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

SummaryThe pressures resulting from a calculation with tetrahedrons are too small. The results with hexahedronsare also small, but the difference to the analytical-experimental results is less. The differencedepends on the size of the elements. Smaller elements result in higher pressure and a bettercorrelation with the experimental results. The smallest element sizes are of the order of 1 mm. It isnot possible to calculate a fluid-structure interaction problem of realistic dimensions with a mesh ofthis size. So, the question which kind of simulation of the loading is most appropriate to be used isimportant (see chapter 3).4.4 Cubic Charge with two Symmetry AxesTo check if the boundary condition of the cone model represents a full 3D model two differentmodels are used. Both models are one eighth of the geometry with FSR conditions at the symmetryfaces. Another advantage with such a model is the possibility to compare the calculations with otherfinite element programs like LS-DYNA.In the first model the charge and the air are built as cubes. A regular mesh with hexahedrons isapplicable with the same size for all elements. The second model uses a spherical charge (seechapter 4.5).An interaction with a structure is not of interest for these calculations. Therefore, the explosive andthe air are built with fluid meshes. An ALE mesh is used for the air, an Eulerian mesh is used forthe explosive (see Figure 27).Figure 27: Model CUB1 – explosive as Eulerian (red), air as ALE (grey)The calculations performed are summarized in Table 6 and shortly described hereafter.38