Reduced Order Nonlinear System Identification Methodology

AIAA Journal ◽  
2006 ◽  
Vol 44 (8) ◽  
pp. 1895-1904 ◽  
Author(s):  
Peter J. Attar ◽  
Earl H. Dowell ◽  
John R. White ◽  
Jeffrey P. Thomas
Keyword(s):  
System Identification ◽  
Nonlinear System ◽  
Nonlinear System Identification ◽  
Reduced Order

Nonlinear System Identification of Frictional Connections in a Bolted Beam Assembly

2012 ◽  
Author(s):  
Melih Eriten ◽  
Mehmet Kurt ◽  
Guanyang Luo ◽  
Donald M. McFarland ◽  
Lawrence A. Bergman ◽  
...  
Keyword(s):  
System Identification ◽  
Nonlinear System ◽  
Energy Levels ◽  
Nonlinear System Identification ◽  
Flow Analysis ◽  
Nonlinear Damping ◽  
Experimental Measurements ◽  
Slow Flow ◽  
Reduced Order Models ◽  
Reduced Order

In modern structures, mechanical joints are ubiquitous, significantly influencing a structure’s dynamics. Frictional connections contained in a joint provide coupling of forces and moments between assembled components as well as localized nonlinear energy dissipation. Certain aspects of the mechanics of these friction connections are yet to be fully understood and characterized in a dynamical systems framework. This work applies a nonlinear system identification (NSI) technique to characterize the influence of frictional connections on the dynamics of a bolted beam assembly. The methodology utilized in this work combines experimental measurements with slow-flow dynamic analysis and empirical mode decomposition, and reconstructs the dynamics through reduced-order models. These are in the form of single-degree-of-freedom linear oscillators (termed intrinsic modal oscillators — IMOs) with forcing terms derived directly from the experimental measurements through slow-flow analysis. The derived reduced order models are capable of reproducing the measured dynamics, whereas the forcing terms provide important information about nonlinear damping effects. The NSI methodology is applied to model nonlinear friction effects in a bolted beam assembly. A ‘monolithic’ beam with identical geometric and material properties is also tested for comparison. Three different forcing (energy) levels are considered in the tests in order to study the energy-dependencies of the damping nonlinearities induced in the beam from the bolted joint. In all cases, the NSI technique employed is successful in identifying the damping nonlinearities, their spatial distributions and their effects on the vibration modes of the structural component.

Nonlinear System Identification of a Cantilever Beam With Attached Cubic Nonlinear Spring at Its Free End

2012 ◽  
Author(s):  
Mehmet Kurt ◽  
Melih Eriten ◽  
D. Michael McFarland ◽  
Lawrence A. Bergman ◽  
Alexander F. Vakakis
Keyword(s):  
System Identification ◽  
Nonlinear System ◽  
Cantilever Beam ◽  
Nonlinear System Identification ◽  
Original System ◽  
Slow Flow ◽  
Reduced Order Models ◽  
Essential Information ◽  
Nonlinear Spring ◽  
Reduced Order

This paper presents the identification of the local nonlinear effects on the essential dynamics of distributed parameter systems. The system considered is a simple cantilever beam with an attached cubic nonlinear spring at its tip. Nonlinear system identification (NSI) method applied in this work uses numerical simulation results and combines slow-flow dynamic analysis and empirical mode decomposition (EMD) to reconstruct the dynamics in modal coordinates as reduced-order models. The reduced-order models are single-degree-of-freedom linear oscillators, which are termed intrinsic modal oscillators (IMOs), with a forcing computed through slow-flow analysis. These forced oscillators are capable of reproducing the modal dynamics, and their forcing amplitudes provide essential information about modal interactions and energy transfer. The proposed NSI method was applied to 3 main cases, corresponding to weakly nonlinear, strongly nonlinear and linear dynamics, respectively. A discrete model of the original system is used to investigate the internal resonances and nonlinearity effects in the original system, by making use of Frequency-Energy plots (FEPs).

scholarly journals Bolt loosening detection in a jointed beam using empirical mode decomposition–based nonlinear system identification method

2019 ◽  
Vol 15 (9) ◽  
pp. 155014771987565 ◽  
Author(s):  
Chao Xu ◽  
Chen-Chen Huang ◽  
Wei-Dong Zhu
Keyword(s):  
System Identification ◽  
Nonlinear System ◽  
Nonlinear System Identification ◽  
Reduced Order Model ◽  
Order Model ◽  
Reduced Order ◽  
System Identification Method ◽  
Identification Method ◽  
Mode Decomposition ◽  
Bolt Loosening

In this work, a state-of-art nonlinear system identification method based on empirical mode decomposition is utilized and extended to detect bolt loosening in a jointed beam. This nonlinear system identification method is based on identifying the multi-scale dynamics of the underlying system. Only structural dynamic response signals are needed to construct a reduced-order model to represent the system concerned. It makes the method easy to use in practice. A new bolt loosening identification procedure based on the constructed system nonlinear reduced-order model is proposed. A new damage feature to indicate bolt loosening is presented. Experimental works are carried out to validate the proposed method. The results show that the proposed damage detection method can detect bolt loosening effectively, and the proposed damage feature values increase with the increase of bolt torques. The damage feature calculated from the response solution of the reduced-order model can give robust and sensitive indication of bolt loosening.

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