Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

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ScientistRenzo
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Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

Post by ScientistRenzo »

Good day.
I imported a mesh from COMSOL. (.mphtxt)
This is the COMSOL model, deconstructed: https://imgur.com/a/oKqaHFJ
It has 8-9 Bodies, 2 materials, and a large number of boundaries.

The mesh in Elmer is complex: https://imgur.com/a/8FjIqpd
It has 34 Bodies and 158 Boundaries.

To simplyfy this I grouped all of the externally-exposed-boundaries into one boundary, per group, i.e. combining the four sides of an internal rectangular layer using "Unify Surface".

1. Can I combine the surfaces of the stacked-rectangular-layers if they are the same material?
2. Here are the boundaries remaining after I "Hide" all of the externally-exposed-grouped-boundaries: https://imgur.com/a/Yre0zE0. Do I need to apply any b.c.'s to these "internal" boundaries? I will not be looking at body-to-body radiation, I will be looking at heat transfer due to a heat source and radiation-to-external-environment. Henceforward, the grouped boundaries will have a b.c. including the external temperature and idealized radiation. Regarding the other countless (100+) boundaries, I don't know what to do for their boundary condition(s). Grouping them by material, likely.

--------------------

About the Bodies (Body Property x)
I tried to identify all of the bodies by clicking on them, then making a note of the red highlighted piece on notepad.
Three bodies appear in red, 1, 4, and 6.
I tried double-clicking on Body Property 33, 34 and Elmer keeps crashing.
Here: https://imgur.com/a/M4LrtE3

Thanks, you're amazing!
kevinarden
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Re: Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

Post by kevinarden »

You do not need the internal boundaries if the elements in the bodies share the same node.
In 3D ElmerGUI uses the boundaries to display the bodies (using the boundary as a surface mesh). However, internal boundaries can belong to 2 bodies. These are called parents for boundary elements. When this happens ElmerGUI gets confused on how to handle the boundary. It does not know how to display it, and if you double click on a body with a shared boundary it crashes.

If you don't need the internal boundaries you could delete them. Or you can redefine the internal boundaries to have 1 parent.
ScientistRenzo
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Re: Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

Post by ScientistRenzo »

I wonder if I need the internal boundaries between material 1 and material 2 that are not exposed to the external environment. I believe I do not need them BUT I may be wrong because I am new to FEA and do not well understand the physics-geometry-relationship yet.

Here, Because I want to look at the heat transfer through this geometry, consisting of 2 materials, and I want to include idealized radiation happening on the surface of the model with the external environment ("surface-to-ambient radiation"),
these internal boundaries are redundant, no?

I DON'T know what boundary conditions would be important for these internal boundaries. For example, I do not know if internal boundaries require any parts of the "Idealized Radiation, .5 Emissivity, 273 External Temperature" boundary condition that the externally-exposed boundaries will be assigned. Do they?

IF THE INTERNAL BOUNDARIES ARE REDUNDANT, I hope my model will be accurate.
I will combine all of the externally-exposed boundaries by material, and delete the remaining boundaries.

Again, I feel these might be important, because my geometry consists of 2 materials, and they seem geometrically important as I am new to FEA; The internal boundaries appear as walls, and I feel like I am deleting a wall, geometrically, when I delete an internal boundary; I don't know if the bodies will still have this wall and elements dispersed on it.

Thanks for your help kevinarden..
kevinarden
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Re: Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

Post by kevinarden »

You do not need internal boundaries between material 1 and material 2 if the share common nodes at the boundary. The heat will transfer through the nodes. If for some reason the nodes do not match at the interface, or there are coincident nodes, than the material 1 will not know about material 2, unless there is a boundary on each material, that has been defined to handle the interface. However, the easiest solution is to have material 1 and 2 share nodes at the interface, then heat will transfer across that interface with no action required from boundaries.
ScientistRenzo
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Re: Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

Post by ScientistRenzo »

Thanks!

Do you know if/how I can check if the materials share nodes? I built these connected blocks in COMSOL, then meshed the assembly. I imagine that the materials would share nodes.
kevinarden
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Re: Simple questions. B.C.'s and ElmerGUI crashing. Boundaries and Body Properties.

Post by kevinarden »

Most meshers have a coincident node check or merge feature. You can manually zoom in to the interface and look at the node labels for a couple of elements.

the ElmerGrid program can merge coincident nodes you can type ElmerGrid on the command line to get is options for comsol you can use

ElmerGrid 9 2 comsolname.mphtx -merge 1.e-4

where 1.e-4 is the tolerance on merging nodes, it will merge all nodes within the tolerance provided.
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