• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1637-1641
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• 2007

In this paper, we simulate a rotor pole cold forging process by a forging simulator with both tetrahedral and hexahedral element capabilities and compare the predictions obtained by the two approaches with the experiments. Hexahedral element capability runs manually while tetrahedral element capability runs automatically with help of an intelligent remeshing technique. It is shown that the tetrahedral element capability can give quite accurate solution if assisted by the intelligent remeshing technique even though the tetrahedral element itself is not theoretically and numerically clear.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2002.05a
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• pp.150-153
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• 2002

The use of the finite element method for biomechanical analysis is increasing rapidly in recent years. Since biomechanical models are usually in very complex shapes, it takes a lot of time and efforts to build reasonable finite element models. In this paper, a new tetrahedral meshing algorithm from the series of 2-D computed tomography(CT) images has been proposed. In this scheme, the planar sections of three-dimensional objects and the side surfaces between two planar sections are triangulated first, and then an advancing front algorithm is employed to construct tetrahedral elements by using basic operators. A sample finite element model for thoracic vertebra is presented.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3159-3174
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• 1994

A simple octree encoding algorithm based on a tetrahedron root has been developed to be used for fully automatic generation of three dimensional finite element meshes. This algorithm starts octree decomposition from a tetrahedron root node instead of a hexahedron root node so that the terminal mode has the same topology as the final tetrahedral mesh. As a result, the terminal octant can be used as a tetrahedral finite element without transforming its topology. In this part(I) of the thesis, an efficient algorithm for the tetrahedron-based octree is proposed. For this development, the following problems have been solved, : (1) an efficient data structure for storing the octree and finite elements, (2) an encoding scheme of a tetrahedral octree, (3) a neighbor finding technique for the tetrahedron-based octree.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.865-870
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• 2004

This paper describes the generation of chordal surface for various shell structures, such as automobile bodies, plastic injection mold components and shell metal parts. After one-layered tetrahedral mesh is generated by an advancing front algorithm, the chordal surface is generated by cutting a tetrahedral element. It is generated one or two elements at a tetrahedral element and the chordal surface is composed with triangular or quadrilateral elements. This algorithm has been tested on several models with rib structure.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.06a
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• pp.607-610
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• 2005

A remeshing algorithm using tetrahedral elements has been developed, which is adapted to the mesh density map constructed by a posteriori error estimation. In the finite element analyses of metal forging processes, numerical error increases as deformation proceeds due to severe distortion of elements. In order to reduce the numerical error, the desired mesh sizes in each region of the workpiece are calculated by a posteriori error estimation and the density map is constructed. Piecewise density functions are then constructed with the radial basis function in order to interpolate the discrete data of the density map. The sample mesh is constructed based on the point insertion technique which is adapted to the density function and the mesh size is controlled by moving and deleting nodes to obtain optimal distribution according to the mesh density function and the quality optimization function as well. After finishing the redistribution process of nodes, a tetrahedral mesh is constructed with the redistributed nodes, which is adapted to the density map and resulting in good mesh quality. A goodness and adaptability of the constructed mesh is verified with a testing measure. The proposed remeshing technique is applied to the finite element analyses of forging processes.

• Korean Journal of Computational Design and Engineering
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• v.9 no.1
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• pp.27-34
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• 2004

A tetrahedral mesh generation scheme using 3-D operators has been presented. The proposed scheme employs new 3-D operators such as rearranging and modified finishing operators in addition to the previous trimming, wedging, digging, splitting and finishing operators. These new operators have been introduced in order to increase the stability of mesh generation process. Check processings with surrounded element edges and faces have also been optimized by employing a searching algorithm. Sample meshes are constructed to demonstrate the mesh generating capability of the proposed algorithm.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.24 no.9 s.180
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• pp.2397-2405
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• 2000

The remeshing is a method to replace a distorted mesh by a new mesh without interrupting the finite element calculation. The remeshing procedure in this paper refers to the rezoning, for which a sm oothing process is developed to alleviate the distortions of mesh. In the paper, an automatic finite element rezoning system with tetrahedral elements for large deformation analysis has been developed. Our smoothing process is composed of two steps, a surface smoothing and a volume smoothing. In the surface smoothing, checking the dihedral angle and projection on surface patch reduced the change of shape and nodes penetrating die. The constrained Laplacian smoothing has been employed for the volume smoothing process. The state variables are mapped from old mesh to new mesh by using volume coordinates within a tetrahedral element. All these procedures have been linked to the NIKE3D program As illustrated in the examples the overall strategy ensures a robust and efficient rezoning scheme for finite element simulation of metal-forming processes.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1475-1482
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• 2004

In this paper, the rigid-viscoplastic finite element solutions obtained by MINI-elements based triangular elements and tetrahedral elements are compared with those obtained from numerically well-behaved rectangular and hexahedral elements. The theoretical background of the MINI-elements is introduced in detail and the rigid-viscoplastic finite element formulation is also given. Discussion on the results of the MINI-elements is made with emphasis on the effect of a stabilizer simplifying velocity-bubble coupled terms.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.10
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• pp.1517-1525
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• 2004

Shell finite elements are widely used for the analysis of thin section objects such as sheet metal parts, automobile bodies and et al. due to their computational efficiency. Since many of input data for finite element analysis are given as solid models or triangulated surface models, one should extract midsurface information from these input data initially and then construct shell meshes on the extracted midsurfaces. In this paper, a method of generating shell elements on midsurfaces directly from input models has been proposed, in which midsurface generating process can be omitted. In order to construct shell meshes, the input models should be triangulated on surfaces first, and then tetrahedral elements are generated by using an advancing front method, and finally mid shell surfaces are obtained from tetrahedral meshes. Some examples are given to demonstrate the efficiency of the proposed method.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.05a
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• pp.209-214
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• 2005

In this paper, finite element simulation of three-dimensional bulk metal forming processes is performed by an automated adaptive tetrahedral mesh generation scheme. A dynamic data exchange scheme is employed between tetrahedral mesh generator and forging simulator to minimize user intervention. Both number of elements and density distributions are controlled by the octree technique. The presented approach is applied to automatic forging simulation in order to evaluate the efficiency of the developed schemes and the simulation results are compared with $DEFORM^{TM}$.