http://hdl.handle.net/2268/90 Search this channel search http://orbi.ulg.ac.be/simple-search http://hdl.handle.net/2268/148479 Title: Quasi-One-Dimensional Numerical Simulations of Post-Stall Compression Systems <br/> <br/>Author, co-author: Du, Wenhai http://hdl.handle.net/2268/148450 Title: Conception et calcul des éléments de machine <br/> <br/>Author, co-author: Debongnie, Jean-François <br/> <br/>Abstract: Texte du cours de conception mécanique donné par l'auteur aux étudiants ingénieur mécanicien de l'Université de Liège. http://hdl.handle.net/2268/148028 Title: ON THE MODELING OF ADHESIVE CONTACT AND STICTION FAILURE IN MICRO-SWITCHES <br/> <br/>Author, co-author: Wu, Ling; Noels, Ludovic; Golinval, Jean-Claude <br/> <br/>Abstract: Undesirable stiction, which results from contact between surfaces, is a major failure mode in micro-switches. Indeed the adhesive forces can become so important that the two surfaces remain permanently glued, limiting the life-time of the MEMS. This is especially true when contact happens between surfaces where elasto-plastic asperities deform permanently until the surfaces reach plastic accommodation, increasing the surface forces. To predict this behavior, a micro adhesive-contact model is developed, which accounts for the surfaces topography evolutions during elasto-plastic contacts. This model can be used at a higher scale to study the MEMS behavior, and thus its life-time. For illustration purpose, an electrostatic-structural analysis is performed on a micro-switch. http://hdl.handle.net/2268/148024 Title: Conception des pseudo-articulations à col paraboique <br/> <br/>Author, co-author: Debongnie, Jean-François <br/> <br/>Abstract: The elastic behaviour of parabolic notch hinges submitted to the classical sollicitations of a beam is studied. For each sollicitation, an analytical solution is given first. Its asymptotic expression for very narrow hinges is then obtained and finally,, an approximate factor relating the exact solution to the asymptotic one is proposed. http://hdl.handle.net/2268/147968 Title: Development of a generalized steady-state simulation framework for positive displacement compressors and expanders <br/> <br/>Author, co-author: Bell, Ian; Lemort, Vincent; Groll, Eckhard; Braun, James; Horton, W. Travis <br/> <br/>Abstract: In this paper, a generalized framework is presented that can be used to simulate the steady-state performance of a wide range of positive displacement compressors and expanders (scroll, piston, screw, rotary, spool, etc.). The complete simulation algorithm is described, and an emphasis is placed on the numerical methods required to obtain robust behavior of the simulation. This formulation has been implemented into an open-source software package entitled PDSim written in the Python language. PDSim is the first open-source generalized compressor and expander simulation package. The source code can be freely obtained from http://pdsim.sf.net http://hdl.handle.net/2268/147945 Title: Simulation of a cold climate heat pump furnished with a scroll compressor with multiple injection lines <br/> <br/>Author, co-author: Bell, Ian; Groll, Eckhard; Braun, James; Horton, W. Travis <br/> <br/>Abstract: A detailed scroll compressor simulation has been developed as described in a companion paper. In this work, the compressor simulation code is used to investigate vapor injection in scroll compressors for cold climate heat pumps. The required analysis is developed for vapor injection in scroll compressors with one or two injection lines. The improvement in heat pump efficiency at a -20 C evaporation temperature with one injection line is as much as 10% while with two injection lines the increase in efficiency can be as much as 16% http://hdl.handle.net/2268/147942 Title: Study on alternative approaches to corrosion protection of ballast tanks using an economic model <br/> <br/>Author, co-author: De Baere, Kris; Verstraelen, Helen; Rigo, Philippe; Van Passel, Steven; Lenaerts, Silvia; Potters, Geert <br/> <br/>Abstract: One of the most relevant problems in ship construction and maintenance nowadays is corrosion in ballast tanks of modern merchant vessels. On the one hand, there is a general consensus that the economic lifespan of such a vessel depends, to a large degree, upon the corrosion state of its ballast tanks, while on the other hand these ballast tanks, located between the outer hull and the cargo tanks, makes routine inspection