• Korean Journal of Computational Design and Engineering
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• v.21 no.2
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• pp.143-150
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• 2016

In shipbuilding, hull assemblies are manufactured by welding. The thermal deformation caused by the welding produces shape deformation. Counter-deformed design methods have been used in shipyards to cope with the weld-induced deformation of ship assembles. Finite element methods (FEMs) are frequently used to estimate welding distortion in the counter-deformed design. For the estimation of welding distortion, producing uniform rectangular elements is required to enter thermal loads on the welding line and obtain accurate analysis results. In this paper, a new automatic mesh generation method is proposed for prediction of welding deformation in FEM. Meshes are constructed for test cases to demonstrate the feasibility of the proposed mesh generation method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.408-413
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• 1995

Nowadays, manufacturing system is trending toward integrated circumstance by helping of CAD/CAM/CAT. To use this system effectively, it is necessary to get exact 3 dimensional surface data of an object. We have been using contact method to measure 3 dimensional object profile. But his method has demerit of leaving scrach or small distortion on the object. To improve this, a non-contact measuring method using optical system is adopted. In this paper, We propose optical ring method. Withthis system, We could measure displacement of the object in the range of 45mm having 150mm having 150 .mu. m resolution with no scratch or distortion.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.6C
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• pp.384-390
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• 2011

The paper derives formulas for the mean-squared error distortion and resulting signal-to-noise (SNR) ratio of a fixed-rate scalar quantizer designed optimally in the minimum mean-squared error sense for a Gaussian density with the standard deviation ${\sigma}_q$ when it is mismatched to a Laplacian density with the standard deviation ${\sigma}_q$. The SNR formulas, based on the key parameter and Bennett's integral, are found accurate for a wide range of $p\({\equiv}\frac{\sigma_p}{\sigma_q}\){\geqq}0.25$. Also an upper bound to the SNR is derived, which becomes tighter with increasing rate R and indicates that the SNR behaves asymptotically as $\frac{20\sqrt{3{\ln}2}}{{\rho}{\ln}10}\;{\sqrt{R}}$ dB.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.65-69
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• 2004

In the present work, characteristics of an axial flow fan haying distorted inlet flow produced by hub cap are investigated. The distorted inlet flow is generated by the shape of hub cap installed in front of the axial flow fan. Two different cases of hub cap geometry are analyzed to verify the influence of flow distortion. The flow fields are analyzed numerically by solving steady form of three-dimensional Reynolds-averaged Wavier-Stokes equation and standard k-$\epsilon$ model is used for a turbulence closure. The results obtained from the numerical simulation are compared to those from experimental measurements. It is found that the overall performance of the axial flow fan is increased by reducing the flow distortion at the hub. Detailed characteristics of the flow fields of two different geometric conditions are also discussed.

• Korean Journal of Optics and Photonics
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• v.13 no.3
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• pp.182-188
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• 2002

We have analyzed the phase-calculation-error of a three-dimensional shape measurement system using the projection of phase shifted fringe patterns. In this study, we have dealt various errors; an error caused by the variation of quantization levels, an error caused by the defocus of fringe pattern projected images, an error caused by phase-shifting errors, an error caused by the intensity variation of the background and modulation amplitude of fringe pattern projected images during the projection of multiple patterns, an error caused by the distortion of sinusoidal shape of a fringe pattern. The results will contribute to the design of a three-dimensional shape measurment system and give an important meaning to the calculation and the analysis of the accuracy of a system.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2009.01a
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• pp.551-556
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• 2009

3-D CAD (Computer Aided Design) system is an indispensable tool for manufacturing. A lot of engineers have studied for the methods to generate a curved surface on an N-sided shape, which is the basic technology of 3-D CAD systems. This surface generation, however, has three problems on the case of long and narrow shapes: the resultant surface is distorted, the surface is not continuous to adjacent surfaces, or additional user inputs are required to generate the surface. Conventional methods have not yet solved these problems at the same time. In this paper, we propose the method to generate internal curves that divide a long and narrow shape into regular N-sided sections so as to divide the shape into an N-sided section and four-sided ones. Our method controls the shape of internal curves by dividing an N-sided long and narrow shape into an N-sided section and four-sided ones, and solves distortion of the generated curved surface. In addition, each of the generated sections is interpolated with G1-continuous surfaces. This process does not require any user's further input. Therefore, the three problems mentioned above will be solved at the same time.

• Proceedings of the KWS Conference
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• 2005.11a
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• pp.192-194
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• 2005

Joint strength of spot friction welded 5J32 Al alloy were investigated according to the tool shape and the tool penetration depth. General spot friction stir welding tool consists of a shoulder having bigger diameter and a threaded pin projected from the shoulder, which resulted in the generation of large up-lifting of upper plate around the weld nugget because of the deeper penetration and the severe stirring effect of threaded pin. Two kinds of welding tools without the threaded pin were used to avoid the distortion and improve the joint strength. One was a simple cylindrical shape and the other was cylindrical shape with small projection. Therefore, the process was named as spot friction welding comparing to spot friction stir welding because spot friction welding don't use a stirring effect. Using the cylindrical shape tool with small projection, the up-lifting of upper plate were avoided and joint strength were superior to that of the joint using simple cylindrical shape tool. At the 0.5mm of too penetration depth using cylindrical tool with small projection, nugget pull fracture mode can be observed and shear fracture mode were dominant at the rest conditions.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.599-607
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• 2002

During the shape optimization, relocations of nodes happen successively. However, excessive movement of nodes often results in the mesh distortion and eventually deteriorates the accuracy of the optimum solution. To overcome this problem, an efficient method lot the shape optimization has been developed. The method starts from the design domain which is large enough to hold the possible shape of the structure. The design domain has pre-defined uniform fine meshes. In each cycle, the method allots real properties to the elements inside the structure and nearly zero to ones outside. The performance of the method is evaluated through two examples with displacement and frequency constraints.

• Structural Engineering and Mechanics
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• v.68 no.5
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• pp.519-526
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• 2018

In this article, experimental training of the commercial available shape memory alloy fibre (SMA) fibre under the combined thermomechanical loading is reported. SMA has the ability to sense a small change in temperature (${\geq}10^{\circ}C$) and activated under the external loading and results in shape change. The thermomechanical characteristics of SMA at different temperature and mechanical loading are obtained through an own lab-scale experimental setup. The analysis is conducted for two types of the medium using the liquid nitrogen (cold cycle) and the hot water (heat cycle). The experimental data indicate that SMA act as a normal wire for Martensite phase and activated behavior i.e., regain the original shape during the Austenite phase only. To improve the confidence of such kind of behavior has been verified by inspecting the composition of the wire. The study reveals interesting conclusion i.e., while SMA deviates from the equiatomic structure or consist of foreign materials (carbon and oxygen) except nickel and titanium may affect the phase transformation temperature which shifted the activation phase temperature. Also, the grain structure distortion of SMA wire has been examined via the scanning electron microscope after the thermomechanical cycle loading and discussed in details.

• 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.