HYPER GRAPH

Altair Forum User

Dear SIr,

 

I am doing the vibration analysis for motor , we done both experimental and Simulation also, I have Time domain data from Experiment Just i need to Import those time data in to my Hypergraph  then i will do FFT in Hypergraph. But My problem is

 

 

1. The FFT results From Experiment is different from Hypergraph results,

2. In experiment FFT i am getting amplitude as 3000Mm/s2 but in Hyper graph the frequency is same but the amplitude is 6E5, 

 

 

Please can anybody clarify my doubt if you need then i will send the experiment excel also.

 

Here i am attaching Time to frequency conversion Document from Hypergraph

Unable to find an attachment - read this blog

Rahul Rajan_21763

There will be a change in amplitude b/w the time domain and the FFT signal.

This is because, a simple sine curve in time domain is represented as
 Y = A sin (wt), 
 where,
 A > Amplitude,
 T > Time Period of oscillations
 w > 2* PI / T 
 and f = 1/T
 So, when converting the above curve to frequency domain the equation becomes :
 Y = A sin (2*PI*F) T
 This equation is true for a single frequency in which case the amplitude will remain same when you convert from time to frequency.
 But, when you have a complex response curve with multiple frequencies at different time period, the equation will be similar to the one below :
 Y = A1 Sin (w1 t1) + A2 Sin ( w2 t2 ) + A3 Sin (w3 t3) + ....+... 
 In the above equation, since the Amplitude is distributed over different frequencies and hence the amplitude of the resulting curve in the frequency domain changes.
 To cross check this you can do an inverse FFT (IFFT) on the resulted FFT curve to get the original curve.

 I hope this clarifies your query,