Learning Forum

[fabio1997]

Hello everybody , i need to do a static ansys study about 2 elastic toroid between 2 rings .It works like a double ball bearings without rotating.

So i've done a MODAL study but it has non-zero number in Hertz .

Outline + symmetry img.png

[Rameez_ul_Haq]

,so what is the problem?

[fabio1997]

i need hertz=0 .
the system must be isostatic.
Thank you .

[Rameez_ul_Haq]

,why do you need natural freqs equal to 0? You know what 0 Hz means, right?

[fabio1997]

I need to study the body in state of stillness so i need 0 degrees of freedom. So the natural frequency must be 0 ?

[Rameez_ul_Haq]

,having a natural freq of 0 Hz basically means that the complete structure (or a component of the structure) doesn't have any resistance to deformation or rotation along a certain direction. You might be having some non-zero freq natural modes to start with for a model, but they might be so small that the values can be assumed to be zero, if the model is relatively complex. It depends on what values of the natural freq you are having; sometimes for example 0.5 Hz can be assumed to be 0 Hz and sometimes not.
If you have some fixed supports applied to the structure which makes the overall model be static under any loading condition, then you will never observe any zero or near-zero natural freqs because there is resistance to deformation as well as rotation in all the directions for the structure. It is when the there is no stiffness along a certain direction, that is when you should be expecting zero or near-zero natural freqs.

[fabio1997]

Thank you Rameez , very helpful !