Investigation of Two Elemental Error Sources in Boat-Mounted Acoustic Doppler Current Profiler Measurements by Large Eddy Simulations
Publication: Journal of Hydraulic Engineering
Volume 135, Issue 11
Abstract
Measurements of water discharge and flow velocities in riverine and tidal environments are commonly made with acoustic Doppler current profilers (ADCPs) mounted on a moving boat. This paper presents results of high-resolution Large Eddy simulations (LES) conducted to investigate two elemental error sources in ADCP measurements from a moving boat. One of these errors is due to the flow disturbance induced by the boat-mounted ADCP. The other error is due to the lack of flow homogeneity in horizontal layers assumed by the ADCP algorithm to compute orthogonal velocities from the measured radial velocities along the acoustic beams. The first error is investigated by comparing LES results for an undisturbed flow field with LES results for a flow field disturbed by a boat-mounted ADCP. The second error is investigated by comparing the velocities beneath the ADCP simulated by LES with virtual ADCP velocities, which are obtained by applying the ADCP algorithm to LES velocities data mined along the path of the acoustic beams of the virtual profiler. The distribution of the Reynolds stresses beneath the ADCP estimated with the ADCP algorithm from the virtual ADCP velocity data are also compared with those obtained from the LES solutions for both the undisturbed and ADCP-disturbed flows. Results show that the boat significantly disturbs the flow field and that the disturbed flow field is qualitatively different from the flow fields observed around an isolated ADCP (no boat).
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Acknowledgments
This study is part of collaborative work between the IIHR-HydroScience and Engineering and the South Florida Water Management District (SFWMD) aimed at estimating ADCP measurement uncertainty. It builds upon work on measurement errors in ADCP measurements conducted through this collaboration and the work by others. In particular, it sheds light on two sources of measurement uncertainty discussed by Gonzalez-Castro and Muste (2007), namely near-transducer error and the spatial averaging error. The last author gratefully acknowledges the support of Robb Startzman and Matahel Ansar from SFWMD to launch an initiative aimed at evaluating the ADCP measurement uncertainties through collaborative work. The writers thank the National Center for High Performance Computing (NCHC) in Taiwan, in particular Dr. W.H. Tsai, for providing the computational resources needed to perform some of the simulations as part of the collaboration program between NCHC and IIHR-Hydroscience and Engineering. Use of trade, product, or commercial names does not imply endorsement by the South Florida Water Management District.
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Published In
Journal of Hydraulic Engineering
Volume 135 • Issue 11 • November 2009
Pages: 875 - 887
Copyright
© 2009 ASCE.
History
Received: May 21, 2008
Accepted: Feb 26, 2009
Published online: Oct 15, 2009
Published in print: Nov 2009
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