Unable to different esize() and plot boundary and loading

[ay8tb]

Hello,

I'm trying to follow the steps of the 3D Notched Plate where mesh size is specified and then nodes are selected for loading and boundary conditions.

I have an interesting problem where depending on what size I specify in esize (for example esize(0.6) vs esize(0.5)), the node selection set returns nothing. In other words running:

mapdl.cp(5, "UX", "ALL")

# Select a single node in this set and apply a force to it
# We use "R" to re-select from the current node group
mapdl.nsel("R", "LOC", "Y", width / 2)  # selects more than one
single_node = mapdl.mesh.nnum[0]

returns nothing and throws an error (since mapdl.mesh.nnum[0] is empty).

Is there a reason why certain esizes work and others don't? And is there a way to verify that an esize will work before putting a load and boundary condition? Thanks!

[mikerife]

Hi @ay8tb is it possible that the mesh size was so coarse that the meshing failed with too many badly shaped elements? If you capture the mesh output like

mesh_out = mapdl.vmesh(1)
print(mesh_out)

what does the output listing show?

Mike

[ay8tb]

Hi @mikerife,

This is the output after meshing and before selecting nodes to place loads and boundary conditions:
`GENERATE NODES AND ELEMENTS
IN VOLUMES 1 TO 1 IN STEPS OF 1

*** WARNING *** CP = 0.969 TIME= 15:38:24
All of the selected volumes in the set named on the VMESH command were
already meshed. Clear associated elements before remeshing.
`

[ay8tb]

Hi @mikerife,
Following up with a related question, when I switched to SOLID187, esize() is now the only way I can mesh solids with some sort of cut.
If I try to run the following:

mapdl.esize(1.1)
mapdl.et(1,187)
mapdl.mshape(1,'3D')
mapdl.mshkey(0)
mapdl.vmesh('all')

I get the following error:

CRITICAL - pymapdl_global - logging - handle_exception - Uncaught exception
Traceback (most recent call last):
File "C:\Users\XXX\PycharmProjects\XXX\XXX.py", line 56, in
mapdl.vmesh('all')
File "C:\Users\XXX\anaconda3\envs\XXX\lib\site-packages\ansys\mapdl\core_commands\preproc\meshing.py", line 2930, in vmesh
return self.run(command, **kwargs)
File "C:\Users\XXX\anaconda3\envs\XXX\lib\site-packages\ansys\mapdl\core\mapdl_core.py", line 2236, in run
self._raise_errors(text)
File "C:\Users\XXX\anaconda3\envs\XXX\lib\site-packages\ansys\mapdl\core\mapdl_core.py", line 2697, in _raise_errors
self._raise_output_errors(text)
File "C:\Users\XXX\anaconda3\envs\XXX\lib\site-packages\ansys\mapdl\core\mapdl_core.py", line 2774, in _raise_output_errors
raise MapdlRuntimeError(
ansys.mapdl.core.errors.MapdlRuntimeError:

Error in instance GRPC_127.0.0.1:50052

*** ERROR *** CP = 0.375 TIME= 11:31:23
Poorly shaped facets in surface mesh. Either:
(1) Mesh surfaces with triangular elements & modify mesh control or
SmartSize settings to get good triangular mesh, then VMESH again;
AND/OR
(2) Use alternate mesher by setting "MOPT,VMESH,ALTE".
*** NOTE

[mikerife]

Ok, and what happens if you reduce the allowed mesh size and/or use the alternate volume mesher?

[ay8tb]

Hi @mikerife,
For that issue (of not selecting a number for esize()), I realized it was because the .anf file was exporting in m instead of mm, which failed for some reason.

I have another question, is there a command to control how structures are meshed? For example, begin meshing from surface with an X of #, then mesh other surfaces? How does pyMAPDL choose what element 1 is and where to start meshing?