Browse ORBi by ORBi project

- Background
- Content
- Benefits and challenges
- Legal aspects
- Functions and services
- Team
- Help and tutorials

Hysteresis identification using nonlinear state-space models Noël, Jean-Philippe ; ; Kerschen, Gaëtan et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January) Most studies tackling hysteresis identification in the technical literature follow white-box approaches, i.e. they rely on the assumption that measured data obey a specific hysteretic model. Such an ... [more ▼] Most studies tackling hysteresis identification in the technical literature follow white-box approaches, i.e. they rely on the assumption that measured data obey a specific hysteretic model. Such an assumption may be a hard requirement to handle in real applications, since hysteresis is a highly individualistic nonlinear behaviour. The present paper adopts a black-box approach based on nonlinear state-space models to identify hysteresis dynamics. This approach is shown to provide a general framework to hysteresis identification, featuring flexibility and parsimony of representation. Nonlinear model terms are constructed as a multivariate polynomial in the state variables, and parameter estimation is performed by minimising weighted least-squares cost functions. Technical issues, including the selection of the model order and the polynomial degree, are discussed, and model validation is achieved in both broadband and sine conditions. The study is carried out numerically by exploiting synthetic data generated via the Bouc-Wen equations. [less ▲] Detailed reference viewed: 52 (2 ULg)Robust Subspace Identification of a Nonlinear Satellite Using Model Reduction Dossogne, Tilàn ; Noël, Jean-Philippe ; Kerschen, Gaëtan in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January) The frequency-domain nonlinear subspace identification (FNSI) method has recently been successfully applied to large-scale nonlinear structures. One of the key features of FNSI is the nonlinear ... [more ▼] The frequency-domain nonlinear subspace identification (FNSI) method has recently been successfully applied to large-scale nonlinear structures. One of the key features of FNSI is the nonlinear generalisation of the stabilisation diagram. However, as in linear system identification, the selection of the model order in the diagram is complicated by the presence of spurious poles, resulting from noise and modelling errors. Spurious poles have been shown to strongly perturb the estimation of the nonlinear coefficients. The present paper establishes a constructive procedure to discriminate between spurious and genuine poles. This procedure is derived in modal space and is based on a dominancy index and on model reduction techniques. It is demonstrated on a complete satellite structure possessing nonsmooth nonlinearities and high modal density. Spurious frequency variations in the nonlinear coefficients are proved to be effectively removed, significantly improving the quality of the overall identified model. [less ▲] Detailed reference viewed: 28 (0 ULg)Experimental study of isolated response curves in a two-degree-of-freedom nonlinear system Detroux, Thibaut ; Noël, Jean-Philippe ; Kerschen, Gaëtan et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January) In the present paper, the observation and characterization of isolated response curves (IRCs) are experimentally reported in the case of a nonlinear system consisting of two masses sliding on an ... [more ▼] In the present paper, the observation and characterization of isolated response curves (IRCs) are experimentally reported in the case of a nonlinear system consisting of two masses sliding on an horizontal guide. Transverse springs are attached to one mass to provide the nonlinear restoring force, and a harmonic motion of the complete system is imposed by prescribing the displacement of their supports. The existence of an IRC is related to a 3:1 internal resonance between the two modes of the system. The observed IRC is studied in detached and merged conditions using swept-sine excitations and system perturbations. [less ▲] Detailed reference viewed: 37 (9 ULg)Obtaining nonlinear frequency responses from broadband testing Gourc, Etienne ; Grappasonni, Chiara ; Noël, Jean-Philippe et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIV (2016, January) The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a ... [more ▼] The objective of the paper is to obtain the frequency response curves of nonlinear mechanical systems from broadband testing. The proposed approach consists in coupling an identification method with a continuation method. Specifically, the frequency-domain nonlinear subspace identification (FNSI) method is first used to derive an experimental model of the structure in state space from broadband measurements. The harmonic balance method coupled with arclength continuation then utilizes this experimental model to compute the frequency response curves of the system. The method is demonstrated using a numerical example. [less ▲] Detailed reference viewed: 38 (3 ULg)Bifurcation analysis of a spacecraft structure using the harmonic balance method Detroux, Thibaut ; Renson, Ludovic ; Masset, Luc et al in