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Modal Analysis of Nonlinear Vibrating Systems: Recent Progress and Challenges, KEYNOTE LECTURE Kerschen, Gaëtan in Proceeedings of the Eighth European Conference on Structural Dynamics (2011) Theoretical and experimental modal analysis, i.e., the computation of vibration modes from a mathematical model and from experimental data, respectively, is quite sophisticated and advanced in linear ... [more ▼] Theoretical and experimental modal analysis, i.e., the computation of vibration modes from a mathematical model and from experimental data, respectively, is quite sophisticated and advanced in linear structural dynamics. However, nonlinearity is a frequent occurrence in real-world engineering structures, and the existing linear methodologies can no longer be used in this context. Therefore, the development of a nonlinear analog of modal analysis would be a timely contribution. Because nonlinear normal modes (NNMs) provide solid mathematical foundations for a rigorous analysis of nonlinear dynamical behaviors, a framework which includes both their computation from finite element models and their identification from experimental data is proposed in this paper. In view of the still limited use of NNMs in structural dynamics, special attention is devoted to develop tools that have the potential to deal with large-scale structures. [less ▲] Detailed reference viewed: 17 (0 ULg)Proper Orthogonal Decomposition for Nonlinear Radiative Heat Transfer Problems ; Masset, Luc ; Kerschen, Gaëtan et al in Proceedings of the ASME International Design Engineering Technical Conferences (2011) Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive ... [more ▼] Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive, especially if the number of degrees-of-freedom is high. This paper develops modal reduction techniques for such nonlinear multiphysical systems. The paper focuses on Proper Orthogonal Decomposition (POD), a multivariate statistical method that obtains a compact representation of a data set by reducing a large number of interdependent variables to a much smaller number of uncorrelated variables. A fully coupled, thermomechanical model consisting of a multilayered, cantilever beam is described and analysed. This linear benchmark is then extended by adding nonlinear radiative heat exchanges between the beam and an enclosing box. The radiative view factors, present in the equations governing the heat fluxes between beam and box elements, are obtained with a raytracing method. A reduction procedure is proposed for this fully coupled nonlinear, multiphysical, thermomechanical system. Two alternative approaches to the reduction are investigated, a monolithic approach incorporating a scaling factor to the equations, and a partitioned approach that treats the individual physical modes separately. The paper builds on previous work presented previously by the authors. The results are given for the RMS error between either approach and the original, full solution. [less ▲] Detailed reference viewed: 27 (7 ULg)Design of the on-board computer of OUFTI-1 CubeSat ; ; Verly, Jacques et al Conference (2011) Detailed reference viewed: 31 (2 ULg)CubeSat Activities at the University of Liège Denis, Amandine ; Pisane, Jonathan ; Verly, Jacques et al Conference (2011) Detailed reference viewed: 24 (6 ULg)Investigating the performance of model order reduction techniques for nonlinear radiative heat transfer problems ; Masset, Luc ; Kerschen, Gaëtan et al in Proceedings of the International Conference on Advanced Computational Methods in Engineering (2011) The problem of nonlinear radiative heat transfer is one of great importance to the aerospace industry. However, analysing large-scale, nonlinear, multiphysical, dynamical structures, by using mathematical ... [more ▼] The problem of nonlinear radiative heat transfer is one of great importance to the aerospace industry. However, analysing large-scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally expensive. This provides motivation for the development of Model-Order Reduction (MOR) techniques capable of reducing simulation times without the loss of important information. The objective is to demonstrate the method of Proper Orthogonal Decompostition (POD) as a technique for nonlinear MOR. The nonlinear radiative exchanges between a linear benchmark beam within an external box (Figure 1) are analysed and a reduction procedure for this fully coupled, nonlinear, multiphysical, thermomechanical system is established. The solution to the strongly coupled, thermomechanical equations of motion is found by making use of an extended version of the implicit generalized-alpha scheme. In the reduced model, the residual of the unreduced system of equations need to be evaluated at each Newton iteration of each time step. In order to optimise the efficiency of the reduction method it is shown that the internal forces can be split into their linear and nonlinear counterparts. Only the nonlinear terms change at each time step, thus only these terms need to remain in the iterative loop significantly reducing the number of parameters that are to be computed at each step. These efficiency improvements to the method are discussed and the results are given. [less ▲] Detailed reference viewed: 50 (6 ULg)Finite Element Computation of Nonlinear Normal Modes Renson, Ludovic ; Deliège, Geoffrey ; Noels, Ludovic et al in Fifth International Conference on Advanced COmputational Methods in ENgineering (2011) Detailed reference viewed: 45 (8 ULg)Detection and quantification of non-linear structural behavior using principal component analysis ; Kerschen, Gaëtan ; et al in Mechanical Systems & Signal Processing (2011), 26 The detection of non-linear behavior in structural dynamics is a very important step to the extent that the presence of non-linearities, even local, can affect the global dynamic behavior of a structure ... [more ▼] The