Dynamics Of Underwater Shock Wave Interacting With Complex Material Interfaces

In shipbuilding and offshore engineering,the interaction between shock wave and complex material interface is involved in many high-speed flow problems.In the process of underwater explosion,the shock wave will interacting with the explosion bubble,the free surface and the deformable structure,while in the process of underwater cavitation collapse,the shock wave generated by the collapse of the current cavitation bubble will interacting with the surrounding cavitation bubbles and the nearby structures and rigid walls.In this thesis,a high precision compressible flow model,a diffuse interface compressible multiphase flow model,a ghost cell immersed boundary model,and a transient fluid-structure interaction model are improved and then used to solve the physical problems of underwater shock wave interacting with complex material interfaces during underwater explosion and cavitation collapse.Therefore,the physical problems are simplified and classified into three categories: underwater shock wave interacting with gas-liquid interface,interacting with complex rigid wall,and interacting with fluidstructure interface.Different numerical algorithms are improved and used to solve this problems in each chapter.The main work of this paper is as follows:A high precision compressible flow model based on discontinuous Galerkin scheme is established,which is the basis for the accurate interface compressible multiphase flow model and the transient fluid-structure interaction model for solving the underwater explosion problem in the following paper.An one-dimensional Burgers case and an one-dimensional gas-liquid shock tube case are used to verify the model.A diffused interface multiphase flow model based on Allaire equation is established.The MUSCL and WENO reconstruction schemes based on finite volume discretization are used to solve this model.A cavitation model and a low Mach number limiter are used to improve the calculation accuracy.An anti-dissipation technique based on THINC reconstruction is used to reduce the numerical dissipation for the region around the material interface.The stretch mesh technology and the MPI parallel technology are used to improved the computing efficiency.Finally,several of one-and two-dimensional cases are used to verify this diffuse interface model.The diffuse multiphase flow model is used to simulate the interaction between the underwater shock wave and the gas bubble in free field,near a rigid wall,and near a free surface.The typical flow characteristic,the bubble collapse time,the bubble migration characteristic,the bubble jet characteristic,the pressure,temperacture,and circulation characteristic of the whole flow field,and the pressure characteristics of the rigid wall are depply studied for different boundary conditions.The diffuse multiphase flow model is used to simulate the interaction between the underwater shock wave with two gas bubbles,four gas bubble,and nine gas bubbles.And the typical flow characteristic,the pressure and circulation characteristic of the whole flow field,and the collpase characteristics of the bubble are depply studied for different cases.A ghost cell immersed boundary model is embedded into the framework of the diffuse interface model to solve the interaction between the underwater shock wave and the complex rigid walls.The implementation of the ghost cell immersed boundary model mainly mainly includes the classification of the global cells,the interpolation of the ghost cells,the application of the boundary conditions,and the processing of the moving boundary.Finally,this algorithm is used to study the effects of the underwater shock wave interacting with a sigle cylindrical rigid wall,multiple cylindrical rigid walls,a single triangular rigid wall,and multiple triangular rigid walls.An improved RKDG-RGFM model is proposed based on the previously high-precision flow model,which is used to solve the compressible multiphase flow problems for underwater explosion near a free surface.The implementation of the algorithm mainly includes the capture of the moving interface,the treatment of the gas-water interface,the positivity-preserving treating of the flow region,and the adaptive mesh refinement.The algorithm is verified by an one-dimensional gas-gas shock tube case,an one-dimensional gas-water shock tube case,and a two-dimensional disk interface evolution case.Finally,the accurate interfacial multiphase flow model is used to simulate underwater explosion in free field and near a free surface.An improved RKDG-FEM model is proposed based on the previously high-precision flow model,which is used to solve the transient fluid-structure interaction problem for underwater explosion near deformable structures.The implementation of the algorithm mainly includes the simulation of the structure,the treatment of the fluid-structure interface,and simulation of the flow cavitation.Several one-and two-dimensional examples are given to verity this algorithm.Finally,the characteristics for underwater explosion near a single-layer steel plate and a multilayer composite sandwich plate are studied by using this algorithm.