topic FFT domain switch in DIAdem
https://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4141505#M28430
<P>Good morning,</P>
<P>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 <STRONG>ω</STRONG>? The equation would be <STRONG>ω </STRONG>= 2*pi*f where f is the frequency.</P>
<P>Furthermore is there any way to plot the FTT output in wavenumber (k) domain provided that</P>
<P>k*U = 2*pi*f = <STRONG>ω</STRONG></P>
<P>where U is the mean velocity that I can easily calculate? </P>
<P>So that would be 3 functions:</P>
<P>AplitudePeak(frequency) <-> AmplitudePeak(angular frequency) <-> AmplitudePeak(Wavenumber)</P>
<P> </P>
<P>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.</P>
<P> </P>
<P>Thank you in advance</P>
<P> </P>
<P> </P>
<P> </P>Thu, 08 Apr 2021 16:17:01 GMTFrutis2021-04-08T16:17:01ZFFT domain switch
https://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4141505#M28430
<P>Good morning,</P>
<P>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 <STRONG>ω</STRONG>? The equation would be <STRONG>ω </STRONG>= 2*pi*f where f is the frequency.</P>
<P>Furthermore is there any way to plot the FTT output in wavenumber (k) domain provided that</P>
<P>k*U = 2*pi*f = <STRONG>ω</STRONG></P>
<P>where U is the mean velocity that I can easily calculate? </P>
<P>So that would be 3 functions:</P>
<P>AplitudePeak(frequency) <-> AmplitudePeak(angular frequency) <-> AmplitudePeak(Wavenumber)</P>
<P> </P>
<P>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.</P>
<P> </P>
<P>Thank you in advance</P>
<P> </P>
<P> </P>
<P> </P>Thu, 08 Apr 2021 16:17:01 GMThttps://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4141505#M28430Frutis2021-04-08T16:17:01ZRe: FFT domain switch
https://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4143069#M28441
<P>Hi Frutis,</P>
<P>In DIAdem there is no parameter for the FFT function to do this, but it is easy to calculate it afterwards.</P>
<P>For this you can use the Calculator with this equation:<BR /><BR />ch("[1]/angular frequency")= 2 * Pi * ch("[1]/Frequency")</P>
<P><BR />or this in a script:</P>
<P> </P>
<P>Call Calculate("ch(""[1]/angular frequency"")= 2 * Pi * ch(""[1]/Frequency"")")</P>
<P> </P>
<P>Similar things can be done for the Wavenumber.</P>
<P> </P>
<P>Greetings</P>
<P>Walter</P>Thu, 15 Apr 2021 06:17:46 GMThttps://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4143069#M28441Walter_Rick2021-04-15T06:17:46ZRe: FFT domain switch
https://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4148553#M28482
<P>Hi Frutis,</P>
<P> </P>
<P>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.</P>
<P> </P>
<P>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.</P>
<P> </P>
<P>Brad Turpin</P>
<P>Principal Technical Support Engineer</P>
<P>NI</P>Thu, 06 May 2021 20:58:52 GMThttps://forums.ni.com/t5/DIAdem/FFT-domain-switch/m-p/4148553#M28482Brad_Turpin2021-05-06T20:58:52Z