Approximations for modal coupling in scattered fields from orifices

Previous investigations have used Hankel transforms to establish the veloci ty potentials of the wave fields resulting from arbitrary angle plane wave impingement on a circular orifice in a rigid, thick wall. The scattered fie ld from the orifice is examined, in particular the modal contributions to t he amplitude of its velocity potential. For each m,n mode the amplitude is dependent upon the amplitude of the in-orifice waves and a driving term uni que to each m,n mode. In establishing the amplitudes of the in-orifice wave s, the effects of modal coupling are also considered. In this work these tw o components of the scattered wave amplitude are investigated on a modal ba sis and approximations given for coupling effects. These approximations are then used to calculate the scattered field and the results compared with c onventional solutions that use full modal coupling. (C) 2000 Acoustical Soc iety of America. [S0001-4966(00)00708-6].