• Proceedings of the KSME Conference
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• 2000.11b
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• pp.404-409
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• 2000

Characteristics of secondary vortices is topologically investigated in the near-wake region of a circular cylinder where the Taylor hypothesis does not hold. The three-dimensional flow fields in the wake-transition regime were measured by a time-resolved PIV. For the analysis in a moving frame of reference, the convection velocity of the Karman vortices is evaluated from the trajectory of vortex center which is defined as the centroid of the vorticity field. Then, a saddle point is obtained by applying the critical point theory. Science the distributions of fluctuating Reynolds stresses defined by triple-decomposition are closely related with the existence of secondary vortices. the physical meaning of them is explained in conjunction with vortex center and saddle point trajectories. Finally, the temporal evolution of streamwise vortex is also discussed.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.104-110
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• 2008

A lot of straight bevel gears have been manufactured by the cold forging process in order to improve the productivity and mechanical property of the product. The die for the cold forging of the gear needs high precision and reproducibility. In the study, cold forging die has been modeled by CAD/CAM and manufactured by machining center using ball end mill coated by (Al, Ti)N for heat-treated alloy steel(STD11, HRC 60). Through the measurement of the machined die, satisfactory dimensional accuracy and surface roughness were obtained. In the future, many 3-d cold forging dies will be directly machined instead of electric discharge machining.

• Journal of the Korean Society for Railway
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• v.9 no.3 s.34
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• pp.298-304
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• 2006

An active application of concrete track is being expected for the future constructions of Korean railroad. For the successful concrete track construction and design in earthwork areas, the roadbed behavior should be reasonably estimated using the proper analysis method. In this paper, behaviors of concrete track on the reinforced roadbed constructed with the standard stiffness and depth were estimated thorough numerical analyses and field measurements. A three dimensional finite difference method was employed to model the concrete tracks and subground. The settlement and vertical pressures caused by train load were estimated by the numerical method and compared with the field measurement results. The bearing characteristics of roadbed were presented and the proper method for the analysis of concrete track was proposed.

• Tunnel and Underground Space
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• v.10 no.3
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• pp.481-485
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• 2000

Vibration screening trench is very effective to reduce the ground vibration, but to construct the trench in the rock mass is not easy. Various line drilling methods have been tried to replace the trenching. In this study, UDEC was applied to simulate the screening effect of drilling holes in 2 dimensional ground model. Field measurement was conducted and compared to numerical analysis.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.5
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• pp.5-11
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• 1994

현대산업사회의 발달에 따라 제품의 고기능화, 고성능화, 고부가가치화의 경향이 현저하여지고 그에 따른 기계 및 전자분야의 눈부신 발전은 고정도 부품의 제작을 위한 초정밀 가공기술 및 초정밀 측정기술의 발전에 더욱 박차를 가하여 왔다. 그 중에서 정밀측정기술은, 설계정보로 주어진 Criterion에 대한 적부 판정이라는 종래의 계측개념에서 탈피하여, 제품의 종합적인 가치평가이외에도 창조과정의 중요한 역할을 담당하는 주요기술로서 개념이 자리를 굳히고 있다. 즉 물리량의 검출에 의한 적부검사 및 가동에의 Feedback 정보제공이라는 단순한 역할에서, 고도의 정보처리기술의 도입에 의한 적절한 요구사항의 처리에 의하여 기술전략, 가공 및 조립, 보수 및 관리, 설계 및 개발, 판매전략 등에 그 정보가 적극적으로 활용 되게 되었다.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.1
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• pp.50.3-51
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• 2017

Discovered in the South Pole Telescope Sunyaev-Zel'dovich (SPT-SZ) survey, the galaxy cluster SPT-CL J0205-5829 at z = 1.322 might be the most massive known SZ-selected galaxy cluster at z > 1.2. The SZ and X-ray combined mass estimate is $M500=(4.8{\pm}0.8){\times}10^{14}M_{\odot}$. To confirm this extreme mass, we perform weak lensing analysis of SPT-CL J0205-5829 using HST data. Our analysis produces a mass estimate consistent with the previous results obtained from non-lensing methods. In this poster, we describe details of the method including shape measurement, PSF correction, source selection, and mass estimation. We also present a two-dimensional mass map and compare this to the galaxy distribution.

• Journal of the Korean Ceramic Society
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• v.47 no.4
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• pp.290-295
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• 2010

This study has been focused on properties of mirror surface grinding technology by ELID(Electrolytic In-process Dressing) for structural ceramics using in high precision structural parts as like semi-conductor manufacturing processes. The experimental studies have been carried out to get mirror surface for grinding of structural ceramics, SiC, $Al_2O_3$ and AlN. Grinding process of the ceramics is carried out with varying mesh type, depth of cut and feed rate using diamond wheel. The machining result of the surface roughness and condition of ground surface, have been analyzed by use of surface roughness tester, SEM, AFM and three dimensional surface profiler measurement system.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.50 no.1
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• pp.30-36
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• 2001

In this paper, propagation and damping characteristics of PD pulse in GIS are analyzed using SNM. These characteristics are very important to make a diagnosis and protection of accident in GIS. SNM is numerical method in time domain and very useful method to analyze 3-Dimensional structure such as GIS. GIS modeling is made simply as the form of coaxial cable and then spacers are inserted in it. The scattering and reflection in the GIS are appeared and damping characteristics of PD pulse are shown. When simulation using SNM compare to measurement, two results are similar.

• 제어로봇시스템학회:학술대회논문집
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• 2000.10a
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• pp.188-188
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• 2000

The most important problem in target tracking can be said to be modeling the tracking system correctly. Although the simple linear dynamic equation for this model has used until now, the satisfactory performance could not be obtained owing to uncertainties of the real systems in the case of designing the filters baged on the dynamic equations. In this paper, we propose the extended robust Kalman filter (ERKF) which can be applied to the real target tracking system with the parameter uncertainties. A nonlinear dynamic equation with parameter uncertainties is used to express the uncertain system model mathematically, and a measurement equation is represented by a nonlinear equation to show data from the radar in a Cartesian coordinate frame. To solve the robust nonlinear filtering problem, we derive the extended robust Kalman filter equation using the Krein space approach and sum quadratic constraint. We show the proposed filter has better performance than the existing extended Kalman filter (EKF) via 3-dimensional target tracking example.

• Journal of Biomedical Engineering Research
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• v.5 no.1
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• pp.47-54
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• 1984

In order to research the flow in the thin wall compliant tube, this present study is attempt to measure the cross sectional area according to change of external pressure and flow by ultrasonic method different from willy used impedance technique for flow analysis about one dimensional Steads flow. The experimental results are as follows. 1) Measurement of cross sectional area ratio by ultrasonic method by comparison with experimental results of impedance technique & theoretical results were well consent. 2) Pressure difference of upstream and down stream is alwap's maximum range at 0.4 < $\alpha$ <0.5, and have no connection with changing external pressure. 3) when the external pressure is fixed and resistance is varied, Self excited oscillation occurs in the region at 0.5 < $\alpha$ <0.6, and oscillation disappear almost at R2>=1.2