Help regarding Base excitation

[wajahatf]

Hey. I am trying to study the modal properties of cantilever beam. The experimental apparatus that I have include an electromagnetic shaker and a power amplifier. The beam under testing is clamped to the shaker at one end and is free at the other. I have theoretically calculated the displacement of the beam at the free end at each of the natural frequencies. I need to know if there is a formula to theoretically estimate the base accleration that is required from the shaker at the fixed end to create the deflection using the natural frequency , the mass of the beam and the deflection produced. I am probably using a sine sweep (one frequency ata time) excitation. I do not have a signal analyzer or accelerometer at disposal so I am only counting on a theoretical estimate.

 

[Twoballcane]

Why do you have to do a sin sweep? You already know the Fn of the beem. If you know the Fn and deflection, you should be able to solve for g.

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

 

[Twoballcane]

Also, I would like to add that working without some sort of data collection (Data Physics analyzer), you’re really poking around in the dark. Hand calcs will get you there at most 80%.

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

 

[IRstuff]

How can you know the deflection if you don't know the forcing function?

You either have the transmissibility, which tells you what the "gain" of the system is at resonance, and you can easily determine the amount of stimulus to get a particular deflection.

Or, you already have the deflection, in which case you've already input some sort of stimulus.

TTFN

FAQ731-376