Papers by Keyword: Remeshing

Abstract: In computational fluid dynamics (CFD), the physical domain is usually discretized by using mesh/grid, cells, nodes or particles generation. Although there are many advantages, these methods are required to have high computational storage/time cost, especially for solving the complex, deforming, and moving flows/bodies. Hence, we developed the vortex-in-cell (VIC) algorithm which is hybrid combination of grid-based and mesh-free method. VIC method, which was originally developed to simulate incompressible single-phase flows, becomes a very promising alternative for simulating complex flows. In addition, to simulate flows over deforming geometries, we utilized an immersed boundary method for enforcing the boundary condition. VIC interpolates the particle strength to an underlying mesh. VIC method has the advantage that the Poisson inversion can be accomplished by Fast Fourier Transform (FFT) techniques, this accelerates the computational time and provides accurate results. Here we consider an anguilliform swimming motion based on lateral displacement of the “backbone” which describes a complex, deforming, and moving body. “Flow over an Impulsively Started Circular Cylinder” problem are also simulated to validate the developed numerical method.

Abstract: Recently, new sheet metal forming technique, incremental forming has been introduced. It is based on using a single spherical tool, which is moved along CNC controlled tool path. During the incremental forming process, the sheet blank is fixed in sheet holder. The tool follows a certain tool path and progressively deforms the sheet. Nowadays, numerical simulations of metal forming are widely used by industry to predict the geometry of the part, stresses and strain during the forming process. Because incremental forming is a dieless process, it is perfectly suited for prototyping and small volume production [1, 2]. On the other hand, this process is very slow and therefore it can only be used when a slow series production is required. As the sheet incremental forming process is an emerging process which has a high industrial interest, scientific efforts are required in order to optimize the process and to increase the knowledge of this process through experimental studies and the development of accurate simulation models. In this paper, a comparison between numerical simulation and experimental results is realized in order to assess the suitability of the numerical model. The experimental investigation is realized using a three-axis CNC milling machine. The forming tool consists in a cylindrical rotating punch with a hemispherical head. A subroutine has been developed to describe the tool path from CAM procedure. A numerical model has been developed to simulate the sheet incremental forming process. The finite element code Abaqus explicit has been used. The simulation of the incremental forming process stays a complex task and the computation time is often prohibitive for many reasons. During this simulation, the blank is deformed by a sequence of small increments that requires many numerical increments to be performed. Moreover, the size of the tool diameter is generally very small compared to the size of the metal sheet and thus the contact zone between the tool and the sheet is limited. As the tool deforms almost every part of the sheet, small elements are required everywhere in the sheet resulting in a very high computation time. In this paper, an adaptive remeshing method has been used to simulate the incremental forming process. This strategy, based on adaptive refinement and coarsening procedures avoids having an initially fine mesh, resulting in an enormous computing time. Experiments have been carried out using aluminum alloy sheets. The final geometrical shape and the thickness profile have been measured and compared with the numerical results. These measurements have allowed validating the proposed numerical model. References [1] M. Yamashita, M. Grotoh, S.-Y. Atsumi, Numerical simulation of incremental forming of sheet metal, J. Processing Technology, No. 199 (2008), p. 163 172. [2] C. Henrard, A.M. Hbraken, A. Szekeres, J.R. Duflou, S. He, P. Van Houtte, Comparison of FEM Simulations for the Incremental Forming Process, Advanced Materials Research, 6-8 (2005), p. 533-542.

Abstract: A numerical model for a multiphysics problem is presented. It includes the movement of subdomains, which are embedded in a global air domain. The description of the movement is based on a discrete level set representation of the moving boundaries. It is based on the original geometry of the moving tools, such that the mesh quality is not reduced in subsequent time steps.

