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Validation of differential drag propellantless maneuvers using 6 DoF simulations and stochastic dynamics Dell'Elce, Lamberto ; Kerschen, Gaëtan in Proceedings of the 9th International ESA Conference on Guidance, Navigation & Control Systems (2014) Differential drag is regarded as a promising technique in low-Earth orbits, since it allows to turn the often-undesired drag perturbation into a control force for relative maneuvers. Nonetheless, relevant ... [more ▼] Differential drag is regarded as a promising technique in low-Earth orbits, since it allows to turn the often-undesired drag perturbation into a control force for relative maneuvers. Nonetheless, relevant uncertainties in drag modeling make its practical realization a challenge, especially if no other propulsive means is available to accommodate them. The main outcome of this study is the identification and characterization of the uncertainty sources affecting differential-drag-based maneuvers. This characterization is carried out by using statistical methods in conjunction with mechanical modeling considerations to infer a probabilistic model of the sources from observed data. The developments are illustrated in the framework of the QARMAN mission through high-fidelity simulations involving coupled attitude and orbital dynamics. [less ▲] Detailed reference viewed: 29 (6 ULg)Ray tracing enhancement for space thermal analysis: isocell method Jacques, Lionel ; Masset, Luc ; Kerschen, Gaëtan Conference (2013, December 04) 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 is still dominant. Radiative exchange factors (REFs), used to calculate radiative thermal exchanges in space, are usually computed through Monte Carlo ray-tracing. Due to the large number of elements composing a FE model, the computation of the REFs is prohibitively expensive. In the frame of a global approach, several research axes will be investigated to reduce the computational effort of the REFs with FEM. The first one focuses on accelerating the convergence and enhancing the accuracy of the ray-tracing process to decrease the number of rays required to achieve a given accuracy. The developments of the new Isocell quasi-Monte Carlo ray tracing method are presented. Based on Nusselt’s analogy, the ray direction sampling is carried out by sampling the unit disc to derive the ray directions. The unit disc is divided into cells into which random points are then generated. The cells have the particularity of presenting almost the same area and shape. This enhances the uniformity of the generated quasi-random sequence of ray directions and leads to faster convergence. This Isocell method has been associated with different surface sampling to derive the REFs. The method is benchmarked against ESARAD, the standard thermal analysis software used in the European aerospace industry. Various geometries have been used. In particular, one entrance baffle of the Extreme Ultraviolet Imager (EUI) instrument developed at the Centre Spatial de Liège in Belgium is used. The EUI instrument of the Solar Orbiter European Space Agency mission and will be launched in a Sun-centered (0.28 perihelion) orbit in 2018. [less ▲] Detailed reference viewed: 30 (3 ULg)Frequency-domain subspace identification for nonlinear mechanical systems Noël, Jean-Philippe ; Kerschen, Gaëtan in Mechanical Systems & Signal Processing (2013), 40 This paper introduces a new frequency-domain subspace-based method for the identification of nonlinear mechanical systems. The technique exploits frequency-domain data and interprets nonlinearities as ... [more ▼] This paper introduces a new frequency-domain subspace-based method for the identification of nonlinear mechanical systems. The technique exploits frequency-domain data and interprets nonlinearities as feedback forces exciting the underlying linear system. It is first demonstrated using two academic examples, namely a Duffing oscillator and a five-degree-of-freedom system comprising two nonlinearities. The identification of an experimental beam exhibiting geometrically nonlinear behaviour is then addressed. [less ▲] Detailed reference viewed: 35 (13 ULg)Performance and Robustness of the Nonlinear Tuned Vibration Absorber Detroux, Thibaut ; Masset, Luc ; Kerschen, Gaëtan in Proceedings of the GDR DYNOLIN 3437 (2015) (2013, October 17) Detailed reference viewed: 14 (2 ULg)Numerical computation of nonlinear normal modes of nonconservative systems Renson, Ludovic ; Kerschen, Gaëtan in Proceedings of the ASME IDETC/CIE 2013 (2013, August) Since linear modal analysis fails in the presence of nonlinear dynamical phenomena, the concept of nonlinear normal modes (NNMs) was introduced with the aim of providing a rigorous generalization of ... [more ▼] Since linear modal analysis fails in the presence of nonlinear dynamical phenomena, the concept of nonlinear normal modes (NNMs) was introduced with the aim of providing