The Challenge
Low-cost wave energy production is governed by the WEC’s ability to operate at maximum efficiency in the ever-changing ocean environment. Power is force multiplied by velocity, and both need to be optimised for best WEC efficiency. In this project, better ways to predict wave forces on WECs oscillating with optimum (large) velocity will be developed. The ideal WEC operational window is broad – from short choppy wind seas to long swell waves – ensuring power production even as weather patterns and seasons change. Moreover, real-time control comprising instantaneous fine-tuning of the power take-off settings delivers increased energy absorption from each passing wave.
Successful design of a WEC thus requires realistic predictions of device motions, power output and the corresponding forces experienced by all parts of the WEC system in varying ocean conditions.
Computational efficiency of numerical models is critical in the following areas:
- Early design stages, where numerous iterations of the WEC geometry need to be tested in a wide range of wave conditions
- Deriving estimates for fatigue and (approximate) extreme loading in the detailed design process.
- Real-time control in operating devices, where rapid WEC response calculations are needed based on the approaching waves which will reach the device in the next 30 seconds or so.
Existing models were originally developed to meet the needs of the offshore oil and gas industry for structures where equipment and/or other fixtures were to remain largely motionless to allow safe operations on deck. On the other hand, WECs are designed to move in response to waves – the large wave-induced oscillatory motions drive the power take-off which converts mechanical energy into electricity.
Relying on traditional linear wave structure interaction models, which are unable to satisfactorily capture the dynamic effects associated with large body motions, has negative cost implications in terms of compromised performance and higher design safety margins. The challenge for wave energy lies in deriving new modelling tools able to take WEC motions into account with minimal additional computational cost.
Project Approach
Timeline
Project Start – 2022
Project Completion – 2024
Phase 1: Laboratory experiments. Planning and execution of high-precision bespoke model-scale wave flume experiments designed to isolate non-linear dynamic features through careful post-processing and analysis of the data.
Phase 2: Numerical model development. Identification of dominant nonlinear hydrodynamic effects from the laboratory measurements. Establishing methodology for their simplified representation in efficient partially nonlinear numerical models.
Phase 3: Validation using field data. Simulation of WEC behaviour and evaluation of the non-linear modelling strategies through a unique comparison with CorPower Ocean CPO’s fully instrumented full-scale ocean deployment. Quantification of improvements and knowledge sharing with industry.
Current Status
Current State of the project and findings
The UWA team have completed Phase 1 of the project. A large experimental campaign was conducted in UWA Coastal and Offshore Engineering Lab, which contains a 54m long wave flume. In a simulated ocean environment, wave forces on a fixed and a moving sphere (mimicking CPO’s device design) were measured, in 3 blocks of tests:
- diffraction tests with the sphere held fixed at a number of different static immersion levels and subject to short-duration incident wave groups,
- radiation tests in still water with the sphere actuated vertically with its motion consistent with resonant WEC behaviour due to the incident wave conditions in the diffraction tests,
- combined tests with the actuated sphere and the incident wave groups.
Tests with increasing amplitude of the incident waves and of the imposed motions allow identification of nonlinear hydrodynamic effects.
Application of results to industry
As previously explained, the UWA research team are developing next-generation numerical models for WEC hydro-mechanical systems using CorPower’s wave energy converter in commercial testing in Portugal. This research project is an outgrowth of a previous collaboration between CPO and UWA.
The CorPower Ocean WEC is of the point-absorber type, which by many experts is seen as the most promising category for the development of industrial-scale harvesting of wave energy. The results from this project may benefit any development into this kind of wave power device, or other devices where large amplitude oscillations of rigid WECs are critical.
In October 2022, CorPower launched the company’s HiWave-5 demonstration project in Portugal. This project is the result of 10 years of product development and 40 years of research on wave hydrodynamics. CPO explained that this project marks a final push toward commercialization as part of a broader mission to make wave energy competitive with wind and solar by 2030. Descriptions of CorPower’s WEC are included below.
CorPower C4
The company describes the technology as a heaving buoy on the surface absorbing energy from ocean waves, and the buoy is connected to the seabed using a tensioned mooring system. “Energy stored in waves are converted into electricity through the rise and fall as well as the back-and-forth motion of waves” CorPower explains on its website. “The composite buoy, interacting with this wave motion, drives a power take-off inside the buoy that converts the mechanical energy into electricity.”
The new numerical formulations resulting from the project will be used by CorPower Ocean to:
- increase the accuracy of mathematical models used in deriving design loads and power output estimates,
- improve the performance of control algorithms, and
- help optimise the system design in future generations of the technology.
The benefits of the new methods developed in the project will be tested by comparison with the currently used models, using data both from simulations and ocean trials.
Who are the project partners?
Marine Energy Research Australia (MERA), a University of Western Australia research centre dedicated to advancement of offshore renewable technologies, providing innovative ocean engineering solutions underpinned by world-class research.
For detailed research data and information, contact the UWA research team leads:
Jana Orszaghova at jana.orszaghova@uwa.edu.au
Hugh Wolgamot at hugh.wolgamot@uwa.edu.au
CorPower Ocean is a leading wave energy technology developer with an advanced wave energy device which can oscillate with optimum (large) amplitudes in a wide range of conditions. Their WEC is serving as the technology basis upon which UWA’s research is being conducted.
To learn more about CorPower, its technology and commercial demonstration project, contact:
Jørgen Hals Todalshaug at jorgen.hals@corpowerocean.com
Kevin Rebenius at kevin.rebenius@corpowerocean.com
An industry-led cluster whose aim is to accelerate commercialisation of Australia’s ocean energy sector. AOEG is helping extend the reach of this research project to Australia’s ocean energy sector.
To learn more about how AOEG is driving collaborative innovation in the ocean energy sector, nationally and internationally, contact:
Stephanie Thornton stephanie@oceanenergygroup.org.au
This research is funded by the ARC through Linkage Project LP210100397