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http://dx.doi.org/10.3741/JKWRA.2021.54.11.933

Calculation of surface image velocity fields by analyzing spatio-temporal volumes with the fast Fourier transform  

Yu, Kwonkyu (Department of Civil Engineering, Dong-eui University)
Liu, Binghao (Department of Civil Engineering, Dong-eui University (Department of Civil Engineering, Hunan Institute of Engineering))
Publication Information
Journal of Korea Water Resources Association / v.54, no.11, 2021 , pp. 933-942 More about this Journal
Abstract
The surface image velocimetry was developed to measure river flow velocity safely and effectively in flood season. There are a couple of methods in the surface image velocimetry. Among them the spatio-temporal image velocimetry is in the spotlight, since it can estimate mean velocity for a period of time. For the spatio-temporal image velocimetry analyzes a series of images all at once, it can reduce analyzing time so much. It, however, has a little drawback to find out the main flow direction. If the direction of spatio-temporal image does not coincide to the main flow direction, it may cause singnificant error in velocity. The present study aims to propose a new method to find out the main flow direction by using a fast Fourier transform(FFT) to a spatio-temporal (image) volume, which were constructed by accumulating the river surface images along the time direction. The method consists of two steps; the first step for finding main flow direction in space image and the second step for calculating the velocity magnitude in main flow direction in spatio-temporal image. In the first step a time-accumulated image was made from the spatio-temporal volume along the time direction. We analyzed this time-accumulated image by using FFT and figured out the main flow direction from the transformed image. Then a spatio-temporal image in main flow direction was extracted from the spatio-temporal volume. Once again, the spatio-temporal image was analyzed by FFT and velocity magnitudes were calculated from the transformed image. The proposed method was applied to a series of artificial images for error analysis. It was shown that the proposed method could analyze two-dimensional flow field with fairly good accuracy.
Keywords
Spatio-temporal image; Spatio-temporal volume; Surface-image velocimetry; Fast Fourier transform;
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Times Cited By KSCI : 3  (Citation Analysis)
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