 3-dimensional source sink method, and the hydrodynamic characteristics of VLFS are obtained by using hydro interaction theory.

フーティング付きコラム支持超大型浮体の流力弾性応答

村井基彦、井上義行、木部智之

日本造船学会論文集 ( 191 ) 317 - 326 2002.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

ポンツーン型浮体を想定する場合,その設置海域は,湾内などの穏やかな海域にするか,あるいは防波堤などにより創出された静穏海域でなければならない。しかし,防波堤などの付随施設の建設は,沖合いの水深が深い場所や地盤の柔らかい場所では困難で建設コストもかかるだけでなく,周辺海洋環境への影響の少なさという浮体式構造物の利点を失いかねない。そこで,最近ではポンツーン型だけでなく, コラム支持型やセミサブ型の超大型浮体に関しても検討の必要性が挙げられてきている。既に,円柱型コラム支持による浮体の研究結果がいくつか示され,一般的にポンツーン型よりも優れた応答特性を持つことが数値計算上は確認されている。しかし一方で,コラム単体での運動の固有周期コラムの配置による trapped mode による同調現象などの課題点も指摘されている。
そこで,本研究では,上下方向の波強制力の働かない波無し周期のあるフーティング付コラムに着目し,フーティング付コラムによって支持された超大型浮体式構造物の弾性応答について検討を行う。

A Frequency and Time domain study on Response Analyses of Large Floating Structures due to Seaquakes,,

ISOPE 2002 Proc. 335 - 341 2002.5 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

コラム支持型浮体の波浪中弾性応答への粘性影響について

村井基彦、影本浩

日本造船学会論文集 ( 191 ) 69 - 76 2002.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

多数のコラム群の波浪中の流体干渉問題に関して、物体表面での粘性減衰効果を付加し、非線形現象を再現すると水槽実験結果を良く再現できることが確認されている。本研究ではそうした微小な減衰効果が大型浮体の弾性応答へ与える影響を示すと共に、周辺波浪場に与える影響について検討を行うと共に、kmオーダーの２つの大型浮体間での干渉影響についても検討を行った。

Drift force on an array of vertical cylinders

17th Int. Workshop on Water Waves and Floating Bodies, Cambridge(U.K.) Proc. 65 - 68 2002.4 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

多数コラムに作用する漂流力の計算について

村井基彦

九州大学応用力学研究所研究集会報告書 13ME-S5 38 - 47 2002.3

Language：Japanese Publishing type：Research paper (scientific journal) Single Work

大型浮体の流力弾性応答への海底地形の影響

村井基彦

九州大学応用力学研究所研究集会報告書 14ME-S2 32 - 42 2002.3

Language：Japanese Publishing type：Research paper (scientific journal) Single Work

Experimental and theoretical analysis of the wave decay along a long array of vertical cylinders

Jounal of Fluid Mechanics ( 456 ) 113 - 135 2002 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

Non-linear Simulation of Relative Wave Height of Ship in Short Crested Irregular Wave

RINA Proc. 2001.11

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Effect of Wind, Current and Non-linear Second Order Drift Forces on a Moored Multi-Body System in an Irregular sea

OCEANS 2001 3 1915 - 1922 2001.11 [Reviewed]

DOI

Language：English Publishing type：Research paper (international conference proceedings) Publisher：OCEANS, 2001. MTS/IEEE Conference and Exhibition Joint Work

大型浮体の海震による応答解析

井上義行、村井基彦、野間祐一郎

第１６回海洋工学シンポジウム Proc. 89 - 96 2001.7 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体は内湾や防波堤に囲まれた海域においては通常の波浪環境外力により誘起される流力弾性応答の絶対量は小さく、操業上や安全上の問題はないと考えられている。しかし、地震の多い島国である日本においては、直下型の地震に対する対策について十分に検討をしていく必要がある。本研究では海底地震の発生にともなう海震現象が浮体の流力弾性応答に与える影響について有限要素法を用いて解析を行いその特性を示した。

