how to get the cantilever's amplitude under resonant frequency ANSYS

[guoren]

I am tyring to get the resonant frequency of a microcantilever. I built the model using solid element (solid185), then A Block Lanczos Modal Analysis was applied to the model, after solving, i can get the exact frequencies, but the shown DMX value is on the scale of e+6, instead of e-6, incredibly huge.
Can anybody give me some advices?
I really appreciate any help.

 

[BobM3]

There's an ANSYS Forum here under "Engineering Computer Programs". You may have more comments there. How is the piece restrained? Is Mx a restraint or an applied load? It looks to be a torque. (Given the coordinate directions (x,y,x) as shown.)

 

[guoren]

hi, BobM3, thank you for your comment.
As a cantilever, one end is fixed, while another end is free, which shows the amplitude. But in my analysis, the frequencies values are correct, the amplitude should be on the scale of the micrometer sale, from the result you can see it is meter e6 now. I have no idea what the problem is. I didn't give any load or torque, only used modal analysis.
Thank you.

 

[MikeyP]

It probably depends on the mass scaling used for the modal analysis, the two main scales are "unity maximum" and "unity modal mass".

Remember that modeshapes are just shapes. They do not have scale.

M

--
Dr Michael F Platten

 

[hacksaw]

The amplitude of the forces exiting the motion determine the amplitudes. It is the next step in your analysis.

 

[sreid]

Is it possible that driving a spring-mass system with a really high Q (Silicon?) results in a high amplitude (not actually achieable before failure)?

 

[MikeyP]

sreid, the OP looking at the results of a modal analysis not a forced response analysis. This is a mode shape not a displacement response.

guoren, if you want to look at the displacement response then you need to do as hacksaw says and apply a dynamic force and look at the response.

M

--
Dr Michael F Platten

 

[guoren]

Thanks very one for giving advices.
Dr Michael F Platten, how can I apply a dynamic force for amplitude, by exerting force or pressure on the free end of the cantilever, but each time I can only give one force value instead of a series of, I really appreciate the help from you.

 

[elogesh]

Guoren,

There are options to input variable force with respect to time using tables in ansys...You can refer

http://www.ansys.net

or

http://www.xansys.org

for leads....

But it is preferrable to perform the response analysis in frequency domain rather than in time domain.

also based on the characterictics of the system,if the response can be captured using modal space (modal super-position) method then it is preferrable and econmical rather than direct(physical) method.

Regards,
Elogesh

 

[spongebob007]

In order to get the response of the cantilever you need to run a harmonic response analysis in ANSYS. For a harmonic response analysis you need either displacement or force as an input boundary condition. You also need to apply some sort of damping to your model. When setting up the solution you supply a frequency range that you want the response calculated over.