Comparison of wave load effects on a TLP wind turbine by using computational fluid dynamics and potential flow theory approaches

Abstract Tension Leg Platform (TLP) is one of the concepts which shows promising results during initial studies to carry floating wind turbines. One of the concerns regarding tension leg platform wind turbines (TLPWTs) is the high natural frequencies of the structure that may be excited by nonlinear waves loads. Since Computational Fluid Dynamics (CFD) models are capable of capturing nonlinear wave loads, they can lead to better insight about this concern. In the current study, a CFD model based on immersed boundary method, in combination with a two-body structural model of TLPWT is developed to study wave induced responses of TLPWT in deep water. The results are compared with the results of a potential flow theory-finite element software, SIMO-RIFLEX (SR). First, the CFD based model is described and the potential flow theory based model is briefly introduced. Then, a grid sensitivity study is performed and free decay tests are simulated to determine the natural frequencies of different motion modes of the TLPWT. The responses of the TLPWT to regular waves are studied, and the effects of wave height are investigated. For the studied wave heights which vary from small to medium amplitude (wave height over wavelength less than 0.071), the results predicted by the CFD based model are generally in good agreement with the potential flow theory based model. The only considerable difference is the TLPWT mean surge motion which is predicted higher by the CFD model, possibly because of considering the nonlinear effects of the waves loads and applying these loads at the TLPWT instantaneous position in the CFD model. This difference does not considerably affect the important TLPWT design driving parameters such as tendons forces and tower base moment, since it only affects the mean dynamic position of TLPWT. In the current study, the incoming wave frequency is set such that third-harmonic wave frequency coincides with the first tower bending mode frequency. However, for the studied wave conditions a significant excitation of tower natural frequency is not observed. The high stiffness of tendons which results in linear pitch motion of TLPWT hull (less than 0.02 degrees) and tower (less than 0.25 degrees) can explain the limited excitement of the tower first bending mode. The good agreement between CFD and potential flow theory based results for small and medium amplitude waves gives confidence to the proposed CFD based model to be further used for hydrodynamic analysis of floating wind turbines in extreme ocean conditions.

[1]  Jason Jonkman,et al.  Comparison of Hydrodynamic Load Predictions Between Reduced Order Engineering Models and Computational Fluid Dynamics for the OC4-DeepCwind Semi-Submersible , 2014 .

[2]  Amitabh Kumar,et al.  Ringing of Heidrun TLP In High And Steep Random Waves , 2002 .

[3]  Torgeir Moan,et al.  Benchmarking of a Computational Fluid Dynamics-Based Numerical Wave Tank for Studying Wave Load Effects on Fixed and Floating Offshore Structures , 2017 .

[4]  Arne Nestegård,et al.  A New Nonslender Ringing Load Approach Verified Against Experiments , 1998 .

[5]  Hideaki Miyata,et al.  Fully non‐linear free‐surface simulations by a 3D viscous numerical wave tank , 1999 .

[6]  Sandy Butterfield,et al.  Feasibility of Floating Platform Systems for Wind Turbines: Preprint , 2004 .

[7]  Gretar Tryggvason,et al.  A Nonlinear Computational Model for Floating Wind Turbines , 2012 .

[8]  Erin Elizabeth Bachynski.  Design and Dynamic Analysis of Tension Leg Platform Wind Turbines , 2014 .

[9]  Jinping Ou,et al.  Coupled wind-wave time domain analysis of floating offshore wind turbine based on Computational Fluid Dynamics method , 2014 .

[10]  Cheng Liu,et al.  Hydrodynamic analysis of a semi-submersible type floating wind turbine , 2014 .

[11]  Odd M. Faltinsen,et al.  Nonlinear wave loads on a slender vertical cylinder , 1995, Journal of Fluid Mechanics.

[12]  Cheng Liu,et al.  CFD Simulation of a Floating Wind Turbine Platform in Rough Sea Conditions , 2014 .

[13]  Eldad J. Avital,et al.  Large Eddy Simulation of Flow Past Free Surface Piercing Circular Cylinders , 2008 .

[14]  J. Jonkman,et al.  Definition of a 5-MW Reference Wind Turbine for Offshore System Development , 2009 .

