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See detailEnriched Element Free Galerkin Method for Gradient Elasticity
Natarajan, S; Kerfriden, P; Bordas, Stéphane UL et al

Scientific Conference (2011, June)

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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 ▲]

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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)

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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 ▲]

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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,

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 ▲]

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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 ▲]

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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 ▲]

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See detailAn equation-free multiscale method applied to discrete networks
Beex, Lars UL; Kerfriden, Pierre

Scientific Conference (2017, June 06)

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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)

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See detailAn equation-free, nested, concurrent multiscale approach without scale-separation
Beex, Lars UL; Kerfriden, Pierre

Scientific Conference (2018, September)

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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 ▲]

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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 ▲]

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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 ▲]

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See detailEquilibrium models in multimodal container transport systems
Corman, Francesco; Viti, Francesco UL; Negenborn, Rudy

in Flexible Services and Manufacturing Journal (2017), 29

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See detailErmüdungseigenschaften des Wabenkerns von sandwichpaneelen aus Aluminium
Wahl, Laurent UL

Doctoral thesis (2013)

In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application where little weight is important, like airplanes, railway ... [more ▼]

In comparison to their weight, honeycomb composite structures have a high bending stiffness, which makes them very suited for every application where little weight is important, like airplanes, railway-cars and vehicles. These structures are subjected to cyclic loading. The sandwich panels consist of two thin and stiff aluminium face sheets, which are bonded to a thick and lightweight aluminium honeycomb core. The shear stresses in the core of these structures depend strongly on the angle of the load application, because the core is not homogeneous. The distribution and the level of the shear stresses are investigated using analytical calculations. The load direction which induces highest stresses in the honeycomb core is derived. This direction is not the W-direction, which is the most compliant one. In literature, there are few fatigue properties of the honeycomb core described. The fatigue properties of the core are investigated in this work using the finite element method and experiments. The experimental investigations consist of three-point bending tests, pulsating roller tests, Food-Cart Roller tests and several tests on real components. Depending on the load application, the honeycomb core fails either through core indentation or shear failure. Several fatigue tests were carried out at constant load amplitude and the failure mode is investigated. The sandwich structures were modeled with the ANSYS finite element software. The number of elements is reduced by replacing the honeycomb core with a homogeneous core with orthotropic properties. In order to get the stresses in the honeycomb core at the critical location, a submodel was created. In this work, some equations are derived in order to calculate the real shear stresses from the shear stresses of the homogeneous core. In addition, imperfections are included in the model. Furthermore, buckling analyses were used to examine core indentation failure. Based on these simulations, both failure modes described above can be explained. Core indentation occurs, when the honeycomb cells are buckling due to the load application. The buckling of the cells can be avoided by using a smoother load application. In this case, the core fails in the three-point bending test by shear failure. The fatigue life of the examined specimens is successfully approximated in this manuscript, with the lifetime analysis being based on the FKM-guideline. Every simulation is validated by experimental results. [less ▲]

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See detailError estimation and bounding in energy norm based on a displacement recovery technique
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in Eberhardsteiner, Josef; Böhm, Helmut; Rammerstorfer, F G (Eds.) 6th European Congress on Computational Methods in Applied Sciences and Engineering (ECCOMAS 2012) (2012)

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See detailError estimation and error bounding in energy norm based on a displacement recovery technique
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers (2012)

Traditionally, recovery based error estimators in linear elasticity have considered the evaluation of an enhanced stress field obtained from the raw Finite Element (FE) stress solution. Instead of that ... [more ▼]

Traditionally, recovery based error estimators in linear elasticity have considered the evaluation of an enhanced stress field obtained from the raw Finite Element (FE) stress solution. Instead of that, one can also obtain a recovered displacement field from the FE displacements. Herein, we describe a superconvergent patch recovery of the displacement field which considers the local fulfilment of boundary and internal equilibrium equations, Dirichlet constraints and, for singular problems, the splitting of the displacement and stress fields into singular and smooth parts. Numerical tests using problems with known analytical solution have been carried out to validate the proposed technique for error estimation and error bounding in energy norm and quantities of interest. [less ▲]

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See detailError estimation and error bounding in quantities of interest based on equilibrated recovered displacement fields
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in ECCOMAS 2012 - European Congress on Computational Methods in Applied Sciences and Engineering, e-Book Full Papers (2012)

Over the last ten years there has been an increase on the use of goal-oriented error estimates aimed to quantify the local error on a (non)linear quantity of interest (QoI) that might result relevant for ... [more ▼]

Over the last ten years there has been an increase on the use of goal-oriented error estimates aimed to quantify the local error on a (non)linear quantity of interest (QoI) that might result relevant for design purposes. Residual-based error estimators have been used recursively to obtain upper and lower bounds of the error in quantities of interest for finite element approximations. In this paper, we present a recovery technique for 2D linear elasticity problems, based on the superconvergent patch recovery (SPR), which provides recovered displacement and stress fields that are then utilised to evaluate practical upper and lower error bounds in QoI. [less ▲]

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See detailError estimation and space-time adaptivity for the isogeometric analysis of transient structural dynamics
Yu, Peng; Claus, Susanne; Bordas, Stéphane UL et al

Scientific Conference (2016, April 01)

This paper presents a new adaptive scheme for the error-controlled simulation of transient dynamics problem. We rely on spline bases for the higher-order spatial description of our kinematic fields. Local ... [more ▼]

This paper presents a new adaptive scheme for the error-controlled simulation of transient dynamics problem. We rely on spline bases for the higher-order spatial description of our kinematic fields. Local adaptivity is performed by employing a hierarchical T-mesh technology, in combination with geometry independent field approximation. The Newmark algorithm is chosen to solve the semidiscrete equation of motion. We will present some simple local error estimates to drive the adaptivity, and show how we can ensure that the mechanical energy of conservative systems is preserved during the refinement process. [less ▲]

Detailed reference viewed: 95 (4 UL)