• 한국측량학회지
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• 제20권3호
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• pp.265-272
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• 2002

지금까지 토공량계산을 위한 많은 방법들이 단순식에서부터 복잡한 방법으로 개발되어 왔다. 일찍이 토공량계산을 위한 기본적인 방법은 상부면적을 x, y방향으로 뻗은 경계선의 사각격자로 나누어 계산한다. 그러나 이들 방법은 많은 측량현장에서 요구되는 토공량견적을 정확하게 계산할 수 없다. 1998년 Easa는 x, y 각 방향으로 같은 선상을 따라 사각격자를 나누었다. 이 방법은 격자 양방향으로 3차의 Hermite 다항식을 이용하였다. 이것은 반드시 동일한 x, y방향의 경계를 따라 표고데이터가 존재해야 하므로 지형의 최대, 최소점 같은 점의 선택을 불가능하게 한다. 이 연구에서 제시된 토공량 계산법은 Easa(1998)방법의 단점을 피하고 장점을 결합시켰다. 제안된 방법은 가로x, 세로y 방향의 각 경계를 따라 3차의 Hermite 다항식을 이용하지만 각각의 부등간격의 격자는 양방향으로 일정하지 않고 부분적으로 비격자형태로 이루어져 있다. 새롭게 제시된 방법은 다른 재래식 방법보다 더 나은 정확도를 제공한다.

• 전자공학회논문지A
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• 제30A권1호
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• pp.1-7
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• 1993

The radiation characteristics of a phased array antenna consisted of rectangular waveguides with a slant grid are investigated here. In particular, the effects of the slant angle on the radiation patterns are calculated by solving numerically the integral equation to the electric field over the waveguide aperture in view of the modal analysis. And it is found that the blindness on the radiation pattern can be moved by inserting a dielectric plug or sheath properly.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.66-72
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• 1997

Circular-to-rectangular transition ducts are used as exhaust components of high performance fighter aircraft with vectored thrust nozzles. Three-dimensional incompressible Navier-Stokes solver is used to analyze the transition duct. Cross sections of transition duct are defined by superelliptic equation. The grid system is generated by Non-Uniform Rational B-Spline, after generating surface grid by blending the cross sections. Good agreement between the results of the computational simulation and the experimental data is observed.

• 한국공간구조학회논문집
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• 제2권1호
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• pp.85-92
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• 2002

Two way grid single-layer domes are of great advantage in fabrication and construction because of the simple fact that they have only four members at each junction. But, from a point of view of mechanics, the rectangular latticed pattern gives rise to a nonuniform rigidity-distribution in the circumferential direction. If the equivalent rigidity is considered in the axial direction of members, the in-plane equivalent shearing rigidity depends only on the in-plane bending rigidity of members and its value is very small in comparison to that of the in-plane equivalent stretching rigidity. It has a tendency to decrease buckling -strength of dome considerably by external force. But it is possible to increase buckling strength by the use of roofing covering materials connected to framework. In a case like this, shearing rigidity of roofing material increases buckling strength of the overall structure and can be designed economically from the viewpoint of practice. Therefore, the purpose of this paper, in Lamella dome and rectangular latticed dome that are a set of 2-way grid dome, is to clarify the effects of roofing covering materials for increasing of buckling strength of overall dome. Analysis method is based on FEM dealing with the geometrically nonlinear deflection problems. The conclusion were given as follows: 1. In case of Lamella domes which have nearly equal rigidity in the direction of circumference, the rigidity of roofing covering materials does not have a great influence on buckling-strength, but in rectangular latticed domes that has a clear periodicity of rigidity, the value of its buckling strength has a tendency to increase considerably with increasing rigidity of roofing covering materials 2. In case of rectangular latticed domes, as rise-span-ratio increases, models which is subjected to pressure -type-uniform loading than vertical-type-uniform loading are higher in the aspects of the increasing rate of buckling- strength according to the rate of shear reinforcement rigidity, but in case of Lamella dome, the condition of loading and rise-span-ratio do not have a great influence on the increasing rate of buckling strength according to the rate of shear reinforcement rigidity.

• Ocean Systems Engineering
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• 제10권2호
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• pp.201-226
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• 2020

A systematic numerical comparative study of the performance of semicircular and rectangular submerged breakwaters interacting with solitary waves is the basis of this paper. To accomplish this task, Nwogu's extended Boussinesq model equations are employed to simulate the interaction of the wave with breakwaters. The finite difference technique has been used to discretize the spatial terms while a fourth-order predictor-corrector method is employed for time discretization in our numerical model. The proposed computational scheme uses a staggered-grid system where the first-order spatial derivatives have been discretized with fourth-order accuracy. For validation purposes, five test cases are considered and numerical results have been successfully compared with the existing analytical and experimental results. The performances of the rectangular and semicircular breakwaters have been examined in terms of the wave reflection, transmission, and dissipation coefficients (RTD coefficients) denoted by K_R, K_T, K_D. The latter coefficient K_D emerges due to the non-energy conserving K_R and K_T. Our computational results and graphical illustrations show that the rectangular breakwater has higher reflection coefficients than semicircular breakwater for a fixed crest height, but as the wave height increases, the two reflection coefficients approach each other. un the other hand, the rectangular breakwater has larger dissipation coefficients compared to that of the semicircular breakwater and the difference between them increases as the height of the crest increases. However, the transmission coefficient for the semicircular breakwater is greater than that of the rectangular breakwater and the difference in their transmission coefficients increases with the crest height. Quantitatively, for rectangular breakwaters the reflection coefficients K_R are 5-15% higher while the diffusion coefficients K_D are 3-23% higher than that for the semicircular breakwaters, respectively. The transmission coefficients K_T for rectangular breakwater shows the better performance up to 2.47% than that for the semicircular breakwaters. Based on our computational results, one may conclude that the rectangular breakwater has a better overall performance than the semicircular breakwater. Although the model equations are non-dissipative, the non-energy conserving transmission and reflection coefficients due to wave-breakwater interactions lead to dissipation type contribution.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.153-158
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• 2005

