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See detailPhD Day - Complex Particle Laden Fluid Structure Interaction
Adhav, Prasad UL

Presentation (2022, May 10)

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See detailPresentation in Computational Sciences PhD Presentation Day
Shang, Lan UL

Presentation (2022, March 22)

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See detailOn the sociopolitical and institutional production of digital cities
Carr, Constance UL

Presentation (2022)

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See detailExploring the Exposomewith HPC
Schymanski, Emma UL

Presentation (2021, November 10)

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See detailDyPS: Dynamic, Private and Secure GWAS (Summary) - GenoPri'21 Talk
Pascoal, Túlio UL; Decouchant, Jérémie; Boutet, Antoine et al

Presentation (2021, September 22)

Genome-Wide Association Studies (GWAS) identify the genomic variations that are statistically associated with a particular phenotype (e.g., a disease). GWAS results, i.e., statistics, benefit research and ... [more ▼]

Genome-Wide Association Studies (GWAS) identify the genomic variations that are statistically associated with a particular phenotype (e.g., a disease). GWAS results, i.e., statistics, benefit research and personalized medicine. The confidence in GWAS increases with the number of genomesanalyzed, which encourages federated computations where biocenters periodically include newly sequenced genomes. However, for legal and economical reasons, this collaboration can only happen if a release of GWAS results never jeopardizes the genomic privacy of data donors, if biocenters retain ownership and cannot learn each others’ data. Furthermore, given the reduced cost of sequencing DNA nowadays, there is now a need to update GWAS results in a dynamic manner, while enabling donors to withdraw consent at any time. Therefore, two challenges need to be simultaneously addressed to enable federated and dynamic GWAS: (i) the computation of GWAS statistics must rely on secure and privacy-preserving methods; and (ii) GWAS results that are publicly released should not allow any form of privacy attack. In this talk, we will introduce the problem we consider in more detail and present DyPS, the framework we have designed and recently presented at the Privacy Enhancing Technologies Symposium (PETS). We refer the reader to the full paper1 for the details we cannot cover in this short version. [less ▲]

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See detailEarly Career Researchers in Digital Medieval Studies: A Round Table Discussion
Busch, Hannah; Dubuisson, Bastien UL; Davies, Helen et al

Presentation (2021, July 06)

As a relatively young and constantly emerging field, the Digital Humanities (DH) encompasses a large group of early career researchers with different backgrounds and diverse career paths. Digital Medieval ... [more ▼]

As a relatively young and constantly emerging field, the Digital Humanities (DH) encompasses a large group of early career researchers with different backgrounds and diverse career paths. Digital Medieval Studies as a subfield of DH is characterised by various disciplines as well as a high number of international collaborations and is populated by scholars with different educational backgrounds: from scholars trained as medievalists who implemented digital components only during their postgrad studies to scholars who approached medieval studies through their technical skills. This round table discussion brings together early career scholars from this domain on the border between traditional humanities research and DH to discuss the challenges and opportunities of their diverse career paths. [less ▲]

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See detailOpen Science @LCSB-ECI
Schymanski, Emma UL

Presentation (2021, June 17)

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See detailUncertainty, precision and reliability of eco-hydrological models
Mingo Ndiwago, Damian UL

Presentation (2021, May 21)

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See detailData Science and Environmental Cheminformatics (SanDAL Workshop, Uni Lu)
Schymanski, Emma UL

Presentation (2020, October 13)

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See detailClustering Based Model Order Reduction For Hyper Elastoplastic Material Models
Vijayaraghavan, Soumianarayanan UL; Beex, Lars UL; Noels, Ludovic et al

Presentation (2019, July 29)

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See detailHigh Performance Parallel Coupling of OpenFOAM+XDEM
Besseron, Xavier UL; Pozzetti, Gabriele; Rousset, Alban UL et al

Presentation (2019, June 21)

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See detailProbabilistic modeling natural way to treat data
Rappel, Hussein UL

Presentation (2019, February 12)

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See detailProject Advanced Discretisaztion Methods
Farina, Sofia UL

Presentation (2019, February 01)

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See detailParallel Coupling of CFD-DEM simulations
Besseron, Xavier UL; Pozzetti, Gabriele UL; Rousset, Alban UL et al

Presentation (2018, August 20)

