get_sub_elements function

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get_sub_elements function

Postby svenrich » Thu Jul 04, 2013 5:51 am

I use Cubit version 13.2 and need to find all faces belonging to a hex element.

As described in the manual the function get_sub_elements(entity_type, entity_id, dimension) should return this information. It seems to work fine for a quad returning 4 lines. But applied to a hex element the function returns from 0 to 3 IDs althought there are 6 faces.

It seems to that this is a bug.
svenrich
 
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Joined: Thu Jul 04, 2013 5:41 am

Re: get_sub_elements function

Postby svenrich » Mon Jul 08, 2013 7:15 am

@aaronwelch: Thanks a lot. This certainly helped to solve my problem.

In my opinion this advice should be included into the decribtion of the function.
svenrich
 
Posts: 4
Joined: Thu Jul 04, 2013 5:41 am

Re: get_sub_elements function

Postby svenrich » Tue Dec 10, 2013 4:51 am

The "set fullhex use on" command works fine and allows to find all sub elements of a hex for given sidesets. But it somehow has an impact on the number and location (!) of nodes which in some cases may cause major trouble with the center node of HEX27 elements.

When used BEFORE creating the first mesh the "set fullhex use on" command creates extra nodes (as many as there are elements) which are simply double entities of the center node. The list of of nodes ("cubit.get_nodal_coordinates(node)" ) is extended and the "former" center nodes do not show up in the connectivity. This may not cause any trouble as long as all coordinates are read and the size of the system of equation is determined using the connectivity.
Interesting to mention here is that Cubit 13.2 as well as Trelis 14.0.4 return the correct number of nodes for "list node all" after renumbering all ids. The python interface for both versions on the other hand seems to stick to the extra nodes.

Things are even worse if "set fullhex use on" is switched on AFTER a model has been meshed once. The necessary remeshing ("remesh volume all") leads to weird locations of the extra center nodes. The resulting element is messed. Deleting all mesh information will not help it. So far I have not found any workaround to fix the extra nodes.

Trying to delete and create a new block will increase the number of nodes even further. Switching to HEX8 and back to HEX27 to force Cubit to rethink the location of the center node will cause Cubit to crash.

I am really curious about any idea how to fix that problem.
svenrich
 
Posts: 4
Joined: Thu Jul 04, 2013 5:41 am


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