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See detailMédias et médiations culturelles au Luxembourg
Colas-Blaise, Marion UL; Tore, Gian Maria UL

Book published by Binsfeld (2011)

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See detailMEMBRANE ASSEMBLY
Shah, Pranjul UL; Wilmes, Paul UL

Patent (2013)

Detailed reference viewed: 101 (8 UL)
See detailMerging DEMs from VHR Optical Imagery with Drone Data - A High-resolution DEM for Tristan da Cunha
Backes, Dietmar UL; Teferle, Felix Norman UL

Scientific Conference (2018, December 12)

The extraction of high-resolution, Digital Elevation Models (DEM) from very high-resolution (VHR) optical satellite imagery, as well as low altitude drone images by Photogrammetric methods or modern ... [more ▼]

The extraction of high-resolution, Digital Elevation Models (DEM) from very high-resolution (VHR) optical satellite imagery, as well as low altitude drone images by Photogrammetric methods or modern Structure from Motion (SFM) engines, has rapidly matured. Today both data sources are representing cost-effective alternatives to dedicated airborne sensors, especially for remote and difficult to access regions. Ever-growing archives of high-resolution Satellite imagery, are providing a rich data source which covers even the most remote locations with high-resolution imagery up to 0.30m ground sample distance multiple times enabling the generation of high-resolution DEMS. Furthermore, low-cost, low weight and easy to use drones can easily be deployed in remote regions and capture limited areas with very high resolution. Dense point clouds derived from this method provide an invaluable data source to fill the gap between globally available low-resolution DEMs and highly accurate terrestrial surveys. The presented case study investigates the use of VHR archive imagery as well as low-cost drone imagery to generate high-quality DEMs using photogrammetric tools over a remote region which is difficult to access by manned airborne platforms. We highlight the potential and limitations of both data sources to provide high resolution, accurate elevation data. [less ▲]

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See detailMesh adaptivity driven by goal-oriented locally equilibrated superconvergent patch recovery
González-Estrada, O. A.; Nadal, E.; Ródenas, J. J. et al

in Computational Mechanics (2013)

Goal-oriented error estimates (GOEE) have become popular tools to quantify and control the local error in quantities of interest (QoI), which are often more pertinent than local errors in energy for ... [more ▼]

Goal-oriented error estimates (GOEE) have become popular tools to quantify and control the local error in quantities of interest (QoI), which are often more pertinent than local errors in energy for design purposes (e.g. the mean stress or mean displacement in a particular area, the stress intensity factor for fracture problems). These GOEE are one of the key unsolved problems of advanced engineering applications in, for example, the aerospace industry. This work presents a simple recovery-based error estimation technique for QoIs whose main characteristic is the use of an enhanced version of the Superconvergent Patch Recovery (SPR) technique previously used for error estimation in the energy norm. This enhanced SPR technique is used to recover both the primal and dual solutions. It provides a nearly statically admissible stress field that results in accurate estimations of the local contributions to the discretisation error in the QoI and, therefore, in an accurate estimation of this magnitude. This approach leads to a technique with a reasonable computational cost that could easily be implemented into already available finite element codes, or as an independent postprocessing tool. © 2013 Springer-Verlag Berlin Heidelberg. [less ▲]

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See detailMeshfree methods for shear-deformable structures based on mixed weak forms
Hale, Jack UL

Scientific Conference (2014, July 24)

Similarly to the finite element method, meshfree methods must be carefully designed to overcome the shear-locking problem when discretising the shear-deformable structural theories. Many successful ... [more ▼]

Similarly to the finite element method, meshfree methods must be carefully designed to overcome the shear-locking problem when discretising the shear-deformable structural theories. Many successful treatments of shear-locking in the finite element literature are constructed through the application of a mixed variational form, where the shear stress is treated as an independent variational quantity in addition to the usual displacements. Because of its sound mathematical underpinnings this is the methodology I have chosen to solve the shear-locking problem when using meshfree basis functions. In this talk I will discuss the mathematical origins of the shear-locking problem and the applicability of the celebrated LBB stability condition for designing well-behaved mixed meshfree approximation schemes. I will show results from two new formulations that demonstrate the effectiveness of this approach. The first method is a meshfree formulation for the Timoshenko beam problem that converges to a classic inf-sup stable finite element method when using Maximum- Entropy basis functions. The second method is a generalised displacement meshfree method for the Reissner- Mindlin problem where the shear stress is eliminated prior to the solution of the linear system using a local patch-projection technique, resulting in a linear system expressed in terms of the original displacement unknowns only. Stability is ensured by using a stabilised weak form which is necessary due to the loss of kernel coercivity for the Reissner-Mindlin problem. [less ▲]