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See detailFree boundary problems: numerical methods and data-driven simulations
Bordas, Stéphane UL

Presentation (2018, March 05)

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See detailData-driven modelling and simulation: fracture and medical simulations
Bordas, Stéphane UL

Presentation (2018, February 08)

Predicting failure in aircraft structures – simulating fracture across scales and times You could fly every day of your life in a commercial aircraft for twenty thousand years without suffering a fatal ... [more ▼]

Predicting failure in aircraft structures – simulating fracture across scales and times You could fly every day of your life in a commercial aircraft for twenty thousand years without suffering a fatal accident. This extraordinary level of safety is the product of decades of engineering and materials science research. Simultaneously, engineers have strived to produce lighter and stronger aircraft, with increased range and metals have thus been gradually replaced by lighter advanced composite materials which take up more than half of the structural weight of today's most advanced aircraft. Such progress has been largely enabled by modeling and simulation of materials and structures, which have revolutionized design by enabling engineers to investigate virtually various design strategies. This presentation will focus on the challenges which have been posed, are posed, and will be posed to such modeling and simulation tools in the strive to predict the durability of lighter, stronger, longer-ranging and more reliable aircraft. [less ▲]

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See detailPresentation of work in social network analysis
During, Marten UL

Presentation (2018)

Detailed reference viewed: 84 (2 UL)
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See detailNumerical methods for fracture/cutting of heterogeneous materials
Sutula, Danas UL; Agathos, Konstantinos UL; Ziaei Rad, Vahid UL et al

Presentation (2016, December)

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See detailThe European Association for Data Science, its main goals and tasks
Krolak-Schwerdt, Sabine; Böhmer, Matthias UL

Presentation (2016, December)

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See detailWeakening the tight coupling between geometry and simulation in isogeometric analysis
Tomar, Satyendra UL; Atroshchenko, Elena; Xu, Gang et al

Presentation (2016, June 07)

In the standard paradigm of isogeometric analysis, the geometry and the simulation spaces are tightly integrated, i.e. the same non-uniform rational B-splines (NURBS) space, which is used for the geometry ... [more ▼]

In the standard paradigm of isogeometric analysis, the geometry and the simulation spaces are tightly integrated, i.e. the same non-uniform rational B-splines (NURBS) space, which is used for the geometry representation of the domain, is employed for the numerical solution of the problem over the domain. However, there are situations where this tight integration is a bane rather than a boon. Such situations arise where, e.g., (1) the geometry of the domain is simple enough to be represented by low order NURBS, whereas the unknown (exact) solution of the problem is sufficiently regular, and thus, the numerical solution can be obtained with improved accuracy by using NURBS of order higher than that required for the geometry, (2) the constraint of using the same space for the geometry and the numerical solution is particularly undesirable, such as in the shape and topology optimization, and (3) the solution of the problem has low regularity but for the curved boundary of the domain one can employ higher order NURBS. Therefore, we propose to weaken this constraint. An extensive study of patch tests on various combinations of polynomial degree, geometry type, and various cases of varying degrees and control variables between the geometry and the numerical solution will be discussed. It will be shown, with concrete reasoning, that why patch test fails in certain cases, and that those cases should be avoided in practice. Thereafter, selective numerical examples will be presented to address some of the above-mentioned situations, and it will be shown that weakening the tight coupling between geometry and simulation offers more flexibility in choosing the numerical solution spaces, and thus, improved accuracy of the numerical solution. [less ▲]

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See detailGeneralizing the isogeometric concept: weakening the tight coupling between geometry and simulation in IGA
Tomar, Satyendra UL; Atroshchenko, Elena; Xu, Gang et al

Presentation (2016, June 02)

In the standard paradigm of isogeometric analysis [2, 1], the geometry and the simulation spaces are tightly integrated, i.e. the non-uniform rational B-splines (NURBS) space, which is used for the ... [more ▼]

