What To Do When you get the “Excessive Displacement” Warning in SOLIDWORKS Simulation
What to do when you get the "Excessive Displacement" warning in SOLIDWORKS
Most people that use SOLIDWORKS Simulation have run into the Excessive Displacement Warning message at some point in their analysis and have wondered why the error message came up and what can you do to resolve it. This is a very important question to consider because, if not handled correctly, this could significantly impact the accuracy of your results. The error message that is seen is “Excessive displacements were calculated in this model. If your system is properly restrained, consider using the Large Displacement option to improve the accuracy of the calculations…”
This error message most often comes up when people are running linear static studies so before going over common troubleshooting for this warning, it is important to overview the 3 main assumptions made when running linear static studies, which are:
- The material is linear (Generally means the stresses not going past the yield point of the material)
- The loads are applied slowly (Doesn’t account for the effects of dynamics)
- The deformations are small
If any of these assumptions are violated, then for accurate results you will have to run either a dynamic and/or non-linear study that is available in the SOLIDWORKS
Simulation Premium Package. The last assumption of “the deformations are small” is the assumption that is violated when the warning message comes up and will happen if the rough size of the model (the characteristic length) compared to the amount of deformation is greater than 10%. Now before you run off and think that you now need a Simulation Premium License to run the higher-level simulation when this error message comes up, I will show that most often this warning is telling us that we set up our simulation incorrectly and it needs to be reviewed
Consider the two following scenarios of a classic cantilever beam.
The only difference between these two scenarios is that the 1st one has a fixture on the left side and the 2nd one has no fixture. In this circumstance, the 2nd scenario would always get the “excessive displacement” error because nothing is resisting the load on the beam and it would just fly off in space. Obviously, having it fly off in space is not the intended behavior and the excessive displacement is just a warning sign that we set up the problem incorrectly.
While the cantilever beam example is it very clear what is wrong, in your assembly it may not be as obvious. If you are analyzing an assembly or multi-body part, it might not be the fixture that is missing but the connections between bodies. If one body is not connected to a different body as you were expecting and therefore can’t resist the load, then you likely will get the large displacement warning. In circumstances like this, utilizing tools such as the “Interaction Viewer” tool to visualize the connections in your part or the “Find Underconstrained Bodies…” tool to identify the degrees of freedom that a part can move can be invaluable for your troubleshooting. You can also get a good idea by looking at the results after you run your study and look for any parts that aren’t connected to the other bodies.
When the Excessive Displacement Warning message comes up you almost always want to select “No” in the message and look at the results to see if parts are flying off and analyze/change your setup as previously discussed.
Now in a few circumstances, if you are intending for the large loads to give large displacements to your part (And you didn’t just accidentally add an extra zero to the end of your force input) if you select “Yes” it will turn on an option in the solver for a basic non-linear solver that can get rid of the “deformations are small” assumption previous discussed. Now in most circumstances, if you are intending to analyze large displacement, a full non-linear solver is needed, which is available in SOLIDWORKS Simulation Premium or some of our high-end Abaqus/SIMULIA products. If your part isn’t permanently deforming (when you remove the load the part will return to its original shape) then clicking “Yes” in this error message to activate the “Large Displacement” option can be used to get good results.
Overall, the main thing to remember from this article is that whenever this message comes up you should first think that the simulation is probably set up incorrectly and the setup needs to be looked at and reviewed.
If you are interested in learning more about Simulation, consider taking our 3-day training course designed to help give you the confidence and skills to accurate run linear static simulations on your own: SOLIDWORKS Simulation Course
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