Study On The Numerical Simulation Of The Propagation Of Stress Waves And The Penetration Of Jet Projectile By SPH Method

The study of the propagation of stress waves and the penetration of the earth-projectile is the important topic interested in the civil engineering and the research of new weapons in the field of impact engineering. Jet-projectile is one of the new concept weapons with the spout of high pressure and high speed airflow to strengthen the function of earth projectile penetration and hence, it becomes a central issue now in the impact and military engineering. The research of this thesis aims at the numerical simulations of the propagation of stress waves and the earth penetration of jet-projectile by a meshless method-SPH method and so it has obvious significant both in science and military.SPH is a Lagrange meshless particle method in which the continuum is represented by a number of mass particles and the governing equations are transformed into particle summation by means of kernel approximation. To compare with the traditional computational method, such as finite element method and finite difference method, the superiority of SPH is that it abolishes the mesh and hence avoids many defects that would occur in numerical simulation of impact engineering by mesh method, such as the difficulties in the computation of large distortion and the simulation of fluid-solid coupling problems. Besides, the behavior of the particle in SPH causes the method to simulate the spout of airflow more directly and naturally and therefore, SPH is convinced of a good and suitable method for the numerical study of the penetration of the jet projectile.On the description of the fundamentals of SPH method, several critical problems, such as the accuracy of kernel approximation of function and the derivative of the function, the accuracy of kernel approximation of particle and the derivative of particle, the discrete form of governing equations, the numerical simulation of shock waves and so on, are discussed in detail in the thesis. Considering the Lagrange form of SPH method, it is stressed that the momentum equation is the only one of the conservation equations that should be expressed as the discrete particle formulation. The variables determined by mass equation and energy equation can be obtained by the computation of the constitutive equations after the momentum equation. Therefore, three independent discrete particle formulations corresponding to the conservation equations widely used in SPH method now are reduced to be one particle discrete equation and so that the total discrete equations for continuum mechanics are reduced and simplified greatly and the computational efficient is raised.The propagation of stress waves is the most popular event in impact engineering and hence to reproduce exactly the stress waves becomes the basic demands for all numerical method in impact engineering. Based on the particle discrete formulation of wave equation, the effects of smoothed length and kernel function in the numerical simulation of wave propagation are studied carefully by the computational examples and the basic conditions to exactly reproducing the wave motion are discussed. Moreover, an accurate method better than CSPM is proposed to simulate the wave motion in which the particles are scattered in the computational domain. Numerical examples with the new method are described and the results show that the disturbance behind the wave front is reduced obviously and thus the computational accuracy of the stress wave is increased. Afterwards the numerical simulations with the new method are carried out for the spallation of ceramic plate and composite ceramic plate and some interested results are obtained.Considering the numerical situation in the penetration area now, a coupling method combining SPH and finite element method is proposed for simulating the penetration of jet projectile. Explicit schemes of conservation equations in SPH and finite element method are established and it is emphasized that since the Lagrange form described in the method, only momentum equation in the three conservation equations are required to transfer to the discrete formulation and the other equations (mass equation and energy equation) do not be required. All the variables determined by mass equation and energy equation can be got by the computations following the momentum equation and so that the numerical computations for conservation equations are simplified greatly. All the various interface occurred in the coupling method are studied and the corresponding computational methods at the interfaces between finite element and SPH and the particles of different materials are proposed and these research work are closely related to the numerical simulation of jet projectile penetration.The numerical simulations of jet projectile penetrating concrete and soil are carried out by the coupling method proposed in the thesis. According to the operation pattern of the jet projectile, the methods how to simulate the airflow spouted out of projectile head and how to generate the airflow particles automatically in the computation are suggested. A series of numerical simulations of jet projectile penetrating the concrete and soil are carried out and the results shown that the spouting airflow possess the performance to reduce the resistance of the penetrating projectile and to increase the damage domain of the target and so that the penetrating effects of the jet projectile increase greatly. A serious computational result also indicated that the pressure of the airflow is much more important than the velocity of the airflow for jet projectile penetration and the material density is a critical parameter of anti-penetration of the target but the strength of the target is not as so important as density. The researches in the thesis can be used for the further investigation of jet projectile and it is also a valuable work for military engineering.