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See detailCombined implicit/explicit time-integration algorithms for the numerical simulation of sheet metal forming
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in Journal of Computational & Applied Mathematics (2004), 168(1-2, Sp. Iss. SI), 331-339

In order to simulate stamping processes, an explicit method, which is conditionally stable, is generally thought to be the most adapted. Such an algorithm presents the advantage of being noniterative ... [more ▼]

In order to simulate stamping processes, an explicit method, which is conditionally stable, is generally thought to be the most adapted. Such an algorithm presents the advantage of being noniterative while, the contact configuration evolves rapidly, and the conditional stability is not a disadvantage since time steps must be small enough anyway for an accurate computation. But during the springback simulation, an implicit method, which is iterative, presents the advantage of unconditional stability. The optimal solution is then to have both implicit and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide to switch from a method to another, depending on the current dynamic, have been developed. Implicit restarting conditions are also proposed that annihilate numerical oscillations resulting from an explicit calculation. (C) 2003 Elsevier B.V. All rights reserved. [less ▲]

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See detailOn the use of large time steps with an energy momentum conserving algorithm for non-linear hypoelastic constitutive models
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal of Solids and Structures (2004), 41(3-4), 663693

This paper presents an extension of the energy momentum conserving algorithm, developed by the authors for hypoelastic constitutive models. For such a material, contrarily to hyperelastic models, no ... [more ▼]

This paper presents an extension of the energy momentum conserving algorithm, developed by the authors for hypoelastic constitutive models. For such a material, contrarily to hyperelastic models, no potential can be defined, and thus the conservation of the energy is ensured only if the elastic work of deformation can be restored by the scheme. In a previous paper, we proposed a new expression of internal forces at the finite element level which is shown to verify this property. We also demonstrated that the work of plastic deformation is positive and consistent with the material model. In this paper, the second order terms that were neglected in the previous work are now taken into account. Several numerical applications are presented to demonstrate the necessity of taking these terms into account once large time step sizes are used. The limitations of the Newmark algorithm in the non-linear range are also illustrated. (C) 2003 Elsevier Ltd. All rights reserved. [less ▲]

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See detailCombined implicit/explicit algorithms for crashworthiness analysis
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal of Impact Engineering (2004), 30(8-9, SEP-OCT), 1161-1177

In order to simulate an industrial process, an explicit method, which is conditionally stable, is the most adapted while the non-linearities evolve rapidly (impact phase, stamping process, etc.). But when ... [more ▼]

In order to simulate an industrial process, an explicit method, which is conditionally stable, is the most adapted while the non-linearities evolve rapidly (impact phase, stamping process, etc.). But when the dynamics becomes quasi-linear (post-impact analysis, springback simulation, etc.), an implicit method, which is iterative, presents the advantage of unconditional stability. The optimal solution is then to have both implicit and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide to switch from one method to another, depending on the current dynamics, have been developed. Implicit restarting conditions are also proposed that annihilate numerical oscillations resulting from an explicit calculation. (C) 2004 Elsevier Ltd. All rights reserved. [less ▲]

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See detailAn energy-momentum conserving algorithm for non-linear hypoelastic constitutive models
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal for Numerical Methods in Engineering (2004), 59(1), 83-114

This paper presents an extension of the energy momentum conserving algorithm, usually developed for hyperelastic constitutive models, to the hypoelastic constitutive models. For such a material no ... [more ▼]

This paper presents an extension of the energy momentum conserving algorithm, usually developed for hyperelastic constitutive models, to the hypoelastic constitutive models. For such a material no potential can be defined, and thus the conservation of the energy is ensured only if the elastic work of the deformation can be restored by the scheme. We propose a new expression of internal forces at the element level which is shown to verify this property. We also demonstrate that the work of plastic deformation is positive and consistent with the material model. Finally several numerical applications are presented. Copyright (C) 2003 John Wiley Sons, Ltd. [less ▲]

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See detailA Consistent Dissipative Time Integration Scheme for Structural Dynamics. Application to Rotordynamics.
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

(2004)

Recently, robust implicit energy and momentum conserving algorithms have been developed in the non-linear range. In previous works, the authors extended these algorithms to hypoelasticity-based ... [more ▼]

Recently, robust implicit energy and momentum conserving algorithms have been developed in the non-linear range. In previous works, the authors extended these algorithms to hypoelasticity-based constitutive models. In this paper we introduce numerical dissipation, opening the way to more complex simulations such as blade-loss in a turbofan. [less ▲]

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See detailModeling the elastic-plastic behavior of a rotor support structure under a large unbalance: numerical simulations
Stainier, Laurent ULg; BUI, Q. V.; Ponthot, Jean-Philippe ULg

in Proceedings of ISMA 2004, International Conference on Noise & Vibration Engineering (2004)

