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The SPAIR method: Isolating incident and reflected directional wave spectra in multidirectional wave basins


Citation S. Draycott, S., Davey, T., Ingram, D.M., Day, A. and Johanning, L. The SPAIR method: Isolating incident and reflected directional wave spectra in multidirectional wave basins, Coastal Engineering, 114: 265-283, 2017. https://doi.org/10.1016/j.coastaleng.2016.04.012.
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Author(s) S. Draycott, S., Davey, T., Ingram, D.M., Day, A. and Johanning, L.
Project partner(s) FloWave Ocean Energy Research Facility, University of Edinburgh, University of Exeter, University of Strathclyde,
Publisher Coastal Engineering, 114: 265-283
DOI https://doi.org/10.1016/j.coastaleng.2016.04.012
Abstract Wave tank tests aiming to reproduce realistic or site specific conditions will commonly involve using directionally spread, short-crested sea states. The measurement of these directional characteristics is required for the purposes of calibrating and validating the modelled sea state. Commonly used methods of directional spectrum reconstruction, based on directional spreading functions, have an inherent level of uncertainty associated with them. In this paper we aim to reduce the uncertainty in directional spectrum validation by introducing the SPAIR (Single-summation PTPD Approach with In-line Reflections) method, in combination with a directional wave gauge array. A variety of wave conditions were generated in the FloWave Ocean Energy Research Facility, Edinburgh, UK, to obtain a range of sea state and reflection scenarios. The presented approach is found to provide improved estimatesof directional spectra over standard methods, reducing the mean apparent directional deviation down to below 6% over the range of sea states. Additionally, the method isolates incident and reflected spectra in both the frequency and time domain, and can separate these wave systems over 360. The accuracy of the method is shown to be only slightly sensitive to the level of in-line reflection present, but at present cannot deal with oblique reflections. The SPAIR method, as presented or with slight modification, will allow complex directional sea states to be validated more effectively, enabling multidirectional wave basins to simulate realistic wave scenarios with increased confidence.

Highlights
  • An effective combined wave generation-measurement approach is presented.
  • The method is trialled at a unique circular wave tank, FloWave.
  • It is shown to reduce the directional spectrum measurement error significantly.
  • Isolates incident and reflected directional spectra in frequency and time domain
  • Reduces uncertainty in the use of complex, directional sea states
This work was partly funded via IDCORE, the Industrial Doctorate Centre for Offshore Renewable Energy, which trains research engineers whose work in conjunction with sponsoring companies aims to accelerate the deployment of offshore wind, wave and tidal-current technologies
Associated Project(s) ETI-MA2003: Industrial Doctorate Centre for Offshore Renewable Energy (IDCORE)
Associated Dataset(s) EDC0000134: Tidal Energy Site Environmental Conditions Measured During the ReDAPT Tidal Project 2011-2014
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