Effects of second-order difference-frequency wave forces on a new floating platform for an offshore wind turbine

To better access the abundant offshore wind resource, efforts are being made across the world to develop and improve floating offshore wind turbine technologies. A critical aspect of creating reliable, mature floating wind turbine technology is the development, verification, and validation of efficient computer-aided-engineering (CAE) tools. The National Renewable Energy Laboratory (NREL) has created FAST, a comprehensive, coupled analysis CAE tool for floating wind turbines, which has been verified and utilized in numerous floating wind turbine studies. Several efforts are underway to validate the floating platform functionality of FAST to complement its already validated aerodynamic and structural simulation capabilities. The research employs the 1/50th-scale DeepCwind wind/wave basin model test dataset, which was obtained at the Maritime Research Institute Netherlands (MARIN) in 2011. This paper describes further work being undertaken to continue this validation. These efforts focus on FAST’s ability to replicate global response behaviors associated with dynamic wind forces and second-order difference-frequency wave-diffraction forces separately and simultaneously. The first step is the construction of a FAST numerical model of the DeepCwind semi-submersible floating wind turbine that includes alterations for the addition of second-order difference-frequency wave-diffraction forces. The implementation of these second-order wave forces, which are not currently standard in FAST, are outlined and discussed. After construction of the FAST model, the calibration of the FAST model’s wind turbine aerodynamics, tower-bending dynamics, and platform hydrodynamic damping using select test data is discussed. Subsequently, select cases with coupled dynamic wind and irregular wave loading are simulated in FAST, and these results are compared to test data. Particular attention is paid to global motion and load responses associated with the interaction of the wind and wave environmental loads. These loads are most prevalent in the vicinity of the rigid-body motion natural frequencies for the DeepCwind semi-submersible, with dynamic wind forces and the second-order difference-frequency wave-diffraction forces driving the global system response at these low frequencies. Studies are also performed to investigate the impact of neglecting the second-order wave forces on the predictive capabilities of the FAST model. The comparisons of the simulation and test results highlight the ability of FAST to accurately capture many of the important coupled global response behaviors of the DeepCwind semi-submersible floating wind turbine.

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Effects of Second-Order Difference-Frequency Wave Forces on Floating Wind Turbine Under Survival Condition

Transactions of Tianjin University ◽

10.1007/s12209-017-0037-2 ◽

2017 ◽

Vol 23 (2) ◽

pp. 130-137 ◽

Cited By ~ 2

Author(s):

Jiawen Li ◽

Yichen Jiang ◽

Yougang Tang ◽

Xiaoqi Qu ◽

Jiawei Zhai

Keyword(s):

Wind Turbine ◽

Second Order ◽

Difference Frequency ◽

Wave Forces ◽

Frequency Wave ◽

Order Difference ◽

Floating Wind Turbine ◽

Survival Condition

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Coupled Numerical Analysis of a Concept TLB Type Floating Offshore Wind Turbine

Volume 10: Ocean Renewable Energy ◽

10.1115/omae2019-95244 ◽

2019 ◽

Author(s):

Iman Ramzanpoor ◽

Martin Nuernberg ◽

Longbin Tao

Keyword(s):

Wind Turbine ◽

Renewable Energy Sources ◽

Second Order ◽

Offshore Wind ◽

Design Stage ◽

Offshore Wind Turbine ◽

Clear Understanding ◽

Mooring System ◽

Floating Platform ◽

Floating Offshore Wind Turbine

Abstract The main drivers for the continued decarbonisation of the global energy market are renewable energy sources. Moreover, the leading technological solutions to achieve this are offshore wind turbines. As installed capacity has been increasing rapidly and shallow water near shore sites are exhausted, projects will need to be developed further from shore and often in deeper waters, which will pose greater technical challenges and constrain efforts to reduce costs. Current floating platform solutions such as the spar and semi-submersible rely on large amounts of ballast and complex structural designs with active stabilisation systems for stability of the floating offshore wind turbine platform (FOWT). The primary focus of this study is to present a design concept and mooring arrangement for an alternative floating platform solution that places emphasis on the mooring system to achieve stability for a FOWT. The tension leg buoy (TLB) is designed to support future 10MW offshore wind turbine generators. This paper presents the numerical methodology used for a coupled hydro-elastic analysis of the floater and mooring system under combined wind, wave and current effects. A concept TLB design is presented and its platform motion and mooring line tension characteristics are analysed for a three-hour time domain simulation representing operating and survival conditions in the northern North Sea with water depths of 110 metres. The importance of wave drift forces and the other non-linear excitation forces in the concept design stage are evaluated by comparing the motion and tension responses of three different numerical simulation cases with increasing numerical complexity. The preliminary TLB system design demonstrated satisfactory motion response for the operation of a FOWT and survival in a 100-year storm condition. The results show that accounting for second-order effect is vital in terms of having a clear understanding of the full behaviour of the system and the detailed response characteristics in operational and survival conditions. Extreme loads are significantly reduced when accounting for the second-order effects. This can be a key aspect to not overdesign the system and consequently achieve significant cost savings.

