Water surface line model test based on roughness rate determination of organic glass in a certain canal
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Abstract:
To address the issue of variations in normal water levels across different segments during the operational phase of the canal characterized by a gentle slope and curved trajectory, a smooth organic glass material was utilized to simulate the water surface line in model tests conducted on the canal. The experimental approach adopted a normal distribution model and was formulated on the basis of gravity similarity principles, employing a geometric scale ratio of 1:40. The outcomes of the experiment indicated a notable disparity between the water levels recorded in the flume model test and those calculated using the uniform flow formula. Specifically, the measured water level surpassed the calculated water level, prompting an investigation into the underlying causes of the elevated measured water level and the attainment of precise water level estimations within the spillway. This study employed a tripartite methodology encompassing model tests, theoretical analysis, and numerical simulations. The analysis of various factors influencing water levels in the aqueduct model test revealed several key aspects. Firstly, the curvature of the aqueduct impacted the flow pattern, resulting in elevated water levels. Secondly, discrepancies in roughness ratio scales were observed, with the model's roughness being excessive, leading to heightened head loss and subsequently increased water levels. Lastly, the discrepancy between the actual aqueduct section, which featured a reduced water area, and the rectangular section utilized in the uniform flow calculation formula contributed to the rise in water levels. Subsequent roughness determination tests were conducted on the smooth organic glass material utilized in the model test, and the obtained roughness data were scrutinized. A water level correction method was later devised based on the calibration test results and the uniform flow calculation formula to rectify situations where roughness ratio scales were contradictory, thereby correcting the measured water levels. Furthermore, a three-dimensional finite element numerical simulation study was conducted to analyze the water surface line of the flume. The accuracy of the numerical simulation was verified against the data obtained from the flume model test, affirming the efficacy of the proposed water level correction method for addressing dissimilar roughness ratio scales. The study revealed that the water level at the bend of the fishway was 8-10 centimeters higher than that of the straight section. As the distance from the bend increased, the water level gradually decreased until it aligned with the calculated water level, indicating that the bend no longer influenced the water level. Additionally, the water level of the aqueduct's cross section design was 4-6 centimeters higher than that of a rectangular cross section. The primary factor contributing to the substantial disparity between the measured water level in the aqueduct and the calculated water level for uniform flow was the dissimilarity in roughness ratio scales. The roughness coefficient was not merely indicative of wall surface roughness, but was also influenced by hydraulic factors and water flow characteristics. The surface roughness of the polished organic glass plate ranged from 0.007 9 to 0.008 3. The data indicated a decline in roughness as flow rate rises, and conversely, an increase in roughness with steeper slopes.
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