A fully coupled frequency domain model for floating offshore wind turbines

2019 ◽  
Vol 5 (2) ◽  
pp. 135-158 ◽  
Author(s):  
Meysam Karimi ◽  
Brad Buckham ◽  
Curran Crawford
Keyword(s):  
Frequency Domain ◽  
Wind Turbines ◽  
Domain Model ◽  
Offshore Wind ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Fully Coupled

scholarly journals Iterative Frequency-Domain Response of Floating Offshore Wind Turbines with Parametric Drag

2018 ◽  
Vol 6 (4) ◽  
pp. 118 ◽  
Author(s):  
Frank Lemmer ◽  
Wei Yu ◽  
Po Cheng
Keyword(s):  
System Dynamics ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Domain Model ◽  
Offshore Wind ◽  
Viscous Drag ◽  
Drag Coefficients ◽  
Reduced Order ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines

Methods for coupled aero-hydro-servo-elastic time-domain simulations of Floating Offshore Wind Turbines (FOWTs) have been successfully developed. One of the present challenges is a realistic approximation of the viscous drag of the wetted members of the floating platform. This paper presents a method for an iterative response calculation with a reduced-order frequency-domain model. It has heave plate drag coefficients, which are parameterized functions of literature data. The reduced-order model does not represent more than the most relevant effects on the FOWT system dynamics. It includes first-order and second-order wave forces, coupled with the wind turbine structural dynamics, aerodynamics and control system dynamics. So far, the viscous drag coefficients are usually defined as constants, independent of the load cases. With the computationally efficient frequency-domain model, it is possible to iterate the drag, such that it fits to the obtained amplitudes of oscillation of the different members. The results show that the drag coefficients vary significantly across operational load conditions. The viscous drag coefficients converge quickly and the method is applicable for concept-level design studies of FOWTs with load case-dependent drag.

scholarly journals A Fully Coupled Computational Fluid Dynamics Method for Analysis of Semi-Submersible Floating Offshore Wind Turbines Under Wind-Wave Excitation Conditions Based on OC5 Data

2018 ◽  
Vol 8 (11) ◽  
pp. 2314 ◽  
Author(s):  
Yin Zhang ◽  
Bumsuk Kim
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Wind Turbine ◽  
Wind Turbines ◽  
Wind Wave ◽  
Offshore Wind ◽  
Wave Excitation ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Fully Coupled

Accurate prediction of the time-dependent system dynamic responses of floating offshore wind turbines (FOWTs) under aero-hydro-coupled conditions is a challenge. This paper presents a numerical modeling tool using commercial computational fluid dynamics software, STAR-CCM+(V12.02.010), to perform a fully coupled dynamic analysis of the DeepCwind semi-submersible floating platform with the National Renewable Engineering Lab (NREL) 5-MW baseline wind turbine model under combined wind–wave excitation environment conditions. Free-decay tests for rigid-body degrees of freedom (DOF) in still water and hydrodynamic tests for a regular wave are performed to validate the numerical model by inputting gross system parameters supported in the Offshore Code Comparison, Collaboration, Continued, with Correlations (OC5) project. A full-configuration FOWT simulation, with the simultaneous motion of the rotating blade due to 6-DOF platform dynamics, was performed. A relatively heavy load on the hub and blade was observed for the FOWT compared with the onshore wind turbine, leading to a 7.8% increase in the thrust curve; a 10% decrease in the power curve was also observed for the floating-type turbines, which could be attributed to the smaller project area and relative wind speed required for the rotor to receive wind power when the platform pitches. Finally, the tower-blade interference effects, blade-tip vortices, turbulent wakes, and shedding vortices in the fluid domain with relatively complex unsteady flow conditions were observed and investigated in detail.

scholarly journals An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

2018 ◽  
Vol 3 (2) ◽  
pp. 693-712 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Henrik Bredmose
Keyword(s):  
Wind Speed ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Degrees Of Freedom ◽  
Bending Moment ◽  
Domain Model ◽  
Offshore Wind ◽  
Hydrodynamic Damping ◽  
Floating Offshore Wind Turbines ◽  
Load Analysis

Abstract. A model for Quick Load Analysis of Floating wind turbines (QuLAF) is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: floater surge, heave, pitch and first tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are pre-computed in WAMIT and FAST, respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower base is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real time.

