Natural Excitation Technique (NExT)

Returns impulse response functions (IRF) using Natural Excitation technique with time domain method and frequency domain method

Returns impulse response functions (IRF) using Natural Excitation technique with time domain method (NExTT) and frequency domain method (NExTF) for systems subjected to white noise excitation. Example file is provided for estimating IRF of 2DOF system subjected to Gaussian white noise excitation with added uncertainty (also Gaussian white noise) to the response.

1-function IRF= NExTT(data,refch,maxlags)

Inputs :

data: An array that contains response data.its dimensions are (nch,Ndata) where nch is the number of channels. Ndata is the total length of the data
refch: A vecor of reference channels .its dimensions (numref,1) where numref is number of reference channels
maxlags: Number of lags in cross-correlation function

Outputs :

IRF: Impulse Response Function matrix of size (nch,numref*(maxlags+1))

2-function IRF= NExTF(data,refch,window,N,p)

Inputs :

data: An array that contains response data.its dimensions are (nch,Ndata) where nch is the number of channels. Ndata is the total length of the data
refch: A vecor of reference channels .its dimensions (numref,1) where numref is number of reference channels
window: window size to get spectral density
N: Number of windows
p: overlap ratio between windows. from 0 to 1

Outputs :

IRF: Impulse Response Function matrix of size (nch,numref*(ceil(window/2+1)-1))

References:
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[1] James, G. H., Thomas G. Carne, and James P. Lauffer. "The natural excitation technique (NExT) for modal parameter extraction from operating structures." Modal Analysis-the International Journal of Analytical and Experimental Modal Analysis 10.4 (1995): 260.

[2] Al Rumaithi, Ayad, "Characterization of Dynamic Structures Using Parametric and Non-parametric System Identification Methods" (2014). Electronic Theses and Dissertations. 1325.
https://stars.library.ucf.edu/etd/1325

[3] Al-Rumaithi, Ayad, Hae-Bum Yun, and Sami F. Masri. "A Comparative Study of Mode Decomposition to Relate Next-ERA, PCA, and ICA Modes." Model Validation and Uncertainty Quantification, Volume 3. Springer, Cham, 2015. 113-133.