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Thread Subject:
FRF of a time series data.

Subject: FRF of a time series data.

From: Krishna Kumar

Date: 19 Jan, 2011 06:23:04

Message: 1 of 4

Hi everyone,
                I am writing a code for damage identification in structures (output-only). I need to find frf for time series data for this . Can anyone help me to calculate FRF using the output data alone.

Subject: FRF of a time series data.

From: Wayne King

Date: 20 Jan, 2011 13:23:03

Message: 2 of 4

"Krishna Kumar" <skrishnakumar.accet@gmail.com> wrote in message <ih6008$6th$1@fred.mathworks.com>...
> Hi everyone,
> I am writing a code for damage identification in structures (output-only). I need to find frf for time series data for this . Can anyone help me to calculate FRF using the output data alone.

Hi Krishna, I don't see how you can estimate the transfer function of a system (an operator) if you only observe the output without any knowledge of the input. You can certainly estimate the power spectral density (PSD) of the output. The Signal Processing Toolbox has both nonparametric and parametric PSD estimators. If you have some a priori information about the system, you may be able to parametrize the PSD and obtain a smooth PSD estimate.

Wayne

Subject: FRF of a time series data.

From: Krishna Kumar

Date: 21 Jan, 2011 04:10:21

Message: 3 of 4

"Wayne King" <wmkingty@gmail.com> wrote in message <ih9cvn$mmn$1@fred.mathworks.com>...
> "Krishna Kumar" <skrishnakumar.accet@gmail.com> wrote in message <ih6008$6th$1@fred.mathworks.com>...
> > Hi everyone,
> > I am writing a code for damage identification in structures (output-only). I need to find frf for time series data for this . Can anyone help me to calculate FRF using the output data alone.
>
> Hi Krishna, I don't see how you can estimate the transfer function of a system (an operator) if you only observe the output without any knowledge of the input. You can certainly estimate the power spectral density (PSD) of the output. The Signal Processing Toolbox has both nonparametric and parametric PSD estimators. If you have some a priori information about the system, you may be able to parametrize the PSD and obtain a smooth PSD estimate.
>
> Wayne
Hi Wayne,
             Yes Wayne, I learnt that i certainly need the input data. I am trying to give a white noise input to the system and use it for FRF generation. Is there any function is MATLAB to do this ? Plz clarify.

Subject: FRF of a time series data.

From: Gaurav

Date: 30 May, 2012 16:22:09

Message: 4 of 4

"Krishna Kumar" wrote in message <ihb0vd$egk$1@fred.mathworks.com>...
> "Wayne King" <wmkingty@gmail.com> wrote in message <ih9cvn$mmn$1@fred.mathworks.com>...
> > "Krishna Kumar" <skrishnakumar.accet@gmail.com> wrote in message <ih6008$6th$1@fred.mathworks.com>...
> > > Hi everyone,
> > > I am writing a code for damage identification in structures (output-only). I need to find frf for time series data for this . Can anyone help me to calculate FRF using the output data alone.
> >
> > Hi Krishna, I don't see how you can estimate the transfer function of a system (an operator) if you only observe the output without any knowledge of the input. You can certainly estimate the power spectral density (PSD) of the output. The Signal Processing Toolbox has both nonparametric and parametric PSD estimators. If you have some a priori information about the system, you may be able to parametrize the PSD and obtain a smooth PSD estimate.
> >
> > Wayne
> Hi Wayne,
> Yes Wayne, I learnt that i certainly need the input data. I am trying to give a white noise input to the system and use it for FRF generation. Is there any function is MATLAB to do this ? Plz clarify.

No way......that is not used generally....we dont use white noise....input is like a shaker excitation - random/burst random/periodic chirp/sine or impulse force using hammer imparted on the structure. so once u have an input signal in freq domain and output signal(response) in freq domain. the frf is cross power spectrum divided by autopower of input.

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