• 전자공학회논문지B
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• 제31B권2호
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• pp.69-79
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• 1994

The conventional machine vision system which has uniform rectangular grid requires tremendous amount of computation for processing and analysing an image especially in 2-D image transfermations such as scaling, rotation and 3-D reconvery problem typical in robot application environment. In this study, the imaging system with nonuiformly distributed image sensors simulating human visual system, referred to as Ploar Exponential Grid(PEG), is compared with the existing conventional uniform rectangular grid system in terms of image resolution and computational complexity. By mimicking the geometric structure of the PEG sensor cell, we obtained PEG-like images using computer simulation. With the images obtained from the simulation, image resolution of the two systems are compared and some basic image processing tasks such as image scaling and rotation are implemented based on the PEG sensor system to examine its performance. Furthermore Fourier transform of PEG image is described and implemented in image analysis point of view. Also, the range and heading-angle measurement errors usually encountered in 3-D coordinates recovery with stereo camera system are claculated based on the PEG sensor system and compared with those obtained from the uniform rectangular grid system. In fact, the PEC imaging system not only reduces the computational requirements but also has scale and rotational invariance property in Fourier spectrum. Hence the PEG system has more suitable image coordinate system for image scaling, rotation, and image recognition problem. The range and heading-angle measurement errors with PEG system are less than those of uniform rectangular rectangular grid system in practical measurement range.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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• pp.824-828
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• 2000

Prior to the downloading of the NC codes to a machining center, the NC tool-path can be verified in a computer. The Z-map is one of the tools for the verification of NC tool-path. The Z-map is a two dimensional array in which the height values of the Z-axis direction vectors are stored. The Z-axis direction vectors are arranged in a rectangular grid pattern on the XY plane. The accuracy of the simulation comes from the grid interval. In the rectangular Z-map, the distances between the grid points are different. The distance in diagonal direction is larger than those in X or Y axis directions. For the rendering of the Z-map, a rectangular grid is divided into two triangular facets. Depending on the selection of a diagonal, there are two different cases. In this paper, triangular Z-map, in which the Z-axis direction vectors are arranged in a triangular grid pattern on XY plane, is proposed. In the triangular Z-map, the distances between grid points are equal. There is no ambiguity to make triangular facets for the rendering.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1998년도 추계 학술대회논문집
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• pp.55-61
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• 1998

The purpose of this study is to compare the predictive behaviors of the extended $k-{\varepsilon}$ turbulence model and the standard $k-{\varepsilon}$ turbulence model. Grid dependency is tested with the H-type grid and the O-type grid. Computations have been performed for a circular-to-rectangular transition duct. Numerical results for several sections along the streamwise have been obtained to compare with experimental results. The Reynolds number is 390,000 based on the bulk velocity at the inlet. The computed axial velocity contours, transverse velocity profiles, static pressure contours, peripheral skin friction coefficient, and peripheral wall static pressure distributions have been compared with experimental results. The computed results obtained with the extended $k-{\varepsilon}$ turbulence model show better agreement with experimental results than those obtained with the standard $k-{\varepsilon}$ turbulence model. Comparing to the computed results obtained with the H-type grid and O-type grid, those with H-type grid agree well with experimental results.

• 한국전산유체공학회지
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• 제3권2호
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• pp.9-16
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• 1998

Predictive behaviors by the extended k-${\varepsilon}$ turbulence model and the standard k-${\varepsilon}$ turbulence model are compared. Grid dependency is tested with the H-type grid as well as the O-type grid. Computations have been performed on a circular-to-rectangular transition duct. The Reynolds number is 390,000 based on the bulk velocity at the inlet. The computed axial velocity contours, transverse velocity profiles, static pressure contours, peripheral skin friction coefficient, peripheral wall static pressure distributions and turbulence kinetic energy have been compared with experimental results. The computed results than those obtained with the standard k-${\varepsilon}$ turbulence model. Comparing to the computed results obtained with the H-type grid and O-type grid, those with H-type grid seem to agree well with experimental results.

• 한국음향학회지
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• 제14권1호
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• pp.115-122
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• 1995

균일한 소자 (안테나 또는 감지기) 간격으로 계수치를 체감하는 것보다 균일한 계수치로 소자의 간격을 체감하는 것이 실용적이며, 직사각형 어레이에서는, 삼각형 격자 구조가 직사각형 격자구조 보다 소자 수를 줄이는데 더 경제적이다. 접지판 위에 설치된 삼각형 격자 구조를 가진 직사각형 위상어레이의 성능을 향상시키기 위하여 소자간격 체감 방법을 제안하였다. 소자간격 체감이 주빔(main beam)의 폭과 측면로브(sidelobe)의 높이에 미치는 영향을 논의하였다. 제안된 방법을 사용한 결과 측면로브의 성능이 향상되었으나 주빔폭은 약간 넓어지는 것이 밝혀졌다.