a rigorous generalization of linear normal modes to nonlinear systems. Initially defined as periodic solutions, numerical techniques such as the continuation of periodic solutions were used to compute NNMs. Because these methods are limited to conservative systems, the present study targets the computation of NNMs for nonconservative systems. Their definition as invariant manifolds in phase space is considered. Specifically, the partial differential equations governing the manifold geometry are considered as transport equations and an adequate finite element technique is proposed to solve them. The method is first demonstrated on a conservative nonlinear beam and the results are compared to standard continuation techniques. Then, linear damping is introduced in the system and the applicability of the method is demonstrated. [less ▲] Detailed reference viewed: 44 (5 ULg)Experimental identification of the complex dynamics of a strongly nonlinear spacecraft structure Noël, Jean-Philippe ; Renson, Ludovic ; Kerschen, Gaëtan in Proceedings of the ASME IDETC/CIE 2013 (2013, August) The present paper addresses the identification of a real-life spacecraft structure possessing an impact-type nonlinear component. The complete identification procedure, i.e. from nonlinearity detection to ... [more ▼] The present paper addresses the identification of a real-life spacecraft structure possessing an impact-type nonlinear component. The complete identification procedure, i.e. from nonlinearity detection to parameter estimation, is carried out using experimental data collected during a typical spacecraft qualification test campaign. The complementary use of several techniques reveals particularly interesting and complex phenomena such as nonlinear jumps, nonlinear modal interactions, internal force relaxation and chattering during impacts. [less ▲] Detailed reference viewed: 49 (13 ULg)Identification of mechanical systems with local nonlinearities through discrete-time Volterra series and Kautz functions ; Noël, Jean-Philippe ; Kerschen, Gaëtan et al in Proceedings of the 11th International Conference on Recent Advances in Structural Dynamics (2013, July) Mathematical modeling of mechanical structures is an important research area in structural dynamics. One of the goals of this area is to obtain a model that accurately predicts the dynamics of the system ... [more ▼] Mathematical modeling of mechanical structures is an important research area in structural dynamics. One of the goals of this area is to obtain a model that accurately predicts the dynamics of the system. However, the nonlinear eff ects caused by large displacements and boundary conditions like gap, backlash or joint are not as well understood as the linear counterpart. This paper identifies a non-parametric discrete-time Volterra model of a benchmark nonlinear structure consisting of a cantilever beam connected to a thin beam at its free end. Time-domain data experimentally measured are used to identify the Volterra kernels, which are expanded with orthogonal Kautz functions to facilitate the identification process. The nonlinear parameters are then estimated through a model updating process involving optimization of the residue between the numerical and experimental kernels. The advantages and drawbacks of the Volterra series for modeling the behavior of nonlinear structures are finally indicated with suggestions to overcome the disadvantages found during the tests. [less ▲] Detailed reference viewed: 102 (5 ULg)A new computational method for nonlinear normal modes of nonconservative systems Renson, Ludovic ; Kerschen, Gaëtan in Proceedings of the Euromech Colloquium n. 541 - New Advances in the Nonlinear Dynamics and Control of Composites for Smart Engineering Design (2013, June) The concept of nonlinear normal modes (NNMs) was introduced with the aim of providing a rigorous generalization of normal modes to nonlinear systems. Initially, NNMs were defined as periodic solutions of ... [more ▼] The concept of nonlinear normal modes (NNMs) was introduced with the aim of providing a rigorous generalization of normal modes to nonlinear systems. Initially, NNMs were defined as periodic solutions of the underlying conservative system, and continuation algorithms were recently exploited to compute them. To extend the concept of NNMs to nonconservative systems, Shaw and Pierre defined an NNM as a two-dimensional invariant manifold in the system’s phase space. This contribution presents a novel algorithm for solving the set of partial differential equations governing the manifold geometry numerically. The resolution strategy takes advantage of the hyperbolic nature of the equations to progressively solve them in annular regions. Each region is defined by two different iso-energy curves and equations are discretized using a specific finite element technique. The proposed strategy also offers the opportunity to estimate the frequency-energy dependence