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See detailPaCER - A fully automated method for electrode trajectory and contact reconstruction in deep brain stimulation
Husch, Andreas UL; Petersen, Mikkel V.; Gemmar, Peter et al

in NeuroImage: Clinical (2018), 17

Abstract Deep brain stimulation (DBS) is a neurosurgical intervention where electrodes are permanently implanted into the brain in order to modulate pathologic neural activity. The post-operative ... [more ▼]

Abstract Deep brain stimulation (DBS) is a neurosurgical intervention where electrodes are permanently implanted into the brain in order to modulate pathologic neural activity. The post-operative reconstruction of the DBS electrodes is important for an efficient stimulation parameter tuning. A major limitation of existing approaches for electrode reconstruction from post-operative imaging that prevents the clinical routine use is that they are manual or semi-automatic, and thus both time-consuming and subjective. Moreover, the existing methods rely on a simplified model of a straight line electrode trajectory, rather than the more realistic curved trajectory. The main contribution of this paper is that for the first time we present a highly accurate and fully automated method for electrode reconstruction that considers curved trajectories. The robustness of our proposed method is demonstrated using a multi-center clinical dataset consisting of N=44 electrodes. In all cases the electrode trajectories were successfully identified and reconstructed. In addition, the accuracy is demonstrated quantitatively using a high-accuracy phantom with known ground truth. In the phantom experiment, the method could detect individual electrode contacts with high accuracy and the trajectory reconstruction reached an error level below 100 μm (0.046 ± 0.025 mm). An implementation of the method is made publicly available such that it can directly be used by researchers or clinicians. This constitutes an important step towards future integration of lead reconstruction into standard clinical care. [less ▲]

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See detailPANEL: Position-based Aggregator Node Election in Wireless Sensor Networks
Buttyán, Levente; Schaffer, Peter UL

in International Journal of Distributed Sensor Networks (2010), 2010

We introduce PANEL a position-based aggregator node election protocol for wireless sensor networks. The novelty of PANEL with respect to other aggregator node election protocols is that it supports ... [more ▼]

We introduce PANEL a position-based aggregator node election protocol for wireless sensor networks. The novelty of PANEL with respect to other aggregator node election protocols is that it supports asynchronous sensor network applications where the sensor readings are fetched by the base stations after some delay. In particular, the motivation for the design of PANEL was to support reliable and persistent data storage applications, such as TinyPEDS; see the study by Girao et al. (2007). PANEL ensures load balancing, and it supports intra and intercluster routing allowing sensor-to-aggregator, aggregator-to-aggregator, base station-to-aggregator, and aggregator to-base station communications. We also compare PANEL with HEED; see the study by Younis and Fahmy (2004) in the simulation environment provided by TOSSIM, and show that, on one hand, PANEL creates more cohesive clusters than HEED, and, on the other hand, that PANEL is more energy efficient than HEED. [less ▲]

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See detailA parallel and efficient multi-split XFEM for 3-D analysis of heterogeneous materials
Bansal, Manik; Singh, I.V.; Mishra, B.K. et al

in Computer Methods in Applied Mechanics and Engineering (2018)

We propose a parallel and computationally efficient multi-split XFEM approach for 3-D analysis of heterogeneous materials. In this approach, multiple discontinuities (pores and reinforcement particles ... [more ▼]

We propose a parallel and computationally efficient multi-split XFEM approach for 3-D analysis of heterogeneous materials. In this approach, multiple discontinuities (pores and reinforcement particles) may intersect any given element (we call those elements multi-split elements). These discontinuities are modeled by imposing additional degrees of freedom at the nodes. The main advantage of the proposed scheme is that the mesh size remains independent of the relative distance among the heterogeneities/discontinuities. The pores and reinforcement particles are assumed to be spherical. The simulations are performed for uniform and non-uniform heterogeneity distribution. The Young’s modulus of the heterogeneous material is evaluated for different amount of pores and reinforcement particles. To demonstrate the computational efficiency of the multi-split XFEM, elastic damage analysis is performed for the unit cell with 5% pores and 5% reinforcement particles under uniaxial tensile loading. These simulations show that the Young’s modulus decreases linearly with the increase in the volume fraction of the pores and increases linearly with the increase in volume fraction of reinforcement particles. The multi-split XFEM is found to be at least 1.8 times computationally efficient than standard XFEM and at least 6.7 times computationally efficient than FEM. [less ▲]

