September 15, 2022 at 6:47 amjulius.langenhorstSubscriber
I have a complex truss structure that has the following natural frequencies. Some of them are multiples and some are very close to the multiples. How can I verify mathematically that I really have repeated eigenfrequencies and not some frequencies that are just close to each other?
Is it possible to recognize repeated eigenfrequencies from the values alone? If yes, at which decimal place do numerical errors start to falsify the results?
Thank you for your help!
September 15, 2022 at 11:14 ampeteroznewmanSubscriber
If the structure has two planes of symmetry (both geometric and boundary conditions), then you expect repeated eigenfrequencies because the structure will move in the XY plane for one and move in the YZ plane for the repeated frequency due to those being the planes of symmetry. If the structure, including the mesh, is not perfectly symmetric, then a small difference can be introduced between the two planes, but I would still call that a repeated eigenfrequency.
It’s possible to have two very close frequencies that have totally different mode shapes. You can see that when you animate the two modes. You can’t tell from the values alone, you need to look at the mode shape.
September 15, 2022 at 4:44 pmjulius.langenhorstSubscriber
Thank you for your answer!
I'll have a look at animating the modes. But it's save to say that frequencies which are equal up to the 6th decimal place or so are repeated eigenfrequencies?
September 15, 2022 at 5:10 pmpeteroznewmanSubscriber
Yes, that is a safe assumption.
September 19, 2022 at 11:54 amjulius.langenhorstSubscriber
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