Proceedings of the ASME 2015 International Design Engineering Technical Conferences (2015, August) The harmonic balance (HB) method has been widely used in the past few years, as a numerical tool for the study of nonlinear models. However, in its classical formulation the HB method is limited to the ... [more ▼] The harmonic balance (HB) method has been widely used in the past few years, as a numerical tool for the study of nonlinear models. However, in its classical formulation the HB method is limited to the approximation of periodic solutions. The present paper proposes to extend the method to the detection and tracking of bifurcations in the codimension-2 system parameters space. To validate the methodology, the forced response of a real spacecraft is examined. The paper first provides some numerical evidence of the presence of quasiperiodic oscillations and isolated solutions. It then demonstrates how the tracking of Neimark-Sacker and fold bifurcations can help get a deeper understanding of these attractors. [less ▲] Detailed reference viewed: 33 (5 ULg)Nonlinear ground vibration identification of an F-16 aircraft - Part 2: Understanding Nonlinear Behaviour in Aerospace Structures Using Sine-sweep Testing Dossogne, Tilàn ; Noël, Jean-Philippe ; Grappasonni, Chiara et al in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2015, June) Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic ... [more ▼] Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the analysis of sine-sweep measurements in order to get an insightful understanding about the nonlinear behaviour of the aircraft. To this extent, restoring force surface and wavelet transform methods are applied both on the collected GVT data and simulation results performed on a simple numerical model of the F-16 wing and its payload. [less ▲] Detailed reference viewed: 96 (14 ULg)A frequency-domain method for identifying nonlinear vibrating structures Noël, Jean-Philippe ; Dossogne, Tilàn ; Kerschen, Gaëtan Conference (2015, June) System identification, which refers to the construction of mathematical models from experimental data, plays a key role in the design process of engineering systems. In structural dynamics, the ... [more ▼] System identification, which refers to the construction of mathematical models from experimental data, plays a key role in the design process of engineering systems. In structural dynamics, the theoretical and experimental aspects of linear system identification have been successfully addressed since the early seventies, and mature analytical, computational and testing tools have emerged. Nonlinear system identification of vibrating structures has also enjoyed significant advances during the past few years. However, the common practice in industry is to ignore nonlinearities, arguably because their analysis is still regarded as impractical. The present work describes a rigorous nonlinear generalisation in the frequency domain of the classical subspace identification algorithms, termed FNSI method. This method is applicable to large-scale systems comprising strong nonlinearities, closely-spaced modes and potentially high, nonproportional damping. Another distinct advantage of the approach is that it offers a convenient way to select an appropriate order for the nonlinear model by means of stabilisation diagrams. The FNSI method is demonstrated in this study using a complete satellite structure with nonsmooth nonlinearities, and a solar panel assembly exhibiting complex nonlinear stiffness and damping mechanisms. [less ▲] Detailed reference viewed: 57 (7 ULg)Numerical study of intrinsic features of isolas in a 2-dof nonlinear system Detroux, Thibaut ; Noël, Jean-Philippe ; Masset, Luc et al in Proceedings of the ICEDyn conference (2015, June) In the present paper, isolated response curves in a nonlinear system consisting of two masses sliding on a horizontal guide are examined. Transverse springs are attached to one mass to provide the ... [more ▼] In the present paper, isolated response curves in a nonlinear system consisting of two masses sliding on a horizontal guide are examined. Transverse springs are attached to one mass to provide the nonlinear restoring force, and a harmonic motion of the complete system is imposed by prescribing the displacement of their supports. Numerical simulations are carried out to study the conditions of existence of isolated solutions, their bifurcations, their merging with the main response branch and their basins of attraction. This is achieved using tools including nonlinear normal modes, energy balance, harmonic balance-based continuation and bifurcation tracking, and global analysis. [less ▲] Detailed reference viewed: 53 (6 ULg)Nonlinear ground vibration identification of an F-16 aircraft - Part 1: Fast nonparametric analysis of distortions in FRF measurements ; ; et al in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2015, June) Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic ... [more ▼] Although they are generally modelled as linear systems, aircraft structures are known to be prone to nonlinear phenomena. A specific challenge encountered with fighter aircraft, besides aeroelastic nonlinearity, is the modelling of the