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A probabilistic model for predicting the uncertainties of the humid stiction phenomenon on hard materials Hoang Truong, Vinh ; Wu, Ling ; et al in Journal of Computational & Applied Mathematics (2015), 289 Stiction is a major failure in microelectromechanical system (MEMS) devices in which two contacting surfaces can remain stuck together because of the adhesive forces. Due to the difference between the ... [more ▼] Stiction is a major failure in microelectromechanical system (MEMS) devices in which two contacting surfaces can remain stuck together because of the adhesive forces. Due to the difference between the surfaces roughness and the adhesive force range, the real contact areas are usually smaller than the apparent one, resulting in a scatter in the adhesive forces. Consequently, the stiction is an uncertain phenomenon. In this work, we develop a probabilistic model to predict the uncertainties of stiction due to the capillary forces acting on stiff materials. This model contains two levels: at the deterministic level, the model can predict the pull-out adhesive contact forces for a given surface topology; at the probabilistic level, the model generates independent identically distributed surfaces on which the deterministic solution can be applied to evaluate the uncertainties related to the stiction phenomenon. [less ▲] Detailed reference viewed: 214 (89 ULg)An Energy-Based Variational Model of Ferromagnetic Hysteresis for Finite Element Computations François-Lavet, Vincent ; ; Stainier, Laurent et al in Journal of Computational & Applied Mathematics (2013), 246 This paper proposes a macroscopic model for ferromagnetic hysteresis that is well-suited for finite element implementation. The model is readily vectorial and relies on a consistent thermodynamic ... [more ▼] This paper proposes a macroscopic model for ferromagnetic hysteresis that is well-suited for finite element implementation. The model is readily vectorial and relies on a consistent thermodynamic formulation. In particular, the stored magnetic energy and the dissipated energy are known at all times, and not solely after the completion of closed hysteresis loops as is usually the case. The obtained incremental formulation is variationally consistent, i.e., all internal variables follow from the minimization of a thermodynamic potential. [less ▲] Detailed reference viewed: 270 (48 ULg)Innovative modelling of 3D unsaturated flow in porous media by coupling independent models for vertical and lateral flows Paulus, Raphaël ; Dewals, Benjamin ; Erpicum, Sébastien et al in Journal of Computational & Applied Mathematics (2013), 246 Detailed reference viewed: 68 (32 ULg)Numerical simulation of finite strain viscoplastic problems ; ; et al in Journal of Computational & Applied Mathematics (2013), 246 A large strain elastoplastic constitutive model based on hyperelasticity and multiplicative decomposition of deformation gradient tensor is extended to viscous case, in a framework similar to the one that ... [more ▼] A large strain elastoplastic constitutive model based on hyperelasticity and multiplicative decomposition of deformation gradient tensor is extended to viscous case, in a framework similar to the one that has been proposed by Ponthot in an hypoelastic context. In this way a very useful framework can be obtained, able to deal with both rate dependent and rate independent problems. In this work a review of theoretical details and numerical implementation of the model are discussed. Similarly to what is done in rate independent plasticity, a Newton–Raphson scheme has been used to solve the non linear consistency condition in order to compute the viscoplastic multiplier. A plane strain plate with a central circular hole under tension is simulated in order to test the proposed model. Large deformation effects are considered in all the simulations carried out. Different parameters of the constitutive model are varied in order to study the sensitivity of the proposed algorithm. [less ▲] Detailed reference viewed: 20 (4 ULg)The Impact of Surface Higher Order Differentiability in Two-dimensional Contact Elements Nguyen, Duc Tue ; ; Ponthot, Jean-Philippe in Journal of Computational & Applied Mathematics (2013), 246 The aim of this work is to propose new contact elements of higher order of differentiability for analysing two-dimensional frictionless contact problems. Several methods were proposed in the literature to ... [more ▼] The aim of this work is to propose new contact elements of higher order of differentiability for analysing two-dimensional frictionless contact problems. Several methods were proposed in the literature to solve the problem caused by the lack of continuity resulting from the discretization. Among them are