Subspace Identification Methods for Modal Analysis

Stochastic Subspace Identification(SSI), Deterministic Subspace Identification(DSI), Deterministic Stochastic Subspace Identification(DSSI)

System identification using subspace identification methods.

Along with the functions example file is provided for the identification of 2DOF system subject to gaussian white noise excitation with added uncertainty (also gaussian white noise) to both excitation and response.

Stochastic Subspace Identification(SSI)
function [Result]=SSI(output,fs,cut)

Input:
output: output data of size (No. output channels, No. of data)
fs: Sampling frequency
cut: cutoff value=2*no of modes

Outputs :
Result : A structure consist of the below components
Parameters : NaFreq : Natural frequencies vector
DampRatio : Damping ratios vector
ModeShape : Mode shape matrix
Matrices A,C: Discrete A and C matrices
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Deterministic Subspace Identification(DSI)
function [Result]=DSI(output,input,fs,cut)

Input:
output: output data of size (No. output channels, No. of data)
input: input data of size (No. input channels, No. of data)
fs: Sampling frequency
cut: cutoff value=2*no of modes

Outputs :
Result : A structure consist of the below components
Parameters : NaFreq : Natural frequencies vector
DampRatio : Damping ratios vector
ModeShape : Mode shape matrix
Matrices A,B,C,D: Discrete A,B,C and D matrices
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Deterministic Stochastic Subspace Identification(DSSI)
function [Result]=DSSI(output,input,fs,cut)

Input:
output: output data of size (No. output channels, No. of data)
input: input data of size (No. input channels, No. of data)
fs: Sampling frequency
cut: cutoff value=2*no of modes

Outputs :
Result : A structure consist of the below components
Parameters : NaFreq : Natural frequencies vector
DampRatio : Damping ratios vector
ModeShape : Mode shape matrix
Matrices A,B,C,D: Discrete A,B,C and D matrices

References:
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Van Overschee, Peter, and B. L. De Moor. Subspace identification for linear systems: Theory—Implementation—Applications. Springer Science & Business Media, 2012.