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Automatic time stepping algorithms for implicit numerical simulations of blade/casing interactions Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe et al in International Journal of Crashworthiness (2001), 6(3), 351-362 An automatic time stepping algorithm for non-linear problems, solved by implicit schemes, is presented. The time step computation is based on the estimation of an integration error calculated from the ... [more ▼] An automatic time stepping algorithm for non-linear problems, solved by implicit schemes, is presented. The time step computation is based on the estimation of an integration error calculated from the acceleration difference. It is normalised according to the size of the problem and the integration parameters. This time step control algorithm modifies the time step size only if the problem has a long time physical change. Additionally, the Hessian matrix can be kept constant for several iterations, even though the problem is non-linear. A criterion selecting if the Hessian matrix must be calculated or not is developed. Finally, a criterion of iterations divergence is also proposed. It avoids the determination, by the user, of a maximal iteration number. This minimises the total number of iterations, and thus the computation cost. Industrial numerical examples are presented that demonstrate the performances (precision and computational cost) of the algorithms. [less ▲] Detailed reference viewed: 56 (5 ULg)Augmented Lagrangian procedure for implicit computation of contact-impact between deformable bodies. ; Ponthot, Jean-Philippe ; Stainier, Laurent in International Journal of Crashworthiness (2001), 6(2), 209-221 This paper shows how efficiency can be improved by using an adequate Augmented Lagrangian procedure instead of the classical and well-known Penalty method for solving contact-impact problems between ... [more ▼] This paper shows how efficiency can be improved by using an adequate Augmented Lagrangian procedure instead of the classical and well-known Penalty method for solving contact-impact problems between deformable bodies, including frictional contact, large deformations, dynamical effects and inelasticity phenomena The Augmented Lagrangian method has already enjoyed great success in solving constrained minimisation problems or incompressibility conditions. Alternatives to existing automation techniques for augmentations are presented. Starting from a Penalty method, it will be seen how the Augmented Lagrangian decreases ill-conditioning of governing equations and gives a more precise solution with a lower CPU-cost. Several original simultaneous criteria are proposed for optimising the number and the location of the augmentations in an incremental implicit resolution. Application of the method is done for two axisymmetric impact problems. [less ▲] Detailed reference viewed: 52 (3 ULg)Self-adapting time integration strategies for non-linear structural dynamics Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe (2001) Adaptive strategies are specially well suited to deal with problems characterized by high non-linearity and contact/impact. Constant step size strategies do not give a satisfactory answer for this kind of ... [more ▼] Adaptive strategies are specially well suited to deal with problems characterized by high non-linearity and contact/impact. Constant step size strategies do not give a satisfactory answer for this kind of problems, 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 adaption 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 (in regime) to very short (impact), thus ensuring precision while keeping the computation cost to a minimum. This algorithm is applicable both to implicit and explicit time integration schemes. Additionally, in the case of implicit schemes, the proposed algorithm automatically takes decisions regarding the necessity of updating the tangent matrix or stopping the iterations, further reducing the computational cost. This is specially true when the selective updating scheme is combined with the augmented Lagrangian procedure for the treatment of contact. As an illustration, numerical simulations of the buckling of an automobile stringer under crash impact are presented, demonstrating the versatility, the capabilities and the efficiency of the proposed strategy. [less ▲] Detailed reference viewed: 40 (8 ULg)Metal Forming Processes Optimization Using Inverse Problems ; Stainier, Laurent ; Ponthot, Jean-Philippe in Proceedings of the Fifth National Belgian Congress on Theoretical and Applied Mechanics (2000) Detailed reference viewed: 5 (1 ULg)STAINIER ; Ponthot, Jean-Philippe ; Stainier, Laurent in Proceedings of IJCRASH 2000 (2000) Detailed reference viewed: 11 (2 ULg)Damage Model Identification Using Inverse Problem Methodology ; Ponthot, Jean-Philippe ; Stainier, Laurent in proceedings of Plasticity’2000 (2000) Detailed reference viewed: 32 (2 ULg)Efficient implicit schemes for the treatment of the contact between deformable bodies. Application to shock absorber devices ; Stainier, Laurent ; Ponthot, Jean-Philippe in Proceedings of the Fifth National Belgian Congress on Theoretical and Applied