Title page for ETD etd-42798-161027

Type of Document Master's Thesis
Author Siethoff, Eric Ten
Author's Email Address esiethof@vt.edu
URN etd-42798-161027
Title A Formulation for Updating Finite Element Models Through Consistent Use of Laser Vibrometer Data
Degree Master of Science
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
West, Robert L. Jr. Committee Chair
Knight, Charles Eugene Committee Member
Saunders, William R. Committee Member
  • laser Doppler vibrometer
  • updating
  • finite element
Date of Defense 1998-04-28
Availability unrestricted
This thesis suggests a formulation for updating physically

meaningful parameters in analytical finite element(FE)

models using scanning laser Doppler vibrometer(SLDV) dynamic

response data. The update formulation is demonstrated in

several computer simulations.

The formulation is the result of incorporating an analytical

FE model into an experimental model. The experimental model

efficiently utilizes SLDV data to fully exploit the

instrument's capability to automatically make measurements

at many locations. The data in the experimental model is

posed in a manner consistent with an analytical FE model's

representation for harmonic response, simplifying

comparison between the two. The experimental model, which

uses finite element shape functions as a basis for a least

squares fit to the data, can be solved to give a velocity

field based only on that data. The function resulting from

inserting the analytical model into the experimental model

is an expression of the prediction error of the FE model as

compared to the test data. This function is minimized using

a quasi-Newton optimization routine, reducing the error and

resulting in an updated model.

Computer simulations of the update algorithm indicate that:

1. Analytically supplied derivatives and variable scaling

are required by the optimization routine to consistently


2. The percentage error of updated parameters falls within

two standard deviations of the data's percentage error,

3. Error in the position of the laser results in the update

algorithm's failure, and,

4. Error in the parameters not included in the update will

appear as error in the updated parameters' solution.

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