In the standard paradigm of isogeometric analysis [2, 1], the geometry and the simulation spaces are tightly integrated, i.e. the non-uniform rational B-splines (NURBS) space, which is used for the geometry representation of the domain, is also employed for the numerical solution of the problem over the domain. However, in certain situations, such as, when the geometry of the domain can be represented by low order NURBS but the numerical solution can be obtained with improved accuracy by using NURBS of order higher than that required for the geometry; or in the shape and topology optimization where the constraint of using the same space for the geometry and the numerical solution is not favorable, this tight coupling is disadvantageous. Therefore, we study the effect of decoupling the spaces for the geometry representation and the numerical solution, though still using the prevalent functions in CAD/CAGD. To begin with, we perform the patch tests on various combinations of polynomial degree, geometry type, and various cases of varying degrees and control variables between the geometry and the numerical solution. This shows that certain cases, perhaps intuitive, should be avoided in practice because patch test fails. The above-mentioned situations are further explored with some numerical examples, which shows that weakening the tight coupling between geometry and simulation offers more flexibility in choosing the numerical solution spaces. [1] J. Cottrell, T.J.R. Hughes, and Y. Bazilevs. Isogeometric Analysis: Toward Integration of CAD and FEA, volume 80. Wiley, Chichester, 2009. [2] T.J.R. Hughes, J. Cottrell, and Y. Bazilevs. Isogeometric analysis: CAD, finite elements, NURBS, exact geometry and mesh refinement. Computer Methods in Applied Mechanics and Engineering, 194:4135–4195, 2005. [less ▲]

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See detailComputational mechanics of interfaces
Bordas, Stéphane UL

Presentation (2016, May 22)

The course will present an overview of recent developments, which will enable students to make informed choices in terms of discretization and model selection in solving numerical problems in mechanics ... [more ▼]

The course will present an overview of recent developments, which will enable students to make informed choices in terms of discretization and model selection in solving numerical problems in mechanics. We will cover discretization strategies ranging from the standard finite element method, the smoothed finite element method, the extended finite element method, polygonal and virtual element methods, meshfree methods. The applications range between fracture of heterogeneous materials and biomedical simulations. The intended learning outcomes of the course are such that the students will be: - able to critically assess discretization schemes in mechanics - able to implement simple error estimators for finite element methods - familiar with basic multi-scale methods for fracture and their limitations - able to follow basic literature in model error and model selection, in particular based on Bayesian inference Course participants will learn these topics through lectures and hands-on numerical experiments. [less ▲]

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See detailTrading Zones of Digital History
Kemman, Max UL

Presentation (2016)

Detailed reference viewed: 148 (17 UL)
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See detailUsing Bayes' theorem to infer the material parameters of human soft tissue
Hale, Jack UL; Farrell, Patrick; Bordas, Stéphane UL

Presentation (2015, October 21)

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See detailIsogeometric and multi-scale fracture
Bordas, Stéphane UL

Presentation (2015, July 31)

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See detailA Bayesian inversion approach to recovering material parameters in hyperelastic solids using dolfin-adjoint
Hale, Jack UL; Farrell, Patrick E.; Bordas, Stéphane UL

Presentation (2015, July 01)

In the first part of the talk I will describe in general terms the link between classical optimisation techniques and the Bayesian approach to statistical inversion as outlined in the seminal book of ... [more ▼]

In the first part of the talk I will describe in general terms the link between classical optimisation techniques and the Bayesian approach to statistical inversion as outlined in the seminal book of [Kaipio and Somersalo, 2005]. Under the assumption of an additive Gaussian noise model, a Gaussian prior distribution and a linear parameter-to-observable map, it is possible to uniquely characterise the Bayesian posterior as Gaussian with the maximum aposteriori (MAP) point equal to the minimum of a classic regularised minimisation problem and covariance matrix equal to the inverse of the Hessian of the functional evaluated at the MAP point. I will also discuss techniques that can be used when these assumptions break down. In the second part of the talk I will describe a method implemented within dolfin-adjoint [Funke and Farrell, arXiv 2013] to quantify the uncertainty in the recovered material parameters of a hyperelastic solid from partial and noisy observations of the displacement field in the domain. The finite element discretisation of the adjoint and higher-order adjoint (Hessian) equations are derived automatically from the high-level UFL representation of the problem. The resulting equations are solved using PETSc. I will concentrate on finding the eigenvalue decomposition of the posterior covariance matrix (Hessian). The eigenvectors associated with the lowest eigenvalues of the Hessian correspond with the directions in parameter space least constrained by the observations [Flath et al. 2011]. This eigenvalue problem is tricky to solve efficiently because the Hessian is very large (on the order of the number of parameters) and dense (meaning that only its action on a vector can be calculated, each involving considerable expense). Finally, I will show some illustrative examples including the uncertainty associated with deriving the material properties of a 3D hyperelastic block with a stiff inclusion with knowledge only of the displacements on the boundary of the domain. J. Kaipio and E. Somersalo, Statistical and Computational Inverse Problems, vol. 160. New York: Springer-Verlag, 2005. S. W. Funke and P. E. Farrell, “A framework for automated PDE-constrained optimisation,” arXiv:1302.3894 [cs], Feb. 2013. H. P. Flath, L. C. Wilcox, V. Akçelik, J. Hill, B. van Bloemen Waanders, and O. Ghattas, “Fast Algorithms for Bayesian Uncertainty Quantification in Large-Scale Linear Inverse Problems Based on Low-Rank Partial Hessian Approximations,” SIAM J. Sci. Comput., vol. 33, no. 1, pp. 407–432, Feb. 2011. [less ▲]

