How to get the attack point of force?
 

Dear all,

i am doing simulations regarding incompressible flow through a pipe, which then flows on a piece of metal. Because of secrecy reasons, i can't give my case or other things out, so my paint artwork and side view needs to be enough.

So, the flow comes from an inlet with a massflow, flows through the small pipe to the metalface ( treated as a baffle simulationwise, thin white line in first picture) and then can flow out through an outlet.

Now i need to now the pressure force acting on the metalsurface, more precicely, at which point on it is the resulting force acting. Openfoam gives me the pressure force for the whole area, and also with paraview for each cell vie postprocessing.

So in the end, i have the pressure, areavector and the resulting force in every cell - but how can i finally calculate the resulting force vector, on which cell it´s acting?

Furthermore, OF gives you the force and moment in x,y,z direction - is it possible to somehow use these?

I appreciate every help!!

Maybe i have an idea, but i am not sure at all.

The pressure difference results in a force on the metal surface, in aerodynamics, the Center of Pressure is a point, at which the resultant force vector acts - instead of all small force vectors of each cell.
By defintion, this CoP has no Moment, so in order to find it, the Center of Rotation in OF´s controlDict needs to be adjusted to give an approximately result of 0 in x,y,z space for the moment.
Is this true? Logically, it should.

My idea comes from this:
https://www.cfd-online.com/Forums/ma...re-body-2.html

So nobody answered, but if someone is still interested in this:

To find the Center of Pressure or attack Point of force, the Momentum about a point is (0,0,0). So it`s needed to solve this equation:

M = r X F (X - Crossproduct)

This equation isn't satisfied, so i set the coordinate fo x to 0 regarding the symetry aspect of the metalsurface, so that the CoP just has to be exactly in the middle. So, the eq can be solved for y and z. Furthermore, it´s needed to set some Values for y and z and then let OF solve. Aftwerwards, you can check the Momentum which should come close to 0 for every coordinate. If not, change y/z accordingly - it's more or less an iterative process, but it makes sense.