Support framework for rotating centrifuge
Support framework for rotating centrifuge
(OP)
First off, I am not a mechanical engineer. I'm a structural engineer and my last exposure to anything like this was a course in structural dynamics in grad school 35 years ago. What I have is a centrifuge which rotates at 3200 rpm which is going into a wastewater plant. The centrifuge, which comes on its own skid and has vibration isolators, will be set on 2 steel WF beams which will be simply supported and have a span of about 14 feet. The centrifuge will be placed in an existing building which has a suspended concrete slab floor and the proposed beams will transfer the loads to walls in the basement. Intuitively, I tried to design the beams to be as stiff as possible. Based on loads provided by the centrifuge manufacturer, I should only have about .04" of deflection. However, the question has been raised about possible vibrations and/or effect of resonance. I have calculated the natural frequency of my steel beams and it appears to be about 940 cycles/min. The centrifuge engineer is not much help but he thinks that the only time we might have a problem is at shut down as the centrifuge slows down from 3200 rpm to zero. I'm thinking of putting vibration isolators under midspan of each beam to help damp any possible vibrations. Am I going to have a problem with vibrations and possible resonance??? Any help or guidance here will be greatly appreciated.





RE: Support framework for rotating centrifuge
Was the "steel beam resonance" a vertical resonance of the beam with centrifuge aboard?
Here's a link to an old paper that discusses multi-mass systems.
http:
I expect the centrifuge would demonstrate a "critical speed" or two when slowing down on its own isolation mounts on a perfect floor. Even if running speed is OK on you new system, I think there will likely be a few extra critical speeds on shut down that personnel nearby will talk about.
RE: Support framework for rotating centrifuge
If you can't design the structure so that all modes are >115% of the operating speed then an isolator approach may work. I don't think harmonic dampers are a good idea in this case as the power available is so great, and continuous.
Do you know what the maximum out of balance is likely to be?
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?
RE: Support framework for rotating centrifuge
If you intend to stiffen your structure so that it's resonant frequency is > 3680 Hz (3200 * 115% as mentioned by Greg) you will most likely need to get creative (i.e. curved or tapered beams as you are a long way off at 940.
Keep in mind that as the natural frequency increases the displacement (and therefore the stresses) will decrease by a factor of w^2. So Even if you can't stiffen your structure to eliminate all resonances, maybe you can push it past the point where it is harmful to your structure.
Hope this help.
-Daniel Kuntz
RE: Support framework for rotating centrifuge
Cheers
Greg Locock
New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?