Fit Node on Curved Geometry

[synt]

dear Matej,

this is extended discussion from a comment on YouTube channels.

an STL files are widely used supported by many CAD due to it simply formats. however, it has lack on curved geometry.

as you suggested, it can be refined inside CAD and set before exporting. still it would not works for quadratic element mesh.

add capabilities to refines by smoothing group of nodes selected to fit and follow curve/cylinder geometry can improve the accuracy.

user input is required to define value of radius at these steps, however pre-estimated values can be done based on statistical max (greater of any radius catches).

regards,

[jaguar36]

STL should be used with extreme caution for doing analysis with. As you see, STL files are just made up of triangles and will never perfectly match a curve as they are intended. This can be reduced by increasing the fidelity of the STL file, but that can cause issues with meshing, and drastically increases file sizes.

A STEP file or IGES file can outputted by most CAD software and should be used instead.

[synt]

STP/IGS file format are complex and costly, also not all CAD program capable to exports and support.

on my experiences for simple to moderate complexity models. i’ve no serious problem using 2D STL file as geometry imported.

both 3D mesh based on STP or STL file format are not guarantee to avoid any problems for the solver.

(example STP files & mesh results)

so, here i’m seek for refining/smoothing of node to fit on curvature geometry after mesh is generate.

[Matej]

So there are two problems. The first one is a coarse STL file. Here I can only recommend exporting a better resolution of the STL file or use some other tool to improve its quality. The other problem is the position of the midside nodes when using the second-order elements.

Currently, two meshers are used in PrePoMax. Netgen is used for solid and shell CAD files and solid STL files. For some reason, it does not work with shell STL files, so I added a mmg mesher that is used to mesh the shell STL files only.

Netgen mesher supports second-order elements and the projection of the midside nodes to the geometry. So there is no problem.

Mmg mesh at the time I added it to the PrePoMax project did not support second-order elements. So only first-order elements with straight edges are created. Then PrePoMax creates second-order elements from the first-order elements by splitting their edges and the edges remain straight. So there is a possibility to add a feature that would project the midside nodes to the geometry to solve this issue. The doubt that I have with this feature is that while projecting the midside nodes to the geometry the element quality degrades and elements could become unusable for Calculix (that is why by default this feature is disabled for the Netgen meshing in the first place).

[synt]

thank you to keep importing 2D STL file possible, and works more on quadratic type based on linear MMG results.

in case of distorted mesh using manual fitting, mostly can deal due to it’s quadratic type element. still usable even the accuracy may become less.

an example of results from PMX files i previously share,