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# Convert nodal force to pressure distribution and vice versa

Valued Contributor

Hi,

I have to do an analysis for a section of the fuselage.

I am given forces on each node for a very rough mesh. The problem is I want to convert the nodal forces to a pressure function so that I can apply to the geometric surfaces regardless of the elememnt sizes.

I was wondering if there was a way in Femap to convert nodal forces over a surface to an equivalent pressure and vice versa (convert pressure over an area to nodal forces).

Regards,

Saptarshi

# Re: Convert nodal force to pressure distribution and vice versa

Phenom

Hi,

This question often comes up, but make no mistake: it is not a trivial matter.

Have a look here where the problem is explained for ANSYS:

http://ansys.net/ansys/tips/Week_17_STI52_TNT_converting_pressures_to_nodal_forces.pdf

Going back to NASTRAN the same can be done using OLOADs: if you want to convert pressures to forces, simply ask for the resulting OLOAD on your nodes.

Converting forces => pressure is a different story. I would say the method can be applied backwards: you would need to recreate a notion of continous force flux throughout the surface using shape functions, then probably average it using Gaussian integration on each element.
Or to avoid the math you need to use the coefficients in the pdf in the figures. I guess you could add fractions of force vectors coming from each node, divide it by element surface, and that would give a pretty good approximation of the actual pressure.

But even that is not immediate: you need to write it as an API.

AP