超小型水槽による水理実験に関する研究

村井基彦、井上義行、田中康平、高橋祐介

第１６回海洋工学シンポジウム Proc. 505 - 512 2001.7 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超小型水槽を用いた大型浮体の大縮尺模型による水理実験では全ての現象が、1mmに満たない微小な現象となり、非接触で高精度な計測技術の確立が非常に重要となる。本研究では水面をスクリーン化し、特性格子状のスリットと光源を用いることで生じるモアレ縞により波浪分布を可視化するだけでなく、0.1mmに近い浮体の弾性応答に関しても可視化可能であることを示した。

超大型浮体構造物の津波による応答解析

井上義行、村井基彦、松本耕介、多部田茂

第１６回海洋工学シンポジウム Proc. 81 - 88 2001.7 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

性挙動が誘起されることが指摘されているが内湾においてはその絶対量は小さいと予想されている。しかし、地震の多い島国である日本においては、直下型の地震に対する対策について十分に検討をしていく必要があり、地震の発生伴う津波にさらされた場合の検討をする必要がある。本研究では海水流動のモデルを拡張することで、津波の伝播と浮体構造物の流力弾性応答を表現する手法を提案し、相模湾内の断層を震源とする地震が発生した場合を想定した解析を行い、その安全性について検討を行った。

A Study on Motions and Drift Forces of a Multibody Floating System in Waves

Jounal of The Society of Naval Architects Japan ( 188 ) 127 - 134 2000.11 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

超大型浮体の最適化に関する研究（その１）

村井基彦、影本浩

日本造船学会論文集 ( 187 ) 175 - 184 2000.5

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

形構造物が主流となってきているが、本研究では矩形型にこだわらず多様な形状の浮体について、その波浪中弾性応答について数値的な解析を行い、最適化に関する検討を行った。その結果、単純矩形よりも波浪中の応答が小さくなる浮体の可能性を示した。

超小型水槽を用いた超大型浮体の水槽試験

影本浩、村井基彦、加藤孝義

日本流体力学会年会2000講演論文集 .279 - 280 2000.4 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体は波浪中において顕著な弾性応答が引き起こされることが指摘されているが、実海域での実験は大がかりになり、時間的にも費用の面でも負担が大きく、浮体模型による水槽実験手法の確立が種々の検討の上で極めて重要である。本研究ではその水槽実験に関して、超大型浮体の大縮尺模型を用いてわずか数ｍの規模の水槽実験の可能性について検討を行い、水面をスクリーン化し、特性スリットと光源を用いることで生じるモアレ縞により波浪分布を計測できる可能性を示した。

On the hydroelastic responses of a very large floating structure in waves

Journal of Marine Science and Technology ( 4 ) 123 - 153 1999.12 [Reviewed]

DOI

Language：English Publishing type：Research paper (scientific journal) Joint Work

New numerical methods are presented for hydroelastic analyses of a very large floating structure (VLFS) of several kilometers length and width. Several methods are presented that accelerate computation without an appreciable loss of accuracy. The accuracy and efficiency of the proposed methods are validated through comparisons with other numerical results as well as with existing experimental results. After confirming the effectiveness of the methods presented, various characteristics of the hydroelastic behavior of VLFSs are examined, using the proposed methods as numerical tools

Experiments of a Very Large Floating Structure in a very small water tank,

3rd International Workshop on Very Large Floating Structures, Proc. 555 - 561 1999.12 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Effect of Wave Drift Forces on Huge Floating Structures in Wind and Waves,

3rd International Workshop on Very Large Floating Structures, Proc. 132 - 138 1999.12 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

セミサブ型超大型浮体周囲の波浪減衰について　第３報

影本浩、藤野正隆、村井基彦、石井祐司、斉藤雅宣

日本造船学会論文集 ( 185 ) 163 - 168 1999.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

セミサブ型超大型浮体は、多数のコラムに作用する浮力で超大型浮体構造物を支える浮体である。この多数のコラム群の中で特定周波数において、波浪減衰あるいは周囲の波浪場においては円柱群の後方になるほど波浪が卓越するような特異な同調現象があることを示した。この点に関して、水槽実験並びに数値的にも検討を行った

