The Research Of Characteristic And Strength Of Tension Leg Floating Offshore Wind Turbine On Vortex Induced Vibration

With the increase of the proportion of wind energy in the energy and the stability of the deep sea wind speed,offshore wind power generation develops from shallow to deep sea,at the same time the basis of offshore wind turbine develops from stationary type to floating type.With the low cost and good overall performance,the tension leg foundation,one of the floating basises,get more attention and research.The tension leg becomes longer and longer,the structure stiffness becomes samller and smaller.Therefore,the vortex induced vibration response of tension leg due to ocean current is dominant factor in the all load factors,it can cause strength damage,fatigue damage and stress concentration.More serious is that it not only causes the overturning of the tension leg platform,but also reduces the service life of the tension leg.In this paper,the research uses ANSYS CFX software to simulate the vortex-induced vibration of two-dimension tension leg and three-dimension tension leg basing on the theory of computational fluid mechanics and SST k-w turbulence model.The vortex induced vibration simulation of three-dimension tension leg uses two-way fluid-solid coupling to solve the fluid domain and the solid domain.The research firstly simulates the vortex-induced vibration of two-dimension tension leg when Re = 200,3900 and compares the simulaton data with related experimental data such as the karman vortex street,lift coefficient and drag coefficient to verify the accuracy of the meshing method,size and the boundary conditions,next simulate the the vortex-induced vibration of the real scale tension leg.Secondly,the research simulates the vortex-induced vibration of classic experiment and compare the results with the experimental data to analyze the reliability of the numerical simulation method of three-dimension vortex induced vibration.Next the research simulates five groups current conditions to analyze the vortex-induced vibration characteristics and strength.With the three-dimensional features of the tension leg vortexinduced vibration,the vibration of tension leg is variable amplitude and sinusoidal oscillation compared with the two-dimension vortex-induced vibration.As the current speed increases,we found that the required time to form stable vortex-induced vibration is declining,the curve of drag coefficient appears secondary growth,and the most dangerous working condition is 0.325 m/s.Finally,the research through the numerical simulation to analyze the influence of the current form,boundary constraint conditions and the magnitude of the pretension to vortex-induced vibration Characteristic and provides reference basis for actual engineering.In actual project,the stress concentration of tension leg is reduced after the loss of pretension,but the transverse and longitudinal displacement of tension leg increases.With the elastic restraint condition,the stress concentration at the top of the tension leg more slowly down than the hinged constraints,but the stress of the bottom increase.Under shear current v=0.199m/s,we find the trend of the lateral vibration displacement and Z/L = 0.75 area is part of the biggest displacement and stress.On the other hand,drag coefficient,the lift coefficient and lateral displacement grow 5%,79%,300% respectively due to light movement of tension leg platform.As a whole,the fatigue damage and the intensity of damage is greater than the theory research of the numerical simulation,so these factors should be considered in the design and use process,at the same time we should strengthen the constraint condition of the top.