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See detailA tutorial on multiple crack growth and intersections with XFEM
Sutula, Danas; Bordas, Stéphane UL

Presentation (2015, May 12)

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See detailThe stable GFEM. Convergence, accuracy and Diffpack implementation
Alves Paladim, Daniel; Natarajan, Sundarajan; Bordas, Stéphane UL et al

Presentation (2015, May 12)

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See detailError estimation in homogenisation
Alves Paladim, Daniel; Kerfriden, Pierre; Moitinho de Almeida, José et al

Presentation (2015, January 30)

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See detailGamifying the Commute
McCall, Roderick UL

Presentation (2014, November 14)

The seminar outlined the I-GEAR project which examines the use of gamification to reduce traffic congestion. Topics included user interfaces for gamified applications, requirements capture methodologies ... [more ▼]

The seminar outlined the I-GEAR project which examines the use of gamification to reduce traffic congestion. Topics included user interfaces for gamified applications, requirements capture methodologies and a sample gamified application. [less ▲]

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See detailMultiscale Quasicontinuum Methods for Dissipative Truss Models and Beam Networks
Beex, Lars UL; Peerlings, Ron; Geers, Marc et al

Presentation (2014, November 05)

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See detailDiscrete Multiscale Modelling and Future Research Plans concerning Metals
Beex, Lars UL; Bordas, Stéphane UL; Rappel, Hussein UL et al

Presentation (2014, October 14)

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See detailSTUDYING COMMUTER BEHAVIOUR FOR GAMIFYING MOBILITY
Kracheel, Martin UL; McCall, Roderick UL; Koenig, Vincent UL

Presentation (2014, September 30)

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See detailAn overview of our research directions in advanced discretisation methods for PDEs
Hale, Jack UL

Presentation (2014, July 10)

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See detailDirect image-analysis methods for surgical simulation and mixed meshfree methods
Hale, Jack UL; Bordas, Stéphane UL; Kerfriden, Pierre et al

Presentation (2014, May 28)

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See detailReduced order modelling: towards tractable computational homogenisation schemes
Kerfriden, Pierre; Goury, Olivier; Akbari, Ahmad et al

Presentation (2014, May 15)

Towards rationalised computational expense for simulating fracture over multiple scales The project focuses on the numerical simulation of the failure of complex, heterogeneous structures. The simulation ... [more ▼]

Towards rationalised computational expense for simulating fracture over multiple scales The project focuses on the numerical simulation of the failure of complex, heterogeneous structures. The simulation of such physical phenomena is of particular interest to practitioners as it enables to limit the number of destructive tests required to design and assess structures, and, ultimately, to decrease the safety factors used in design. In such heterogeneous media, the description of crack or damage initiation and propagation must be done at the scale of the inhomogeneities (e.g. aggregates in a concrete structure) in order for the results to be predictive. If one uses such a fine-scale material model to simulate structures at an engineering scale (e.g. an aircraft composite panel or a concrete beam), very large numerical problems need to be solved. In addition, there is a strong need for engineers to run their models numerous times, for different sets of the design parameters (e.g. loading conditions, geometry or material properties). Tackling such parametric multiscale problems is prohibitively expensive when using brute force parallel computing. However, one can use the fact that solutions to parametric problems usually evolve in a relatively coarse space: solutions to nearby parameter sets are usually close in a certain sense. This idea is classically used in Model Order Reduction, which proposes to reduce the size of the initial problem by several order of magnitude by simply reusing the information generated when solving the initial problem for several different sets of parameters. However, in the case of fracture, the information provided by the initial problem is most of the time insufficient to describe the behaviour of the system for arbitrary parameters. Crack paths, defects, and subsequent ultimate strengths are strongly influenced by an even slight variation in the parameter set. Fortunately, we showed in our previous research that this characteristic only affects a local region surrounding the structural defects, whilst the behaviour far from these regions is remains relatively unchanged for a wide range of parameter values. The proposed project will make use of this observation in a generic way, by coupling Reduced Order Modeling and Domain Decomposition. The structure will be divided in smaller subcomponents, on which Reduced Order Modeling will be applied separately. The consequence will be that the computational efforts will be greatly decreased in the regions that are far away from the damaged zone. Within the process zone itself, the substructuring framework will allow us to automatically switch to classical direct solvers. In this sense, the research aims at rationalising the computational costs associated to the simulation of parametrised multiscale fracture simulations, by concentrating the numerical effort where it is most required and with minimal intervention of the user. [less ▲]

