Large-scale testing of a hydraulic non-linear mooring system for floating offshore wind turbines

Spar-type floating offshore wind turbines commonly vibrate excessively when under the coupling impact of wind and wave. The wind turbine vibration can be controlled by developing its mooring system. Thus, this study proposes a novel mooring system for the spar-type floating offshore wind turbine. The proposed mooring system has six mooring lines, which are divided into three groups, with two mooring lines in the same group being connected to the same fairlead. Subsequently, the effects of the included angle between the two mooring lines on the mooring-system’s performance are investigated. Then, these six mooring lines are connected to six independent fairleads for comparison. FAST is utilized to calculate wind turbine dynamic response. Wind turbine surge, pitch, and yaw movements are presented and analyzed in time and frequency domains to quantitatively evaluate the performances of the proposed mooring systems. Compared with the mooring system with six fairleads, the mooring system with three fairleads performed better. When the included angle was 40°, surge, pitch, and yaw movement amplitudes of the wind turbine reduced by 39.51%, 6.8%, and 12.34%, respectively, when under regular waves; they reduced by 56.08%, 25.00%, and 47.5%, respectively, when under irregular waves. Thus, the mooring system with three fairleads and 40° included angle is recommended.

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Dynamic Responses of a Spar Type Floating Offshore Wind Turbine With Failed Moorings

Volume 9: Ocean Renewable Energy ◽

10.1115/omae2020-18353 ◽

2020 ◽

Author(s):

Yajun Ren ◽

Vengatesan Venugopal

Keyword(s):

Wind Turbine ◽

Wind Turbines ◽

Dynamic Responses ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Mooring System ◽

Floating Offshore Wind Turbine ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Platform Motions

Abstract The complex dynamic characteristics of Floating Offshore Wind Turbines (FOWTs) have raised wider consideration, as they are likely to experience harsher environments and higher instabilities than the bottom fixed offshore wind turbines. Safer design of a mooring system is critical for floating offshore wind turbine structures for station keeping. Failure of mooring lines may lead to further destruction, such as significant changes to the platform’s location and possible collisions with a neighbouring platform and eventually complete loss of the turbine structure may occur. The present study focuses on the dynamic responses of the National Renewable Energy Laboratory (NREL)’s OC3-Hywind spar type floating platform with a NREL offshore 5-MW baseline wind turbine under failed mooring conditions using the fully coupled numerical simulation tool FAST. The platform motions in surge, heave and pitch under multiple scenarios are calculated in time-domain. The results describing the FOWT motions in the form of response amplitude operators (RAOs) and spectral densities are presented and discussed in detail. The results indicate that the loss of the mooring system firstly leads to longdistance drift and changes in platform motions. The natural frequencies and the energy contents of the platform motion, the RAOs of the floating structures are affected by the mooring failure to different degrees.

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Demonstration of the Intelligent Mooring System for Floating Offshore Wind Turbines

ASME 2019 2nd International Offshore Wind Technical Conference ◽

10.1115/iowtc2019-7544 ◽

2019 ◽

Cited By ~ 1

Author(s):

Magnus J. Harrold ◽

Philipp R. Thies ◽

Peter Halswell ◽

Lars Johanning ◽

David Newsam ◽

...

Keyword(s):

Wind Turbines ◽

Oil And Gas ◽

Oil And Gas Industry ◽

Offshore Wind ◽

Mooring System ◽

Gas Industry ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Physical Testing ◽

Line Loads

Abstract Existing mooring systems for floating offshore wind turbines are largely based on designs from the oil and gas industry. Even though these can ensure the safe station keeping of the floating wind platform, the design of the mooring system is currently largely conservative, leading to additional expense in an industry striving to achieve cost reduction. Recent interest in the usage of mooring materials with non-linear stiffness has shown that they have the potential to reduce peak line loads, ultimately reducing cost. This paper reports on the combined physical testing and numerical modeling of a hydraulic-based mooring component with these characteristics. The results suggest that the inclusion of the component as part of the OC4 semi-submersible platform can reduce the peak line loads by 10%. The paper also discusses a number of challenges associated with modeling and testing dynamic mooring materials.

