We present a cell-centered Lagrangian scheme for numerical simulation of condensed-explosive detonation. It utilizes finite volume method to discrete detonation equations. Velocity and pressure of grid nodes are obtained with characteristics theory of hyperbolic partial differential equations. They are used to update position of grid nodes and calculate numerical flux of grid cells. Solution of grid nodes obtained by characteristics theory is a "genuinely multi-dimensional" theoretical solution, which is a generalization of one-dimensional Godunov scheme in two-dimensional Riemann problem. Semi-discrete system of detonation equations obtained by finite volume scheme is solved with an implicit-explicit Runge-Kutta method. Convection terms are explicitly treated, and stiff source terms of chemical reactions are implicitly treated. The numerical schemes select ZND model for detonation, JWL equations of state for unreacted explosives and detonation products, and use Ignition-Growth model to simulate evolution process in reaction zone. Typical numerical results show that the cell-centered Lagrangian scheme simulates condensed-explosive detonation problems well.

We present a second order cell-centered finite volume method of 2D Lagrangian hydrodynamics based on semi-discrete framework.Velocity and pressure on vertex of a cell are computed with characteristics theory,Then,they are used to compute numerical flux through cell interface by trapezoidal integration rule.With a reconstruction procedure,the method is extended to second order.Several numerical experiments confirm convergence and symmetry of the method.The method permits large CFL numbers and can be applied on structured and unstructured grids.It is robust in multi-material flow simulations.

A Brownian dynamic simulation of perikinetic flocculation of fine sediment with ionization is presented.Langevin equation is used as dynamical equation in tracking particles in a floc.Monte Carlo method is used in simulating random variation in particle movement.Sludge particles are supposed in uncharged and charged state in dispersion system.Electrostatic force on a particle in a simulation cell is considered as a sum of electrostatic force from other particles in the original cell.Particle initial place is decided by particle diameter and sludge density.Particle initial velocity is determined by Gauss random distribution.Effects of particle diameter and sludge density on flocculation and floc structure are discussed.On the other hand,effects of electrostatic force on flocculation are presented.The model proposed coincide well with practical situations.

We present a cell-centered finite volume method for 2D invicsous Lagrangian hydrodynamics.Velocity and pressure on vertex of a cell are computed with characteristics theory,which is derived from governing equations of Lagrangian form linearized by freezing Jacobian matrices about a known reference state.The velocity is used to update coordinate of vertex of a cell.Product of two variables is used to compute numerical flux through cell interface by a trapezoidal integration rule.Convergency,symmetry and conservation of total energy of the method are demonstrated.The method can be applied to structured or unstructured grids,and does well spontaneously for multi-material flows in a robust way.The scheme is one order precision,and can be easily draw on two order precision.

We develop a conservative piece-wise parabolic advecting remapping method(PPRM).The first part of it is an alternate sweeping average method(ASAM) for improving symmetrization of advecting remapping method.The second part is a piece-wise parabolic distributing function for improving order.We use one-and two-dimesional examples to test order and symmetrization of PPRM.

Stability of normal shock waves in viscous materials is analyzed with linear stability theory (LST). Equation of state of material adopts "stiff gas" expression. Stability problem of one-dimensional shock waves with arbitrary shock strength in viscous material is attribute to an eigenvalue problem with regard to complex number. The eigenvalue problem concerns two first-order ordinary differential equations and one second-order equation. Their coefficients depend on physics variables and gradients. The eigenvalue problem is discretized and solved in a four-order precision finite difference scheme. With analysis on stability of shock waves in aluminum under high pressure, it is shown that one dimensional shock wave is stable. It shows that the velocity of shock wave has opposite effects on attenuation of perturbation ahead and behind shock front. Viscosity of material makes the attenuation more rapidly.

We investigate numerically refraction of shock waves at ferrum-beryllium (Fe-Be) interface. Equations of state for Fe and Be adopt "stiffen gas" formulas. A shock polar theory is employed to analyze critical angles of transition from regular refraction to irregular refraction. A shock-capturing method in finite volume scheme with two order of precision and wave propagation is employed to discretize and solve hydrodynamics equations of shock waves. For regular refraction, numerical results agree well with shock polar theory. For irregular refraction, precursory refracted shock waves are observed, and refraction images vary with shock intensity and incident angles.

An adaptive generation method about two dimensional structured grids is presented.Several variational methods are used to control the mesh spacing,smoothness,orthogonality and regularity of grids generated.The all governing equations have identical dimensions.Some typical examples demonstrate that the method of adaptively generating grids can well converge to the unique solution of the governing partial differ-ential equations, and in the meanwhile can get structured grids.

In calculating one-dimensional cylindrical flow problems,famous Wilkins finite difference scheme under Cartesian coordinate system can get exact symmetry with peripheral grids zoned by equal angle,and get severe non-symmetry with peripheral grids zoned by unequal angle.By analyzing the reason that the Wilkins scheme may damage symmetry under the condition of peripheral grids zoned by unequal angle in computing 1-dimensional cylindrical problems,it is pointed out that the unequal angle zoning of peripheral grids results in peripheral pressure component,accordingly, peripheral acceleration and velocity components.On the basis of the analysis,a modified scheme is brought forward,which operates an arithmetic average on the peripheral pressure component at each point in order to eliminate the peripheral pressure component and automatically to maintain only the radial component.So the modified scheme can preserve exact symmetry under the condition of peripheral grids zoned by arbitrary angle.The conclusion is shown by several representative examples,and the modified method has very consistent results with the primary method for the symmetry flows and very little differences from the primary method for the unsymmetry flows.The representative examples demonstrate that the modified scheme is reasonable.

By discussing the mechanism of turbulence plasma scattering electromagnetic wave in hypersonic reentry wake, the first order distorted wave Born approximation model about the radar cross section is derived from the underdense turbulence plasma for engineering application. Applicability to fully-developed turbulence wake plasma field is analyzed, the program about 3-D wake plasma is improved and compiled. Based on the flow field parameters about the turbulent wake and this scattering model, the effects of reentry wake turbulent plasma is analyzed on the radar cross section. Several representative factors chosen to examine are turbulence modeling, turbulent transition course, turbulent scale and the initial condition for the fluctuation intensity of electron concentration. The conclusions drawn is that turbulent transition course and scale are not too important, the initial condition for fluctuation intensity of electron concentration is very important, and turbulence modeling plays a little role under the specific conditions.