Show the element submerged in the liquid distance ( h) from the liquid surface as inĮxpress the forces on the horizontal plane. The location of total pressure is referred as the center of pressure which is always below the center of gravity of the surface in contact. Since all the wind is not hitting the curved surface perpendicular, it's not correct to use a curved surface model, which would be (2Pi.r.h)/2. I think the best way to calculate it is by using the a rectangle with the dimensions 2.r.h. We're trying to find the force exerted, which then requires which kinda of cross section to use. If the liquid is at rest then there is no tangential force, and hence the total pressure will act perpendicular to the surface with contact. The horizontal and vertical force components can be vector composed, giving in general a single vector plus a moment.Hydrostatic force refers to the total pressure acting on the layer or surface which is in touch with the liquid or water at rest. The vertical force passes through the centroid of the vertical (axis) cylinder of fluid with director represented by the contour of the surface. By considering two directions in the horizontal plane, the corresponding two horizontal components can be determined and vector composed to calculate the total horizontal force acting on the surface, resulting, in general, in a single horizontal vector plus a moment which is required to render them coplanar. A horizontal component of the force passes through the centroid of the vertical projection of the surface on a plane normal to the horizontal direction considered.

It is also convenient to resolve the total force acting on the surface into horizontal and vertical components. In practice, it is convenient to adopt integral balance equation for a control volume partly (or completely) delimited by the surface, and then to balance the forces acting on the external surface and body forces. If the surface at contact with the fluid is curved, the action of the fluid can be computed by integrating the elementary forces due to the local pressure by the infinitesimal area of the surface.

Forces on curved survaces