ABSTRACT
Numerical approaches to solving the so-called Helmholtz equation in the frequency domain have matured during the past decades and have proven reliability. Most environmental noise sources are broadband in nature. A major advantage of a time-domain approach is that, after exciting a short acoustic pulse at the source position, the response over a broad frequency range can be obtained with a single simulation. Another advantage of time-domain models is that they allow more easily for non-linear effects near high-amplitude sources. This is because a time-domain approach directly models the waveform and, therefore, the waveform distortion corresponding to the transfer of sound energy between sound frequencies can be captured. The chapter describes a popular time-domain approach, the finite-difference time-domain method, which uses finite-differences for discretizing the spatial and temporal derivatives appearing in the governing sound propagation equations. It is straightforward to model propagation in inhomogeneous media by using a volume-discretization technique.