detection of non-linear behavior in structural dynamics is a very important step to the extent that the presence of non-linearities, even local, can affect the global dynamic behavior of a structure. A large number of techniques that enable engineers to detect non-linear behavior can be found in the literature but most of these methods exploit frequency domain data and give better results with a stepped-sine excitation. The goal of this paper is to propose an alternative methodology that is based on the principal component analysis and uses time responses obtained with a random excitation. Two criteria will be used to quantify the difference between two response subspaces, based on the angle between them and the residual error resulting from the projection of one on the other. The concept of limit of linearity and design decision margins is also addressed in this paper. The methodology is demonstrated using an academic simulated system and then using measured data of a simplified solar array system. [less ▲] Detailed reference viewed: 10 (0 ULg)Vandalism Prevention of a Footbridge with Cable Vibrations Canor, Thomas ; Kerschen, Gaëtan ; Denoël, Vincent in Biliszczuk, Jan; Bien, Jan; Hawryszkow, Pawel (Eds.) et al 4th International Conference Footbridge : Attractive structures at reasonable costs, Wroclaw 6-8 July 2011 (2011) This work studies an unusual way to improve comfort of a footbridge with cables. Cables can be seen as a means of dissipating energy in a structure. This complementary source of dissipation does not ... [more ▼] This work studies an unusual way to improve comfort of a footbridge with cables. Cables can be seen as a means of dissipating energy in a structure. This complementary source of dissipation does not prohibit resonance from taking place, but it is a way to limit vibrations and to impede vandals’ actions. This study is illustrated with measurements realized on a specific footbridge. This structure is a metallic arch characterized by a first natural frequency of 3.2Hz and a corresponding damping ratio of 0.55%. Intolerable accelerations (around 6m/s²) are easily reached when an ill-intentioned person is bouncing at an appropriate frequency. After installation of a single cable at a suitable location in the structure, the measured damping ratios are almost doubled and the maximum accelerations at resonance are reduced by 30%. With three cables on the footbridge, the damping ratio becomes significantly nonlinear: it reaches up to 3% for low amplitude oscillations, but drops down to 1% for moderate to high amplitudes. For higher accelerations, it does not seem to depend on the number of cables. According to these observations, a notable effect of cables is to reduce the maximum acceleration, but the main effect is to prolong the transient phase and to make the resonance frequency hardly identifiable by vandals. [less ▲] Detailed reference viewed: 47 (5 ULg)Modal testing of nonlinear vibrating structures based on nonlinear normal modes: Experimental demonstration Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude in Mechanical Systems & Signal Processing (2011), 25 Detailed reference viewed: 27 (1 ULg)Dynamic testing of nonlinear vibrating structures using nonlinear normal modes Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude in Journal of Sound & Vibration (2011), 330 Detailed reference viewed: 28 (1 ULg)Nonlinear Normal Modes of a Full-Scale Aircraft Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude et al in 29th International Modal Analysis Conference, Jacksonville, 2011 (2011) Detailed reference viewed: 37 (5 ULg)Contract 21539/08/NL/SFe - Advancement of mechanical verification methods for non-linear spacecraft: Nonlinearity identification methods: predictive analyses Kerschen, Gaëtan ; Noël, Jean-Philippe Report (2010) The objective of this technical note is to explore the applicability of nonlinear system identification techniques to spacecraft structures. To this end, numerical experiments carried out using the finite ... [more ▼] The objective of this technical note is to explore the applicability of nonlinear system identification techniques to spacecraft structures. To this end, numerical experiments carried out using the finite element model of the SmallSat spacecraft are used, without, however, having access to the model itself. The constraints imposed by the considered techniques for breadboard testing are also highlighted. [less ▲] Detailed reference viewed: 31 (6 ULg)Model order reduction techniques for thermomechanical systems with nonlinear radiative heat transfer using proper orthogonal decomposition Hickey, Daryl ; Hoffait, Sébastien ; Rothkegel Ide, José Ignacio et al in Proceedings of ISMA 2010 (2010, September) Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive ... [more ▼] Analysing large scale, nonlinear, multiphysical, dynamical structures, by using mathematical modelling and simulation, e.g. Finite Element Modelling (FEM), can be computationally very expensive, especially if the number of degrees-of-freedom is high. This paper develops modal reduction techniques for such nonlinear multiphysical systems. The paper focuses on Proper Orthogonal Decomposition (POD), a multivariate statistical method that obtains a compact representation of a data set by reducing a large number of interdependent variables to a much smaller number of uncorrelated variables. A fully coupled, thermomechanical model consisting of a multilayered, cantilever beam is described and analysed. This linear benchmark beam is then extended to incorporate an external box. The nonlinear radiative exchanges between the beam and the external box are analysed and a reduction procedure is proposed for this fully coupled, nonlinear, multiphysical, thermomechanical system. Two alternative approaches to the reduction are investigated, a monolithic scaled approach and a partitioned approach that treats the individual physical modes separately. [less ▲] Detailed