The usual form of the Particle-In-Cell (PIC) hydrodynamic code is compared with the PIC-SS modification. A one-dimensional excavation problem is presented for purposes of comparison: A slab of material having uniform pressure, density, and specific internal energy moves downward at a constant speed and strikes a half space of stationary material in another constant state at t = 0. At the instant of impact, the upper slab boundary is released and a "time-varying" pressure is imposed on it. Accurate solutions to the problem are obtained and compared with the results of PIC and PIC-SS. In this framework, the applicability of shock-fitting schemes is examined. It is found that the sharp solution requires a number of physical restrictions and leads to a class of problems that would not warrant the use of a PIC computational scheme. 26 pp. Ref. (KB)
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