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.
Importance of structural damping in the dynamic analysis of compliant deployable structures - Dewalque, Florence; Rochus, Pierre; Bruls, Olivier
Compliant mechanisms such as tape springs are often used on satellites to deploy appendices, e.g. solar panels, antennas, telescopes and solar sails. Their main advantage comes from the fact that their motion results from the elastic deformation of structural components, unlike usual hinges or prismatic joints, the motion of which is dictated by contact surfaces. No actuators or external energy sources are required and the deployment is purely passive, which appears as a decisive feature for the design of low-cost missions with small satellites or cubesats. The mechanical behaviour of a tape spring is intrinsically complex and nonlinear involving buckling,...
Space radiation parameters for EUI and the Sun Sensor of Solar Orbiter, ESIO and JUDE instruments - Rossi, Laurence; Jacques, Lionel; Halain, Jean-Philippe; Grodent, Denis; Renotte, Etienne; Thibert, Tanguy
This paper presents predictions of space radiation parameters for four space instruments performed by the Centre Spatial de Liège (ULg – Belgium); EUI, the Extreme Ultra-violet Instrument, on-board the Solar Orbiter platform; ESIO, Extreme-UV solar Imager for Operations, and JUDE, the Jupiter system Ultraviolet Dynamics Experiment, which was proposed for the JUICE platform.
For Solar Orbiter platform, the radiation environment is defined by ESA environmental specification and the determination of the parameters is done through ray-trace analyses inside the EUI instrument.
For ESIO instrument, the radiation environment of the geostationary orbit is defined through simulations of the trapped particles flux, the energetic...
Solar simulation test up to 13 solar constants for the thermal balance of the Solar Orbiter EUI instrument - Rossi, Laurence; zhukova, Maria; Jacques, Lionel; Halain, Jean-Philippe; Hellin, Marie-Laure; Jamotton, Pierre; Renotte, Etienne; Rochus, Pierre; Liébecq, Sylvie; Mazzoli, Alexandra
Solar Orbiter EUI instrument was submitted to a high solar flux to correlate the thermal model of the instrument.
EUI, the Extreme Ultraviolet Imager, is developed by a European consortium led by the Centre Spatial de Liège for the Solar Orbiter ESA M-class mission. The solar flux that it shall have to withstand will be as high as 13 solar constants when the spacecraft reaches its 0.28AU perihelion.
It is essential to verify the thermal design of the instrument, especially the heat evacuation property and to assess the thermo-mechanical behavior of the instrument when submitted to high thermal load.
Therefore, a thermal...
Modal identification of time-varying systems using Hilbert transform and signal decomposition - Bertha, Mathieu; Golinval, Jean-Claude
The present work investigates modal identification of time-varying dynamical systems by exploiting the Hilbert transform. The proposed method, initially based on the Hilbert Vibration Decomposition (HVD) method, first identifies the instantaneous frequencies of the system. Their corresponding components and modal deflection shapes are then extracted from a set of dynamic responses of the system. The proposed method is first presented and then is illustrated on an experimental set-up. The system under investigation is a recurrent experiment in the field of time-varying systems consisting in a beam travelled by a non-negligible mass while excited by a random external force. The results...
Liquid oxygen compatibility of materials for space propulsion needs - Bozet, Jean-Luc; Heyen, Georges; Dodet, Claude; Duquenne, Marc; Kreit, Patrick
Since the origin, the use of liquid oxygen as oxidizer is widespread in space propulsion. It has been the source of numerous incidents. Many materials can burn violently in an oxygen enriched environment when ignited. Consequently, it is mandatory to perform oxygen compatibility tests. In the present work, compatibility tests are impact tests and auto ignition tests. Both standardized test methods are illustrated by test results on polymeric materials (i.e. fluorinated resins, polyimides, polyetherketone) for seals and ball bearing cage. For future needs, in order to face the increase of pressure of injection of propellants in cryogenic engines, the adiabatic...
