Title page for ETD etd-101397-153920


Type of Document Dissertation
Author Li, Zhonglin
Author's Email Address zli@vt.edu
URN etd-101397-153920
Title Design of Active Structure Acoustic Control Systems Using Eigenassignment Approach
Degree PhD
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Fuller, Christopher R. Committee Chair
Baumann, William T. Committee Member
Burdisso, Ricardo A. Committee Member
Cudney, Harley H. Committee Member
Robertshaw, Harry H. Committee Member
Keywords
  • Feedforward Control
  • Active Structural Acoustic Control
  • Structural Acoustics
Date of Defense 1997-10-30
Availability unrestricted
Abstract
Design of Active Structural Acoustic Control

Systems Using Eigenassignment Approaches

by

Zhonglin Li

Chris R. Fuller, Committee Chairman

Department of Mechanical Engineering

(ABSTRACT)

Active structural acoustic control (ASAC) in conjunction with the

adaptive feedforward control has been proved to be an efficient

practical approach to reduce structure-borne sound. ASAC works on the

principles of reducing the vibration amplitude of the structure (modal

reduction), as well as changing the vibration distributions of the

structure so that the vibration distributions of each structural modes

destructively interfere with one another in their associated radiating

acoustic field (modal restructuring). Based on these observations, two

different but related design strategies, namely the non-volumetric

design and the minimum supersonic wavenumber design, were developed

for designing efficient ASAC system. The eigenassignment method for

feedforward control system serves as the fundamental design tool for

both formulations.

In this study, the dynamic characteristics of a multiple-input,

multiple-output (MIMO) feedforward controlled system was investigated

both analytically and experimentally on a simply supported plate under

harmonic excitation. It was demonstrated that, when the control system

has equal number of control inputs and error sensor outputs, the

feedforward controller can effectively modify the system dynamics (i.e.,

resonance frequencies and mode shapes). This provides the theoretical

basis for the eigenassignment method.

For the non-volumetric design, the single-input, single-output (SISO)

eigenassignment technique is used to modify the eigenproperties of a

planar structure using structure actuators and sensors so that all the

controlled modes are non-volumetric (inefficient sound radiators at

low frequencies, i.e., k_0a << 1), leading large global sound

attenuation in the far field. The effectiveness of this formulation

was demonstrated through numerical simulations for the control of

radiation from simply supported and clamped-free beams. The

experimental validation of the non-volumetric design was also carried

out on a simply supported beam using PZT actuators and shaped PVDF

film as error sensor. The filtered-x LMS algorithm was used in the experiment. Excellent

global sound attenuation was achieved in the low frequencies.

The minimum supersonic wavenumber design stems from the fact that only

supersonic wavenumber components of the structural velocity spectra

radiate to the far field. A SISO eigenassignment technique is used to

modify the eigenproperties of a planar structure so that the

eigenfunctions of the controlled system have minimum supersonic

wavenumber in the frequency range of study. The sound pressure or

sound power radiated by the structure is therefore reduced. The design

was demonstrated on a simply supported beam to minimize the supersonic

wavenumber components contributed by the odd-order modes only.

Significant global sound attenuation was achieved in the frequency

range of study.

The main advantage of the proposed design methods is that they do not

depend on the characteristics of the external disturbance, such as the

form, location and frequency contents. Also, the error sensor and

control input are optimized simultaneously, resulting in better

acoustic control performance. The practical implementations of the

proposed designs require accurate system modeling, this is the major

limitation of the proposed designs.

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