of the mode without using time integration. The algorithm is applied to both conservative and nonconservative systems. [less ▲] Detailed reference viewed: 41 (5 ULg)Nonlinear dynamic analysis of an F-16 aircraft using GVT data Noël, Jean-Philippe ; Renson, Ludovic ; Kerschen, Gaëtan et al in Proceedings of the International Forum on Aeroelasticity and Structural Dynamics (2013, June) This paper aims at investigating the nonlinear dynamics of an F-16 aircraft, based upon sine-sweep data collected during a ground vibration test (GVT) campaign. Various analysis techniques, including the ... [more ▼] This paper aims at investigating the nonlinear dynamics of an F-16 aircraft, based upon sine-sweep data collected during a ground vibration test (GVT) campaign. Various analysis techniques, including the mere visual inspection of the time series, the wavelet transform and the restoring force surface method, are utilised and reveal that the F-16 wing-to-payload mounting interfaces exhibit both softening and hardening nonlinearities. [less ▲] Detailed reference viewed: 88 (16 ULg)Comparison between analytical and optimal control techniques in the differential drag based rendez-vous Dell'Elce, Lamberto ; Kerschen, Gaëtan in Proceedings of the 5th International Conference on Spacecraft Formation Flying Missions & Technologies (2013, May 29) The focus of this study is on differential drag for propellantless satellite rendez-vous. This technique is particularly attractive for low-Earth-orbit small satellites for which stringent weight ... [more ▼] The focus of this study is on differential drag for propellantless satellite rendez-vous. This technique is particularly attractive for low-Earth-orbit small satellites for which stringent weight constraints apply. Most existing contributions are based on bang-bang strategies, which may be difficult to implement in practice. This is why the present paper proposes a novel strategy integrating pseudospectral optimal control for maneuver planning and model predictive control for dealing with uncertainties and unmodeled dynamics. One important advantage of this methodology is that it can naturally account for attitude dynamics and constraints, which, in turn, paves the way for the practical realization of differential drag-based rendez-vous. A realistic scenario involving two nanosatellites of the QB50 constellation is considered to illustrate and validate the proposed developments. In addition, a comparison of this numerical technique with an existing analytic solution is carried out, and their respective pros and cons are discussed. [less ▲] Detailed reference viewed: 21 (9 ULg)Computation of nonlinear normal modes through continuation methods Renson, Ludovic ; Kerschen, Gaëtan Conference (2013, May) In mechanical engineering, performance enhancement usually results in lighter and more flexible structures and pushes the limits of the system operating envelope. Nonlinearity is therefore becoming a ... [more ▼] In mechanical engineering, performance enhancement usually results in lighter and more flexible structures and pushes the limits of the system operating envelope. Nonlinearity is therefore becoming a frequent occurrence and linear design tools show their limitations. To overcome these issues, nonlinear normal modes (NNMs) were introduced in structural dynamics as a direct extension of linear normal modes to nonlinear systems. Our contribution reviews the history and the new trends for the computation of NNMs in mechanical engineering. Specifically, algorithms for the continuation of periodic solutions were first developed. Such algorithms are now well-established and applicable to large-scale systems such as real-life aerospace structures. To further extend the concept of NNMs to nonconservative systems, the definition of an NNM as an invariant manifold in the system’s phase space was introduced. Again, continuation techniques are particularly well suited for computing these invariant manifolds. The geodesic level set method developed by Krauskopf and Osinga [1] as well as the “PDE formulation” method of Guckenheimer and Vladimirsky [2] are both considered. [1] Krauskopf, B. and H. Osinga (2003). "Computing Geodesic Level Sets on Global (Un)stable Manifolds of Vector Fields." SIAM Journal on Applied Dynamical Systems 2(4): 546-569. [2] Guckenheimer, J. and A. Vladimirsky (2004). "A Fast Method for Approximating Invariant Manifolds." SIAM Journal on Applied Dynamical Systems 3(3): 232-260. [less ▲] Detailed reference viewed: 16 (3 ULg)Frequency-domain subspace identification of nonlinear mechanical systems Noël, Jean-Philippe ; Kerschen, Gaëtan in Proceedings of the 5th International Operational Modal Analysis Conference (2013, May) The objective of the present paper is to address the identification of a real-life strongly nonlinear space structure, the EADS-Astrium SmallSat spacecraft. To this end, a new nonlinear subspace ... [more ▼] The objective of the