Estimate the input excitation energy

[wajahatf]

Hi. I am using an electomagnetic shaker coupled to a power amplifier to excite rectangular aluminium beams at their first and second natural frequencies. I have estimated the deflections of the beam at each of the frequencies and know the mass and dimensions of the beams. I want to to know, if there is any formula to calculate the input excitation provided by the shaker to excite the beam, using the mass and deflection. The beams are fixed at one end to the shaker(cantilever). I am attaching an image of the setup to avoid any confusions.

 

[GregLocock]

Sure, the work done in one cycle of the excitation is the integral of the force *in phase component of the displacement at the point of attachment. So at quadrature you are supplying no work, in an undamped system, as you'd expect.





Cheers

Greg Locock


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

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[wajahatf]

Cheers for that. Yeah I figured that out, but my concern is how do I estimate the force exerted by the shaker? I mean I know the frequency of excitation of the shaker and the voltage of the power amplifier at that frequency but do not know how to determine the force.

 

[IRstuff]

force = mass * acceleration

TTFN

FAQ731-376

 

[Twoballcane]

In order to figure out force in (Fin) to the system, you will have to calculate transmissibility Q which is (this will get you 80% there) Q=(Fn)^(1/2). You will also have to calculate how much force out(Fo) to create the deflections that you want. Once this is done, force in is Fin=Fo/Q. With this said, why would you want to calculate the force? Once you program the controler with either random or sin, the contoler will take over from there.

Tobalcane
"If you avoid failure, you also avoid success."

 

[wajahatf]

cheers folks.... Still confused though... The thing is I am exciting beams that are fixed at one end to the shaker. I can estimate the deflections induced in the beam and from that , I can calculate the effective load applied at the free end to cause that amount of deflection. However,I am interested in determining, using the mass and deflection of the beam, how much acceleration is provided by the shaker to the beam at the fixed end.I am trying to determine the input from the outputs obtained(reverse calculate).The exciter is connected to a power amplifier which generates random signals at constant voltage. I hope I am clearer this time.

 

[IRstuff]

Huh? A shaker should ALWAYS have a control accel to ensure that the system isn't violating it's operational limits. Otherwise, your excitation results may be completely bogus because the machine was bottoming out, or not putting out the stimulus that you thought it should have.

Why would anyone run it open loop?

TTFN

FAQ731-376

 

[DLite30]

Best bet would be to put a load cell in the system somehow to measure the transmitted force.

However, if you're exciting natural frequencies of the beam, input force can be very low to start and maintain vibration at that frequency.