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Nonlinear Structural Dynamics: Theory, Simulation and Testing, KEYNOTE LECTURE Kerschen, Gaëtan in Proceedings of the 18th Symposium on Vibrations, Shocks and Noise (2012) Nonlinearity is a frequent occurrence in engineering structures. It is at the origin of rich and complex dynamical phenomena that cannot be observed in linear structures. The analysis of the dynamics of ... [more ▼] Nonlinearity is a frequent occurrence in engineering structures. It is at the origin of rich and complex dynamical phenomena that cannot be observed in linear structures. The analysis of the dynamics of nonlinear systems therefore warrants the development of rigorous and effective methods and is the focus of this presentation. Several theoretical, computational and experimental methods will be presented and applied to a real-life, full-scale nonlinear structure, the EADS- Astrium SmallSat spacecraft. [less ▲] Detailed reference viewed: 32 (0 ULg)Non-linear structures ; Kerschen, Gaëtan in Calvi, A.; Roy, N. (Eds.) Spacecraft Loads Analysis (2012) Non-linearity is a frequent occurrence in engineering structures including spacecraft structures. It can take different forms, and it is at the origin of various dynamical phenomena with no linear ... [more ▼] Non-linearity is a frequent occurrence in engineering structures including spacecraft structures. It can take different forms, and it is at the origin of various dynamical phenomena with no linear counterpart. These phenomena include jumps, harmonics, bifurcation and non-unicity of the solutions. Even when they are local, non-linearities can affect the global dynamical behaviour of a structure and have a substantial impact on spacecraft loads. What makes non-linear dynamics challenging to analyse and model is the well-known result that the principle of linear superposition does not (generally) apply to non-linear systems. Even if linearisation may suffice in some cases, the rigorous analysis of non-linear structures requires adequate and dedicated numerical and experimental methodologies. The main objective of this chapter is to describe how to handle non-linearities for an accurate estimation of loads in spacecraft structures. Specifically, guidelines for both modeling and testing are provided. [less ▲] Detailed reference viewed: 27 (2 ULg)Topics in Nonlinear Dynamics ; Kerschen, Gaëtan ; Book published by Springer (2012) Topics in Nonlinear Dynamics, Volume 3, Proceedings of the 30th IMAC, A Conference and Exposition on Structural Dynamics, 2012, the third volume of six from the Conference, brings together 26 ... [more ▼] Topics in Nonlinear Dynamics, Volume 3, Proceedings of the 30th IMAC, A Conference and Exposition on Structural Dynamics, 2012, the third volume of six from the Conference, brings together 26 contributions to this important area of research and engineering. The collection presents early findings and case studies on fundamental and applied aspects of Structural Dynamics. [less ▲] Detailed reference viewed: 17 (3 ULg)The Sun-earth Imbalance radiometer for a direct measurement of the net heating of the Earth ; ; et al Conference (2012) Although it is generally accepted that the climate on earth is changing due to a radiative energy imbalance at the top of the atmosphere, up to now this radiation imbalance has not been measured directly ... [more ▼] Although it is generally accepted that the climate on earth is changing due to a radiative energy imbalance at the top of the atmosphere, up to now this radiation imbalance has not been measured directly. The measurement is challenging both in terms of space-time sampling of the radiative energy that is leaving the earth and in terms of accuracy. The incoming solar radiation and the outgoing terrestrial radiation are of nearly equal magnitude – of the order of 340 W/m² – resulting in a much smaller difference or imbalance of the order of 1 W/m². The only way to measure the imbalance with sufficient accuracy is to measure both the incoming solar and the outgoing terrestrial radiation with the same instrument. By reanalyzing data from the NASA LARC Earth Radiation Budget Experiment, we have been able to demonstrate that the sampling problem can be overcome, even with the low resolution Wide Field of View radiometer. We have combined the measurements of the precessing ERBS satellite for midlatitude and equatorial regions with measurements of the sun synchronuous NOAA9 satellite for the polar regions. For the accuracy requirement an improved instrument design is needed. We propose a new instrument, which we