Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailEnhancing Bus Holding Control Using Cooperative ITS
Laskaris, Georgios; Seredynski, Marcin; Viti, Francesco UL

in IEEE Transactions on Intelligent Transportation Systems (2020), 21(4), 1767-1778

Detailed reference viewed: 47 (2 UL)
Full Text
Peer Reviewed
See detailEnhancing Rover Teleoperation on the Moon With Proprioceptive Sensors and Machine Learning Techniques
Coloma Chacon, Sofia UL; Martinez Luna, Carol UL; Yalcin, Baris Can UL et al

in IEEE Robotics and Automation Letters (2022)

Geological formations, environmental conditions, and soil mechanics frequently generate undesired effects on rovers’ mobility, such as slippage or sinkage. Underestimating these undesired effects may ... [more ▼]

Geological formations, environmental conditions, and soil mechanics frequently generate undesired effects on rovers’ mobility, such as slippage or sinkage. Underestimating these undesired effects may compromise the rovers’ operation and lead to a premature end of the mission. Minimizing mobility risks becomes a priority for colonising the Moon and Mars. However, addressing this challenge cannot be treated equally for every celestial body since the control strategies may differ; e.g. the low latency EarthMoon communication allows constant monitoring and controls, something not feasible on Mars. This letter proposes a Hazard Information System (HIS) that estimates the rover’s mobility risks (e.g. slippage) using proprioceptive sensors and Machine Learning (supervised and unsupervised). A Graphical User Interface was created to assist human-teleoperation tasks by presenting mobility risk indicators. The system has been developed and evaluated in the lunar analogue facility (LunaLab) at the University of Luxembourg. A real rover and eight participants were part of the experiments. Results demonstrate the benefits of the HIS in the decision-making processes of the operator’s response to overcome hazardous situations. [less ▲]

Detailed reference viewed: 70 (18 UL)
Full Text
See detailEnriched Element Free Galerkin Method for Gradient Elasticity
Natarajan, S; Kerfriden, P; Bordas, Stéphane UL et al

Scientific Conference (2011, June)

Detailed reference viewed: 113 (0 UL)
Full Text
Peer Reviewed
See detailAn enriched quadtree/octree implicit boundary finite element method for the simulation of incompressible hyperelastic materials
Hale, Jack UL; Bordas, Stéphane UL; Kerfriden, Pierre et al

Scientific Conference (2014, April 03)

Octree (and quadtree) representations of computational geometry are particularly well suited to modelling domains that are defined implicitly, such as those generated by image segmentation algorithms ... [more ▼]

Octree (and quadtree) representations of computational geometry are particularly well suited to modelling domains that are defined implicitly, such as those generated by image segmentation algorithms applied to medical scans. In this work we consider the simulation of soft-tissue which can be modelled with a hyperelastic constitutive law. We include the effects of both non-linear geometry and material properties. Similarly to Legrain et al. (10.1002/nme.3070) and Moumnassi et al. (10.1016/j.cma.2010.10.002) we use the implicitly designed level set functions as the basis for a partition of unity enrichment to more accurately represent the domain boundary. Furthermore we use traditional extended finite element (XFEM) ideas to introduce arbitrary cuts and discontinuities in the domain. We explore the use of a two-field u-p mixed approach as well as a smoothed finite element method (SFEM) to deal with the problem of volumetric-locking in the incompressible limit. We will discuss the extension of our method towards both traditional parallel and GPU implementation. We aim to solve extremely large problems as well as produce snapshots to feed into model order reduction methods for real-time surgical simulations. [less ▲]

Detailed reference viewed: 421 (26 UL)
Full Text
See detailAn Enriched Quasi-Continuum Approach to Crack Propagation in Discrete Lattices
Rokos, Ondrej; Peerlings, Ron; Zeman, Jan et al

Scientific Conference (2017, June 14)

