Title page for ETD etd-93197-1508


Type of Document Dissertation
Author Lam, Margaretha Johanna
Author's Email Address mjlam@cooper.edu
URN etd-93197-1508
Title Hybrid Active/Passive Models with Frequency Dependent Damping
Degree PhD
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Inman, Daniel J. Committee Chair
Cudney, Harley H. Committee Member
Inman, Daniel J. Committee Member
Robertshaw, Harry H. Committee Member
Saunders, William R. Committee Member
Wicks, Alfred L. Committee Member
Keywords
  • model reduction
  • frequency dependent damping
  • hybrid
  • passive
  • active
  • feedback
Date of Defense 1997-10-27
Availability unrestricted
Abstract
To add damping to structures, viscoelastic materials (VEM)

are added to structures. In order to enhance the damping

effect of the VEM, a constraining layer is attached,

creating a passive constrained layer damping treatment

(PCLD). When this constraining layer is an active element,

the treatment is called active constrained layer damping

(ACLD). Recently, the investigation of ACLD treatments has

shown it to be an effective method of vibration suppression.

In this work, two new hybrid configurations are introduced

by separating the passive and active elements. In the first

variation, the active and passive element are constrained

to the same side of the beam. The other variation allows

one of the treatments to be placed on the opposite side of

the beam. A comparison will be made with pure active, PCLD,

ACLD and a variation which places the active element

underneath PCLD. Energy methods and Lagrange's equation

are used to obtain equations of motion, which are

discretized using assumed modes method. The frequency

dependent damping is modeled using the Golla-Hughes-McTavish

(GHM) method and the system is analyzed in the time domain.

GHM increases the size of the original system by adding

fictitious dissipation coordinates that account for the

frequency dependent damping. An internally balanced model

reduction method is used to reduce the equations of motion

to their original size. A linear quadratic regulator and

output feedback are used to actively control vibration. The

length and placement of treatment is optimized using

different criteria. It is shown that placing the active

element on the opposite side of the passive element is

capable of vibration suppression with lower control effort

and more inherent damping. If the opposite surface is not

available for treatment, a suitable alternative places the

PZT underneath the PCLD. LQR provides the best control,

since it assumes all states are available for feedback.

Usually only select states are available and output

feedback is used. It is shown that output feedback, while

not as effective as full state feedback, is still able to

damp vibration.

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