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See detailMeshfree Point Collocation Schemes for 2D Steady State Incompressible Navier-Stokes Equations in Velocity-Vorticity Formulation for High Values of Reynolds Number
Bourantas, Georgios UL; Skouras, Eugene; Loukopoulos, Vasilios et al

in Computer Modeling in Engineering & Sciences (2010), 59(1), 31-63

A meshfree point collocation method has been developed for the velocity- vorticity formulation of two-dimensional, steady state incompressible Navier-Stokes equations. Particular emphasis was placed on ... [more ▼]

A meshfree point collocation method has been developed for the velocity- vorticity formulation of two-dimensional, steady state incompressible Navier-Stokes equations. Particular emphasis was placed on the application of the velocity-correc- tion method, ensuring the continuity equation. The Moving Least Squares (MLS) approximation is employed for the construction of the shape functions, in conjunc- tion with the general framework of the point collocation method. Computations are obtained for regular and irregular nodal distributions, stressing the positivity con- ditions that make the matrix of the system stable and convergent. The accuracy and the stability of the proposed scheme are demonstrated through two representative, well-known, and established benchmark problems. The numerical scheme was also applied to a case with irregular geometry for marginally high Reynolds numbers [less ▲]

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See detailMeshfree volume-averaged nodal pressure methods for incompressible elasticity
Hale, Jack UL; Ortiz Benardin, Alejandro; Cyron, Christian J.

Scientific Conference (2014, April 03)

We present a generalisation of the meshfree method for incompressible elasticity developed in Ortiz et al. (10.1016/j.cma.2010.02.013). We begin with the classical u-p mixed formulation of incompressible ... [more ▼]

We present a generalisation of the meshfree method for incompressible elasticity developed in Ortiz et al. (10.1016/j.cma.2010.02.013). We begin with the classical u-p mixed formulation of incompressible elasticity before eliminating the pressure using a volume-averaged nodal projection technique. This results in a family of projection methods of the type Q_p/Q_p-1 where Q_p is an approximation space of polynomial order p. These methods are particularly robust on low-quality tetrahedral meshes. Our framework is generic with respects to the type meshfree basis function used and includes various types of existing finite element methods such as B-bar and nodal-pressure techniques. As a particular example, we use maximum-entropy basis functions to build a scheme Q_1+/Q_1 with the displacement field being enriched with bubble-like functions for stability. The flexibility of the nodal placement in meshfree methods allows us to demonstrate the importance of this bubble-like enrichment for stability; with no bubbles the pressure field is liable to oscillations, whilst with bubbles the oscillation is eliminated. Interestingly however with half the bubbles removed, a scheme we call Q_1*/_Q_1, certain undesirable tendencies of the full bubble scheme are also eliminated. This has important applications in non-linear hyperelasticity. We also discuss some difficulties associated with moving to second-order maximum entropy shape functions associated with numerical integration errors. [less ▲]

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See detailMeshfree volume-averaged nodal projection method for nearly-incompressible elasticity using meshfree and bubble basis functions
Ortiz-Benardin, Alejandro; Hale, Jack UL; Cyron, Christian J.

in Computer Methods in Applied Mechanics & Engineering (2015), 285

We present a displacement-based Galerkin meshfree method for the analysis of nearly-incompressible linear elastic solids, where low-order simplicial tessellations (i.e., 3- node triangular or 4-node ... [more ▼]

We present a displacement-based Galerkin meshfree method for the analysis of nearly-incompressible linear elastic solids, where low-order simplicial tessellations (i.e., 3- node triangular or 4-node tetrahedral meshes) are used as a background structure for numerical integration of the weak form integrals and to get the nodal information for the computation of the meshfree basis functions. In this approach, a volume- averaged nodal projection operator is constructed to project the dilatational strain into an approximation space of equal- or lower-order than the approximation space for the displacement field resulting in a locking-free method. The stability of the method is provided via bubble-like basis functions. Because the notion of an ‘ele- ment’ or ‘cell’ is not present in the computation of the meshfree basis functions such low-order tessellations can be used regardless of the order of the approximation spaces desired. First- and second-order meshfree basis functions are chosen as a particular case in the proposed method. Numerical examples are provided in two and three dimensions to demonstrate the robustness of the method, its ability to avoid volumetric locking in the nearly-incompressible regime, and its improved performance when compared to the MINI finite element scheme on the simplicial mesh. [less ▲]