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See detailReducing the Mesh-burden and Computational Expense in Multi-scale Free Boundary Engineering Problems
Bordas, Stéphane UL; Kerfriden, Pierre; Hale, Jack UL et al

Presentation (2014, May 12)

We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second ... [more ▼]

We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second part, we describe methodologies to isolate the user from the burden of mesh generation and regeneration as moving boundaries evolve. Results include advances in implicit boundary finite elements, (enriched) isogeometric boundary elements and extended finite element methods for multi-crack propagation. ABOUT THE PRESENTER In 1999, Stéphane Bordas joined a joint graduate programme of the French Institute of Technology (Ecole Spéciale des Travaux Publics) and the American Northwestern University. In 2003, he graduated in Theoretical and Applied Mechanics with a PhD from Northwestern University. Between 2003 and 2006, he was at the Laboratory of Structural and Continuum Mechanics at the Swiss Federal Institute of Technology in Lausanne, Switzerland. In 2006, he became permanent lecturer at Glasgow University’s Civil Engineering Department. Stéphane joined the Computational Mechanics team at Cardiff University in September 2009, as a Professor in Computational Mechanics and directed the institute of Mechanics and Advanced Materials from October 2010 to November 2013. He is the Editor of the book series “Advances in Applied Mechanics” since July 2013. In November 2013, he joined the University of Luxembourg as a Professor in Computational Mechanics. The main axes of his research team include (1) free boundary problems and problems involving complex geometries, in particular moving boundaries and (2) ‘a posteriori’ discretisation and model error control, rationalisation of the computational expense. Stéphane’s keen interest is to actively participate in innovation, technological transfer as well as software tool generation. This has been done through a number of joint ventures with various industrial partners (Bosch GmbH, Cenaero, inuTech GmbH, Siemens-LMS, Soitec SA) and the release of open-source software. In 2012, Stéphane was awarded an ERC Starting Independent Research Grant (RealTcut), to address the need for surgical simulators with a computational mechanics angle with a focus on the multi-scale simulation of cutting of heterogeneous materials in real-time. [less ▲]

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See detailModel and mesh-burden reduction for multiscale fracture: applications to polycrystals, delamination and surgical simulation
Bordas, Stéphane UL; Kerfriden, Pierre; Hale, Jack UL et al

Presentation (2014, April 23)

ABSTRACT We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a ... [more ▼]

