NExT-ERA with Mode Condensation

Natural Excitation Technique with Eigensystem Realization Algoirthm including Mode Condensation Algorithm

Natural Excitation Technique (Frequency method and Time method) with Eigensystem Realization Algoirthm and Mode Condensation Algorithm.

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.

1-Time Domain NExT-ERA with Mode Condensation

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[Result] = NExTTERA_CONDENSED(data,refch,maxlags,fs,ncols,nrows,initialcut,maxcut,shift,EMAC_option,LimCMI,LimMAC,LimFreq,Plot_option)

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 (The algorithm takes each reference channel separately)

maxlags: Number of lags in cross-correlation function

fs: Sampling frequency

ncols: The number of columns in hankel matrix (more than 2/3*(maxlags+1) )

nrows: The number of rows in hankel matrix (more than 20 * number of modes)

initialcut: initial cutoff value of mode order

maxcut: maximium cutoff value of mode order

shift: Shift value in the final row and column blocks (Increase EMAC sensitivity) usually =10

EMAC_option: if this value equals to 1, EMAC will be independent of the number of columns (calculated only from observability matrix not from controllability)

LimCMI: Minmium allowable CMI for modes

LimMAC & LimFreq: Minimium value of MAC and maximium value of frequency difference to assume two modes are referring to the same real mode

Plot_option: if 1 plots stabilization diagram

Outputs :

Result: A structure consist of the below components

Parameters: NaFreq : Natural frequencies vector

DampRatio: Damping ratios vector

ModeShape: Mode shape matrix

Indicators: MAmC : Modal Amplitude Coherence

EMAC: Extended Modal Amplitude Coherence

MPC: Modal Phase Collinearity

CMI: Consistent Mode Indicator

2-Frequency Domain NExT-ERA with Mode Condensation

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[Result] = NExTFERA_CONDENSED(data,refch,window,N,p,fs,ncols,nrows,initialcut,maxcut,shift,EMAC_option,LimCMI,LimMAC,LimFreq,Plot_option)

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 (The algorithm takes each reference channel separately)

window: window size to get spectral density

N: Number of windows

p: overlap ratio between windows. from 0 to 1

fs: Sampling frequency

ncols: The number of columns in hankel matrix (more than 2/3*(ceil(window/2+1)-1) )

nrows: The number of rows in hankel matrix (more than 20 * number of modes)

initialcut: initial cutoff value of mode order

maxcut: maximium cutoff value of mode order

shift: Shift value in the final row and column blocks (Increase EMAC sensitivity) usually =10

EMAC_option: if this value equals to 1, EMAC will be independent of the number of columns (calculated only from observability matrix not from controllability)

LimCMI: Minmium allowable CMI for modes

LimMAC & LimFreq: Minimium value of MAC and maximium value of frequency difference to assume two modes are referring to the same real mode

Plot_option: if 1 plots stabilization diagram

Outputs :

Result: A structure consist of the below components

Parameters: NaFreq : Natural frequencies vector

DampRatio: Damping ratios vector

ModeShape: Mode shape matrix

Indicators: MAmC : Modal Amplitude Coherence

EMAC: Extended Modal Amplitude Coherence

MPC: Modal Phase Collinearity

CMI: Consistent Mode Indicator

References:

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[1] R. Pappa, K. Elliott, and A. Schenk, “A consistent-mode indicator for the eigensystem realization algorithm,” Journal of Guidance Control and Dynamics (1993), 1993.

[2] R. S. Pappa, G. H. James, and D. C. Zimmerman, “Autonomous modal identification of the space shuttle tail rudder,” Journal of Spacecraft and Rockets, vol. 35, no. 2, pp. 163–169, 1998.

[3] 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.

[4] 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

[5] 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.