Simulation studies require proper geometry setup to ensure that the solver can run. The most common source of studies that fail to solve is from missing bonded or contact definitions. There are techniques, as shown in our troubleshooting unstable models blog article, to help determine the problem area.
SOLIDWORKS Simulation 2021 adds significant functionality to assist in stabilizing the model from the beginning. Small gaps and imperfections in models can be overcome with a few settings.
The default options automatically assign allowable gaps within a range percentage. The characteristic length is a length that represents the overall size of the model based on an equation and the sum of all nodes.
SOLIDWORKS Simulation 2020
So let’s start with SOLIDWORKS 2020 and how these gaps can cause headaches. Here we have a model that from a distance appears that the two blocks are touching. On zoom, we can see there is a slight gap.
In SOLIDWORKS 2020 and prior, the Global Component Contact only applies to initially coincident faces (at least for No Penetration contact). Therefore we’d typically add a local Contact Set to these specific faces.
With this particular study, we’ve fixed the bottom face and applied roller/slider fixtures on all the sides. This would cause the top curved block to drop down until it hits the rectangular block. There is a large 100,000N force pushing down for good measure. We have an initial instant “jump” at the start until it even comes in contact. The instability may cause the solver to fail.
Here it does solve, but we receive a warning that there are excessive displacements. Reviewing the displacement plot, we can see that the top block just kept going. We’ve set the scale to a very small value for visual purposes. The few nodes still touching have extremely high stresses.
SOLIDWORKS Simulation 2021
Move to Simulation 2021 and we no longer need a Contact Set (now referred to as Local Interaction contact). The Contact Interaction can specify a Gap range to consider contact based on a gap less than 10% of the characteristic length. You can change this percentage or calculated distance value. In this case, our 0.1mm gap will be taken into account.
Next up is the issue with instability of the “jump”. The new Stabilize area gap size provides small stiffnesses to these close contact locations to assist the solvers. By default at 1% of the characteristic size, our 0.1mm gap is less then the calculated 0.375mm threshold.
Now we have a stable model with proper contacts to provide realistic results.
If you specify a Global Bonded Interaction, the gap range for bonding is similar to the ‘non-touching faces’ option in prior releases. However Simulation 2021 automatically includes a 0.01% range for any imperfections of the model.
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