Experimental identification of distributed nonlinearities in the modal domain

Anastasio, Dario; Marchesiello, Stefano; Kerschen, Gaëtan; Noël, Jean-Philippe

doi:10.1016/j.jsv.2019.07.005

Cited by 16 publications

(9 citation statements)

References 22 publications

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“…However, it has not been applied to structures with geometrical Fig. 19 Comparison of the NNM shapes extracted from the HFS (solid lines) with the ones determined from the identified nonlinear modal constants (dashed lines) at various displacement amplitude levels of the driving point nonlinearity. The main contribution of this current paper is the validation of the framework on the identification of a doubleclamped thin beam that exhibits continuously distributed geometrical nonlinearity due to large amplitude oscillations.…”

Section: Discussionmentioning

confidence: 99%

“…Although the NNM-based system identification approaches [7,9,13,15] mentioned above are potentially suitable for the identification of distributed nonlinearities, to the best knowledge of the authors, only the PLL technique [16] and the method proposed in [18] were experimentally validated on structures that exhibit continuously distributed geometrical nonlinearity. Recently, there have been also other interesting attempts [19,20] that use a modal perspective somewhat different than the NNM perspective for the identification of geometrically nonlinear structures. In [19], a double-clamped thin beam was identified by processing the experimental data measured under broadband Gaussian excitation with an ad-hoc version of the nonlinear subspace identification (NSI) algorithm [21,22].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, there have been also other interesting attempts [19,20] that use a modal perspective somewhat different than the NNM perspective for the identification of geometrically nonlinear structures. In [19], a double-clamped thin beam was identified by processing the experimental data measured under broadband Gaussian excitation with an ad-hoc version of the nonlinear subspace identification (NSI) algorithm [21,22]. On the other hand, the method proposed in [20] determines the nonlinear stiffness and damping coefficients of a parametric model by using residuals obtained from the correlation of measured dynamics at low and high vibration levels.…”

Section: Introductionmentioning

confidence: 99%

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Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Karaağaçlı

Özgüven

2021

Exp Mech

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Background Various nonlinear system identification methods applicable to distributed nonlinearities have been developed over the last decade. However, many of them are not eligible to accurately quantify a high degree of nonlinearity. Furthermore, there exist few studies that actually validate the identified nonlinear properties. Objective The main objective of this paper is the validation of a novel nonlinear system identification framework recently developed by the authors on a double-clamped thin beam structure that exhibits continuously distributed strong geometrical nonlinearity due to large amplitude oscillations and considerable damping nonlinearity due to micro-slip in the beam-base connections. Methods The identification framework consists of response-controlled stepped-sine testing (RCT) and the harmonic force surface (HFS) concept. The framework is implemented by using standard hardware and software in modal testing. The RCT approach is based on keeping the displacement amplitude of the driving point constant throughout the frequency sweep and its basic assumptions are well-separated modes and no internal resonance. Constant-force frequency response curves and backbone curves of the first nonlinear normal mode (NNM) are identified at multiple measurement points from HFSs constructed by using measured harmonic excitation force spectra. The NNM shapes of the first mode at various vibration levels are then constructed from the identified NNM backbone curves. On the other side, the response level-dependent modal parameters are identified by applying standard linear modal analysis techniques to frequency response functions (FRFs) measured at constant displacement amplitude levels throughout RCT. ResultsThe RCT-HFS framework quantifies about a 20% shift of the natural frequency and an order of magnitude change of the modal damping ratio (from 0.5% to 4%) for the first mode of the double-clamped beam, which indicates a considerably high degree of stiffness and damping nonlinearities in the vibration range of interest. The identified nonlinear modal parameters are successfully validated by comparing near-resonant constant-force frequency response curves synthesized from these parameters with the ones measured by constant-force stepped-sine testing and with the ones extracted from the HFSs. The HFSs are determined for the first time in an experiment at multiple measurement points other than the driving point. The NNM shapes determined from HFSs are also validated by comparing them with the ones obtained from the identified nonlinear modal constants. Conclusions The RCT-HFS framework is successfully validated for the first time on a structure that exhibits continuously distributed geometrical nonlinearity. This study is a humble contribution towards making nonlinear experimental modal analysis a standard engineering practice.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Karaağaçlı

