The frequency response of acoustic Doppler current profilers: Spatiotemporal response and implications for tidal turbine site assessment

Romain U.G. Guion, Anna M. Young

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

The lifespan of a tidal turbine is strongly affected by the unsteady loading it experiences, so knowledge of the mean flow speed is not sufficient: unsteadiness must also be quantified. One of the most common turbulence measurement devices in the marine environment is the Acoustic Doppler Current Profiler (ADCP). The variance of steady velocity measurements from ADCPs has been studied in detail, but very little attention has been given to the fundamental limits of ADCPs in terms of the frequencies and lengthscales that they can capture. In this paper, it is shown that the ADCP acts as a low-pass filter to eddies and that even optimistic calculations predict significant attenuation at lengthscales up to ten times the blade chord of a typical tidal turbine. For a typical 40 m deep channel wavelengths below 3-4 m are attenuated by 90% or more. Those eddies that are not filtered out are then subject to a distortion that will either amplify or attenuate the signal depending on the precise turbulence characteristics of the site in question. While this low-pass filtering may alter some global statistics by truncating the observed spectrum, it is most damaging when data is extracted for particular frequencies, as a turbine designer may do when assessing unsteady loading and fatigue life. It is therefore recommended that high-resolution turbulence data, e.g. from a hotwire, is captured over part of the water column and that this is used to calibrate ADCP data.

Original languageEnglish
Title of host publication2014 Oceans - St. John's, OCEANS 2014
PublisherIEEE
ISBN (Electronic)9781479949182
DOIs
Publication statusPublished - 1 Jan 2015
Event2014 Oceans - St. John's, OCEANS 2014 - St. John's, UK United Kingdom
Duration: 14 Sep 201419 Sep 2014

Publication series

NameOCEANS
PublisherIEEE
ISSN (Electronic)0197-7385

Conference

Conference2014 Oceans - St. John's, OCEANS 2014
CountryUK United Kingdom
CitySt. John's
Period14/09/1419/09/14

Keywords

  • ADCP
  • capture
  • dispersion relationships
  • energy site
  • filter
  • response
  • spatiotemporal
  • tidal
  • turbines
  • turbulence

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Ocean Engineering
  • Computer Networks and Communications

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