CNCS Graduate Certificate Recipient

Mark M. Murray

Thesis Title: Hydroelasticity Modeling of Flexible Propulsors

Ph.D. Final Defense Date:  December 16, 1999

Ph.D. Dissertation Committee:

Laurens E. Howle (Chair)
Edward J. Shaughnessy
Donald B. Bliss
Kenneth C. Hall
David G. Schaeffer

Abstract:

The intent of this thesis project is to introduce and develop simplified numerical models which simulate the important coupled fluid-structure dynamics of a flexible propulsor immersed in a constant velocity potential flow. A brief introduction into the use of flexible propulsors and the history of research on oscillating propulsion is given at the beginning of the work to give relevance to the models presented.

The first model develops the series of time independent coupled equations which describe the statics of a two-dimensional flexible propulsor utilized as a simple planing control surface. A two-dimensional vortex lattice model describes the hydrodynamics and is coupledto a simple beam equation that describes the two-dimensional structure. The change in liftproduction due to changes in bending stiffness and propulsor cross section is analyzed.

The second model develops the series of time dependent coupled equations that describe the dynamics of a two-dimensional flexible propulsor oscillated about the pinned quarter chord and producing thrust by the Knoller-Betz effect. An unsteady vortex lattice method describes the the unsteady hydrodynamics and is coupled to an unsteady beam equation that describes the time dependent two-dimensional structure. Several simplifications are justified during the model development and numerical analysis. The efficiency and thrust production over a range of driving frequencies and bending stiffness values are analyzed.

The third model describes the dynamics of a two-dimensional oscillating flexible propulsor allowed to translate perpendicular to the mean flow. The heave is determined implicitly from the fluid-structure interactions, and is coupled to the unsteady vortex lattice and unsteady beam models. Allowing passive heave significantly alters the thrust and efficiency response of the oscillating propulsor.

There are several key contributions introduced in this project. The first is a numerical method that calculates the thrust and efficiency of an oscillating propulsor without specifying the shape response of the propulsor. The second is the concept of allowing a passive heave to be determined implicitly and not predetermined.