Centre of Pressure
General Submerged surface
The centre of pressure is the point where the equivalent force (PAA) acts.
For a flat surface it is found using the equation:
Rectangular Surface
Where Ixx,C is the second moment of area around the centroid, and yC is the depth of the centroid. The centroid is the point where, for any line drawn through it on that plane, the areas on the two sides of the line will be equal. (See 'Forces on a flat surface' for more details)
For the case where the surface is a rectangle, as shown in the second diagram, the equation becomes
Where s is the distance to the surface of the fluid along the line of the submerged surface, and b is the length of the rectangle.
Often we are interested in gauge pressure, so P0 becomes 0 and both equations become a lot simpler. Notice here the angle no longer makes a difference since the whole term becomes 0.