Time domain integral equation solution for acoustic scattering from fluid targets

The responses of fluid targets are computed using space–time integral equations formulated in the time domain. The incident pressure wave is a ’’smoothed-impulse’’ with a Gaussian shaped time dependence whose width is of the order of a target dimension. A space–time integral equation for the pressure field on the outside of the target surface and a space–time integral equation for the pressure field on the inside of the target surface are solved simultaneously for the pressure and the pressure gradient by stepping on in time and making use of the boundary conditions (continuity of pressure and displacement). The farfield is then computed from these source fields. The technique is applicable to targets of arbitrary contour and is demonstrated for a sphere and right circular cylinder at various angles of incidence. Fluid targets support interior compression waves; sound-hard and sound-soft targets are treated as limiting cases of this formulation. The technique has been verified for the case of a sphere by comparison with the response computed by classical expansions.