A HYBRID CALCULATION TECHNIQUE OF THE INDIRECT BOUNDARY-ELEMENT METHOD AND THE ANALYTICAL SOLUTIONS FOR 3-DIMENSIONAL PROBLEMS OF TOPOGRAPHY

We present a new approach of the indirect Boundary Element Method (IBE M) for 3-D topographic problems which can be used to deal with an infi nitely spread free surface owing to the introduction of a reference so lution, that is the analytical solution for the half-space with a flat free surface. This approach is an efficient countermeasure for the no n-physical waves owing to the domain truncation which contaminates the computed results in the ordinary approach. Theoretical consideration shows that this newly proposed approach is a higher-grade approximatio n than some existing ones and achieves a higher efficacy and accuracy than those of existing ones. The discretization of the resulting bound ary integral equation for this formulation is carried out with triangu lar elements. Their contributions to the solution are calculated by Ga ussian numerical integration except in the case where the wavefield is evaluated on the source element itself. For this case, we present an analytical formula based on the reasonable assumption that the element s are much smaller than the wavelengths appearing in the calculation. Several numerical examples used for validation show acceptably precise results.