wing-to-payload mounting interfaces. For large amplitudes of vibration, friction and gaps may be triggered in these connections and markedly impact the dynamic behaviour of the complete structure. In this series of two papers, the nonlinear dynamics of an F-16 aircraft is investigated using rigorous methods applied to real data collected during a ground vibration test campaign. The present work focuses on the detection, qualification and quantification of nonlinear distortions affecting frequency response function (FRF) measurements. The key idea of the approach is to excite the structure using a random signal with a user-defined amplitude spectrum, where only a set of well-selected frequencies is different from zero in the band of interest. It is demonstrated that this careful choice of the input frequencies allows, without any further user interaction, to quantify the importance of odd and even nonlinear distortions in the output spectra with respect to the noise level. At high excitation amplitude, the F-16 dynamics is found to exhibit substantial odd nonlinearities and less significant, yet not negligible, even nonlinearities. [less ▲] Detailed reference viewed: 100 (6 ULg)Nonlinear model updating by means of identified nonlinear normal modes ; Renson, Ludovic ; Noël, Jean-Philippe et al Conference (2015, June) Modal parameters are the most common features used for linear model updating. Although the modal analysis theory does not hold for nonlinear dynamic systems, its popularity encouraged researchers to come ... [more ▼] Modal parameters are the most common features used for linear model updating. Although the modal analysis theory does not hold for nonlinear dynamic systems, its popularity encouraged researchers to come up with an equivalent version of normal modes for nonlinear systems, i.e., nonlinear normal modes (NNMs). A nonlinear system vibrates in NNMs when all masses have periodic motions of the same period, and at any time, the position of all the masses is uniquely defined by the position of any one of them. This paper investigates the feasibility of nonlinear model updating by minimizing the difference between the model-predicted and measured/identified nonlinear normal modes. A two degree-of-freedom mass-spring system with three linear springs and a cubic nonlinear spring is considered as the case study. The energy-dependent natural frequency and NNM of the first vibration mode of the system are identified at three different levels of energy. The stiffness parameters of the system are estimated by minimizing an objective function which is defined as the discrepancy between model-predicted natural frequency and NNM of the first mode, and their identified counterparts at the three measured energy levels. Performance of the proposed updating approach is evaluated at different levels of noise and different levels of modeling errors (i.e., nonlinear model classes). [less ▲] Detailed reference viewed: 75 (2 ULg)Testing of a Spacecraft Structure with Non-Smooth Nonlinearities Renson, Ludovic ; Noël, Jean-Philippe ; Kerschen, Gaëtan Conference (2015, May) The dynamics of the SmallSat, a real-life spacecraft possessing a complex isolation device with multiple nonsmooth nonlinearities is investigated. Experiments show that nonlinearities induce modal ... [more ▼] The dynamics of the SmallSat, a real-life spacecraft possessing a complex isolation device with multiple nonsmooth nonlinearities is investigated. Experiments show that nonlinearities induce modal interactions between modes with non-commensurate linear frequencies. A model of the structure with a simplified description of the nonlinear connections is first built using techniques available in industry. Numerical continuation is then exploited to compute nonlinear normal modes and uncover interaction phenomena that can jeopardize the structural integrity. [less ▲] Detailed reference viewed: 25 (9 ULg)Measuring nonlinear distortions: from test case to an F-16 fighter ; ; et al Conference (2015, March) What are the similarities and differences between the behavior of a small vibrating test system and an F-16 fighter? To find it out, we compare measurements of the test system to measurements from the ... [more ▼] What are the similarities and differences between the behavior of a small vibrating test system and an F-16 fighter? To find it out, we compare measurements of the test system to measurements from the bolted connection of the wing and the missile of a F-16 Fighter Falcon from the Belgian air force. These measurements were done during a ground vibration test (GVT) campaign. Essentially, the behavior of these systems match, even though the test system is only the heart of a self-study kit for nonlinear system identification and the F-16 is a complex real life mechanical structure. This clearly shows the added value of an experiment driven nonlinear educational system identification package. It provides safe small-scale toy examples for hands-on exercises that react like real systems. We believe that this practical approach lowers the gap between learning system identification concepts and applying it on real systems. [less ▲] Detailed reference viewed: 61 (17 ULg)A comparison of grey-box and black-box