ADVANCED PRE-PROCESSING WITH ANSA FOR A STRUCTURAL ANALYSIS WITH IP SUBSTRATE MODELS
JORGE LOZANO
Advanced CFD Meshing using ANSA
Challenge - 7
ADVANCED PRE-PROCESSING WITH ANSA FOR A STRUCTURAL ANALYSIS WITH IP SUBSTRATE MODELS
Objective
5 CAD models are given to perform a geometry clean up separately being meshed separately specifically for structural analysis with a target element size of 5mm for the mesh (creating an offset mid-surface geometry)
All structural meshes must have the following conditions for the quality mesh criteria:
Theory
Automotive and Aerospace Substrates
Automotive and aerospace components are made from a growing variety of materials, including a wide range of plastics, metals, glass, ceramics, and exotic composites. The push for maximum performance, durability, light weighting, and cost-effectiveness make material changes a fact of life in these industries as the application in Fig. 1. Add to this the range of potential surface coatings applied to parts and coding these components can be a real challenge. Selecting the right coding technology and a coding partner that truly understands the importance of matching solution to substrate is critical in achieving repeatable, quality codes.
[1] Fig. 1 Automotive application substrate assembly.
TOPO-TOOL: MID-SURFACE
Mid.Surface [Casting]
This completely automatic function is used to create FE shell elements that represent the middle skin of a solid description.
Operations:
1.- Activate the Mid surface [Casting] function.
2.- Select the faces that compose the solid description. (Preferably by box selection since the whole structure can be transformed automatically into middle skin FE shell elements). If necessary, deselect with right mouse button the faces you want to exclude from the middle skin extraction.
3.- Press the middle mouse button to confirm selection.
4.- The Automatic Middle-Surface Mesh Generator window pops up.
A.- Minimum Thickness: Give the minimum thickness of the solid description.
B.- Element Type: Choose the element type for the FE mesh.
C.- Target element length: Define the Target element length
D.- Join perimeters with distance: Perimeters that are closer than this value will be joined.
E.- Paste triple boundary: Triple bounds that are closer than this distance will be joined.
F.- Add feature lines to Set: Creates a set of shell edges that will define the feature lines of the FE part. User can specify directly the id of the set or open the Sets list using the and pick one of the already existing ones. If no id is defined, a new set will be created.
G.- T-junction treatment: Defines the treatment of T-junctions, according to the icons.
H.- Stop at geometry errors: A geometry check will be performed before the middle skin extraction. If any errors exist, then the procedure will stop.
I.- Handle as single solid: In cases of two closed volumes the one inside the other, the middle skin will be calculated in the space between the two.
5.- Define the desired options and press OK.
6.- The middle skin extraction is performed.
Remarks:
1.- The function calculates nodal thickness values and assigns them to the nodes of the FE model. the visibility of the nodal thickness is controlled by the element thickness draw mode.
2.- if size boxes are visible during the procedure, they will affect accordingly the maximum element length of the elements they enclose.
3.- Depending on the complexity of the initial geometry, the resulting FE model might need some manual improvement using the corresponding functions.
Procedure
By using the TOPO tools for pasting close enough adjacent coons, New for selecting a coon’s algorithm for creating a new face, project cut, project, etc. We can apply the knowledge learned and perform several pre-processes a lot easier with ANSA than most of the commercial software for CFD.
By performing a Mid-Surface tool, it finds a created a default mesh with the condition parameters and mesh type, quality mesh criteria are important to define it before, for creating it from the beginning correctly.
The first step is to perform a clean up geometry adding surfaces with single coons, deleting unnecessary surfaces, needle coons, in general by using the manager check – geometry, all selections checked must be run and those considerations must be corrected before continuing to the next step.
In Fig. 2 [A-E], are the IP substrate models to pre-process, some have more geometry errors than others, but nevertheless they should be taken care of before performing an FEA analysis.
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Fig. 2 [A-E] 3D CAD substrates models
By using the Mid-surface: CASTING tool, we obtain as seen in the Fig. 3 [A-B] examples a well define mesh directly after using the tool, by inserting the necessary data as in Fig.3 [B], the target mesh element size, the element type and the minimum thickness for bending or turns. Besides the offset tool, the mid-surface: casting tool too, facilitates the work and shortens the pre-processing time.
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Fig. 3 [A-E] 3D CAD substrates models
Once the Mid-Surface: Casting tool is applied, we obtain the following meshes seen in Fig. 4 [A-E], although they have several colored elements that represents the color parameters for the mesh quality criteria, mainly obtaining skewness, min length, max length, and Taper mesh quality errors, that by using the fix selection in the check manager- mesh, some elements may get to fix them selves by depending in the error generating a specific algorithm but no to result with a wrong effect with other correct elements. The other way is to recognize each of the mesh parameters and depending on the variables to obtain the quality, modify each on of them manually, the last choice for managing with the quality mesh criteria is to select fix element in the OFF selection on the left-side workbench section. For obtaining a faster corrected mesh, is to go through all three techniques to modify the mesh and obtain different results by modifying the algorithm variables so the result we obtain is different, closer to the desirable mesh parameters.
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Fig. 4 [A-E] 3D CAD substrates models
As result after the mesh correction to obtain the mesh quality parameters the Fig. 5 [A-E], show the final FEA mesh obtaining a desirable mesh quality in the negative view to see better any OFF element colored by each one of the errors, also we obtain the triangles and quads quantity, and the total elements mentioning that depending on the results or application for this parts the mesh could get more refined obtaining a better, close to error-free results.
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Fig. 5 [A-E] 3D CAD substrates models.
Conclusion
All substrate CAD models, were properly cleaned up, by using the TOPO window tools, and by using a mid surface tool, the surface FEA mesh was performed although obtaining quality mesh errors, taking care of them with the procedure mention, mainly manually, resulting great quality meshed models ready to be analyze, maintaining the same structure geometry.
The PIDs were left as they were (1 for each one of the models), but forces, restrictions, connections, weldments, or any kind of selection needed for the analysis must be defined individually and exported in the correct FEA software.
References
[1] https://plasticscar.blogspot.com/2017/02/thin-wall-ip-substrate.html
[2] BETA-ANSA documentation, meshing tools