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See detailSimulation of complex impact problems with implicit time algorithms. Application to crashworthiness problems
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in Matériaux et Techniques (2004)

Recently, robust implicit energy and momentum conserving algorithms have been developed in the non-linear range. The authors extended these algorithms to hypoelasticity-based constitutive models and ... [more ▼]

Recently, robust implicit energy and momentum conserving algorithms have been developed in the non-linear range. The authors extended these algorithms to hypoelasticity-based constitutive models and introduced numerical dissipation, opening the way to more complex simulations such as blade-loss in a turbofan. [less ▲]

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See detailAdvances in the time integration of Dynamical Systems. Applications to Crashworthiness problems
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in Proceedings of the International Crashworthiness and Design Symposium 2003 (2003, December)

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See detailOptimization of sheet metal forming processes using inverse problems methodology
KLEINERMANN, J. P.; Ponthot, Jean-Philippe ULg; Stainier, Laurent ULg

in Proceedings of COMPLAS 2003, VII International Conference on Computational Plasticity. Fundamentals and Applications (2003, April)

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See detailCombined implicit/explicit time integration algorithms for crashworthiness analysis and metal forming simulation
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in Proceedings of IMPLAST'2003, 8th International Symposium on Plasticity and Impact Mechanics (2003, March)

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See detailA new formulation of internal forces for non-linear hypoelastic constitutive models verifying conservation laws
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg et al

in Bathe, K. J. (Ed.) Second MIT Conference on Fluid and Solid Mechanics (2003)

This paper proposes a new formulation of the internal forces for hypoelastic constitutive models ensuring that the elastic work of deformation can be restored by the scheme. Moreover, we demonstrate that ... [more ▼]

This paper proposes a new formulation of the internal forces for hypoelastic constitutive models ensuring that the elastic work of deformation can be restored by the scheme. Moreover, we demonstrate that the work of the plastic deformation is positive and consistent with the material model. [less ▲]

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See detailOptimization methods for parameter identification of constitutive models in finite viscoplasticity and damage
Stainier, Laurent ULg; KLEINERMANN, J.-P.; Ponthot, Jean-Philippe ULg

in Proceedings of PLASTICITY 2003 (2003)

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See detailUn nouveau schéma d'intégration conservatif pour des modèles constitutifs hypoélastiques irréversibles.
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in Potier-Ferry, M.; Bonnet, M.; Bignonnet, A. (Eds.) Actes du Sixième Colloque National en Calcul des Structures (2003)

Ce travail propose une nouvelle évaluation des forces internes pour les modèles constitutifs hypoélastiques irréversibles dans le cadre de la méthode des éléments-finis en grandes transformations. Nous ... [more ▼]

Ce travail propose une nouvelle évaluation des forces internes pour les modèles constitutifs hypoélastiques irréversibles dans le cadre de la méthode des éléments-finis en grandes transformations. Nous démontrons que cette expression des forces internes utilisée avec un schéma d'intégration du point milieu conduit à un algorithme d'intégration consistant avec les lois de la thermodynamique. [less ▲]

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See detailDétermination automatique de la taille du pas de temps pour les schémas implicites en dynamique non-linéaire
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg et al

in Mécanique & Industries (2002), 3(1), 63-77

Pour les problèmes caractérisés par de fortes non-linéarités, ainsi que des phénomènes d'impacts et de contacts, une stratégie d'intégration à pas de temps variables est particulièrement intéressante. Ces ... [more ▼]

Pour les problèmes caractérisés par de fortes non-linéarités, ainsi que des phénomènes d'impacts et de contacts, une stratégie d'intégration à pas de temps variables est particulièrement intéressante. Ces phénomènes sont par exemple rencontrés lors de l'étude dynamique d'une interaction aube-carter d'un moteur d'avion, le cas le plus critique étant la perte de l'aube. Une stratégie d'intégration implicite à pas de temps constant donne rarement satisfaction du fait qu'il est pratiquement impossible de déterminer une durée de pas qui ne conduise pas à la divergence ou à un coût de calcul prohibitif. Une gestion automatique du pas de temps, qui tient compte de l'histoire récente des accélérations dans le corps considéré, est proposée. En fait, l'algorithme est basé sur la mesure de l'erreur d'intégration des équations d'équilibre. Cela permet d'intégrer correctement les phénomènes transitoires avec un pas de temps très long (en régime) ou très petit (lors de la perte d'aube), en garantissant une bonne précision en un temps de calcul raisonnable. De plus, un algorithme qui décide automatiquement de recalculer ou non, la matrice hessienne est proposé. Cet algorithme permet d'éviter un nombre important de remises à jour de cette matrice, ce qui permet de réduire le coût de calcul tout en assurant la convergence. Enfin, un critère de divergence des itérations est proposé. Afin d'illustrer l'efficacité des algorithmes développés, des simulations numériques sont présentées. Il s'agit aussi bien de problèmes académiques que de problèmes industriels (contacts aubes carter). [less ▲]

