• 대한수학회보
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• 제39권4호
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• pp.681-685
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• 2002

It is shown that, an immersion of n-dimensional compact manifold without boundary into (n + 1)-dimensional Euclidean space, hyperbolic space or the open half spheres, is a totally umbilic immersion if for some r, r =2, 3, …, n the r-th mean curvature Hr does not vanish and there are nonnegative constants $C_1$, $C_2$, …, $C_{r}$ such that (equation omitted)d)

• 통합자연과학논문집
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• 제5권1호
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• pp.42-45
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• 2012

In this paper, when N is a compact Riemannian manifold, we discuss the nonexistence of conformal deformations on Riemannian warped product manifold $M=({\alpha},\;{\infty}){\times}_fN$ with prescribed scalar curvature functions.

• 한국해안해양공학회지
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• 제10권2호
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• pp.55-63
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• 1998

최근 몇몇 연구자들이 서로 다른 방법을 이용하여 수정 완경사방정식을 개발하였는데, 이는, Berkhoff 의 완경사방정석과 비교해 볼 때, 바닥 경사의 제곱 및 바닥 곡율에 비례하는 항들을 추가로 포함하고 있다. 이 식을 검토한 결과, 천이해역에서는 두 항들이 다같이 중요하지만, 천해에서는 바닥 경사 제곱항의 영향은 중요한 반면 바닥 곡률항의 영향은 작아짐을 보였다. 이 항들의 중요성을 좀더 면밀히 검토하기 위하여, 일정 사면, 비일정사면 및 주기성을 갖는 물결진 바닥으로부터의 파의 반사 문제에 대하여 수정 완경사방정식과 Berkhoff의 완경사방정식을 적용하였다. 바닥 경사만을 생각할 때, 완경사방정식이 지금까지 그 적용 한계로 알려져 왔던 1:3보다 더급한 1:1의 경사까지 정확한 결과를 나타냄을 보였다. 또한, 비교적 변화가 적은 해저면 위에서의 파의 전파를 모의할 때는 바닥 곡률항만이 중요한 역할을 하지만, 바닥 경사가 작지 않은 경우에는 보다 정확한 결과를 얻기 위하여 바닥 경사의 제곱항도 포함시켜야 함을 보였다.

• 한국광학회지
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• 제16권5호
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• pp.423-427
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• 2005

본 연구는, 원리적인 다양한 장점에도 불구하고 현실적인 제약으로 인해 실제 설계과정에서 잘 적용되지 않는, 자이델 3차 수차를 간편하게 다룰 수 있는 방안을 제안한다. 먼저 유한 물체거리를 갖는 2 반사경계에 대해 자이델 3차의 구면수차계수를 유도한다. 여기서, 유도된 구면수차계수는 고차의 비선형 방정식으로 표현되는데, 그 구성은 설계변수(물체거리, 주경 및 부경의 곡률, 주경과 부경 사이의 거리)와 유효초점거리로 이루어진다. 해석적으로 표현된 고차의 비선형 구면수차 방정식은 컴퓨터를 이용한 수치기법에 의해 근사적인 제로조건을 만족하도록 풀려진다. 이렇게 구해진 다양한 수치 해들을 주의 깊게 통찰하면 주경과 부경의 곡률 간에 선형성이 존재함을 파악할 수 있다. 즉, 결과적으로 주경과 부경의 곡률들을 선형맞춤(linear fitting)하면 곡률선형방정식이 얻어지는데, 이의 의미는 약간의 대수적인 계산으로 최적화의 초기 입력 데이터를 손쉽게 얻을 수 있는 가능성을 제시한 것이다. 한편, 응용외의 순수 수차론적인 관점에서 본다면, 본 연구의 특징은 유한 물체거리를 갖는 2 반사경계의 주경 및 부경의 곡률들이 구면수차가 거의 제로가 되는 조건 하에서 상호간에 선형 관계가 존재하였다는 것이다.

