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[FAQ]

It is expected that the pressure impulse calculated by AUTODYN is less than that calculated analytically by a small percentage. The main reason that some analytical models over-predict the impulse is that they often do not account for the negative phase of pressure, where absolute pressure is less than the ambient pressure. If you plot the pressure time history, you will find that there is always a negative phase in the curve. AUTODYN takes the negative phase into account and thus it is in a better agreement with experiment data. Besides that, you also need to make sure you have a correct amount of explosive in the part. You can find the mass of the explosive in the AUTODYN print file “”ident.prt””. If 1D wedge model is used, you need to adjust the external radius of HE or the material density because a 1D wedge does not allow zero internal radius of HE. If the HE mass in the print file is less than it should be, you need to increase the external radius or the material density to compensate the mass loss. You also need a fine mesh in the HE part. A coarse mesh will under-predict the overpressure and thus get a lower value of impulse.