Özgüven

2021

Exp Mech

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“…In [6], the proposed method is successfully applied to a circular plate and a Chinese gong but fails in the case of a piezoelectric cantilever beam where the backbone curves are almost straight lines which cannot be represented with quadratic and cubic coefficients. Another interesting technique is proposed in [9], where a clamped-clamped beam is identified by applying an ad hoc version of the nonlinear subspace identification (NSI) algorithm [10,11] to the experimental data measured under broadband Gaussian excitation. This technique takes into account the modal interactions; however, it requires the experimental extraction of linear normal modes which may not always be determined accurately by using low-excitation level tests especially in the case of friction type of nonlinearity which is widely encountered in many engineering systems comprising mechanical joints (e.g., bolted connections).…”

Section: Introductionmentioning

confidence: 99%

Experimental Modal Analysis of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Karaağaçlı

Özgüven

2021

Conference Proceedings of the Society for Experimental Mechanics Series

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The everlasting competition in the industry to achieve higher performance in aircraft, satellites, and wind turbines encourages lightweight design more than ever, which eventually gives birth to more flexible engineering structures exhibiting large deformations in operational conditions. Accordingly, continuously distributed geometrical nonlinearity resulting from large deformations is currently an important design consideration. Being guided with this motivation, this paper investigates the performance of a recently developed promising nonlinear experimental modal analysis method on a clamped-clamped beam structure which exhibits geometrical nonlinearity continuously distributed throughout the entire structure. The method is based on response-controlled stepped-sine testing (RCT) where the displacement amplitude of the excitation point is kept constant during the frequency sweep. In this study, the nonlinear beam structure is instrumented with multiple accelerometers at several different locations along its length and is excited at a single point. Tests are conducted at energy levels where no internal resonance occurs, yet the beam structure exhibits strong stiffening nonlinearity which results in jump phenomenon in the case of classical constant-force sine testing. Nonlinear modal parameters are experimentally identified as functions of modal amplitude by applying standard linear modal identification methods to quasi-linear frequency response functions (FRFs) measured with RCT. Validation of the identified modal parameters is accomplished by comparing the constant-force FRFs synthesized using the identified modal parameters with the ones obtained from constant force testing and also with the ones extracted from the harmonic force surface (HFS).

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“…Most structural systems show a certain extent of nonlinearity associated with different sources [ 12 , 13 ]. However, neglecting the nonlinearity is acceptable in many cases for the sake of simplification of analysis [ 14 , 15 ]. In other cases, nonlinear behavior plays a dominant role.…”

Section: Introductionmentioning

confidence: 99%

A Critical Review of Nonlinear Damping Identification in Structural Dynamics: Methods, Applications, and Challenges

Al-hababi

Cao

Saleh

et al. 2020

Sensors

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In recent decades, nonlinear damping identification (NDI) in structural dynamics has attracted wide research interests and intensive studies. Different NDI strategies, from conventional to more advanced, have been developed for a variety of structural types. With apparent advantages over classical linear methods, these strategies are able to quantify the nonlinear damping characteristics, providing powerful tools for the analysis and design of complex engineering structures. Since the current trend in many applications tends to more advanced and sophisticated applications, it is of great necessity to work on developing these methods to keep pace with this progress. Moreover, NDI can provide an effective and promising tool for structural damage detection purposes, where the changes in the dynamic features of structures can be correlated with damage levels. This review paper provides an overview of NDI methods by explaining the fundamental challenges and potentials of these methods based on the available literature. Furthermore, this research offers a comprehensive survey of different applications and future research trends of NDI. For potential development and application work for nonlinear damping methods, the anticipated results and recommendations of the current paper can assist researchers and developers worldwide to find out the gaps and unsolved issues in the field of NDI.

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Experimental identification of distributed nonlinearities in the modal domain

Cited by 16 publications

References 22 publications

Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Experimental Quantification and Validation of Modal Properties of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

Experimental Modal Analysis of Geometrically Nonlinear Structures by Using Response-Controlled Stepped-Sine Testing

A Critical Review of Nonlinear Damping Identification in Structural Dynamics: Methods, Applications, and Challenges

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