Investigation of Local Scour Effects in Alluvial Rivers
Date Issued
2011
Date
2011
Author(s)
Chen, Feng-Kun
Abstract
In this thesis, the flow field and physical mechanism of local scour problem around the bridge piers is mainly used by numerical simulation. Two different field cases are studied: they are the bridge scour effects surrounding the Hou-Feng Bridge and the gap scour effects about the stepped concrete block grade control structure in Ta-Jia river, respectively. It is an extremely difficult problem by using the numerical programming to solve these problems. Hence we seek the help from the commercial software, Flow-3D, to analyze the problem. The problem setting includes the rigid-bed and mobile-bed simulation and the laboratory experiments are aided in the meantime. The numerical results of the rigid-bed simulation are compared with the laboratory results in terms of the fluid depth in front of the first pier. The results from numerical studies and laboratory experiments match very well. In the mobile-bed simulation, the ultrasound device is added in the experiment and the scour depth and the variation of the whole flow field are interfered with the sensor. Hence after the ultrasound device is removed, the influence of the overfall flow in the bridge scour simulation can be clearly classified. The mainly scour hole is concentrated in front of the first pier in the numerical simulation with the overfall flow. In the meantime, the upstream of the first pier is borne by the current flow and the maximum flow velocity is measured close the bottom of the first pier. If the overfall flow is not considered in the simulation, the mainly scour hole is concentrated around the first pier. The reasons are attributed to the down flow and the horseshoe vortex. As for the rigid-bed simulation of the gap scour, the third step of the stepped concrete block grade control structure always existed the obvious velocity on the Z-axis and the strong vortex near the edge of the stepped concrete block grade control structure in the numerical simulation no matter how strength of the flow. In the gap scour simulation, it is difficult to observe the accurate physical phenomenon during the numerical simulation in light of its physical problem setting belongs to the discontinuous arrangement. Hence the applied numerical simulation still requires further development.
Subjects
local scour
Hou-Feng bridge
stepped concrete block grade control structure
gap scour
numerical simulation
overfall scour
Type
thesis
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