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Author ORCID Identifier

https://orcid.org/0000-0001-7320-7414

AccessType

Campus-Only Access for Five (5) Years

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

Year Degree Awarded

2021

Month Degree Awarded

February

First Advisor

Yahya Modarres-Sadeghi

Subject Categories

Acoustics, Dynamics, and Controls | Aerodynamics and Fluid Mechanics | Electro-Mechanical Systems | Propulsion and Power

Abstract

The present thesis investigates modeling and control techniques for nonlinear continuous vibratory systems in contact with flow. The objective is to derive and solve the nonlinear partial differential equations which represent these systems and explore their behavior through numerical simulations and experiments. A series of examples are considered to motivate the applicability of these techniques to a wide variety of problems. The common thread in each of these examples is the fundamental assumption that the underlying structural dynamics can be approximated by a continuous nonlinear beam and that the motion is influenced by the flow forces that interact with it. First, a system in which the structure is controlled through an open loop input waveform is considered. Here the flow forces follow the structure’s motion in a one-way fluid structure interaction(FSI) problem. An example transient dynamic problem is introduced related to the locomotion of fish and bio-inspired engineering. In this case, a robotic fish is designed and constructed, which relies on the passive dynamics of a buckled beam to generate rapid transient underwater locomotion. The continuous beam generates kinematics similar to those observed in live systems. A nonlinear dynamic model is derived and solved to investigate the experimentally observed behavior. The buckled structure is shown to undergo a snap-through bifurcation. The snap-through bifurcation is found to have an intuitive description in the coupled nonlinear equations of motion when cast into the modal domain. Experiments on the snap-through bifurcation in air and in water confirm the modal dynamics and the stability of fixed points determined from the derived discretization of the continuous nonlinear partial differential equation. In a subsequent example, the dynamics of an iv aeroelastic system is investigated. The aeroelastic problem is characterized by a system where the structure’s response is due to the coupling of the fluid and structure. A nonlinear coupled fluid-structure interaction aeroelastic model is derived utilizing a continuous representation of the structure and the ONERA dynamic stall model for the aerodynamic loading. The model is used to predict post-critical behavior of systems undergoing stall flutter at large angles of attack. The stall flutter response is observed experimentally and compared to theoretical simulations, for the onset of stall flutter and the amplitude and frequency of post-critical response. A modal control strategy is applied to influence the coupled response of the structure.

Available for download on Tuesday, February 01, 2022

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