Spencer Funk

Topic

Impact of Mooring Systems on Wave Energy Converter Control and Useful Power Capture

Department of Mechanical Engineering

Date & location

• Friday, April 26, 2024

• 1:00 P.M.

• Engineering Office Wing and

• Virtual Defence

Reviewers

Supervisory Committee

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

• Dr. Flavio Firmani, Department of Mechanical Engineering, UVic (Member) 

External Examiner

• Dr. Rick Driscoll, Department of Mechanical Engineering, NREL 

Chair of Oral Examination

• Dr. Karen Courtney, School of Health Information Science, UVic

Abstract

With the effects of climate change becoming more extreme each year there is a dire need to reduce carbon emissions – especially in the energy sector. An energy source currently not in use by any sector is the energy stored in ocean waves. Wave energy can be captured by wave energy converters (WECs) which transform said energy into electricity using a power take-off device. However, these devices are currently too expensive to build and operate for the power they produce.

The common approach to designing a WEC is to optimize its design with modelling and testing and then deploy it in the ocean with a mooring system. Notably, the mooring system is typically neglected at the modelling and testing stages. But the significance of the mooring dynamics to the system response is not fully understood. This work demonstrates that neglecting the mooring system can lead to up to a 50% power loss by modelling the power production of a controlled self-reacting point absorber (SRPA) with and without knowledge of the mooring system.

To address these outstanding questions, four mooring designs were characterized using a unique approach and incorporated into a mechanical circuit model of the SRPA. The characterization approach was used to fit high-fidelity mooring simulation data to linear transfer function models with a high degree of accuracy. Such models significantly reduce simulation time of the SRPA by reducing the mooring dynamics to just the force at its connection to the SRPA. This new model was then used to determine impacts on dynamics and power production. The circuit model was also used to demonstrate the effect of the mooring on three control types.

The effects amounted to up to a 40% reduction of the control variable, suggesting that current controllers may be overdesigned and more expensive as a result. Finally, the annual energy production of three control types were compared by modelling and simulating a moored SRPA in a realistic sea. The simulation results indicated that the performance gains previously seen for a new control type are not eroded by the mooring system or by the realistic sea, with the new control type resulting in four times more annual energy production than the others.