Drakoo Wave Energy Converter Wave Flume Test Report Passed DNV-GL’s Final Verification
On February 6th, 2020, the Drakoo-B0015 Wave Energy Converter (WEC) Full-Scale Wave Flume Test Report was approved by DNV-GL, a world-leading certification society in the marine industry, after one and a half years of rigorous review.
The DNV-GL review consists of two parts: 1) witnessing the test and 2) reviewing the test report. Part 1 includes reviews of the test protocol and test set-up including calibrations of the sensors, in addition to the witness of the test. Part 2 covers the evaluation of test data analysis from the aspects of Hydrodynamics and Electrics. With regards to each question raised rigorously and systematically by DNV-GL during the review process, such as computation methodology, inputs, assumptions, data reliability and deviations in the report, Hann-Ocean made detailed explanations or necessary updates accordingly, so as to achieve consensus.
As no relevant rules and regulations are available for wave energy converters, DNV-GL and Hann-Ocean applied the first-principle approach to evaluate the inputs and outputs of the wave energy conversion system and verify its energy conversion efficiencies. The biggest challenge encountered during the review was how to accurately determine the time windows when the incident waves were steady, and the wave power fluxes within the same windows. The limited distance between the wavemaker and the Drakoo WEC made the valid time windows too short for accurate computations of the incident wave power due to the existence of fast-coming secondary reflective waves. To overcome this difficulty and to ensure high accuracy of Drakoo WEC efficiency computations, Hann-Ocean decided to remove the Drakoo of 13 tons from the wave flume and spent another four months in testing and analysing the characteristics of the pure incident waves of a complete spectrum in the wave flume. Dr Olav Rognebakke, Head of Section of Hydrodynamics and Stability in DNV-GL Norway, commented in the review report:
"The new revision (of the report) is a high-quality, thorough and complete description of the tests done to document the efficiency of the WEC in regular waves, as well as quantifying the hydrodynamic forces acting on the WEC. The results are well-substantiated and create a good basis for selecting and sizing a Drakoo unit and support for specific power requirements and wave environment."
The maximum overall conversion efficiency from wave to electricity of the 15kW Drakoo WEC has been validated to be 29% in a real wind-wave environment (up to Tz 8s and Hw 0.9m). To date, Drakoo is one of the world's most efficient WECs with a broad-band conversion spectrum that has been verified with a full-scale prototype in a full-scale wave tank by DNV-GL an independent accredited certification body.
During the same period, Hann-Ocean, together with China Ship Science Research Center (CSSRC), completed the hydrodynamic load test for the Drakoo WEC and validated Hann-Ocean’s Computational Fluid Dynamics (CFD) simulation models successfully.
This is not only a new milestone for the Research & Development (R&D) of Drakoo WEC but also a great achievement resulting from Hann-Ocean’s five-year hard work and a 3-million US dollar investment on the prototype, wave flume and super workstations. Moreover, it reflects the true spirit of Hann-Ocean: Seek Innovation, Keep Improving and Become indomitable.
It is the first case of DNV-GL witnessing and reviewing a full-scale WEC prototype performance test in a large-scale wave flume. As such, Dr Rognebakke of DNV-GL remarked:
"I am very much impressed by the effort you (Hann-Ocean) have spent in doing the proper analysis of the WEC efficiency. The final report is an exemplary document and should serve you well when promoting the Drakoo WEC."