Study On The Numerical Modeling Methods For Underwater Fluid-structure-acoustic Wave Interaction Problems Based On Lattice Boltzmann Method

In many applications,the fluid-structure interaction(FSI)effect has important influence on underwater acoustic wave generation and propagation,such as flow noise radiation from subma-rine propeller,acoustic scattering from submarine anechoic tile and seafloor.Especially in the context of the application of new underwater acoustic stealth and sound detection technologies,understanding the interaction mechanism of fluid,solid and sound fields becomes more impor-tant,which poses higher requirements for related numerical modeling methods.Considering the complexity of the problem,conventional numerical methods have their own limitations,while the lattice Boltzmann method(LBM)has great potential in underwater acoustic field calculation due to its efficient processing of moving boundaries and low numerical dispersion and low dis-sipation.Therefore,the study on numerical modeling methods for underwater fluid-structure-acoustic wave coupling problems is carried out in this dissertation using the advanced tool of LBM.The problems of acoustic scattering and flow noise radiation are taken as the application background.The main contributions are as follows:1.An improved immersed boundary-lattice Boltzmann method(IB-LBM)is proposed for fluid-structure interactions involving complex moving boundaries.In the method,the fluid flow is solved by the LBM,and the interactions of fluid and solid domain are modeled by the immersed boundary method.By introducing a force correction coefficient,the no-slip boundary conditions are much better enforced compared with the the conventional direct-forcing method.In addition,the implicit calculation is avoided thus much computational cost is reduced.The FSI problems involving static,moving and deformable boundaries are simulated in the numerical experiments.The accuracy and efficiency of the present method are verified through the comparisons with the conventional IJB-LBMs.2.A hybrid numerical method which couples the IB-LBM with the smoothed point inter-polation method(S-PIM)is presented in this paper for the fluid-structure interaction problems involving large solid deformation.Owing to the gradient smoothing technique,the S-PIM is able to handle large solid deformation in a more accurate way compared with the finite element method.In addition,a time-average coupling technique is proposed to improve the robustness of the method.The steady and unsteady FSI problems involving large solid deformation are simulated in the numerical experiments.The accuracy,stability and efficiency of the present method are verified through the comparisons with the conventional IB-LBMs and the finite ele-ment method.3.The study on the numerical modeling for acoustic scattering problems involving complex fluid-structure interaction are carried out based on the present IB-LBM.The direct simulation approach is employed in the present model to solve the flow field,and the sound field is obtained as part of the flow field information.Compared with the conventional methods,the present model is able to describe the influence of the fluid-solid interaction effect on the scatter:ing sound field.For acoustic scattering from static and moving curve boundaries,the better performance in terms of accuracy and efficiency of the present method is verified by the comparisons with conventional IB-LBMs.In addition,The case with elastic body is also considered and the influence of the elasticity on the scattering field are discussed.In the simulation of acoustic scattering from moving particle,the Doppler effect is accurately captured,and the efficiency of the present model for acoustic scattering involving complex fluid-structure interaction are further verified.4.The study on the numerical modeling for flow-induced noise involving complex fluid-structure interaction are carried out based on the present IB-LBM.For the near-field acoustic modeling,the direct simulation approach is employed to capture the fluid-structure interactions,and the GPU based parallel computing technique is used to improve the computational perfor-mance(the speed-up ratio is over 100 compared with the CPU based serial computing).For the far-field acoustic modeling,the KFWH equation based acoustic analogy approach is employed.The accuracy of the simulations are verified through the numerical experiments of acoustic radi-ation from rotating ellipse and point source,respectively.The simulation of flow-induced noise from 3D elastic rotating body is also carried out,in which the influence of solid elasticity on the frequency spectrum,directivity and far-field decay of the sound wave are discussed,and the efficiency of the present model for the flow-induced noise prediction involving complex fluid-structure interaction is further verified.