# FFT:Frequency-Amplitude plot

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May 20, 2019, 22:44
FFT:Frequency-Amplitude plot
#1
Member

liyong
Join Date: Feb 2017
Posts: 66
Rep Power: 9
In the line plotting section, I use the Fast Fourier Transform(FFT) function to deal with cylinder pressure. After click preview FFT, a frequency spectrum figure appears, shown as in attachment. But the amplitude is surprisingly large. The original cylinder pressure is also attached. I think the amplitude is incorrect. the Y-coordinate is not the amplitude so what is that?
Attached Images
 pressure.jpg (44.1 KB, 30 views) prequency-amp.jpg (55.6 KB, 22 views)

 May 24, 2019, 10:54 #2 Senior Member     Sameera Wijeyakulasuriya Join Date: Jan 2016 Location: Convergent Science, Madison WI Posts: 117 Rep Power: 10 Hello, You should carry out the inverse FFT operation to obtain the filtered pressure from this calculator. Thanks, __________________ Sameera Wijeyakulasuriya Principal Engineer, Applications CONVERGECFD

May 25, 2019, 06:19
#3
Member

liyong
Join Date: Feb 2017
Posts: 66
Rep Power: 9
Quote:
 Originally Posted by SamWijey Hello, You should carry out the inverse FFT operation to obtain the filtered pressure from this calculator. Thanks,
I don't need the filtered pressure, and I just want to attain the frequency- amplitude. I want to know which frequency on which the pressure amplitude is large.

 Tags amplitude, fft, frequency

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