Understanding Hierarchical Meshes
A hierarchical mesh is a composite of the top-level mesh (the mesh of the current assembly) and any component-level meshes (the pre-existing component meshes in that assembly). When it creates a hierarchical mesh, Creo Simulate traverses the assembly hierarchy from top to bottom looking for pre-meshed components. Each time it finds one, it evaluates the component-level mesh and determines whether the mesh is:
• Complete—A component has its own mesh in which all subcomponents have a mesh.
• Partial—A subassembly has its own mesh, but not all its subcomponents have meshes. This can occur if you mesh a subassembly, add a new unmeshed component to that subassembly, and then do not remesh the subassembly as a whole.
• Inherited—A component mesh is part of a larger component mesh. For example, assume that pre-meshed part a is included in pre-meshed subassembly b, which, in turn, is part of top-level assembly c. In this case, subassembly b and part a both contribute inherited meshes to assembly c. Part a also contributes an inherited mesh to subassembly b.
Here is how the mesh generator treats each situation:
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Component Mesh State
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Action
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Unmeshed
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Includes the component in the list of components to be meshed.
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Complete mesh
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Excludes the component from the list of components to be meshed.
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Partial mesh
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Displays a message asking if you want to remove the current mesh. If so, the mesh generator adds the component to the list of components to be meshed.
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Inherited mesh
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Excludes the component from the list of components to be meshed.
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After it has prepared the list of components that it needs to mesh, the mesh generator creates the top-level mesh. The resulting mesh model contains the top-level mesh, which includes meshes for all connections and unmeshed components. The mesh model also contains any complete or inherited component-level meshes. In creating the mesh, the software respects all properly established
connections between subcomponents, ensuring that the solver will be able to correctly recognize the assembly load paths. Here is how the mesh generator treats connections:
• Creates consistent meshes for connected components. These components can transmit loads.
• Does not create consistent meshes for components that it considers disconnected. These components remain in place and are part of the overall mesh, but cannot participate in the load path.
As it proceeds, the mesh generator checks for any situations that
invalidate the mesh or cause unacceptable mesh inconsistencies. The mesh generator either ignores the factor causing the problem or removes the mesh. The mesh generator also checks for any node, element, or local mesh entity ID conflicts. If it finds any, it warns you of the situation, providing a list of nodes, elements, and local mesh entities that have numbering conflicts. To resolve this conflict, use the
Mesh Numbering or
Mesh ID Offset mesh control, as appropriate.
When you output the model for use with the NASTRAN solver, Creo Simulate creates a single file for the assembly. This file lists all the meshes in the model, starting with the lowest level and working upward. It places the properties, materials, and coordinate system records in the lower mesh structures, enabling you to separate individual meshes from the whole and run these separately.
For other solvers, the file lists all model meshes, but does not arrange them hierarchically. In this case, Creo Simulate arranges the file so that all nodes in the assembly are in one section of the file, all elements are in another, all materials in another, and so on. When it works with the file, the solver recreates the hierarchy using information from each of these sections.
To see an example of how the mesh generator processes a hierarchical mesh, see
Example: Hierarchical Mesh Generation.