Numerical Simulation Methods in Shock-Wave Chemistry

Numerical Simulation Methods in Shock-Wave Chemistry 

In shock-wave-chemistry research, compacts of solid powders are usually used as samples. Because of porosity, the samples are inhomogeneous and not a continuous medium, so models based on continuum physics are not suitable for the numerical simulation of these problems. A discrete meso-dynamic method (denoted as DM2) developed by Tang et al. in recent years is a better method for this purpose [20]. 

This model is based on quasimolecular dynamics, in which the medium is assumed to be composed of an assembly of meso-scale discrete particles (i.e., finite elements). The movement and deformation of the material system and its evolution are described by the aggregate movements of these elements. Two types of basic characteristics, geometrical and physical, are considered. In the geometrical aspect, shapes and sizes of elements and the manner of their initial aggregation and arrangement are the important factors. In the physical aspect, mechanical, physical, and chemical characteristics, such as the interaction potential, phase transition, and chemical reactivity may be the important ones. To construct this model, many physical factors, including interaction potential, friction of particles, shear resistance force, energy dissipation and temperature increase, stress and strain at the meso- and macro-levels, phase transition, and chemical reaction are considered. In fact, simulation of chemical reactions is one of the most difficult tasks, but it is the most important aspect in shock-wave chemistry. 

Preliminaiy analyses were carried out by the authors, and a tentative DM2 method was developed. Using this tentative method some practical examples were investigated, among them the shock-induced reaction of Al + Ni fine powder mixture and the stress profile of HMX explosive powders under the action of shock waves. The calculated results using this model are in better agreement 

To make further improvement, Tang s group is now working on the development of a 3D DM2 method, in which the pore collapse process is considered. At the same time, a new region method is suggested to replace the previous window method to reduce requirements for CPU time and RAM. [21]. 

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