Application of energy relations at modeling scattering by FEM on resonant frequencies

In this paper FEM is applied to research of sound scattering on an elastic object, whose sizes are ~1-10 wavelengths (in water) and that has eigen modes. The paper provides a revision of analyti-cal expressions, that were previously applied in theoretical research and that can be applied to the results of numerical modeling. They allow determining various parameters of scattering, help to formulate a physical interpretation of the results of the calculation and provide an additional test of the precision. In particular, application of central optical theorem allows finding a full scattered and absorbed power, basing on calculated characteristics of the scattered field - ampli-tude and phase of the forward scattered wave. Basing on this approach, one can investigate typi-cal parameters of the structure, at which maximum (minimum) levels of integral scattering are reached. In addition to that, we discuss an acceptable degree of simplification of a finite element model at solving scattering problems. An extra motivation for considering the central optical theorem is the fact, that a rather large piece of information about the object can be obtained, basing on characteristics of scattering only forward direction. And such characteristics could be found by the modern near-field means of measurement.