present paper is to address the identification of a real-life strongly nonlinear space structure, the EADS-Astrium SmallSat spacecraft. To this end, a new nonlinear subspace identification method formulated in the frequency domain is exploited, referred to as the FNSI method. The frequency response functions of the underlying linear spacecraft and the amplitudes of the nonlinear internal forces are estimated based on a periodic-random data set corrupted by noise. This application is challenging for several reasons, including high modal density, highly non-proportional damping and the non-smooth nature of the nonlinearities. [less ▲] Detailed reference viewed: 72 (7 ULg)Nonparametric subspace identification of nonlinear structures - Application to a spacecraft Noël, Jean-Philippe ; Kerschen, Gaëtan in Proceedings of the 54th AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference (2013, April) The objective of the present paper is to address the identification of a strongly nonlinear satellite structure by exploiting a new nonlinear subspace identification method formulated in the frequency ... [more ▼] The objective of the present paper is to address the identification of a strongly nonlinear satellite structure by exploiting a new nonlinear subspace identification method formulated in the frequency domain, referred to as the FNSI method. The modal parameters of the underlying linear structure and the coefficients of the nonlinear internal forces will be estimated by this approach. Moreover, because a priori knowledge about nonlinear behaviour may be limited, the paper also proposes a nonparametric spline-based modelling strategy, encapsulated in the FNSI method. The application of interest is the SmallSat spacecraft developed by EADS-Astrium, which possesses an impact-type nonlinear device consisting of eight mechanical stops limiting the motion of an inertia wheel mounted on an elastomeric interface. [less ▲] Detailed reference viewed: 40 (9 ULg)Frequency-domain subspace identification of nonlinear mechanical systems - Application to a solar array structure Noël, Jean-Philippe ; Kerschen, Gaëtan ; et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXI (2013, February) The present paper addresses the experimental identification of a simplified realisation of a solar array structure in folded configuration. To this end, a nonlinear subspace identification technique ... [more ▼] The present paper addresses the experimental identification of a simplified realisation of a solar array structure in folded configuration. To this end, a nonlinear subspace identification technique formulated in the frequency domain, referred to as the FNSI method, is exploited. The frequency response functions of the underlying linear structure and the nonlinear coefficients are estimated by this approach. Nonlinearity is caused by impacts between adjacent panels and friction and gaps appearing in their clamping interfaces. This application is challenging for several reasons, which include high modal density and the complicated nature of the involved nonlinear mechanisms. [less ▲] Detailed reference viewed: 81 (8 ULg)Uncertainty quantification of the aerodynamic force of a convex-shaped spacecraft in free-flow regime Dell'Elce, Lamberto ; Kerschen, Gaëtan Conference (2013) Non-spherical gravitational effects and aerodynamic force are the dominant perturbations for low-Earth-orbiting spacecraft. If the former can be modeled with arbitrary accuracy for most applications, it ... [more ▼] Non-spherical gravitational effects and aerodynamic force are the dominant perturbations for low-Earth-orbiting spacecraft. If the former can be modeled with arbitrary accuracy for most applications, it is not possible for the latter. Uncertainties in the aerodynamic force invalidate any attempt to perform deterministic propagations of the position of the spacecraft, regardless the duration of the simulation. However, the effect of drag, which is largely the main component of the force, is a monotonic decrease of the semi-major axis of the orbit, so that these uncertainties are a major concern for long-term predictions. The purpose of this study is the characterization, propagation, and sensitivity analysis of the uncertainty source in the aerodynamic force of a convex-shaped spacecraft. To illustrate the usefulness of this analysis in real-life applications, the uncertainty quantification of the orbital lifetime of a QB50 nanosatellite is proposed as case study. [less ▲] Detailed reference viewed: 16 (1 ULg)Nonlinear modal analysis of a full-scale aircraft Kerschen, Gaëtan ; ; Golinval, Jean-Claude et al in Journal of Aircraft (2013), 50 Nonlinear normal modes (NNMs), which are defined as a nonlinearextension of the concept of linear normal modes, are a rigorous tool for nonlinear modal analysis. The objective of this paper is to ... [more ▼] Nonlinear normal modes (NNMs), which are defined as a nonlinearextension of the