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Peer Reviewed
See detailComputation of the flow field resulting from dam failure
Pirotton, Michel ULg

Conference (1991, April 08)

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See detailComputation of the Malpasset dam break with a 2D conservative flow solver on a multiblock structured grid
Erpicum, Sébastien ULg; Archambeau, Pierre ULg; Dewals, Benjamin ULg et al

in Proceedings of the 6th International Conference of Hydroinformatics (2004)

In the global framework of safety, the study of the hydraulic consequences of a dam breaking, sudden and instantaneous for concrete structures, gradual for earth ones, is of major interest in the scope of ... [more ▼]

In the global framework of safety, the study of the hydraulic consequences of a dam breaking, sudden and instantaneous for concrete structures, gradual for earth ones, is of major interest in the scope of prevention policies or protection plans for populations and goods. Suitable numerical models, coupled with contemporary computational possibilities, allow engineers to forecast these complex situations with a great reliability. In this field, WOLF 2D is an efficient analysis and optimisation tool, which has been completely developed by the Applied Hydrodynamics and Hydraulic Constructions team (HACH – http://www.ulg.ac.be/hach) of the University of Liege. It is part of WOLF free surface flows computation package, which includes in the same development environment the resolutions of the 1D Saint-Venant equations, the 2D shallow-water equations as well as a physically based hydrological model and powerful optimisation capabilities based on Genetic Algorithms. The interactive and unique user-interface, with high performance pre- and post-processing, allows monitoring 3-D large-scale runs graphically while they proceed, as well as generation of 3D videos. Each code handles general multiblock meshes, dealing with natural topography and mobile bed simultaneously, for any unsteady situation with mixed regimes and moving hydraulic jumps. By this way, WOLF deals with all free surface hydraulic phenomena, from hydrological runoff and river propagation to extreme erosive flows on realistic mobile topography, such as gradual dam breaching processes. It has moreover proved its efficiency and reliability for years by numerous real applications. The first part of this paper covers a brief description of the 2D multiblock flow solver WOLF 2D and the underlying mathematical model. The second part depicts the application of WOLF computation capabilities to the well-known Malpasset dam break (France, 1959), which induced a catastrophic almost instantaneous release of 48 millions m³ of water in the Reyran river valley down to the town of Frejus and the Mediterranean sea. Data available thanks to the CADAM EU-project are used to assess the results. [less ▲]

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See detailComputation of the sensitivity matrix used for Elasto-plastic material parameter identification by inverse methods
Cooreman, Steven; Bouffioux, Chantal ULg; Lecompte, David et al

in Congress on theoretical and applied Mechanics, Mons, Belgium, May 2006 (2006)

Inverse methods offer a powerful tool for the determination of the elasto-plastic material properties. Contrary to standard tests, these methods can deal with heterogeneous stress and strain-fields which ... [more ▼]

Inverse methods offer a powerful tool for the determination of the elasto-plastic material properties. Contrary to standard tests, these methods can deal with heterogeneous stress and strain-fields which have a larger information contents and hence allow the simultaneous identification of several material parameters. Moreover, it is expected that the obtained material parameters are more accurate, since these heterogeneous deformation fields are much closer to those occurring in real (metal) forming operations. The principle of the inverse method for the identification of material parameters presented in this paper is to compare an experimentally measured strain field to that computed by a Finite Element (FE) model. The material parameters in the FE model are iteratively tuned in such a way that both strain fields match each other as closely as possible. One of the building blocks in this identification procedure is the updating algorithm for the material parameters in the FE model. The key problem of this updating algorithm is the determination of the sensitivity matrix, which expresses the sensitivities of the strains with respect to the material parameters. This paper presents an analytical method for the calculation of this sensitivity matrix in case of simple tensile tests. [less ▲]

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See detailComputation of worst operation scenarios under uncertainty for static security management
Capitanescu, Florin; Wehenkel, Louis ULg

in IEEE Transactions on Power Systems (2013), 28(2), 1697-1705

This paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a ... [more ▼]