Experimental investigation on the wave decay characteristics along a long array of cylindrical legs

14th Int. Workshop on Water Waves and Floating Bodies Proc. 60 - 63 1999.4 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Some Efficient Calculation Techniques for Hydroelastic Analyses of a Very Large Floating Structure in Waves

2nd Int. Conf. on Hydroelasticity Proc. 201 - 210 1998.12 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

ポンツーン型浮体とコラム支持型浮体の波浪中弾性応答の比較

村井基彦、太田真、影本浩、藤野正隆

日本造船学会論文集 ( 184 ) 247 - 256 1998.11 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体式構造物は浮力によって洋上に浮かぶ施設であるが、浮体全体が箱形のポンツーン型浮体とコラム部分で浮力を受けるコラム支持型では波浪中での流力弾性応答特性がかなり異なっている。本研究では、同一解析コードを用いて両者の応答特性の相違点について検討を行った。

セミサブ型超大型浮体周囲の波浪減衰について　第２報

影本浩、藤野正隆、村井基彦、石井祐司、斉藤雅宣

日本造船学会論文集 ( 184 ) 275 - 286 1998.11 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

セミサブ型超大型浮体は、多数のコラムに作用する浮力で超大型浮体構造物を支える浮体である。この多数のコラム群の中で特定周波数において、波浪減衰が発生することを示し、その実現象について実験結果を通して検討を行った。

超小型水槽を用いた超大型浮体の水槽試験

影本浩、藤野正隆、村井基彦、近藤良和

第1４回海洋工学シンポジウム Proc. 467 - 474 1998.7 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体は波浪中において顕著な弾性応答が引き起こされることが指摘されているが、実海域での実験は大がかりになり、時間的にも費用の面でも負担が大きい。したがって、浮体模型による水槽実験手法の確立が種々の検討の上で極めて重要である。本研究ではその水槽実験に関して、超大型浮体の大縮尺模型を用いてわずか数ｍの規模の水槽実験の可能性について検討を行った。

超大型浮体の波浪中弾性挙動の推定法について　－第３報－

村井基彦、影本浩、藤野正隆

日本造船学会論文集 ( 183 ) 199 - 210 1998.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体は長さや幅が数ｋｍに及ぶのに対し、厚みが数ｍと相対的に極めて薄い洋上に浮かぶ構造物である。したがって、波浪中において波の力で剛体運動ではなく顕著な弾性変形が誘起されることが予想される。しかし、対象構造物が巨大であるが故に構造物を多数の要素浮体に分けて直接的に計算することは、現実的に不可能である。本研究では解析解を階層的に用い、従来の直接的計算手法に比べて、理論的には数千分の１の計算時間で精度の良い解を得る定式化を示し、実験結果と比較することでその有効性を示した

Wave decay characteristics along a long array of cylindrical legs,

13rd Int. Workshop on Water Waves and Floating Bodies Proc. 55 - 58 1998.4 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

Theoretical and experimental predictions of the hydroelastic response of a very large floating structure in waves

Journal of Applied Ocean Research 20 ( 3 ) 135 - 144 1998 [Reviewed]

Language：English Publishing type：Research paper (scientific journal) Joint Work

超大型浮体の波浪中弾性応答の効率的計算法

影本浩、藤野正隆、村井基彦、朱庭耀

第3回日本計算工学講演会論文集 3 1057 - 1060 1998 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

波浪中で顕著な弾性挙動をすると考えられている超大型浮体の波浪中弾性挙動の推定法に関して、浮体の弾性応答の表現には弾性モード関数の重ね合わせを用い、浮体に作用する流体力の推定には特異点分布法にモード関数を導入することで、未知数を大幅に減らし、効率的で現実的な解析時間で計算できる手法を提案し、その有効性を検討した。

Hydrodynamic and hydroelastic analyses of a very large floating structure in waves

Intl. Conf. On Offshore Mechanics and Arctic Engineering Proc. Paper No38 171 - 178 1997.6 [Reviewed]

