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

culation fails. This limit depends on the radial and the tangential size of the elements. It seems thatthe elements are not usable when they are too thin. The pressures are overestimated if the aspectratio is about 10. When exceeding this ratio, the pressure is also not symmetric. It appears to behigher near the edges and smaller in the diagonal of the model. This difference between the edgeand the diagonal begins approximately at a distance of 0.45. The aspect ratio is there 8.0. It seemsthat the boundary conditions can not act with this exceptional element sizes. Respecting this, alsothe values for the calculation SPHE3 would not be applicable over a distance of 0.60 m. This has tobe considered for further calculations with the conical model and the spherical model. The aspectratio reaches the critical value 10 at a certain distance. This distance is calculated in Table 7.SPHE8This model is a coarse spherical model with a size of 2.0 m. The results follow the results of themodels with a size of 1 m. The pressure is approximately half the experimental value.SPHE9This calculation uses a finer mesh than model SHPE8. The pressures are a little bit larger than thepressures in model SHPE8.4.6 Comparison between the Different Models4.6.1 Maximum PressureThe comparison will be done with the fine meshes of the different models summarized in Table 8.Case Element size Charge[kg TNT]Size of the model[m]Steps CPU [s] ElementsCON4 (Tet) 0.02-0.005 12.8 1.3 8956 9 914.3 1582CON8 (Hex) 0.001-0.01 12.8 3.0 2205 13 3625 860CON9 (Hex) 0.001-0.01 1.0 3.0 2205 13 3482 805SPHE3 0.01 12.8 1.0 698 98 8375SPHE9 0.013 12.8 2.0 917 691 49000Table 8: Comparison of different modelsThe summery of the different curves (Figure 34) shows that the conical model with the tetrahedralelements results not in a realistic maximum pressure-distance curve. The closest agreement with the46