Fast slow cook-off simulation through scaling of thermal parameters

A scaling method is proposed to speed up the numerical calculations of energetic materials subject to slow cookoff where the applied heating rate is typically of a few degrees per hour. To speed up the thermal-chemical-mechanical simulation, it is proposed that the thermal parameters and heating rate be scaled up by a large constant factor. The method was applied to simulate the Scaled Thermal Explosion Experiment (STEX) in LSDYNA using user-defined subroutines that determine the dynamics of the energetic material. A total of four valid scaling factors were tested with all the results in perfect agreement with one another in the temperature, pressure and reacted mass fraction time profiles. A fifth scale factor served as a control to demonstrate that the method is feasible if the resulting enhanced thermal velocity is below the sound speed. The computed ignition time also agreed well with the results from literature. Immediately after the cook-off was initiated, the scale factor was gradually downsized to unity with the maximum temperature and pressure attained in the ignited region computed.