converting to RMS value from Harmonic response spectrum

  • Last Post 03 May 2019
Hadi96 posted this 26 March 2019

Good Day,

Dear Guys,

I had a problem to converting spectrum data to Rms Value, i did not want the negative value to be appeared , how can i do it?

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vishavjeet062 posted this 03 May 2019

how can @Hadi96 ,you get a amplitude graph ?

have to apply the rotating force and fixed rotation 

Hadi96 posted this 30 March 2019

Thank you for your help sir, i had change to amplitude, are you sure it indicate the RMS value, since its look too different between the imiginary result before




jj77 posted this 29 March 2019

RMS is more for summing stresses in response spectrum analysis (PSD or response spectra/earthquake say).


I think you mean amplitude.


The FRF is a complex function/number, and you are showing the imaginary part of that complex number.


Complex numbers and FRFS can be represented thus by a phase and an amplitude (positive number). Thus for complex number z:

z = x + i*y = ¦z¦*exp(i*phase),


So you need/mean the amplitude of the FRF which is:



You can set amplitude under details, options, and display in the frequency response.

Search the ansys help manual for:

Frequency Response and Phase Response

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kcao posted this 29 March 2019

I am not sure if I understand your question. RMS means root mean squared. You will square the value, so eventually everything is positive under square root.


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