call the Sun-earth IMBAlance (SIMBA) radiometer. It is an improved wide field of view cavity radiometer based on our long experience with the DIARAD type of instrument for the measurement of Total Solar Irradiance. Currently we have two DIARAD instruments in space, on SOHO and on the ISS, and a third one will be launched this year on the Picard microsatellite. In this paper, we will present the ERBE sampling study and the SIMBA instrument and nanosatellite design [less ▲] Detailed reference viewed: 40 (3 ULg)Nonlinear modal analysis of the SmallSat spacecraft Renson, Ludovic ; Kerschen, Gaëtan ; in Proceedings of the SEM IMAC XXX Conference (2012) Non-linear elements are present in practically all spacecraft structures. The assumption of a (quasi-)linear structure is nevertheless adequate for structural analyses and design verification purposes in ... [more ▼] Non-linear elements are present in practically all spacecraft structures. The assumption of a (quasi-)linear structure is nevertheless adequate for structural analyses and design verification purposes in those cases where these structural non-linearities are relatively weak or not substantially activated by the mechanical environments encountered during the launch or during ground testing. However, when significant non-linear effects in spacecraft structures are no longer negligible then linear modal analysis will not be able to handle non-linear dynamical phenomena in an adequate manner: the development of a non-linear analogue of linear modal analysis becomes an urgent and important issue. The objective of this paper is to show that nonlinear normal modes (NNMs) represent a useful and practical tool in this context. A full-scale spacecraft structure is considered and is modeled using the finite element method. Its NNMs are computed using advanced numerical algorithms, and the resulting dynamics is then carefully analyzed. Nonlinear phenomena with no linear counterpart including nonlinear modal interactions are also highlighted. [less ▲] Detailed reference viewed: 58 (15 ULg)Educational assessment of four years of CubeSat activities at the University of Liège, Belgium. Denis, Amandine ; Pisane, Jonathan ; Verly, Jacques et al Conference (2011, October) Detailed reference viewed: 40 (20 ULg)Contract 21539/08/NL/SFe - Advancement of mechanical verification methods for non-linear spacecraft: Exploitation of test data Noël, Jean-Philippe ; Kerschen, Gaëtan Report (2011) The objective of this technical note is to apply the nonlinear system identification techniques described in the technical note "Nonlinearity identification methods: predictive analyses" to the ... [more ▼] The objective of this technical note is to apply the nonlinear system identification techniques described in the technical note "Nonlinearity identification methods: predictive analyses" to the experimental data gathered on the SmallSat spacecraft structure. Guidelines for nonlinear spacecraft testing and identification are also be provided. [less ▲] Detailed reference viewed: 17 (4 ULg)Nonlinear modal analysis of aerospace structures Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude et al in Proceedings of the 3rd International Conference on Computational Methods in Structural Dynamics and Earthquake Engineering (2011) The dynamic systems theory is well-established for linear systems and can rely on mature tools such as the theories of linear operators and linear integral transforms. This is why theoretical and ... [more ▼] The dynamic systems theory is well-established for linear systems and can rely on mature tools such as the theories of linear operators and linear integral transforms. This is why theoretical and experimental modal analysis, i.e., the computation of vibration modes from a mathematical model and from experimental data, respectively, is really quite sophisticated and advanced. Even though linear modal analysis served, and is still serving, the structural dynamics community for applications ranging from bridges to satellites, it is commonly accepted that nonlinearity is a frequent occurrence in engineering structures. Because linear modal analysis fails in the presence of nonlinear dynamical phenomena, the development of a practical nonlinear analog of modal analysis would be an extremely timely contribution; it is clearly missing in the structural dynamics literature. A new framework for nonlinear modal analysis of real-world structures, which includes the computation of nonlinear modes from finite element models, is introduced in this paper. This framework will permit a rigorous, yet understandable by