• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1997년도 추계 학술대회논문집
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• pp.131-135
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• 1997

Effect of wall curvature on flow characteristics is studied for mildly and strongly curved duct flows. The ducts are S-shaped, and the flow is partially blocked at the rear of the downstream. The presence of blockage in combination with curvature generates secondary flows on the concave surface; the magnitude of the secondary flow being dependent on the degree of wall curvature. Objectives are to compare the flow structures for mild and strong cases and to illuminate the changes in flow structure as the flow turns. Sensitivity on numerical solutions due to different inflow boundary conditions is also examined.

• 한국인터넷방송통신학회논문지
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• 제16권6호
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• pp.239-242
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• 2016

본 논문에서는 이중 곡률을 갖는 오목 렌즈를 제안하였다. 이중 곡률 렌즈는 HDPE (High Density Polyethylene)를 이용하여 제작하였다. 이중 곡률 렌즈는 두 개의 오목 구조로 구성되었다. 두 개의 오목 구조의 역할은 빔을 균일하게 넓게 보내기 위함이다. 작은 오목 구조는 큰 오목 구조 보다 더 큰 곡률 반경을 갖는다. 이러한 이중 곡률 렌즈는 밀리미터파 이미징 시스템에 적용 가능하다. 제작된 이중 곡률 렌즈를 250 GHz VDI 소스를 이용하여 검증하였다. 광학 시뮬레이션 툴인 ZEMAX를 이용하여 설계하고 제작된 렌즈는 균일한 빔과 확장 성능을 충분히 수행함을 확인하였다.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2005년도 학술발표회(1)
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• pp.581-582
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• 2005

• 한국전산유체공학회지
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• 제7권1호
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• pp.28-35
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• 2002

The effect of concave curvature on the natural convection has been numerically studied using the higher-order finite difference method. The heating wall in a enclosure is approximated by a cosine function. The heat transfer coefficient is analyzed for three Rayleigh numbers and five amplitudes. For Ra = 10/sup 8/ the separation and reattachment are observed on the adiabatic walls. The wall heat transfer are slightly changed by the increasing curvatures.

• International Journal of Fluid Machinery and Systems
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• 제1권1호
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• pp.10-23
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• 2008

The development of pre-set wavelength G$\ddot{o}$rtler vortices are studied in the boundary-layer flows on concave surfaces of 1.0 and 2.0 m radius of curvature. The wavelengths of the vortices were pre-set by thin wires of 0.2 mm diameter placed 10 mm upstream and perpendicular to the concave surface leading edge. Velocity contours were obtained from velocity measurements using a single hot-wire anemometer probe. The most amplified or dominant wavelength is found to be 15 mm for free-stream velocity of 2.1 m/s and 3.0 m/s on the concave surface of R = 1 m and 2 m, respectively. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on the growth rate of the vortices. The occurrence of a secondary instability mode is also shown in the form of mushroom-like structures as a consequence of the non-linear growth of the G$\ddot{o}$rtler vortices. By pre-setting the vortex wavelength to be much larger and much smaller than the most amplified one, the splitting and merging of G$\ddot{o}$rtler vortices can be respectively observed.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2000년도 사면안정 학술발표회
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• pp.213-220
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• 2000

Numerical modeling of cut slope has some limits in simulating the real slopes. In the case of 2D analysis of slope stability, it is assumed that slope is simply straight even when it is concave or convex in plan view. In this study, 3D analysis in curved shape slopes has been conducted for the comparison with 2D analysis in terms of failure mode and factor of safety. For this, 3D analysis by FLAC3D was compared with 2D analysis in plane strain condition and axi-symmetric model condition by FLAC. It was also observed how safety factors of slopes were affected by the variation of the tensile strength and cohesion, which are important variables to decide whether the slope fails or not. 2D analysis of concave slopes under plane strain condition showed much smaller safety factors by 16-40 % errors depending on the radius of curvature of slopes, compared to the more realistic values from 3D analysis. In case of convex slopes, the lower values by 7-10 % has been reported. 2D analysis of axi-symmetric model showed also smaller safety factors by 6-10 % and by 2-4 %, in case of concave and convex slopes, respectively. Such results are expected to contribute to the better understanding of failure process and could be applied for improved design of slopes.

• 소성∙가공
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• 제17권7호
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• pp.491-495
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• 2008

Incremental forming path to manufacture a thick concave steel plate using the line array roll set is designed. To find the optimum forming path, the forming processes are simulated by the finite element method. A general-purpose commercial software, MSC MARC is used. A modeling with 8-node hexahedral elastic-plastic solid is performed to predict accurate springback and the analysis process was composed of 18 passes. The proposed forming paths are verified through experiments carried out in the prototype line array roll set. It is found that the process can be successfully applied to the fabrication of the dual curvature ship hull plate.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 춘계학술대회 논문집
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• pp.361-364
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• 2008

Incremental forming path to manufacture a thick concave steel plate using the line array roll set is designed. To find the optimum forming path, the forming processes are simulated by the finite element method. A general-purpose commercial software, MSC.MARC is used. The rolls are modeled as rigid surfaces and the thick plate is modeled as 8-node hexahedral elastic-plastic solid elements to predict accurate springback. It is found that the process can be successfully applied to the fabrication of the dual curvature ship hull plate

• 한국통신학회논문지
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• 제14권2호
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• pp.121-136
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• 1989

圓筒形 物體의 오목면과 블록면의 表面에 密着하여 設置한 마이크로스트립 어레이 안테나의 輻射 特性에 관하여 理論的 解析을 試圖하였으며, 實驗을 통하여 檢證하였다. 單一素子 안테나의 解析은 傳送線路 모델法을 適用하였고, 어레이 안테나의 理論은 曲面 위에 2次元的으로 配列된 각각의 單一素子에 대하여 座標移動과 回轉을 考慮한 座標變換法으로 解析하여 遠距離에서의 合成 電界 强度를 數値計算으로 구하였으며, 10GHz에서 4素子 竝列 어레이 안테나 및 마이크로스트립 給電線路를 設計 製作하여 여러 가지 曲率半徑에 대하여 反射損失, 共振周波數, 輻射패턴, 半 電力 비임幅, 利得 등과 같은 諸 輻射特性을 測定하겨 理論値와 比較 考察하였다. 理論에서 豫測한 바와 같이 오목면과 블록면에서 모두 曲率半徑의 減少에 따라 輻射 패턴의 비임 폭이 더 커지는 것을 確認하였으며, 曲面에서 座標變換法으로 計算한 마이크로스트립 竝列 어레이 안테나의 合成 輻射電力 패턴이 測定値와 잘 一致하였다. 아울러 曲率半徑의 變化에 따른 周波數의 變化, 入力 임피던스 및 利得의 變化는 無視할 수 있을 程度임을 確認하였다.

• 대한기계학회논문집
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• 제19권3호
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• pp.846-857
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• 1995

An experimental study is made of turbulent shear flows in a nearly two-dimensional 90.deg. curved duct by using the hot-wire anemometer. The Reynolds normal and shear stresses, triple velocity products, integral length scales, Taylor micro length scales and dissipation length scales are measured and analyzed. For a positive shear at the inlet, the afore-mentioned turbulence quantities are all suppressed. However, when the inlet shear flow is negative, they are augmented, i.e., the convex curvature suppresses the turbulence whereas the concave curvature augments it. It is found that the curvature effects are rather sensitive to the triple velocity products than the Reynolds stresses. The evolution of turbulence under the curvature with the different shear conditions is well described by the modified curvature parameter S' and the non-dimensional development time ${\tau}$.'