That FEA problem used to drive me mad

It happened to me a countless number of times.

I had just finished to set up my FEA model and run the analysis and I knew more or less what range of stresses I wanted to find.

I was waiting for the results to confirm that…

BUT…As you know there is always a factor between le results you expect and what you actually get… that’s normal in FEA.

…but why was the error so big???

I was looking at the maximum Von Mises Stress and I realized the average values inside the model were more or less OK, but I was just getting a small red point that was changing everything.

Inside this red area, the “normal” von mises stresses were 3 or 4 times the expected value and it clearly indicated that there was a big problem in my model…

So what did I do?

Of course, I started to search on the Internet! 🙂

And I found I was not alone to have such a problem… in fact, this problem was very common.

It was a singularity.

A “SINGULARITY” !!

This word sounds like coming right from Star Trek…

Do you know what is a singularity?

You see the image below?

Well…a singularity is basically the same… but inside your FE model!

Now I knew what it was…a singularity… but I still knew nothing.

The very famous physicist Richard Feynman said something I always remember:

“Even if you know the name of a bird in hundred languages, you still know nothing about the bird.”

So I decided to learn more about singularities and by what they were caused.

But, maybe before I explain that, you are wondering why singularities are such a pain in your model??

After all…I didn’t discuss that

Why is a single singularity in your model such a pain?

Well, singularities are causing many problems, but the major ones are:

– They cause an accuracy problem inside your model near the singularity.

– They cause a problem of visualization of your results by extending the range of the color inside your legend.

Those 2 problems are very painful…and that’s why I was wondering what ultimately causes singularities.

What causes a singularity

At first, I searched the answer on the Internet, but I couldn’t find it.

(I always thought that all the answers were available on the Internet for free, but that’s really not true)

Finally, I had to ask someone more expert than me about this topic to understand finally what was the major cause of singularities.

And it was …boundary conditions!

I didn’t want to believe it at first, but when I modified a bit the boundary conditions of my model, I discovered that the singularity vanished immediately.

Who knew that boundary conditions had such an impact…

Since then, I made a lot and a lot of progress (this situation I described happened 6 years ago when I just started to use FEA seriously)

I understood that there are a lot of ways to tackle singularity problems and also to set up boundary conditions so you will never get singularities…but that really took a lot of time to understand and a lot of efforts.

Maybe I’ll do some short course about it to explain all that in real details to you. That will save you a lot of time for sure.

Ok, it’s already late here… I’ll write more in a next article.

Just tell me:

Would you like to learn more about this topic?

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