dynamic frequency analysis

[lonely_fighter]

My problem is: sin vibration with the amplitude of acceleration 147 m/s^2 (15G) at the frequency range 10 ... 100 Hz.
I perfom dynamic frequency analysis with base excitation in PRO/Mechanica. In the direction of base excitation I define -9810 mm/s^2 (mmNs - system of units).
1) What function should I define for acceleration in PRO/M?
2) What is the numerical reference between
base excitation and prescribed amplitudeof acceleration 15G?

 

[Luis Aguirre]

lonely_fighter


In the dynamic frequency analysis window were you specified the base excitation you need to enter 147 m/s^2 in the correct units. In other words intead of assigning 1 G (-9810 mm/s^2) you need to assign 15 Gs (147000 mm/s^2). In the case of base excitation the amplitude, velocities, and accelerations from the base are removed from the results. In other words, if you place an accelerometer in the base and one in the structure the results that mechanica will yield will be the accelerometer on the structure minus the accelerometer in the base, thus, amplitude, velocities and acceleration are relative to the base.





Luis

 

[lonely_fighter]

Thank you, Luis, for your answer, but I`ve tried to do so.


I defined -147000 mm/s^2 as base excitation acceleration and uniform function. Other time I define -9810 mm/s^2 as base accel. and my function was 15, if 10<=frequency<=500Hz or 0, if freq.>500Hz. The result, given me by PRO/Mechanica, was 10 times greater then measured at real structure.


What is incorrect?


The amplitude of sin vibration is 15g. Is it in time or frequency domain? And what does Pro/M mean as base acceleration amplitude: time or frequency domain amplitude?


If someone could help me with my problem, please send me message and I`ll send youprintscreens, which describe my actions, because it is not clear for me at all, why pro/m results are 10 times the real numbers

 

[nschlueter]

Above you stated you were investigating ranges from 10 to
100 HZ, below you stated 10 to 500 HZ.

I'm sure you have already done this but I would look over
your numbers again.

It appears that you have everything setup correctly.