Static analysis -- what does it mean to have negative eigenvalues? 1

[apal21]

Hello,

I am using the dynamic, implicit mode (hence static solver) for the first ever time. My last job gave me many 'Negative eigenvalue' warnings. Could someone please tell me what this means?

 

[FEA way]

Negative eigenvalue warnings suggest that there are some instabilities in the model. They might be related to buckling but more likely reason is presence of rigid body modes.

 

[apal21]

Thank you. I believe mine is due to a buckling instability.

 

[IceBreakerSours]

".. using the dynamic, implicit mode (hence static solver) .." is confusing.

Are you taking inertia into account or not?

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[apal21]

Yes, I do have inertia in my simulation. What are the consequences of that?

 

[IceBreakerSours]

In general, the closer your simulation is to the "real-world", the better. [What constitutes "real-world" is another matter.] So, inertia is a good thing to take into account. A lot of issues you run into in static analyses can simply be addressed by running a dynamic analysis. However, one has to be aware of the consequences i.e., unlike a static analysis, time and inertia are meaningful.

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[apal21]

Indeed! So, would a quasi-static dynamic analysis be the optimal way to go?

 

[IceBreakerSours]

Everything in numerical analysis depends on the specifics of a given problem. If there are instabilities in the model, you need to figure out the source of those instabilities and try to address them. Inertia is not going to fix issues with model set-up.

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