Reflected secondary shocks : some observations using afterburning

Afterburn models are typically used for charges in enclosed spaces to estimate quasi-static pressure. Also, any reflected shock that interacts with detonation products has the potential to add energy to the shock due to afterburning via additional gas mixing and heating.

Air blast tests that included normally reflected pressure measurements by the University of Sheffield, provided evidence of the so called ‘secondary shock,’ i.e. the recompression and expansion of the detonation products. This repeat test data provided an opportunity to explore calibration of the LSDYNA afterburning model parameters to match the measured time of arrival and magnitude of the secondary shock. While the measured pressure histories alone are insufficient to uniquely calibrate the afterburn model, this manuscript attempts to illustrate the effect on the secondary shock of changing the four afterburn model parameters: 1. Start time for adding energy 2. End time for adding energy 3. Amount of energy to be added 4. Rate at which the energy is added, i.e. either linearly increasing or constant.