Non-linear or linear propagation in high intensity blasts from firearms: where is the boundary?

Acoustic nonlinearity increases the degree of modelling complexity but is nevertheless necessary to fully capture the time-frequency content of an impulsive event. Both national and international standards commonly deployed to predict free-field outdoor sound propagation from firearms (ISO 9613, NT Acou 099, ISO 17201) not only neglect nonlinear phenomena, but also fail in providing a clear-cut methodology to discriminate between linear and nonlinear regimes. Correctly establishing the extent of the transition region between the nonlinear and linear solvers allows to optimize the prediction strategies, by allocating the right computational resources where most needed. The present study attempts to make clarity on the subject by observing the evolution of key metrics in the propagation of blasts from small and large caliber weapons. On-field test campaigns were carried out to obtain the datasets needed for the analysis and the free-field propagation of the muzzle blast is simulated with a Nonlinear Progressive Wave Equation solver.