Bézier interpolation, Hermitian interpolation and splines. One of the difficulties in using Hermitian interpolation is to verify the partition of unity. Therefore, new elements that satisfy the C1 and C2 continuity at the interface are presented in this paper. These new contact elements are based on Hermitian polynomials for ensuring a higher order of continuity. The advantage is that this approach can be easily developed not only for linear elements but also for quadratic elements with higher order of differentiability. The performance of different surface representations is assessed through a comparison with a C0 surface discretization. Some numerical examples are used for assessing the accuracy and the convergence behaviour [less ▲] Detailed reference viewed: 38 (6 ULg)Comparison of supervised learning techniques for atmospheric pollutant monitoring in a Kraft pulp mill Sainlez, Matthieu ; Heyen, Georges in Journal of Computational & Applied Mathematics (2012) In this paper, supervised learning techniques are compared to predict nitro- gen oxide (NOx) pollutant emission from the recovery boiler of a Kraft pulp mill. Starting from a large database of raw process ... [more ▼] In this paper, supervised learning techniques are compared to predict nitro- gen oxide (NOx) pollutant emission from the recovery boiler of a Kraft pulp mill. Starting from a large database of raw process data related to a Kraft recovery boiler, we consider a regression problem in which we are trying to predict the value of a continuous variable. Generalization is done on the worst case configuration possible to make sure the model is adequate: the training period concerns stationary operations while test periods mainly fo- cus on NOx emissions during transient operations. This comparison involves neural network techniques (i.e., multilayer perceptron and NARX network), tree-based methods and multiple linear regression. We illustrate the potential of a dynamic neural approach compared to the others in this task. [less ▲] Detailed reference viewed: 32 (10 ULg)Simulation of two-fluid flows using a Finite Element/level set method. Application to bubbles and vesicle dynamics ; Guyot, Yann ; et al in Journal of Computational & Applied Mathematics (2012) Detailed reference viewed: 32 (6 ULg)An exact Riemann Solver and Godunov Scheme for Simulating Highly Transient Mixed Flows Kerger, François ; Archambeau, Pierre ; Erpicum, Sébastien et al in Journal of Computational & Applied Mathematics (2011), 235 Detailed reference viewed: 130 (25 ULg)Enhanced FEM-based Modeling of Brain Shift Deformation in Image-Guided Neurosurgery ; Boman, Romain ; Ponthot, Jean-Philippe et al in Journal of Computational & Applied Mathematics (2010), 234 We consider the problem of improving outcomes for neurosurgery patients by enhancing intraoperative navigation and guidance. Current navigation systems do not accurately account for intraoperative brain ... [more ▼] We consider the problem of improving outcomes for neurosurgery patients by enhancing intraoperative navigation and guidance. Current navigation systems do not accurately account for intraoperative brain deformation. We focus on the brain shift deformation that occurs just after the opening of the skull and dura. The heart of our system is a nonrigid registration technique using a biomechanical model. We specifically work on two axes: the representation of the structures in the biomechanical model and the evaluation of the surface landmark displacement fields between intraoperative MR images. Using the modified Hausdorff distance as an image similarity measure, we demonstrate that our approach significantly improves the alignment of the intraoperative images. ' 2009 Elsevier B.V. All rights reserved. [less ▲] Detailed reference viewed: 85 (26 ULg)Dam-break flow computation based on an efficient flux-vector splitting Erpicum, Sébastien ; Dewals, Benjamin ; Archambeau, Pierre et al in Journal of Computational & Applied Mathematics (2010), 234 Dam-break flow computation is a task of prime interest in the scope of risk analysis processes related to dams and reservoirs. In this paper, a 2D finite volume multiblock flow solver, able to deal with ... [more ▼] Dam-break flow computation is a task of prime interest in the scope of risk analysis processes related to dams and reservoirs. In this paper, a 2D finite volume multiblock flow solver, able to deal with natural topography variation, is presented in details. The model is based on an efficient Flux Vector Splitting method developed by the authors. A number of validation examples are comprehensively described. [less ▲] Detailed reference viewed: 174 (67 ULg)Proceedings of the Fourth International Conference on Advanced Computational Methods in Engineering (ACOMEN 2008) Hogge, Michel ; ; et al in Journal