An acoustic boundary integral formulation for open shells allowing different impedance conditions, top and bottom surfaces

In the automotive, aerospace industries as well as the underwater acoustics defense applications the addition of coatings to modify the response of the vibrating structure is commonplace. The formulation developed is an extension of the existing thin body formulation currently found in commercial noise prediction codes such as SYSNOISE in order to allow problems requiring different boundary condition on both sides of the thin shell to be solved. For instance, a generalised thin body acoustic formulation would allow for a local impedance boundary condition to be specified on the top surface and a hard Neumann boundary condition to be specified on the bottom surface. Such a formulation would allow for different local impedance coatings to be specified on the top and bottom surfaces.Due to the lack of analytical solutions for such problems (even for the simplest geometries) it is difficult to validate such a formulation, however, three test cases are presented, two flat plate examples and a open cylinder with a point monopole source excitation at its centre.