Numerical Simulation of Nonlinear Infrasound Propagation Based on Optimized High-order Compact Finite Differences

Abstract:

An algorithm is in development to model nonlinear infrasound propagation in the atmosphere from surface explosions and other sources. The scheme uses high-order compact finite differences for spatial derivatives, combined with a low storage Runge-Kutta method for time integration. The spatial and temporal schemes are optimized together for maximum wave number resolution. A high-order spatial filter is applied at each time step, with the coefficients chosen to suppress wavelengths that are not resolved by the difference scheme. An additional low order filter is applied in the vicinity of shocks to prevent spurious oscillations. This numerical scheme is used to solve the compressible Navier-Stokes equations of fluid dynamics in two dimensions on a rectangular Cartesian grid with, and without, molecular relaxation effects. This algorithm will be used to study the effects of nonlinearity on the amplitudes and spectra of infrasound signals of various phase types at up to first-bounce distances.