融冰期加厚冰盖糙率物理模型试验研究

Research on the Roughness of Thickened Ice Cover during the Ice-melting Period Based on Physical Model Experiments

流凌期输水能力可能成为制约输水工程冰期输水能力的瓶颈,而流凌期允许冰凌下潜,采用加厚冰盖下输水方式运行可以有效提高工程输水能力。加厚冰盖糙率的合理选择直接影响加厚冰盖形成后渠道水位和过流能力计算的正确性,但是加厚冰盖的糙率受到多种因素的影响,见刊的实测资料中,其糙率分布范围很宽。现以冻结模型冰为试验材料,以南水北调中线工程总干渠为原型,通过物理模型试验研究得到:输水渠道融冰期加厚冰盖形成初期糙率约为0.029,以供南水北调中线工程冰期输水调度和冰害防治提供参考。试验研究同时表明:水力加厚冰盖底面的最大水流弗劳德数取值0.09是合适的;力学加厚冰盖前缘都是水力加厚类型的,其长度大约与水面宽度相近;力学加厚冰盖形成和发展的过程是这样的一个循环:前缘发展→推挤增厚→前缘发展。

The capacity of water diversion during the ice-flowing period may hinder the ability to transfer water ot the water diversion projects. Allowing the submergence of ice slush and adopting the water diversion method with a thickened ice cover can effectively improve the capacity of water diversion during the ice-flowing period. The reasonable selection of the roughness of thickened ice cover is directly related to the calculation accuracy of the canal water level after the formation of the thickened ice cover and the conveyance capacity. However, the roughness of the thickened ice cover is affected by many factors, and its distribution has a broad range. In this paper, the frozen model ice was selected as the experiment material, and the main canal of the South-to-North Water Diversion Project was considered as the study area, both of which can help determine the roughness of the thickened ice cover based on the physical model experiments. The results showed that the roughness of the thickened ice cover in the conveyance canal is approximately 0. 029 during the ice-melting period,which can provide references for the water diversion regulation and ice hazards prevention in the South-to-North Water Diversion project. Moreover, the physical model experiments showed that （1） It is reasonable that the value for the maximum flow Froude number in the bottom of hydraulic thickened ice cover is 0. 09;（2） The frontal edges of the mechanical thickened ice cover are the type of the hydraulic thickened ice cover,and the length of the frontal edges is close to the width of the water surface in the canal; （3） The formation and development of the mechanic thickened ice cover are a circulation process： developing of frontal edges, thickening through pushing, and developing of frontal edges again