Effects of Platform Mounting Orientations on the Long-Term Performance of a Semisubmersible Wind Turbine

2019 ◽  
Author(s):  
Shengtao Zhou ◽  
Chao Li ◽  
Yiqing Xiao ◽  
Frank Lemmer ◽  
Wei Yu ◽  
...  
Keyword(s):  
Wind Turbine ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Wind Wave ◽  
Domain Model ◽  
Offshore Wind ◽  
Wave Load ◽  
Symmetrical Configuration ◽  
Floating Offshore Wind Turbines

Abstract Due to the non-fully-symmetrical configuration, the platform laying angle of semi-submersible floating offshore wind turbines relative to wind/wave load directions has a noticeable influence on the dynamics characteristics of the whole structure, which indicates that the platform mounting orientation should be carefully considered before installation at sea. The directionality effects of short-term wind/wave loads had been discussed in previous studies, which are, however, insufficient to make a full understanding of the directionality impacts. In our study, based on a 25-year met-ocean database, long-term analysis is carried out by means of an efficient frequency-domain model with eight degrees of freedom. The nonlinear quantities such as aerodynamic loads, aerodynamic damping and mooring stiffness are derived from the time-domain simulation tool FAST, serving as a preprocessing database for the frequency-domain model. A case study is carried out by comparing the long-term responses of a Y-shape semi-submersible floating wind turbine in four mounting orientations. Significant differences can be seen. The platform mounted in the most unfavorable orientation tends to suffer from larger peak nacelle acceleration, which would increase the loads and cause higher tower base fatigue damage. These findings highlight the importance of platform mounting orientations and can serve as a basis for the installation of semi-submersible floating wind turbines.

scholarly journals Establishing a fully coupled CFD analysis tool for floating offshore wind turbines

2017 ◽  
Vol 112 ◽  
pp. 280-301 ◽  
Author(s):  
Yuanchuan Liu ◽  
Qing Xiao ◽  
Atilla Incecik ◽  
Christophe Peyrard ◽  
Decheng Wan
Keyword(s):  
Wind Turbines ◽  
Offshore Wind ◽  
Analysis Tool ◽  
Cfd Analysis ◽  
Offshore Wind Turbines ◽  
Floating Offshore Wind Turbines ◽  
Fully Coupled

scholarly journals An efficient frequency-domain model for quick load analysis of floating offshore wind turbines

2018 ◽  
Author(s):  
Antonio Pegalajar-Jurado ◽  
Michael Borg ◽  
Henrik Bredmose
Keyword(s):  
Wind Speed ◽  
Frequency Domain ◽  
Wind Turbines ◽  
Degrees Of Freedom ◽  
Bending Moment ◽  
Domain Model ◽  
Offshore Wind ◽  
Hydrodynamic Damping ◽  
Floating Offshore Wind Turbines ◽  
Load Analysis

Abstract. A model for Quick Load Analysis of Floating wind turbines, QuLAF, is presented and validated here. The model is a linear, frequency-domain, efficient tool with four planar degrees of freedom: platform surge, heave, pitch and tower modal deflection. The model relies on state-of-the-art tools from which hydrodynamic, aerodynamic and mooring loads are extracted and cascaded into QuLAF. Hydrodynamic and aerodynamic loads are precomputed in WAMIT and FAST respectively, while the mooring system is linearized around the equilibrium position for each wind speed using MoorDyn. An approximate approach to viscous hydrodynamic damping is developed, and the aerodynamic damping is extracted from decay tests specific for each degree of freedom. Without any calibration, the model predicts the motions of the system in stochastic wind and waves with good accuracy when compared to FAST. The damage-equivalent bending moment at the tower bottom is estimated with errors between 0.2 % and 11.3 % for all the load cases considered. The largest errors are associated with the most severe wave climates for wave-only conditions and with turbine operation around rated wind speed for combined wind and waves. The computational speed of the model is between 1300 and 2700 times faster than real-time.

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