• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.82.1-82.1
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• 2011

We present a new code for solving non-LTE radiative transfer problems in a general grid (RIG). RIG develops from RATRAN code (Hogerheijde & van der Tak 2000) using the Accelerated Monte-Carlo method, and it can cope with line overlap effect among multiple molecular and atomic species. In this algorithm we make grids in arbitrary coordinates adequate to the problem, but, on the other hand, photons propagate in the Cartesian coordinates. For spherical, cylindrical and other well defined coordinate, the problem of tracing photon's path reduces to solving simple quadratic equations. For example, the outflow in the star formation have high dynamic range in scales from a few AU to ~ 0.1 pc and have also cylindrical symmetry. So, we have used (r, ${\alpha}$) coordinate system, where r is the distance from the origin and ${\alpha}$ is z/ R2 in the cylindrical coordinate of (R,z). The (r, ${\alpha}$) coordinate realizes the density - power function of r - and temperature distributions of the problems with smaller numbers of grid than the cylindrical coordinate does, and the former consumes less time to solve the problems than the latter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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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.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.1
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• pp.98-108
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• 2004

This study concerns a large eddy simulation (LES) of turbulent flow around a bluff body inside a sudden expansion cylindrical chamber, a configuration which resembles a premixed gas turbine combustor The simulation code is constructed by using the general coordinate system based on the physical contravariant velocity components. The Smagorinsky model is employed and the calculated Reynolds number is 5,000 based on the bulk velocity and the diameter of the inlet pipe. The combined grid technique and cylindrical grid are tested in the numerical simulation with complex geometry. The predicted turbulent statistics are evaluated by comparing with LDV measurement data. The numerical flow visualizations depict the behavior of turbulent mixing process behind the flame holder.

• Geophysics and Geophysical Exploration
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• v.5 no.3
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• pp.206-216
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• 2002

The finite element method (FEM), a powerful numerical modeling tool for solving various engineering problems, is frequently applied to three-dimensional (3-D) modeling thanks to its capability of discretizing and simulating the shape of model with finite number of elements. Considering the accuracy of the solution and computing time in modeling of engineering problems, it is preferable to construct physical continuity and simplify mesh system. Although there exist systematic mesh generation systems for arbitrary shaped model, it is hard to model a simple cylinder in terms of 3-D coordinate system especially in the vicinity of the central axis. In this study I adopt cylindrical coordinate system for modeling the 3-D model space and define the origin of the coordinates with mathematically clear coordinate transformation. Since we can simulate the whole space with hexahedral elements, the cylindrical coordinate system is effective in handling the 3-D model structure. The 3-D do resistivity modeling scheme developed in this study provides basie principle for borehole-to-surface resistivity survey, which can be a useful tool for the application to environmental problem.

• Progress in Superconductivity and Cryogenics
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• v.18 no.2
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• pp.30-36
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• 2016

For the magnetic field analysis or design, it is important to know the behavior of the magnetic field in an interesting space. Magnetic field mapping becomes a useful tool for the study of magnetic field. In this paper, a numerical way for mapping the magnetic field within the cylindrical center volume of magnet is presented, based on the solution of the Laplace's equation in the cylindrical coordinate system. The expression of the magnetic field can be obtained by the magnetic flux density, which measured in the mapped volume. According to the form of the expression, the measurement points are arranged with the parallel cylindrical line (PCL) method. As example, the magnetic flux density generated by an electron cyclotron resonance ion source (ECRIS) magnet and a quadrupole magnet were mapped using the PCL method, respectively. The mapping results show the PCL arrangement method is feasible and convenience to map the magnetic field within a cylindrical center volume generated by the general magnet.

• Journal of Electrical Engineering and Technology
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• v.11 no.5
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• pp.1395-1403
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• 2016

• Proceedings of the Korea Information Processing Society Conference
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• 2023.05a
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• pp.735-737
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• 2023

본 논문에서는 대퇴골의 3D 메쉬 모델에 대해 원통형 좌표계(cylindrical coordinate system)를 생성하는 방법을 제안한다. 원통형 좌표계는 대퇴골 메쉬의 방향에 따라 장축 및 단축을 결정한 뒤, 대퇴골을 포함하는 원통(right circular cylinder)을 계산하여 생성된다. 실험을 통해, 생성된 원통형 좌표계에서 균일하게 생성한 삼각형 메쉬(triangular mesh)를 대퇴골 메쉬에 투사한 결과를 보인다.

• Journal of KIISE
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• v.43 no.5
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• pp.562-568
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• 2016

Point cloud data can be expressed in a specific coordinate system of a data set with a large number of points, to represent any form that generally has different characteristics in the three-dimensional coordinate space. This paper is aimed at finding a cylindrical pipe in the point cloud of the three-dimensional coordinate system using RANSAC, which is faster than the conventional Hough Transform method. In this study, the proposed cylindrical pipe is estimated by combining the results of parameters based on two mathematical models. The two kinds of mathematical models include a sphere and line, searching the sphere center point and radius in the cylinder, and detecting the cylinder with straightening of center. This method can match cylindrical pipe with relative accuracy; furthermore, the process is rapid except for normal estimation and segmentation. Quick cylinders matching could benefit from laser scanning and reverse engineering construction sectors that require pipe real-time estimates.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.34 no.2
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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.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.4
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• pp.484-490
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• 2012

This paper is devoted to investigate the feasibility of using a medium power ground-based laser to produce a torque on LEO satellites of various shapes. The laser intensity delivered to a satellite is calculated using a simple model of laser propagation in which a standard atmospheric condition and linear atmospheric interaction mechanism is assumed. The laser force is formulated using a geocentric equatorial system in which the Earth is an oblate spheroid. The torque is formulated for a cylindrical satellite, spherical satellites and for satellites of complex shape. The torque algorithm is implemented for some sun synchronous low Earth orbit cubesats. Based on satellites perigee height, the results demonstrate that laser torque affecting on a cubesat has a maximum value in the order of $10^{-9}$ which is comparable with that of solar radiation. However, it has a minimum value in the order of $10^{-10}$ which is comparable with that of gravity gradient. Moreover, the results clarify the dependency of the laser torque on the orbital eccentricity. As the orbit becomes more circular it will experience less torque. So, we can conclude that the ground based laser torque has a significant contribution on the low Earth orbit cubesats. It can be adjusted to obtain the required control torque and it can be used as an active attitude control system for cubesats.