Detailed reference viewed: 94 (0 UL)
Full Text
Peer Reviewed
See detailEnriched residual free bubbles for semiconductor device simulation
Simpson, R. N.; Bordas, Stéphane UL; Asenov, A. et al

in Computational Mechanics (2012), 50(1), 119-133

This article outlines a method for stabilising the current continuity equations which are used for semiconductor device simulation. Residual-free bubble functions (RfBF) are incorporated into a finite ... [more ▼]

This article outlines a method for stabilising the current continuity equations which are used for semiconductor device simulation. Residual-free bubble functions (RfBF) are incorporated into a finite element (FE) implementation that are able to prevent oscillations which are seen when using the conventional Bubnov-Galerkin FE implementation. In addition, it is shown that the RfBF are able to provide stabilisation with very distorted meshes and curved interface boundaries. Comparison with the commonly used SUPG scheme is made throughout, showing that in the case of 2D problems the RfBF allow faster convergence of the coupled semiconductor device equations, especially in the case of distorted meshes. [less ▲]

Detailed reference viewed: 116 (0 UL)
Full Text
Peer Reviewed
See detailThe Enthusiast, the Interested, the Sceptic, and the Cynic: Understanding User Experience and Perceived Value in Location-Based Cultural Heritage Games Through Qualitative and Sentiment Analysis
Jones, Catherine UL; Theodosis, Efstathios UL; Lykourentzou, Ioanna

in Journal on Computing and Cultural Heritage (2019), 12(1),

We discuss the user study of a mobile cultural heritage game, designed to stimulate reflection about a city’s history. Aided by location-aware technology, the game fosters the serendipitous discovery of ... [more ▼]

We discuss the user study of a mobile cultural heritage game, designed to stimulate reflection about a city’s history. Aided by location-aware technology, the game fosters the serendipitous discovery of Points-Of-Interest, historical images and stories, whilst players wander the city. This exploration differs from the typical pre-calculated path recommendations used by other location-based applications. It triggers reflection about the city’s past that is as unique as its visitors. Ours is one of the first studies to attempt an understanding of the effects of serendipitous urban discovery and historic reflection-triggering technologies on user experience. We combined field trials with controlled experiments, analysing perceptions of the experience and value using responses expressed in open-ended questionnaire items. Using thematic coding and sentiment analysis, we observed types of emotional responses, indicating four potential profiles of their likelihood towards future technology adoption. Enthusiastic and Interested users appreciated the freedom of movement choice that created an autonomous experience that fostered a sense of personal accomplishment. The interface interactions of the game, designed to stimulate reflection, supported a feeling of connectedness to others. In contrast, Cynical and Sceptical users were less tolerant of perceived technological issues, and required more perfection in functionality and design. These users are less likely to be the early adopters of serendipitous location-based apps. The game was developed as part of a large cultural informatics project, but unlike typical evaluations, we conducted this study midway through the project and not at its end. This approach (1) gave the team the possibility to take stock, pause and reflect and (2) provided insight on future design improvements for increasing the perceived value of serendipitous urban discovery applications. Our results contribute towards a grounded understanding of user experience, and help progress the development of cultural heritage applications that incorporate elements of reflection and/or place-based exploration into their functionalities. [less ▲]

Detailed reference viewed: 88 (11 UL)
Full Text
Peer Reviewed
See detailEntwicklungsmethodik nach Pahl und Beitz und Design thinking. Vergleich und Einordnung
Gericke, Kilian UL; Beinke, Christian; Gemmer, Pascal et al

in Proceedings of 19th Symposium Design for X (2010)

Die Konstruktionsforschung strebt danach die Entwicklungspraxis zu unterstützen indem Methodiken, Methoden, Tools und Empfehlungen erarbeitet werden, welche die Arbeit der Entwickler erleichtern sollen ... [more ▼]