concept of linear normal modes, are a rigorous tool for nonlinear modal analysis. The objective of this paper is to demonstrate that the computation of NNMs and of their oscillation frequencies can now be achieved for complex, real-world aerospace structures. The application considered in this study is the airframe of the Morane-Saulnier Paris aircraft. Ground vibration tests of this aircraft exhibited softening nonlinearities in the connection between the external fuel tanks and the wing tips. The NNMs of this aircraft are computed from a reduced-order nonlinear finite element model using a numerical algorithm combining shooting and pseudo-arclength continuation. Several NNMs, involving, e.g., wing bending, wing torsion and tail bending, are presented, which highlights that the aircraft can exhibit very interesting nonlinear phenomena. Specifically, it is shown that modes with distinct linear frequencies can interact and generate additional nonlinear modes with no linear counterpart. [less ▲] Detailed reference viewed: 41 (3 ULg)Vibrational dynamics of vocal folds using nonlinear normal modes ; Kerschen, Gaëtan in Medical Engineering & Physics (2013), 35 Many previous works involving physical models, excised and in vivo larynges have pointed out nonlinear vibration in vocal folds during voice production. Moreover, theoretical studies involving mechanical ... [more ▼] Many previous works involving physical models, excised and in vivo larynges have pointed out nonlinear vibration in vocal folds during voice production. Moreover, theoretical studies involving mechanical modeling of these folds have tried to gain a profound understanding of the observed nonlinear phenomena. In this context, the present work uses the nonlinear normal mode theory to investigate the nonlinear modal behavior of 16 subjects using a two-mass mechanical modeling of the vocal folds. The free response of the conservative system at different energy levels is considered to assess the impact of the structural nonlinearity of the vocal fold tissues. [less ▲] Detailed reference viewed: 42 (8 ULg)Scientific and Technological Payloads Aboard the B3LSat CubeSat of the QB50 Network Dell'Elce, Lamberto ; Kerschen, Gaëtan ; et al in Proceedings of the 2nd IAA Conference on University Satellite Missions and Cubesat Workshop (2013) Detailed reference viewed: 95 (8 ULg)Nonlinear Normal Modes of Nonconservative Systems Renson, Ludovic ; Kerschen, Gaëtan in Proceedings of the SEM IMAC XXXI Conference (2013) Linear modal analysis is a mature tool enjoying various applications ranging from bridges to satellites. Nevertheless, modal analysis fails in the presence of nonlinear dynamical phenomena and the ... [more ▼] Linear modal analysis is a mature tool enjoying various applications ranging from bridges to satellites. Nevertheless, modal analysis fails in the presence of nonlinear dynamical phenomena and the development of a practical nonlinear analog of modal analysis is a current research topic. Recently, numerical techniques (e.g., harmonic balance, continuation of periodic solutions) were developed for the computation of nonlinear normal modes (NNMs). Because these methods are limited to conservative systems, the present study targets the computation of NNMs for nonconservative systems. Their definition as invariant manifolds in phase space is considered. Specifically, a new finite element technique is proposed to solve the set of partial differential equations governing the manifold geometry. [less ▲] Detailed reference viewed: 35 (5 ULg)Nonlinear Dynamic Analysis of Aerospace Structures Kerschen, Gaëtan ; Noël, Jean-Philippe ; Renson, Ludovic et al Conference (2012, October) Current practice in industry is to rely on linear finite element simulations. However, nonlinearity is a frequent occurrence in engineering structures. It is at the origin of rich and complex dynamical ... [more ▼] Current practice in industry is to rely on linear finite element simulations. However, 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. Solving both the direct and inverse problems in nonlinear structural dynamics therefore warrants the development of appropriate methodologies. The focus of the presentation will first be on the inverse problem. We will describe the different steps of the nonlinear system identification process and discuss the current capabilities of existing methods. The presentation will then address the direct problem during which the identified model is used for accurately predicting the structure’s dynamic characteristics. A rigorous nonlinear extension of modal analysis will be presented, and we will show that it represents a very useful framework for understanding nonlinear dynamical phenomena and supporting design decisions. Two real-life aerospace structures will be considered for illustrating the proposed developments. [less ▲] Detailed reference viewed: 75 (11 ULg) |
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