CalWave seeks to conduct scaled, experimental prototype testing for a total duration of 10 working days at the W2 Basin at University of Maine. Scaled wave tank testing of a representative scaled wave energy converter prototype in a controlled environment will greatly de-risk CalWave’s upcoming deployment of a larger scale prototype off San Diego, California and ensure operation of CalWave’s open water demonstrator is safe and efficient.
This experimental testing would be conducted at a point of CalWave’s open water demonstration project at which there is little uncertainty in the system specifications of the ocean-going wave energy device that are directly reflected in the scaled experimental testing (e.g. physical properties of the device, properties of the targeted ocean deployment side that can be replicated in the scaled wave tank experiment, final control algorithms).
Hence, the experimental test setup will be more closely aligned to the upcoming large-scale ocean deployment, compared to tank tests performed in previous project stages. This significantly increases the quality of the experimental test results due to lower uncertainty in the correct scaled setup and significantly reduces risk for the ocean deployment.
All proposed wave tank testing conducted under this project will follow guidelines from IEC 62600-103 - Best practices for testing of pre-prototype scale devices.
Post Access: CalWave successfully completed the wave tank testing campaign at UMaine during February 1st, 2021 – February 12th 2021. In this period, CalWave completed 148 distinct cases, totaling 19.1 hours of recorded data.
All testing objectives (See section 3) have been met:
- System identification of the revised absorber geometry revealed changes to the hydrodynamic characteristics of the absorber body. As absorber body design changes were mostly due to hardware constraints for the larger ocean going device, the hydrodynamic similarity with the previous absorber design was desired and confirmed.
- A set of nine irregular wave cases representative for a scaled open water demonstration in southern California were thoroughly assessed. All nine wave cases showed expected performance results with respect to power absorption. Furthermore, force and stroke estimates were confirmed to be in range of expected values and ensured safe operation of the open water demonstration device at that resource. The data collected will act as a comparison set to data collected via the open water demonstration that will be conducted later this year (2021).
- An autonomous controller for the xWave device was experimentally assessed using “Combo” wave cases: Concatenated wave cases with different sea state characteristics (Hs, Tp, peak enhancement factor gamma). Controller logic on gain scheduling based on autonomous sea state detection was confirmed. Tests revealed a high sensitivity to tuning gains for the wave state estimator with respect to significant wave height. The control logic of autonomous control of the WEC and governing equations facilitating the controls were validated.
- Higher order dynamic models predicted parametric resonance effects of the device that were experimentally assessed: Coupled degrees of freedom and energy spilling in between them was on purpose excited, with the objective to detect the parametric resonance. For specific monochromatic cases, parameter/gain selections, and ramp up times, the parametric resonances were, in fact, detected and observed (which itself is already remarkable). Magnitude of the resonances were, however, significantly lower than analytically predicted; this stems from a lack of viscous drag characterization in coupled degrees of freedom. Furthermore, during irregular waves, parametric resonance barely has the chance to grow and hence, was barely observed.