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See detailMeshless Elasticity Model and Contact Mechanics-based Verification Technique
Aras, Rifat; Shen, Yuzhong; Audette, Michel et al

in MICCAI Computational Biomechanics for Medicine (2014, January 01)

Mesh-based techniques are well studied and established methods for solving continuum biomechanics problems. When the problem at hand involves extreme deformations or artificial discontinuities, meshless ... [more ▼]

Mesh-based techniques are well studied and established methods for solving continuum biomechanics problems. When the problem at hand involves extreme deformations or artificial discontinuities, meshless methods provide sev-eral advantages over the mesh-based methods. This work discusses the Moving Least Square approximation-based meshless collocation method for simulating de-formable objects and presents a verification technique that is based on the Hertzian theory of non-adhesive elastic contact. The effectiveness of the Hertzian contact theory as a means for verification was first tested and proven through a well-established FEM code, FEBio. The meshless method was implemented as a reusable component for the SOFA framework, an open source software library for real-time simulations. Through experimentation, the Hertzian theory has been tested against SOFA hexahedral FEM and the meshless models within the SOFA framework. Convergence studies and L2 error curves are provided for both mod-els. Experimental results demonstrated the effectiveness of the implementation of the meshless method. [less ▲]

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See detailA Meshless Method for the Reissner-Mindlin Plate Equations based on a Stabilized Mixed Weak Form
Hale, Jack UL; Baiz, P. M.

Scientific Conference (2013, September)

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See detailMeshless Methods for the Reissner-Mindlin Plate Problem based on Mixed Variational Forms
Hale, Jack UL

Presentation (2013, October 31)

Meshless numerical methods such as the element free Galerkin (EFG) method and $hp$-clouds method rely on a field of particles to construct a basis for the solution of partial differential equations (PDEs ... [more ▼]

Meshless numerical methods such as the element free Galerkin (EFG) method and $hp$-clouds method rely on a field of particles to construct a basis for the solution of partial differential equations (PDEs). This is in contrast with methods such as the finite element method (FEM) and finite difference method (FDM) which rely upon a mesh or grid. Because of this increased flexibility, meshfree methods have shown themselves to be effective tools for simulating difficult problems such as those with discontinuities, complex geometries and large deformations. The Reissner-Mindlin problem is widely used by engineers to describe the deformation of a plate including the effects of transverse shear. A well-known problem which must be overcome when designing an effective numerical method for the Reissner-Mindlin problem is shear-locking. Shear-locking is the inability of the constructed approximation space (meshless or otherwise) to richly represent the limiting Kirchhoff mode. This inability manifests itself as an entirely incorrect solution as the thickness of the plate approaches zero. We will demonstrate and explain the shear-locking problem and potential solutions to it using a simple one-dimensional example. The most effective, robust and general approaches to the shear-locking problem developed in the FEM literature are based on mixed variational forms, where a combination of displacements, stresses and strains are approximated directly. In our approach we start with a mixed variational form before eliminating the extra stress unknowns using the local patch projection technique of A Ortiz et. al. We will discuss the issues presented by the well-known LBB stability conditions and present a solution based upon the stabilising properties of both the augmented Lagrangian and additional `bubble' type functions. We will then show the good performance of the method and its shear-locking free properties. [less ▲]

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See detailMeshless methods: A review and computer implementation aspects
Nguyen, V. P.; Rabczuk, T.; Bordas, Stéphane UL et al

in Mathematics & Computers in Simulation (2008), 79(3), 763-813

The aim of this manuscript is to give a practical overview of meshless methods (for solid mechanics) based on global weak forms through a simple and well-structured MATLAB code, to illustrate our ... [more ▼]

The aim of this manuscript is to give a practical overview of meshless methods (for solid mechanics) based on global weak forms through a simple and well-structured MATLAB code, to illustrate our discourse. The source code is available for download on our website and should help students and researchers get started with some of the basic meshless methods; it includes intrinsic and extrinsic enrichment, point collocation methods, several boundary condition enforcement schemes and corresponding test cases. Several one and two-dimensional examples in elastostatics are given including weak and strong discontinuities and testing different ways of enforcing essential boundary conditions. © 2008 IMACS. [less ▲]

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See detailA Method for Designing Virtual Places
McCall, Roderick UL; O'Neill, Shaleph; Benyon, David et al

Scientific Conference (2004)

