exporting to LS-Dyna

General topics about Trelis/Cubit, such as localization, GUI, etc.

exporting to LS-Dyna

Postby swainwc » Mon Feb 18, 2013 6:41 pm

What is the difference between the layers of blocks/parts? The overall structure has Groups and blocks and parts, is this correct? When I export the group is never requested, only blocks. The K-File lists the block and the parts contained in it.

The main reason for my request is to have two parts together, but one of steel and another connected of aluminum. Would these be created at the group level as two blocks? Or would it be two parts in the same block.

Also, the phrase Sidesets has a common snense meaning, but is confusing when thought of with node sets. Are they different? and for what reason would a side set by different that a nodeset on a side?
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Re: exporting to LS-Dyna

Postby csimsoft Moderator » Mon Feb 25, 2013 12:30 pm

The definition of blocks is:
Element Blocks (also referred to as simply, Blocks) are a logical grouping of elements all having the same basic geometry and number of nodes. All elements within an Element Block are required to have the same element type. Access to an Element Block is accomplished through a user-specified integer Block ID. Typically, Element Blocks can also be assigned material properties to associate material properties with a group of elements.
Additionally, blocks are used to identify the elements that the user is interested in exporting. You can specify certain blocks to export or all blocks.

Groups are just used to collect geometry or mesh entities. Typically they are not used when exporting the mesh.

You mention "parts", but are you referring to "Volumes"? These are the actual geometry that you are looking at in the graphics window.

Typically your want to create separate blocks for each material property. So in your case, you would put the elements representing the steel in one group and aluminum in another group. Here is a simple example:

#create two volumes touching
brick x 1
vol 1 copy move x 1
merge all
mesh vol all
block 1 volume 1
block 2 volume 2

When to use sidesets vs. nodesets? That is something that will ultimately be determined by the input deck that will analyze the mesh. Most often, CFD analysis use sidesets, where FEA use nodesets. Nodesets are used when the specific locations of the nodes need to be fixed or some point loads applied. You are right that sidesets can allow you to specify a 'side'. Sidesets might be used when a pressure is applied to a surface. Cubit is meant to be mutli-purpose so what you use to group your mesh entities will be constrained by the requirements of the downstream application that does the analysis.

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