PREDICTION OF LOW-FREQUENCY RADIATION EFFICIENCIES USING THE NORMAL MODE APPROACH AND FINITE ELEMENT METHODS

For homogeneous, isotropic plates at low-frequencies and non-homogeneous, anisotropic plates, estimates for the radiation efficiency that assume high modal density are not always sufficiently accurate for use in prediction models. This paper considers two different plates under point force excitation, a concrete floor with low modal density and a dowelled-joist timber floor which represents a complex inhomogeneous, anisotropic plate. Both the normal mode model and Finite Element Methods (FEM) are used to predict the radiation efficiency for a concrete floor into a specific room. The results for the concrete floor provide more evidence that a reasonable approximation for masonry/concrete walls and floors is to limit Leppington’s predicted radiation efficiency values to unity. For the dowelled-joist timber floor, an experimentally validated FEM model for the dynamic structural response is used with a transfer plate to account for the non-continuous nature of the FEM model that would not normally be suitable for FEM modeling of fluid-structure interaction. The models for both floors demonstrate the potential to use coupled room-plate models to determine radiation efficiencies which are specific to the form of excitation and the modal response of the plate and the room.