The tangency point is known as the pitch point. 兩節圓的切點成為節點。
The steamline curve ratio in the bucket of a spillway gradually changes in the flow direction, but the wall curve ratio changes in the point of contact of the bucket suddenly. 溢流反弧段流線的曲率呈沿程變化，而反弧上下切點位置處邊壁曲率卻發生突變。
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