ABSTRACT We present recent results aiming at affording faster and error-controlled simulations of multi scale phenomena including fracture of heterogeneous materials and cutting of biological tissue. In a second part, we describe methodologies to isolate the user from the burden of mesh generation and regeneration as moving boundaries evolve. Results include advances in implicit boundary finite elements, (enriched) isogeometric extended boundary elements/finite element methods for multi-crack propagation and an asynchronous GPU/CPU method for contact and cutting of heterogeneous materials in real-time with applications to surgical simulation. ABOUT THE PRESENTER In 1999, Stéphane Bordas joined a joint graduate programme of the French Institute of Technology (Ecole Spéciale des Travaux Publics) and the American Northwestern University. In 2003, he graduated in Theoretical and Applied Mechanics with a PhD from Northwestern University. Between 2003 and 2006, he was at the Laboratory of Structural and Continuum Mechanics at the Swiss Federal Institute of Technology in Lausanne, Switzerland. In 2006, he became permanent lecturer at Glasgow University’s Civil Engineering Department. Stéphane joined the Computational Mechanics team at Cardiff University in September 2009, as a Professor in Computational Mechanics and directed the institute of Mechanics and Advanced Materials from October 2010 to November 2013. He is the Editor of the book series “Advances in Applied Mechanics” since July 2013. In November 2013, he joined the University of Luxembourg as a Professor in Computational Mechanics. The main axes of his research team include (1) free boundary problems and problems involving complex geometries, in particular moving boundaries and (2) ‘a posteriori’ discretisation and model error control, rationalisation of the computational expense. Stéphane’s keen interest is to actively participate in innovation, technological transfer as well as software tool generation. This has been done through a number of joint ventures with various industrial partners (Bosch GmbH, Cenaero, inuTech GmbH, Siemens-LMS, Soitec SA) and the release of open-source software. In 2012, Stéphane was awarded an ERC Starting Independent Research Grant (RealTcut), to address the need for surgical simulators with a computational mechanics angle with a focus on the multi-scale simulation of cutting of heterogeneous materials in real-time. [less ▲]

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See detailFrom image to analysis: an extended finite element method to simulate the mechanical response of soft-tissue
Hale, Jack UL; Bordas, Stéphane UL; Kerfriden, Pierre

Presentation (2014, April 10)

In this seminar we consider the problem of constructing a numerical method particularly well suited to modelling domains described by segmented image data of the human body. Instead of constructing a ... [more ▼]

In this seminar we consider the problem of constructing a numerical method particularly well suited to modelling domains described by segmented image data of the human body. Instead of constructing a conforming mesh of the problem domain, we use implicitly defined domains described using the level-set method. We then include information about the implicitly defined domains by enriching the usual finite element basis functions defined on a cartesian quadtree or octree mesh with hanging nodes. This approach introduces significant complexities compared with classical finite element methods. We will discuss difficulties with the treatment of hanging nodes, numerical integration and imposing Dirichlet boundary conditions. We will discuss the possible future of extensions of this work, including cutting of soft tissue, multiscale problems with complex microstructure, and model order reduction problems. [less ▲]

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See detailDie Online-Testplattform OASYS
Keller, Ulrich UL; François, Eric UL; Fischbach, Antoine UL et al

Presentation (2014, January)

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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 detailSpace-Time Shear-Slip Mesh Update Method for Fluid-Structure Interaction Problems
Schippke, Henning; Zilian, Andreas UL

Presentation (2013)

Many practical problems in engineering consist of a structure surrounded by a fluid. These are all from the theoretical point of view fluid-structure interaction problems, in which the movement of the ... [more ▼]

Many practical problems in engineering consist of a structure surrounded by a fluid. These are all from the theoretical point of view fluid-structure interaction problems, in which the movement of the structure influences the flow field of the fluid and vice versa. In this contribution the structure is described in a total Lagrangian representation based on velocities and the 2nd Piola-Kirchhoff stress state as primal variables in a hybrid-mixed formulation, while the fluid is modelled via the incompressible Navier-Stokes equations with velocities and pressure as unknowns. The governing equations of fluid and structural dynamics are uniformly discretised using space-time finite elements [1]. The discretised model equations of the fluid are stabilised using a SUPG/PSPG approach. Shape and test functions are continuous within the space-time slabs, while across the space- time slabs the shape and test functions are continuous only in space, but discontinuous in time yielding a time-discontinuous Galerkin approach. The space-time discretisation of the coupled system with velocities and pressure as remaining unknowns lays the basis for a mathematically profound analysis due to its methodical uniformity. During the mesh generation of the fluid-structure problem a fitting mesh at the conjoint interface of fluid and structure is generated ensuring natively the geometric continuity. In the discretised flow domain, which model equations are formulated in the Eulerian framework, a mesh-moving scheme needs to be applied to avoid severe mesh distortions. In case of large but regular structural displacements a discontinuous mesh-moving scheme like the Shear-Slip Mesh Update Method (SSMUM) is applicable [2]. In order to increase robustness and conservation behaviour of the classical SSMUM a modification based on the space-time discretisation of the problem described above is investigated. In the Space- Time SSMUM (ST-SSMUM) the alteration of the spatial connectivity takes place continuously in the space-time domain. By avoiding sudden changes in the spatial connectivity between two adjacent space-time slabs any difficulty in evaluating the jump term is circumvented. The properties of the introduced ST-SSMUM is shown by a computation of the flow field of a rotating impeller, which can be interpreted as a simplified water turbine or blood pump. [less ▲]

