For a given solution of Riemann problem for elastic perfectly plastic solid Euler equations ignoring vacuum, we give condition that the initial physical quantity should be satisfied and prove completeness of the initial condition corresponding to a particular solution. That is, for any given initial physical quantity, it corresponds to only one solution of Riemann problem. Therefore, the solution of Riemann problem can be judged directly and accurately according to the initial condition in the design of exact or approximate Riemann solvers.

Effects of thickness and density of plate on impact load and cavitation evolution in non-contact underwater explosions are investigated.A modified ghost fluid method developed recently is extended to treat nonlinear interaction between compressible flow and elastic plate.With assumption that fracture of a plate does not occur, it discloses that relatively small thickness or density of plate weakens impact of blast wave on structure.Impact load tends to result of rigid wall boundary nonlinearly with increase of thickness or density.Furthermore, smaller thickness or density causes cavitation to occur earlier and creates a larger cavitation region.It delays and weakens secondary impact on structure induced by cavitation collapse as well.

By analyzing ghost fluid method for compressible multi-medium flows, fundamentals for defining ghost fluid state with a general equation of state are described. All possible definitions of ghost fluid states are derived according to wave patterns and free variables in ghost fluid region. Following these treatments, it reveals that solution of multi-medium Riemann problem can be obtained exactly in theory. Several simple but effective definitions independent with wave patterns in ghost fluid region, are further summarized. One of these ways is similar to reflective boundary condition. An essential prerequisite is that interfacial velocity must be predicted exactly. Numerical results show that this methodology indeed works reasonably for multi-medium flows.