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A nonlinear state-space solution to a hysteretic benchmark in system identification Noël, Jean-Philippe ; ; Kerschen, Gaëtan et al Conference (2016, April) Detailed reference viewed: 16 (2 ULg)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: 66 (8 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: 37 (4 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: 40 (11 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: 41 (5 ULg)Direction and surface sampling in ray tracing for spacecraft radiative heat transfer Jacques, Lionel ; Masset, Luc ; Kerschen, Gaëtan in Aerospace Science and Technology (2015), 47 This paper addresses the computation of radiative exchange factors through Monte Carlo ray tracing with the aim of reducing their computation time when dealing with the finite element method. Both ... [more ▼] This paper addresses the computation of radiative exchange factors through Monte Carlo ray tracing with the aim of reducing their computation time when dealing with the finite element method. Both direction and surface samplings are studied. The recently-introduced isocell method for partitioning the unit disk is applied to the direction sampling and compared to other direction sampling methods. It is then combined to different surface sampling schemes with either one or multiple rays traced per surface sampling point. Two promising approaches present better performances than standard spacecraft thermal analysis software. The first approach combines a Gauss surface sampling strategy with a local isocell direction sampling, whereas the second approach fires one ray per surface points using a global isocell direction sampling scheme. The advantages and limitations of the two methods are discussed, and they are benchmarked against a standard thermal analysis software using the entrance baffle of the Extreme Ultraviolet Imager instrument of the Solar Orbiter mission. [less ▲] Detailed reference viewed: 41 (13 ULg)Finite Element Model Reduction for Spacecraft Thermal Analysis Jacques, Lionel ; Masset, Luc ; Kerschen, Gaëtan Scientific conference (2015, November 03) The finite element method (FEM) is widely used in mechanical engineering, especially for space structure design. However, FEM is not yet often used for thermal engineering of space structures where the ... [more ▼] The finite element method (FEM) is widely used in mechanical engineering, especially for space structure design. However, FEM is not yet often used for thermal engineering of space structures where the lumped parameter method (LPM) is still dominant. Both methods offer advantages and disadvantages and the proposed global approach tries to combine both methods: - The LPM conductive links are error-prone and still too often computed by hand. This is incompatible with the increasing accuracy required by the thermal control systems (TCS) and associated thermal models. Besides offering the automatic and accurate computation of the conductive links, the FEM also provides easy interaction between mechanical and thermal models, allowing better thermo-mechanical analyses. - On another hand, due to the large number of elements composing a FE model, the computation of the radiative exchange factors (REFs) is prohibitively expensive. New methods to accelerate the REFs computation by ray-tracing are necessary. Ray-tracing enhancement methods were presented in the previous editions, providing at least a 50% reduction of the number of rays required for a given accuracy. Another way to speed up the REF computation consists in grouping the FE external facets into super-faces. Surfaces in FEM are approximated where primitives are used in the LPM. In parallel to super-faces, quadric surface fitting of selected regions in the FE mesh is therefore performed where high surface accuracy is required for the computation of the radiative links and environmental heat loads. Last year’s presentation focused solely on the first point. Developments of super-face ray-tracing with quadrics fitting will be presented. In addition to REFs, orbital heat loads computation is also implemented with significant improvement. The presentation will also address the global process involving first the detailed FE model conductive reduction, then the super-faces generation with selective quadric fitting for the computation of REFs and orbital heat loads and finally the computation of the reduced model temperatures. Detailed FE model temperature field can then be computed back from