CASE STUDY
Breaking Waves of Progress: Experimental Testing of Wave Energy Converters with OAV Air Bushings
Ghent University researchers used OAV Air Bushings to allow frictionless linear guidance in a five-unit wave energy converter array, improving control, repeatability, and experimental accuracy.
CUSTOMER
Ghent University
INDUSTRY
Renewable Energy
APPLICATION
Wave Energy Testing
PRODUCT USED
Air Bushings
BENEFIT
Frictionless Linear Motion
THE CHALLENGE
Wave energy is a renewable form of energy which is largely untapped. Wave energy converters (WECs) are devices made to harness this energy source and convert it to electricity. In the last few decades, a considerable amount of effort has been made by industries and academia to bring WECs to a commercial stage. There was a need for available real-life data to validate numerical models in the wave energy sector, but publicly available databases from WEC array experiments were limited because of high costs and complexities related to conducting these experiments.
The ‘WECfarm’ project, initiated by Ghent University, aimed to improve the understanding of interactions between the individual WECs within an array, and address the need for experimental data on WEC array tests. A team from the Coastal Engineering Research Group of Ghent University, Belgium performed experiments focused on the extraction of wave energy using an array of five point absorber WECs. Similar to offshore wind turbines, multiple point absorber WECs were installed in an array configuration to increase the total capacity and to benefit from the economies of scale. Whereas wind turbines always interact destructively due to wake effects, WECs can interact constructively since hydrodynamic interactions between the WECs occur through radiation and diffraction of waves, changing the direction of the incoming wave energy.
THE SOLUTION
The WECfarm system uses point-absorber wave energy converters (WECs), each consisting of a floating buoy that captures energy from incoming waves. To accurately evaluate the performance of the five-WEC array, the researchers required a linear guiding system capable of supporting dynamic wave-induced loads without introducing unwanted mechanical friction into the experiment.
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OAV Air Bushings were integrated into each WEC to provide frictionless linear guidance in the heave direction. Wave excitation could generate moments on the guiding system, so the researchers used a configuration of three 40 mm OAV Air Bushings per WEC to distribute these forces while maintaining a consistent air film between the bushings and guide shafts. Each 40 mm air bushing was rated to support a maximum radial load of 720 N at a nominal pressure of 5.5 bar.
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Clean, dry compressed air supplied through a two-stage filtration system maintained the air gap required for non-contact motion. The air bushings operated along 40.00 mm +0.00/-0.02 mm guide shafts, allowing the WECs to move vertically with minimal mechanical resistance while reducing the variability associated with conventional contacting bearing systems.
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The five-WEC array was installed and tested at the Coastal & Ocean Basin Ostend in Belgium, where researchers evaluated array configurations and control strategies under controlled wave conditions. By minimizing friction in the linear guidance system, the OAV Air Bushings helped isolate the hydrodynamic and control behavior being studied, supporting more accurate system identification, responsive control, and repeatable experimental measurements.
Figure 1. Rendering of the ‘WECfarm’ WEC used within the experimental campaign. The OAV Air Bushings are placed within the mounting blocks for axial frictionless motion along the guide shafts in the heave direction.
Figure 2. Five-WEC array installed in the Coastal & Ocean Basin Ostend for controlled wave-energy testing.
Figure 3. Close-up of the five-WEC experimental array and linear guidance systems used during wave-basin testing.
THE RESULTS
The OAV Air Bushings are pivotal components in the design of the ‘WECfarm’ WEC, as the experiments target high quality data with low uncertainties. The air bushings excluded the variability in mechanical losses and energy dissipation associated with traditional bearing systems, as for example ball or plain bearings. Additionally, the use of air bushings enhanced the controllability and responsiveness of the WEC system, allowing for more precise and efficient power capture from the waves. The team opted for OAV air bushings due to superior pricing, quality, and technical support during the project.
Eliminated friction-related variability in the linear guiding system
Improved WEC controllability and dynamic response
Enabled more precise, repeatable experimental measurements
Supported efficient power-capture testing across a five-WEC array
By minimizing mechanical friction and energy losses in the guiding system, OAV Air Bushings helped the research team achieve more controlled and repeatable WEC array testing while improving the quality of experimental data used to evaluate wave-energy performance.
REFERENCES
1. Vervaet, T., Stratigaki, V., De Backer, B., Stockman, K., Vantorre, M., & Troch, P. (2022). Experimental modelling of point-absorber wave energy converter arrays : a comprehensive review, identification of research gaps and design of the WECfarm setup. Journal of Marine Science and Engineering, 10(8). 1062. DOI: 10.3390/jmse10081062
2. Vervaet, T. (2023). Experimental modelling of point absorber wave energy converter arrays with control design based on impedance matching. Ghent University. Faculty of Engineering and Architecture, Ghent, Belgium.​