This paper deals with day-ahead static security assessment with respect to a postulated set of contingencies while taking into account uncertainties about the next day system conditions. We propose a heuristic approach to compute the worst-case under operation uncertainty for a contingency with respect to overloads. We formulate this problem as a non-convex nonlinear bilevel program that we solve approximately by a heuristic approach which relies on the solution of successive optimal power flow (OPF) and security-constrained optimal power flow (SCOPF) problems of a special type. The method aims at revealing those combinations of uncertainties and contingencies for which the best combination of preventive and corrective actions would not suffice to ensure security. Extensive numerical results on a small, a medium, and a very large system prove the interest of the approach. [less ▲]

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Peer Reviewed
See detailComputational advances in quasi-optimal domain decomposition methods for time-harmonic electromagnetic wave problems
Marsic, Nicolas ULg; Vion, Alexandre ULg; Geuzaine, Christophe ULg

Conference (2015)

In this talk we will present recent advances in the construction of quasi-optimal domain decomposition methods for time-harmonic electromagnetic wave problems. In particular, we will discuss the parallel ... [more ▼]

In this talk we will present recent advances in the construction of quasi-optimal domain decomposition methods for time-harmonic electromagnetic wave problems. In particular, we will discuss the parallel implementation and computational efficiency of sweeping-type preconditioners, as well as the use of high order finite element discretizations, potentially mixing orders for the volume and interface formulations. Results on several large scale test cases will be analysed. [less ▲]

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See detailComputational benchmarking for ultrafast electron dynamics: wavefunction methods vs density functional theory
Oliveira, Micael J. T.; Mignolet, Benoît ULg; Kus, Tomasz et al

in Journal of Chemical Theory and Computation (2015), 11

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See detailComputational biology — Modeling of primary blast effects on the central nervous system
Moore, David; Jérusalem, Antoine; Nyen, Michelle et al

in NeuroImage (2009), 47(Sup. 2), 10-20

Objectives Recent military conflicts in Iraq and Afghanistan have highlighted the wartime effect of traumatic brain injury. The reason for the prominence of TBI in these particular conflicts as opposed to ... [more ▼]

Objectives Recent military conflicts in Iraq and Afghanistan have highlighted the wartime effect of traumatic brain injury. The reason for the prominence of TBI in these particular conflicts as opposed to others is unclear but may result from the increased survivability of blast due to improvements in body armor. In the military context blunt, ballistic and blast effects may all contribute to CNS injury, however blast in particular, has been suggested as a primary cause of military TBI. While blast effects on some biological tissues, such as the lung, are documented in term of injury thresholds, this is not the case for the CNS. We hypothesized that using bio-fidelic models, allowing for fluid-solid interaction and basic material properties available in the literature, that a blast wave would interact with CNS tissue and cause a possible concussive effect. Methods The blast shockwave on CNS tissue was modeled using a coupled computational fluid-solid dynamic simulation. The model included a complex finite element mesh of the head and intra-cranial contents. The effects of threshold and 50% lethal blast lung injury were compared with concussive impact injury using the full head model allowing know upper and lower bounds of tissue injury to be applied using pulmonary injury as the reference tissue. Results The effects of a 50% lethal dose blast lung injury (LD50) were comparable with concussive impact injury using the DVBIC – MIT full head model. Interpretation CNS blast concussive effects were found to be similar between impact mild TBI and the blast field associated with LD50 lung blast injury sustained without personal protective equipment. With the ubiquitous use of personal protective equipment this suggests that blast concussive effects may more readily occur in personnel due to enhanced survivability in the current conflicts. [less ▲]

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See detailComputational Considerations for the Prediction of Stall Flutter
Watrin, Damien ULg; Dimitriadis, Grigorios ULg; Perry, Tristan et al

in Proceedings of the 53rd AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics and Materials Conference (2012, April 25)

A solver has been developed within the OpenFoam framework to compute large amplitude motion of two-dimensional rigid configurations. The results obtained with this code were successfully validated on ... [more ▼]