• 한국해안해양공학회지
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• 제15권3호
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• pp.190-195
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• 2003

연안 및 해안에서 발생하는 파랑변형, 조석 전파, 부유사 이동 및 확산 현상 등을 예측하기 위해서는 수치모형이 주로 사용된다 대표적인 수치모형 기법으로는 유한차분법 및 유한요소법이 있다. 유한차분법을 사용하는 경우에는 관심영역의 각 격자점에서 유한차분 방정식을 풀어야하므로, 격자망 및 경계조건 등이 설정되어야 한다. 유한차분용 격자망은 유한요소법과는 달리 격자망이 간단하지만, 지형이 복잡한 경우에 편리하게 사용 할 수 있는 격자정보 생성기법이 별로 개발되어 있지 않다. 또한, 상업용으로 많이 개발되어 있는 프로그램도 대부분 유한요소법에 근거한 수치모형에서 사용하는 격자생성을 목적으로 하고 있다. 본 연구에서는 디지타이저(Summagrid IV 기종)를 사용하여 유한차분모형을 위한 동일한 간격의 직사각형 격자 수심자료를 만드는 세부과정을 자료로 소개하고자 한다. 필요한 프로그램은 Golden Software사의 Didger(dititiger 지원 S/W)와 Surfer(gridding & contouring S/W)로서, 비교적 간단하게 정확한 수심 자료를 얻을 수 있으며, 임의의 지점 떠는 영역에 제시된 정보로부터 필요한 직사각형 격자정보를 추출하는 방법에 적용이 가능하다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.36-37
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• 2003

Three-dimensional numerical analysis of the flow around rectangular cylinders with various side ratios, D/H, from 0.2 to 2.0 is carried out for Reynolds number of 1000 by using multi-directional finite difference method in multi-grid. The predicted results are well compared with the experimental data. It is found that fluid dynamics characteristics alternate between high pressure mode. and low pressure mode of the base pressure for rectangular cylinder of D/H=0.2-0.6.

• Journal of Advanced Marine Engineering and Technology
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• 제26권4호
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• pp.485-492
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• 2002

The present study is aimed to reveal macroscopic aerodynamic characteristics of two-dimensional rectangular prisms with three aspect ratios(D/H=1, 2 and 3) and six angles of attack($0^{circ}, 10^{circ}, 13.5^{circ}, 20^{circ}, 30^{circ} and 45^{\circ}$). The Reynolds number is fixed as $1\times10^4$. The SOLA-based revised finite difference method for the conservation form on irregular grid was adopted as a new numerical method. Instantaneous flow patterns at $45^{\circ}$ in case of D/H=2 and D/H=3 show larger asymmetric wake development which is closely related to the sharp decrease of drag coefficients at higher angles of attack range. Vorticity propagation into enlarged wake region is conjectured to be responsible for this phenomenon. The Strouhal number is found to be sensitive to the angle of attack at higher aspect ratios(D/H=2 and 3).

• 한국정보통신학회논문지
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• 제9권2호
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• pp.415-421
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• 2005

어레이 소자의 방사 또는 수신 특성은 소자 상호결합 효과 때문에 고립된 소자의 특성과 달라지게 되며, 따라서 어레이 성능은 고립된 소자를 가정하여 설계할 경우의 성능과 다르게 된다. 접지판 위에 위치한 삼각형 격자 구조를 가진 직사각형 다이폴 어레이에 미치는 상호 결합의 영향을 소자패턴을 고려하여 논의하였다. 소자 이득 함수를 이용하여 소자가 균일하게 분포되거나 소자간격이 체감된 어레이에서 부엽(sidelobe)에 미치는 소자 상호결합 효과의 영향을 점검하였다. 상호결합 효과가 존재할 때, 소자간격이 체감된 어레이에서의 부엽의 성능이 소자간격이 균일하게 분포된 어레이와 비교하여 향상되는 것을 보여주었다. 컴퓨터 시뮬레이션을 제시하였다.

• Wind and Structures
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• 제34권1호
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• pp.151-159
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• 2022

The aerodynamics of blunt bodies with separation at the sharp corner of the leading edge and reattachment on the body side are particularly important in civil engineering applications. In recent years, a number of experimental and numerical studies have become available on the aerodynamics of a rectangular cylinder with chord-to-thickness ratio equal to 5 (BARC). Despite the interest in the topic, a widely accepted set of guidelines for grid generation about these blunt bodies is still missing. In this work a new, well resolved Direct Numerical Simulation (DNS) around the BARC body at Re=3000 is presented and its results compared to previous DNSs of the same case but with different numerical approaches and mesh. Despite the simulations use different numerical approaches, mesh and domain dimensions, the main discrepancies are ascribed to the different grid spacings employed. While a more rigorous analysis is envisaged, where the order of accuracy of the schemes are kept the same while grid spacings are varied alternately along each spatial direction, this represents a first attempt in the study of the influence of spatial resolution in the Direct Numerical Simulation of flows around elongated rectangular cylinders with sharp corners.