Influence of liquid oxygen environment on the tribological behaviour of PCTFE/440C steel contact - Cautain, Satia; Duquenne, Marc; Robbe-Valloire, François; Bozet, Jean-Luc
This article proposes a tribological study of contact between polychlorotrifluoroethylene (PCTFE) and 440C steel. The tests are performed on a pin-on-disc cryotribometer specifically designed to overcome the additional issues due to the use of cryogenic fluid. Test parameters such as speed, contact pressure and sliding distance are kept the same for the whole campaign, leaving the environment as the only variable. This study focuses on the analysis of friction, wear of PCTFE pin and appearance of disk after tests. The test results show the influence of the state of environment (gas or liquid), its temperature and its reactivity (neutral or...
Practical design of a nonlinear tuned vibration absorber - Grappasonni, Chiara; Habib, Giuseppe; Detroux, Thibaut; Wang, Fengwen; Kerschen, Gaëtan; Jensen, Jakob Søndergaard
The aim of the paper is to develop a new nonlinear tuned vibration absorber (NLTVA) capable of mitigating the vibrations of nonlinear systems which are known to exhibit frequency-energy-dependent oscillations. A nonlinear generalization of Den Hartog’s equal-peak method is proposed to ensure equal peaks in the nonlinear frequency response for a large range of forcing amplitudes. An analytical tuning procedure is developed and provides the load-deflection characteristic of the NLTVA. Based on this prescribed relation, the NLTVA design is performed by two different approaches, namely thanks to (i) analytical formulas of uniform cantilever and doubly-clamped beams and (ii) numerical shape...
Experimental modal analysis of a beam travelled by a moving mass using Hilbert Vibration Decomposition - Bertha, Mathieu; Golinval, Jean-Claude
In this paper the problem of modal identification of time-varying system is investigated. To do so, a technique based on the sifting process of the Hilbert Vibration Decomposition (HVD) method is presented. The key idea is to estimate the instantaneous frequency of the dominant mode, to extract its corresponding component by demodulation of the recorded signals and then to iterate with the subsequent dominant mode. In the case of multiple recorded signals, a source separation method is used as a preprocessing step to facilitate the identification of the instantaneous frequency for the following demodulation step.
To illustrate the method, an...
Experimental Validation of a Thermal Model of a LOx Flooded Ball Bearing - Servais, Christophe; Bozet, Jean-Luc; Kreit, Patrick; Guingo, Sébastien
Ball bearings of turbopumps of rocket engines work in very singular conditions; they are flooded into liquid oxygen or liquid hydrogen. Therefore, the use of any conventional lubricants (oil or grease) is proscribed. Although cryogenic fluids can cool this kind of ball bearing, they cannot separate the surfaces in contact. As a result, there is a significant increase in frictional power losses. This paper presents tests performed on a cryotechnic ball bearing flooded in liquid oxygen. The test results showed that beyond a critical loading of the bearing, a sudden increase in temperature occurred. A thermal model is also put...
Test equipments for characterizing the behavior of materials, bearings and dynamic seals in cryogenic fluid environments - Bozet, Jean-Luc; Servais, Christophe; Duquenne, Marc; Kreit, Patrick; Dodet, Claude
Test rigs available at the cryogenic test site of the University of Liège concern quite delicate high rotational speed components of cryogenic rocket engines. That is to say bearings and dynamic seals. These rigs gave successfully important results for the understanding and the improvement of the running of the so called components. Until now the test zone is equipped for handling liquid oxygen and liquid nitrogen.
Influence of tribology of cage material on ball bearing cage instability - Servais, Christophe; Duquenne, Marc; Bozet, Jean-Luc
By creating a solid lubricant thickness on both bearing races, a cage material of cryogenic ball bearing plays a significant role in the good dynamical behavior of the cage. This role is essential because of the lack of conventional lubricant into this kind of bearing.
In this paper, a method able to identify if a particular potential cage material can correctly fulfill its function is described. In other words, if it can lead to a stable movement of the cage. From the identification of fundamental tribological parameters governing the cage behavior, this method presents an example of ranking of such materials....