A solver has been developed within the OpenFoam framework to compute large amplitude motion of two-dimensional rigid configurations. The results obtained with this code were successfully validated on rigid airfoils at static and dynamic conditions, as well as correlated with experimental data and numerical solutions from similar unsteady solvers. The results demonstrated that while current computational methods are able to predict the self-sustained oscillations characterizing a pitch-dominated stall flutter, including energy transfer, improvements are needed. The influence of grid, temporal integration, turbulence modeling, and flow equations is examined for the stall flutter starting solution of dynamic stall. [less ▲]

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See detailComputational environment for the design of flexible mechanisms with feedback control
Bruls, Olivier ULg; Duysinx, Pierre ULg; Golinval, Jean-Claude ULg

in Proceeding of 6th National Congress on theorical and Applied Mechanics (2003, May)

In this article, numerical methods are exploited for the design of mechatronic systems. A method is presented for the simulation of a flexible mechanism subject to the action of a digital control system ... [more ▼]

In this article, numerical methods are exploited for the design of mechatronic systems. A method is presented for the simulation of a flexible mechanism subject to the action of a digital control system. In the context of model-based control, reduction techniques of mechanical models are also discussed. [less ▲]

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See detailComputational FE² scheme for heterogeneous shell structures
Massart, Thierry J.; Mercatoris, Benoît ULg; Berke, Peter et al

Conference (2011)

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See detailComputational Fluid Mechanics for Civil Engineering Applications
Terrapon, Vincent ULg

Scientific conference (2012, May 23)

Detailed reference viewed: 35 (9 ULg)
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See detailComputational Hemodynamics Coupled with Mechanical Behaviour of the Surrounded Materials, in the Specific Case of the Brachial Artery
Paulus, Raphaël ULg; Erpicum, Sébastien ULg; Dewals, Benjamin ULg et al

in Proceedings of Biomed 2009 - Eighth International Conference on Modelling in Medicine and Biology (2009)

Detailed reference viewed: 40 (11 ULg)
See detailComputational homogenization for hydro‐mechanical coupling in multi‐scale modelling, FEM x FEM
van den Eijnden, Abraham Pieter ULg; Bésuelle, Pierre; Chambon, René et al

Scientific conference (2013, January 31)

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See detailComputational Homogenization for Laminated Ferromagnetic Cores in Magnetodynamics
Niyonzima, Innocent ULg; V Sabariego, Ruth; Dular, Patrick ULg et al

in IEEE Transactions on Magnetics (2013), 49(5), 2049-2052

In this paper, we investigate the modeling of ferromagnetic multiscale materials. We propose a computational homogenization technique based on the heterogeneous multiscale method (HMM) that includes both ... [more ▼]

In this paper, we investigate the modeling of ferromagnetic multiscale materials. We propose a computational homogenization technique based on the heterogeneous multiscale method (HMM) that includes both eddy-current and hysteretic losses at the mesoscale. The HMM comprises: 1) a macroscale problem that captures the slow variations of the overall solution; 2) many mesoscale problems that allow to determine the constitutive law at the macroscale. As application example, a laminated iron core is considered. [less ▲]

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See detailComputational Homogenization for Laminated Ferromagnetic Cores in Magnetodynamics
Niyonzima, Innocent ULg; Vazquez Sabariego, Ruth ULg; Henrotte, François et al

in Proceedings of the 15th Biennial IEEE Conference on Electromagnetic Field Computation (CEFC2012) (2012, November)

In this paper, we investigate the modeling of fer- romagnetic multiscale materials. We propose a computational homogenization method based on the heterogeneous multiscale method (HMM) that includes eddy ... [more ▼]

In this paper, we investigate the modeling of fer- romagnetic multiscale materials. We propose a computational homogenization method based on the heterogeneous multiscale method (HMM) that includes eddy currents and hysteretic losses at the mesoscale. The HMM comprises: 1) a macroscale problem that captures the slow variations of the overall solution; 2) many microscale problems that allow to determine the constitutive law at the macroscale. As application example, a laminated iron core is considered. [less ▲]

