Simplified numerical approach for incremental sheet metal forming process

The current work presents a finite element approach for numerical simulation of the incremental sheet metal forming (ISF) process, called here ‘‘ISF-SAM’’ (for ISF-Simplified Analysis Modelling). The main goal of the study is to develop a simplified FE model sufficiently accurate to simulate the ISF process and quite efficient in terms of CPU time. Some assumptions have been adopted regarding the constitutive strains/stresses equations and the tool/sheet contact conditions. A simplified contact procedure was proposed to predict nodes in contact with the tool and to estimate their imposed displacements. A Discrete Kirchhoff Triangle shell element called DKT12, taking into account membrane and bending effects, has been used to mesh the sheet. An elasto-plastic constitutive model with isotropic hardening behaviour and a static scheme have been adopted to solve the nonlinear equilibrium equations. Satisfactory results have been obtained on two applications and a good correlation has been shown compared to experimental and numerical results, and at the same time a reduction of CPU time more than 60% has been observed. The bending phenomenon studied through the second application and the obtained results show the reliability of the DKT12 element

A solver combining reduced basis and convergence acceleration with applications to non-linear elasticity

International audienceAn iterative solver is proposed to solve the family of linear equations arising from the numerical computation of non‐linear problems. This solver relies on two quantities coming from previous steps of the computations: the preconditioning matrix is a matrix that has been factorized at an earlier step and previously computed vectors yield a reduced basis. The principle is to define an increment in two sub‐steps. In the first sub‐step, only the projection of the unknown on a reduced subspace is incremented and the projection of the equation on the reduced subspace is satisfied exactly. In the second sub‐step, the full equation is solved approximately with the help of the preconditioner. Last, the convergence of the sequences is accelerated by a well‐known method, the modified minimal polynomial extrapolation. This algorithm assessed by classical benchmarks coming from shell buckling analysis. Finally, its insertion in path following techniques is discussed. This leads to non‐linear solvers with few matrix factorizations and few iterations

Modal Competition for Freight in Land Transportation on Jakarta-Surabaya corridor

As a part of a set of research studies about the railways transport in Indonesia, we propose this results advancement. Nowadays, the freight railways system in Indonesia suffers a complex and an apparently not easy to solve situation. The freight service is in constant degradation and it lost demand progressively, more the new highways development plans threat to increase the attractively of road transport in detriment of railways. The identifications of the structural problems will let us to propose aimed and precisely solutions to broke the current vicious circle of the freight railways system. Our analysis is supported by questionnaires applied to 93 forwarders/shippers in 186 opinions that usually contract freight transport services on the link. Each forwarder answered the same questions about his/her preferences for rail and for road freight services. We analyzed this data by the Logit model to identify the “factors of service” or variables which influence the decision of forwarders/shippers in the most important way. The results show clearly the relative importance of some railways “factors and service” in function with the others for the same mode, as well as their relative influence for the modal decision compared with the road freight transports. This paper aims to identify the structural problems of the freight railways service of “KERETA API” in the Java Island, especially between the cities of Jakarta and Surabaya which are the most important city in Indonesia. Key words: Indonesia railway development, modal competition, freight transportation, modal choic

A New Triangular Hybrid Displacement Function Element for Static and Free Vibration Analyses of Mindlin-Reissner Plate

A new 3-node triangular hybrid displacement function Mindlin- Reissner plate element is developed. Firstly, the modified variational functional of complementary energy for Mindlin-Reissner plate, which is eventually expressed by a so-called displacement function F, is proposed. Secondly, the locking-free formulae of Timoshenko’s beam theory are chosen as the deflection, rotation, and shear strain along each element boundary. Thirdly, seven fundamental analytical solutions of the displacement function F are selected as the trial functions for the assumed resultant fields, so that the assumed resultant fields satisfy all governing equations in advance. Finally, the element stiffness matrix of the new element, denoted by HDF-P3-7β, is derived from the modified principle of complementary energy. Together with the diagonal inertia matrix of the 3-node triangular isoparametric element, the proposed element is also successfully generalized to the free vibration problems. Numerical results show that the proposed element exhibits overall remarkable performance in all benchmark problems, especially in the free vibration analyses

