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苏州地区的圩口闸数量较多,其主要作用是汛期挡水。对于通航河道,圩口闸的孔径不是根据过闸流量、而是由过往船只的大小决定,即由船型宽度加两侧安全宽度后确定。安全宽度取值不当时,不是闸孔定得过宽造成浪费,便是过小闸墙被船只撞坏。苏州地区圩区三闸2585座中约近半数都不同程度地被撞坏过。安全宽度过去都是根据经验确定。笔者认为可从水力学的观点,经过计算加以确定。在顺直河道上建闸,将引起边界条件的改变,水流受到压缩,流速分布剧变,液体质点间的碰撞和摩擦加剧,从而使两侧闸墙附近各形成一个离体边界层。船行此处,即会增加船只与闸墙碰撞的可能性。边界层厚度δ与闸墙长度1有关,可用平板上紊流边界层的公式计算:
Xu area in Suzhou a large number of gates, its main role is to block the flood season. For navigable rivers, the gate size of the gate is not based on the gate flow but rather the size of the passing vessel, which is determined by the width of the ship plus the safety width at both sides. When the safety width is not appropriate, it is not a problem that the gate hole is too wide, causing the waste. Suzhou area polder three gate 2585 about half of the crashed into varying degrees. The width of security in the past are based on experience. I believe that from the hydraulics point of view, calculated to be determined. When the gates are built on the straight river, the boundary conditions will be changed, the water flow will be compressed, the flow velocity distribution will be drastically changed, and the collision and friction between the liquid particles intensify. As a result, an isolated boundary layer will be formed near each of the two side walls. Here, the possibility of collisions between the vessel and the gate will increase. The thickness δ of the boundary layer is related to the length of the sluice wall 1 and can be calculated by the formula of the turbulent boundary layer on the slab: