OMAE2009-79793 MEASUREMENT OF THE EFFECT OF POWER ABSORPTION IN THE LEE OF A WAVE ENERGY CONVERTER

ABSTRACT Monitoring the effect of floating wave energy converter (WEC) devices on the surrounding wave field will be an important tool for monitoring impacts on the local wave climate and coastlines. Measurement will be hampered by the natural variability of ocean waves and the complex response of WEC devices, causing temporal and spatial variability in the effects. Measurements taken during wave tank tests at MARINTEK are used to analyse the effectiveness of point wave measurements at resolving the influence of an array of WEC on the local wave conditions. The variability of waves is measured in front and in the lee of a device, using spectral analysis to identify changes to the incident wave field due to the operating WEC. The power capture and radiation damping are analysed in order to predict the measured changes. Differences in the wave field across the device are clearly observable in the frequency domain. However, they do not unanimously show a reduction in wave energy in the lee of a device and are not well predicted by measured power capture

Basin Testing of Wave Energy Converters in Trondheim: Investigation of Mooring Loads and Implications for Wider Research

This paper describes the physical model testing of an array of wave energy devices undertaken in the NTNU (Norwegian University of Science and Technology) Trondheim basin between 8 and 20 October 2008 funded under the EU Hydralabs III initiative, and provides an analysis of the extreme mooring loads. Tests were completed at 1/20 scale on a single oscillating water column device and on close-packed arrays of three and five devices following calibration of instrumentation and the wave and current test environment. One wave energy converter (WEC) was fully instrumented with mooring line load cells, optical motion tracker and accelerometers and tested in regular waves, short- and long-crested irregular waves and current. The wave and current test regimes were measured by six wave probes and a current meter. Arrays of three and five similar WECs, with identical mooring systems, were tested under similar environmental loading with partial monitoring of mooring forces and motions. The majority of loads on the mooring lines appeared to be broadly consistent with both logistic and normal distribution; whilst the right tail appeared to conform to the extreme value distribution. Comparison of the loads at different configurations of WEC arrays suggests that the results are broadly consistent with the hypothesis that the mooring loads should differ. In particular; the results from the tests in short crested seas conditions give an indication that peak loads in a multi WEC array may be considerably higher than in 1-WEC configuration. The test campaign has contributed essential data to the development of Simulink™ and Orcaflex™ models of devices, which include mooring system interactions, and data have also been obtained for inter-tank comparisons, studies of scale effects and validation of mooring system numerical models. It is hoped that this paper will help to draw the attention of a wider scientific community to the dataset freely available from the Marintek website