• Transactions of Materials Processing
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• v.20 no.4
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• pp.316-323
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• 2011

The hot curvature-forming of large aluminum thick plate using a grid-typed hybrid die is a process for the production of a spherical LNG tank. Many variables such as the initial die surface quality, grid size, grid thickness, size of blank plate and cooling line design, control the success of the process. In addition, the plate used in this process is generally larger than $10{\times}10m$ in size. Thus, it is very difficult to predict the surface characteristics of the plate during forming and to measure the different parameters due to the high cost of the experiments. In order to optimize the process design for the grid-type die, the development of an analytical method to predict the surface characteristics of the final product in hot curvature-forming is needed. This paper described the development of the method and procedures for FE simulations of the hot curvature-forming process, including hot forming, air flow, cooling, and thermal deformation analyses. An experiment for a small scale model of the process was conducted to check the validity of the numerical method. The results showed that the curvature of the plate in the analysis agrees well with that of the experiment within 0.037 and 0.016% tolerance margins for its side and corner, respectively.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.2
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• pp.199-207
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• 2001

In this paper, we suggest an edge-based surface segmentation algorithm of 3D image using curvature. For the first, in this proposed method, we approximate 3D depth data to second order curves by each scan line and decide splitting points of 3D edges by curvature of the approximated curves. And finally make a group as 3D surface with the region of input image by the 3D edges. In the conventional algorithms, there are some difficulties in detecting 3D edge with the separated processes for the jump edge and the crease edge and especially, in deciding the ambiguous discontinuity of surface directions about the crease edge. The proposed algorithm decides curvature discontinuity using curvature which is simply calculated by a geometrical approximation. Furthermore, the algorithm has a cooperated process to calculate the jump and crease edges. The results of computer simulations with several 3D images show that the proposed method yields better performance as comparing with the conventional methods.

• Journal of Korea Multimedia Society
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• v.8 no.1
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• pp.34-45
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• 2005

In this paper, a novel implementation of a person verification system based on depth-weighted Hausdorff distance (DWHD) using the surface curvature of the face is proposed. The definition of Hausdorff distance is a measure of the correspondence of two point sets. The approach works by finding the nose tip that has a protrusion shape on the face. In feature recognition of 3D face image, one has to take into consideration the orientated frontal posture to normalize after extracting face area from original image. The binary images are extracted by using the threshold values for the curvature value of surface for the person which has differential depth and surface characteristic information. The proposed DWHD measure for comparing two pixel sets were used, because it is simple and robust. In the experimental results, the minimum curvature which has low pixel distribution achieves recognition rate of 98% among the proposed methods.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.3
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• pp.834-845
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• 1995

An experimental study is made in a nearly two-dimensional 90.deg. curved duct to investigate the effects of interaction between streamline curvature and mean strain on turbulence. The initial shear at the entrance to the curved duct is varied by an upstream shear generator to produce five different shear conditions ; a uniform flow (UF), a positive weak shear (PW), a positive strong shear(PS), a negative weak shear (NW) and a negative strong shear(NS). With the mean field data of the case UF, variations of the momentum thickness, the shape factor and the skin friction over the convex(inner) surface and the concave (outer) surface are scrutinized quantitatively in-depth. It is found that, while the pressure loss due to curvature is insensitive to the inlet shear rates, the distributions of wall static pressure along both convex and concave surfaces are much influenced by the inlet shear rates.

• Journal of the Korean Mathematical Society
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• v.47 no.5
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• pp.967-983
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• 2010

Let M be an n-dimensional complete simply connected Riemannian manifold with sectional curvature bounded above by a nonpositive constant $-{\kappa}^2$. Using the cone total curvature TC($\Gamma$) of a graph $\Gamma$ which was introduced by Gulliver and Yamada [8], we prove that the density at any point of a soap film-like surface $\Sigma$ spanning a graph $\Gamma\;\subset\;M$ is less than or equal to $\frac{1}{2\pi}\{TC(\Gamma)-{\kappa}^2Area(p{\times}\Gamma)\}$. From this density estimate we obtain the regularity theorems for soap film-like surfaces spanning graphs with small total curvature. In particular, when n = 3, this density estimate implies that if $TC(\Gamma)$ < $3.649{\pi}\;+\;{\kappa}^2\inf\limits_{p{\in}F}Area(p{\times}{\Gamma})$, then the only possible singularities of a piecewise smooth (M, 0, $\delta$)-minimizing set $\Sigma$ are the Y-singularity cone. In a manifold with sectional curvature bounded above by $b^2$ and diameter bounded by $\pi$/b, we obtain similar results for any soap film-like surfaces spanning a graph with the corresponding bound on cone total curvature.

