Journal of Marine Science and Engineering

Research

16 pages, 1334 KiB

Open AccessArticle

A Comparative Investigation of Prevalent Hydrodynamic Modelling Approaches for Floating Offshore Wind Turbine Foundations: A TetraSpar Case Study

by Jonas Bjerg Thomsen, Amélie Têtu and Henrik Stiesdal

J. Mar. Sci. Eng. 2021, 9(7), 683; https://doi.org/10.3390/jmse9070683 - 22 Jun 2021

Cited by 10 | Viewed by 2835

Abstract

Numerical models have been used extensively in the design process of the TetraSpar floating offshore wind turbine (FOWT) foundation to optimize and investigate the influence from a number of structural and environmental conditions. In traditional offshore design, either the Morison approach or a [...] Read more.

Numerical models have been used extensively in the design process of the TetraSpar floating offshore wind turbine (FOWT) foundation to optimize and investigate the influence from a number of structural and environmental conditions. In traditional offshore design, either the Morison approach or a linear boundary element method (BEM) is applied to investigate the hydrodynamic loads on a structure. The present study investigated and compared these two methods and evaluated their applicability on the TetraSpar FOWT concept. Furthermore, a hybrid model containing load contributions from both approaches was evaluated. This study focuses on motion response. In the evaluation, hydrodynamic data from BEM codes are applied, while the commercial software package OrcaFlex is utilized for time series simulations of the coupled structure. The investigation highlights the difference between the modelling approaches and the importance of particularly drag and inertia contributions. By optimizing the input coefficients, reasonable agreement between the models can be achieved. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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21 pages, 9098 KiB

Open AccessArticle

Impact of Typhoons on Floating Offshore Wind Turbines: A Case Study of Typhoon Mangkhut

by Jiawen Li, Jingyu Bian, Yuxiang Ma and Yichen Jiang

J. Mar. Sci. Eng. 2021, 9(5), 543; https://doi.org/10.3390/jmse9050543 - 17 May 2021

Cited by 10 | Viewed by 3406

Abstract

A typhoon is a restrictive factor in the development of floating wind power in China. However, the influences of multistage typhoon wind and waves on offshore wind turbines have not yet been studied. Based on Typhoon Mangkhut, in this study, the characteristics of [...] Read more.

A typhoon is a restrictive factor in the development of floating wind power in China. However, the influences of multistage typhoon wind and waves on offshore wind turbines have not yet been studied. Based on Typhoon Mangkhut, in this study, the characteristics of the motion response and structural loads of an offshore wind turbine are investigated during the travel process. For this purpose, a framework is established and verified for investigating the typhoon-induced effects of offshore wind turbines, including a multistage typhoon wave field and a coupled dynamic model of offshore wind turbines. On this basis, the motion response and structural loads of different stages are calculated and analyzed systematically. The results show that the maximum response does not exactly correspond to the maximum wave or wind stage. Considering only the maximum wave height or wind speed may underestimate the motion response during the traveling process of the typhoon, which has problems in guiding the anti-typhoon design of offshore wind turbines. In addition, the coupling motion between the floating foundation and turbine should be considered in the safety evaluation of the floating offshore wind turbine under typhoon conditions. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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19 pages, 2323 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Seakeeping Tests of a FOWT in Wind and Waves: An Analysis of Dynamic Coupling Effects and Their Impact on the Predictions of Pitch Motion Response

by Giovanni A. Amaral, Pedro C. Mello, Lucas H. S. do Carmo, Izabela F. Alberto, Edgard B. Malta, Alexandre N. Simos, Guilherme R. Franzini, Hideyuki Suzuki and Rodolfo T. Gonçalves

J. Mar. Sci. Eng. 2021, 9(2), 179; https://doi.org/10.3390/jmse9020179 - 10 Feb 2021

Cited by 11 | Viewed by 2878

Abstract

The present work highlights some of the dynamic couplings observed in a series of tests performed in a wave basin with a scaled-model of a Floating Offshore Wind Turbine (FOWT) with semi-submersible substructure. The model was moored by means of a conventional chain [...] Read more.

The present work highlights some of the dynamic couplings observed in a series of tests performed in a wave basin with a scaled-model of a Floating Offshore Wind Turbine (FOWT) with semi-submersible substructure. The model was moored by means of a conventional chain catenary system and an actively controlled fan was used for emulating the thrust loads during the tests. A set of wave tests was performed for concomitant effects of not aligned wave and wind. The experimental measurements illustrate the main coupling effects involved and how they affect the FOWT motions in waves, especially when the floater presents a non-negligible tilt angle. In addition, a frequency domain numerical analysis was performed in order to evaluate its ability to capture these effects properly. The influence of different modes of fan response, floater trim angles (changeable with ballast compensation) and variations in the mooring stiffness with the offsets were investigated in the analysis. Results attest that significant changes in the FOWT responses may indeed arise from coupling effects, thus indicating that caution must be taken when simplifying the hydrodynamic frequency-domain models often used as a basis for the simulation of FOWTs in waves and in optimization procedures for the design of the floater and mooring lines. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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21 pages, 6379 KiB

