A study of broadband and periodically time-varying vibration control of building services equipment

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A study of broadband and periodically time-varying vibration control of building services equipment

 

Author: Wang, Junfang
Title: A study of broadband and periodically time-varying vibration control of building services equipment
Degree: Ph.D.
Year: 2014
Subject: Noise control.
Vibration.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xviii, 126 leaves : ill. ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2681831
URI: http://theses.lib.polyu.edu.hk/handle/200/7387
Abstract: Vibration and noise control of equipment have been a long-standing research topic because of its effect on people's health and comfort. The common characteristics of building services equipment pose great challenges to current methods of structure-borne sound control. Some of building services equipment experience frequent transient excitations which may disable the spring isolators traditionally designed for steady-state vibration isolation. Besides, broadband vibration isolation is desirable when the vibratory system has high modal density and the frequency of interest fluctuates in a wide band. In addition, the oversimplification of time-varying systems as time-invariant systems may lead to the failure of an active vibration control system. These problems is not only limited to the area of building service engineering, but can be commonly seen in the field of machine-induced vibration and acoustics. To solve these problems, this research aims to present a power transmissibility approach for the assessment of transient vibration isolation by spring isolators, develop adaptive-passive methods for broadband vibration control using periodic structures, and propose an active control system for the suppression of periodically time-varying vibration. Firstly, a transient power transmissibility approach is proposed to assess the performance of isolators in the situation of a transient vibration excitation. The numerical study demonstrates the necessity of using transient power transmissibility in the selection of isolators for a system that experiences a transient vibration. Secondly, this part focuses on the broadband vibration attenuation by adaptive-passive methods of periodic structures with smart materials. The application of a dual-beam periodic structure with SMA branches to broadband vibration control is explored, and two methods are developed to determine the optimal Young{174}s modulus of the SMA branches. As this semi-two-dimensional periodic structure is a realistic simulation of a real-life problem, this study provides an insight into the general problem of broadband vibration control using smart periodic structures. Thirdly, an active control system is proposed to attenuate periodically time-varying vibration. It is characterized by an adaptive process for system identification and a nonadaptive process for controller design to avoid the coupling effect between the two adaptive processes in many AVC systems. The convergence and the stability of proposed system are proved by rigorous derivation and numerical simulation.

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