• Journal of the Korean Mathematical Society
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• v.49 no.3
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• pp.585-604
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• 2012

In this paper we consider the evolution of the rolling stone with a rotationally symmetric nonconvex compact initial surface ${\Sigma}_0$ under the Gauss curvature flow. Let $X:S^n{\times}[0,\;{\infty}){\rightarrow}\mathbb{R}^{n+1}$ be the embeddings of the sphere in $\mathbb{R}^{n+1}$ such that $\Sigma(t)=X(S^n,t)$ is the surface at time t and ${\Sigma}(0)={\Sigma}_0$. As a consequence the parabolic equation describing the motion of the hypersurface becomes degenerate on the interface separating the nonconvex part from the strictly convex side, since one of the curvature will be zero on the interface. By expressing the strictly convex part of the surface near the interface as a graph of a function $z=f(r,t)$ and the non-convex part of the surface near the interface as a graph of a function $z={\varphi}(r)$, we show that if at time $t=0$, $g=\frac{1}{n}f^{n-1}_{r}$ vanishes linearly at the interface, the $g(r,t)$ will become smooth up to the interface for long time before focusing.

• Korean Journal of Agricultural Science
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• v.47 no.4
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• pp.829-844
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• 2020

A vacuum metering device for garlic seeds was developed, and its metering performance was tested according to the design factors. Three design factors were as follows: suction surface diameter (Edge), suction surface curvature (Type), and guide height (Guide). The suction surface curvature represents the distance between the center of the grooved suction plate and the bottom of suction plate. The metering rate and multiple metering rate were analyzed as the metering performance of the developed device with two varieties of garlic seeds: Namhae (warm region-adapted garlic) and Uiseong (cold region-adapted garlic). The best metering performance for the Namhae seeds were found with the following conditions: An Edge, Guide and Type of 40, 4, and 35 mm, respectively. In the case of the Uiseong seeds, the best conditions were as follows: An Edge, Guide and Type of 35, 4, and 30 mm, respectively. The guide height was found to be the most influential design factor on the metering performance of the metering rate and multiple rate for both Namhae seeds and Uiseong seeds. Additionally, the interaction between the area of the suction surface and the curvature of the suction surface had some effects on the multiple rate for the Uiseong seeds. It was concluded that the guide height should be 4 mm or higher so that more than 90% of the metering rate could be achieved for the tested garlic seeds with the developed metering device.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.430-433
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• 2004

The ophthalmic lens manufacturing processes need to extract the aspherical surface equation from the unknown surface since its real profile can be adjusted by the process variables to make the ideal curve without the optical aberration. This paper presents a procedure to get the aspherical surface equation of an aspherical ophthalmic lens. Aspherical form generally consists of the Schulz formula to describe its profile. Therefore, the base curvature, conic constant, and high-order polynomial coefficient should be set to the original design equation. To find an estimated aspherical profile, firstly lens profile is measured by a contact profiler, which has a sub-micrometer measurement resolution. A mathematical tool is based on the minimization of the error function to get the estimated aspherical surface equation from the scanned aspherical profile. Error minimization step uses the Nelder-Mead simplex (direct search) method. The result of the refractive power measurement is compared with the curvature distribution on the estimated aspherical surface equation

• Journal of the Korean Society of Clothing and Textiles
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• v.32 no.9
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• pp.1478-1486
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• 2008

The human body composed of concave and convex curvatures, and the current 3D scanning technology which involves inherent measurement errors make it difficult to extract distinct curvature plot directly. In this study, a method of extracting the clear curvature plot and its application to the cycling pants design were proposed. We have developed the ergonomic pattern from the 3D human body reflecting cycling posture. For the ergonomic design line on the 3D human body, the 3D information on the lower part of four male bodies with flexed posture was analyzed. The 3D scan data of four subjects were obtained using Cyberware. As results, the iteration of the tessellated shell was executed 100 times to obtain optimized curvature plots of the muscles on the body surface, and the boundaries of the curvature plots were applied to the design lines. Maximum(Max-pattern) and mean curvature plots(Mean-pattern) were adopted in the design line of the cycling pants, and performance of those lines was compared with that of conventional princess line(Con-pattern). The average error of total area and length in the 2D pattern developed from the 3D flexed body surface in this study were very minimal($4.58cm^2$(0.19%) and 0.15mm(0.46%)), which was within the range of tolerable limits in clothing production. The pattern obtained from the flexed body reflecting cycling posture already included the contraction and extension of the cycling skin, so that the extra ease for movement and good fit was not need to be considered.

• Bulletin of the Korean Mathematical Society
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• v.50 no.4
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• pp.1261-1275
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• 2013

We establish an integral formula for the first Chern number of a compact almost Hermitian surface and derive curvature identities from the integral formula. Further, we provide some results as applications of the identities.