Results extraction at a given coordinate without node.

disla

Hi,

I need to extract a stress value (Sxx) at a certain coordinate in my model.

In my particular case I do not have a node there and I don’t want to refine as I’m comparing the element performance with respect to other formulations.
I can also imagine this could be useful to extract Stresses on the hidden layers of a composite or inside a solid where it is difficult to access or generate a node.

¿Does someone know any trick to sort this in MECWAY? If possible, I would like to avoid postprocessing the data.
¿Maybe Paraview?

In case I do not find a simple way to do it, ¿does anybody knows which could be the most appropriate technique to do that?. I read about Radial basis function interpolation (RBF) but I do not have any experience on this.

Regards

Victor

You can do the interpolation with a script but it's a bit of work. Here's an example for hex8 elements. For other shapes, you would need to use the appropriate shape functions.

To use the script, specify an element and a point inside the element using its isoparametric coordinates r, s, t. If you run it as is with the example model, it uses (0,-1,0) which is in the center of the face that has 222 Pa stress.

disla

Hi Victor ,

You are right ..., in build shape functions are probably the natural way.
I will look your code in detail.

Thank you very much

cwharpe

@disla,
Learning something new every day. Never heard of Radial Basis Functions until your post. Looks like the beast. Along the way discovered various geospatial interpolation techniques out there.....
But yes, ...Shape functions seem to be the elegant approach.

For a less elegant solution, something called Cross-Interpolation, or this web post titled Intensity Surface-Interpolation seemed suitable:



Uses the "Inverse Lever Rule" technique we used back in Chemistry. It was easy enough to code for tri's and quadrilaterals. Trick would be to determine which sides of the quad the scan line (through point P) intersects, probably some vertical point ranking on y-coord. w.r.t. point P. Here is a 2D example, with its 3D Sketchup proof:





I think by extension this could work also for wedges & bricks, where first finding Ip(top) surface, Ip(bott) surface, then interpolating through those to the elevation of Ip desired(?).

Anyway, for whatever use it may or may not have, it was a fun post.

disla

Thank you very much cwharpe.
This is very simple to implement in an Excel file.

cwharpe

@disla,
No worries. If it proves accurate enough, was kind of hoping to see it evolve into a Python script for the Mecway API cache. I'm an old Fortran guy, so I would need assistance.

The vertical slope/divide by zero "quick patch" was bugging me, so here is a verified fix.

Again, some routine to determine which edges the scan line crosses seems critical for an arbitrarily chosen element in a random orientation w.r.t. the coordinate axis.

Cheers.