| The development of new energy has always been the focus of energy technology research around the world.Wind energy has become one of the important directions of new energy development with its advantages of clean and renewable.The high-quality wind energy resources in deep sea are extremely rich.In order to better develop offshore wind power resources,scholars from various countries have carried out research on offshore floating wind turbines.Among them,Spar floating wind turbine has attracted much attention because of its suitable water depth,strong ability to withstand harsh sea conditions and low cost.However,as the foundation structure of Spar floating wind turbine is a cylindrical structure,this type of structure will produce alternate shedding vortex behind the current,and the shedding of the vortex will produce periodic pulse power on the foundation structure,thus triggering the vortex-induced motion of the foundation structure of Spar floating wind turbine.When the pulse dynamic frequency is close to the natural frequency of the floating wind turbine system,the frequency locking will cause a large displacement,and the large eddy displacement will shorten the fatigue life of the foundation structure and the mooring system.Therefore,the research on vortexinduced motion of Spar floating foundation structure has important theoretical significance and engineering value.In this paper,computational fluid dynamics(CFD)numerical simulation method is used to study the vortex-induced motion characteristics of the foundation structure of Spar floating wind turbine.In the process of numerical simulation,the motion system is simplified as a mass(m)–spring(k)–damping(ζ)system,and the motion equation is written by using the custom function(UDF),embedded in the Fluent solver,and combined with the overlapping grid technology to realize the fluid-structure interaction.The vortexinduced motion characteristics of the foundation structure of Spar floating wind turbine are analyzed from the aspects of vortex-induced motion response amplitude,frequency ratio,displacement and flow field morphology.Before analyzing the vortex-induced motion of the Spar-type floating wind turbine foundation,the flow around the three-dimensional cylinder and the vortex-induced motion characteristics are studied first.The flow around a three-dimensional cylinder is numerically simulated.The variation of lift and drag coefficients of the cylinder at Reynolds number 4900～60000 is studied.The vortex shedding frequency of the cylinder is analyzed by fast Fourier transform.It is found that the vortex shedding frequency increases linearly with the increase of flow velocity.Subsequently,the convection field was analyzed to reproduce the classical Karman vortex street phenomenon;however,at different heights,the streamlines show significant differences,showing threedimensional characteristics.Then,the three-dimensional cylindrical vortex-induced motion is numerically simulated,and the response amplitude,frequency ratio and motion trajectory of the cylindrical vortex-induced motion are analyzed.It is found that when Ur=5.28～11.88,the vortex-induced motion enters the locking interval.At this time,the frequency ratio is 1,and the response amplitude is large.It is also found that the motion trajectory of the cylindrical vortex-induced motion is ‘8’ shape.The reliability of the numerical simulation method in this paper is verified by comparing the numerical simulation results with the classical test results.The above method is applied to study the flow around the foundation structure and vortex-induced motion of Spar floating wind turbine.In this paper,the scale of Spar floating wind turbine foundation structure is 1 : 100,and the scale model is used for numerical simulation.After the numerical simulation of the vortex-induced motion,it is found that when the mass ratio of the low-damping Spar floating wind turbine foundation structure is 1,the vortex-induced motion response enters the locking range when Ur=9.18～13.25,and the frequency ratio remains near 1.The maximum amplitude of the vortex-induced motion sway response can reach 2.3D,and the maximum amplitude of the sway response can reach 1D.The trajectory of this stage is also ’ 8 ’ shaped.The suppression of vortex-induced motion is also the focus of this study.In this paper,the vortex-induced motion is suppressed by installing a spiral side plate on the surface of the Spar floating wind turbine foundation structure.Fifteen spiral side plates with different parameters were set to analyze the inhibitory effect of different spiral side plates.It is found that the spiral side plate with pitch ratio P/D = 5 and height H = 0.15 D has the best effect on suppressing vortex-induced motion on the basic structure of Spar floating wind turbine.In summary,in this paper,the vortex-induced motion characteristics of Spar floating wind turbine foundation structure are studied by numerical simulation method,and the spiral side plate parameters with good effect of suppressing vortex-induced motion are given,which provides certain theoretical basis and technical support for subsequent theoretical research and engineering design. |
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