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Fault Detection of the Mooring system in Floating Offshore Wind Turbines based on the Wave-excited Linear Model

Journal of Physics Conference Series ◽

10.1088/1742-6596/1618/2/022049 ◽

2020 ◽

Vol 1618 ◽

pp. 022049

Author(s):

Yichao Liu ◽

Alessandro Fontanella ◽

Ping Wu ◽

Riccardo M.G. Ferrari ◽

Jan-Willem van Wingerden

Keyword(s):

Fault Detection ◽

Linear Model ◽

Wind Turbines ◽

Offshore Wind ◽

Mooring System ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

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Hydrodynamic coefficients and pressure loads on heave plates for semi-submersible floating offshore wind turbines: A comparative analysis using large scale models

Renewable Energy ◽

10.1016/j.renene.2015.04.003 ◽

2015 ◽

Vol 81 ◽

pp. 864-881 ◽

Cited By ~ 37

Author(s):

Carlos Lopez-Pavon ◽

Antonio Souto-Iglesias

Keyword(s):

Comparative Analysis ◽

Wind Turbines ◽

Large Scale ◽

Offshore Wind ◽

Hydrodynamic Coefficients ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Scale Models

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Mooring Designs for Floating Offshore Wind Turbines Leveraging Experience From the Oil & Gas Industry

10.1115/omae2021-60739 ◽

2021 ◽

Author(s):

Kai-tung Ma ◽

Yongyan Wu ◽

Simen Fodstad Stolen ◽

Leopoldo Bello ◽

Menno ver der Horst ◽

...

Keyword(s):

Wind Turbines ◽

Large Scale ◽

Wind Farms ◽

Offshore Wind ◽

Synthetic Fiber ◽

Extensive Experience ◽

Gas Industry ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines

Abstract As renewable energy developers start venturing into deeper waters, the floating offshore wind turbines (FOWTs) are becoming the preferred solutions over fixed supporting structures. Many similarities can be identified between a FOWT and a floating oil & gas facility, such as floater concepts (spar, semi-submersible, tension leg platform, etc) and their mooring system designs. This paper focuses on the mooring designs for FOWTs by leveraging the extensive experience gained from the offshore oil & gas industry. Similarities and differences are highlighted in design criteria, mooring analysis, long-term integrity management, installation method and project execution. The established practices regarding mooring design and analysis are reviewed. Anchor radius is recommended based on water depth by referencing sample mooring designs from the oil & gas industry. Long-term mooring integrity and failure rates are summarized. Meanwhile, a few well-known issues are discussed, such as line break due to fatigue, corrosion on chain, and known issues with components such as clump weights. Regarding mooring installation, the established method for prelay and hook-up is reviewed. Finally, opportunities for cost reduction of mooring systems of FOWTs are presented related to project execution of large scale wind farms as well as potential areas of innovation, such as installation methods, use of synthetic fiber rope, and digitalization. In summary, the state-of-the-art practices from the oil & gas industry are reviewed and documented to benefit the developments of upcoming FOWT projects.

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Investigation of Hydrodynamic Forces for Floating Offshore Wind Turbines on Spar Buoys and Tension Leg Platforms with the Mooring Systems in Waves

Applied Sciences ◽

10.3390/app9030608 ◽

2019 ◽

Vol 9 (3) ◽

pp. 608 ◽

Cited By ~ 1

Author(s):

Yu-Hsien Lin ◽

Shin-Hung Kao ◽

Cheng-Hao Yang

Keyword(s):