This paper discusses our experiences of using a range of methods and techniques to measure the sense of place in real and virtual environments. The paper presents a discussion on presence and how this is ... [more ▼]

This paper discusses our experiences of using a range of methods and techniques to measure the sense of place in real and virtual environments. The paper presents a discussion on presence and how this is linked directly with our sense of place. From here we discuss the development of ‘The Place Probe’ a bundle of measurement techniques that allows for the direct comparison of real and virtual scenes. We show how the data gathered from the probe can be used to inform the design of virtual places. The whole approach is predicated on the premise that by understanding place we can improve our sense of presence in virtual environments. [less ▲]

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See detailMethodenentwicklung zur numerischen Strömungsanalyse von Freispiegelströmungen bei Schaufelwasserrädern
Schippke, Henning; Seidel, Christian; Dinkler, Dieter et al

Scientific Conference (2014, March)

Der Ausbau der Wasserkraft gewinnt im Kontext der Energiewende weltweit an Bedeutung. Neben der Turbinentechnologie erweisen sich Wasserräder im Hinblick auf ihre hohe ökologische Verträglichkeit und ihr ... [more ▼]

Der Ausbau der Wasserkraft gewinnt im Kontext der Energiewende weltweit an Bedeutung. Neben der Turbinentechnologie erweisen sich Wasserräder im Hinblick auf ihre hohe ökologische Verträglichkeit und ihr hohes ganzjähriges Arbeitsvermögen als besonders geeignet. Das sich drehende Wasserrad, umgeben von Wasser und Luft, stellt mechanisch ein gekoppeltes Drei- Feld-System bestehend aus einer Struktur und zwei Fluiden dar. Hinreichend genau ist es möglich, die Wasserradstruktur als Starrkörper zu beschreiben, während Luft und Wasser mit Hilfe der inkom- pressiblen Navier-Stokes Gleichungen gut modelliert werden können. Durch Anwendung der Raum-Zeit-Finite-Elemente-Methode zur Diskretisierung der inkompressiblen Navier-Stokes Gleichungen wird die Grenzfläche zwischen dem Starrkörper und den Fluiden explizit beschrieben und stets automatisch korrekt erfasst. Die Beschreibung der freien Wasseroberfläche als Grenzfläche zwischen den beiden Fluiden erfolgt implizit mit Hilfe der Level-Set Methode. Die Netzknoten der Fluid-Struktur-Grenzfläche verändern ihre Position infolge der Wasserraddrehung mit der Zeit, so dass ein Netzbewegungsalgorithmus notwendig ist. Die shear-slip mesh update method (SSMUM) ermöglicht als diskontinuierliches Netzbewegungsverfahren eine durchgehende Berechnung des Gesamtsystems, ohne dass das gesamte Gebiet neu vernetzt werden muss. Anhand verschiedener Testbeispiele wird die Güte der entwickelten numerischen Methode im Hinblick auf Ihre Erhaltungseigenschaften untersucht. Besonderes Augenmerk wird auf die Lösungsübertragung am shear-slip layer sowie auf die Abbildung der implizit beschriebenen freien Wasseroberfläche gelegt. [less ▲]

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See detailMethodenentwicklung zur numerischen Strömungsanalyse von Schaufelwasserrädern
Schippke, Henning; Zilian, Andreas UL; Seidel, Christian et al

in PAMM (2013)

Es wird ein Berechnungsmodell vorgestellt, mit dem eine numerischen Analyse der Strömungsvorgänge innerhalb von Schau- felwasserrädern möglich ist. Der Arbeitsschwerpunkt liegt dabei auf der ... [more ▼]

Es wird ein Berechnungsmodell vorgestellt, mit dem eine numerischen Analyse der Strömungsvorgänge innerhalb von Schau- felwasserrädern möglich ist. Der Arbeitsschwerpunkt liegt dabei auf der strömungsmechanischen Optimierung von Hochleis- tungswasserrädern der Weiterentwickelten Wasserradtechnologie. In dem Berechnungsmodell werden die inkompressiblen Navier-Stokes-Gleichungen in den unabhängigen Variablen Geschwindigkeiten und Druck mit Hilfe der zeit-diskontinuierlichen Raum-Zeit-Finite-Elemente-Methode diskretisiert und die auftretende Gebietsveränderung infolge der sich drehenden Struk- tur mit der Shear-Slip Mesh Update Methode als diskontinuierlichem Netzbewegungsverfahren erfasst. [less ▲]

