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wjakob / instant-meshes

Interactive field-aligned mesh generator
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Face corner angles too close to 180 #83

Open yw5aj opened 6 years ago

yw5aj commented 6 years ago

Dear all,

I found one issue about using instant meshes for FEA. Some of the angles are too close to 180 degrees, causing singularities in Jacobian calculation. It’ll be ideal that the angle will be having some margins between 0 < angle < 180.

It seems like the problematic angles are all coming from pentagon faces. I am guessing that we can move the nodes around to solve this issue eventually. I am also reading the paper and trying to figure out whether there are more elegant ways to solve it (e.g. redefine the smoothness energy or reassign the weight function).

I'd appreciate it if you would have any thoughts on how to improve the angles!

Best, Shawn

(top - before splitting to pure quad; below - after splitting to get pure quad)

image image

PhillipzAlexander commented 6 years ago

This is bothering me, you could have just added a single edge. fix

Also you can fix that triangle by adding another edge like so.

fix2

You should only double resolution once the topology is clean, otherwise it will make working on it more difficult.

Also make sure the edges are not diagonal, they should be straight up and down, might need to find some references of clean topology. Clean topology allows the model to divide smoothly with less errors.

yw5aj commented 6 years ago

@PhillipzAlexander Thank you for your response! However, the resolution you proposed seems to be causing more very "flat" angles, if you look at the yellow circles:

image

I am trying to resolve this issue because these will cause severe numerical issues for finite element analysis.

Thanks, Shawn