Die Konstruktionsforschung strebt danach die Entwicklungspraxis zu unterstützen indem Methodiken, Methoden, Tools und Empfehlungen erarbeitet werden, welche die Arbeit der Entwickler erleichtern sollen, mit dem Ziel bessere Produkte zu entwickeln. Das Umfeld der Entwicklungspraxis ist dabei gekennzeichnet durch Komplexität, Wettbewerb auf globalen Märkten, Dynamik und sich ständig ändernden Kundenwünschen und -bedürfnissen. Die daraus erwachsenden Herausforderungen nehmen fortlaufend zu und tangieren alle Entwicklungsprozesse unabhängig davon ob eine Maschine, eine Software, ein Service oder ein andere Produktform entwickelt wird. Neben den genannten Aspekten stellt auch das veränderte Konsumentenverhalten eine Herausforderung für die Produktentwicklung dar. Das Internet ermöglicht eine nie dagewesene Auswahl- und Vergleichsmöglichkeit von Produkten, wodurch wesentlich selektiver konsumiert wird und infolge dessen Produkte immer differenzierter und tärker an die Kundenwünsche und –bedürfnisse angepasst werden müssen. Abhängig von Entwicklungsgegenstand, Marktsegment, Branche und weiteren Faktoren sind die existierenden methodischen Hilfsmittel unterschiedlich gut geeignet, die Arbeit des Entwicklers zu erleichtern und die Entwicklung besserer Produkte zu unterstützen. Dies bedeutet, dass methodische Ansätze Kontext-abhängig ausgewählt bzw. adaptiert werden müssen. In jüngster Zeit hält Design Thinking, ein neuer Ansatz zur methodischen Produktentwicklung, Einzug in verschiedenste Branchen. Im nachfolgenden Artikel wird Design Thinking kurz beschrieben und exemplarisch mit dem methodischen Vorgehen nach Pahl und Beitz verglichen. Der Vergleich beinhaltet den Prozessumfang (welche Phasen des Entwicklungsprozesses werden abgebildet) und ausgewählte Kontext-Aspekte (für welche Art von Entwicklungsvorhaben ist der Ansatz anwendbar). Anhand dieser Aspekte wird diskutiert, welche wesentlichen Unterschiede zwischen den Ansätzen bestehen, wo Überschneidungen existieren und welches Potential die Kombination beider Ansätze in sich birgt. [less ▲]

Detailed reference viewed: 237 (2 UL)
Full Text
See detailEnvironmental performance assessment of an innovative modular construction concept composed of a permanent structure and flexible modular units
Rakotonjanahary, Tahiana Roland Michaël UL

Doctoral thesis (2022)

To face the challenges of global warming, the building sector is currently undergoing a noticeable revolution. Buildings are tending to consume less energy, use more renewable energy sources, be built ... [more ▼]

