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See detailA finite element for thermo-mechanical problems.
Bourdouxhe, Michel; Charlier, Robert ULiege; Cescotto, Serge ULiege

in Proceedings Numiform Conference Göteborg (1986, August)

Detailed reference viewed: 21 (4 ULiège)
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See detailFinite element formulation and couplings
Habraken, Anne ULiege; Collin, Frédéric ULiege

Conference (2013)

Detailed reference viewed: 20 (3 ULiège)
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See detailA finite element formulation for spectral problems in optical fibers
Guenneau, S.; Nicolet, A.; Zolla, F. et al

in COMPEL (2001), 20(1), 120--131

Detailed reference viewed: 13 (2 ULiège)
See detailFinite element grid optimization with geometric approach
Hwang, H. T.; Fleury, Claude ULiege

in The 33rd Aiaa/Asme/Asce/Ahs/Asc Structures, Structural Dynamics and Materials Conference: April 13-15, 1992/Dallas, Tx (1992)

Detailed reference viewed: 5 (1 ULiège)
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See detailFinite element investigation of size effects on the mechanical behavior of nickel single crystals
Keller, Clément; Habraken, Anne ULiege; Duchene, Laurent ULiege

in Materials Science & Engineering : A (2012), 550(30), 342-349

The influence of dimensions on the mechanical behavior of f.c.c. single crystals with dimensions larger than a few micrometers has been the topic of many experimental investigations and controversies ... [more ▼]

The influence of dimensions on the mechanical behavior of f.c.c. single crystals with dimensions larger than a few micrometers has been the topic of many experimental investigations and controversies during the 1970s and this question is still open. The objective of this article is to shed new light on this point by performing finite element simulations thanks to a strain gradient crystal plasticity model. Based on the model identification for nickel, several single crystal samples with various thicknesses and orientations were tested numerically in tension. The effect of dimensions was then analyzed considering the spatial distribution of dislocation densities. Near loading boundaries, dislocation density gradients appeared perpendicular to the Burgers vector direction of the primary activated slip system which modified the mechanical behavior. These gradients are discussed in terms of boundary conditions, crystal orientation and dislocation interactions with surfaces. [less ▲]

Detailed reference viewed: 101 (24 ULiège)
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See detailFinite Element Magnetic Models via a Coupling of Subproblems of Lower Dimensions
Dular, Patrick ULiege; V Sabariego, Ruth ULiege; Geuzaine, Christophe ULiege et al

in IEEE Transactions on Magnetics (2010), 46(8), 2827-2830

Model refinements of magnetic circuits are performed via a subdomain finite element method based on a perturbation technique. A complete problem is split into subproblems, some of lower dimensions, to ... [more ▼]

Model refinements of magnetic circuits are performed via a subdomain finite element method based on a perturbation technique. A complete problem is split into subproblems, some of lower dimensions, to allow a progression from 1-D to 3-D models. Its solution is then expressed as the sum of the subproblem solutions supported by different meshes. A convenient and robust correction procedure is proposed allowing independent overlapping meshes for both source and reaction fields, the latter being free of cancellation error in magnetic materials. The procedure simplifies both meshing and solving processes, and quantifies the gain given by each model refinement on both local fields and global quantities. [less ▲]

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See detailFinite Element Mesh Adaptation Strategy From Residual and Hierarchical Error Estimators in Eddy Current Problems
Dular, Patrick ULiege; Le Menach, Yvonnick; Tang, Zuqi et al

in IEEE Transactions on Magnetics (2015), 51(3),

A strategy of mesh adaptation in eddy current finite element modeling is developed from both residual and hierarchical error estimators. Wished distributions of element sizes of adapted meshes are ... [more ▼]

A strategy of mesh adaptation in eddy current finite element modeling is developed from both residual and hierarchical error estimators. Wished distributions of element sizes of adapted meshes are determined from the element-wise local contributions to the estimators and define constraints for the mesh generator. Uniform distributions of the local error are searched. [less ▲]

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See detailA finite element method for poro mechanical modelling of geotechnical problems using local second gradient models
Collin, Frédéric ULiege; Chambon, René; Charlier, Robert ULiege

in International Journal for Numerical Methods in Engineering (2006), 65(11), 1749-1772

