Lerch R., Kaltenbacher M.

Modern numerical simulation tools allow a precise analysis of the generation and propagation of sound. However, up to now, a variety of computational features enhancing their applicability are missing in these codes. Therefore, it is sometimes cumbersome to come to practically useful results when applying such numerical codes to real life problems. In this paper, some of these lacking features will be addressed and, furthermore, their implementation and test in a finite element environment is reported. Frequency Dependent Damping of Propagation Medium Many sound propagation media exhibit frequency dependent damping. This asks for special treatment within finite element codes. We will demonstrate how damping of a medium with an arbitrary frequency dependent damping coefficient can be handled by finite elements. Nonmatching Grids When computing sound in neighbouring domains with quite different propagation velocities (wavelengths) it is useful to use different finite element grids for these domains. We present a scheme for which it is not necessary that the grids match at their neighbouring boundaries. Perfectly Matched Layers When using finite elements in open domain problems one has to overcome the difficulty of reflexions at the boundaries of the computational domain. We will present a new technique based on Perfectly Matched Layers (PML) which is able to deliver excellent results, even for computational domains limited to the nearfield. Pollution Error When computing the propagation of sound over long distances the numerical errors due to spatial and time discretization errors will accumulate. We will present some techniques to overcome these errors.