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: 13 (5 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: 12 (5 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: 10 (0 ULg)Suppression of Limit Cycle Oscillations using the Nonlinear Tuned Vibration Absorber Habib, Giuseppe ; Kerschen, Gaëtan in Proceeding IMAC XXXIII A Conference and Exposition on Structural Dynamics, Orlando 2-5 February 2015 (2015, February 03) The objective of the present study is to mitigate, or even completely eliminate, the limit cycle oscillations in mechanical systems using a passive nonlinear absorber, termed the nonlinear tuned vibration ... [more ▼] The objective of the present study is to mitigate, or even completely eliminate, the limit cycle oscillations in mechanical systems using a passive nonlinear absorber, termed the nonlinear tuned vibration absorber (NLTVA). An unconventional aspect of the NLTVA is that the mathematical form of its restoring force is not imposed a priori, as it is the case for most existing nonlinear absorbers. The NLTVA parameters are determined analytically using stability and bifurcation analyses, and the resulting design is validated numerically using the MATCONT software. The proposed developments are illustrated using a Van der Pol-Du ng primary system. [less ▲] Detailed reference viewed: 64 (13 ULg)Bridging the gap between Nonlinear Normal Modes and Modal Derivatives ; Renson, Ludovic ; et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February) Nonlinear Normal Modes (NNMs) have a clear conceptual relation to the classical linear normal modes (LNMs), yet they offer a solid theoretical framework for interpreting a wide class of non-linear ... [more ▼] Nonlinear Normal Modes (NNMs) have a clear conceptual relation to the classical linear normal modes (LNMs), yet they offer a solid theoretical framework for interpreting a wide class of non-linear dynamical phenomena with no linear counterpart. The main difficulty associated with NNMs is that their calculation for large-scale models is expensive, particularly for distributed nonlinearities. Repeated direct time integrations need to be carried out together with extensive sensitivity analysis to reproduce the frequency-energy dependence of the modes of interest. In the present paper, NNMs are computed from a reduced model obtained using a quadratic transformation comprising LNMs and Modal Derivatives (MDs). Previous studies have shown that MDs can capture the essential dynamics of geometrically nonlinear structures and can greatly reduce the computational cost of time integration. A direct comparison with the NNMs computed from another standard reduction technique highlights the capability of the proposed reduction method to capture the essential nonlinear phenomena. The methodology is demonstrated using simple examples with 2 and 4 degrees of freedom. [less ▲] Detailed reference viewed: 20 (1 ULg)Experimental demonstration of a 3D-printed nonlinear tuned vibration absorber Grappasonni, Chiara ; Habib, Giuseppe ; Detroux, Thibaut et al in Proceedings of the International Modal Analysis Conference (IMAC) XXXIII (2015, February) Engineering structures are designed to be lighter and more flexible, hence reducing the extent of application of linear dynamic models. Concurrently, vibration mitigation is required for enhancing the ... [more ▼] Engineering structures are designed to be lighter and more flexible, hence reducing the extent of application of linear dynamic models. Concurrently, vibration mitigation is required for enhancing the performance, comfort or safety in real-life applications. Passive linear vibration absorbers are purpose-built, often designed using Den Hartog's equal-peak strategy. However, nonlinear systems are known to exhibit frequency-energy-dependent oscillations which linear absorbers cannot effectively damp out. In this context, the paper introduces a new nonlinear tuned vibration absorber (NLTVA) whose nonlinear functional form is tailored according to the frequency-energy dependence of the nonlinear primary structure. The NLTVA design aims at ensuring equal peaks in the nonlinear receptance function for an as large as possible range of forcing amplitudes, hence generalizing Den Hartog's method to nonlinear systems. Our focus in this study is on experimental demonstration of the NLTVA performance using a primary structure consisting of a cantilever beam with a geometrically nonlinear component at its free end. The absorber is implemented using a doubly-clamped beam fabricated thanks to 3D printing. The NLTVA performance is also compared with that of the classical linear tuned vibration absorber. [less ▲] Detailed reference viewed: 42 (5 ULg)Nonlinear generalization of Den Hartog׳s equal-peak method Habib, Giuseppe ; Detroux, Thibaut ; et al in Mechanical Systems & Signal Processing (2015), 52-53 This study addresses the mitigation of a nonlinear resonance of a mechanical system. In view of the narrow bandwidth of the classical linear tuned vibration absorber, a nonlinear absorber, termed the ... [more ▼] This study addresses the mitigation of a nonlinear resonance of a mechanical system. In view of the narrow bandwidth of the classical linear tuned vibration absorber, a nonlinear absorber, termed the nonlinear tuned vibration absorber (NLTVA), is introduced in this paper. An unconventional aspect of the NLTVA is that the mathematical form of its restoring force is tailored according to the nonlinear restoring force of the primary system. The NLTVA parameters are then determined using a nonlinear generalization of Den Hartog׳s equal-peak method. The mitigation of the resonant vibrations of a Duffing oscillator is considered to illustrate the proposed developments. [less ▲] Detailed reference viewed: 26 (6 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: 27 (2 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: 27 (8 ULg)Optimal propellantless rendez-vous using differential drag Dell'Elce, Lamberto ; Kerschen, Gaëtan in Acta Astronautica (2015), 109 Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us ... [more ▼] Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us to turn the often-undesired drag perturbation into a control force for relative motion, differential drag is among the most promising propellantless techniques for low-Earth orbiting satellites. An optimal control approach to the problem of orbital rendez-vous using differential drag is proposed in this paper. Thanks to the scheduling of a reference maneuver by means of a direct transcription, the method is flexible in terms of cost function