Wind Turbines ◽

Time Domain ◽

Simulation System ◽

Offshore Wind ◽

Modular System ◽

Mooring System ◽

Mooring Lines ◽

Offshore Wind Turbines ◽

Motion Responses ◽

Floating Offshore Wind Turbines

This study aims to develop a modularized simulation system to estimate dynamic responses of floating Offshore Wind Turbines (OWTs) based on the concepts of spar buoy and Tension Leg Platform (TLP) corresponding with two typical mooring lines. The modular system consists of the hydrodynamic simulator based the Cummins time domain equation, the Boundary Element Method (BEM) solver based on the 3D source distribution method, and an open-source visualization software ParaView to analyze the interaction between floating OWTs and waves. In order to realize the effects of mooring loads on the floating OWTs, the stiffness and damping matrices are applied to the quasi-static mooring system. The Response Amplitude Operators (RAOs) are compared between our predicted results and other published data to verify the modularized simulation system and understand the influence of mooring load on the motion responses in regular or irregular waves. It is also demonstrated that the quasi-static mooring system is applicable to different types of mooring lines as well as determining real-time motion responses. Eventually, wave load components at the resonance frequencies of different motion modes for selected floating OWTs would be present in the time domain.

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Development of Coupled Program fast-simdyn and Study of Non-Linear Hydrodynamics, Coupled With Negative Damping and Aerodynamics of Floating Offshore Wind Turbines

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4045188 ◽

2019 ◽

Vol 142 (2) ◽

Author(s):

Alwin Jose ◽

Jeffrey Falzarano ◽

Hao Wang

Keyword(s):

Computer Program ◽

Wind Turbines ◽

Large Amplitude ◽

Offshore Wind ◽

Wave Forces ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Non Linear ◽

Large Amplitude Motions ◽

Negative Damping

Abstract Non-linear hydrostatic and wave forces on floating structures are very important during large amplitude waves. The computer program simdyn is a blended time domain program developed by Marine Dynamics Laboratory at TAMU and is capable of capturing the role of non-linear fluid forces. simdyn has previously been used to demonstrate that nonlinear hydrostatics have become very important in the problem of parametric excitation. In the current work simdyn is coupled with the computer program fast developed by U.S. National Renewable Energy Laboratory (NREL) for numerical simulation of floating offshore wind turbines (FOWTs). fast-simdyn is now a tool that is capable of studying large amplitude motions of FOWTs in extreme seas. fast-simdyn was then used to study the classic instability of negative damping that occurs in FOWTs that use conventional land-based control. The development of platform pitch and platform surge instability are studied in relation to different wave and wind scenarios. The intent was to do an analysis to see if the non-linear forces do play a significant role in large amplitude motions induced by negative damping. This study gives an indication of whether the development and application of higher fidelity hydrodynamic modules are justified.

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Global analysis of floating offshore wind turbines with shared mooring system

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/1201/1/012024 ◽

2021 ◽

Vol 1201 (1) ◽

pp. 012024

Author(s):

H Munir ◽

C F Lee ◽

M C Ong

Keyword(s):

Wind Turbines ◽

Time Domain ◽

Global Analysis ◽

Cost Effective ◽

Offshore Wind ◽

Mooring Line ◽

Mooring System ◽

Offshore Wind Turbines ◽

Floating Offshore Wind Turbines ◽

Restoring Stiffness

Abstract Floating wind turbines (FWTs) with shared mooring systems can be one of the most cost- effective solutions in reducing mooring costs. First, the static configuration of a shared line is estimated using the elastic catenary equation. The present study investigates the global responses of two FWT with a shared mooring system. Two shared mooring configurations with different horizontal distances between the FWTs are considered. In the first configuration, the FWTs are placed 750m apart; and in the second configuration, they are placed 1000m apart. Two different environmental conditions (ECs) are used to simulate the global responses of the system in time domain. The shared mooring line results in higher extreme motions in surge and sway (degree of freedoms) DOFs due to the reduction of mooring restoring stiffness. The lower mooring restoring stiffness can be attributed to the reduction of one seabed anchoring point for each FWT as compared to a single FWT with three anchors installed. In the rotational DOFs, the shared mooring line configurations result in slight mean offset in each direction and significant increase in the motion standard deviations. This is caused by the reduced mooring stiffness associated with the change in platform orientation.

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