In this paper, a new finite element method is described and applied. It is based on a theory developed to model poromechanical problems where the mechanical part is obeying a second gradient theory. The ... [more ▼]

In this paper, a new finite element method is described and applied. It is based on a theory developed to model poromechanical problems where the mechanical part is obeying a second gradient theory. The aim of such a work is to properly model the post localized behaviour of soils and rocks saturated with a pore fluid. Beside the development of this new Coupled theory, a corresponding finite element method has been developed. The elements used are based on a weak form of the relation between the deformation gradient and the second gradient, using a field of Lagrange multipliers. The global problem is solved by a system of equations where the kinematic variables are fully coupled with the pore pressure. Some numerical experiments showing the effectiveness of the method ends the paper. Copyright (c) 2005 John Wiley [less ▲]

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See detailFinite element model for the extension of the direct strength method to hot-rolled profile cross-sections
Li, Yongzhen ULiege; Rossi, Barbara ULiege

in Proceedings of the 12th Nordic Steel Construction Conference (2012, September 05)

Abstract: In the present research, a geometrically and materially nonlinear analysis using the FE method has been conducted to evaluate the resistance of axially compressed hot-rolled H profile cross ... [more ▼]

Abstract: In the present research, a geometrically and materially nonlinear analysis using the FE method has been conducted to evaluate the resistance of axially compressed hot-rolled H profile cross-sections. The FE model was firstly duly verified against experimental data and then used to carry a parametric analysis. The goal of the analysis is to propose a new Direct Strength Method (DSM) strength curve intended for calculating the resistance of non-compact and slender hot-rolled H profile cross-sections. [less ▲]

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See detailFinite element model reduction for space thermal analysis
Jacques, Lionel ULiege; Béchet, Eric ULiege; Kerschen, Gaëtan ULiege

in Finite Elements in Analysis and Design (2017), 127

To alleviate the computational burden of the nite element method for thermal analyses involving conduction and radiation, this paper proposes an automatic conductive-radiative reduction process based on ... [more ▼]

To alleviate the computational burden of the nite element method for thermal analyses involving conduction and radiation, this paper proposes an automatic conductive-radiative reduction process based on the clustering of a detailed mesh coming from a structural model for instance. The proposed method leads to a signi cant reduction of the number of radiative exchange factors (REFs) to compute and size of the corresponding matrix. It further keeps accurate conduction information by introducing the concept of physically meaningful super nodes. The REFs between the super nodes are computed through Monte Carlo ray-tracing on the partitioned mesh, preserving the versatility of the method. The resulting conductive-radiative reduced model is solved using standard iterative techniques and the detailed mesh temperatures can be recovered from the super nodes temperatures for further thermo-mechanical analysis. The proposed method is applied to a structural component of the Meteosat Third Generation mission and is benchmarked against ESATAN-TMS, the standard thermal analysis software used in the European aerospace industry. [less ▲]

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See detailFinite Element Model Reduction for Spacecraft Thermal Analysis
Jacques, Lionel ULiege; Masset, Luc ULiege; Kerschen, Gaëtan ULiege

Scientific conference (2015, November 03)

The finite element method (FEM) is widely used in mechanical engineering, especially for space structure design. However, FEM is not yet often used for thermal engineering of space structures where the ... [more ▼]

The finite element method (FEM) is widely used in mechanical engineering, especially for space structure design. However, FEM is not yet often used for thermal engineering of space structures where the lumped parameter method (LPM) is still dominant. Both methods offer advantages and disadvantages and the proposed global approach tries to combine both methods: - The LPM conductive links are error-prone and still too often computed by hand. This is incompatible with the increasing accuracy required by the thermal control systems (TCS) and associated thermal models. Besides offering the automatic and accurate computation of the conductive links, the FEM also provides easy interaction between mechanical and thermal models, allowing better thermo-mechanical analyses. - On another hand, due to the large number of elements composing a FE model, the computation of the radiative exchange factors (REFs) is prohibitively expensive. New methods to accelerate the REFs computation by ray-tracing are necessary. Ray-tracing enhancement methods were presented in the previous editions, providing at least a 50% reduction of the number of rays required for a given accuracy. Another way to speed up the REF computation consists in grouping the FE external facets into super-faces. Surfaces in FEM are approximated where primitives are used in the LPM. In parallel to super-faces, quadric surface fitting of selected regions in the FE mesh is therefore performed where high surface accuracy is required for the computation of the radiative links and environmental heat loads. Last year’s presentation focused solely on the first point. Developments of super-face ray-tracing with quadrics fitting will be presented. In addition to REFs, orbital heat loads computation is also implemented with significant improvement. The presentation will also address the global process involving first the detailed FE model conductive reduction, then the super-faces generation with selective quadric fitting for the computation of REFs and orbital heat loads and finally the computation of the reduced model temperatures. Detailed FE model temperature field can then be computed back from the reduced ones and the reduction matrices for potential thermo-mechanical analyses. [less ▲]

