Submodeling: Simple Solutions for Large-Scale Problems

If you’re an engineer who has dealt with large simulation models, you know there’s often a trade-off between accuracy and solution time. Submodeling is a technique you can use to reduce solution time without sacrificing accuracy of results.

A common strategy you can use to look at the overall behavior of an assembly or complex part of a large model is to simplify the model during preparation by removing small details, like fillets and holes. Simplifying models in this way can have a significant impact on run times. This simplification, while not excessively affecting overall model stiffness, may result in lower resolution of localized stresses. What you need, then, is a mechanism that allows you to “zoom in” on these details to examine behavior around specific areas.

Submodeling is such a technique — it enables you to solve a locally refined model with all of the geometric details required to solve accurate stresses. The ANSYS submodeling method not only provides accuracy, it solves these regions in a fraction of the time it would take to solve the entire model.

With ANSYS 17.0, we added an enhancement for SpaceClaim Direct Modeler that makes it easy to extract a submodel from solid or surface geometry. The technique is highly automated while still enabling you to enter guidance and input. You can use Direct Modeler to extract the model with only a few mouse button clicks. The technique leverages a useful SpaceClaim viewing method called “Clip with Volume;” you simply designate a spherical region and Direct Modeler automatically extracts the appropriate solid geometry. Not only does it rapidly create the submodel but the cut planes (named selections) are automatically created as part of this process!

The example below shows stress concentration results for a full model gearbox. The geometry has a “sharp” corner — singularity.

sharp-corner-stress-riser-ansys

Sharp corners resulting in high stress concentrations often lead to misleading or inaccurate results.

The stress results would be inaccurate — stresses are over 50 KSI.

high-inaccurate-stress-concentration-zoom-ansys-spaceclaim-submodeling

High stresses along sharp corners.

In SpaceClaim, with a few mouse button clicks, you can extract the submodel using Clip with Volume and use the Pull tool to add a fillet radius.

extract-geometry-pull-chamfer-fillet-ansys-spaceclaim-submodeling

Submodel extraction and rapid geometry modification in SpaceClaim.

This automatically creates a Named Selection at the cut boundaries of the submodel. The next step is to transfer the model into ANSYS Mechanical and apply a fine mesh to specific areas.

fine-mesh-geometry-fillet-chamfer-ansys-spaceclaim-submodeling

Meshing a submodel with a fine resolution.

The Named Selections created from SpaceClaim are used to import displacements  from the full model.

import-cut-boundary-constraint-named-selections-ansys-spaceclaim-submodeling

Transferring displacements using the SpaceClaim generated Named Selections

This gear box submodel is solved with 3 easy steps as shown below and with very accurate stresses of only 20 KSI, as compared to the 50 KSI stress concentration.

stress-distribution-ansys-spaceclaim-submodeling

Realistic and accurate stress concentrations now that geometries have been altered and meshes refined.

To solve the full model with all the detail will require a significant increase in the solve time to get the accuracy of the submodel.

One thought on “Submodeling: Simple Solutions for Large-Scale Problems

  1. as the submodel is finer and thus lower stifness, boundary displacements applied, the reaction loads in boundaries will be different and probably less than those of the full model. Is there an invisible algoritm which scales the applied displacements to get the loads in the same range as if the full analysis at the submodel boundaries? otherwise i think the new and less stress results from the submodel analysis would be questionable ?

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