[vikramrajagopalan]

Hi!

I'm performing an incompressible simulation on a submarine-shaped-underwater-vehicle (image attached). I have two patches, the first being the body, and the second being two tailfins. I also have a patchGroup for the entire vehicle. I'm using the 'forces' tool to find forces and moments, with the entire vehicle as the input. I'm getting reasonable result values. However, I'm under the assumption that these forces and moments act at the center of pressure of whatever patch or patchGroups I input, is that right? And How do I find coordinates for this Center of Pressure?

[yambanshee]

There might be a simpler solution, but I would make use of the moments output to calculate the centre of pressure. At the centre of pressure, your pressure induced moments will be 0, and thus it will become a case of solving for sum of moments in each axis direction based on where you're calculating your moments and the moment there.

ie: if I had a flat plate at some angle of attack, and I'm calculating my sum of moments about the front of the plate, with that moment being 1 Nm (around z axis). Similarly, the pressure force is 4 N (along y axis), I can deduce that my centre of pressure lies on a plane that is 0.25 m away from the leading edge (moment = force*distance, therefore distance = moment/force)

[fra76]

Originally Posted by vikramrajagopalan

Hi!

I'm performing an incompressible simulation on a submarine-shaped-underwater-vehicle (image attached). I have two patches, the first being the body, and the second being two tailfins. I also have a patchGroup for the entire vehicle. I'm using the 'forces' tool to find forces and moments, with the entire vehicle as the input. I'm getting reasonable result values. However, I'm under the assumption that these forces and moments act at the center of pressure of whatever patch or patchGroups I input, is that right? And How do I find coordinates for this Center of Pressure?

Hi,

In the force calculation, you specify the center of moments (CoR), so the moments you get are calculated around that point.
The CoP is a point where to apply the forces, so that the resulting moment vector is zero.
You can calculate it by solving F^CoP=0, which is a 3x3 linear system for which the result has 1 degree of freedom, i.e. it is a line. You can ten calculate a point by intersecting this line with your surface, but the intersection might not exist (think of a doughnut...). You can make any arbitrary decision to fix a coordinate to calculate the other 2 (z=0, center of bounding box of you geometry, etc...)

Cheers,
Francesco