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See detailA Methodological Framework to Design a Machine-Readable Privacy Icon Set
Palmirani, Monica; Rossi, Arianna UL; Martoni, Michele et al

in Schweighofer, Erich (Ed.) Data Protection / LegalTech Proceedings of the 21st International Legal Informatics Symposium IRIS 2018 (2018)

The GDPR suggests icons to convey data practices in a more straightforward way. Although vi- sualizations to represent legal terms have many benefits, there is fear that they could be misrep- resented by ... [more ▼]

The GDPR suggests icons to convey data practices in a more straightforward way. Although vi- sualizations to represent legal terms have many benefits, there is fear that they could be misrep- resented by designers and misinterpreted by individuals, thus hindering instead of facilitating the comprehension. In order to solve these issues, we present a methodology to generate legal visual representations that is based on an analysis of legal requirements, on an ontological representation of the legal knowledge, and on an iterative, multi-stakeholder design approach, followed by empirical evaluation. [less ▲]

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See detailMethods for Biochemical Model Decomposition and Quantitative Submodel Comparison
Mizera, Andrzej UL; Czeizler, Elena; Petre, Ion

in Israel Journal of Chemistry (2011), 51(1), 151164

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See detailMicro-structured materials: inhomogeneities and imperfect interfaces in plane micropolar elasticity, a boundary element approach
Atroshchenko, Elena; Hale, Jack UL; Videla, Javier A. et al

in Engineering Analysis with Boundary Elements (2017), 83

In this paper we tackle the simulation of microstructured materials modelled as heterogeneous Cosserat media with both perfect and imperfect interfaces. We formulate a boundary value problem for an ... [more ▼]

In this paper we tackle the simulation of microstructured materials modelled as heterogeneous Cosserat media with both perfect and imperfect interfaces. We formulate a boundary value problem for an inclusion of one plane strain micropolar phase into another micropolar phase and reduce the problem to a system of boundary integral equations, which is subsequently solved by the boundary element method. The inclusion interface condition is assumed to be imperfect, which permits jumps in both displacements/microrotations and tractions/couple tractions, as well as a linear dependence of jumps in displacements/microrotations on continuous across the interface tractions/couple traction (model known in elasticity as homogeneously imperfect interface). These features can be directly incorporated into the boundary element formulation. The BEM-results for a circular inclusion in an in finite plate are shown to be in excellent agreement with the analytical solutions. The BEM-results for inclusions in finite plates are compared with the FEM-results obtained with FEniCS. [less ▲]

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See detailMinimal dynamical structure realisations with application to network reconstruction from data
Yuan, Y.; Stan, G. B. V.; Warnick, S. et al

in The proceedings of the Joint 48th IEEE Conference on Decision and Control and 28th Chinese Control Conference (2009)

Network reconstruction, i.e., obtaining network structure from data, is a central theme in systems biology, economics, and engineering. Previous work introduced dynamical structure functions as a tool for ... [more ▼]

Network reconstruction, i.e., obtaining network structure from data, is a central theme in systems biology, economics, and engineering. Previous work introduced dynamical structure functions as a tool for posing and solving the problem of network reconstruction between measured states. While recovering the network structure between hidden states is not possible since they are not measured, in many situations it is important to estimate the number of hidden states in order to understand the complexity of the network under investigation and help identify potential targets for measurements. Estimating the number of hidden states is also crucial to obtain the simplest state-space model that captures the network structure and is coherent with the measured data. This paper characterises minimal order state-space realisations that are consistent with a given dynamical structure function by exploring properties of dynamical structure functions and developing algorithms to explicitly obtain a minimal reconstruction. [less ▲]

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See detailMinimal-time network reconstruction for DTLTI systems
Yuan, Y.; Goncalves, Jorge UL

in The proceedings of the 49th IEEE Conference on Decision and Control (CDC) (2010)

This paper considers the problem of obtaining in minimal time the “dynamical network structure” (DNS) from partial state observations of a discrete-time linear time-invariant system. From the DNS, we can ... [more ▼]

This paper considers the problem of obtaining in minimal time the “dynamical network structure” (DNS) from partial state observations of a discrete-time linear time-invariant system. From the DNS, we can not only obtain the network structure of the system at the measurement level, but also estimate the minimal number of hidden states which are not observed directly. First, we discuss when reconstruction of the DNS is and is not possible. Then, we give an algorithm to find the minimal number of successive outputs to find the DNS. Finally, we discuss extensions of the results to non-linear and noisy systems. These results can be directly applied to the decentralised network control problem of multi-agent systems to find network connections of the observed agents. [less ▲]

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