and can easily account for constraints of various nature. Considerations on the practical realization of differential-drag-based maneuvers are also provided. The developments are illustrated by means of high-fidelity simulations including coupled 6-degree-of-freedom simulations and an advanced aerodynamic model. [less ▲] Detailed reference viewed: 10 (2 ULg)Optimal propellantless rendez-vous using differential drag Dell'Elce, Lamberto ; Kerschen, Gaëtan in Acta Astronautica (2015), 109 Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us ... [more ▼] Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us to turn the often-undesired drag perturbation into a control force for relative motion, differential drag is among the most promising propellantless techniques for low-Earth orbiting satellites. An optimal control approach to the problem of orbital rendez-vous using differential drag is proposed in this paper. Thanks to the scheduling of a reference maneuver by means of a direct transcription, the method is flexible in terms of cost function and can easily account for constraints of various nature. Considerations on the practical realization of differential-drag-based maneuvers are also provided. The developments are illustrated by means of high-fidelity simulations including coupled 6-degree-of-freedom simulations and an advanced aerodynamic model. [less ▲] Detailed reference viewed: 10 (2 ULg)Optimal propellantless rendez-vous using differential drag Dell'Elce, Lamberto ; Kerschen, Gaëtan in Acta Astronautica (2015), 109 Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us ... [more ▼] Optimization of fuel consumption is a key driver in the design of spacecraft maneuvers. For this reason, growing interest in propellant-free maneuvers is observed in the literature. Because it allows us to turn the often-undesired drag perturbation into a control force for relative motion, differential drag is among the most promising propellantless techniques for low-Earth orbiting satellites. An optimal control approach to the problem of orbital rendez-vous using differential drag is proposed in this paper. Thanks to the scheduling of a reference maneuver by means of a direct transcription, the method is flexible in terms of cost function and can easily account for constraints of various nature. Considerations on the practical realization of differential-drag-based maneuvers are also provided. The developments are illustrated by means of high-fidelity simulations including coupled 6-degree-of-freedom simulations and an advanced aerodynamic model. [less ▲] Detailed reference viewed: 10 (2 ULg)Dell'Elce, Lamberto ; Kerschen, Gaëtan in Acta Astronautica (2015), 109 Analytic solution for the relative motion of satellites in near-circular low-Earth orbits Martinusi, Vladimir ; Dell'Elce, Lamberto ; Kerschen, Gaëtan in Proceedings of the AAS/AIAA Space FLight Mechanics Meeting (2015) The paper presents the solution to the problem of the relative motion between two satellites orbiting Earth under the influence of the oblateness and atmospheric drag perturbations. Starting from the ... [more ▼] The paper presents the solution to the problem of the relative motion between two satellites orbiting Earth under the influence of the oblateness and atmospheric drag perturbations. Starting from the analytic solution to the problem of the absolute motion, the closed-form equations of motion are obtained. No simplifying assumptions are made on the relative dynamics. [less ▲] Detailed reference viewed: 11 (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: 18 (3 ULg)The Harmonic Balance Method for Bifurcation Analysis of Nonlinear Mechanical Systems Detroux, Thibaut ; Renson, Ludovic ; Masset, Luc et al in Proceedings of the SEM IMAC XXXIII (2015) Because nowadays structural engineers are willing to use or at least understand nonlinearities instead of simply avoiding them, there is a need for numerical tools performing analysis of nonlinear large ... [more ▼] Because nowadays structural engineers are willing to use or at least understand nonlinearities instead of simply avoiding them, there is a need for numerical tools performing analysis of nonlinear large-scale structures. Among these techniques, the harmonic balance (HB) method is certainly one of the most commonly used to study finite element models with reasonably complex nonlinearities. However, in its classical formulation the HB method is limited to the approximation of periodic solutions. For this reason, the present paper proposes to extend the method to the detection and tracking of codimension-1 bifurcations in the system parameters space. As an application, the frequency response of a 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: 86 (22 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: 23 (3 ULg)Piezoelectric vibration damping using resonant shunt circuits: an exact solution Soltani, Payam ; Kerschen, Gaëtan ; et al in Smart Materials & Structures (2014), 23 Detailed reference viewed: 10 (1 ULg)Probabilistic Assessment of Lifetime of Low-Earth-Orbit Spacecraft: Uncertainty Propagation and Sensitivity Analysis Dell'Elce, Lamberto ; Kerschen, Gaëtan in Journal of Guidance Control & Dynamics (2014) This paper is devoted to the probabilistic uncertainty quantification of orbital lifetime estimation of low-altitude satellites. Specifically, given a detailed characterization of the dominant sources of ... [more ▼] This paper is devoted to the probabilistic uncertainty quantification of orbital lifetime estimation of low-altitude satellites. Specifically, given a detailed characterization of the dominant sources of uncertainty, we map this input into a probabilistic characterization of the orbital lifetime through orbital propagation. Standard Monte Carlo propagation is first considered. The concept of drag correction is then introduced to facilitate the use of polynomial chaos expansions and to make uncertainty propagation computationally effective. Finally, the obtained probabilistic model is exploited to carry out stochastic sensitivity analyses, which in turn allow gaining insight into the impact uncertainties have on orbital lifetime. The proposed developments are illustrated using one CubeSat of the QB50 constellation. [less ▲] Detailed reference viewed: 12 (1 ULg)Finite element model reduction for the determination of accurate conductive links and application to MTG IRS BTA Jacques, Lionel ; Thibert, Tanguy ; Jamotton, Pierre et al Conference (2014, October 15) Detailed reference viewed: 25 (6 ULg) |
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