Graduate Thesis Or Dissertation
 

Analysis of waves in the near-field of wave energy converter arrays through image processing

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/3f462881f

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  • Oregon State University conducted a series of laboratory experiments to measure and quantify the near-field wave effects caused within arrays of Wave Energy Converters (WEC). As the waves and WECs interact, the WECs generate radiated waves; these effects vary with the location within the array. Analyzing the near-field waves will help determine the relative importance of radiation as a function of the incident wave conditions and device performance. It is imperative to fully understand the near-field waves before full-scale WEC farms can be installed. The prototype device, Columbia Power Technologies' Manta, was tested in regular wave heights ranging from 6cm to 15cm. Three wave gages measured the water surface elevation in the near-field surrounding and within the WEC arrays. While these gages give a good overall picture of the water surface elevation behavior, it is difficult to resolve the complicated wave field within the WEC array using point gages. Here two image processing techniques were applied to the video data to analyze the near-field in high resolution. First, stereo video methods were applied to extract the incident wave 3D water surface elevations to reconstruct the multi-directional wave field. This method accurately resolved the incident waves within 10% of the wave gage measurements. Second, a previously developed program called Sub-pixel Motion Estimate was used to isolate the radiated waves. The radiated wave’s wavelength, period, and height were calculated using a combination of wave energy spectra and cylindrical wave field equations. The calculated radiated wave profiles were used to define the dominant mode of the radiated waves as either mode zero (prevalent for heaving devices) or mode one (prevalent for surging devices). However, based on the observed radiated wave patterns, it was not possible to determine the dominant mode. Throughout this project limited seeding (texture which was added to the water surface) played a significant role in both the stereo video and Sub-pixel Motion Estimate results. Low seeding levels directly caused large error. Despite this challenge, high-resolution water surface elevation data was generated for the near-field resolving incident and radiated waves.
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