Bisector and zero-macrospin co-rotational systems for shell elements

A principal issue in any co-rotational approach for large displacement analysis of plates and shells is associated with the specific choice of the local reference system in relation to the current deformed element configuration. Previous approaches utilised local co-rotational systems, which are invariant to nodal ordering, a characteristic that is deemed desirable on several fronts; however, the associated definitions of the local reference system suffered from a range of shortcomings, including undue complexity, dependence on the local element formulation and possibly an asymmetric tangent stiffness matrix. In this paper, new definitions of the local co-rotational system are proposed for quadrilateral and triangular shell elements, which achieve the invariance characteristic to the nodal ordering in a relatively simple manner and address the aforementioned shortcomings. The proposed definitions utilise only the nodal coordinates in the deformed configuration, where two alternative definitions, namely, bisector and zero-macrospin definitions, are presented for each of quadrilateral and triangular finite elements. In each case, the co-rotational transformations linking the local and global element entities are presented, highlighting the simplicity of the proposed approach. Several numerical examples are finally presented to demonstrate the effectiveness and relative accuracy of the alternative definitions proposed for the local co-rotational system

The DKMQ-SS Solid-Shell Element: Formulation Aspects and Applications

In this paper we present the formulation of a solid-shell element with 24 dof (the three cartesian components of displacement at the eight nodes of a solid hexahedron element), taking into account previous contributions to avoid shear, trapezoidal and thickness locking. But we also enhance the 3D displacement field by incomplete quadratic terms to improve the bending and transverse shear energies as was done for the performing DKMQ plate bending element proposed by Katili. After the formulation aspects, we present the results for some classical benchmark problems and for the linear analysis of a particular shallow foundation system called 'spider net system footing' used in Indonesia

Développement d'une Approche Simplifiée de la simulation numérique du formage incrémental

La simulation numérique du formage incrémental permet de prédire la formabilité et la qualité de la géométrie pour une trajectoire donnée. Avec les modèles classiques, le temps CPU de la simulation est très long. Le principe de l'Approche Simplifiée est d'éviter la description de l'outil et du contact en le remplaçant par une imposition locale et évolutive de déplacement à certains n uds. L'AS permet d'avoir une bonne estimation de la géométrie et de l'épaisseur de la pièce avec un temps de calcul réduit. Un travail sur l'adaptation d'un élément fini de type coques DKTRF est effectué

Electronic Structures of Quantum Dots and the Ultimate Resolution of Integers

The orbital angular momentum L as an integer can be ultimately factorized as a product of prime numbers. We show here a close relation between the resolution of L and the classification of quantum states of an N-electron 2-dimensional system. In this scheme, the states are in essence classified into different types according to the m(k)-accessibility, namely the ability to get access to symmetric geometric configurations. The m(k)-accessibility is an universal concept underlying all kinds of 2-dimensional systems with a center. Numerical calculations have been performed to reveal the electronic structures of the states of the dots with 9 and 19 electrons,respectively. This paper supports the Laughlin wave finction and the composite fermion model from the aspect of symmetry.Comment: Two figure

Computational Static Aeroelasticity Using Nonlinear Structures and Aerodynamics Models

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106442/1/AIAA2013-1862.pd

Intercity Mode Choice Modelling: Considering the Intracity Transport Systems with Application to the Jakarta-Bandung Corridor

The choice among modes of intercity transport depends on conditions of not only intercity transport modes but also intracity transport in both the departure city and the arrival city. Intracity transport conditions might be advantageous for one intercity mode and disadvantageous for others. Intercity and intracity transport conditions are complex and need to be approached systemically. This study proposes an approach based on the passengers’ preferences. The logit model was adapted to evaluate the transport modes’ choices in competition. This model is called the “Adapted Mixed Multinomial Logit Model” (AMML). It was applied on the Jakarta-Bandung corridor in both directions. It contributes to a complete approach for intercity transport mode choice by considering the influence of the intracity transport conditions in both the departure and arrival cities. The results proved that the choice of intercity transport mode depends not only on its own quality of service but also, importantly, on that of the intracity transport systems