Reference Models: Acoustic field calculations based on wave theory

Wave theoretical acoustic field calculations are based on the fundamental physical relationships between the parameters that describe an acoustic field. These numerical models are capable to simulate the relevant acoustic propagation phenomena exactly without empirical approximations.

For the computation, the region of interest needs to be discretized. At high frequencies, this discretization becomes so fine that the number of points to be calculated limits the applicability. In many cases however it is possible to describe the situation as a cross-section in a two-dimensional geometry, thus greatly reducing the necessary computational effort.

The FDTD simulation software that was developed at Empa some years ago is now used by order of third parties to answer engineering questions such as the optimisation of geometry and absorption of noise protection constructions. Our development of an efficient implementation of generalised boundary conditions allows also for the simulation of wave propagation over grass land over larger distances in inhomogeneous atmosphere. Currently we are implementing the algorithms on a graphics processing unit (GPU). In near future this will allow to simulate sound propagation in three dimensions with acceptable computational effort.
Snapshot of the propagation simulation of a pressure pulse. Sound pressure is colour coded with intense red for high positive and intense blue for high negative values.