Hydraulic-thermal synergistic control method of channel during ice period based on external water transfer into the channel
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Abstract:
With the large negative cumulative temperature of China’s northern latitude in winter, the ice conditions occurring in the channel are prone to develop into ice disasters such as ice jams and ice dams. For the consideration of disaster mitigation, water transmission in the channel during the ice period is often operated by controlling the flow velocity and Fr value, using the mode of water transmission under ice cover, i.e., forming a stable ice cover, changing the heat exchange between water and the outside. However, this method of water conveyance reduces the water flow and restricts the engineering benefits. In the mode of water transmission under the ice cover, it is difficult to get a substantial increase in the way of water transmission capacity based on improving the accuracy of meteorological and ice forecasting, improving the efficiency and quality of hydraulic regulation to shorten the range and length of the channel section of the water transmission during the ice period. Therefore, the channel project with a certain size of trapezoidal section as an example was taken and the sensitive factors affecting the channel water temperature in the ice period was analyzed through a numerical simulation method. On this basis, the formula for the unfrozen length of the channel is obtained through multivariate fitting and researches the hydraulic-thermal synergistic regulation method of transferring water externally into the channel to eliminate the ice condition by increasing the heat of the channel water.According to the established ice-period water transfer model, a 60-km-long channel was simulated. The influence laws of winter air temperature, headwater temperature, and water delivery flow on the along-range attenuation of channel water temperature were analyzed, and the unfrozen length formula of the channel was obtained by the multivariate fitting, the temperature control effect of two offline recharge modes of reservoirs on the channel water body was analyzed, the influence of recharge flow, air temperature and recharge water temperature on the maximal recharge interval was analyzed, and the unfrozen length formula was used to calculate the maximal recharge spacing. From the simulation results, it can be seen that: the channel water temperature decreases along the course during the ice period, and the unfrozen length is proportional to the water flow (Q) and the water temperature in the inlet channel (T0), and inversely proportional to the absolute value of the negative temperature (?Ta). The maximum spacing of recharge water in the two modes of recharge conventional water replenishment and cyclic recharge is related to the recharge flow rate, the air temperature and recharge water temperature, and the larger the recharge flow rate, the higher the outside air temperature, the higher the recharge water temperature, the larger the spacing between the recharge point settings. According to the numerical simulation results, the relationship equations between the maximum spacing of recharge and the ratio of recharge flow rate, the temperature difference between the channel water and the atmosphere, and the temperature difference between the channel water and the recharge water were obtained. From the point of view of unfrozen length, under the same meteorological conditions, water delivery conditions, recharge flow rate, and thermal conditions, the unfrozen length in the recirculating recharge mode increases by about 4.9% to 5.9% compared with the conventional recharge mode, and fewer recharge points need to be set up. The calculated values of the unfrozen length formula are in good agreement with the numerical simulation value.By transferring water externally into the channel, the unfrozen length of the channel can be extended, and the channel can avoid freezing within a certain water transmission distance, thus avoiding ice-covered water transmission, which can solve the bottleneck problem of insufficient water transmission capacity of the long-distance water transmission channel in the ice period.
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