Numerical simulations of two-dimensional steady incompressible lid-driven flow in a square cavity are presented to verify the validity of a new solution code(PowerCFD) with unstructured grids. The code uses the non-staggered(collocated) grid approach which is very popular for incompressible flow analysis because of its numerical efficiency on the curvilinear or unstructured grids. Solutions are obtained for configurations with a Reynolds number as high as 10,000 with both rectangular and hybrid types of unstructured grid mesh. Interesting features of the flow are presented in detail and comparisons are made with benchmark solutions found in the literature. It is found that the code is capable of producing accurately the nature of the lid-driven cavity flow at high Reynolds numbers.

• 한국수소및신에너지학회논문집
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• 제27권5호
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• pp.547-553
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• 2016

This paper presents the effect of a grid system on the performance of a small Savonius wind turbine installed side-by-side. Turbine performance is compared using three different grid systems; tetrahedral grid having a concentrated circular grid around turbine rotors, the tetrahedral grid having a concentrated rectangular grid around turbine rotors and the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid. The commercial code, SC/Tetra has been used to solve the three-dimensional unsteady Reynolds-averaged Navier-Stokes analysis in the present study. The Savonius turbine rotor has a rotational diameter of 0.226m and an aspect ratio of 1.0. The distance between neighboring rotor tips keeps the same length of the rotor diameter. The variations of pressure and power coefficient are compared with respect to blade rotational angles and rotating frequencies of the turbine blade. Throughout the comparisons of three grid systems, it is noted that the symmetric grid having a concentrated tetrahedral grid near the turbine rotor blades and a hexahedral grid has a stable performance compared to the other ones.

• 한국항공우주학회지
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• 제39권6호
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• pp.526-534
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• 2011

위성의 부피 및 무게 절감을 위하여, 전자, 열제어 및 구조를 하나의 시스템으로 일체화 시키는 다기능 구조체가 개발되어 적용되어 왔으며, 다기능 구조체는 전자장비 중 무게가 많이 나가는 섀시/프레임들, 케이블들 및 커넥터들을 제거 할 수 있다. 이런 기존의 다기능 구조체의 주요 사항은 전기·전자의 섀시/프레임들을 개발 비용 및 시간이 많이 요구 되는 MCMs (Multi-Chip Modules)로 대체 하는 것이다. 본 논문은 위성의 부피 및 무게를 효율적으로 절감할 수 있는 새로운 다기능 구조체의 개념을 보여준다. 구조는 열제어 및 우주방사차폐 기능을 포함한 사각형 격자강화 구조체로 설계 및 제작된다. 사각형 격자강화 구조체는 등방격자구조체의 수정형으로 일반적인 인쇄회로기판을 섀시/프레임 없이 내장할 수 있는 충분한 공간을 제공한다.

• 한국대기환경학회지
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• 제16권4호
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• pp.339-350
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• 2000

The three-dimensional new corrdinate system over a single hill double hills and complex terrain with a single hill and a rectangular obstacle was generated using a body-fitted coordinate system. Control of the coordinate line distribution in the field was executed by generalizing the elliptic generating system to Poisson equation. ▽2ξ=P. The new coordinate system was well fitted to the surface boundary of single hill and double hills. But in the case of complex terrain with hill and rectangular obstacle there was smoothing tendency around the rectangular obstacle. In order to show the validity of the body-fitted coordinate system the heat diffusion equation was transformed and the temperature distribution was calculated over the various terrain. The results showed the temperature distribution was very symmetrical and stable around hills and obstacle. As a result the couple of a body-fitted coordinate system and the heat diffusion equation were executed successfully. Wind field over complex terrain with hill and rectangular obstacle which represent urban area was simulated stably in body-fitted coordinate system. The qualitative result show the enhancement of wind speed at the upwind direction of a hill and a rectangular obstacle and the recirculation zone at the downwind direction.

• 한국전산구조공학회논문집
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• 제32권3호
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• pp.183-190
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• 2019

본 논문은 균열선단 그리드 세분화기법을 소개하고 자연요소법을 이용한 균열해석에 이 기법을 적용함으로서 그 유효성을 고찰하였다. 유한요소법에 있어서의 국부적 h-세분화와 같이 높은 응력 특이성을 보이는 균열선단 주위를 따라 자연요소법 그리드를 국부적으로 세분화하였다. 본 논문에서 소개되는 그리드 세분화기법은 2단계로 구성되며, 1단계에서는 그리드 점들이 추가되고 2단계에서는 균열선단 절점을 공유하는 델라우니 삼각형들이 나뉘게 된다. 제안하는 그리드 세분화기법의 타당성과 균열해석에서의 유효성을 입증하기 위해 대칭 엣지 균열을 갖는 평면 변형률 상태의 사각 평판을 해석하였다. 수치해석 결과의 상대비교를 위해 균일한 자연요소 그리드를 이용한 균열해석도 수행하였으며, 균열선단이 세분화된 그리드는 균일한 그리드와는 달리 이론해와 조밀한 그리드와 유사한 균열선단 응력분포를 나타내었다. 또한, 총 그리드 절점수에 대한 해석결과의 전역 상대오차에서도 세분화된 그리드가 균일한 그리드에 비해 높은 수렴율 나타내었다.