• 지구물리와물리탐사
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• 제5권3호
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• pp.206-216
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• 2002

유한요소법은 다양한 공학문제에 대해 수치적으로 해를 구하는 방법으로, 유한개의 요소를 이용하여 모형의 형상을 자유롭게 설정할 수 있기 때문에 3차원 모델링에 많이 적용된다. 공학에서 모델링은 해의 정확도와 계산시간이 중요한 의미를 가지므로, 유한요소법을 이용할 경우 주어진 공간에 대해 물리적인 연속성을 가지며 간단한 방법으로 요소를 구성하는 것이 효율적이다. 그러나 기존의 유한요소법에서는 구조적으로 복잡한 대상에 대해서 체계적인 요소 구성방식이 존재하나, 기하학적으로 단순한 원통형 물체에 대해서는 원통의 중심부에 대한 묘사가 자유롭지 못하다. 이 연구에서는 기존의 좌표변환식에서 처리할 수 없었던 좌표계의 원점을 수학적으로 정의하여 완전한 원통 좌표계에서의 유한요소법을 구성하고자 한다. 원통 좌표계에서는 모든 영역을 육면체 요소로 구성하여 유한요소법을 적용할 수 있으므로 원통형 물체나 공간으로 표현되는 시스템의 구조해석에 효율적이다. 한편, 이 방법은 단일 시추공과 지표의 탐사선으로 구성된 새로운 방식의 시추공-지표간 전기비저항 탐사법을 수행할 수 있는 기초를 제공하며, 이를 이용할 경우 전기비저항탐사의 환경 분야에 대한 적용성을 높일 것으로 판단한다.

• 한국HCI학회:학술대회논문집
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• 한국HCI학회 2008년도 학술대회 1부
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• pp.210-214
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• 2008

로봇이 실제 가정환경에 존재하는 모든 물체를 사전에 모델화하여 데이터베이스에 보존하는 것은 현실적으로 불가능하다. 따라서 본 논문은 이러한 문제를 해결하기 위하여 가정 내에서 흔히 볼 수 있으며 로봇에게도 조작이 용이한 컵, 병, 캔 등의 실린더 형 물체를 우선적 모델링 대상으로 선정하고, 이 물체들의 공통된 범주적 특성을 정의한 보편적 모델(Generic Model)을 사용하여 부분적 데이터로부터 전체 형상을 추정하는, 로봇 자가 모델링에 활용 가능한 새로운 물체 모델링 기법을 제안한다. 구체적으로 3D 센서로부터 얻은 3D 영상으로부터 우리가 모델링 하기를 원하는 실린더 형의 물체를 분리해낸 후 물체 표면상의 점의 좌표와 법선벡터를 이용해서 실린더의 초기 중심축을 구하는 방법, 오차를 가지고 있는 중심축을 교정해주는 방법, 최종적으로 실린더 단면의 중심축과 반지름을 이용하여 전체 실린더 형 물체를 모델링하는 방법 등을 제안하고 또한 실험을 통해서 우리가 제시하는 모델링 기법이 노이즈가 존재하는 실제 환경에서도 얼마 만큼의 정확성을 갖는지를 평가하였다.

• 한국측량학회지
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• 제34권2호
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• pp.171-183
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• 2016

Small-scale maps currently used are made by scanning and editing printed maps and its shortcoming is accumulated errors at the time of editing and low accuracy. TM projection method is used but its accuracy varies. In addition, small-scale maps are made without consideration of usability and compatibility with other scale maps. Therefore, it is necessary to suggest projection and coordinates system improvement methods in consideration of usability and compatibility between data. The results of this study reveal that in order to make the optimum small-scale map, projection that fits the purpose of map usage in each scale, coordinate system and neat line composition should be selected in consideration of interrelation and compatibility with other maps. Conic projection should be used to accurately illustrate the entire country, but considering usability and compatibility with other maps, traversing cylindrical projection should be used instead of conic projection. For coordinates system of the small-scale map, Universal Transverse Mercator (UTM-K) based on the World Geodetic System should be used instead of conventional longitude and latitude coordinate system or Transverse Mercator.

