FFT domain switch

[Frutis]

Good morning,

I have a question about FFT in Diadem. The output of FTT function is frequency (f) in Hz, is there any way to get the output in angular frequency ω? The equation would be  ω = 2*pi*f where f is the frequency.

Furthermore is there any way to plot the FTT output in wavenumber (k) domain provided that

k*U = 2*pi*f = ω

where U is the mean velocity that I can easily calculate? 

So that would be 3 functions:

AplitudePeak(frequency) <-> AmplitudePeak(angular frequency) <-> AmplitudePeak(Wavenumber)

I am new to signal processing and this is for turbulence spectra analysis from a velocity vs time signal from hot wire if this has any meaning.

Thank you in advance

[Walter_Rick]

Hi Frutis,

In DIAdem there is no parameter for the FFT function to do this, but it is easy to calculate it afterwards.

For this you can use the Calculator with this equation:

ch("[1]/angular frequency")= 2 * Pi * ch("[1]/Frequency")

or this in a script:

Call Calculate("ch(""[1]/angular frequency"")= 2 * Pi * ch(""[1]/Frequency"")")

Similar things can be done for the Wavenumber.

Greetings

Walter

[Brad_Turpin]

Hi Frutis,

For the conversion from frequency in Hz to angular frequency (omega), you could very easily select the unit conversion in DIAdem from [1/sec] to [rad/sec].  For the conversion to wavenumber you'd need to either use the Channel Calculator as Walter suggests or the linear scaling function in the "Basic Mathematics" palette of the ANALYSIS panel.

DIAdem 2020 and later has the ability to use formula channels for easy and repeated conversions, that might be a good way to use/re-use the formula approach that Walter suggests.

Brad Turpin

Principal Technical Support Engineer

NI