Modal testing of nonlinear vibrating structures based on nonlinear normal modes: Experimental demonstration

in Mechanical Systems & Signal Processing (2011), 25

Nonlinear Normal Modes of a Full-Scale Aircraft

in 29th International Modal Analysis Conference, Jacksonville, 2011 (2011)

Detection of nonlinearity in a dynamic system using deformation modes obtained from the wavelet transform of measured responses

in Shock and Vibration (2010), 17(4-5), 491-506

An efficient approach to Structural Health Monitoring of dynamical systems based on the Wavelet Transform (WT) and the concept of subspace angle is presented. The objective is to propose a detection ... [more ▼]

An efficient approach to Structural Health Monitoring of dynamical systems based on the Wavelet Transform (WT) and the concept of subspace angle is presented. The objective is to propose a detection method that is sensitive to the onset of nonlinear behaviour in a dynamic system. For this purpose, instantaneous frequencies are identified first from output-only vibration signals using the Wavelet Transform. Time varying deformation shapes are then extracted by analyzing the whole measurement data set on the structure. From this information, different dynamic states of the structure may be detected by inspecting time variations of 'modal' features. The experimental structure considered here as application example is a clamped beam with a geometric nonlinearity. Detection of nonlinearity is carried out by means of the concept of subspace angles between instantaneous deformation modes extracted from measurement data using the continuous Wavelet Transform. The method consists in controlling the angular coherence between active subspaces of the current and reference states respectively. The proposed technique, which shows a good sensitivity to small changes in the dynamic behaviour of the structure, may also be used for damage detection. [less ▲]

Experimental modal analysis of nonlinear vibrating structures using nonlinear normal modes

in IV European Conference on Computational Mechanics, Paris, 2010 (2010)

Nonlinear normal modes, Part 1: Useful framework for the structural dynamicist

in Mechanical Systems & Signal Processing (2009), 23

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartII.BecausethereisvirtuallynoapplicationoftheNNMstolarge-scale engineeringstructures ... [more ▼]

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartII.BecausethereisvirtuallynoapplicationoftheNNMstolarge-scale engineeringstructures,thesepapersareanattempttohighlightseveralaspectsthat mightdrivetheirdevelopmentinthefuture.Specifically,wesupportthat(i)numerical methodsforthecontinuationofperiodicsolutionspavethewayforaneffectiveand practical computationofNNMs,and(ii)time–frequencyanalysisisparticularlysuitable fortheanalysisoftheresultingdynamics.Anotherobjectiveofthepresentpaperisto describe,insimpleterms,andtoillustratethefundamentalpropertiesofNNMs.Thisis achievedtoconvincethestructuraldynamicistnotnecessarilyacquaintedwiththemthat theyareausefulframeworkfortheanalysisofnonlinearvibratingstructures. & 2008ElsevierLtd.Allrightsreserved [less ▲]

Nonlinear normal modes, Part 2: Toward a pratical computation using numerical continuation techniques

in Mechanical Systems & Signal Processing (2009), 23

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartI.OnereasonofthestilllimiteduseofNNMsinstructuraldynamicsis that theircomputationisoftenregardedasimpractical ... [more ▼]

The conceptofnonlinearnormalmodes(NNMs)isdiscussedinthepresentpaperandits companion,PartI.OnereasonofthestilllimiteduseofNNMsinstructuraldynamicsis that theircomputationisoftenregardedasimpractical.However,whenresortingto numericalalgorithms,weshowthattheNNMcomputationispossiblewithlimited implementationeffort,whichpavesthewaytoapracticalmethodfordeterminingthe NNMsofnonlinearmechanicalsystems.Theproposedalgorithmreliesontwomain techniques,namelyashootingprocedureandamethodforthecontinuationofNNM motions. Thealgorithmisdemonstratedusingfourdifferentmechanicalsystems,a weakly andastronglynonlineartwo-degree-of-freedomsystem,asimplifieddiscrete modelofanonlinearbladeddiskandanonlinearcantileverbeamdiscretizedbythefinite elementmethod. [less ▲]

On modal interactions in strongly nonlinear systems

in Euromech 503, Nonlinear Normal Modes, Dimension Reduction and Localization in Vibrating Systems, Frascati, 2009 (2009)

Modal testing of nonlinear vibrating structures based on a nonlinear extension of force appropriation

in ASME International Design Engineering Technical Conferences, San Diego, 2009 (2009)

Nonlinear modal analysis and energy localization in a bladed disk assembly

in ASME Turbo Expo 2008: Power for Land, Sea and Air, Berlin, 2008 (2008, June)

The objective of this study is to carry out modal analysis of nonlinear periodic structures using nonlinear normal modes (NNMs). The NNMs are computed numerically with a method developed in [18] that is ... [more ▼]

The objective of this study is to carry out modal analysis of nonlinear periodic structures using nonlinear normal modes (NNMs). The NNMs are computed numerically with a method developed in [18] that is using a combination of two techniques: a shooting procedureand a method for the continuation of periodic motion. The proposed methodology is applied to a simplified model of a perfectly cyclic bladed disk assembly with 30 sectors. The analysis shows that the considered model structure features NNMs characterized by strong energy localization in a few sectors. This feature has no linear counterpart, and its occurrence is associated with the frequencyenergy dependence of nonlinear oscillations. [less ▲]

Computation of nonlinear normal modes, part II: numerical continuation in Auto

in Sixth EUROMECH Nonlinear Dynamics Conference, Saint Petersbourg, 2008 (2008)

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companion, Part I. Because there is virtually no application of the NNMs to large-scale engineering structures, these ... [more ▼]

The concept of nonlinear normal modes (NNMs) is discussed in the present paper and its companion, Part I. Because there is virtually no application of the NNMs to large-scale engineering structures, these papers are an attempt to highlight one aspect that might drive their development in the future. Specifically, we support that numerical methods for the continuation of periodic solutions pave the way for an effective and practical computation of NNMs. In this context, we show that the NNMs computation is possible using an existing continuation software, namely AUTO07. This is demonstrated using a 2DOF nonlinear system. The results are compared with those obtained with the Matlab algorithm described in Part I. [less ▲]