Numerical Simulation And Application Of Mixed Wave Based On Bimodal Wave Spectrum

With the continuous increase of exchanges around the world and the increasing prosperity of ocean trade,the complex wave environment of the ocean has attracted more and more attention.Ocean waves can be divided into wind waves,swell waves and mixed waves,and different wave environments have different effects on ship motion.At present,many scholars have conducted in-depth research on irregular waves in the marine environment,but the research on mixed waves is still insufficient,and there are few studies on the motion response of ships under mixed waves.But the mixed wave is the superposition of wind wave and swell wave,so it is very important to study its specific characteristics.Therefore,this article will use the self-developed CFD solver HUST-Ship to simulate and analyze on mixed waves in various sea states.Because the mixed wave is superimposed by wind wave and surge wave,its wave spectrum often presents double-peak or even multi-peak characteristics.Therefore,based on a common wave spectrum Ochi-Hubble six-parameter double-peak spectrum used to simulate the mixed wave,this paper carries out numerical simulation for the mixed waves with a total of seven sea conditions,including the fourth stage upper limit to the eighth stage upper limit.In this paper,a numerical wave tank is established by using a self-developed solver.The boundary velocity inlet is used as the wave generation method,the damping source term combined with grid sparsity is used as the wave elimination method.Before the numerical simulation,the independence of grid and time step was verified,and the influences of different discrete methods,discrete number and length of wave elimination region on the simulation results were compared.Finally,the theoretical Ochi-Hubble spectrum of different sea states was discretized into 50 parts by the method of equal frequency division,and the length of wave elimination region was set as 1.5L.After the simulation,the numerical wave making ability of the solver is proved by comparing the characteristics of time domain and frequency domain.And then,the motion response of the ship under the sea conditions of six and eight upper limits is studied.The research object was DTMB5512 ship model,and the ship seakeeping was compared with the ordinary irregular waves discrete by ITTC spectrum under the same energy.Through numerical wave making and ship seakeeping numerical simulation prediction,it is shown that the error of the simulation results obtained by the self-developed solver is small.In addition,it is also shown that under the same energy,the mixed wave with a larger proportion of swell wave is more concentrated in energy,and the significant wave height is larger than the mixed wave with a same proportion of swell wave and wind wave,which poses a greater threat to ship navigation.The mixed waves of the same energy have more concentrated energy,so the impact on the heave and pitch motion response of the ship at some frequencies is greater than that of ordinary irregular waves.Through the prediction and detailed analysis,we know more about the characteristics of mixed waves under high sea conditions.