the practicing engineer, analysis of nonlinear dynamical phenomena. It will also provide solid theoretical foundations for extending finite element model validation to nonlinear aerospace structures. [less ▲] Detailed reference viewed: 46 (1 ULg)Nonlinear normal modes of real-world structures: application to a full-scale aircraft Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude et al in Proceedings of the ASME International Design Engineering Technical Conferences (2011) The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this ... [more ▼] The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this study is the airframe of the Morane-Saulnier Paris aircraft, whose ground vibration tests have exhibited some nonlinear structural behaviors. The finite element model of this aircraft, elaborated from drawings, has more than 80000 degrees of freedom, and softening nonlinearities exist in the connection between the external fuel tanks and the wing tips. From this model, a reduced-order model, which is accurate in the [0-100Hz] range, is constructed using the Craig- Bampton technique. The NNMs of the reduced model are then computed using a numerical algorithm combining shooting and pseudo-arclength continuation. The results show that the NNMs of this full-scale structure can be computed accurately even in strongly nonlinear regimes and with a reasonable computational burden. Nonlinear modal interactions are also highlighted by the algorithm and are discussed. [less ▲] Detailed reference viewed: 26 (2 ULg)Nonlinear normal modes and band zones in granular chains with no precompression ; ; et al in Nonlinear Dynamics (2011), 63 We study standing waves (nonlinear normal modes—NNMs) and band zones in finite granular chains composed of spherical granular beads in Hertzian contact, with fixed boundary conditions. Although these are ... [more ▼] We study standing waves (nonlinear normal modes—NNMs) and band zones in finite granular chains composed of spherical granular beads in Hertzian contact, with fixed boundary conditions. Although these are homogeneous dynamical systems in the notation of Rosenberg, we show that the discontinuous nature of the dynamics leads to interesting effects such as separation between beads, NNMs that appear as traveling waves (these are characterized as pseudo-waves), and localization phenomena. In the limit of infinite extent, we study band zones, i.e., pass and stop bands in the frequency–energy plane of these dynamical systems, and classify the essentially nonlinear responses that occur in these bands. Moreover, we show how the topologies of these bands significantly affect the forced dynamics of these granular media subject to narrowband excitations. This work provides a classification of the coherent (regular) intrinsic dynamics of one-dimensional homogeneous granular chains with no pre-compression, and provides a rigorous theoretical foundation for further systematic study of the dynamics of granular systems, e.g., the effects of disorders or clearances, discrete breathers, nonlinear localized modes, and high-frequency scattering by local disorders. Moreover, it contributes toward the design of granular media as shock protectors, and in the passive mitigation of transmission of unwanted disturbances. [less ▲] Detailed reference viewed: 33 (2 ULg)Computation of nonlinear normal modes of large structures: application to a full-scale aircraft Peeters, Maxime ; Renson, Ludovic ; Kerschen, Gaëtan et al in Proceedings of the 7th European Nonlinear Dynamics Conference (ENOC 2011) (2011) The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this ... [more ▼] The objective of this paper is to demonstrate that the numerical computation of the nonlinear normal modes (NNMs) of complex real-world structures is now within reach. The application considered in this study is the airframe of the Morane-Saulnier Paris aircraft, whose ground vibration tests exhibited some nonlinear structural behaviors. The NNMs are computed using a numerical algorithm combining shooting and pseudo-arclength continuation. [less ▲] Detailed reference viewed: 67 (5 ULg)Nonlinear Normal Modes: A Finite Element Approach Renson, Ludovic ; Kerschen, Gaëtan Conference (2011) Detailed reference viewed: 19 (1 ULg)Phase resonance testing of nonlinear vibrating structures Peeters, Maxime ; Kerschen, Gaëtan ; Golinval, Jean-Claude in 28th International Modal Analysis Conference, Jacksonville, 2010 (2011) Detailed reference viewed: 36 (13 ULg)Thermal model reduction using the super-face concept Masset, Luc ; Bruls, Olivier ; Kerschen, Gaëtan Conference (2011) The