approaches in nonlinear state-space modelling and identification Noël, Jean-Philippe ; ; Kerschen, Gaëtan Conference (2015, March) In the present contribution, it is shown that, in the case of mechanical systems where nonlinearities are physically localised, the general structure of black-box nonlinear state-space models can be ... [more ▼] In the present contribution, it is shown that, in the case of mechanical systems where nonlinearities are physically localised, the general structure of black-box nonlinear state-space models can be drastically simplified. A more parsimonious, grey-box state-space representation is derived, which is found to be compatible with Newton's second law of dynamics. For demonstration purposes, black-box and grey-box state-space models of the Silverbox benchmark, i.e. an electrical mimicry of a single-degree-of-freedom mechanical system with cubic nonlinearity, are identified using a maximum likelihood estimator. It is found that the grey-box approach allows to reduce markedly modelling errors with respect to a black-box model with a comparable number of parameters. It is also suggested that the greater accuracy of the grey-box model lends itself to the computation of reliable confidence bounds on the model parameters. [less ▲] Detailed reference viewed: 34 (2 ULg)Experimental nonlinear identification of an aircraft with bolted connections ; Noël, Jean-Philippe ; Kerschen, Gaëtan et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February) Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling ... [more ▼] Aircraft structures are known to be prone to nonlinear phenomena, especially as they constantly become lighter and hence more flexible. One specific challenge that is regularly encountered is the modeling of the mounting interfaces between aircraft subcomponents. Indeed, for large amplitudes of vibration, such interfaces may loosen and, in turn, trigger complex mechanisms such as friction and clearances. In this context, the present work intends to investigate the nonlinear dynamics of the Morane–Saulnier Paris aircraft, accessible at ONERA. This aircraft possesses multiple bolted connections between two external fuel tanks and wing tips. The objective of the paper is specifically to carry out an adequate identification of the numerous nonlinearities affecting the dynamics of this full-scale structure. Nonlinearity detection and the subsequent subspace-based parameter estimation have been performed on experimental data, collected during an on-ground test campaign. Nonlinearity detection is first achieved by the comparison of frequency response functions estimated at low excitation level, with those obtained at high amplitude level, yielding insight towards accurately characterizing the behavior of the bolted connections. Then, a nonlinear subspace identification method is applied to measured data to estimate the linear and nonlinear parameters of the structure and novel strategies and tools that overcome specific arisen problems are developed. [less ▲] Detailed reference viewed: 86 (3 ULg)Experimental modal analysis of nonlinear structures using broadband data Noël, Jean-Philippe ; Renson, Ludovic ; Grappasonni, Chiara et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February) The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements ... [more ▼] The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements collected under broadband forcing. The use of such a type of forcing signal allows to excite multiple NNMs simultaneously and, in turn, to save testing time. A two-step methodology integrating nonlinear system identification and numerical continuation of periodic solutions is proposed for the extraction of the individual NNMs from broadband input and output data. It is demonstrated using a numerical cantilever beam possessing a cubic nonlinearity at its free end. The proposed methodology can be viewed as a nonlinear generalization of the phase separation techniques routinely utilized for experimental modal analysis of linear structures. The paper ends with a comparison between this new nonlinear phase separation technique and a previously-developed nonlinear phase resonance method. [less ▲] Detailed reference viewed: 80 (17 ULg)Isolated response curves in a base-excited, two-degree-of-freedom, nonlinear system Noël, Jean-Philippe ; Detroux, Thibaut ; Masset, Luc et al in Proceedings of the ASME 2015 International Design Engineering Technical Conferences (2015) In the present paper, isolated response curves in a nonlinear system consisting of two masses sliding on a horizontal guide are examined. Transverse springs are attached to one mass to provide the ... [more ▼] In the present paper, isolated response curves in a nonlinear system consisting of two masses sliding on a horizontal guide are examined. Transverse springs are attached to one mass to provide the nonlinear restoring force, and a harmonic motion of the complete system is imposed by prescribing the displacement of their supports. Numerical simulations are carried out to study the conditions of existence of isolated solutions, their bifurcations, their merging with the main response branch and their basins of attraction. This is achieved using tools