• 한국자동차공학회논문집
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• 제4권6호
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• pp.27-38
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• 1996

A two-dimensional FEM program, which considers bending effects in the membrane fromulation, was developed under plane strain assumption for analyzing forming processes of an arbitrarily shaped draw-die of automotive panels. For the evaluation of bending effects with membrane elements, the bending equivalent forces and stiffnesses are calculated from the bending moment computed using the changes in curvature of the formed shape of two membrane ones. The curves depicted with 3 nodes are described by a circle, a quadratic equation, and a cubic equation, respectively, and in the simulation of the stretch/draw sections of an automotive inner panel, three different description results are compared each other. Also, the bending results are compared with membrane results and measurements in order to verify the validity of the developed program.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2002년도 추계 학술발표회 논문집
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• pp.322-329
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• 2002

The purpose of this study is to develop a reasonable design for transverse confinement reinforcement considering ductility and required transverse confinement reinforcement of RC bridge columns. In order to develop relationships between the curvature ductility and the displacement ductility, the analysis for total 21,600 columns using the computer program NARCC have been carried out for parametric studies. Based on the results from the parametric studies, a correlation equation between the curvature ductility and the displacement ductility was developed. In addition, an equation for calculating the required transverse confinement reinforcement based on ductility demand was developed for seismic design of RC bridge columns. The equations proposed by this study will provide more reasonable and more effective design guidelines for performance-based seismic design of RC bridge columns.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.123-124
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• 2002

A press shoe is an element of a machine for squeezing water from wood pulp in the field of manufacturing paper. This is used to compress the pulp enveloped by felt sheet with a large roller. The squeezing force is made by hydraulic pressure. The press shoe has a mechanism similar to a partial hydrostatic bearing. The pressure profile between press shoe and roller affects their squeezing ability, and partial peak pressure can tear the wet pulp. The curvature of the surface of press shoe varies to reduce the peak pressure and increase the mean pressure simultaneously. Therefore, the prediction of pressure distribution considering partially changed curvature of hydrostatic bearing is very important for designing the press shoe. In this study, the difference formulation of Reynolds' equation for partial hydrostatic bearing is by direct numerical method and a computer program to calculate the pressure distribution is developed. We investigate the effect of partially changed curvature of bearing surface on the pressure distribution. Other design parameter for hydrostatic bearing such as depth of pocket and relative velocity are also studied.

• KSTLE International Journal
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• 제3권2호
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• pp.90-94
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• 2002

A press shoe is an element of a machine for squeezing water from wood pulp in the field of manufacturing paper. This is used to compress the pulp enveloped by felt sheet with a large roller. The squeezing farce is made by hydraulic pressure. The press shoe has a mechanism similar to a partial hydrostatic bearing. The pressure profile between press shoe and roller affects their squeezing ability, and partial peak pressure can tear the wet pulp. The curvature of the surface of press shoe varies to reduce the peak pressure and increase the mean pressure simultaneously, Therefore, the prediction of pressure distribution considering partially changed curvature of hydrostatic bearing is very important far designing the press shoe. In this study, the difference formulation of Reynolds equation far partial hydrostatic bearing is derived by direct numerical method and a computer program to calculate the pressure distribution is developed. We investigate the effect of partially changed curvature of bearing surface on the pressure distribution. Other design parameter far hydrostatic bearing such as depth of pocket and relative velocity are also studied.

• 한국광학회:학술대회논문집
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• 한국광학회 2005년도 하계학술발표회
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• pp.32-33
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• 2005

• 한국철도학회:학술대회논문집
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• 한국철도학회 2008년도 춘계학술대회 논문집
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• pp.1676-1682
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• 2008

The vertical curve of railway is installed in changing point where the gradient is more than a certain degree to ensure safe operation of train and comfort of passengers. As a result of CAD work with 3D coordination by using the existing equation, it was found that the simple equation about vertical curve installation suggested in the surveying engineering or railway regulations did not reflect theoretical curvature of circular curve in a case of steep grade and large vertical radius. In this study, for derive precision equation and transition curve about vertical curve, gradient parameters, equation of circles and transition curve equation were used, and it was verified by CAD that the derived equation is exactly satisfied with parameters of geometrical circular and transition curve. This equation could be used to provide more smoothing operation of train and comfort of passengers on vertical curves, especially in case that railway requires precision vertical alignment of track such as super high-speed railway, LRT or Maglev system.