reference viewed: 98 (22 ULg)Toward robust parameterized reduced-order models of non-linear structures using POD Hoffait, Sébastien ; Kerschen, Gaëtan ; Bruls, Olivier in IV European Conference on Computational Mechanics, Paris, 2010 (2010) Detailed reference viewed: 43 (12 ULg)Finite element analysis of strongly nonlinear phenomena in deployable flexible systems Bruls, Olivier ; Hoffait, Sébastien ; et al in 1st ESA Multibody Dynamics Workshop on Multibody Dynamics for Space Applications, Noordwijk, 2010 (2010) Detailed reference viewed: 31 (4 ULg)Dynamic analysis of the self-locking phenomenon in tape spring hinges Hoffait, Sébastien ; Bruls, Olivier ; et al in Acta Astronautica (2010), 66(7-8), 1125-1132 This paper investigates the dynamic behaviour of tape-spring hinges that are commonly used in space deployable structures. During the deployment of an appendice (e.g. a solar panel or a beam), a tape ... [more ▼] This paper investigates the dynamic behaviour of tape-spring hinges that are commonly used in space deployable structures. During the deployment of an appendice (e.g. a solar panel or a beam), a tape-spring hinge allows the simultaneous achievement of the actuating, guiding and self-locking functions without friction elements. The proposed finite element model is able to capture buckling and hysteresis phenomena, which have a strong influence on the 3D motion of the system. A detailed analysis of those effects is developed, leading to a physical explanation of the crucial self-locking phenomenon. [less ▲] Detailed reference viewed: 144 (20 ULg)Theoretical and experimental modal analysis of nonlinear aerospace structures Peeters, Maxime ; Golinval, Jean-Claude ; Kerschen, Gaëtan in Proceedings of the AIAA Modeling and Simulation Technologies Conference (2010) Because nonlinearity is a frequent occurrence in aerospace applications, there is a need for e cient analysis procedures. In this context, nonlinear normal modes (NNMs) o er a solid mathematical tool for ... [more ▼] Because nonlinearity is a frequent occurrence in aerospace applications, there is a need for e cient analysis procedures. In this context, nonlinear normal modes (NNMs) o er a solid mathematical tool for interpreting a wide class of nonlinear dynamical phenomena. The objective of this study is to highlight the usefulness of NNMs for modeling and testing of nonlinear aerospace structures. Both theoretical and experimental modal analysis are described and are illustrated. [less ▲] Detailed reference viewed: 12 (0 ULg)Modal testing using nonlinear normal modes: experimental demonstration Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude in Proceedings of the International Conference on Noise and Vibration Engineering (2010) Modal testing and analysis is well-established for linear vibrating structures. While the common practice is to assume linear behavior, nonlinearity is a frequent occurrence in engineering applications ... [more ▼] Modal testing and analysis is well-established for linear vibrating structures. While the common practice is to assume linear behavior, nonlinearity is a frequent occurrence in engineering applications and can drastically alter the behavior of mechanical systems. In this paper, an attempt is made to extend experimental modal analysis methodology to a practical nonlinear analog. In this context, nonlinear normal modes (NNMs) offer a solid theoretical and mathematical tool for interpreting a wide class of nonlinear dynamical phenomena, yet they have a clear and simple conceptual relation to the classical linear normal modes. Based on a nonlinear extension of phase resonance testing (also called force appropriation), the proposed methodology excites the structure to isolate one single NNM during the experiments. Thanks to the invariance principle, the energy dependence of that nonlinear mode (i.e., the NNM modal curves and their frequencies of oscillation) can be extracted from the resulting free decay response using time-frequency analysis. The proposed method is demonstrated using an experimental cantilever beam with a geometrical nonlinearity. [less ▲] Detailed reference viewed: 26 (2 ULg)Orbital dynamics characteristics of a QB50 CubeSat performing atmospheric reentry ; ; Kerschen, Gaëtan et al in Proceedings of the AIAA Atmospheric Flight Mechanics Conference (2010) The QB50 mission has the scientific objective to study the temporal and spatial variations of a number of key parameters in the lower thermosphere with a network of 50 CubeSats, each performing identical ... [more ▼] The QB50 mission has the scientific objective to study the temporal and spatial variations of a number of key parameters in the lower thermosphere with a network of 50 CubeSats, each performing identical in-situ measurements. One of these 50 CubeSats, the von Karman Institute Atmospheric Re-Entry CubeSat, will further be equipped by a thermal protection system and a dedicated sensor pack to study the atmospheric re-entry. This paper is devoted to the orbital dynamics analysis performed for the QB50 mission and the atmospheric re-entry trajectory analysis for a double unit CubeSat. The main focus is on the sensitivity of the results on atmospheric models, drag coefficient and the launch date. Typical atmospheric re-entry trajectories, including the stagnation point heat flux values are calculated using three different methods for three different scenarios. The predicted heat flux values will be used in the preliminary design of the thermal protection system of the VKI atmospheric re-entry CubeSat, which is to be the first CubeSat to be used as an atmospheric re-entry demonstrator. [less ▲] Detailed reference viewed: 116 (1 ULg)Detection and quantification of non-linear dynamic behaviour of space structures ; Kerschen, Gaëtan ; et al in 28th International Modal Analysis Conference, Jacksonville, 2010 (2010) Detailed reference viewed: 23 (1 ULg) |
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