• Journal of the Korean Society for Precision Engineering
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• v.17 no.3
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• pp.136-148
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• 2000

In this work, a general method for the mathematical description of three-dimensional trimmed surface is proposed by introducing the base parametric surface and boundary curves. Since mesh density distribution for the analysis may vary by cases, a grid-based mesh generation algorithm using quadtree is proposed in the present work. For the assurance of connectivity of generated meshes among surfaces, a method for the pre-cleaning of boundary curves has been developed to be used in the automatic generation of the finite elements. In addition, mesh-smoothing algorithm is suggested which can be used in the general trimmed surface. In this algorithm nodes are moved on the original surface by the normal projection in each iterative smoothing procedure.

• Transactions of Materials Processing
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• v.9 no.2
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• pp.140-151
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• 2000

The finite element mesh approach for tool surface description is applied effectively to analyze sheet metal stamping processes. To improve the mesh quality and the stability of the mesh generation process, a gybrid method based on the grid approach and the Delaunay triangulation is proposed in the present work. In the present study, a general method for the mathematical description of arbitrarily shaped tool surface is proposed by introducing the parametric surface approach. A polynomial function employed to describe the base parametric surface and the boundary curves are defined to describe arbitrary three-dimensional trimmed surfaces. To verify the validity of the proposed method, automatic mesh generation is carried out for some shosen complicated parts including actual automotive panel.

• Journal of Korea Game Society
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• v.2 no.1
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• pp.62-68
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• 2002

This paper presents a method for tessellating trimmed NURBS surface with preserving sharp shape Although several existing approaches need a large number of triangular meshes to represent sharp shape of surface, resulting triangular meshes may not reflect sharp edges properly. In this study, we flit detect the sharp shape of NURBS surface automatically using C1 continuous condition and then use constraint Delaunay triangulation method to present exact sharp shape with the minimum triangular meshes. And we also use approximated developed surface domain as triangulation domain of rimmed NURBS surface. In this way, the shape of triangular elements on the triangular domains is approximately preserved and can avoid distortion when mapped into three-dimensional space. finally, we show examples that demonstrate the effectiveness of the proposed scheme in terms of reducing the number of triangular meshes and preserving sharp shape of surface more exactly.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.9
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• pp.768-773
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• 2005

A new approach for human foot modelling and last design based on the cross sectional method is presented in this paper. The proposed last design method utilizes the dynamic trimmed parametric patches for the foot 3D data and last 3D data. The cross section a surface of 3D foot for the 3D last, design modeling of free form geometric last shapes. The proposed last design scheme wraps the 3D last data surrounding the measured 3D foot data with the effect of deforming the last design rule The last design rule of the FFD is constructed on the FFD lattice based on foot-last shape analysis. In addition, the control points of FFD lattice are constructed with cross sectional data interpolation methods from the a finite set of 3D foot data. The deformed 3D last result obtained from the proposed FFD is saved as a 3D dxf foot data. The experimental results demonstrate that the last designed with the proposed scheme has good performance.

• Journal of the korean academy of Pediatric Dentistry
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• v.43 no.2
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• pp.176-186
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• 2016

This study was performed to compare the shape and dimension of anterior zirconia crowns to other pediatric crowns using a three-dimensional scanner to investigate adequate amount of tooth preparation. Primary central and lateral anterior zirconia crowns, stainless steel crowns and celluloid strip crowns were scanned by a three-dimensional scanner. Outer and inner surfaces of zirconia and stainless steel crowns, and outer surface of celluloid strip crowns were analyzed. In outer scanned images, all sizes of central and lateral size 1 zirconia crown had the largest labiolingual diameter among the three crowns. In inner scanned images, zirconia crown's mesiodistal diameter was 0.7-1.0 mm smaller and crown length was approximately 1 mm shorter than those of stainless steel crowns. Zirconia crown's labiolingual diameter was larger in central crowns whereas it was smaller in lateral crowns than that of stainless steel crowns. Recommended preparation required for zirconia crown is incisal 2.5-3.0 mm, mesiodistal 1.5-2.0 mm, labial 0.5-1.0 mm. Cingulum should be trimmed parallel to the long axis. No more lingual reduction is needed in central incisors whereas additional 0.5 mm reduction is suggested in lateral incisors.

• Conservation Science in Museum
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• v.25
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• pp.1-8
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• 2021

This study investigated White Porcelain Water Dropper with Openwork Lotus Scroll Design and Eight Trigram Design in Cobalt-blue Underglaze (hereinafter, the "water dropper") in the collection of the National Museum of Korea using computed tomography (CT). A replica was produced to examine both the structure and its original production method. The CT scanning identified no joint lines or pores in the clay, which suggests that the body (the lower part of the water dropper) was shaped in a single piece using a mold and was then matched with a mold-formed lid (the upper part of the water dropper). The inner container of the body portion was roughly trimmed with a bamboo knife so that its upper surface could be securely attached to the bottom of the lid and prevent any leakage in the joined surface. It appears that the inner container for storing water was made first in a cylindrical shape that met the unit of quantity used at the time and could be easily formed by molding. It was transformed into a trapezoid shape during the process of combining it with the lid. A cylindrical inner container was reproduced using silicon 3D printing to compare its capacity with that of the original inner container. The comparison revealed that the reproduced container had a capacity of 152.5㎖, whereas the original container holds approximately 168.6㎖, a figure similar to three hop (around 174㎖) in Joseon-period units of quantity. Since the capacity of the cylindrical inner container corresponds to a known measure from the late Joseon dynasty, it is likely that the water dropper was originally produced to contain a cylindrical inner container.