To face the challenges of global warming, the building sector is currently undergoing a noticeable revolution. Buildings are tending to consume less energy, use more renewable energy sources, be built with eco-friendly materials, and generate less wastes during their construction and end-of-life stage. Yet, they could be more resilient or else capable of quickly responding to the housing demand, which may fluctuate in time and in space. Innovative concepts therefore need to be developed to allow buildings to expand and/or shrink. Modular buildings could be a solution to combine these criteria, since they offer faster construction process, provide better construction quality, allow reducing construction waste and are potentially flexible. Frames of modular units can be made of metal, timber, concrete, or mixed materials but lightweight structures do not always allow erecting high-rise buildings and generally present a higher risk of overheating and/or overcooling. To reconcile these pros and cons, a building typology called Slab was designed by a group of architects jointly with the team of the Eco-Construction for Sustainable Development (ECON4SD) research project. The Slab building is an innovative modular building concept based on plug-in architecture, which is composed of a permanent concrete structure on which relocatable timber modular units come to slot in. With respect to flexibility, the Slab building was designed to adapt to any orientation and location in Luxembourg. This doctoral thesis mainly deals with the environmental performance assessment of the Slab building but also involves the development of an energy concept for this one. In this regard, the minimum required wall thicknesses of the Slab building’s modules were determined in compliance with the Luxembourg standard although the current regulation does not yet cover flexible buildings. In this process, two module variants were designed; the first one fulfils the passive house requirements which match with the AAA energy class requirements, and the second one complies with the current building codes requirements, also known as the requirements for building permit application, which in principle correspond to low energy house requirements. Calculations showed that 40 cm wall thickness is sufficient to fulfil both requirements. The environmental performance assessment focused on the appraisal of specific CO2 footprint, which considers on the one hand the operational energy and on the other hand the building materials. The operational energy of modules was determined by carrying out energy balance calculations on LuxEeB-Tool software by considering the worst-case and best-case scenarios. Besides, a method was developed to estimate the space heating demand and CO2 emissions of module aggregation, which can have different configurations over time. The method proposed in this thesis was established for the Slab building but could potentially be applicable to flexible buildings. A comparative study of the CO2 footprint considering the embodied and operational energy showed that there is no environmental benefit in having the modules comply with the passive house requirements in the worst-case scenario (window facing north and high wind exposure). A thermal comfort assessment was also done by realizing DTS on TRNSYS software, to check the necessity of active cooling. Simulations showed that with adequate solar shading and reinforced natural ventilation by window opening, summertime overheating risk could be avoided for the normal residential use scenario for both module variants. Finally, the LCA of the Slab building consisted, on the one hand of optimizing its life cycle and, on the other hand, of comparing its specific CO2 footprint with benchmarks. LCA based on 100 years of lifetime concluded that the total specific CO2 footprint of the Slab building for a low module occupancy rate is lower than that of the Slab building bis, which is a building designed based on the Slab building. The latter would be built according to conventional construction method and thereby does not provide the same level of flexibility as the Slab building. However, for a high module occupancy rate, the Slab building does not environmentally perform any better than the Slab building bis. Some solutions could be proposed to further reduce the specific CO2 footprint of the Slab building, but these would impact the architectural aspect or even the functionalities of the Slab building. [less ▲]

Detailed reference viewed: 67 (6 UL)
Full Text
Peer Reviewed
See detailEpipolar visual servoing for multirobot distributed consensus
Montijano, E.; Thunberg, Johan UL; Hu, X. et al

in IEEE Transaction on Robotics (2013), 29(5), 1212-1225

In this paper, we give a distributed solution to the problem of making a team of nonholonomic robots reach consensus about their orientations using monocular cameras. We consider a scheme where the ... [more ▼]

In this paper, we give a distributed solution to the problem of making a team of nonholonomic robots reach consensus about their orientations using monocular cameras. We consider a scheme where the motions of the robots are decided using nearest-neighbor rules. Each robot is equipped with a camera and can only exchange visual information with a subset of the other robots. The main contribution of this paper is a new controller that uses the epipoles that are computed from the images provided by neighboring robots, eventually reaching consensus in their orientations without the necessity of directly observing each other. In addition, the controller only requires a partial knowledge of the calibration of the cameras in order to achieve the desired configuration. We also demonstrate that the controller is robust to changes in the topology of the network and we use this robustness to propose strategies to reduce the computational load of the robots. Finally, we test our controller in simulations using a virtual environment and with real robots moving in indoor and outdoor scenarios. [less ▲]

Detailed reference viewed: 86 (1 UL)
Full Text
See detailAn equation-free multiscale method applied to discrete networks
Beex, Lars UL; Kerfriden, Pierre

Scientific Conference (2017, June 06)

Detailed reference viewed: 64 (5 UL)
Full Text
See detailAn equation-free multiscale method: a result of extending the quasicontinuum method to irregular structures
Beex, Lars UL; Kerfriden, Pierre

Scientific Conference (2017, July 16)

Detailed reference viewed: 66 (2 UL)
Full Text
See detailAn equation-free, nested, concurrent multiscale approach without scale-separation
Beex, Lars UL; Kerfriden, Pierre

Scientific Conference (2018, September)

Detailed reference viewed: 66 (0 UL)
Full Text
Peer Reviewed
See detailEquilibrated patch recovery for accurate evaluation of upper error bounds in quantities of interest
González-Estrada, O. A.; Ródenas, J. J.; Nadal, E. et al

in ECCOMAS Thematic Conference - ADMOS 2011: International Conference on Adaptive Modeling and Simulation, An IACM Special Interest Conference (2012)

