ORBi Open Repository and Bibliography
In may 2007, the ULg's Administrative Board (joined in June 2007 by the FUSAGx) decided to create an institutional repository and defined a strong institutional self-archiving policy to increase the visibility, accessibility and impact of the University's publications (Board's decision).
This decision led to the official launch, in November 2008, of the ORBi platform including both the Academic Bibliography and the Institutional Repository of the Wallonia-Europe University Academy.
Performance and Robustness of Nonlinear Systems Using Bifurcation Analysis - Detroux, Thibaut
Nonlinear vibrations can be frequently encountered in engineering applications, and take their origin from different sources including contact, friction or large displacements. Other manifestations of nonlinearities are peculiar phenomena such as amplitude jumps, quasi-periodic oscillations and isolated response curves. These phenomena are closely related to the presence of bifurcations in the frequency response, which dictate the system's dynamics. While recent progress has been achieved to develop tools for nonlinear modal analysis of industrial applications, bifurcation analysis was still limited to reduced models and academic case studies. Along with the lack of an efficient algorithm to detect and study bifurcations, bifurcation...
Etude mécanique et thermo-mécanique du coronographe de la mission Proba-3 - Desselle, Richard
L'objectif de ce travail de fin d'études était de réaliser le design du coronographe de la mission Proba-3 de l'ESA afin de pouvoir le valider à l'aide d'une étude mécanique et thermo-mécanique de celui-ci. Le point de départ de ce projet était le design préliminaire de l'instrument proposé par le LAM et les spécifications de l'ESA.
L'ensemble des designs réalisés dans ce travail ont été dessinés à l'aide du logiciel Catia V5. Certaines études, menant à des résultats numériques utiles pour la réalisation des designs, ont été menées par l'intermédiaire du logiciel Matlab. Ensuite, l'étude mécanique et thermo-mécanique de l'instrument a...
Feasibility of a UV imager onboard a Cubesat platform - Kintziger, Christian
This Master thesis presents the feasibility study of an ultraviolet imager onboard a Cubesat platform. The goal is to observe the Io's torus with the help of a triple unit Cubesat. Similar projects are studied to identify possible components for the mission. A mission analysis is carried out to highlight suitable intervals of time to observe the Io's torus when considering different orbits. Then optical design processes are performed to obtain a telescope that fits in the Cubesat platform. Eventually a final design that fulfils all the scientific requirements is introduced and a few perspectives are proposed for the future...
Aerothermodynamics of Pre-Flight and In-Flight Testing Methodologies for Atmospheric Entry Probes - Sakraker, Isil
Spacecraft, returning back to Earth, experience a very harsh environment during the encounter with the particles of the atmosphere. One of the major issues of the atmospheric entry is the extreme aerodynamic heating and the exothermic chemical reactions due to the gas-surface interaction at hypersonic free stream velocities. There is a constant effort by the space agencies to increase the understanding of the re-entry flight dynamics to optimize the spacecraft and especially its thermal protection system design. During the design process, ground tests and numerical tools are extensively used for their low cost and controlled environment abilities. However, real flight...
Hysteresis identification using nonlinear state-space models - Noël, Jean-Philippe; Esfahani, Alireza; Kerschen, Gaëtan; Schoukens, Johan
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...
Multivariate ARMA Based Modal Identification of a Time-varying Beam - Bertha, Mathieu; Golinval, Jean-Claude
The present paper addresses the problem of modal identification of time-varying systems. The identification is based on a multivariate autoregressive moving-average model in which the time variability of the system is caught using a basis functions approach. In this approach, the time-varying regressive coefficients in the model are expended in the chosen basis functions and only the projection coefficients have to be identified. In that way, the initial time-varying problem then becomes a time-invariant one that can be solved. Because a multivariate model is used, in addition to the time-varying poles, the time-varying mode shapes may be identified too. The...
Robust Subspace Identification of a Nonlinear Satellite Using Model Reduction - Dossogne, Tilàn; Noël, Jean-Philippe; Kerschen, Gaëtan
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...
A Comparison of Reduced Order Modeling Techniques Used in Dynamic Substructuring - Roettgen, Daniel; Seeger, Benjamin; Tai, Wei Che; Baek, Seung Hun; Dossogne, Tilàn; Allen, Matthew; Kuether, Robert; Brake, Matthew; Mayes, Randall
Experimental dynamic substructuring is a means whereby a mathematical model for a substructure can be obtained experimentally and then coupled to a model for the rest of the assembly to predict the response. Recently, various methods have been proposed that use a transmission simulator to overcome sensitivity to measurement errors and to exercise the interface between the substructures; including the Craig-Bampton, Dual Craig-Bampton, and Craig-Mayes methods. This work compares the advantages and disadvantages of these reduced order modeling strategies for two dynamic substructuring problems. The methods are first used on an analytical beam model to validate the methodologies. Then they...
The optical blocking filter for the ATHENA wide field imager: ongoing activities towards the conceptual design - Barbera, M.; Branduardi-Raymont, G.; Collura, A.; Comastri, A.; Eder, J.; Kamisiński, T.; Lo Cicero, U.; Meidinger, N.; Mineo, T.; Molendi, S.; Parodi, G.; Pilch, A.; Piro, L.; Rataj, M.; Rauw, Gregor; Sciortino, L.; Sciortino, S.; Wawer, P.
ATHENA is the L2 mission selected by ESA to pursue the science theme "Hot and Energetic Universe" (launch scheduled in 2028). One of the key instruments of ATHENA is the Wide Field Imager (WFI) which will provide imaging in the 0.1-15 keV band over a 40'x40' large field of view, together with spectrally and time-resolved photon counting. The WFI camera, based on arrays of DEPFET active pixel sensors, is also sensitive to UV/Vis photons. Optically generated electron-hole pairs may degrade the spectral resolution as well as change the energy scale by introducing a signal offset. For this reason, the use...
Experimental study of isolated response curves in a two-degree-of-freedom nonlinear system - Detroux, Thibaut; Noël, Jean-Philippe; Kerschen, Gaëtan; Virgin, Lawrence N.
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.