Numerical Simulation Research On The Impulsive Load Of Based On SPH Method

As a new computational method, the meshless method is originated in the 1970s, but it developed not very fast due to the restriction of computing ability. With the development of computer technology, the meshless method has gained more and more attention and has become a hot spot in the field of computational mechanics at present. Meshless method does not depend on mesh division, it avoids mesh distortion which may occur in the use of traditional finite element method, boundary method or other numerical methods based on the mesh, hence the meshless method is suitable for handling problems that are difficult to handle or almost can’t handle well by finite element method, boundary element method and other numerical methods. The meshless method is suitable for solving motion problems of free surface with intense deformation for the reason that this method uses particle as basic unit in computation, and there is no need to establish a fixed topological relations between the particles. Currently, there are many types of meshless methods, and various meshless methods have been successfully applied in fields such as crack growth, large deformation or super large deformation, materials phase changing, fluid structure interaction, blast shock and micro-nano technology. The first proposed one is the Smoothed Particle Hydrodynamics method (SPH), which was originally used in the simulation of astrophysical phenomena, in the simulation of high speed impact problems, SPH method has also gained successfully application.With the background of near-field underwater explosions of warships, this paper focus on problems of near-field and near-boundary underwater explosions. Near free surface underwater explosion problems involve with some special features, such as large deformations of flow or structure, interaction between shock waves and the boundaries, free surfaces characters, etc. In the process of using conventional grid-based methods to solve these problems, severe mesh grids distortion may occur and thus led to computing crash. The Smoothed Particle Hydrodynamics (SPH) method is a numerical simulation method which is adaptive, mesh-free, in the form of particle and with Lagrangian character. It avoids problems such as mesh deformation and is very suitable to solving problems with large deformation and impact loads, providing a new method for numerical simulation of underwater explosions.In this paper, the author adopted ALE method. SPH method and FEM/SPH coupled method for numerical simulations of underwater blasting respectively, compared the simulation results in terms of accuracy and rate of convergence, and further analyzed the advantages and disadvantages of these three methods through the computing results. After that, the author adopted modified SPH method to study issues about the shock tube and detonation process, using CSPH and GSPH method in the modified SPH method. After analyzing and comparing of computing results of these three SPH methods, we obtain the following results:(1) By using SPH method, ALE method and FEM/SPH Coupling method, numerical simulations of the near free surface underwater explosion was simulated numerically, and after compared and analyzed the computing results, the author find that traditional numerical simulation methods based on grid led to computing interruption because of severe distortions of mesh; and SPH method overcomes the problem of large grid deformation of the conventional method, but the convergence speed is slow; while FEM/SPH coupling method combines the advantages of both above-mentioned methods, avoids computational difficulties caused by large mesh deformation, as well as it has a faster convergence speed.(2) In the numerical simulation of shock-tube problems and detonation problems, we use modified SPH method (GSPH method) to obtain the numerical results, and the modified SPH method (GSPH method) improved computing accuracy and reduced the numerical fluctuation, which greatly promotes the accuracy of SPH method in capturing strong discontinuous problems.(3) We applied the SPH method to the numerical simulation of the underwater explosion, obtained the propagation law of the underwater shock wave and the mechanism of the interaction between the shock wave, provided a new numerical research technique and a shock wave load model for the problem of underwater explosion, and provided a theoretical analysis basis for the protective design of the anti explosion and anti impact of ship structures.(4) Compared with traditional SPH method. GSPH method improves the computing accuracy and compatibility and other issues of traditional SPH method effectively in solving discontinuous problems, improves the accuracy of traditional SPH method to capture intermittent information, improves solution accuracy, and decreased the numerical oscillation, as well as provides a new approach for the study of intermittent problems such as shock waves.