There is an increasing interest on the use of goal-oriented error estimates which help to measure and control the local error on a linear or non-linear quantity of interest (QoI) that might result ... [more ▼]

There is an increasing interest on the use of goal-oriented error estimates which help to measure and control the local error on a linear or non-linear quantity of interest (QoI) that might result relevant for design purposes (e.g. the mean stress value in a particular area, displacements, the stress intensity factor for fracture problems,⋯). In general, residual-based error estimators have been used to obtain upper and lower bounds of the error in quantities of interest for finite element approximations. In this work, we propose a novel a posteriori recovery technique to obtain an upper error bound of the QoI. We use a recovery procedure based on the superconvergent patch recovery (SPR) technique to obtain nearly statically admissible recovered stress fields for the primal and dual problems. This recovery technique was previously used to obtain upper bounds of the error in energy norm and has been used in this paper to obtain a computable version of the upper bound for the quantity of interest. [less ▲]

Detailed reference viewed: 271 (1 UL)
Full Text
Peer Reviewed
See detailEquilibrium and sensitivity analysis of dynamic ridesharing
Viti, Francesco UL; Corman, Francesco

Scientific Conference (2013)

Sharing travels is an effective way to increase car occupancy rates and to reduce the number of cars for the same distances traveled. This is a problem involving operations research (how to best match ... [more ▼]

Sharing travels is an effective way to increase car occupancy rates and to reduce the number of cars for the same distances traveled. This is a problem involving operations research (how to best match travels in time and space, what level of similarity for the routes,…) and behavior challenges (on which conditions users choose to share travels, which type of users is willing to share the travel, what is the accepted detour and rescheduling, …). This research aims at filling the gap in the latter aspect by proposing an equilibrium modeling approach for (dynamic) ridesharing. By using a Nested logit model, , greater insight into the impact of different policies, behavioral factors and matching criteria can be presented. We deal with a theoretically interesting basic model structure of a single-link case, in which we study the complex interaction of multiple factors, and the joint sensitivity to the most relevant parameters. This allows us to derive some basic recommendations from the equilibrium states reached. [less ▲]

Detailed reference viewed: 139 (0 UL)
Full Text
Peer Reviewed
See detailEquilibrium in capacitated network models with queueing delays, queue-storage, blocking back and control
Smith, Mike J.; Huang, Wei; Viti, Francesco UL

in Procedia Social and Behavioral Sciences (2013), 80

This paper considers a steady-state, link-based, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queuing delays and explicit bounds on queue ... [more ▼]

This paper considers a steady-state, link-based, fixed (or inelastic) demand equilibrium model with explicit link-exit capacities, explicit bottleneck or queuing delays and explicit bounds on queue storage capacities. The (spatial queueing) model at the heart of this equilibrium model takes account of the space taken up by queues both when there is no blocking back and also when there is blocking back. The paper shows in theorem 1 that a feasible traffic assignment model has an equilibrium solution provided prices are used to impose capacity restrictions and utilises this result to show that there is an equilibrium with the spatial queueing model, provided queue-storage capacities are sufficiently large. Other results are obtained by changing the variables and sets in theorem 1 suitably. These results include: (1) existence of equilibrium results (in both a steady state and a dynamic context) which allow signal green-times to respond to prices and (2) an existence of equilibrium result which allow signal green-times to respond to spatial queues; provided this response follows the P0 control policy in Smith (1979, 1987). These results show that under certain conditions the P0 control policy maximises network capacity. The spatial queueing model is illustrated on a simple network. Finally the paper includes elastic demand; this is necessary for long-run evaluations. Each of the steady state models here may be thought of as a stationary solution to the dynamic assignment problem either with or without blocking back. [less ▲]

Detailed reference viewed: 205 (4 UL)
Peer Reviewed
See detailAn equilibrium model for Mobility-as-a-Service
Bandiera, Claudia UL; Connors, Richard UL; Viti, Francesco UL

Scientific Conference (2021, May)

Detailed reference viewed: 44 (9 UL)