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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)

Detailed reference viewed: 40 (1 UL)
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See detailA Parallel Multiscale DEM-VOF Method For Large-Scale Simulations Of Three-Phase Flows
Pozzetti, Gabriele UL; Besseron, Xavier UL; Rousset, Alban UL et al

in Proceedings of ECCM-ECFD 2018 (2018)

A parallel dual-grid multiscale DEM-VOF coupling is here investigated. Dual- grid multiscale couplings have been recently used to address different engineering problems involving the interaction between ... [more ▼]

A parallel dual-grid multiscale DEM-VOF coupling is here investigated. Dual- grid multiscale couplings have been recently used to address different engineering problems involving the interaction between granular phases and complex fluid flows. Nevertheless, previous studies did not focus on the parallel performance of such a coupling and were, therefore, limited to relatively small applications. In this contribution, we propose an insight into the performance of the dual-grid multiscale DEM-VOF method for three- phase flows when operated in parallel. In particular,we focus on a famous benchmark case for three-phase flows and assess the influence of the partitioning algorithm on the scalability of the dual-grid algorithm. [less ▲]

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See detailParallel simulations of soft-tissue using an adaptive quadtree/octree implicit boundary finite element method
Hale, Jack UL; Bordas, Stéphane UL; Kerfriden, Pierre et al

in 11th. World Congress on Computational Mechanics (2014, July 23)

Octree (3D) and quadtree (2D) representations of computational geometry are particularly well suited to modelling domains that are defined implicitly, such as those generated by image segmentation ... [more ▼]

Octree (3D) and quadtree (2D) 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 [5]. In this work we consider the simulation of soft-tissue which can be modelled with a incompressible hyperelastic constitutive law. We include the effects of both non-linear geometry and material properties in our model. Similarly to Moumnassi et al. [2] we use the implicitly defined level set functions as the basis for a partition of unity enrichment to more accurately represent the domain boundary on the cartesian quadtree/octree mesh. In addition we introduce arbitrary cuts and discontinuities in the domain using ideas from the classical extended finite element method [3]. Because of its hydrated nature soft-tissue is nearly incompressible [1]. We explore the use of a classical two-field displacement-pressure (u-p) mixed approach to deal with the problem of volumetric-locking in the incompressible limit [4]. We exploit the existing parallel capabilities available in the open-souce finite element toolkit deal.ii [6], including the advanced mesh partitioning and balancing recently introduced in the p4est library [7]. The resulting method scales to run over hundreds of cores on the University of Luxembourg HPC platform. [less ▲]

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See detailA partitioned model order reduction approach to rationalise computational expenses in nonlinear fracture mechanics
Kerfriden, P.; Goury, O.; Rabczuk, T. et al

in Computer Methods in Applied Mechanics & Engineering (2013), 256

We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order ... [more ▼]

We propose in this paper a reduced order modelling technique based on domain partitioning for parametric problems of fracture. We show that coupling domain decomposition and projection-based model order reduction permits to focus the numerical effort where it is most needed: around the zones where damage propagates. No a priori knowledge of the damage pattern is required, the extraction of the corresponding spatial regions being based solely on algebra. The efficiency of the proposed approach is demonstrated numerically with an example relevant to engineering fracture. © 2012 Elsevier B.V. [less ▲]

Detailed reference viewed: 276 (12 UL)
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See detailA PAS-state constrained optimization formulation for the anticipatory network traffic control problem
Rinaldi, Marco UL; Tampère, Chris

Scientific Conference (2016, September)

Detailed reference viewed: 94 (2 UL)
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See detailPerformance monitoring of an industrial boiler: classification of relevant variables with Random Forests
Sainlez, Matthieu UL; Heyen, Georges

in Pierucci, S.; Ferraris, G. Buzzi (Eds.) 20th European Symposium on Computer Aided Process Engineering (2010)

