The tangency point is known as the pitch point. 两节圆的切点成为节点。
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. 溢流反弧段流线的曲率呈沿程变化,而反弧上下切点位置处边壁曲率却发生突变。