• 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.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.137-140
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• 2005

Resin transfer molding (RTM) is one of the most popular processes for producing fiber reinforced polymer composites. In the manufacture of complex thick composite structures, analysis on flow front advancement on the resin impregnating the multi-layered fiber preform is helpful for the optimization of the process. In this study, three-dimensional mold filling simulation of RTM is carried out by using CVFEM (Control Volume Finite Element Method). On the assumption of isothermal flow of Newtonian fluid, Darcy’s law and continuity equation are used as governing equations. Different permeability tensors employed in each layer are obtained by experiments. Numerically predicted flow front is compared with experimental one in order to validate the numerical results. Flow simulations are conducted in the two mold geometries, rectangular plate and hollow cylinder. Permeability tensor of each layer preform in Cartesian coordinate system is transformed to cylinder coordinates system so that the flow within the multi-layered preforms of the hollow cylinder can be calculated exactly. Our emphasis is on the three dimensional flow analysis for circular three-dimensional braided preform, which shows outstanding mechanical properties such as high impact strength and toughness compared with other conventional two-dimensional laminar-structured preforms.

• Wind and Structures
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• 제26권2호
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• pp.89-98
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• 2018

For most full-scale tall buildings the Reynolds number of a flow field around a circular cylinder under strong wind is usually greater than $2{\times}10^7$, which is difficult to achieve in most wind tunnel tests. To explore the wind characteristics of tall cylindrical buildings with equidirectional grooves from subcritical to transcritical flow ($6.6{\times}10^4{\leq}Re{\leq}3.3{\times}10^5$ and $9.9{\times}10^6{\leq}Re{\leq}7.2{\times}10^7$), wind tunnel tests and full-scale large eddy simulations were carried out. The results showed that the rectangular-grooves narrow the wake width due to the downstream movement of the separation point and the deeper grooves cause smaller mean and fluctuating pressure while the peak pressure is little affected. Furthermore, the grooves lead to lower frequency of vortex shedding but the Strouhal number remains at the range from 0.15 to 0.35. The drag coefficient of the cylinders with grooves was found to be 2~3 times as large as that of smooth cylinders.

• 한국가스학회지
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• 제11권2호통권35호
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• pp.37-42
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• 2007

본 논문에서는 밸브몸체와 밸브스템 사이의 사각그루브에 설치한 두 개의 O-링에 대한 누설 안전성을 해석한 결과를 제시하고 있다. O-링시일의 누설 안전성에 대한 해석은 압축률과 LPG 가스압력의 변동에 따라 발생되는 누설 안전성을 유한요소해석 프로그램 MARC로 계산하였다. FEM 해석결과에 따르면, LP가스 충전압력 $8kg/cm^2$에서 안전변의 안전한 작동압력 상한치 $24.8kg/cm^2$에 이르기까지 압력하중을 압력용기 안전기준에 의거 계산한 결과는 안전한 것으로 나타났다. 다만, 두 개의 O-링의 안전성을 충분하게 확보하기 위해서는 O-링소재의 시효경화 효과를 고려하는 것이 바람직하다.

• 대한기계학회논문집B
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• 제40권11호
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• pp.717-726
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• 2016

본 연구는 밀폐계 내부에 고온의 원형 실린더가 존재할 때, 밀폐계의 종횡비 변화에 따른 밀폐계 내부의 3차원 자연대류 현상에 대해 수치해석을 수행하였다. 밀폐계 내부의 원형 실린더는 유한체적법(FVM)에 기초한 가상 경계법(IBM)을 사용하여 구현하였다. 본 연구에서 고려한 Rayleigh 수의 범위는 $10^5{\leq}Ra{\leq}10^6$이며, Prandtl 수는 0.7이다. 밀폐계의 폭을 변화하여 밀폐계의 종횡비를 증가시켰으며, 밀폐계의 종횡비는 $1{\leq}W/L{\leq}4$ 범위에서 1 간격으로 고려하였다. 본 연구에서 고려한 모든 Rayleigh 수와 밀폐계의 종횡비 범위에서 열유동장은 x=0 단면을 기준으로 좌우 대칭을 이루며 정상상태에 도달하였다. 또한 밀폐계의 종횡비가 증가할수록 원형 실린더의 표면 평균 Nusselt수는 증가하는 반면, 밀폐계 벽면의 표면 평균 Nusselt수는 감소하였다.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2003년도 종합학술발표회 논문집 Vol.13 No.1
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• pp.38-42
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• 2003

In this paper, a radar scattering model for forest canopies has been developed based on an empirical rough surface scattering model and the radiative transfer theory. Leaves in the forest canopy are modeled by rectangular resistive sheets, brunches and trunks are modeled by cylinder, which sizes and orientations are randomly distributed. The scattering model has been verified with the measurement data of JPL/AirSAR system.

• Tribology and Lubricants
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• 제8권2호
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• pp.73-79
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• 1992

The pressure distribution between the piston pad and the cylinder wall is analyzed to reduce the friction and to get the dynamic stability in the low friction piston. The calculated results indicate that the rectangular pad may reduce the friction in comparison to the square one. And the low friction piston can be stabilized when the pressure difference between the top and bottom of the piston skirt is very small.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제34회 추계학술대회 개최
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• pp.356-363
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• 2001

Piston seal is a device designed to prevent leakage in split connecctions or between relatively moving part. Contact force, critical pressure at which extrusion occurs, leakage rate, fluid film thickness and friction force have been analyzed for some design parameter such as clearance between cylinder wall piston, depth of rectangular groove and pressure of sealed hydraulic fluid. In this paper, we analyze displacement and stress of Wearing by finite element analysis to understand Contact Behaviour Characters.

• EDISON SW 활용 경진대회 논문집
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• 제3회(2014년)
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• pp.527-532
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• 2014

본 연구에서는 사각 실린더로 근사된 차체 주위에 균일한 층류 유동이 흐를 때, 앞 사각 실린더의 후면에 나타나는 후류의 변화를 정상적인 관점에서 분석하였다. EDISON_CFD를 이용하여 앞 실린더와 뒷 실린더의 변화에 따른 공력계수를 확인하였다. 격자 분해능과 시간 간격에 따른 정확성을 분석하였다. 앞 실린더의 길이 변화, 두 실린더 간의 거리를 통해 나타나는 공력계수의 변화를 실제 상황에서의 운행 안정성 및 공기 저항에 대입하여 분석하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1987년도 전기.전자공학 학술대회 논문집(I)
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• pp.13-17
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• 1987

Electromagnetic wave scattering from the two-dimensional scatterer was calculated by the Boundary Element Method (BEM). For the circular cylindrical scatterer, the BEM solutions agreed very well with the analytic solutions. The rectangular dielectric cylinder was also treated in the case of the lossy scatterer and the lossy medium.