Detailed reference viewed: 46 (0 UL)
See detailA perspective on urban economics and geographical agent-based models. (Keynote Speech)
Caruso, Geoffrey UL

Scientific Conference (2015, September)

In this presentation, we will argue that there are many benefits to further liaise urban economic models and geographically -aware agent-based simulation models for further understanding the structure and ... [more ▼]

In this presentation, we will argue that there are many benefits to further liaise urban economic models and geographically -aware agent-based simulation models for further understanding the structure and dynamics of cities, especially at the scale of city regions but also, eventually, for contributing micro understanding of changes in a system of cities. At first sight it appears that these two fields of urban research are very separated: urban economics relies mostly on mathematical proofs, a parsimonious set of interactions, static equilibria and a rather homogeneous space and set of agents; while geographical agent-based models emphasize the dynamics and complexity of cities, the heterogeneity of agents and space, and rely solely on computational methods. The presentation will showcase a series of theoretical and applied research to stress the idea that the two can fruitfully be combined and that results are then palatable to both urban economists and geographers and can therefore participate to consolidating a wider and formalised urban theory. The geographical turn towards agent-based approaches, compared to more aggregate models and behaviourally-blind geocomputational methods, is actually a chance for geographers to formalise market as well as non-market interactions in a manner that is consistent with urban economic theory and enhance the treatment of space in this theory. Relying on a formal description of agents utility permits to discuss normative instruments where environmental and welfare impacts can be traded-off by policy makers. Furthermore,, land or housing market outcomes of the models and the analytical efforts actually help to reduce parametric space and calibrate or validate models against independent data. [less ▲]

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See detailPIV study of the effect of piston position on the in-cylinder swirling flow during the scavenging process in large two-stroke marine diesel engines
Haider, Sajjad; Schnipper, T.; Obeidat, Anas UL et al

in Journal of Marine Science & Technology (2013), 18(1), 133-143

A simplified model of a low speed large two- stroke marine diesel engine cylinder is developed. The effect of piston position on the in-cylinder swirling flow during the scavenging process is studied ... [more ▼]

A simplified model of a low speed large two- stroke marine diesel engine cylinder is developed. The effect of piston position on the in-cylinder swirling flow during the scavenging process is studied using the stereo- scopic particle image velocimetry technique. The mea- surements are conducted at different cross-sectional planes along the cylinder length and at piston positions covering the air intake port by 0, 25, 50 and 75 %. When the intake port is fully open, the tangential velocity profile is similar to a Burgers vortex, whereas the axial velocity has a wake- like profile. Due to internal wall friction, the swirl decays downstream, and the size of the vortex core increases. For increasing port closures, the tangential velocity profile changes from a Burgers vortex to a forced vortex, and the axial velocity changes correspondingly from a wake-like profile to a jet-like profile. For piston position with 75 % intake port closure, the jet-like axial velocity profile at a cross-sectional plane close to the intake port changes back to a wake-like profile at the adjacent downstream cross-sectional plane. This is characteristic of a vortex breakdown. The non-dimensional velocity profiles show no significant variation with the variation in Reynolds number. [less ▲]

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See detailThe Place of Legal Ontologies in Regulatory Compliance
Kiriinya, Robert Kevin Muthuri UL

Scientific Conference (2015)

This work highlights ongoing PhD research work that is investigating how to appropriate legal ontologies for regulatory compliance. We seek to make the law more accessible to specific contexts of usage ... [more ▼]

This work highlights ongoing PhD research work that is investigating how to appropriate legal ontologies for regulatory compliance. We seek to make the law more accessible to specific contexts of usage where technological advances outpace the development of legal doctrine and principles for these domains. [less ▲]

