center di press

[euGENIO85]

Hello, everyone, I have a problem that's driving me crazy.
for the thesis I am designing a submarine vehicle driven by a ship, in practice it is a torpedo with wings (or a huge suppository with wings...). Now I'm doing some comsol simulations to find the wing profile, wingspan and rope needed to support the vehicle. the problem is that I can get the forces but not their point of application, i.e. I do not find the pressure center, which is fundamental to me.
Can you help me? I tried to use cfx but I have the same problem, instead of fluent I didn't understand a bat.
Thanks to who wants to help me.

 

[euGENIO85]

I add that I have comsol 3.5a and 4.0
I was talking about pressure center, but it would be good if I was given the only moment.
in this regard I realized that with cfx it gives me the "torque" (you confirm that it is the moment of forces?), but respect what point does it give me?
if someone knows something speak!!! Thank you.

 

[SOLID]

Hello eugenio,
speculating a 2d case, you must first find the value of the nodal forces at the fluid/wing interface.
do this you have to calculate the center of these forces (in x and y directions).
formulas should be
fx1*x1+fx2*x2+...+fxn*xn=(fx1+fx2+...+fxn)*xg
fy1*y1+fy2*y2+...+fy*yn=(fy1+fy2+...+fyn)*yg

where
fxi= value of knot forces -ith in x direction
fyi= value of the nodal forces at the node -iesimo in the direction y
xi= coordinate x of the knot -iesimo
yi= coordinate y del nodo -iesimo
xg= cordinate x of the pressure center
yg= coordinated y of the pressure center

the process if it does not the software you have to do it by hand (excell)

 

[euGENIO85]

Hello solid,
I personally solved the problem by changing software, in fact with cfx not only are the provided moments (which however do not allow to trace back to the position of the cop as you get an equation in two unknowns) but greatly reduces the calculation times.

However, before going to cfx, I had tried to solve the problem that is similar to what you suggest. I'll explain why he might come back in handy.

I do not remember if comsol provides the value of the nodal force (which seems difficult to me, as it should do the pressure product for an area: What area do you consider if you calculate it at one point?), I had reasoned in this way: I imagined as if the pressure was a mass (I know, I have a fervent imagination) and therefore, theoretically, the position of the centerpiece would be the position of the cop.

starting from the pressure in the nodes, via excell and the function "if", I got the pressure values in a section (being my case 3d). made this multiplied the value of the pressure in the node for its ascissa and then calculated the position of the cop simply by treating "p" as if it were a force ( hence the reason of considering the pressure as a mass), i.e. calculating the cop with the classic formula.

theoretically I think the speech works, of course the p*x product is not a moment, but finding the cop I could calculate them by applying the forces.
the difficulty lies in the fact that the distribution of the nodes is not uniform, but is more dense in the points of greater curvature (this false the result in the calculation of the cop). I tried to solve the problem by making pressure averages for certain "delta_x" but then I abandoned the uncertainty about the values that came out of me. I know, it's complicated, but by reasoning the speech, I felt like I could work.

The only thing I can say is I've tried!