On some recent optimizations in EUROPLEXUS numerical simulations of urban blast events

This report presents some optimizations that have been recently introduced in the EUROPLEXUS code for the numerical simulation of blast events in urban environments. Two (alternative) types of optimization are considered. In the first type, the calculation of numerical fluxes in the Cell-Centered Finite Volume (CCFV) discrete model used to represent the fluid sub-domain is skipped for all portions of the model that have not yet possibly been reached by the blast wave resulting from the explosion. This is simply derived from the distance between the charge and the fluid FV (or FV interface) under consideration, and from the propagation speed of the blast wave, assumed constant for simplicity. In the second type of optimization, which is outlined but not yet implemented, a combined 1-D/multi-D fluid model would be set up. The 1-D model is similar to that used to produce a so-called map file, i.e. to compute the numerical solution from the detonation instant until the instant in which the blast wave encounters the first obstacle, typically a structure. During this time period, the blast wave is typically spherical or hemispherical and may be represented by a 1-D model instead of a (typically) 3-D one, thus saving a substantial amount of CPU time. Then, the solution would be stored on a map file. In a subsequent simulation, the (1-D) solution would be read back from the map file and mapped onto the real 3D mesh, containing also the structures to be tested. Finally, the 3-D simulation would be carried on until the desired final time.