Numerical Modelling Of Seismic Wave Fields Of Underwater Mobile Bodies

The ocean is extremely rich in oil and gas resources,mineral resources and biological resources,etc.In order to develop the ocean,a large number of underwater observation technology equipment and underwater mobile military equipment have been created.These underwater mobile bodies release vibration and noise as energy into the water column and spread outwards.Among them,low-frequency radiated noise is highly penetrating and will be difficult to suppress,coupling into geoacoustic signals through the subsea water layer and strata,generating seismic waves on the seafloor and forming seismic wave fields,and low-frequency geoacoustic signals can propagate over long distances at the seafloor interface.Considering the influence of the medium system composed of small-scale discontinuities on the seismic wave field,scale effects will appear in the seismic wave field.Therefore,this paper adopts asymmetric elastic wave equations that can express the effect of small-scale microstructure,establishes a parametric model that meets the actual hydrogeological conditions,and conducts numerical modelling experiments on the seismic wave field of underwater mobile bodies.The main research of this paper consists of the following sections:1.Firstly,this paper introduces the asymmetric elastic wave equations and applies its differential discretization to numerical simulations.In this paper,an improved bat swarm optimization algorithm is proposed to optimize the finite difference coefficients,suppressing the computational errors and successfully extracting the scale effects to meet the requirements for high-precision numerical modelling of the asymmetric elastic wave equations,in preparation for high-precision numerical modelling of the seismic wave fields of underwater mobile bodies.2.Secondly,based on actual hydrogeological conditions,a model containing characteristic scale parameters is set up,and the influence of seawater salinity and suspended particulate matter is taken into account.In this paper,the asymmetric elastic wave equations are used to carry out numerical modelling experiments,and the energy attenuation curve of geoacoustic signal,the influence of submarine slope on geoacoustic signal,the absorption effect of submarine stratum and the influence of small-scale discontinuum on Scholte wave are obtained.3.Finally,in order to further investigate the Scholte surface waves in seismic waves on the seabed,a soft subsea model and a hard subsea model are set up for numerical modelling experiments in this paper to investigate the arrival time,frequency and energy characteristics of and Scholte waves,transmitted longitudinal waves,direct longitudinal waves and transmitted shear waves,as well as the effects of seismic source with different excitation frequency and the horizontal and vertical distance between geophone and source on Scholte wave and its associated wave patterns.