Sound waves diffraction by an elastic cylinder with inhomogeneous anisotropic outer layer near the plane

Abstract

The problem of diffraction of a plane monochromatic sound wave by an elastic cylinder with a layered inhomogeneous transversely isotropic outer layer is considered. It is assumed that the cylinder is located near a plane with an ideal surface (absolutely hard or acoustically soft).
In order to get rid of the boundary conditions in the plane, in accordance with the so-called imaginary scatterer method, an additional obstacle is introduced in the form of a second elastic
cylinder, which is mirror-like with respect to the initial one on the other side of the plane. The plane itself is excluded from consideration, and the fulfillment of the boundary conditions on
it is ensured by introducing a second incident plane wave with the same amplitude as that of the first. The direction of propagation of the second wave is mirrored to the direction of the original wave relative to the plane. The phase shift in the second wave is equal to the phase shift in the first if the plane is absolutely rigid. If the plane is absolutely soft, the phase shift in
the second wave is shifted relative to the phase shift in the first one by 𝜋. Thus, the problem is reduced to the problem of scattering of two plane waves by two identical elastic cylinders with parallel axes. Assuming that the incident wave propagates along the normal to the cylinder axis, a two-dimensional problem is solved. The solution of the problem in a modified formulation is carried out using the finite element method. Numerical simulation of the solution in the near zone of a scattered acoustic field is carried out. The calculation results show that in a number
of cases of combinations of the parameters of the cylinder and the incident wave, the anisotropy and inhomogeneity of the material properties of the outer layer of the cylinder have a significant effect on the scattered field.