• Korean Journal of Computational Design and Engineering
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• v.12 no.4
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• pp.255-262
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• 2007

In the finite element analysis of forming process, objects are described with a finite number of elements and nodes and the approximated solutions can be obtained by the variational principle. One of the shortcomings of a finite element analysis is that the structure of mesh has become inefficient and unusable because discretization error increases as deformation proceeds due to severe distortion of elements. If the state of current mesh satisfies a certain remeshing criterion, analysis is stopped instantly and resumed with a reconstructed mesh. In the study, a new remeshing algorithm using tetrahedral elements has been developed, which is adapted to the desired mesh density. In order to reduce the discretization error, desired mesh sizes in each lesion of the workpiece are calculated using the Zinkiewicz and Zhu's a-posteriori error estimation scheme. The pre-constructed mesh is constructed based on the modified point insertion technique which is adapted to the density function. The object domain is divided into uniformly-sized sub-domains and the numbers of nodes in each sub-domain are redistributed, respectively. After finishing the redistribution process of nodes, a tetrahedral mesh is reconstructed 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.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.71-76
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• 2004

An extension of our recently developed locally linear reconstruction scheme to 2 dimensional incompressible flow solver is presented. The solver is based on a semi-implicit fractional step method in which the convective term is discretized by Adams-Bashforth method and the diffusion term by Crank-Nicolson method. Several numerical examples are tested to demonstrate the mesh type independent accuracy of the solver, which include decaying vortex flow, square cavity flow, and flow around a circular cylinder. The above examples are solved on quadrilateral or hybrid meshes. For all numerical examples, we obtained reasonable results.

• Nuclear Engineering and Technology
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• v.20 no.3
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• pp.145-154
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• 1988

This paper is a study on an accurate and computationally efficient method for reconstructing pointwise power distributions from coarse-mesh nodal calculations. The modern nodal codes can calculate global reactor power shapes and criticality very efficiently and accurately. But inherent in the nodal procedures, there is inevitable loss of information on local heterogeneous quantities. In this study, an improved form function method which reflects the exponential transition of the thermal flux near the assembly surface is developed for the reconstruction of the heterogeneous fluxes. Use of the new form function method in several pressurized water reactor (PWR) benchmark problems reduces the maximum errors in the reconstructed thermal flux to those in the reconstructed fast flux. Even for assemblies adjacent to the steel baffle in realistic PWR cores, use of this method also results in improved pointwise power reconstruction.

• Archives of Craniofacial Surgery
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• v.18 no.2
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• pp.117-121
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• 2017

Typical transcranial approaches are insufficient for adequate visualization and resection of skull base tumors. Different approaches with multiple modifications have been attempted. Here, we describe a new approach for a lesion that is central and hard to treat by conventional craniotomy and successful reconstruction with calvarial bone graft and titanium mesh plate. A 69-year-old female patient presented with recurrent meningioma. The tumor had invaded the frontal lobe, right supraorbital rim, and ethmoidal bone. We performed a modified anterior craniofacial approach that fully exposed the tumor and invaded bone. In consideration of the patient's age and cosmetic result, the tumor and invaded bone was resected and the defect area was reconstructed with titanium mesh and calvarial bone graft. At 6 months postoperative the patient had no complications and was satisfied with the esthetic result. We report this case to demonstrate the successful approach and reconstruction using this technique.

• Journal of Institute of Control, Robotics and Systems
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• v.9 no.1
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• pp.50-56
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• 2003

In electrical impedance tomography(EIT), various image reconstruction algorithms have been used in order to compute the internal resistivity distribution of the unknown object with its electric potential data at the boundary. Mathematically the EIT image reconstruction algorithm is a nonlinear ill-posed inverse problem. This paper presents a new combined method based on genetic algorithm(GA) and modified Newton-Raphson(mNR) algorithm via two-step approach for the solution of the static EIT inverse problem. In the first step, each mesh is classified into three mesh groups: target, background, and temporary groups. The mNR algorithm can be used to determine the region of group. In the second step, the values of these resistivities are determined using genetic algorithm. Computer simulations with the 32 channels synthetic data show that the spatial resolution of reconstructed images by the proposed scheme is improved compared to that of the mNR algorithm at the expense of increased computational burden.

• Archives of Reconstructive Microsurgery
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• v.9 no.2
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• pp.127-133
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• 2000

Free TRAM flap is now increasingly suggested to patients requiring breast reconstruction after the mastectomy. This study is to introduce the experiences of bilateral free TRAM flaps for reconstruction of bilateral breasts and to suggest the way of getting the more satisfactory results. A total of 6 breasts were reconstructed in 3 patients using bilateral free TRAM flaps immediately following the mastectomy. Average operative time for bilateral breast reconstruction was 8 hours comparing to 6.5 hours for unilateral breast reconstruction. Partial or total flap loss did not occur in 6 flaps. Abdomen was repaired directly with muscle and fascia sparing technique without necessity of mesh graft. There was no complication in donor site like abdominal hernia. Bilateral breast reconstruction can achieve exceptionally good aesthetic result with low complication if it is performed with skillful technique and experience. The reason for this is that fairly good symmetry usually is obtained in the initial surgery and in most cases only minimal additional surgery is required to achieve a satisfactory aesthetic result. The one disadvantage of bilateral reconstruction with autologous tissue is the length of the surgical procedure. Although the initial bilateral breast reconstruction can be a long, tedious procedure if free flaps are used, it must be a valuable treatment option for bilaterally mastectomized patients.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2007.11a
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• pp.427-428
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• 2007

• Archives of Plastic Surgery
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• v.46 no.4
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• pp.390-391
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• 2019

• Korean Journal of Computational Design and Engineering
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• v.5 no.4
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• pp.347-358
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• 2000

The view dependency of typical spatial-partitioning based NC simulation methods is overcome by polygon rendering technique that generates polygons to represent the workpiece, thus enabling dynamic viewing transformations without reconstruction of the entire data structure. However, the polygon rendering technique still has difficulty in realizing real-time simulation due to unsatisfactory performance of current graphics devices. Therefore, it is necessary to develop a mesh decimation method that enables rapid rendering without loss of display quality. In this paper. we proposed a new mesh decimation algorithm thor a workpiece whose shape varies dynamically. In this algorithm, the 2-map data thor a given workpiece is divided into several regions, and a triangular mesh is constructed for each region first. Then, if any region it cut by the tool, its mesh is regenerated and decimated again. Since the range of mesh decimation is confined to a few regions, the reduced polygons for rendering can be obtained rapidly. Our method enables the polygon-rendering based NC simulation to be applied to the computers equipped with a wider range of graphics cards.

• Journal of KIISE:Computer Systems and Theory
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• v.34 no.1
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• pp.28-37
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• 2007

This paper addresses a new surface reconstruction scheme for approximating the isosurface from a set of tomographic cross sectional images. Differently from the novel Marching cube algorithm, our method does not extract iso-density surface(isosurface) directly from the voxels but calculates the iso-density point(isopoint) first. After building the relatively coarse initial mesh by the Cell-boundary algorithm approximating the isosurface, it produces the final isosurface by iteratively shrinking and smoothing the initial mesh. Comparing with the Marching Cube algorithm, our method is robust and does not make any crack in resulting surface model. Furthermore, the proposed method surmounts the O(1)-adjacency limitation of MC in defining the isopoints by permitting the O(2) and O(3)-adjacent isopoints in surface reconstruction, and can produce more accurate isosurface. According to experiments, it is proved to be very robust and efficient for isosurface reconstruction from cross sectional images.