Simulating transient scattering from obstacles with frequency-dependent surface impedance

This paper presents an algorithm which couples the time domain Boundary Element Method (BEM) with a digital filter surface model. This aims to achieve the same for transient sounds as is possible for time-harmonic excitation using surface impedance and the frequency domain BEM. Accurate representation of surface properties is crucial in obtaining realistic simulations, and the obstacles and boundaries typically encountered in real-world scenarios exhibit frequencydependent surface impedance. In the time domain such frequency-dependency can be modelled using digital filters, and by this approach surface-impedance has been successfully incorporated into some recent Finite Difference Time Domain (FDTD) models, but the best way of achieving this for time domain BEM is currently unresolved. The surface model used herein uses a digital filter to implement the surface reflection coefficient – the accuracy of this approach for nonnormal incidence plane waves has previously been questioned in the FDTD literature, so this scenario is specifically investigated and accuracy is evaluated by comparison with the analytical plane wave pressure reflection coefficient. Computational cost and effect on algorithm stability are also considered.