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Title:Methodology for nonlinear quantification of a cantilever beam with local nonlinearities
Author(s):Herrera, Christopher Angelo
Advisor(s):Bergman, Lawrence A.; Vakakis, Alexander F.
Contributor(s):McFarland, Donald M.
Department / Program:Aerospace Engineering
Discipline:Aerospace Engineering
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Nonlinear Dynamics
Proper Orthogonal Decomposition (POD)
Empirical Mode Decomposition (EMD)
Nonlinear Quantification
Abstract:This study presents a methodology for the identification of linear and nonlinear regions of operation for a system that behaves almost linearly in the limit of extreme values of (a) certain parameter(s). An Euler-Bernoulli cantilever beam with two nonlinear configurations is used to develop and validate the methodology. One configuration consists of a cantilever beam with a cubic spring attached at a specific distance from the beam root to achieve a smooth nonlinear effect. The other configuration is a cantilever beam undergoing vibro-impact between symmetrically-spaced stops. Both systems have the property that, in the limit of small and large values of a parameter, the system is almost linear and can be modeled with negligible error as fixed-free or fixed-pinned, depending on the configuration. For the beam with a cubic spring attachment, the forcing amplitude is the varied parameter. For the vibro-impact beam, the parameter is the clearance between the stops and the beam at static equilibrium. Proper orthogonal decomposition is employed to obtain an optimal basis used to describe the systems with varying parameter values. The frequencies of the modes that comprise the basis are estimated using the Rayleigh quotient. The variations of these frequencies are studied to successfully identify parameter values for which the system is approximately linear and those for which it is highly nonlinear. A criterion based on the Betti-Maxwell reciprocity theorem is used to validate the existence of nonlinear behavior for the set of parameter values suggested by the described methodology. It was found that transition regions in which the dynamics of the system shifted from one linear system to the other exist and that these regions occur for different sets of parameter values for each mode. The effect of heavy damping on proper orthogonal decomposition is found to be important, particularly for the vibro-impact beam, due the method's dependence on the system response. An attempt is also made to isolate parameter values for which transient resonance capture occurs and prove its existence through use of empirical mode decomposition and the Hilbert transform.
Issue Date:2015-07-21
Rights Information:Copyright 2015 Christopher Herrera
Date Available in IDEALS:2015-09-29
Date Deposited:August 201

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