| In recent years,the demand for energy is increasing with the vigorous economic development of many countries.The reserves of traditional fossil energy have declined year by year with the continuous exploitation.Burning fossil fuels causes environmental pollution and global warming.Therefore,people are committed to developing and utilizing renewable and clean energy.At present,wind energy,mainly onshore wind power,accounts for the largest proportion of renewable energy,but onshore wind field will affect the surrounding environment,and onshore wind resources are less abundant than offshore wind resources.Offshore wind power is gradually developing,but the complex Marine environment including wind,waves and ocean currents make it face challenges such as immature technology,limited operational experience,high construction cost and difficult operation,maintenance and implementation.Therefore,it is necessary to analyze the aerodynamic behavior of blades and the hydrodynamic performance of foundation,so as to improve the adaptability and reliability of the offshore wind turbines to the Marine environment.In this paper,dynamic response and mooring tension of OC4 Deep Cwind semi-submersible floating wind turbine platform in various sea conditions are studied by means of computational fluid dynamics(CFD).Compared with potential flow theory,CFD method can effectively consider the viscosity of fluid,has more advantages in solving nonlinear free surface flow,large motion of floating body and other problems,and can simulate the actual fluid movement more accurately.In view of the ocean wave environment,STAR CCM+ software is used to establish a variety of regular wave and irregular wave pools.The free surface is captured by VOF method,and wave damping is set before the outlet for wave elimination.Three regular wave conditions are simulated based on Stokes fifth wave theoretical model,and two irregular wave conditions are simulated based on JONSWAP wave spectrum.The results show that,due to the energy dissipation caused by viscosity and the interaction between wave and boundary,the wave may attenuate to some extent in the process of propagation,but the wave attenuating degree is small,and the overall effect of wave generation and wave elimination is good.The catenary coupling module of STAR CCM+ adopts the quasi-static mooring model,which cannot take into account the phenomenon of mooring line lying on the ground and the corresponding forces.The calculated periods and amplitudes of surge and sway are too large.In order to solve this problem,a user code written in C language is created to couple STAR CCM + with Moor Dyn,a mooring application based on lumped mass method,and improve the problem of large differences between the mooring line simulation of STAR CCM+ and actual situation.The coupled program is also used to calculate the free decay motions of OC4 Deep Cwind floating platform.Accurate platform movement periods of six degrees of freedom are obtained,and the damping ratio results are more accur ate than those of Open FAST.The dynamic response and mooring line tension of the platform in different regular waves and irregular waves are calculated by using the coupl ed program and the overset grid method.The results show that the movement of the plat form is more intense in the early stage.Compared with the FAST simulation results in the literatures,the heave,surge and pitch RAO results of the coupl ed program are more consistent with the experimental results.The platform may resonate with the waves on the heave motion,which may cause a larger heave motion.In addition,the maximum of surge motion of the platform in extreme irregular wave condition is 1.63 times of that in normal wave condition,and the maximum mooring line tension is 1.45 times of that in normal wave conditions. |
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