the reduced ones and the reduction matrices for potential thermo-mechanical analyses. [less ▲] Detailed reference viewed: 10 (1 ULg)The harmonic balance method for bifurcation analysis of large-scale nonlinear mechanical systems Detroux, Thibaut ; Renson, Ludovic ; Masset, Luc et al in Computer Methods in Applied Mechanics and Engineering (2015), 296 The harmonic balance (HB) method is widely used in the literature for analyzing the periodic solutions of nonlinear mechanical systems. The objective of this paper is to exploit the method for bifurcation ... [more ▼] The harmonic balance (HB) method is widely used in the literature for analyzing the periodic solutions of nonlinear mechanical systems. The objective of this paper is to exploit the method for bifurcation analysis, i.e., for the detection and tracking of bifurcations of nonlinear systems. To this end, an algorithm that combines the computation of the Floquet exponents with bordering techniques is developed. A new procedure for the tracking of Neimark–Sacker bifurcations that exploits the properties of eigenvalue derivatives is also proposed. The HB method is demonstrated using numerical experiments of a spacecraft structure that possesses a nonlinear vibration isolation device. [less ▲] Detailed reference viewed: 39 (10 ULg)Grey-box nonlinear state-space modelling for mechanical vibrations identification Noël, Jean-Philippe ; ; Kerschen, Gaëtan in Proceedings of the 17th IFAC Symposium on System Identification (2015, October) In the present paper, a flexible and parsimonious model of the vibrations of nonlinear mechanical systems is introduced in the form of state-space equations. It is shown that the nonlinear model terms can ... [more ▼] In the present paper, a flexible and parsimonious model of the vibrations of nonlinear mechanical systems is introduced in the form of state-space equations. It is shown that the nonlinear model terms can be formed using a limited number of output measurements. A two-step identification procedure is derived for this grey-box model, integrating nonlinear subspace initialisation and maximum likelihood optimisation. The complete procedure is demonstrated on the Silverbox benchmark, which is an electrical mimicry of a single-degree-of-freedom mechanical system with one displacement-dependent nonlinearity. [less ▲] Detailed reference viewed: 11 (1 ULg)Nonlinear normal modes, modal interactions and isolated resonance curves ; Renson, Ludovic ; Detroux, Thibaut et al in Journal of Sound and Vibration (2015), 351 The objective of the present study is to explore the connection between the nonlinear normal modes of an undamped and unforced nonlinear system and the isolated resonance curves that may appear in the ... [more ▼] The objective of the present study is to explore the connection between the nonlinear normal modes of an undamped and unforced nonlinear system and the isolated resonance curves that may appear in the damped response of the forced system. To this end, an energy balance technique is used to predict the amplitude of the harmonic forcing that is necessary to excite a specific nonlinear normal mode. A cantilever beam with a nonlinear spring at its tip serves to illustrate the developments. The practical implications of isolated resonance curves are also discussed by computing the beam response to sine sweep excitations of increasing amplitudes. [less ▲] Detailed reference viewed: 43 (7 ULg)Architecture of educational OUFTI-1 nanosatellite of University of Liège, as tested in preparation for space flight Werner, Xavier ; De Dijcker, Sébastien ; Broun, Valery et al Poster (2015, September) Overview of the OUFTI-1 nanosatellite space segment. The OUFTI-1 project was initiated in September 2007. The nanosatellite is a one-unit (1U) CubeSat. Its main payload is - in essence - a D-STAR repeater ... [more ▼] Overview of the OUFTI-1 nanosatellite space segment. The OUFTI-1 project was initiated in September 2007. The nanosatellite is a one-unit (1U) CubeSat. Its main payload is - in essence - a D-STAR repeater in space, potentially the first one ever. D-STAR is an amateur-radio (“ham”), digital radio communication - protocol (with associated equipment) allowing the simultaneous transmission of voice and data, such as GPS coordinates and call-signs. [less ▲] Detailed reference viewed: 63 (1 ULg)Overview of the ground facilities for controlling the OUFTI-1 nanosatellite and for routing its radio-communications through the worldwide D-STAR repeater network Werner, Xavier ; De