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See detailA Computational Homogenization Method for the Evaluation of Eddy Current in Nonlinear Soft Magnetic Composites
Niyonzima, Innocent ULg; Vazquez Sabariego, Ruth ULg; Dular, Patrick ULg et al

in Proceeding of the 9th International Symposium on Electric and Magnetic Fields, EMF 2013 (2013, April 23)

The use of the soft magnetic composite (SMC) in electric devices has increased in recent years. These materials made from a metallic powder compacted with a dielectric binder are a good alternative to ... [more ▼]

The use of the soft magnetic composite (SMC) in electric devices has increased in recent years. These materials made from a metallic powder compacted with a dielectric binder are a good alternative to laminated ferromagnetic structures as their granular mesoscale structure allows to significantly reduce the eddy current losses. Furthermore unlike the laminated ferromagnetic structures, SMC exhibit isotropic magnetic properties what makes them good candidates for manufacturing machines with 3D flux paths. The isotropy of the thermal conductivity also allows for a more efficient heat dissipation. The use of classical numerical methods such as the finite element method to study the behavior of SMC is computational very expensive. Indeed a very fine mesh would be required in order to capture fine scale variations i.e. variations at level of metallic grains whence the use of multiscale methods for modelling SMC. The application of multiscale method to study the behaviour of SMC is relatively recent. In (A. Bordianu et al “A Multiscale Approach to Predict Classical Losses in Soft Magnetic Composites”, IEEE Trans. Mag., vol. 48, no. 4, 2012.), the authors used a homogenization technique to compute electrical and magnetic constitutive laws on a representative volume element (RVE). These laws were then used in finite element computations. Herein, the RVE has been chosen to account for the grain- grain contact that can occur in a actual SMC structure due to the compaction process and that can lead to the appearance of macroscale eddy currents. In this paper, we will extend the computational homogenization method success- fully used for modelling the behaviour of laminated ferromagnetic cores in mag- netodynamics (I. Niyonzima et al “Computational Homogenization for Laminated Ferromagnetic Cores in Magnetodynamics”, in Proc. of the 15th Biennal Confer- ence on Electromagnetic Field Computation, 2012) to the case of SMC. The method is based on the heterogeneous multiscale method (HMM) and couples two types of problems: a macroscale problem that captures the slow variations of the overall so- lution and many microscale problems that allow to determine the constitutive laws at the macroscale. The choice of RVE will also be discussed. [less ▲]

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See detailComputational homogenization of cellular materials
Nguyen, Van Dung ULg; Noels, Ludovic ULg

in International Journal of Solids and Structures (2014), 51(11-12), 2183-2203

In this work we propose to study the behavior of cellular materials using a second–order multi–scale computational homogenization approach. During the macroscopic loading, micro-buckling of thin ... [more ▼]

In this work we propose to study the behavior of cellular materials using a second–order multi–scale computational homogenization approach. During the macroscopic loading, micro-buckling of thin components, such as cell walls or cell struts, can occur. Even if the behavior of the materials of which the micro–structure is made remains elliptic, the homogenized behavior can lose its ellipticity. In that case, a localization band is formed and propagates at the macro–scale. When the localization occurs, the assumption of local action in the standard approach, for which the stress state on a material point depends only on the strain state at that point, is no–longer suitable, which motivates the use of the second-order multi–scale computational homogenization scheme. At the macro–scale of this scheme, the discontinuous Galerkin method is chosen to solve the Mindlin strain gradient continuum. At the microscopic scale, the classical finite element resolutions of representative volume elements are considered. Since the meshes generated from cellular materials exhibit voids on the boundaries and are not conforming in general, the periodic boundary conditions are reformulated and are enforced by a polynomial interpolation method. With the presence of instability phenomena at both scales, the arc–length path following technique is adopted to solve both macroscopic and microscopic problems. [less ▲]

Detailed reference viewed: 269 (150 ULg)