of Computational & Applied Mathematics (2010), 234(7), Detailed reference viewed: 77 (31 ULg)Influence of friction in material characterization in micro-indentation measurement Guo, Weichao ; ; et al in Journal of Computational & Applied Mathematics (2010), 234 A comprehensive computational study is undertaken to identify the influence of friction in material characterization by indentation measurement based on elasto- plastic solids. The impacts of friction on ... [more ▼] A comprehensive computational study is undertaken to identify the influence of friction in material characterization by indentation measurement based on elasto- plastic solids. The impacts of friction on load versus indentation depth curve, and the values of calculated hardness and Young's modulus in conical and spherical indentations are shown in this paper. The results clearly demonstrate that, for some elasto-plastic materials, the curves of load versus indentation depth obtained either by spherical or conical indenters with different friction coefficients, cannot be distinguished. However, if utilizing the parameter (see text for details), to quantify the deformation of piling-up or sinking-in, it is easy to find that the influence of friction on piling-up or sinking-in in indentation is significant. Therefore, the material parameters which are related to the projected area will also have a large error caused by the influence of friction. The maximum differences on hardness and Young's modulus can reach 14.59% and 6.78%, respectively, for some elastic materials shown in this paper. These results do not agree with those from researchers who stated that the instrumented indentation experiments are not significantly affected by friction. [less ▲] Detailed reference viewed: 80 (17 ULg)Comparison of adaptive filters for gas turbine performance monitoring Borguet, Sébastien ; Léonard, Olivier in Journal of Computational & Applied Mathematics (2010), 234(7), 2202-2212 Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm has proven its capability to track gradual deterioration with a good accuracy. On the other ... [more ▼] Kalman filters are widely used in the turbine engine community for health monitoring purpose. This algorithm has proven its capability to track gradual deterioration with a good accuracy. On the other hand, its response to rapid deterioration is either a long delay in recognizing the fault, and/or a spread of the estimated fault on several components. The main reason of this deficiency lies in the transition model of the parameters that assumes a smooth evolution of the engine condition. The aim of this contribution is to compare two adaptive diagnosis tools that combine a Kalman filter and a secondary system that monitors the residuals. This auxiliary component implements on one hand a covariance matching scheme and on the other hand a generalised likelihood ratio test to improve the behaviour of the diagnosis tool with respect to abrupt faults. [less ▲] Detailed reference viewed: 91 (9 ULg)An improved constitutive model for the numerical simulation of semi-solid thixoforming Koeune, Roxane ; Ponthot, Jean-Philippe in Journal of Computational & Applied Mathematics (2010), 234 In order to model thixoforming processes, previous papers presented a thermomechanical one-phase modelling. This first version of the constitutive model revealed several limitations: the model could not ... [more ▼] In order to model thixoforming processes, previous papers presented a thermomechanical one-phase modelling. This first version of the constitutive model revealed several limitations: the model could not degenerate properly to pure solid or liquid behavior nor to free solid suspensions. The aim of this paper was to propose solutions to overcome these limitations. [less ▲] Detailed reference viewed: 26 (13 ULg)Isotropic continuum damage/repair model for alveolar bone remodelling Mengoni, Marlène ; Ponthot, Jean-Philippe in Journal of Computational & Applied Mathematics (2010), 234 Several authors have proposed mechanical models to predict long term tooth movement, considering both the tooth and its surrounding bone tissue as isotropic linear elastic materials coupled to either an ... [more ▼] Several authors have proposed mechanical models to predict long term tooth movement, considering both the tooth and its surrounding bone tissue as isotropic linear elastic materials coupled to either an adaptative elasticity behavior or an update of the elasticity constants with density evolution. However, tooth movements obtained through orthodontic appliances result from a complex biochemical process of bone structure and density adaptation to its mechanical environment, called bone remodeling. This process is far from linear reversible elasticity. It leads to permanent deformations