Mechanics (2000) Detailed reference viewed: 25 (8 ULg)Automatic time step size determination and automatic Hessian matrix actualisation selection for non-linear dynamic problems solved by implicit schemes Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe (2000) An automatic time step size determination for non-linear problems, solved by implicit schemes, is presented. The time step calculation is based on the estimation of the integration error. This estimation ... [more ▼] An automatic time step size determination for non-linear problems, solved by implicit schemes, is presented. The time step calculation is based on the estimation of the integration error. This estimation is calculated from the acceleration difference. It is normalised according to the size of the problem and the integration parameters. This time step control algorithm modifies the time step size only if the problem has a long time physical change. On the other hand, Hessian matrix can be kept constant for several iterations however the problem is non-linear. According to the fact that the time step size is constant for some time step, the Hessian matrix shouldn’t be recalculated for each time step. A criterion selecting if Hessian matrix must be calculated or not is developed. Finally, a criterion of iterations divergence is also proposed. It avoids the determination, by the user, of a maximal iterations number. The iterations number is the smaller. Industrial numerical examples are presented that demonstrated the performances (precision and computational cost) of the algorithms. [less ▲] Detailed reference viewed: 79 (7 ULg)Automatic time stepping algorithms for implicit numerical simulations of non-linear dynamics Noels, Ludovic ; Stainier, Laurent ; Ponthot, Jean-Philippe et al in Topping, B. H. V.; Motas Soares, C. A. (Eds.) FINITE ELEMENTS: TECHNIQUES AND DEVELOPMENTS (2000) Variable step strategies are specially well suited to deal with problems characterized by high non-linearity and contact/impact. Both phenomena are typical of dynamic simulations of the interactions ... [more ▼] Variable step strategies are specially well suited to deal with problems characterized by high non-linearity and contact/impact. Both phenomena are typical of dynamic simulations of the interactions between a turbine blade and its casing, the most dramatic example being blade loss. Constant step size strategies do not give satisfactory answer for this kind of problems, 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 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 time step to capture correctly the transient phenomena, with characteristic times which can range from relatively long (in regime) to very short (blade loss), thus ensuring precision while keeping the computation cost to a minimum. 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 (the contact/impact between a turbine blade and the casing) problems will be presented. [less ▲] Detailed reference viewed: 47 (5 ULg)Metal Forming Processes Optimization Using Inverse Problems ; Stainier, Laurent ; Ponthot, Jean-Philippe in Proceedings of ECCOMAS 2000/COMPLAS VI, European Congress on Computational Methods in Applied Sciences and Engineering (2000) Detailed reference viewed: 15 (1 ULg)Parameter Identification Using Inverse Problems Methodology in Metal Forming Simulation ; Stainier, Laurent ; Ponthot, Jean-Philippe in Proc. of the Second International Conference on Engineering Computational Technology “Finite Element Techniques and development (2000) Detailed reference viewed: 34 (1 ULg)AN IMPROVED ONE-POINT INTEGRATION METHOD FOR LARGE-STRAIN ELASTOPLASTIC ANALYSIS Stainier, Laurent ; Ponthot, Jean-Philippe in Computer Methods in Applied Mechanics & Engineering (1994), 118(1-2), 163-177 In this paper, we present a new one-point integration method generalizing Flanagan and Belytschko's method (Internat. J. Numer. Methods Engrg. 17 (1981) 679-706) and a modification of Belytschko and ... [more ▼] In this paper, we present a new one-point integration method generalizing Flanagan and Belytschko's method (Internat. J. Numer. Methods Engrg. 17 (1981) 679-706) and a modification of Belytschko and Bindeman's method (Comput. Methods Appl. Mech. Engrg. 88 (1991) 311-340), both in the frame of large deformation elastoplastic analysis. These stabilization methods are combined with the radial return method used to integrate the constitutive law. Plane strain problems are first considered, and the method is then generalized to axisymmetrical situations. The explicit time integration scheme with its critical timestep is also considered. A few examples are presented that show the great time savings that can be obtained with reduced integration without any loss of accuracy, and even with a gain in the solution quality, since the underintegrated elements prove to be 'flexurally superconvergent'. [less ▲] Detailed reference viewed: 41 (12 ULg)Apports d'une formulation eulérienne-lagrangienne pour la simulation des opérations de mise en forme des matériaux Hogge, Michel ; Ponthot, Jean-Philippe ; et al in Actes du Congrès STRUCOME'92 (1992) Detailed reference viewed: 26 (1 ULg) |
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