including nonlinear normal modes, energy balance, harmonic balance-based continuation and bifurcation tracking, and global analysis. [less ▲] Detailed reference viewed: 44 (8 ULg)Identification of nonlinear normal modes of engineering structures under broadband forcing Noël, Jean-Philippe ; Renson, Ludovic ; Grappasonni, Chiara et al in Mechanical Systems & Signal Processing (2015) The objective of the present paper is to develop a two-step methodology integrating system identification and numerical continuation for the experimental extraction of nonlinear normal modes (NNMs) under ... [more ▼] The objective of the present paper is to develop a two-step methodology integrating system identification and numerical continuation for the experimental extraction of nonlinear normal modes (NNMs) under broadband forcing. The first step processes acquired input and output data to derive an experimental state-space model of the structure. The second step converts this state-space model into a model in modal space from which NNMs are computed using shooting and pseudo-arclength continuation. The method is demonstrated using noisy synthetic data simulated on a cantilever beam with a hardening-softening nonlinearity at its free end. [less ▲] Detailed reference viewed: 20 (3 ULg)Complex dynamics of a nonlinear aerospace structure: numerical continuation and normal modes Renson, Ludovic ; Noël, Jean-Philippe ; Kerschen, Gaëtan in Nonlinear Dynamics (2015), 79(2), 1293-1309 This paper investigates the dynamics of a real-life aerospace structure possessing a strongly nonlinear component with multiple mechanical stops. A full-scale finite element model is built for gaining ... [more ▼] This paper investigates the dynamics of a real-life aerospace structure possessing a strongly nonlinear component with multiple mechanical stops. A full-scale finite element model is built for gaining additional insight into the nonlinear dynamics that was observed experimentally, but also for uncovering additional nonlinear phenomena, such as quasiperiodic regimes of motion. Forced/unforced, damped/undamped numerical simulations are carried out using advanced techniques and theoretical concepts such as numerical continuation and nonlinear normal modes. [less ▲] Detailed reference viewed: 46 (7 ULg)Grey-box identification of a non-linear solar array structure using cubic splines Noël, Jean-Philippe ; Kerschen, Gaëtan ; et al in International Journal of Non-Linear Mechanics (2014), 67 Most identification methods in non-linear structural dynamics assume in advance a mathematical model of the non-linearities. This is however possible in specific situations only, since non-linear effects ... [more ▼] Most identification methods in non-linear structural dynamics assume in advance a mathematical model of the non-linearities. This is however possible in specific situations only, since non-linear effects may be caused by numerous phenomena and a priori knowledge is generally limited. The present paper investigates the usefulness of piecewise third-order polynomials, termed cubic splines, to identify the complex non-linear dynamics of solar arrays in their stowed configuration. The estimation of the model parameters is achieved using the frequency-domain non-linear subspace identification (FNSI) method. A distinct advantage of the FNSI approach is its capability to calculate accurately a large number of parameters, while maintaining an acceptable computational burden. This makes tractable the use of cubic splines to represent non-linearity in real-life mechanical systems, as the dimensionality of the inverse problem is known to increase dramatically in this case. The experimental structure of interest consists of two parallel aluminium plates assembled with bolted connections. This application is challenging because of the existence of impacts between the two plates at high excitation amplitude, and of the activation of complicated stiffness and damping mechanisms within the bolted connections. [less ▲] Detailed reference viewed: 62 (4 ULg)A rigorous phase separation method for testing nonlinear structures Noël, Jean-Philippe ; Renson, Ludovic ; Grappasonni, Chiara et al in Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering (2014, September) The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements ... [more ▼] The objective of the present paper is to develop a rigorous identification methodology of nonlinear normal modes (NNMs) of engineering structures. This is achieved by processing experimental measurements collected under broadband forcing. The use of such a type of forcing signal allows to excite multiple NNMs simultaneously and, in turn, to save testing time. A two-step methodology integrating nonlinear system identification and numerical continuation of periodic solutions is proposed for the extraction of the individual NNMs from broadband input and output data. It is demonstrated using a numerical cantilever beam possessing a cubic nonlinearity at its free end. The proposed methodology can be viewed as a nonlinear generalization of the phase separation techniques routinely utilized for experimental modal analysis of linear structures. [less ▲] Detailed reference viewed: 46 (4 ULg) |
||