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

4.6.5 Comparison with results of other authorsExperiments and calculations with spherical explosions without reflections are relatively rare in theliterature.Clutter [9] uses only one element with a different EOS for the explosive. He compares the results ofthe impulse and the peak pressure in a logarithmic scale. The values for the peak pressure are higherfor small scaled distances and are smaller for large scaled distances. The impulses for scaleddistances smaller than 0.8 m/kg 1/3 are definitely too large (up to 2.5 times of the Kingery data). Alsothe values for larger distances are overestimated. A fluid calculation should results in smaller peakpressures and smaller impulses.Fairlie [12] presents calculations with AUTODYN for a small amount of TNT (8 g). Thecomparison of the peak pressures shows a good correlation with the values of Kingery (3%difference). The difference for the impulse is 22%, in the same range as the herein presentedcalculations.The investigation from Alia [1] uses LS-DYNA with a multi material formulation. The amount of454 g C-4 (equivalent to 609 g TNT) is modelled with the JWL-equation. The overpressure at acertain point is smaller than the pressures resulting from Kingery (25%). The impulse is alsosmaller (40%).In the calculations presented the difference between the numerical results and the experimentalresults of Kingery are in a range of 30-40% for the peak pressures as well as for the impulses. Thesmallest elements in the CON-models have a length of 1 mm due to the small angle of the cone.This raises the question whether the modelling of large structures is possible with a JWL-equation.Therefore, the next chapter presents several possibilities for the simulation of air blast waves.4.7 Influence of several parametersAs seen above, there are differences between the experimental results and the numericalcalculations. The computed maximum pressure is too small, the arrival time longer, and the impulsehigher. The potential influence of the several parameters involved should be determined.4.7.1 Specific heat ratio (CON15)Kingery defines the parameter γ in the range of 1.176 to 1.402. The cited literature is still not available,but as stated, γ varies with the overpressure. Without the knowledge of the dependence on theoverpressure it is not possible to define a more accurate material law for the air. Nevertheless, theinfluence of a varying γ can be tested with a calculation which chooses γ to be 1.176 (smallest50