Wave-mode based FRF evaluation of harmonic vibro-acoustic WTG tower emission

Vibroacoustic simulations of complete wind turbine generator (WTG) models using Finite-Element-Method (FEM) often result in tremendous calculation time simply due to the sheer size of modern WTG as this is directly related to the required element density. Hence, this paper proposes a new simulation procedure for increasing simulation performances by reducing the model size and thereby time of calculation, here exemplified by Structure-borne tower radiation. The results of wave-FEM (WFEM) analyses of a meshed ring representing a cut-out of a WTG tower model are used to identify wave-modes for acoustic relevant incoming structural waves which contain both force and deformation information. These wavefield-dependent force terms are then utilized in harmonic analysis of FE-models of real WTG towers, and their acoustic emissions are quantified at observer positions of interest using the Boundary-Element-Method (BEM). The resulting frequency-response-functions (FRFs) utilizing wave-mode coordinates are related to relevant nodal tower top deflection from either simulation results or measurements using a least-square-fit (LSF). Consequently, acoustic emissions from the WTG tower can be represented by the identified significantly reduced wave-mode coordinate driven FRF model which only must be solved once for each tower and frequency band of interest. The described methodology offers a possibility to evaluate harmonic noise responses of a WTG tower by only knowing its tower top deflection shape.