Open AccessArticle

Dynamic Behavior of a Flexible Multi-Column FOWT in Regular Waves

by Taisuke Takata, Mayuko Takaoka, Rodolfo T. Gonçalves, Hidetaka Houtani, Yasuo Yoshimura, Kentaro Hara, Sho Oh, Raúl Dotta, Edgard B. Malta, Kazuhiro Iijima and Hideyuki Suzuki

J. Mar. Sci. Eng. 2021, 9(2), 124; https://doi.org/10.3390/jmse9020124 - 27 Jan 2021

Cited by 15 | Viewed by 2085

Abstract

A tank experiment using a flexible multi-column floating offshore wind turbine (FOWT) model in regular waves was carried out to clarify the floater elastic response and its influence on the floater motion. The model motion response from the experiment was compared with the [...] Read more.

A tank experiment using a flexible multi-column floating offshore wind turbine (FOWT) model in regular waves was carried out to clarify the floater elastic response and its influence on the floater motion. The model motion response from the experiment was compared with the numerical simulations by NK-UTWind and WAMIT codes. The dynamic elastic deformation of the model was also compared between the experiment and NK-UTWind. The experiment observed significant elastic deformation for the decks and columns of the model around the wave period corresponding to the natural period of the structural vibration. Furthermore, comparing the heave response amplitude operator (RAO) between experiments and numerical simulations, a small peak appeared around this period in the experiment and NK-UTWind simulation instead of WAMIT simulation. These results indicated that dynamic elastic deformation affected the heave response of the model. The change in the model rigidity revealed that such elastic deformation could affect the motion response statistics in an actual sea condition if the peak period of the onsite wave spectrum is close to the floater natural vibration period. These investigations indicated the importance of considering the elastic behavior of a FOWT at its design stage. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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14 pages, 2476 KiB

Open AccessArticle

Non-Linear Motion Characteristics of a Shallow Draft Cylindrical Barge Type Floater for a FOWT in Waves

by Hideyuki Suzuki, Yuta Sakai, Yasuo Yoshimura, Hidetaka Houtani, Lucas H. S. Carmo, Haruki Yoshimoto, Ken Kamizawa and Rodolfo T. Gonçalves

J. Mar. Sci. Eng. 2021, 9(1), 56; https://doi.org/10.3390/jmse9010056 - 06 Jan 2021

Cited by 7 | Viewed by 2229

Abstract

A shallow draft cylindrical barge type floater with footing close to the water surface was experimentally evaluated in waves to investigate non-linear motion characteristics. The floater was designed to be used as an option for FOWT—floating offshore wind turbines. The non-linear mechanism can [...] Read more.

A shallow draft cylindrical barge type floater with footing close to the water surface was experimentally evaluated in waves to investigate non-linear motion characteristics. The floater was designed to be used as an option for FOWT—floating offshore wind turbines. The non-linear mechanism can be promoted due to the viscous force that acts on the footing edges and the footing interaction with the free surface. In general, the observed non-linear viscous damping is modeled as a force proportional to the square of the relative velocity between the floater and the water. Therefore, the viscous damping levels is expected to increase, and the response in waves, to decrease. However, an increase in motion responses was observed for a broad range of wave periods. An attempt was made to clarify the hydrodynamic mechanism by comparing wave tank experiments, numerical calculations by CFD—computational fluid dynamics codes, and linear potential theory codes. Regular wave tests for three different wave height conditions were carried out, including free decay tests in still waters. For CFD simulations, the OpenFOAM code was selected. For potential theory simulations, the WAMIT code was chosen. As a result of the research, three points could be highlighted and discussed: first, the hydrodynamic phenomenon that contributed to the non-linear motion of the floater was identified; second, the increase and coupling of the motions response of heave and pitch motions; and finally, the phenomenon that the footing held water mass and lifted it to the water surface. The CFD calculations were able to get good qualitative results compared with the experiments and confirmed the use of CFD as a useful tool to capture the non-linear hydrodynamic phenomenon. The linear potential theory was not able to capture the phenomenon discussed herein. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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18 pages, 3081 KiB

Open AccessArticle

Discussion on Coupling Effect in Structural Load of FOWT for Condensing Wind and Wave Bins for Spectral Fatigue Analysis

by Tomoya Inoue, Ahmad Adilah, Kazuhiro Iijima, Sho Oh and Hideyuki Suzuki

J. Mar. Sci. Eng. 2020, 8(11), 937; https://doi.org/10.3390/jmse8110937 - 18 Nov 2020

Cited by 10 | Viewed by 2147

Abstract

Floating Offshore Wind Turbines (FOWTs) are subject to combined wind and wave loads. The response is not given as a simple sum of the wind-only response and wave-only response due to nonlinear coupling effects, which makes the structural analysis more complex and time-consuming. [...] Read more.