Detailed reference viewed: 56 (11 ULiège)
See detailFinite Element Model Reduction of Thermal Systems with Conductive and Radiative Heat Transfers
Jacques, Lionel ULiege; Masset, Luc ULiege; Kerschen, Gaëtan ULiege

Scientific conference (2015, March 24)

The Lumped parameter method (LPM) is the main method used for space structures thermal design. It is very versatile and allows easy integration of user-defined components but the computation of the ... [more ▼]

The Lumped parameter method (LPM) is the main method used for space structures thermal design. It is very versatile and allows easy integration of user-defined components but the computation of the conductive links is error-prone and still too often computed by hand. Widely used in structural design, the finite element method (FEM) is however not yet often used for thermal analysis. One of the main reasons is that the radiative exchange factors, usually computed through Monte Carlo ray tracing, are extremely expensive to compute due to the large number of elements composing a FE model. A new global approach for FE model reduction of thermal systems is presented. The method is based on an automated FE mesh partitioning leading to super-faces and super-nodes. It is tailored for radiative exchange factors computation, taking into account selected quadric recognition and material constraints. The method also provides accurate conductive links computation and enables a direct mapping of the reduced temperatures back onto the detailed FE mesh (for e.g. thermo-elastic analyses). The application to two instruments developed at the Centre Spatial de Liège in Belgium will be presented, namely the Extreme Ultraviolet Imager (EUI) onboard Solar Orbiter and the Back Telescope Assembly (BTA) onboard Meteosat Third Generation. [less ▲]

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See detailFinite Element Model Updating Based On Holographic and Speckle Interferometry Measurements: Rapport VIA-25
Simon, Daniel; Golinval, Jean-Claude ULiege

Conference given outside the academic context (1999)

Optical measurement techniques look very promising for finite element (F.E.) model updating or error localisation of plate-like structures in the field of structural dynamics. The purpose of this paper is ... [more ▼]

Optical measurement techniques look very promising for finite element (F.E.) model updating or error localisation of plate-like structures in the field of structural dynamics. The purpose of this paper is to investigate a way to better exploit the high spatial resolution inherent to these techniques in order to correct FE mesh discretisation errors and/or model parameter errors. An important assumption in F.E. model error detection is first to consider the initial mesh as sufficiently fine to well represent the measured (displacement or stress) field. In the case of model updating, the adjustment of the model is performed by minimising the difference between the outputs of the model and the exact solution with respect to design parameters. In the case of FE mesh adaptation, the exact solution has to be estimated whereas in the case of model parameter errors, it is directly measured. The idea developed in this paper is to take advantage of the high spatial resolution offered by optical techniques to calculate successively two error estimators using only measurements. The experimental field is first used for the detection of singular regions corresponding to high gradients. This estimator indicates the regions where a mesh refinement is required. Thus a second estimator is calculated and used for parameter error detection. [less ▲]

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See detailFinite Element Model Updating of Plate-like Structures Using Modal Holographic Measurement Field
Simon, Daniel; Golinval, Jean-Claude ULiege

Conference given outside the academic context (2002)

Optical measurement techniques are very promising for finite element (F.E.) model updating or error localisation of plate-like structures in the field of structural dynamics. The purpose of this work is ... [more ▼]

