Title page for ETD etd-204411102971680


Type of Document Dissertation
Author Maillard, Julien
URN etd-204411102971680
Title Advanced Time Domain Sensing For Active Structural Acoustic Control
Degree PhD
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Burdisso, Ricardo A.
Inman, Daniel J.
Robertshaw, Harry H.
Wicks, Alfred L.
Fuller, Christopher R. Committee Chair
Keywords
  • active control
  • structural acoustics
  • smart structures
Date of Defense 1997-02-27
Availability unrestricted
Abstract
Active control of sound radiation from

vibrating structures has been an area of much

research in the past decade. In Active

Structural Acoustic Control (ASAC), the

minimization of sound radiation is achieved by

modifying the response of the structure through

structural inputs rather than by exciting the

acoustic medium (Active Noise Control,

ANC). The ASAC technique often produces

global far-field sound attenuation with

relatively few actuators as compared to ANC.

The structural control inputs of ASAC systems

are usually constructed adaptively in the time

domain based on a number of error signals to

be minimized. One of the primary concerns in

active control of sound is then to provide the

controller with appropriate ``error''

information. Early investigations have

implemented far-field microphones, thereby

providing the controller with actual radiated

pressure information. Most structure-borne

sound control approaches now tend to

eliminate the use of microphones by

developing sensors that are integrated in the

structure. This study presents a new sensing

technique implementing such an approach. A

structural acoustic sensor is developed for

estimating radiation information from vibrating

structures. This technique referred to as

Discrete Structural Acoustic Sensing (DSAS)

provides time domain estimates of the radiated

sound pressure at prescribed locations in the

far field over a broad frequency range. The

structural acoustic sensor consists of a set of

accelerometers mounted on the radiating

structure and arrays of digital filters that

process the measured acceleration signals in

real time. The impulse response of each filter is

constructed from the appropriate radiation

Green's function for the source area associated

with each accelerometer.

Validation of the sensing technique is

performed on two different systems: a baffled

rectangular plate and a baffled finite cylinder.

For both systems, the sensor is first analyzed

in terms of prediction accuracy by comparing

estimated and actual sound pressure radiated

in the far field. The analysis is carried out on a

numerical model of the plate and cylinder as

well as on the real structures through

experimental testing. The sensor is then

implemented in a broadband radiation control

system. The plate and cylinder are excited by

broadband disturbance inputs over a

frequency range encompassing several of the

first flexural resonances of the structure.

Single-sided piezo-electric actuators provide

the structural control inputs while the sensor

estimates are used as error signals. The

controller is based on the filtered-x version of

the adaptive LMS algorithm. Results from

both analytical and experimental investigations

are again presented for the two systems.

Additional control results based on error

microphones allow a comparison of the two

sensing approaches in terms of control

performance.

The major outcome of this study is the ability

of the structural acoustic sensor to effectively

replace error microphones in broadband

radiation control systems. In particular, both

analytical and experimental results show the

level of sound attenuation achieved when

implementing Discrete Structural Acoustic

Sensing rivaled that achieved with far-field

error microphones. Finally, the approach

presents a significant alternative over other

existing structural sensing techniques as it

requires very little system modeling.

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