due to biochemical actions. The proposed biomechanical constitutive law, inspired from Doblaré and García (2002) [30], is based on a elasto-viscoplastic material coupled with Continuum isotropic Damage Mechanics (Doblaré and García (2002) [30] considered only the case of a linear elastic material coupled with damage). The considered damage variable is not actual damage of the tissue but a measure of bone density. The damage evolution law therefore implies a density evolution. It is here formulated as to be used explicitly for alveolar bone, whose remodeling cells are considered to be triggered by the pressure state applied to the bone matrix. A 2D model of a tooth submitted to a tipping movement, is presented. Results show a reliable qualitative prediction of bone density variation around a tooth submitted to orthodontic forces. [less ▲] Detailed reference viewed: 108 (22 ULg)Lattice Boltzmann 3D flow simulations on a metallic foam Beugre, Djomice Antoine ; Calvo, Sébastien ; Dethier, Gérard et al in Journal of Computational & Applied Mathematics (2009) Detailed reference viewed: 299 (32 ULg)A hybrid optimization technique coupling evolutionary and local search algorithms Kelner, Vincent ; Capitanescu, Florin ; Léonard, Olivier et al in Journal of Computational & Applied Mathematics (2008), 215(2), 448-456 Evolutionary Algorithms are robust and powerful global optimization techniques for solving large scale problems that have many local optima. However, they require high CPU times, and they are very poor in ... [more ▼] Evolutionary Algorithms are robust and powerful global optimization techniques for solving large scale problems that have many local optima. However, they require high CPU times, and they are very poor in terms of convergence performance. On the other hand, local search algorithms can converge in a few iterations but lack a global perspective. The combination of global and local search procedures should offer the advantages of both optimization methods while offsetting their disadvantages. This paper proposes a new hybrid optimization technique that merges a Genetic Algorithm with a local search strategy based on the Interior Point method. The efficiency of this hybrid approach is demonstrated by solving a constrained multi-objective mathematical test-case. [less ▲] Detailed reference viewed: 65 (20 ULg)Discrete finite element characterizations of source fields for volume and boundary constraints in electromagnetic problems ; ; Dular, Patrick et al in Journal of Computational & Applied Mathematics (2008), 215(2), 438-447 The consideration of electromagnetic field sources in potential formulations necessitates the definition of source fields. Such source fields are first defined for both volume and boundary constraints in ... [more ▼] The consideration of electromagnetic field sources in potential formulations necessitates the definition of source fields. Such source fields are first defined for both volume and boundary constraints in static electromagnetic models. Then, automatic procedures are proposed to conveniently and efficiently characterize discrete source fields, with regard to their use in finite element formulations, their supports, their direct expression requiring no pre-computation, and their associated constraints. Two application examples are proposed to illustrate the approach. [less ▲] Detailed reference viewed: 16 (0 ULg)A time-domain homogenization technique for lamination stacks in dual finite element formulations Dular, Patrick in Journal of Computational & Applied Mathematics (2008), 215(2), 390-399 A time-domain homogenization technique is developed to take the eddy currents in lamination stacks into account with dual 3-D magnetodynamic b- and h-conform finite element formulations. The lamination ... [more ▼] A time-domain homogenization technique is developed to take the eddy currents in lamination stacks into account with dual 3-D magnetodynamic b- and h-conform finite element formulations. The lamination stack is considered as a source region carrying predefined current density and magnetic flux density distributions describing the eddy currents and skin effect in each lamination. These distributions are related and are approximated with sub-basis functions. The stacked laminations are then converted into continuums with which terms are associated for considering the eddy current loops produced by parallel fluxes, through the homogenization of the sub-basis function contributions. [less ▲] Detailed reference viewed: 12 (2 ULg)Iterative solvers and stabilisation for mixed electrostatic and magnetostatic formulations Deliège, Geoffrey ; ; in Journal of Computational & Applied Mathematics (2008), 215(2), 348-356 Detailed reference viewed: 17 (4 ULg) |
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