基于平封冰盖生消模拟的长距离渠系冰期自动化控制模型

Mathematical model for automatic operation of long distance canal system with juxtaposition ice cover formation and decaying

在小流量输水前提下,以面流冰密度为封冻判别指标,考虑了渠系中倒虹吸进口前和闸门前拦冰索的拦冰作用,考虑了不同冰情阶段(封冻前明渠流、流冰期、冰盖期和文开河期)的热量交换来源以计算水温传递过程、冰花输移过程和冰盖范围和厚度变化过程,建立了长距离渠系平封冰盖生消的自动化控制运行模型,并通过南水北调中线工程总干渠京石段进行仿真模拟,呈现了平封冰盖从下游拦冰索处向上游的封冻推进过程、冰盖厚度变化过程和从上游到下游的文开河过程及相应冰情阶段的渠系水位和流量波动过程。同时指出,判断封冻时的临界面流冰密度和流冰层厚度可影响渠池的封冻范围、封冻过程和冰盖厚度,进而导致渠系水力响应的不同,须要在工程的实际运行中率定。

This study developed a mathematical automatic operation model for a long distance canal system featured with juxtaposition ice cover formation and decaying under the condition of low flow transport, based on the concept of floating ice area concentration. This model calculates water temperature, ice transport and changes of ice cover scope and thickness, considering the ice-blocking effect of an ice-block cable at the front of siphon entrance and sluice and the effect of heat exchange, under different ice situations of open flow period, ice flow period, steady ice cover period, thermal breakup period of ice cover, etc. Simulations of the Jingshi canal of the middle route south to north water transfer project show the ice cover formation starting at the cable toward the upstream of each canal pool, its decaying toward the downstream, and the variations in its thickness and the water level during these two processes. This paper points out that the calculations of ice floating scope, ice cover expanding and thickness, etc, could depend on two parameters used for estimating ice cover formation, i.e. the area concentration of ice floating and the assumed thickness of ice floating layer. Thus, the calculated water levels could also depend on these parameters that should be calibrated in actual operation.