What Does Double Amplitude (D.A.) Mean in Sine Vibration?
When you input your frequency and acceleration data into a sine vibration frequency response NASTRAN deck, you may run into that cryptic notation, 0.32 inch D.A. from 10-20Hz. This is what is known as a vibrational amplitude. But since NASTRAN does not know what D.A. is, and you probably don't either, you need to convert that value into something everyone understands, such as a vibrational acceleration, which could be measured in g's or in/sec2 or m/s2. Fortunately, this conversion is not difficult to do.
Start with the fact that acceleration is the second time derivative of length:
At maximum amplitude (ignore the minus sign):
Therefore:
By definition xo is the single amplitude:
Also, we know:
Finally we get the acceleration in terms of the length you are using (length/sec2):
If you are working in an inch/pound system and you want your answer in g, here is the final equation:
Ryan Simmons
August 2002