Dijcker, Sébastien ; Broun, Valery et al Poster (2015, September) Overview of the current state and upgrade plan of the OUFTI-1 nanosatellite ground segment. The OUFTI-1 project was initiated in September 2007. The OUFTI-1 nanosatellite is a one-unit (1U) CubeSat. Its ... [more ▼] Overview of the current state and upgrade plan of the OUFTI-1 nanosatellite ground segment. The OUFTI-1 project was initiated in September 2007. The OUFTI-1 nanosatellite is a one-unit (1U) CubeSat. Its main payload is - in essence - a D-STAR repeater in space, potentially the first one ever. D-STAR is an amateur-radio (“ham”), digital radio-communication protocol (with associated equipment) allowing the simultaneous transmission of voice and data, such as GPS coordinates and call-signs. The satellite was tested in 2014 and 2015 within the ESA’s Education Office Fly Your Satellite! (FYS) project, and it is now fully qualified and ready for launch and operation in space. [less ▲] Detailed reference viewed: 47 (1 ULg)Thermal-vacuum and vibration test campaigns that led to the OUFTI-1 nanosatellite being fully qualified by ESA for launch and operation in Earth orbit De Dijcker, Sébastien ; Werner, Xavier ; Broun, Valery et al Conference (2015, September) OUFTI-1’s test campaigns were divided into two phases. The goal of Phase 1 is to demonstrate that the different functionalities of the satellite work as intended. The goal of Phase 2 is to subsequently ... [more ▼] OUFTI-1’s test campaigns were divided into two phases. The goal of Phase 1 is to demonstrate that the different functionalities of the satellite work as intended. The goal of Phase 2 is to subsequently demonstrate that the satellite can withstand the launch into orbit, and then work properly in the conditions of space. The corresponding tests thus involve both thermal-vacuum environmental tests (in appropriate test chambers) and vibration tests (on appropriate vibration pods). The conditions simulated during these tests are as close as possible to those that the satellite will encounter during its mission, covering as many cases as possible, amid uncertainties, since neither the launcher nor the orbit were known prior to the tests. Both phases involve the flight model (FM), in accordance with the so-called "protoflight" approach. [less ▲] Detailed reference viewed: 90 (6 ULg)The harmonic balance method for bifurcation analysis of large-scale nonlinear mechanical systems Detroux, Thibaut ; Renson, Ludovic ; Masset, Luc et al Conference (2015, August 26) The harmonic balance (HB) method is widely used in the literature for analyzing the periodic solutions of nonlinear mechanical systems. The objective of this paper is to extend the method for bifurcation ... [more ▼] The harmonic balance (HB) method is widely used in the literature for analyzing the periodic solutions of nonlinear mechanical systems. The objective of this paper is to extend the method for bifurcation analysis, i.e., for the detection and tracking of bifurcations of nonlinear systems. To this end, an algorithm that combines the computation of the Floquet exponents with bordering techniques is developed. A new procedure for the tracking of Neimark-Sacker bifurcations that exploits the properties of eigenvalue derivatives is also proposed. As an application, the frequency response of a structure spacecraft is studied, together with two nonlinear phenomena, namely quasiperiodic oscillations and detached resonance curves. This example illustrates how bifurcation tracking using the HB method can be employed as a promising design tool for detecting and eliminating such undesired behaviors. [less ▲] Detailed reference viewed: 19 (1 ULg)A principle of similarity for nonlinear vibration absorbers Habib, Giuseppe ; Kerschen, Gaëtan Conference (2015, August 05) With continual interest in expanding the performance envelope of engineering systems, nonlinear components are increasingly utilized in real-world applications. This causes the failure of wellestablished ... [more ▼] With continual interest in expanding the performance envelope of engineering systems, nonlinear components are increasingly utilized in real-world applications. This causes the failure of wellestablished techniques to mitigate resonant vibrations. In particular, this holds for the linear tuned vibration absorber (LTVA), which requires an accurate tuning of its natural frequency to the resonant vibration frequency of interest. This is why the nonlinear tuned vibration absorber (NLTVA), the nonlinear counterpart