Title page for ETD etd-41898-17429

Type of Document Master's Thesis
Author Betts, Juan Fernando
Author's Email Address jbetts@vt.edu
URN etd-41898-17429
Title Finite Element Study of Plane Wave Acoustic Phenomena in Ducts
Degree Master of Science
Department Mechanical Engineering
Advisory Committee
Advisor Name Title
Knight, Charles Eugene Committee Chair
Burdisso, Ricardo A. Committee Member
West, Robert L. Jr. Committee Member
  • Finite Elements
  • Acoustics
  • Waves
  • Ducts
Date of Defense 1998-04-29
Availability unrestricted
This thesis studied the finite element modeling of plane wave acoustic phenomena

in ducts. The study looked into finite element factors such as shape functions, mesh

refinement, and element distortion.

The study concluded that the higher order shape function eight-node quadrilateral

element gave considerably better results than lower order shape function four-node

quadrilateral element. The eight-node element converged much faster to the analytical

solution than the four-node element. The average error, taking all the cases in

consideration, for the four-node element was around 30 % for a mesh refinement of about

14 elements per wavelength at 100 Hz frequency. The eight-node element in the other

hand had average absolute errors of less than 1% under the same conditions.

This section also found that the eight-node element was substantially more

resistant to solution deterioration due to element distortion than the four-node element.

For example distorting the four-node element up to 60* degrees usually increased errors

very rapidly to above 100 % errors. The eight-node element on the other hand usually

produced errors of less than 5 % for the same level of distortion.

The study showed that the type of boundary condition used had a significant

effect on the solution accuracy. The study demonstrated that the effect of the natural

boundary conditions was more global. Meeting this kind of boundary condition through

mesh convergence produced accurate results throughout the duct.

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