Breakout Analysis of Parts in An Assembly

I’ve recently discussed how local regions can be broken out of large models to more quickly calculate accurate stresses. These regions can have ragged boundaries as shown in the example below:

This does not affect the accuracy of the results as long as elements on the ragged boundary are treated as sacrificial. But sometimes the region of interest for more accurate stresses is a part in an assembly. For this case it is nice to have the entire part be the breakout region and figure out how to automatically extract it. Working with a CAD model, with access to the model tree makes this straightforward to implement. StressRefine’s interface with Solidworks Simulation does that, for example, by determining which surfaces form the boundary of a part using information from the Application Programming Interface (API). Through the API it is also easy to determine which surfaces are free boundaries and which are interfaces with other parts, from which the breakout boundary conditions can be determined. Here is an example using the Solidworks interface:

Working with Nastran models it appears the equivalent information is not available. However, recently I figured out how to use interface constraints (“bsurfs”) to cleanly breakout out parts from assemblies for use as local regions. Working from the center of the region of interest (which is either specified by the user by selecting a node, or is the point of max stress in the model), the mesh is traversed topologically, but does not go past faces with bsurfs.

The traversal to identify the part is shown progressing in the figure below. I also made a slide show that is a time-lapse sequence of the traversal which is shown here (you need to download it and run it with powerpoint or the powerpoint reader for it to show automatically, or in google slides hit view/present (ctrl-F5) to show the show but you’ll have to use page down or right arrow to advance it, it powerpoint it is automatic).

The overall model has 297,000 elements but extraction of the local region only took 2.4 secs, and stressRefine achieved a accurate p-adaptive solution of the local region in 18 secs. It helps that the local region is only 9963 elements, that’s the beauty of breakout analysis.

I think this “breakout by part” procedure is a useful enhancement to this technology. Just specify a point in the region of interest (or specify using the point of max stress in the model), and the appropriate part in an assembly will be automatically extracted as a local region. If that part has a very large mesh, stressRefine can also use a subset of the mesh in the part as the local region, again extracted automatically.

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