Hello to all,

Welcome to this new edition of the SOLIDWORKS Support Monthly News, coauthored by members of the SOLIDWORKS Technical Support teams worldwide.

Hotline Story: How a report of incorrect buckling results in SOLIDWORKS Simulation turned out instead to validate them

By Julien Boissat

This true story serves as a good reminder that it’s a natural tendency to be overly confident and unfairly blame the software for giving unexpected results. Recently, I worked on a case where the user reported abnormal buckling load factor (BLF) results when solving a buckling study. The results were considered abnormal because they differed significantly from the results obtained in another simulation software. Which software exactly is of little importance here. What matters is that the user must have had a considerable trust in that other software to choose to blame SOLIDWORKS Simulation over it. Needless to say, this user had even more confidence in themselves by being certain they hadn’t made any mistake.

When such a case arises, with suspected incorrect results – let’s call it a discrepancy – the explanation can come from one reason or a combination thereof:

  • Bug in SOLIDWORKS Simulation (as promptly pointed by the user)
  • Bug in the other software (yes, that happens)
  • Discrepancy in the geometry or simulation setups in either software (“user error” we call it, but does that ever happen? )
  • Discrepancy in the theory or assumptions made by each software

Consequently, in general, we like to ask users to explain in detail what the “bad” results consist of exactly, but more importantly what would be considered “good” results. And to justify why the presumed “good” results in the other software are relevant and reliable. In other words, were both software tools asked to answer the exact same question using the exact same set of tools?

As in the majority of cases like this one, we are not given full access to the setup and results in the other software. And we have to fall back to comparing SOLIDWORKS Simulation with theory. Easy enough if the geometry is simple, not so much otherwise. I got lucky there. The geometry was a simple straight rectangular tube, with dimensions as shown below, and a Force value of 1N:

As the formula for Euler’s critical load is quite standard and available from many sources, I elected to use the formula from Wikipedia.

In the above formula, E is 2.1E11 N/m^2 (obtained from the Material dialog box.

I is easy to obtain from the the Section Properties of SOLIDWORKS, but you have to make sure to use the lowest of the three moments of inertia of the area, at the centroid, among Lxx, Lyy and Lzz. The lowest value allows you to consider the critical load of the first buckling mode, while the value immediately higher usually allows you to calculate the critical load of the second buckling mode. In the present case, the value is Lxx = 80592 mm^4.

The length L is 1 m and the column effective length factor K is 2, based on the applied fixture.

So the formula gives Pcr = 39771 N.

In SOLIDWORKS Simulation, using a solid mesh gives this result:

Using shell and beam mesh give very similar results, summarized below:

Pcr from Simulation results (N) Discrepancy with theory
Solid mesh396570.29%
Beam mesh396090.41%
Shell mesh396590.28%

 

As you can see SOLIDWORKS Simulation results are spot-on. This validates, by the way, the buckling load factor calculated by SOLIDWORKS Simulation for all three available element types.

This therefore rules out the possible explanation by a bug in SOLIDWORKS Simulation. That leaves us with a bug in the other software, a discrepancy in the theory or assumptions made by each software (both unlikely for something this simple), or a user error.

As the user was convinced by the demonstration I gave, the user was reassured and the case was closed. We may never know the exact cause of the different results between both software, but we learned a valuable lesson nonetheless.

Note: you can find in Solution Id: S-073170 the SOLIDWORKS model with the setup of all three studies, and a spreadsheet with the theoretical results.

SOLIDWORKS 2018 Beta is Here…What Are You Waiting For?

The SOLIDWORKS 2018 Beta Program has already started. Are you hesitating to participate? Don’t. Here’s everything you can do when you become a tester:

For more information on the Beta Program, please visit the Beta website. If you have any specific questions, don’t hesitate to email us at beta@solidworks.com.

 

Simulation Step-Up Series

Last month, Reza discussed the topic of Accuracy and Convergence. This month, Ramesh discusses the topic of Viewing results (Parts 1 & 2).

Next month, Brian will discuss the topic of Correlating Simulation to Physical Tests.

.

 

Noteworthy Solutions from the SOLIDWORKS Knowledge Base

icon - SW General Hotfix for SOLIDWORKS® 2017 SP3 (SPR#1024009)
A hotfix is available for SOLIDWORKS® 2017 SP3 that addresses a problem where the dimension decimal separator is applied to material custom properties.
The hotfix is included in the attachment of Solution Id: S-073155.

icon - SW When installing the SOLIDWORKS® Student Edition software, how do I troubleshoot ‘Error 1334’?
See the procedure in Solution Id: S-072915.

Icon - EPDM Using SOLIDWORKS® PDM 2017, what are the recommended steps to set up and configure Microsoft® SQL Server Enterprise edition for database replication?
To use the database replication functionality of SOLIDWORKS® PDM 2017, you must first purchase and license Microsoft® SQL Server® Enterprise edition for each of the servers that will replicate the vault database. The SQL Server Standard software does not include this functionality. SQL licenses that are sold together with SOLIDWORKS PDM seats also do not include this functionality.
For more detailed information, see Solution Id: S-072960.

Icon - EPDM In the SOLIDWORKS® PDM software, is there a way to determine if a specific notification was delivered to the desired user or group?
There is not always evidence that a specific notification message was delivered to the desired user or group. However, it is possible to track the message in some cases.
For more detailed information, see Solution Id: S-072946.
How do I restart and check the HYDRA service on a worker agent or coordinator for Offloaded Simulation?
If the list of computers in the SOLIDWORKS Simulation Network Manager window is completely blank, you might need to restart and check the HYDRA service on the worker agent and coordinator computers. See the procedure in Solution Id: S-072953.

Can the worker system used with SOLIDWORKS® Simulation Offloaded functionality use multiple CPU cores?
Yes. The worker system used with SOLIDWORKS® Simulation Offloaded functionality can use multiple CPU cores. For more details, see Solution Id: S-073100.


That’s it for this month. Thanks for reading this edition of SOLIDWORKS Support News. If you need additional help with these issues or any others, please contact your SOLIDWORKS Value Added Reseller.

Also, comments and suggestions are welcome. You can enter them below.

 

Julien Boissat

Julien Boissat

Sr. Technical Customer Support Engineer, SolidWorks, EMEA at DS SolidWorks Corp.
I have been a Tech Support engineer for Simulation products since 2002. I was previously a product manager at SRAC, the original makers of COSMOS for those who remember that time! ;-). I am currently in charge of the content of the certification exams for simulation products. I also initiated and still author the Simulation Knowledge Base and participate as much as possible in the expansion and evolution of the SolidWorks Knowledge Base. Finally, I handle the SolidWorks Support Monthly News blog.


Categories: SOLIDWORKS Support Monthly News, Support, Tips & Tricks

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