create_mesh issue on a two materials foil

[jbocreative]

Hi all
I am trying to mesh these of two geometries with different materials.

The mesh process starts but never ends

Both geometries have been meshed individually successfully.
I tried also to create construction points before merging the geometries.

Any clues ?

from sectionproperties.pre import Geometry

## structure

points=[(243.2,59.7),(548.5,49.3),(547.7,26.0),(483.4,28.2),(476.3,21.6),(475.6,0.0),(460.4,0.0),(461.4,29.0),
        (272.8,35.4),(271.6,0.0),(261.2,0.0),(261.9,20.9),(247.6,36.2),(242.4,36.4)]

facets = []
for i in range(len(points) - 1):
    facets.append((i, i + 1))
facets.append((len(points) - 1, 0))  # connect last to first

control_points = [(points[0][0] + 1,
                   points[0][1] -1)]

struct_geom = Geometry.from_points(
    points=points,
    facets=facets,
    control_points=control_points,
)
# struct_geom.plot_geometry()

## Fairing

points=[(5.4,0.0),(6.4,5.0),(9.2,9.8),(12.0,12.9),(16.0,16.4),(21.2,20.0),(27.9,23.8),(36.7,27.8),(41.8,29.9),
        (47.8,32.1),(54.6,34.3),(62.4,36.6),(71.2,39.0),(81.0,41.3),(92.0,43.7),(103.9,45.9),(116.8,48.1),(130.4,50.1),
        (144.6,51.8),(159.3,53.4),(174.4,54.8),(189.8,56.1),(205.5,57.1),(221.3,57.9),(237.4,58.6),(253.6,59.0),
        (269.9,59.4),(286.4,59.6),(302.9,59.6),(319.6,59.5),(336.3,59.3),(353.1,59.0),(369.9,58.5),(386.9,58.0),
        (403.9,57.3),(420.9,56.5),(438.0,55.7),(455.1,54.8),(472.2,53.7),(489.4,52.6),(506.6,51.5),(523.9,50.2),
        (541.2,48.9),(558.5,47.5),(575.8,46.1),(593.1,44.6),(610.5,43.1),(627.9,41.5),(645.3,39.8),(662.6,38.1),
        (680.0,36.3),(699.4,34.3),(700.0,39.7),(680.6,41.7),(663.2,43.5),(645.8,45.2),(628.4,46.8),(611.0,48.4),
        (593.6,50.0),(576.3,51.5),(558.9,52.9),(541.6,54.3),(524.3,55.6),(507.0,56.9),(489.8,58.0),(472.6,59.1),
        (455.4,60.2),(438.2,61.1),(421.1,61.9),(404.1,62.7),(387.1,63.4),(370.1,63.9),(353.2,64.4),(336.4,64.7),
        (319.6,64.9),(302.9,65.0),(286.3,65.0),(269.8,64.8),(253.4,64.5),(237.2,64.0),(221.1,63.3),(205.1,62.5),
        (189.4,61.4),(173.9,60.2),(158.7,58.8),(143.9,57.2),(129.6,55.4),(115.9,53.4),(103.0,51.3),(90.9,49.0),
        (79.8,46.6),(69.8,44.2),(60.9,41.8),(53.0,39.5),(46.0,37.2),(39.9,34.9),(34.5,32.8),(25.5,28.6),(18.4,24.6),
        (12.7,20.7),(8.2,16.8),(4.7,12.8),(1.3,6.9),(0.0,0.0)]

facets = []
for i in range(len(points) - 1):
    facets.append((i, i + 1))
facets.append((len(points) - 1, 0))  # connect last to first

control_points = [(1,1)]

fair_geom = Geometry.from_points(
    points=points,
    facets=facets,
    control_points=control_points,
)

## Union geometries

temp_geom = (fair_geom - struct_geom) | fair_geom
geom = (struct_geom - fair_geom) + temp_geom

# geom.plot_geometry()

# geom.create_mesh(mesh_sizes=6)

[robbievanleeuwen]

Hi @jbocreative I had a play around with your geometry and could not get it to work, I suspect the issue is the extremely sharp angle between the fairing and the structural geometry. I believe the meshing algorithm first meshes this area and then eats away the holes later, so I think it is probably having an issue in this area. I also tried changing the min_angle parameter of create_mesh() to no avail.

If you are only interested in geometric and plastic properties, the mesh converges by setting coarse=True, however you have no real control over the mesh density and may get inaccurate results for warping analyses (which is mesh dependent unlike the other two analyses).

You could "artificially" improve the mesh by introducing more nodes in your geometry, which would be forced to be within the mesh but this would be a bit more pre-processing work for you. Probably the best solution would be to change your geometry so that you don't have such a sharp junction, e.g. square it off - I haven't tried this but suspect it would work. The results should not be vastly different.

Sorry I don't have a better answer! Best of luck!

[jbocreative]

Hi
Thanks for trying.
I made several attempts myself.
The only thing that would eventually work is splitting and reassembling.
The issue is that the following does note create all the nodes it should
temp_geom = (fair_geom - struct_geom) | fair_geom
Anyway I ended up with analytically placing intersection nodes on both geometries.
then it is possible to compound them and mesh the whole.
Globally I have a poor experience with operations on geometries within sectionproperties.

[robbievanleeuwen]

I'm not sure this is the issue. I get perfect geometry without any node or facet issues by using:

geom = fair_geom - struct_geom  + struct_geom
geom.plot_geometry(labels=("points","facets"))

I wouldn't use the union here as I don't think it's necessary or appropriate. Glad you got it working eventually 👍