Floating Offshore Wind Turbines (FOWTs) are subject to combined wind and wave loads. The response is not given as a simple sum of the wind-only response and wave-only response due to nonlinear coupling effects, which makes the structural analysis more complex and time-consuming. When a spectral approach for the structural fatigue analysis is considered, it is necessary to accurately estimate the variance of the combined stress taking account of the coupling effect. In this study, firstly the characteristics of the combined response are investigated. It is found out the coupling effects are two-fold; one is the aerodynamic exciting load increase for the forced motion in the wave frequency range. The other is the aerodynamic damping effect due to the increase of the relative wind speed, which is prominent in the structural vibration frequency range. Mathematical models to account for these coupling effects are developed. Then, a series of simulations are performed on three types of FOWTs to validate the models. It is shown that the characteristics of the combined response are different among the three types of the platforms and the developed model can explain the increase/decrease of the variance of the combined stress when compared with two decoupled wave-only and wind-only simulations. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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15 pages, 4935 KiB

Open AccessArticle

Demonstration Experiment and Numerical Simulation Analysis of Full-Scale Barge-Type Floating Offshore Wind Turbine

by Ko Matias Adrian Kosasih, Hideyuki Suzuki, Hideyuki Niizato and Shigeki Okubo

J. Mar. Sci. Eng. 2020, 8(11), 880; https://doi.org/10.3390/jmse8110880 - 05 Nov 2020

Cited by 22 | Viewed by 4036

Abstract

The development of Floating Offshore Wind Turbines (FOWT) has been progressing steadily. To utilize the moderate water depth of 50–100 m ocean space around Japan, a barge-type FOWT was installed in Kitakyushu as part of a demonstration project conducted by the New Energy [...] Read more.

The development of Floating Offshore Wind Turbines (FOWT) has been progressing steadily. To utilize the moderate water depth of 50–100 m ocean space around Japan, a barge-type FOWT was installed in Kitakyushu as part of a demonstration project conducted by the New Energy and Industrial Technology Development Organization (NEDO) of Japan. The FOWT mounts a 3 MW two-bladed wind turbine with blade diameter of 100 m and hub height of 72 m. The barge-type floating support structure is equipped with a moonpool in the center and a skirt at its bottom and is moored with 9 lines of catenary chains. To investigate the dynamic behavior of the barge-type FOWT in extreme condition and the validity of the numerical simulation in modeling the effect of the complex flow around the floating structure to the FOWT’s motion response, the FOWT’s motion data during typhoon Tapah on 23 September 2019 were measured and compared with the simulation results. As the results, the simulation results showed a good agreement in general to the measurement data. However, some shifts in the peak frequency of the simulation’s motion spectrum and a disagreement in waves with shorter wave periods were also observed. The possible causes of these differences are discussed thoroughly in this paper. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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21 pages, 5383 KiB

Open AccessFeature PaperArticle

Wave and Wind Responses of a Very-Light FOWT with Guy-Wired-Supported Tower: Numerical and Experimental Studies

by Hideyuki Suzuki, Hiroki Shiohara, Anja Schnepf, Hidetaka Houtani, Lucas H. S. Carmo, Shinichiro Hirabayashi, Ken Haneda, Toshiki Chujo, Yasunori Nihei, Edgard B. Malta and Rodolfo T. Gonçalves

J. Mar. Sci. Eng. 2020, 8(11), 841; https://doi.org/10.3390/jmse8110841 - 26 Oct 2020

Cited by 16 | Viewed by 2807

Abstract

A floating offshore wind turbine (FOWT) concept with a guy-wire-supported tower was investigated to obtain motion results in waves considering its elastic model characteristics. The FOWT concept studied aims to reduce the construction costs by using a light-weight structure tensioned with guy wires [...] Read more.

A floating offshore wind turbine (FOWT) concept with a guy-wire-supported tower was investigated to obtain motion results in waves considering its elastic model characteristics. The FOWT concept studied aims to reduce the construction costs by using a light-weight structure tensioned with guy wires and a downwind type. Wave tank experiments of an elastically similar segmented backbone model in the 1:60 scale were carried out to clarify the dynamic elastic response features of the structure. The experimental results were compared with numerical simulations obtained from NK-UTWind and WAMIT codes. The bending moment measured at the tower and pontoons had two peak values for different wave periods carried out. The short-wave period peak was due to sagging/hogging when the wavelength matched the floater length. The second peak was due to the large tower top acceleration, which caused a large bending moment at the tower base and pontoon to support the inertia force. The wind force was not significant to modify the FOWT response. The sensibility analysis in pontoons and tower rigidities confirmed the importance of the guy wires to support the inertia due to the waves and wind incidence. The new concept of a very-light FOWT with a guy-wire-supported tower may be an option for future FOWT developments. Full article

(This article belongs to the Special Issue FOWT–Floating Offshore Wind Turbine: Experimental and Numerical Modelling of Motion Behaviour in Waves, Wind and Current)

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