Use of Statistical Energy Analysis for Rotating Machinery, Part II: Coupling Loss Factors Between Indirectly Coupled Substructures

Abstract

Indirect coupling between physically uncoupled substructures is present when either the coupling between the directly coupled substructures is strong, or the sizes of the substructures are small compared to the wavelength, or the junction between the substructures is in the near field of another junction. The coupling loss factors between indirectly coupled structures are generally not taken into account in traditional Statistical Energy Analysis (SEA). In this paper, theoretical expressions are developed for calculating the indirect coupling loss factors between physically uncoupled substructures. The derived formulae show that the indirect coupling loss factors, when compared to the direct coupling loss factors, are signficant if strong direct coupling exists between the substructures. However, the indirect coupling loss factors are negligible if weak coupling exists between any two coupled substructures. A series of experiments are carried out to verify the theoretical analysis for the determination of the indirect coupling loss factors. Also, the influence of the indirect coupling loss factors on the response of a complex machine structure, predicted using SEA, is demonstrated. Better agreement between the predicted results and the directly measured results is obtained when the indirect coupling loss factors are included in the SEA model.