Structure-borne sound transmission from vibratory equipment to coupling structures in buildings

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Structure-borne sound transmission from vibratory equipment to coupling structures in buildings

 

Author: Yun, Yi
Title: Structure-borne sound transmission from vibratory equipment to coupling structures in buildings
Degree: Ph.D.
Year: 2010
Subject: Buildings -- Environmental engineering
Sound -- Transmission
Noise control
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiii, 130 leaves : ill. ; 30 cm.
InnoPac Record: http://library.polyu.edu.hk/record=b2441533
URI: http://theses.lib.polyu.edu.hk/handle/200/6101
Abstract: This thesis addresses the problems of vibration-isolated machines and the structure-borne sound transmission in coupling building structures. It first presents a study of the comprehensive assessment of the stability as well as the power transmissibility on the use of inertia blocks for vibration-isolated systems. The results indicate that the primary use of an inertia block does not affect the isolation performance, but it decreases the vibration velocity of the isolated vibratory machine and in turn increase the stability especially for a source machine of highly uneven mass distribution. An insight into the selection of the inertia block for the comprehensive performance of a vibration-isolated system is also provided. Secondly, a theoretical research of the flexural and longitudinal wave motion in a semi-infinite coupling periodic dual-layered beam structure is presented. A new transfer matrix method is derived for the fully coupled flexural and longitudinal waves, and the numerical calculation is performed to investigate the propagation of characteristic wave types in the structure. It is found that three symmetric and three antisymmetric types of characteristic coupled wave motion in a periodic structure, and the energy contribution of the wave motion depends on both of the pass-forbidden band of the characteristic wave types and the combination of the excited wave types. Thirdly, the experimental research for the flexural-longitudinal motions in a finite coupling dual-layered beam structure is conducted to validate the developed method. The results of measurement agree well with the numerical results from the developed method. The analysis using the validated method shows that the longitudinal energy transmitted in the cross-layer can be enhanced not only at the longitudinal resonant modes of the finite beam but also at the flexural resonant modes of the beam branches. Moreover, a simulation of vibration control design implies that the cross-layer transmitted vibration can be decreased by the attached cantilevers with mass. Fourthly, the power flow transmission through a finite coupling dual-layered beam structure with a boundary condition is studied. The model considering the mono-coupling of flexural wave only is compared with the model considering the multi-coupling of flexural and longitudinal waves. The simulation suggests that the transmission of power flow through the structure largely depends on the characteristic of the periodic coupling elements and the exciting position. The multi-coupling model is similar to the mono-coupling model mainly in the relatively low frequency. Finally, the coupling effect on the vibration control of two coherent vibratory machines placed on a dual-layered floor plate is investigated. The total power of structure-borne sound transmitted from two coherent sources to a coupling floor structure is found to be different from that transmitted from the independent source on a plate without coupling, especially at some strong coupling modes. It is suggested that the power transmissibility method should consider the interactions of the mounting points of coherent machine sources on a coupling floor structure as well as the effective floor mobility for the independent machine source. The whole study promotes the fundamental understanding and prediction method of structure-borne sound control for vibratory machines on the coupling multi-layered structures.

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