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See detailPOD-based model order reduction for the simulation of strong nonlinear evolutions in structures: Application to damage propagation
Kerfriden, P.; Gosselet, P.; Adhikari, S. et al

in IOP Conference Series: Materials Science and Engineering (2014), 10(1),

In this paper, we develop a bridge between POD-based model order reduction techniques and the classical Newton-Krylov solvers to derive an efficient solution procedure for highly nonlinear problems ... [more ▼]

In this paper, we develop a bridge between POD-based model order reduction techniques and the classical Newton-Krylov solvers to derive an efficient solution procedure for highly nonlinear problems undergoing strong topological changes. [less ▲]

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See detailPOD-based reduction methods, the Quasicontinuum Method and their Resemblance
Beex, Lars UL; Schenone, Elisa; Hale, Jack UL

Scientific Conference (2016, June 27)

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See detailPOD-based Reduction Methods, the Quasicontinuum Method and their Resemblance
Schenone, Elisa; Hale, Jack UL; Beex, Lars UL

Scientific Conference (2016, June)

POD-based reduction methods and the quasicontinuum method share two similar reduction steps to increase the computational speed of large mechanical models. Here, they are compared with each other.

Detailed reference viewed: 59 (8 UL)
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See detailA posteriori error estimation for extended finite elements by an extended global recovery
Duflot, M.; Bordas, Stéphane UL

in International Journal for Numerical Methods in Engineering (2008), 76(8), 1123-1138

This contribution presents an extended global derivative recovery for enriched finite element methods (FEMs), such as the extended FEM along with an associated error indicator. Owing to its simplicity ... [more ▼]

This contribution presents an extended global derivative recovery for enriched finite element methods (FEMs), such as the extended FEM along with an associated error indicator. Owing to its simplicity, the proposed scheme is ideally suited to industrial applications. The procedure is based on global minimization of the L2 norm of the difference between the raw strain field (C-1) and the recovered (C0) strain field. The methodology engineered in this paper extends the ideas of Oden and Brauchli (Int. J. Numer. Meth. Engng 1971; 3) and Hinton and Campbell (Int. J. Numer. Meth. Engng 1974; 8) by enriching the approximation used for the construction of the recovered derivatives (strains) with the gradients of the functions employed to enrich the approximation employed for the primal unknown (displacements). We show linear elastic fracture mechanics examples, both in simple two-dimensional settings, and for a three-dimensional structure. Numerically, we show that the effectivity index of the proposed indicator converges to unity upon mesh refinement. Consequently, the approximate error converges to the exact error, indicating that the error indicator is valid. Additionally, the numerical examples suggest a novel adaptive strategy for enriched approximations in which the dimensions of the enrichment zone are first increased, before standard h- and p-adaptivities are applied; we suggest to coin this methodology e-adaptivity. Copyright © 2008 John Wiley & Sons, Ltd. [less ▲]

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See detailPotentials for Realising a Consistent Transition Between Function Modelling with the IFM Framework and Early System Simulation
Eisenbart, Boris UL; Dohr, Fabio; Gericke, Kilian UL et al

in Proceedings of 19th International Conference on Engineering Design (2013)

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. Sound decision-making across ... [more ▼]

Conceptual design is considered one of the most demanding design tasks requiring a joint effort of the involved designers, particularly in interdisciplinary design. Sound decision-making across disciplines on alternative solution concepts may be considerably facilitated through early system simulation. A consistent transition of the available information in function modelling to early system simulation may thus support designers in this task. The IFM framework intends to support cross-disciplinary collaboration of involved designers by providing an integrated function modelling approach. In the paper it is analysed in how far a consistent transition from the IFM framework to established modelling techniques for simulation may be realised. The paper compares the information required for early system simulation in an interdisciplinary design context to the specific information conveyed in the different views of the IFM framework. The analysis identifies specific potentials and barriers for a consistent transition between them. Finally, the implications of the derived insights are discussed. [less ▲]

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See detailPractical error bounds in energy norm based on a recovered displacement field
Nadal, E.; González-Estrada, O. A.; Ródenas, J. J. et al

in Pimienta, P M (Ed.) 10th World Congress on Computational Mechanics (WCCM 2012) (2012)

Detailed reference viewed: 222 (2 UL)