摘要：In a computational model for outdoor sound propagation, the relevant
propagation phenomena, among which are refraction and diffraction, must be
implemented. All numerical methods applied in this field so far have
disadvantages or limits. The Finite Element Method has to discretize the
domain and hence is restricted to closed or at least moderate sized
domains. The Boundary Element Method can hardly consider inhomogeneous
domains and the computation effort increases exponentially for large systems.
Geometric acoustics algorithms like ray tracing consider sound as particles
and are hence not able to represent wave phenomena. It is the aim of this
work to combine the advantages of the BEM and of the ray method: In the
nearfield where obstacles and complex geometries occur - and so diffraction
and multiple reflection are expected - the model uses the BEM. Then, a ray
model is coupled to compute the sound emission at large distances, because
this model can take into account refraction resulting from wind or
temperature profiles. The ray model requires point sources as input data.
However, a boundary element calculation always delivers the pressure or its
normal derivative along the boundary. Hence, for the coupling of both models
it is necessary to convert the BEM results into equivalent point sources. The
Method of Fundamental Solutions (MFS) is found suitable for this
purpose. To couple the BEM and ray model, the acoustic half-space is divided
into a BEM domain and a ray domain by defining a virtual interface. Along
this interface, the pressure is computed with the BEM. The idea behind the
MFS is to place a number of sources with unknown intensities around the
domain of interest. These intensities are then computed in order to fulfill
prescribed boundary conditions at discrete points on the boundary of the
domain. The MFS can be either applied with fixed source positions or with an
optimization algorithm, which finds the optimal source positions by
minimizing the residual along the boundary in a least-squares sense. Both
types of the MFS are used in this work. The verification of this new coupling
procedure is shown for a two-dimensional problem consisting of a of a noise
barrier in a homogeneous atmosphere, for which a reference solution is known.
