Fast Fourier Transform (FFT) in Tecplot 360

g.woyczynski · February 17, 2014, 14:17

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, 06:41

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, 13:01

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, 19:57

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, 09:04

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

ksingh · October 26, 2017, 12:09

Generally, You can divide magnitude by number of sample data points to get correct amplitude.

February 17, 2014, 14:17	Fast Fourier Transform (FFT) in Tecplot 360	#1
g.woyczynski New Member Wojo Woyczynski Join Date: Jan 2014 Posts: 5 Rep Power: 12	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

May 11, 2014, 06:41		#2
cfdonline2mohsen Senior Member Mohsen KiaMansouri Join Date: Jan 2010 Location: CFD Lab Posts: 118 Rep Power: 16	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 Luttappy likes this. __________________ “If you have an apple and I have an apple and we exchange these apples then you and I will still each have one apple. But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas.”

May 12, 2014, 13:01		#3
JerimiahLee New Member Jerimiah Join Date: May 2014 Location: Bellevue, Washington Posts: 13 Rep Power: 16	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 likes this.

October 23, 2014, 19:57	FFT tutorial link	#4
scott_rumage Senior Member Scott Rumage Join Date: May 2009 Location: Seattle, WA Posts: 152 Rep Power: 17	Here is a link to a tutorial on performing FFT in Tecplot 360 EX: https://www.youtube.com/watch?v=hDhhpH0fOMA Scott vivek05 likes this.

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