Date of Award

2026

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Mechanical Engineering-Engineering Mechanics (PhD)

Administrative Home Department

Department of Mechanical and Aerospace Engineering

Advisor 1

Gordon G. Parker

Committee Member 1

Jung Yun Bae

Committee Member 2

Shangyan Zou

Committee Member 3

David Labyak

Abstract

This dissertation develops analytical modeling, numerical simulation, experimental validation, and data driven control methods for nonlinear point absorber wave energy converters, with particular emphasis on cone--cone buoy geometries. Geometry dependent nonlinear force models are first derived using pressure field and displaced volume formulations. These models show how buoy geometry produces nonlinear Froude--Krylov and restoring forces, including the dominant cubic behavior of cone--cone geometries.

The derived models are incorporated into a feedback linearization framework that compensates selected nonlinear dynamics while retaining the incident wave terms. An analytical optimal control formulation is also developed to maximize harvested energy in nonlinear, nonautonomous systems subject to dynamic and control constraints.

The predicted nonlinear behavior is investigated experimentally using a low-friction heave platform and a manufactured truncated--cone--cone buoy. Harmonic force experiments reveal amplitude dependent resonance, waveform distortion, and subharmonic responses, confirming measurable Duffing like dynamics.

Finally, a hybrid physics based and data driven control architecture is developed for cases in which only part of the WEC force balance can be modeled reliably from the duffing behavior predicted before. The known geometry dependent force is retained analytically, while the aggregate unknown force is reconstructed from measured motion and PTO force data and compensated through the actuator. Real time wave basin experiments demonstrate that partial residual compensation can increase measured PTO power and substantially reduce the closed loop force mismatch. The results also show that the compensation gain that maximizes energy extraction differs from the gain that provides the strongest residual cancellation.

Overall, the dissertation shows that nonlinear WEC performance can be improved by combining geometry based models, nonlinear and optimal control, experimental characterization, and real time residual force compensation.

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