Abstract: As a material removal process, metal milling process involves large geometry deformation, material thermo-visco-plastic flow coupled with damage and complex contact-friction problems. During simulation of metal milling, the finite elements distort severely at the local regions with high gradient of physical field such as stress, strain and temperature due to these problems. This paper presents numerical adaptive remeshing procedure dedicated to metal milling process. The procedure integrates Explicit solver of ABAQUS, OPTIFORM mesher and python script program transfer to execute step by step the incremental milling process. At each step, the meshes are refined and coarsened automatically based on geometrical and physical error estimations; the physical fields are transferred (point to point) from old to the new one using advanced algorithm. Johnson-cook material model is used to simulate the material plastic flow with ductile damage. Some numerical results are given to demonstrate the efficiency of the proposed procedure.

Abstract: Simulations of Single Point Incremental Forming generally require a very high computation time because the tool path is long and small elements are required everywhere on the sheet. In this paper, a remeshing method based on refinement and coarsening strategies is used with abaqus/explicit to reduce the computational time. The simulation of a semi-spherical cup with a fine mesh is considered as a reference simulation. The remeshing method allows reducing the number of elements and therefore the CPU time during the simulations. A good prediction is observed with the remeshing method.

Abstract: An important part of the numerical simulation is the grid which the quality has great influence on the calculation precision, and also the influence often is crucial factor in most of situation. Water-entry at high speed is a complex unsteady process, and its numerical simulation needs to take consider of natural cavitation as well as rotation of the underwater body. In this paper, a new meshing method was given with using the Layering, Smoothing and Remeshing for calculating the unsteady flow field. Numerical simulation shows that the mesh given in this paper has better quality, and can be used to calculate the multi-phase mode of water-entry at the high speed.

Abstract: In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming considering coupled constitutive equations formulated in the framework of irreversible processes accounting for isotropic hardening as well as isotropic ductile damage. The experimental study is dedicated to the identification of stress-strain flow from the global measure of pole displacement, thickness evolution and internal pressure expansion. Indeed, Hill48 yield surface anisotropy parameters and coefficients of the Swift law coupled to ductile damage allowing to locate plastic instability zones of hydroformed sheets are identified with three dies cavities shapes. Or during the hydroforming processes severe mesh distortion of element occur after a few incremental steps. Hence an automatic mesh generation with remeshing capabilities is essential to carry out the FEA. The proposed technique based on geometrical criteria includes adaptive refinement and coarsening procedure is integrated in a computational environment.

Abstract: In this study, we present an experimental/numerical methodology which aims to improve 3D thin sheet hydroforming considering coupled constitutive equations formulated in the framework of of irreversible processes accounting for isotropic hardening as well as isotropic ductile damage. The experimental study is dedicated to the identification of stress-strain flow from the global measure of pole displacement, thickness evolution and internal pressure expansion. Or during the hydroforming processes severe mesh distortion of element occur after a few incremental steps. Hence an automatic mesh generation with remeshing capabilities is essential to carry out the FEA. The proposed technique based on geometrical criteria includes adaptive refinement and coarsening procedure is integrated in a computational environment.

Abstract: As soon as it is question of modelling the follow-up of a geometry during an operation of forming process, the difficulties of meshing and remeshing are often emphases. If the part is situated between rigid tools (case of the deep drawing), in the problems of remeshing are also added difficulties on the management of the contact between the parts. In this case, the deformations are caused by the contact with the tools whose geometry are fixed. The piece must take the shape of the tool geometries during the deformation. In this paper, we present a method coupling an adaptive remeshing strategy and a technique of projection on the tool. The remeshing is based on refinement and coarsening procedures. The projection of the new nodes on the tool allows keeping the contact between the part and the tools. Numerical examples show the efficiency of the method.

Abstract: In the procedure of cutting, its corner radius influences cutting forces, chip breaking, chip shaping, and the distribution status of residual stress. The author adopts the Finite Element Method (FEM) in this paper, and establishes the reasonable two-dimension milling model based on the orthogonal cutting process, which is used the adaptive meshing criteria. And, a typical work-piece chip breaking process with different cutting tools corner radius, which gets the cutting forces curves and the total status of residual stress distribution and the status is simulated in this paper.