Grid dispersion and filtering in broadband acoustic emission (AE) source modeling

Abstract

The spatial grid of numerical models of acoustic emission (AE) sources acts as a spatial filter for elastic wave signals. The filtering effects are particularly prominent for short-time, broadband signals – typical for AE. In this paper, we investigate the filtering influence of spatial discretization (meshing) on broadband AE source modeling. The AE source – generating AEs propagating as elastic waves – was modeled using cohesive zone approach, and the numerical simulations were performed in commercial FEM software COMSOL Multiphysics. Results were processed using Fast Fourier Transform, filtered, and subsequently analyzed in terms of the filtering effects of spatial discretization on AE source modeling. In this paper, it is shown that spatial grids in numerical models effectively work like low-pass filters with the cut-off frequency corresponding to the numerical Brillouin zone. The latter induces short wavelength limitation, and the frequency components near (below) the zone edge are amplified in magnitude. It was found that the amplified frequencies represent numerical errors. Also, it was inferred that the filtering effect of spatial discretization can mask the AE source characteristics and affect the quality of the results.