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

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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
Case Size of the model Description t end Steps CPU [s] ElementsCUB1 0.5 X 0.5 X 0.5 m Charge 12.8 kg TNT,element size 0.02 mCUB2 1.0 X 1.0 X 1.0 m Charge 12.8 kg TNT,element size 0.02 mCUB3 0.5 X 0.5 X 0.5 m Charge 12.8 kg TNT,element size 0.01 mCUB4 1.0 X 1.0 X 1.0 m Charge 1.0 kg TNT,element size 0.0167 m4.7e-4 415 181.5 156254.7e-4 270 790.6 1250004.7e-4 911 2275.9 1250006.0e-4 291 1367.7 216000Table 6: Calculations with cubic chargesCUB1In this calculation a small model with a coarse mesh is used. The charge has a mass of 12.8 kg. Thedevelopment of the pressure can be shown in Figure 28. At t=2 10 -5 the explosive has burned downexcept for the explosive in the corners of the cube. The pressure in the air is the atmosphericpressure of 10 5 Pa. After the explosion (e.g. t=6 10 -5 ) the pressure of the gas produced from theexplosive is decreasing and the pressure wave is running into the air. At t=10 -4 there can beobserved a discontinuous pressure along the three axes at the same distance from the detonationinitiation point. The reason could be the cubical shape of the charge. At t=1.4 10 -4 the pressurewave is reaching the surface (FSR condition) and is reflected.39
Page 1 and 2: Simulation of the Effectsof an Air
Page 3 and 4: Distribution ListLechner S.Anthoine
Page 5 and 6: 1 IntroductionThis work is being co
Page 7 and 8: • Far zone. The blast wave result
Page 9 and 10: Figure 2: Model of Kingery [14] wit
Page 11 and 12: 2.2.3 ImpulseThe impulse of the air
Page 13 and 14: Figure 5: Different parameters for
Page 15 and 16: 250200Impulse from KingeryImpulse w
Page 17 and 18: the specific heat ratio and the spe
Page 19 and 20: determined with a fluid pre-calcula
Page 21 and 22: From this asymptotic form it can al
Page 23 and 24: 2.0E+101.6E+10without burn mass fra
Page 25 and 26: Case opening d pyra d ex,in d ex,en
Page 27 and 28: Pressure [Pa]2.4E+102.0E+101.6E+101
Page 29 and 30: 5.0E+094.0E+09EUROPLEXUS x=0.105EUR
Page 31 and 32: Cased pyr /d ex,in /d ex,end /d air
Page 33 and 34: Figure 21: Comparison of a coarse w
Page 35 and 36: CON9This model has approximately th
Page 37: 4E+7Max. pressure [Pa]3E+72E+7Kinge
Page 41 and 42: CUB4This model uses a finer mesh th
Page 43 and 44: 6. Complete the volumes by adding t
Page 45 and 46: Figure 33: Maximum pressures versus
Page 47 and 48: experimental values is obtained wit
Page 49 and 50: 4.6.3 Arrival TimeThe arrival time
Page 51 and 52: value in [13]). These results show
Page 53 and 54: Modell airl bBubbleBubbleBubbleTNT
Page 55 and 56: Several calculations are done with
Page 57 and 58: 3. Calculation of the factor α bub
Page 59 and 60: quadratic. Therefore, the size of t
Page 61 and 62: 400Impulse [Pa sec]300200.Kingery 5
Page 63 and 64: 5 = hemispherical detonation (half
Page 65 and 66: 9 References[1] Alia, A.; Souli, M.
Page 67 and 68: 10 Apendix10.1 EUROPLEXUS Codedyms.
Page 69 and 70: CALLMECVAL(GET_FMT(6),NEWMAT%MATVAL
Page 71 and 72: 10.2 Miscellaneous codeairblastresu
Page 73 and 74: else{ //Kingerydouble t=log10(z);do
Page 75 and 76: maxar=0;REPE I0 (NBEL vges);ar = as
Page 77 and 78: *defining the surfaces around the a
Page 79 and 80: lpyr1 = p1 d ppy2;lpyr2 = p1 d ppy3
Page 81 and 82: lpyr2 = p1 d ppy3;lpyr3 = p1 d ppy4
Page 83: *Cube intermediaire (centre=o0 et a
Page 86: The mission of the JRC is to provid

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

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