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Rotor-floater-tether coupled dynamics including second-order sum–frequency wave loads for a mono-column-TLP-type FOWT (floating offshore wind turbine)

Ocean Engineering ◽

10.1016/j.oceaneng.2013.01.010 ◽

2013 ◽

Vol 61 ◽

pp. 109-122 ◽

Cited By ~ 29

Author(s):

Y.H. Bae ◽

M.H. Kim

Keyword(s):

Wind Turbine ◽

Second Order ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Wave Loads ◽

Coupled Dynamics ◽

Frequency Wave ◽

Floating Offshore Wind Turbine ◽

Sum Frequency

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Effects of Second-Order Hydrodynamics on the Dynamic Responses and Fatigue Damage of a 15 MW Floating Offshore Wind Turbine

Journal of Marine Science and Engineering ◽

10.3390/jmse9111232 ◽

2021 ◽

Vol 9 (11) ◽

pp. 1232

Author(s):

Xuan Mei ◽

Min Xiong

Keyword(s):

Wind Turbine ◽

Fatigue Damage ◽

Second Order ◽

Dynamic Responses ◽

Offshore Wind ◽

Extreme Condition ◽

Offshore Wind Turbine ◽

Floating Platform ◽

Floating Offshore Wind Turbine ◽

The Cost

In order to investigate the effects of second-order hydrodynamic loads on a 15 MW floating offshore wind turbine (FOWT), this study employs a tool that integrates AQWA and OpenFAST to conduct fully coupled simulations of the FOWT subjected to wind and wave loadings. The load cases covering normal and extreme conditions are defined based on the met-ocean data observed at a specific site. The results indicate that the second-order wave excitations activate the surge mode of the platform. As a result, the surge motion is increased for each of the examined load case. In addition, the pitch, heave, and yaw motions are underestimated when neglecting the second-order hydrodynamics under the extreme condition. First-order wave excitation is the major contributor to the tower-base bending moments. The fatigue damage of the tower-base under the extreme condition is underestimated by 57.1% if the effect of second-order hydrodynamics is ignored. In addition, the accumulative fatigue damage over 25 years at the tower-base is overestimated by 16.92%. Therefore, it is suggested to consider the effects of second-order wave excitations of the floating platform for the design of the tower to reduce the cost of the FOWT.

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Influence of Wave Induced Second-Order Forces in Semisubmersible FOWT Mooring Design

Journal of Offshore Mechanics and Arctic Engineering ◽

10.1115/1.4030241 ◽

2015 ◽

Vol 137 (3) ◽

Cited By ~ 6

Author(s):

Carlos Lopez-Pavon ◽

Rafael A. Watai ◽

Felipe Ruggeri ◽

Alexandre N. Simos ◽

Antonio Souto-Iglesias

Keyword(s):

Wind Turbine ◽

Large Scale ◽

Transfer Functions ◽

Subsequent Development ◽

Second Order ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Floating Platform ◽

Numerical Predictions ◽

Floating Offshore Wind Turbines

AZIMUT project (Spanish CENIT R&D program) is designed to establish the technological groundwork for the subsequent development of a large-scale offshore wind turbine. The project (2010–2013) has analyzed different alternative configurations for the floating offshore wind turbines (FOWT): SPAR, tension leg platform (TLP), and semisubmersible platforms were studied. Acciona, as part of the consortium, was responsible of scale-testing a semisubmersible platform to support a 1.5 MW wind turbine. The geometry of the floating platform considered in this paper has been provided by the Hiprwind FP7 project and is composed by three buoyant columns connected by bracings. The main focus of this paper is on the hydrodynamic modeling of the floater, with especial emphasis on the estimation of the wave drift components and their effects on the design of the mooring system. Indeed, with natural periods of drift around 60 s, accurate computation of the low-frequency second-order components is not a straightforward task. Methods usually adopted when dealing with the slow-drifts of deep-water moored systems, such as the Newman's approximation, have their errors increased by the relatively low resonant periods of the floating system and, since the effects of depth cannot be ignored, the wave diffraction analysis must be based on full quadratic transfer functions (QTFs) computations. A discussion on the numerical aspects of performing such computations is presented, making use of the second-order module available with the seakeeping software wamit®. Finally, the paper also provides a preliminary verification of the accuracy of the numerical predictions based on the results obtained in a series of model tests with the structure fixed in bichromatic waves.

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Influence of Wave Induced Second-Order Forces in Semi-Submersible FOWT Mooring Design

Volume 8: Ocean Renewable Energy ◽

10.1115/omae2013-10459 ◽

2013 ◽

Cited By ~ 1

Author(s):

Carlos López-Pavón ◽

Rafael A. Watai ◽

Felipe Ruggeri ◽

Alexandre N. Simos ◽

Antonio Souto-Iglesias

Keyword(s):

Wind Turbine ◽

Large Scale ◽

Transfer Functions ◽

Subsequent Development ◽

Second Order ◽

Offshore Wind ◽

Offshore Wind Turbine ◽

Floating Platform ◽

Numerical Predictions ◽

Floating Offshore Wind Turbines

AZIMUT project (Spanish CENIT R&D program) is designed to establish the technological groundwork for the subsequent development, of a large-scale offshore wind turbine. The project (2010–2013) has analysed different floating offshore wind turbines (FOWT): SPAR, TLP and Semi-Submersible platforms were studied. Acciona, as part of the consortium, was responsible of scale-testing a Semi-submersible platform to support a 1.5MW wind turbine. The floating platform geometry considered in this paper has been provided by the Hiprwind FP7 project and is composed by three buoyant columns connected by bracings. The main focus of this paper is on hydrodynamic modelling of the floater, with especial emphasis on the estimation of the wave drift components and their effects on the design of the mooring system. Indeed, with natural periods of drift around 60 seconds, accurate computation of the low-frequency second-order components is not a straightforward task. As methods usually adopted when dealing with the slow-drifts of deep-water moored systems, such as Newman’s approximation, have their errors increased by the relatively low resonant periods, and as the effects of depth cannot be ignored, the wave diffraction analysis must be based on full Quadratic Transfer Functions (QTF) computations. A discussion on the numerical aspects of performing such computations is presented, making use of the second-order module available with the seakeeping software WAMIT®. Finally, the paper also provides a preliminary verification of the accuracy of the numerical predictions based on the results obtained in a series of model tests with the structure fixed in bichromatic waves.

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