Simulation of the Effects of an Air Blast Wave - ELSA - Europa

Figure 30: Maximum pressures versus scaled distance – cubical models4.5 Spherical Charge with two Symmetry AxesThe weaknesses of using a cubical charge can be avoided by using a spherical charge. There are noproblems with a spherical charge from the different ending times of the detonation at the cornersand with effects resulting from the different surfaces.As mentioned initially, these first investigations disregard the interaction with the structure. So it ispossible to use a spherical volume for the surrounding air, too. This allows an easier modelling ofthe mesh, which can be done in several ways. At this point, the first approach of a sphericallysymmetric regular mesh with the centre of the charge is in CAST3M neither possible in an easyway nor is it necessary in considering the behaviour of the explosive and the air.The method used instead converts a cubical model via the INCL operator to a spherical model. Theresulting model seems to be relatively regular. The method can be done with the following steps:1. Modelling of a cubic surface for the outer charge (half volume) (Figure 31a, green).2. Modelling of a cubic surface for the inner charge. This part will be meshed with regular hexahedrons(half volume) (Figure 31a, blue).3. Modelling of a cubic surface for the air volume around of the charge (half volume) (Figure 31a,red).4. Projection of the outer charge surface and of the air surface with the PROJ operator to spheres(Figure 31b).5. Filling the volumes between the surfaces with hexahedrons (Figure 31c).42