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-   -   Fast Fourier Transform (FFT) in Tecplot 360 (http://www.cfd-online.com/Forums/tecplot/129976-fast-fourier-transform-fft-tecplot-360-a.html)

 g.woyczynski February 17, 2014 14:17

Fast Fourier Transform (FFT) in Tecplot 360

Hi All,

I am trying to use Tecplot 360 to get the frequency of my wave. I am using the "Fourier Transform" tool in the "Data" menu. For the plot that gets output, the frequency I am getting looks correct but the amplitude is way higher than the amplitude of my wave.

What is problem here? Does anybody know the exact fourier equation that Tecplot 360 uses?

Thanks

 cfdonline2mohsen May 11, 2014 05:41

Dear Wojo
We have encountered the same problem in Tecplot.
The Trend of the output graph and the frequency are very similar to the results obtaind using Excel but the amplitude is very high.
If we use different Window function (Rectangular, Triangular, Hann, Hamming) then different amplitudes are obtained but all of them are very High.

Have you solved this problem?
Thanks in advance

 JerimiahLee May 12, 2014 12:01

Hello,

Tecplot 360 uses FFTW to perform the FFT calculation.

As with most DFT's a gain or scaling factor is introduced. We have chosen to leave the calculation as is and let the user decide if they need it scaled down. If you divide the amplitude by your sampling size, you should receive a more reasonable value. You can use the Data > Alter > Specify Equations tool to do this.

 scott_rumage October 23, 2014 18:57

FFT tutorial link

Here is a link to a tutorial on performing FFT in Tecplot 360 EX: https://www.youtube.com/watch?v=hDhhpH0fOMA

Scott

 freeday September 21, 2016 08:04

How much I have to scale down? Is there any information about it? Tb4

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