Luke Friedl

Topic

Design and Simulation of a Three-Body Self Reacting Point Absorber Wave Energy Converter Using Inertial Control

Department of Mechanical Engineering

Date & location

• Thursday, November 27, 2025

• 8:30 A.M.

• MacLaurin Building, Room D202c

• And Virtual Defence

Reviewers

Supervisory Committee

• Dr. Brad Buckham, Department of Mechanical Engineering, University of Victoria (Supervisor)

• Dr. Andrew Rowe, Department of Mechanican Engineering, UVic (Member) 

External Examiner

• Dr. Solomon Yim, Department of Civil & Construction Engineering, Oregon State University 

Chair of Oral Examination

• Dr. Kate Moran, School of Earth and Ocean Sciences, UVic

   

Abstract

Global energy systems are rapidly transitioning through the increasing introduction of renewable energy sources. Most renewable generation sources are intermittent, creating challenges for grid stability and reliability. Diversifying these generation sources can mitigate this issue. Integrating ocean wave generation sources into the energy mix represents a candidate strategy for this diversification.

Despite their potential, ocean wave energy converters remain underutilized due to their comparatively high cost relative to other renewable generation technologies. Recent research has shown that significant increases in the power production of wave energy converters can be achieved through advanced control strategies that utilize a mechanical device called an inerter to tune the system into resonance with incident ocean waves. These studies assumed idealized inerters and system dynamics, and relied on frequency domain analyses, which neglect nonlinear hydrodynamic and mechanical losses. Additionally, limited consideration was given to the physical constraints required to integrate the inerter into an actual wave energy converter system. 

To address this gap in the research, this work develops a time-domain simulation tool to model the coupled dynamics of the wave energy converter and inerter system, incorporating both nonlinear mechanical and hydrodynamic forces. The inerter was then analyzed under design and operational objectives and reduced to its core design parameters. A genetic algorithm was applied to optimize the inerter design in order to satisfy these objectives. Finally, the simulation tool was used to model the wave energy converter coupled with the optimized inerter to evaluate the effects of the nonlinear mechanical and hydrodynamic forces on the power production of the system under optimal control. 

The optimized inerter design was able to achieve the effective mass response required for optimal power capture. However, when implemented with the optimal control scheme, the wave energy converter system exhibited unrealistic motion under low frequency wave conditions. To compensate for the unrealistic motion, an adapted control approach was applied, which led to substantial losses in power production below a wave frequency of 2.96 rad/s. The addition of friction forces in the inerter, end stop forces and viscous drag forces also led to significant losses in power production. 

This research developed a time-domain simulation tool to evaluate the realistic performance of coupled wave energy converter-inerter systems. By demonstrating the limitation of optimal control schemes when applied to realistic systems, the significant gap between idealized control models and physically achievable systems was revealed. This work also demonstrated that while the friction force induces a parasitic dissipation of power the primary source of loss is due to the control algorithms ignorance to the change in the system impedance that the friction force causes. This is the opposite for viscous drag where the loss in power from the dissipation of energy due to drag outweighed the control related loss. 

The insights gained in this research identify key mechanisms responsible for these losses and point towards strategies that could be used to mitigate them. Future challenges that must be addressed to advance this research area include linearizing the nonlinear forces and incorporating them into the optimal control algorithm as well as developing higher-fidelity inerter models to better capture real-world dynamics. Ultimately, future work should apply this research when constructing a real-world prototype device and experimentally validate the results and insights obtained in this research. 

Overall, this work established a foundation for future researchers to refine realistic control approaches, mitigate the effect of non-linear forces and advance the practical viability of inerter-based wave energy converter control methods.