Abstract
This paper proposes a novel particle image velocimetry (PIV) technique to generate an instantaneous two-dimensional velocity field for sediment-laden fluid based on the optical flow algorithm of ultrasound imaging. In this paper, an ultrasonic PIV (UIV) system is constructed by integrating a medical ultrasound instrument and an ultrasonic particle image velocimetry algorithm. The medical ultrasound instrument with a phased sensor array is used to acquire acoustic echo signals of particles in water and generate two-dimensional underwater ultrasound images. Based on the optical flow field, the instantaneous velocity of the particles in water corresponding to the pixels in the ultrasonic particle images is derived from the grayscale change between adjacent images under the L-K local constraint based on the optical flow field, and finally, the two-dimensional flow field is obtained. Through multiple sets of experiments, the proposed algorithm is verified. The experimental results are compared with those of the conventional cross-correlation algorithms. The results show that the L-K optical flow method can not only obtain the underwater velocity field accurately, but also has the advantages of good smoothness and extensive suitability, especially for the flow field measurement in sediment-laden fluid than conventional algorithms.
Highlights
The measurement of the depth-averaged velocity in sediment-laden flow is a prerequisite for many research works on river engineering, such as river-bank erosion and sediment transportation
The results demonstrate that ultrasonic PIV (UIV) is a promising technique to generate instantaneous two-dimensional fields of flow velocities in sedimentladen fluids [14]
The ultrasound instrument is connected to a computer, which converts the echo signals collected by the probe into ultrasound images and transmits them to the ultrasound particle velocimetry software in the computer for analysis, processing, and display of flow field information
Summary
The measurement of the depth-averaged velocity in sediment-laden flow is a prerequisite for many research works on river engineering, such as river-bank erosion and sediment transportation. Light cannot penetrate through turbid water because it rapidly attenuates when travelling in turbid flow, which affects its application in sediment-laden flow To overcome those disadvantages and meet the requirements of high-precision measurements, ultrasonic imaging techniques have been introduced into the field of PIV for. Compared with Doppler-based techniques, an advantage of the UIV is its ability to measure the flow velocity components in both parallel and perpendicular directions to the ultrasonic beam It has excellent performance on simplicity, accuracy, and accessibility, while it does not have the limitations of the Doppler-based algorithm [7]. For improving the accuracy and efficiency of the flow field measurement, the multigrid deformation algorithm is used to calculate the flow velocity with ultrasonic particle images of sandy water streams with volume sediment concentration less than 5‰ [4].
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