AN ANALYSIS OF COMPACTION WAVE IN GRANULAR MATERIAL
颗粒材料中致密波结构研究

A one-dimensional, two-phase flow model and the intragranular stress function is used to describe the structure and its formation of compaction wave in granular material. The piston impact problem for a compressible porous solid has been solved using a simplified model neglecting gas phase effects. With this model, it is possible to obtain an solution for the compaction wave speed, final porosity, and final pressure. At low piston velocities, the compaction wave travels at speeds less than the ambient solid sound speed. The structure is characterized by a smooth rise in pressure from the ambient to a higher pressure. As the compaction wave travels at speeds greater than the ambient solid sound speed, a discontinuous shock preceeding the compaction wave structure is predicted. The simplified model result shows that subsonic compaction wave is a direct consequence of nonideal state effect, and there exists a shock preceeding the compaction wave for supersonic compaction wave, but no leading shock exists for subsonic wave.The dynamic compaction process of granular bed is simulated using two-phase flow model. A numerical technique of method-of-lines is used to solve the coupled multiphase flow equations. The space and time variation of pressure, volume fraction and particle speed are determined. From numerical analysis, a steady compaction wave following a short time transient is predicted in the porous bed. The structures of the compaction waves are also studied for various piston-impact velocity and initial volume fraction increasing the compaction wave speed, final pressure, final volume fraction and paticle speed will increase, but the compaction zone thickness will decrease.The results of simplified model and numerical analysis are compared for various piston-impact velocity and it is shown that the simplified model results are good approximation to the numerical results, so that the neglection of gas phase effects in the simplified model is reasonable.