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See detailNumerical analysis of free-surface flow through rotating machines
Schippke, Henning; Zilian, Andreas UL

Presentation (2013)

In the context of the transformation process currently taking place in the energy production sector, energy gained from renewable power sources shall replace the present mixture, which mostly relies on ... [more ▼]

In the context of the transformation process currently taking place in the energy production sector, energy gained from renewable power sources shall replace the present mixture, which mostly relies on fossil burnings. Therefore, in the future most of the energy shall be gained by harvesting power from sun, wind or water, geothermal heat or biomass. In case of converting energy from wind into electrical power wind turbines are used in general, while hydropower turbines are the state-of-the-art machinery to derive energy from running water. In order to convert the potential energy from running water as well water wheels pose the method of choice. Turbines in air or water represent mechanically a two-field system, in which the structure of the turbine is surrounded by a streaming fluid. Due to the elasticity of the rotor blades the stresses of the fluid onto the structure deform the blades, which in return yield a time-dependent flow domain. Therefore turbines in a streaming fluid represent a typical example of fluid-structure interaction. Furthermore, in case of water wheels the surrounding air as third field and additional fluid phase comes into play introducing a free surface. In this contribution the governing equations of incompressible fluid flow are presented using primal variables and discretised via the space-time finite element method [3]. The discretised model equations of the fluid are stabilised using an SUPG/PSPG approach. Shape and test functions are continuous within the space-time slabs, while across the space- time slabs the shape and test functions are continuous only in space, but discontinuous in time yielding a time-discontinuous Galerkin approach. Due to the moving rotor blades a mesh moving technique needs to be incorporated into the computational set-up. Considering the occurring large but regular displacements of the flow boundary arising from the rotating rotor blades the shear-slip mesh update method (SSMUM) [1] as discontinuous mesh moving technique is applied. In case of water wheels the free surface is described implicitly via a Level-Set function [2] yielding a single fluid phase with almost discontinuous density and viscosity. The verification and validation of the developed numerical scheme is carried out with the help of computing classical benchmark problems as well as via a comparison to existing experimental data. [less ▲]

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See detailModelling Thermochemical Processes in Granular Media
Hoffmann, Florian UL

Presentation (2012, October 26)

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See detailData mining in geographical contexts and texts
Caruso, Geoffrey UL

Presentation (2010)

An increasing number of institutions, acting at different scales and within different sectors, create in-house geographical information systems, e.g. for regional statistics, for land and transport ... [more ▼]

An increasing number of institutions, acting at different scales and within different sectors, create in-house geographical information systems, e.g. for regional statistics, for land and transport management, for local urban planning, etc. In addition, with the advent of new technologies, such as GPS's or web-mapping facilities, the use of such geographical data is being more and more popular and data is made more easily accessible (sometimes even contributed by the end-users). Geographers find themselves in rather data rich environments today (irrespective of homogeneity and quality). Also geographical objects require specific visualization and statistical methods. The application and adaptation of data mining approaches in geographical contexts is an increasingly important research topic. In this lecture we will start from theoretical considerations on data mining in geography, particularly emphasizing what is special with exploratory spatial data analysis. We will then refer to ongoing research related to geographical data mining undertaken at the University of Luxembourg in collaboration with colleagues from other institutions. A first example will refer to a large and homogeneous dataset of all dwellings within a Belgian province. Using graph theory and local spatial statistics, the data is used to identify and categorize urbanisation patterns across scales in an iterative way. A second example will depict an application of 'self-organizing maps' to understand patterns of 'territorial cohesion' in Europe using a rather small and lacunary dataset. The third example will be dedicated to a text-mining application to a rather large corpus of documents related to spatial development in Europe. This work funded under the ESPON (European Spatial Observatory Network) aims at producing a relevant thematic structure to the online regional statistics database of the ESPON network. [less ▲]

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See detailGeographical Modelling with Cellular-Automata
Caruso, Geoffrey UL

Presentation (2009)

Detailed reference viewed: 65 (0 UL)