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See detailCombined implicit-explicit algorithms for non-linear structural dynamics
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg et al

in Revue Européenne des Éléments Finis (2002), 11(5), 565-591

To solve fast dynamic problems, an explicit method is the most adapted. But for slower dynamics, an implicit method is more stable. The industrial problems are governed by high frequency (impact ... [more ▼]

To solve fast dynamic problems, an explicit method is the most adapted. But for slower dynamics, an implicit method is more stable. The industrial problems are governed by high frequency (impact, ...) during short time intervals and slower dynamics (spring-back, ...) during other time intervals. The optimal solution is then to have both implicit algorithm and explicit methods readily available in the same code and to be able to switch automatically from one to another. Criteria that decide when to shift from a method to another have been developed here. Implicit balanced restarting conditions that annihilate numerical oscillations resulting for an explicit calculation are also proposed. [less ▲]

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See detailSelf-adapting time integration management in crash-worthiness and sheet metal forming computations
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg

in International Journal of Vehicle Design (2002), 30(1-2), 67-114

Variable step strategies are especially well suited to deal with problems characterized by high non-linearity and contact/impact, and resolved with an implicit scheme. Both phenomena are typical of ... [more ▼]

Variable step strategies are especially well suited to deal with problems characterized by high non-linearity and contact/impact, and resolved with an implicit scheme. Both phenomena are typical of dynamic simulations of contact-impact problems, as well as sheet metal forming. Constant step size strategies do not give a satisfactory answer for this kind of problem, since it is very difficult, if not impossible, for the user to find an appropriate time step that does not lead to divergence nor generate extremely costly computations. An automatic time stepping algorithm is proposed, which takes into account the recent history of accelerations in the deformable bodies under consideration. More precisely, the adaptation algorithm is based on estimators of the integration error of the differential dynamic balance equations. This allows for adaptation of the step size to capture correctly the transient phenomena, with characteristic times which can range from relatively long (after contact, or during sheet metal forming) to very short (during contact-impact). thus ensuring precision while keeping the computation cost to a minimum. Furthermore, we will see that this strategy can be used in explicit schemes. Additionally, the proposed algorithm automatically takes decisions regarding the necessity of updating the tangent matrix or stopping the iterations, further reducing the computational costs especially, when the Augmented Lagrangian method is used. As an illustration of the capabilities of this algorithm, several numerical simulations (shock absorber devices for vehicle crash-worthiness or sheet metal forming) problems will be presented. Other simulations pertaining to the sheet metal forming for vehicle structures will also be investigated, thus demonstrating the versatility, the capabilities and the efficiency of the proposed strategy. [less ▲]

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See detailAutomatic time stepping algorithms for implicit numerical simulations of non-linear dynamics
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg et al

in Advances in Engineering Software (2002), 33(7-10, JUL-OCT), 589-603

When an implicit integration scheme is used, variable step strategies are especially well suited to deal with problems characterized by high non-linearities. Constant step size strategies generally lead ... [more ▼]

When an implicit integration scheme is used, variable step strategies are especially well suited to deal with problems characterized by high non-linearities. Constant step size strategies generally lead to divergence or extremely costly computations. An automatic time stepping algorithm is proposed that is based on estimators of the integration error of the differential dynamic balance equations. Additionally, the proposed algorithm automatically takes decisions regarding the necessity of updating the tangent matrix or stopping the iterations, further reducing the computational cost. As an illustration of the capabilities of this algorithm, several numerical simulations of both academic and industrial problems are presented. (C) 2002 Civil-Comp Ltd and Elsevier Science Ltd. All rights reserved. [less ▲]

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See detailImplicit-explicit time integration algorithms for the numerical simulation of blade-casing interactions
Noels, Ludovic ULg; Stainier, Laurent ULg; Ponthot, Jean-Philippe ULg et al

in Rajendran, A. M.; Jones, B. N.; Brebbia, C. A. (Eds.) Structures under Shock and Impact VII (2002)

In order to solve fast dynamic problems, an explicit method is the most adapted. But for slower dynamics, an implicit method is more stable. Typical industrial problems are governed by high frequency, e.g ... [more ▼]

In order to solve fast dynamic problems, an explicit method is the most adapted. But for slower dynamics, an implicit method is more stable. Typical industrial problems are governed by high frequency, e.g. impact, during short time intervals and slower dynamics, e.g. spring-back, during other time intervals. The optimal solution is then to have both implicit algorithm and explicit methods readily available in the same code and to be able to switch automatically from one to the other. Criteria that decide when to shift from a method to another have been developed here. Implicit balanced restarting conditions that annihilate numerical oscillations resulting for an explicit calculation are also proposed. [less ▲]

Detailed reference viewed: 77 (4 ULg)