THE USE OF “ECTOPLASM” TO PREDICT RADIATION AND TRANSMISSION LOSS OF A HOLED PLATE IN A CAVITY

The purpose of this paper is to extend the use of “ectoplasm” to a vibro-acoustic problem. The notion of ectoplasm had been presented in a previous paper treating the prediction of natural model shapes of plates with holes of any shape. It was shown that a structure originally defined on a complex domain can be prolonged by an insubstantial mechanical medium (ectoplasm) in order to be defined on a canonical domain. Then, a semi-analytical calculus can be used. Ectoplasm characteristics must not perturb the structure behaviour, but must cover round-off errors of the computer. Here it is shown that such a compromise is still valid when the structure is coupled to a fluid. A holed plate is considered, separating a rectangular cavity in two parts. An integral formulation is used to describe the pressure field. The cavity Green function is expanded on twice indexed functions, implicitly allowing to take into account the pressure field discontinuity, and save running time. The plate is considered as a heterogeneous plate containing ectoplasm, defined on all the sections of the cavity and a variational formulation is used. Radiation and transmission loss of a holed plate is discussed and compared with the case of a full plate. The case of the non-baffled free plate is also presented. The method is validated by comparison with experimental data.