Force from rotating cylinder 1

[jdmmech]

I have a hollow cylinder rotating at about 2800rpm max. I welded the bottom of a small tab to the end of the cylinder, and want to find the force acting on the tab that would bend it away from the cylinder at those high speeds. Any thoughts?

 

[desertfox]

Hi

My thought is can you post a picture of your situation

 

[dhengr]

Jdmmech:
Centrifugal force maybe? You know the weight/mass and the C.G. of the tab. You know how it is connected to the cylinder. You know the angular velocity of the tab. That ought to about do it.

 

[IRstuff]

If I understand the scenario, the tab is tangent to the cylinder wall, and you're looking to see how the tab might bend under centrifugal force. This would identical to one of the examples in Roark and Young, so you'd have a simple plate that fixed at one edge with a uniform force applied.

TTFN
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[Tmoose]

I'd plug the rpm/cpm and diameter the tab is affixed to into the "MILS pk-pk" this calculator. It will solve for the resulting pk acceleration the tab is subjected to.

http://onlinevib.yolasite.com/vibration-calculator-nojava.php

It accepted at least 20,000 mils ( 20" diameter ) input

 

[jdmmech]

IRStuff:

Yes it will be like a fixed edge, and then a force at the other end. I don't know how to calculate the "lateral force" though based on the rotation of the drum. Hopefully the picture helps to explain...it is a very simple sketch to just get my idea across.

 

[IRstuff]

?? but it's rotating on its axis of symmetry, no?

If so, there is no bending force because all the force is in-plane to the tab. I was expecting the tab to the parallel to the tangent of the circle, in which case, the force =V^2/R

TTFN
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[jdmmech]

Yes it would be rotating on the cylinders axis. If the tab was parallel to the tangent of the circle, I could see the centrifugal force that would make it bend. But since it is in the same plane as the tab, it won't bend at all? Even at high rpm with a thin gauge steel tab? I appreciate all your input!

 

[rb1957]

well the center of mass of the tab is a distance from the base so there'd be a small inertial force and so a small in-plane moment.

what is it now ? acceleration is w^2*r, mass = m, offset from base = h/2 ... moment = m*w^2*r*h/2

another day in paradise, or is paradise one day closer ?

 

[dhengr]

Jdmmech:
In the orientation you show the tab, it will not have a bending moment under ideal conditions, as Irstuff suggests, the loads will be in the same plane as the tab. But, a thin tab at that angular velocity might likely act as a thin, unstable airfoil, and vibrate off the cylinder in short order. Also, that tab will cause the entire cylinder to be out of balance if that can be a problem.

 

[rb1957]

the way I see it, it would ... the shaft rotates about it's axis, there'd be a (small) inertial load in the tangential direction from the rotation, causing bending about the strong axis of the tab.

another day in paradise, or is paradise one day closer ?

 

[IRstuff]

The load should be radial, since that's the direction in which the velocity is changing.

TTFN
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[jdmmech]

rb1957 & IRstuff: So you are suggesting it would bend slightly at the top of the tab in the direction shown in this pic attached?
That direction would be insignificant to me. However, any bending/vibration in the other direction previously posted would be damaging.

Balancing is not relevant to this question, simply because this is oversimplified.

 

[jdmmech]

Pic attached now^^ whoops

 

[jdmmech]

Wrong file!! Sorry again.

 

[rb1957]

mea culpa ... don't post unless you know what you're talking about !

agree with IR. I thought there'd be some small tangential inertial effect, but not now. there is as the shaft accelerates, as w changes; but not when w is constant.

I think ...




another day in paradise, or is paradise one day closer ?

 

[IRstuff]

There would a TINY aerodynamic drag force in that direction, but the centrifugal force is radially outward, like the force that keeps a car against the track in a loop the loop.

TTFN
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