and maintenance a difficult task. Today, ship's ballast tanks are usually constructed in steel and protected with an epoxy coating backed up by sacrificial zinc anodes. Such a construction has been applied without significant alterations for many years. The objective of this economic study is to compare this construction method with some potential alternatives. The considered alternatives are: (1) an increase in structural scantlings, eliminating the necessity to replace corroded at a cost of real cargo carrying capacity of the ship, (2) application of the novel and more durable TSCF25 coating (3), the use of corrosion resistant steel in ship construction and (4) a standard PSPC15 coating combined with lifetime lasting aluminum sacrificial anodes. A cost model was used to evaluate these alternative options together with sensitivity analysis. It is concluded that the durable coating and the use of lifetime lasting aluminum anodes are bound to improve the actual basic tank concept. Corrosion resistant steel becomes attractive when the steel price becomes competitive. <br/> <br/>Commentary: Ballast tank; Total cost of ballast tanks; Corrosion; Corrosion resistant steel; Coating; Sensitivity analysis http://hdl.handle.net/2268/147586 Title: Adaptive remeshing strategies using solid-shell elements in the numerical simulation of incremental forming processes <br/> <br/>Author, co-author: de Sena, Jose Idlio; Duchene, Laurent; Habraken, Anne; Alves de Sousa, Ricardo; Valente, Robertt http://hdl.handle.net/2268/147331 Title: Ship Manoeuvring Behaviour in Crossing Current Near-by a Lock <br/> <br/>Author, co-author: HASEGAWA, K; OH, K G; Ahmed, Y A; Rigo, Philippe <br/> <br/>Abstract: Ship behaviour in current is one of the classical problems in ship manoeuvrability. However, it is not yet fully investigated. The study is motivated by an assessment study on the ship navigation near by a river lock where relatively strong current exists. It is demonstrated how a ship behaves in the current and relatively large drift angle may happen, if the current is comparative to ship speed. In this situation, the hydrodynamic forces and moment acting on a ship is not any more at the range of lift force/moment, and therefore normal mathematical model cannot be applied. Similar situation may occur in case of rapid river stream condition, when a ship losts its power in current. At East Japan Great Earthquake happened in 2011, many ships without their power were drifting in tsunami. It is urgent matter to investigate on the ship behaviour in such situation. http://hdl.handle.net/2268/147162 Title: Vibrational dynamics of vocal folds using nonlinear normal modes <br/> <br/>Author, co-author: Pinheiro, A.P.; Kerschen, Gaëtan <br/> <br/>Abstract: 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. http://hdl.handle.net/2268/147138 Title: The fracture studies of polycrystalline silicon based MEMS <br/> <br/>Author, co-author: Mulay, Shantanu Shashikant; Becker, Gauthier; Vayrette, Renaud; Raskin, Jean-Pierre; Pardoen, Thomas; Galceran, Montserrat; Godet, Stéphane; Noels, Ludovic <br/> <br/>Abstract: The advantages of micro-electro-mechanical systems (MEMS), such as low power requirement, miniaturized sizes and costs reduction, have already made significant impact in many technological fields. MEMS are now widely used as accelerometers, pressure sensors, and resonators etc. However, the determination of the mechanical properties of MEMS devices with high accuracy is still a challenging task due to their small dimensions and often anisotropic behaviour. This paper focuses on the modelling and simulation of the fracture of a key MEMS component, which is a polycrystalline silicon beam, by discontinuous Galerkin (DG) formulation combined with an extrinsic cohesive law (ECL) to describe the fracture process. As the beam is modelled by plane-stress 2D elements, an analytical equation to compute the effective fracture strength and the effective critical strain energy release rate in terms of the through-the-thickness fracture mode and of the orientation of the facet with respect to the crystal is also developed. At the end, a model is simulated, and the results are verified as per the physics of the problem and experiments. http://hdl.handle.net/2268/146707 Title: Damage detection and local resonances model in CFRP composite material by vibrothermography <br/> <br/>Author, co-author: Demy, Philippe; Golinval, Jean-Claude; Simon, Daniel <br/> <br/>Abstract: Vibrothermography (VT) is an active non destructive technique able to detect singularities like delamination, even if the defect internal faces are in contact. Under sonic or ultrasonic mechanical vibrations, a delamination may behave like a heat source principally due to friction between the rubbing faces and/or stress concentration in the area. The present article focuses on the understanding of the underlying phenomenon so-called "local resonances" and its correlation with the presence of temperature peaks observed at certain frequencies. For this purpose, a simplified finite element modal analysis of the delamination model is compared with the heating rate vs. frequency data's acquired by an infrared camera. Then, some conclusive results of sine sweep and chirp testing will be presented and discussed in regards to this theory. http://hdl.handle.net/2268/145998 Title: Multiscale computational homogenization methods with a gradient enhanced scheme based on the discontinuous Galerkin formulation <br/> <br/>Author, co-author: Nguyen, Van Dung; Becker, Gauthier; Noels, Ludovic <br/> <br/>Abstract: When considering problems of dimensions close to the characteristic length of the material, the size e ects can not be neglected and the classical (so–called first–order) multiscale computational homogenization scheme (FMCH) looses accuracy, motivating the use of a second–order multiscale computational homogenization (SMCH) scheme. This second–order scheme uses the classical continuum at the micro–scale while considering second–order continuum at the macro–scale. Although the theoretical background of the second–order continuum is increasing, the implementation into a finite element code is not straightforward because of the lack of high–order continuity of the shape functions. In this work, we propose a SMCH scheme relying on the discontinuous Galerkin (DG) method at the macro–scale, which simplifies the implementation of the method. Indeed, the DG method is a generalization of weak formulations allowing for inter-element discontinuities either at the C0 level or at the C1 level, and it can thus be used to constrain weakly the C1 continuity at the macro–scale. The C0 continuity can be either weakly constrained by using the DG method or strongly constrained by using usual C0 displacement–based finite elements. Therefore, two formulations can be used at the macro–scale: (i) the full–discontinuous Galerkin formulation (FDG) with weak C0 and C1 continuity enforcements, and (ii) the enriched discontinuous Galerkin formulation (EDG) with high–order term enrichment into the conventional C0 finite element framework. The micro–problem is formulated in terms of standard equilibrium and periodic boundary conditions. A parallel implementation in three dimensions for non–linear finite deformation problems is developed, showing that the proposed method can be integrated into conventional finite element codes in a straightforward and e cient way. http://hdl.handle.net/2268/145692 Title: Robust stress intensity factors evaluation for 3D cracks with X-FEM <br/> <br/>Author, co-author: Minnebo, Hans; Béchet, Eric; Moës, Nicolas http://hdl.handle.net/2268/145691 Title: Explicit dynamics with X-FEM to handle complex geometries <br/> <br/>Author, co-author: Moes, Nicolas; Rozycki, P.; Béchet, Eric http://hdl.handle.net/2268/145331 Title: Satellitenbasiertes Kollisionsvermeidungssystem <br/> <br/>Author, co-author: Christen, Fréderic; Eckstein, Lutz; Katriniok, Alexander; Abel, Dirk <br/> <br/>Abstract: Gegenwärtig entwickelt die RWTH Aachen University im Rahmen des Projekts „Galileo above“ (Anwendungszentrum für bodengebundenen Verkehr) ein Kollisionsvermeidungssystem (Collision Avoidance System, CAS) unter Einbeziehung von Galileo-Daten. Die hierfür benötigten Galileo-Signale werden von den im automotiveGATE errichteten Pseudoliten (Pseudo-Satelliten) ausgestrahlt. Das Vorhaben wird von der Raumfahrt-Agentur des Deutschen Zentrums für Luft­ und Raumfahrt e. V. mit Mitteln des Bundeministeriums für Wirtschaft und Technologie (Förderkennzeichen 50 NA 0902) gefördert. Im Rahmen dieses Beitrags werden Erläuterungen zu Perzeption und Sensorfusion, Deeskalationsstrategie und Eingriffsentscheidung sowie zu ersten Testergebnisse bei Auffahrsituationen des CAS gege-ben. http://hdl.handle.net/2268/145330 Title: Satellite-Based Collision Avoidance System <br/> <br/>Author, co-author: Christen, Fréderic; Eckstein, Lutz; Katriniok, Alexander; Abel, Dirk <br/> <br/>Abstract: Currently the RWTH Aachen University is developing a collision avoidance system (CAS) using Galileo data within the framework of the project ‘Galileo above’ (application centre for ground based traffic). The needed Galileo-signals are emitted by so-called pseudolites (pseudo-satellites) installed on the automotiveGATE. The research project is sponsored by the Space Agency of the German Aero-space Centre (DLR) with funding by the Federal Ministry of Economics and Technology, in compliance with a resolution of the German Parliament (pro-ject/grant no. 50 NA 0902). This paper will give some de-tails on the perception and sensor fusion, the de-escalation and intervention decision as well as on first testing results regarding rear-end collisions. http://hdl.handle.net/2268/145274 Title: Comparison of a fluid and a solid approach for the numerical simulation of Friction Stir Welding with a non-cylindrical pin <br/> <br/>Author, co-author: Bussetta, Philippe; Dialami, Narges; Boman, Romain; Chiumenti, Michele; Agelet de Saracibar, Carlos; Cervera, Miguel; Ponthot, Jean-Philippe <br/> <br/>Abstract: Friction Stir Welding (FSW) process is a solid-state joining process during which materials to be joined are not melted. As a consequence, the heat-affected zone is smaller and the quality of the weld is better with respect to more classical welding processes. Because of extremely high strains in the neighbourhood of the tool, classical numerical simulation techniques have to be extended in order to track the correct material deformations. The Arbitrary Lagrangian Eulerian (ALE) formulation is used to preserve a good mesh quality throughout the computation. With this formulation the mesh displacement is independent from the material displacement. Moreover, some advanced numerical techniques such as remeshing or a special computation of transition interface is needed to take into account non-cylindrical tools. During the FSW process, the behaviour of the material in the neighbourhood of the tool is at the interface between solid mechanics and fluid mechanics. Consequently, a numerical model of the FSW process based on a solid formulation is compared to another one based on a fluid formulation. It is shown that these two formulations essentially deliver the same results in terms of pressures and temperatures. http://hdl.handle.net/2268/145238 Title: A micro-meso-model of intra-laminar fracture in fi ber-reinforced composites based on a Discontinuous Galerkin/Cohesive Zone Method <br/> <br/>Author, co-author: Wu, Ling; Tjahjanto, Denny; Becker, Gauthier; Makradi, Ahmed; Jérusalem, Antoine; Noels, Ludovic <br/> <br/>Abstract: The recently developed hybrid discontinuous Galerkin/extrinsic cohesive law framework is extended to the study of intra{laminar fracture of composite materials. Toward this end, micro-volumes of di erent sizes are studied. The method captures the debonding process, which is herein proposed to be assimilated to a damaging process, before the strain softening onset, and the density of dissipated energy resulting from the damage (debonding) remains the same for the di erent studied cell sizes. Finally, during the strain softening phase a micro{crack initiates and propagates in agreement with experimental observations. We thus extract a resulting mesoscale cohesive law, which is independent on the cell sizes, using literature methods. http://hdl.handle.net/2268/145175 Title: Sensitivity analysis for multibody systems formulated on a Lie group <br/> <br/>Author, co-author: Sonneville, Valentin; Bruls, Olivier <br/> <br/>Abstract: A direct differentiation method and an adjoint variable method are proposed for the efficient semi-analytical evaluation of the sensitivities of multibody systems formulated in a matrix Lie group framework. These methods rely on the linearization of the equations of motion and/or of the time integration procedure. The simpler structure of the equations of motion in the Lie group formalism appears as an advantage for that purpose. Lie bracket contributions and the non-linearity of the exponential map need to be taken into account in the sensitivity algorithms. Nevertheless, essential characteristics of formulations of the direct differentiation method and the adjoint variable method on linear spaces are recovered. Some implementation issues are discussed and two relevant examples illustrate the properties of these methods.