Natural frquency of a large vibrating screen 2

[marcostorres]

Hello,

I modeled a large vibrating screen in ANSYS to determine the stress. I did a static model simulating the vibrations as acceleration and it was fine to find the stress. Now I need to determine the natural frequency and I found 0,739 as a result and I have no ideia if it could be wrong. What I did was just make a modal analysis. Does it seem right?


Thanks

 

[btrueblood]

I get 1.289 when I generated a modal analysis for MY large screen. Wonder if maybe it is different than the one you failed to describe.

 

[jhardy1]

I got 2.467 Hz for my last screen!

http://julianh72.blogspot.com

 

[GregLocock]

What my colleagues are saying is that we have even less idea whether your answer is right than you do. If it is a relatively simple structure you may be able do a hand calculation, and RD Blevins gives solutions for all sorts of systems.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[marcostorres]

sorry for the lack of information, it's a complex structure and would be quite a effort to try to decribe it in a reliable manner. It's a vibrating screen used to separate ore. What I wanted was values that are usually obtained for this kind of structure and it seems that the ones I found vary a lot from the ones found by other enginners. I'm gonna study a bit more both my model and the concept of natural frequency and then I come back with my results.

Thank you for your help,

 

[btrueblood]

Oy. I completely made my number up, as the information you posted that would allow somebody to estimate the frequency was zero, none, nada. What size (height, width) is the screen, what wire size, what mesh opening, what kind of weave? How are the edges supported? What typical material load do you estimate is lying on the screen during use, and what is its distribution, or do you care about the frequency in that condition (realize it will not be the same as an unloaded screen). Finally, if it really is a woven wire mesh, realize that friction damping occurs where the wires rub against each other, and this can shift the frequency slightly higher than for a welded or bonded wire mesh. Sounds pretty complicated, huh? Can you see why your original question lacked information to allow a decent answer to be given (although Greg's answer is really the right one - start with hand calcs before you even consider touching a keyboard).

 

[amanuensis]

You have to verify the six first natural frequencies. If they all are near to zero then it means that your structure fas free-free boundary conditions. Those are the modes of rigid-body.