• Structural Engineering and Mechanics
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• 제4권3호
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• pp.227-242
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• 1996

An important class of problems in the field of geotechnical engineering may be analyzed with the aid of a simple integro-differential equation. Behavior of "rigid" piles(say concrete piles), "deformable" piles(say gravel piles), pile groups, pile-raft foundations, heavily reinforced earth, flow within circular silos and down drag on cylindrical structures (for example the crusher unit of a mineral processing complex) are the type of situations that can be handled by this type of equation. The equation under consideration has the form; $$\frac{{\partial}w(r,\;z)}{{\partial}z}+f(z){\int}^z_0g({\xi})(\frac{{\partial}^2w(r,\;{\xi})}{{\partial}r^2}+\frac{1}{r}\frac{{\partial}w(r,\;{\xi})}{{\partial}r})d{\xi}+h(r,\;z)=0$$ where w(r, z) is the vertical displacement of a soil particle expressed as a function of the polar cylindrical space coordinates (r, z) and the symbols f, g and h represent soil properties and the loading conditions. The merit of the analysis is its simplicity (both in concept and in application) and the ease with which it can be expressed in a computer code. In the present paper the analysis is applied to investigate the behavior of a single rigid pile to bedrock. The emphasis, however, is placed on developing the equation, the numerical techique used in its evaluation and validation of the technique, hereafter called the ID technique, against a formal program, CRISP, which uses the FEM.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1366-1371
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• 2003

Molecular dynamics (MD) simulations are conducted to investigate the thermophysical characteristics and the stability of liquid threads for various conditions. A cylindrical thread in the simulation domain is made of Lennard-Jones molecules. The surface tension of liquid threads can be determined from local densities, local normal and transverse components of the pressure force. In order to understand the effects of thread radii on surface tensions, the Tolman equation is modified on the basis of the cylindrical coordinates for prediction of surface tensions. Surface tensions calculated from the MD simulation agree with the prediction from the modified Tolman equation. In addition, surface tensions decrease linearly with increasing system temperature. For a binary system, the surface tension decreased linearly compared to that for a pure system with increasing binary ratio of solute molecules which have relatively large value of the affinity coefficient. For a fixed binary ratio, the surface tension increased slightly with the affinity coefficient and the maximum value appear around where the affinity coefficient is 1.5 and decreased rapidly for upper value of 1.5. In addition, the critical wavelengths of perturbations are proven to be directly proportional to the equimolar dividing radii of the liquid threads.

• 한국측량학회지
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• 제6권1호
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• pp.13-24
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• 1988

원형 구조물의 표면에 대한 삼차원 위치 결정은 여러 면에서 그 응용이 기대된다. 구조물의 진단을 고려해 볼때 이것은 광범위한 범주에서 하나의 의미있는 Topic이 될 것이며, 이러한 위치 결정을 함에 있어 수렴사진의 활용은 종내의 측량에 비해 많은 이점을 가지고 있다. 본 논문은 Metric과 Non-metric Camera를 이용하여 원사형의 피사체를 수렴사진으로 촬영하고 Bundle-Adjustment에 의해 그 결과를 고찰한 것이다. Bundle-Adjustment에 의한 오차 해석으로부터 표준 오차를 비교함과 아울러 Metric과 Nonmetric Camera로부터 얻은 피사체의 삼차원 좌표도 비교하였다.

• 대한기계학회논문집B
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• 제28권4호
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• pp.433-440
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• 2004

Since the numerical analysis was adopted in the mold design, lots of computational methods have been proposed for the simulations of casting processes for the various shaped molds. Today, it is possible to simulate the filling and solidification processes of most casts using the VOF technique. Though the three-dimensional numerical model based on the Cartesian coordinate system can be applied to any shape of cast, it becomes very inefficient when the three-dimensional model is applied to the cast of axi-symmetrical shape since the control volume includes at least 11 of the physical model. In addition, the more meshes should be distributed along the circumferential boundaries of curved shape in the Cartesian coordinate system fur the better results, while such curved circumferential boundary does not need to be considered in the two-dimensional cylindrical coordinate system. This motivates the present study i.e. developing a two-dimensional numerical model for the axi-symmetrically shaped casts. The SIMPLER algorithm, the VOF method, and the equivalent specific heat method have been adopted in the combined algorithm for the flow calculation, the free surface tracking, and the phase change heat transfer, respectively. The numerical model has been applied to the casting process of a pulley, and it was proven that the mesh and time effective calculation was accomplished comparing to the calculation using three-dimensional model.