Optical measurement techniques are very promising for finite element (F.E.) model updating or error localisation of plate-like structures in the field of structural dynamics. The purpose of this work is to investigate a way to better exploit the high spatial resolution inherent to these techniques in order to correct FE mesh discretisation errors and/or model parameter errors. An important assumption in F.E. model error detection is first to consider the initial mesh as sufficiently fine to well represent the measured (displacement or stress) field. In the case of model updating, the adjustment of the model is performed by minimising the difference between the outputs of the model and the exact solution with respect to design parameters. In the case of FE mesh adaptation, the exact solution has to be estimated whereas in the case of model parameter errors, the reference solution is assumed to be the measured one. The idea developed in this paper is to take advantage of the high spatial resolution offered by optical techniques to calculate successively two error estimators using only measurements. The experimental field is first used for the detection of singular regions corresponding to high gradients. This estimator indicates the regions where a mesh refinement is required. Thus a second estimator is calculated and used for parameter error detection. [less ▲]

Detailed reference viewed: 28 (1 ULiège)
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See detailFinite Element Model Updating of the Garteur SM-AG19 Structure
Thonon, Carole; Golinval, Jean-Claude ULiege

Conference given outside the academic context (2001)

This paper reports the procedure followed by the "LTAS-Vibrations et Identification des Structures" research group to generate a low order nite element (F.E.) model of the GARTEUR SM-AG19 structure ... [more ▼]

This paper reports the procedure followed by the "LTAS-Vibrations et Identification des Structures" research group to generate a low order nite element (F.E.) model of the GARTEUR SM-AG19 structure proposed as benchmark in the framework of the European COST Action F3 in structural dynamics. The model is made of beam elements, local inertia and rigid body elements. First, the correlation of the experimental data with the results of the F.E. model shows different levels of discrepancies. To perform local error detection, the size of the measured mode shape vectors is first expanded to the size of the F.E. eigenvectors. Model error localisation is based on the computation of residual strain energy due to errors in the constitutive equations. Updating parameters are then selected using eigenvalue sensitivity and local error analyses. The error localisation procedure is followed by the updating process in order to improve the accuracy of the FE models. The quality of the results is assessed in terms of accuracy of the response prediction to structural modifications. [less ▲]

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See detailFinite element modeling of an electrostatic painting device
Deliège, Geoffrey ULiege; Henrotte, François; Hameyer, Kay

in IEEE Transactions on Magnetics (2003), 39(3), 1432-1435

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See detailFinite Element Modeling of Electro-Mechanical Coupling in Capacitive Micro-Systems
Rochus, Véronique ULiege; Rixen, Daniel; Golinval, Jean-Claude ULiege

Conference given outside the academic context (2005)

In this paper advanced multi-physics simulations of micro-electro-mechanical systems (MEMS) are used to investigate their dynamic behaviour. The strong coupled electro-mechanical Finite Element (FE ... [more ▼]

In this paper advanced multi-physics simulations of micro-electro-mechanical systems (MEMS) are used to investigate their dynamic behaviour. The strong coupled electro-mechanical Finite Element (FE) formulation is used to model the electro-mechanical interactions and to perform modal and transient analysis taking into account large deformation e®ects. The application examples simulate two micro-resonators consisting in a clamped-clamped beam suspended over a substrate (the lower electrode). When a voltage is applied between the beam and the substrate, electrostatic forces appear which force the beam to bend. When the applied voltage is increased up to the pull-in limit, the electrostatic force becomes dominant and the plates stick together. The pull-in voltage is an essential design parameters in capacitive micro-systems. Here we also de¯ne a new design parameter describing the limit dynamic behaviour, namely the dynamic pull-in voltage. [less ▲]

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See detailFinite element modeling of electrostatic MEMS including the impact of fringing field effects on forces
Boutaayamou, Mohamed ULiege; V Sabariego, Ruth ULiege; Dular, Patrick ULiege

in Sensor Letters (2008), 6(1), 115-120

The numerical models describing the behaviour of electrostatically actuated microsystems often disregard fringing fields. However, taking fringing fields into account is crucial for an accurate ... [more ▼]

The numerical models describing the behaviour of electrostatically actuated microsystems often disregard fringing fields. However, taking fringing fields into account is crucial for an accurate computation of the electrostatic forces. In this work, the finite element method is applied for modeling electrostatic actuators. The electrostatic force distribution is obtained by locally applying the virtual work method. A micro-beam and a comb drive are considered as test cases. The impact of the fringing field effects on the accurate computation of electrostatic forces and capacitances is shown through 2D and 3D parametric studies. [less ▲]

Detailed reference viewed: 140 (48 ULiège)