[15]  M. A. MacIver,et al.  A versatile implicit iterative approach for fully resolved simulation of self-propulsion , 2010 .

[16]  Frederick Stern,et al.  Sharp interface immersed-boundary/level-set method for wave-body interactions , 2009, J. Comput. Phys..

[17]  John Lonergan.  Dynamic Behaviour of Models of Tethered Buoyant Platforms , 1980 .

[18]  P. Queutey,et al.  A NUMERICAL SIMULATION OF VORTEX SHEDDING FROM AN OSCILLATING CIRCULAR CYLINDER , 2002 .

[19]  Carl Trygve Stansberg,et al.  Integrated Vessel Motion And Mooring Analysis Applied In Hybrid Model Testing , 1999 .

[20]  Po Wen Cheng,et al.  Analysis of floating offshore wind turbine hydrodynamics using coupled CFD and multibody methods , 2013 .

[21]  Lehigh Preserve,et al.  Oscillations of a vertical elastically-mounted cylinder in a wave , 1999 .

[22]  Torgeir Moan,et al.  Wind-wave misalignment effects on floating wind turbines: motions and tower load effects , 2014 .

[23]  Gretar Tryggvason,et al.  Nonlinear simulation of a spar buoy floating wind turbine under extreme ocean conditions , 2014 .

[24]  S. Osher,et al.  Regular ArticleUniformly High Order Accurate Essentially Non-oscillatory Schemes, III , 1997 .

[25]  Gretar Tryggvason,et al.  A Nonlinear Computational Model of Floating Wind Turbines , 2013 .

[26]  Moo-Hyun Kim,et al.  Rotor-floater-tether coupled dynamics including second-order sum–frequency wave loads for a mono-column-TLP-type FOWT (floating offshore wind turbine) , 2013 .

[27]  Torgeir Moan,et al.  Ringing loads on tension leg platform wind turbines , 2014 .

[28]  T. Yabe,et al.  The constrained interpolation profile method for multiphase analysis , 2001 .

[29]  Rolf Baarholm,et al.  Ultra-Deepwater Model Testing of a Semisubmersible and Hybrid Verification , 2008 .

[30]  John A. Mercier,et al.  Evaluation of Hutton TLP Response to Environmental Loads , 1982 .

[31]  Jason Jonkman,et al.  Coupled Dynamic Modeling of Floating Wind Turbine Systems , 2006 .

[32]  R. W. Walker.  Deep Water Oil Production System , 1968 .

[33]  Torgeir Moan,et al.  Comparison of Wave-induced Response of a TLP Wind Turbine Obtained by CFD Method and Potential Theory , 2014 .

[34]  Torgeir Moan,et al.  Design considerations for tension leg platform wind turbines , 2012 .

[35]  Jason Jonkman,et al.  The effect of second-order hydrodynamics on floating offshore wind turbines , 2013 .

[36]  Gretar Tryggvason,et al.  Direct Numerical Simulations of Gas–Liquid Multiphase Flows: Preface , 2011 .

[37]  Paul D. Sclavounos,et al.  Floating Offshore Wind Turbines , 2008 .

[38]  Erin Elizabeth Bachynski,et al.  Global Analysis of Floating Wind Turbines: Code Development, Model Sensitivity And Benchmark Study , 2012 .

[39]  Turgut Sarpkaya,et al.  Force on a circular cylinder in viscous oscillatory flow at low Keulegan—Carpenter numbers , 1986, Journal of Fluid Mechanics.

[40]  Jason Jonkman,et al.  Dynamics of offshore floating wind turbines—analysis of three concepts , 2011 .

[41]  Lei Wang,et al.  Multibody dynamics of floating wind turbines with large-amplitude motion , 2013 .

[42]  S. Osher,et al.  A level set approach for computing solutions to incompressible two-phase flow , 1994 .

[43]  Ronald Fedkiw,et al.  Level set methods and dynamic implicit surfaces , 2002, Applied mathematical sciences.

[44]  S. Osher,et al.  Uniformly high order accurate essentially non-oscillatory schemes, 111 , 1987 .

[45]  J. Sethian,et al.  Fronts propagating with curvature-dependent speed: algorithms based on Hamilton-Jacobi formulations , 1988 .