Numerical Simulation Of Rogue Waves And Their Interaction With Structures Based On SPH Method

In recent years,the phenomena of rogue waves attacking marine structures have occurred frequently.As a kind of instantaneous wave with huge wave height,the rogue wave has a complicated cause and is accompanied by a certain degree of randomness.In the process of interacting the marine structure,it often cause great damage to the structures,leading to a series of marine accidents.The research on the problem of rogue waves mainly includes mechanism analysis,experimental investigation and numerical simulation.Among them,numerical simulation has attracted more and more attention from scholars because of its repeatability and applicability in simulating freak waves and analyzing the interaction between rogue waves and structures.As a meshless particle method,the Smoothed Particle Hydrodynamics(SPH)method has particular advantages in studying the interaction between waves and structures with large free surface deformation.The basic theory of numerical simulation of rouge waves by SPH method has yet to be perfected,and the problems in the construction of transfer function,the elimination of secondary reflection,the judgment of boundary particles in wave making area,and control of flow field stability still need to be solved at this stage.How to simulate the freak wave accurately and stably becomes the first problem to be solved when the SPH method is used to study the interaction between the rogue wave and the structure.In this paper,through the study of the initial pressure field assignment method,fixed boundary processing method and parallel calculation method of the SPH method,the improved methods for improving the stability of flow field and calculation efficiency of SPH numerical tank are pointed out.On this basis,a non-reflecting momentum source wave-making method based on the envelope superposition of the freak wave components is proposed to establish the numerical wave tank of the rogue wave to verify the accuracy and stability of the numerical wave tank of the rogue wave,and to study the interaction between the rogue wave and the two-dimensional and three-dimensional structures.The main research contents of the paper are as follows:1.Research on the method of the initial pressure field assignment in SPH method.There are usually two ways to assign the initial pressure field: the hydrostatic pressure method and the weakly compressible assumption method;the difference between the two methods in the matching of the equation of state and the hydrostatic pressure equation will affect the stability of the initial flow field.In this paper,the effects of particle number,artificial sound velocity and artificial viscosity on the steady convergence conditions of the initial flow field under the conditions of regular boundary,arc boundary and complex boundary model are analyzed.The research results show that the weakly compressible hypothesis method has good robustness,and has a significant effect on promoting the rapid stability of the initial flow field and reducing the pressure oscillation phenomenon.2.Research on the improved fixed particle assignment method with stable and efficient high precision.A high-precision stable boundary processing method plays an important role in suppressing the non-physical oscillation of the numerical tank.Based on the analysis and summary of the advantages and disadvantages of the three commonly used boundary interpolation algorithms such as Moving Least Squares(MLS),Simplified Finite Difference Interpolation Method(SFDI),and Regularization Methods,an improved Shepard interpolation method is introduced in this paper.The comparative research results on the problems of still water,dam breaking and interaction between solitary waves and structures show that improved Shepard method has the same calculation accuracy as MLS(secondary basis),and the calculation efficiency is 10 times that of MLS(secondary basis)and 1.5 times that of the regularization method.3.Research on the parallel computing method of SPH numerical tank.In the parallel framework of Message-Passing Interface(MPI),particle pair method and dynamic load balancing method are used to discuss SPH parallel strategy.The results of the parallel acceleration test under different particle numbers and different process conditions show that the parallel method based on MPI has a significant acceleration effect in large-scale particle number calculation,and the maximum acceleration ratio is close to 17.4.Research on the wave making method of numerical tank for the rogue wave based on the non-reflecting momentum source.By analyzing the characteristics of the Peregrine breather solution,combined with the principle of superposition and the method of non-reflection momentum source wave generation,a numerical tank model of non-reflection momentum source based on the envelope superposition method of freak wave components is proposed.The simulation results of the rogue wave with different nonlinear characteristics showed that,the the pressure field can evolve stably in the non-reflecting momentum source numerical tank for freak wave;a more ideal rogue wave waveform can be obtained by the non-reflecting momentum source numerical tank,and the mean square error of the wave surface time is less than 3%;the non-reflected momentum source tank of the rogue wave can better show the wavefront fragmentation of the freak wave under the strong nonlinear wavefront.By the study of the configuration of asymmetric numerical tank of non reflecting momentum sources,we found that it is effective and necessary to set up free surface evolution zones in asymmetric tanks to eliminate the reflected waves of rogue waves.5.Research on the interaction between freak waves and two-dimensional fixed and floating structures with different size features.First,the wave evolution of two-dimensional plate with different horizontal heights is investigate.It is found that the wave shape of the green water changes more drastically in the front area of the deck bow.The closer the deck is to the free surface of the still water,the kinetic energy of the green water,the wave collapse and the propagation speed are relatively faster.Secondly,based on the study of the interaction between regular waves and two-dimensional fixed structures,the relationship between the green water process of freak wave and the structure load under different structural size characteristics is studied.The results showed that the structure load under the action of the rogue wave is closely related to the propagation ability of the wave diffraction.The more significant the diffraction of the freak wave is,the smaller the horizontal load and moment on the structure is subjected to.Finally,taking the interaction between regular waves and two-dimensional floating structures as a reference,the motion response of floating structures with different size characteristics under the action of rogue waves is investigated.It is found that the load history of different floating bodies are roughly the same,and the sensitivity of horizontal load to waveform variation is higher than that of vertical loads and acting moment.6.Research on the problem of green water on a three-dimensional rectangular horizontal deck and a deck with different bow lines.Firstly,the wave evolution characteristics of rogue waves on the three-dimensional rectangular deck are investigated,and the green water process at different times and various positions is analyzed.It is found that the green water field exhibited good symmetry characteristics with the longitudinal centerline of the deck as the axis,and its propagation speed is faster than that in other regions due to the wave convergence effect in the vicinity of the longitudinal center line of the deck.After that,the influence of the change of bow line shape on the wave surface shape of the green water is studied.The simulation results of freak wave with different deck line structure show that in the initial stage of green water,the advancing shape of wave surface adapts to the change characteristics of deck line shape,and the influence of line shape change on the evolution of green water of freak wave is gradual in the stage of wave surface evolution.The influence of bow line shape change on the green water is mainly reflected in the converging area near the center line of the deck,and the effect becomes more and more significant with the wave propagation progresses.