Numerical Study On Nonlinear Parameters Of Random Waves Propagating Over Submerged Bars

With the increase of population on earth,and resources on land began to tense,the need for development of marine resources increasingly urgent.For offshore engineering,the wave characteristics of offshore and coastal areas are the prerequisites for engineering design,construction and maintenance.When the waves spread to shallow water,its movement is very different from deep water.There is a strong nonlinear interaction between the wave components,wave wavelength,wave velocity and other elements and the wave nonlinear characteristic quantity will change.The study shows that the propagation and deformation of the waves on the dive is very complicated,and it is very instructive to understand the evolution of the waves on the submerged bar.The SWASH non-hydrostatic wave model is adopted to simulate waves,and verified against experimental data and theoretical solution.Simulate the random waves propagation over a submerged bar and study the influence of the length of the embankment on the wave nonlinear parameters.It is found that the nonlinear interaction of the waves is still developing after reaching the top of the dive,and the wave nonlinear parameters need to propagate a distance of about 3 times the spectrum peak wavelength to achieve a stable value.The crest width has little effect on the value of wave skewness,kurtosis and Ursell number,but has some influence on the value of asymmetry.In addition,the relationship between wave kurtosis and skewness,the relationship between the wave asymmetry and Ursell number in the upslope region,downslope region and back crest are discussed,and the corresponding formula is given by referring to the present formulae with previous studies.Additionally,the submerged bar is used as a simplified model to study the freak wave in nearshore shallow water.The physical model experiment and numerical simulation results show that the probability of the freak wave in the upslope region close to the top of the bar is the largest.The wavefront time course of the abnormal wave is analyzed,and it is found that the freak wave is originated in a wave group.In the process of the wave group spreading into shallow water,one of the large waves evolves into the freak wave.By using the bandpass filtering and bicoherence spectra to analyze the variation of the wave composition during the generation and evolution of the freak wave,it is found that the instantaneous high frequency component is closely related to the appearance and disappearance of the freak wave.The method of wavelet energy spectrum is used to study the change of energy time-frequency structure before and after the occurrence of the abnormal wave.It is found that the generation of high-order harmonics and the phase synchronization of high-frequency components lead to the appearance of the abnormal wave.Finally,the independent wave group and the double wave group are designed by using the Gaussian function,and chirp wave group is also designed to simulate the generation of abnormal wave.It is concluded that the formation of the freak wave is the result of high-order harmonics and shallow operation at the same time and it contains the dual factors of wave linear focusing and nonlinear interaction,and the nonlinear interaction is more dominant.