Language：English Publishing type：Research paper (international conference proceedings) Joint Work

超大型浮体の波浪中弾性挙動の推定法について　－第２報－

村井基彦、影本浩、藤野正隆

日本造船学会論文集 ( 181 ) 123 - 134 1997.5 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体は長さや幅が数ｋｍに及ぶのに対し、厚みが数ｍと相対的に極めて薄い洋上に浮かぶ構造物である。したがって、波浪中において波の力で剛体運動ではなく顕著な弾性変形が誘起されることが予想される。本研究では超大型浮体の波浪中における流力弾性挙動の推定法について、ポンツーン型浮体でもコラム支持型浮体にも適用できる定式化を示し、浮体をいくつかの要素浮体の集合体として扱う定式化を示し、その分割数の収束性について検討を行った。

超大型浮体の波浪中動的挙動の解析法について

影本浩、藤野正隆、朱庭耀、村井基彦

第45回応用力学連合講演会講演予稿集 283 - 284 1996.3 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

波浪中で顕著な弾性挙動をすると考えられている超大型浮体の波浪中弾性挙動の推定法に関して、浮体の弾性応答の表現には弾性モード関数の重ね合わせを用い、浮体に作用する流体力の推定には特異点分布法にモード関数を導入する手法を提案し、その浮体の弾性モードの運動方程式と流体問題の方程式を連立させて一括して解く手法を提案した。

2．超大型浮体の波浪中弾性挙動の推定法について　－ポンツーン型浮体の場合－

村井基彦、影本浩、藤野正隆

日本造船学会論文集 ( 178 ) 213 - 224 1995.11 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体は長さや幅が数ｋｍに及ぶのに対し、厚みが数ｍと相対的に極めて薄い洋上に浮かぶ構造物である。したがって、波浪中において波の力で剛体運動ではなく顕著な弾性変形が誘起されることが予想される。本研究ではポンツーン型の超大型浮体の波浪中における流力弾性挙動の推定法について、ポンツーン型浮体の特長を生かした定式化を示すと共に、水槽実験との比較からその有効性を示し浮体の流力弾性問題の数値的解を初めて示した。

ポンツーン型弾性模型を用いた波浪中応答実験

影本浩、藤野正隆、村井基彦、加藤孝義

第13回海洋工学シンポジウム Proc. 217 - 222 1995.1 [Reviewed]

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

大型浮体は波浪中で顕著な流力弾性応答をすることが予想されているが、本研究ではバックボーンモデルを拡張したモデルによるポンツーン型弾性模型による水槽実験手法を提案し、その有効性を数値解析結果と比較し検討した。

超大型浮体の波浪中における流力弾性現象に関する研究

藤野正隆、影本浩、朱庭耀、村井基彦

東京大学工学部・工学系研究科紀要 A-33 38 - 39 1995

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

超大型浮体の流力弾性応答に関する解析手法に関して、喫水を考慮した３次元特異点分布法に基づく流体解析と、弾性変形モードの重ね合わせによる弾性応答解析を組み合わせた解析手法を提案し、その有効性を示した。

アクティブ制御による大水深ライザーのリエントリーに関する研究

鈴木英之、吉田宏一郎、南東浩、村井基彦、宇佐美陽生、石田成幹

日本造船学会論文集 ( 174 ) 865 - 872 1993.11

Language：Japanese Publishing type：Research paper (scientific journal) Joint Work

大水深ライザーとは水深数千メートルを超える大水深において海底から石油などを洋上の施設に送り出す管である。この石油掘削において、一度悪天候になった場合、洋上の浮体施設の安全性を保つために、海底の油井からライザーを一時的に切り離す必要がある。その後、再びライザー管の先端を再び油井につなぐ作業をリエントリーと呼ぶ。このリエントリー作業の効率化を図るためには、長さに比して径が小さく柔軟な構造物ライザーの形状制御をする必要がある。本研究ではアクチュエーターを用いアクティブ制御によって、形状を制御する手法を検討し、数値シミュレーション・水槽実験を通してその有効性を示した。

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