objective of this presentation is to carry out thermal model reduction in the context of the finite element method. The finite element model is decomposed in several sets of adjacent faces called ... [more ▼] The objective of this presentation is to carry out thermal model reduction in the context of the finite element method. The finite element model is decomposed in several sets of adjacent faces called super-faces. Specialized algorithms such as the METIS partitioning algorithm are used to automatically generate the super-faces. Several constraints may be imposed, e.g., the size of the super-face, its aspect ratio or its aperture angle. Once the model is decomposed, view factors between super-faces are calculated with direct numerical integration or ray-tracing methods. This method offers a very substantial reduction of the computational burden compared to the full model, which is particularly interesting for pre-design studies or specific applications such as deployable structures. [less ▲] Detailed reference viewed: 40 (13 ULg)Assessment of nonlinear system identification methods using the SmallSat spacecraft structure Kerschen, Gaëtan ; ; et al in Proceedings of the 29th International Modal Analysis Conference (2011) In this paper, several techniques for nonlinear system identification are applied to a real-world structure, the SmallSat spacecraft structure developed by EADS-Astrium. This composite structure comprises ... [more ▼] In this paper, several techniques for nonlinear system identification are applied to a real-world structure, the SmallSat spacecraft structure developed by EADS-Astrium. This composite structure comprises two vibration isolation systems, one of which possesses mechanical stops. The loading case considered in the present study is a random (local) excitation. A careful progression through the different steps of the system identification process, namely detection, characterization and parameter estimation, is carried out. Different methods are applied to data resulting from numerical experiments, without having access to the finite element model which generated these data. [less ▲] Detailed reference viewed: 17 (0 ULg)Identification expérimentale et recalage d'une structure au comportement élastodynamique non-linéaire ; Kerschen, Gaëtan ; et al in Actes du 20ème Congrès Francais de Mécanique (2011) This paper studies of the COST-F3 beam experimental benchmark that exhibits a geometric non-linear behavior. The whole identification process, i.e. the non-linear behaviour detection, characterisation and ... [more ▼] This paper studies of the COST-F3 beam experimental benchmark that exhibits a geometric non-linear behavior. The whole identification process, i.e. the non-linear behaviour detection, characterisation and the parameter estimation, is carried out using measured time and frequency responses. A finite element model is also built in order to update the non-linear parameter using the hybrid multi-harmonic balance extended constitutive relation error method. [less ▲] Detailed reference viewed: 17 (1 ULg)Tuning methodology of nonlinear vibration absorbers coupled to nonlinear mechanical systems ; Kerschen, Gaëtan in Proceedings of the ASME International Design Engineering Technical Conferences (2011) A large body of literature exists regarding linear and nonlinear dynamic absorbers, but the vast majority of it deals with linear primary structures. However, nonlinearity is a frequent occurrence in ... [more ▼] A large body of literature exists regarding linear and nonlinear dynamic absorbers, but the vast majority of it deals with linear primary structures. However, nonlinearity is a frequent occurrence in engineering applications. Therefore, the present paper focuses on the mitigation of vibrations of nonlinear primary systems using nonlinear dynamic absorbers. Because most existing contributions about their design rely on extensive parametric studies, which are computationally demanding, or on analytic methods, which may be limited to small-amplitude motions, this study proposes a tuning procedure which is computationally tractable and can treat strongly nonlinear regimes of motion. The proposed methodology relies on a frequency-energy based approach followed by bifurcation analysis. The results are illustrated using a one-degree-of-freedom primary system, which can, for instance, represent the vibrations of a specific mode of a multi-degree-of-freedom structure. [less ▲] Detailed reference viewed: 19 (0 ULg)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) |
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