• Structural Engineering and Mechanics
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• 제49권4호
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• pp.427-448
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• 2014

At present, the time of easy oil and gas is over. Now, the largest part of fossil fuels is concentrated in the deepest levels of tectonic structures and in the sea shelves. One of the most cumbersome operations of their extraction is the bore-hole drilling. In connection with austere tectonic and climate conditions, their drivage every so often is associated with great and diversified technological difficulties causing emergencies on frequent occasions. As a rule, they are linked with drill string accidents. A key role in prediction of these situations should play methods of theoretical modelling. For this reason, there is a growing need for development and implementation of new numerical methods for computer simulation of critical and post-critical behavior of drill strings (DSs). In this paper, the processes of non-linear deforming of a DS in cylindrical cavity of a deep bore-hole are considered. On the basis of the theory of curvilinear flexible rods, non-linear constitutive differential equations are deduced. The effects of the longitudinal non-uniform preloading, action of torque and interaction between the DS and the bore-hole surface are taken into account. Owing to the use of curvilinear coordinates in the constraining cylindrical surface and a specially chosen concomitant reference frame, it became possible to separate the desired variables and to reduce the total order of the equation system. To solve it, the method of continuation the solution by parameter and the transfer matrix technique are applied. As a result of the completed numerical analysis, the critical states of the DS loading in the cylindrical channels of inclined bore-holes are found. It is shown that the modes of the post-critical deforming of the DS are associated with its irregular spiral curving prevailing in the zone of bottom-hole-assembly. The possibility of invariant state generation during post-critical deforming is established, condition of its bifurcation is formulated. It is shown that infinite variety of loads can correspond to one geometrical configuration of the DS. They differ each from other by contact force functions.

• 한국정보통신학회논문지
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• 제11권6호
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• pp.1054-1061
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• 2007

본 논문에서는 2D 원통형 좌표계 구조를 해석하기 위한 전자기 수치 해석 방법 중 하나인 시간영역 유한차분법(FDTD)에서 필요한 흡수경계조건으로 UPML과 Liao 흡수경계조건을 비교하였다. 일반적인 2D 직각 좌표계에서는 UPML의 성능이 Liao의 흡수경계조건보다 우수하지만, 본 논문에서 가정한 2D 원통형 좌표계에서는 Liao에 의해 제안된 고유의 흡수경계조건이 UPML과 수정된 Liao 흡수경계조건보다 우수한 것으로 나타났다. 원통형 좌표계는 축에 대해서 대칭이기 때문에 3D 구조를 2D 구조로 가정할 수 있다는 점에서 안테나를 비롯한 다양한 마이크로파 회로의 특성해석에 널리 사용될 수 있는데, 정확한 수치해석 결과를 얻기 위해서 다양한 구조에 대한 흡수경계조건들의 비교와 검증이 필요하다.

• 전기학회논문지
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• 제62권11호
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• pp.1541-1543
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• 2013

This paper presents a spherical motor which can control in multi-degree of freedom operation. The spherical motor has been researched by many types of structure. Thhis paper shows a spherical shaped airgap and surfaced permanent magnets. Especially, The motor consists of dual rotor cores. Unlike a cylindrical motor, the spherical motor design can be considered with azimuth direction on spherical coordinates. Therefore the permanent magnet surfaced on the rotor need to be designed optimally in order to generate a sinusoidal magnetic flux density in the airgap. This paper presents results of optimal design for reducing torque ripple of the multi-degree of freedom spherical motor.