of the LTVA, has been recently developed. An unconventional aspect of this absorber is that its restoring force is tailored according to the nonlinear restoring force of the primary system. This allows the NLTVA to extend the so-called Den Hartog’s equal-peak rule to the nonlinear range. In this work, a fully analytical procedure, exploiting harmonic balance and perturbation techniques, is developed to define the optimal value of the nonlinear terms of the NLTVA. The developments are such that they can deal with any polynomial nonlinearity in the host structure. Another interesting feature of the NLTVA, discussed in the paper, is that nonlinear terms of different orders do not interact with each other in first approximation, thus they can be treated separately. Numerical results obtained through the shooting method coupled with pseudoarclength continuation validate the analytical developments. [less ▲] Detailed reference viewed: 54 (3 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, August) 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: 46 (9 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: 35 (6 ULg)Performance, robustness and sensitivity analysis of the nonlinear tuned vibration absorber Detroux, Thibaut ; Habib, Giuseppe ; Masset, Luc et al in Mechanical Systems & Signal Processing (2015), 60-61 The nonlinear tuned vibration absorber (NLTVA) is a recently developed nonlinear absorber which generalizes Den Hartog׳s equal peak method to nonlinear systems. If the purposeful introduction of ... [more ▼] The nonlinear tuned vibration absorber (NLTVA) is a recently developed nonlinear absorber which generalizes Den Hartog׳s equal peak method to nonlinear systems. If the purposeful introduction of nonlinearity can enhance system performance, it can also give rise to adverse dynamical phenomena, including detached resonance curves and quasiperiodic regimes of motion. Through the combination of numerical continuation of periodic solutions, bifurcation detection and tracking, and global analysis, the present study identifies boundaries in the NLTVA parameter space delimiting safe, unsafe and unacceptable operations. The sensitivity of these boundaries to uncertainty in the NLTVA parameters is also investigated. [less ▲] Detailed reference viewed: 36 (17 ULg)Enforcing Force-Displacement Proportionality in Nonlinear Systems through the Addition of Nonlinearity Habib, Giuseppe ; Kerschen, Gaëtan Conference (2015, July 07) Detailed reference viewed: 13 (0 ULg)Theoretical and experimental investigation of a structurally and aerodynamically nonlinear pitch and flap wing Verstraelen, Edouard ; Boutet, Johan ; Grappasonni, Chiara et al in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics, IFASD 2015 (2015, June 29) This paper presents and experimental and theoretical investigation of a novel nonlinear aeroelastic system. It consists of a wing with pitch and flap degrees of freedom, suspended from a leaf spring ... [more ▼] This paper presents and experimental and theoretical investigation of a novel nonlinear aeroelastic system. It consists of a wing with pitch and flap degrees of freedom, suspended from a leaf spring secured in a nonlinear clamp. Both the structural and the aerodynamic forces acting on the wing can be nonlinear, depending on the amplitude of oscillations. Wind tunnel experiments show that the system undergoes a supercritical Hopf bifurcation that leads to small amplitude limit cycle oscillations. At a particular airspeed, the pitch amplitude jumps to a much higher value and dynamic stall starts to occur. Three mathematical models of the system are formulated, one based on linear aerodynamics and two based on the Leishman-Beddoes dynamic stall model. The objective of the modelling is to determine whether the jump in pitch oscillation amplitude is due to dynamic stall. The predictions for amplitude, frequency and mean angle of the limit cycle oscillations are compared to the experimental observations. All three models predict the small amplitude oscillations with satisfactory accuracy. The complete Leishman-Beddoes model predicts the occurrence of a jump in pitch amplitude but the magnitude of this jump is signi cantly overestimated. The other two models completely fail to model the jump. The failure of the Leishman-Beddoes model to predict the correct post-jump oscillation amplitude may be due to the values selected for the model parameters. [less ▲] Detailed reference viewed: 67 (14 ULg) |
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