how to use ANSYS for vibration analysis?

[4WillyWonka]

I want to measure the spectrum of the vibration of a machine. Later I want to place antivibratory elements to isolate of the support using ansys. Can someone help me? Thank you very much.

 

[cbrn]

Hi,
I fear you provided too few info in order to receive direct tips.
However, here are some (very) general questions/suggestions that may help you:
- does your model have non-linearities? If yes, then you have nochoice but to perform a transient analysis with time-variant boundary conditions (displacements calculated from vibration spectra... VERY not easy...)
- can you linearize your model? I.e., are the "behavioural" non-linearities really important for the response of the structure? Sometimes you can analyze a "worst-case" by figuring out a BC configuration which ensures linearity. If so, you have many more options (see below)
- do you need only the natural frequencies (to be compared to well-known excitation frequencies so that you can verify that they are "well apart")? If so, a modal analysis is enough. There are also two solvers that can account for damping, if you need it (I think so, if you want to check the effectiveness of anti-vib supports).
- you can also check the response of the system to a single-frequency excitation source: harmonic analysis
- or you can operate in the frequency domain (only linear, however) and set up a spectral analysis (there are several sub-options under this type of analysis: see the Help, it is VERY well described). If you deal with a structure which doesn't have non-linearities (or that can be "reduced" to linear), and you want to check it against, for example, something like an earthquake acceleration spectrum, then this is THE way to go.

Hope this helps...

Regards
-

 

[4WillyWonka]

Hi Cbrn,
Still I don't know exactly which is my aim. Could you send me your information? Pobably some things serve me. I am sorry if my English is not very good. My intention is to do the study physically and later to simulate it with Ansys, for this reason, if you have investigated on this, I would be grateful if you send me your information or recommend me some literature. Thank you very much.
Regards, Javier

 

[Drej]

Some recommended literature to be read:

(1) Mechanics of Materials book
(2) Any engineering literature on the theory of vibrations
(3) The ANSYS help manual
(read all structural sections, starting with linear statics)



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[4WillyWonka]

What I really want to do is to place a vibratory machine on a table and to measure its response in frequency. After, insert something like rubber between the table and the machine, and repeat the experiment. Thank you very much. Regards, Javier

 

[cbrn]

Hi,
as I understand it, you need to find the response of a structure to a single-frequency excitation. In fact, the experiment may be done with a frequency sweep, but that doesn't change the philosophy of the simulation (several loadcases with varying excitation frequency will recreate the experimental sweep). In this case, and PROVIDED THAT THE STRUCTURE DOESN'T CONTAIN NON-LINEARITIES (contacts, combin37 elements, non-linear materials, just to make some examples), the way to go with Ansys is the harmonic response analysis.
If you need the non-linearities, you must do a full-transient analysis.

Regards