Two-Dimensional Study of the Influence on Target Loading of Numerical Wave Reflections from Transmissive Computational Boundaries

摘要

This report quantifies the changes in the loading on a target caused by the arrival of artificial, numerically-induced reflections of waves from the transmissive boundaries of a computational grid. Several computations were performed, using the two-dimensional Cartesian coordinates mode of the Ballistic Research Laboratory's version of the airblast HULL hydrodynamics computer code. HULL uses a two-step, explicit differencing method to solve the inviscid, unsteady Euler equations. A target is simulated in the computational grid by generating aggregates of rigid, immobile, and impermeable flow-field cells. The simple transmissive boundaries in HULL simulate a zero-gradient condition across the boundary for both the pressure and the normal component of velocity. Simple transmissive boundaries such as these will partially reflect waves that strike them, including shock, compression, and expansion waves. The strength of these reflected waves is directly related to the strength of the incident waves. These reflected waves then travel back into the computational grid, modifying the flow-field conditions in the regions through which they pass, thereby ending the simulation of free-field conditions.