• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.3
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• pp.177-182
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• 2007

The effects of three fuselage head shapes and nonplanar ground surface on the aerodynamic characteristics of FAST fuselages are investigated using a boundary element method. Wind tunnel test is also performed to validate the present method and to identify the wall effect on the frictional drag which cannot be analyzed using the present method. It is found that the channel has an effect of increasing the lift of those investigated fuselages. The optimal head shape depends on the design conditions of the FAST and its guideway channel. Comparing the calculated induced drag with the measured total drag, it can be concluded that the profile drag is independent of the ground height. Thus, the present numerical method can be applied to the conceptual design of the high-speed ground transporters if only the profile drag of the vehicle in free flight is assumed to be known.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.2
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• pp.39-45
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• 2002

The effect of reefing-line length and reefing methods on drag and inflated shape of the conical ribbon parachute were experimentally investigated. Tests were performed to determine reefing-line length of the parachute models, demonstrate aerodynamic adequacy of the reefing method, and confirmed that performance met the design requirement. The reefing ratio, drag-area ratio, was decreased in relation to the decrease in the length of the reefing-line and the stability of the parachute models was increased with reefing. The test results were compared with the avilable similar data. Fair to good agreement was obtained.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.747-752
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• 2003

Many clinical studies have suggested that the blood flow in ideal geometry is involved in the development of atherosclerosis. This study simulated blood flow in the abdominal artery with real geometry to investigate MWSS(mean wall shear stress), AWSS(amplitude of wall shear stress) and OSI(oscillator shear index). The calculation grid for the real geometry was constructed by extracting the surface of arterial wall from CT(Computed Tomography) or MRI(Magnetic Resonance Imaging) sheets called as DICOM (Digital Imaging and Communications in Medicines). The calculated MWSS, AWSS and OSI are much different from those of ideal geometry calculation. The MWSS increased while the AWSS decreased. Many shear forces are related to shapes of gradient. This paper will give clinical datum where the MWSS, AWSS and OSI are strong or weak. The hemodynamic analysis based on real geometry can provide surgeons with more reliable information about the effect of blood flow.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.89-93
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• 2008

The effect of pintle shapes and position to the thrust performance of Solid Rocket Motor was studied by experimental-aided Computational Fluid Dynamic(CFD). Among the turbulent models for RANS in Fluent, Spalart-Allmaras model was better agreement with the nozzle wall pressure distribution attained by cold-flow test than other models. When nozzle throat area was decreased, magnitude of thrust was increased. The bigger pintle size was, the more thrust of pintle tip pressure was obtained. Meanwhile the more thrust of nozzle and chamber pressure decreased. Hence, total thrust of big pintle was less than a small pintle under same throat area condition.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2476-2481
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• 2007

An inverse radiation analysis is presented for the estimation of the wall emissivities for an absorbing, emitting, and scattering media with diffusely emitting and reflecting opaque boundaries. In this study, a repulsive particle swarm optimization(RPSO) algorithm which is a relatively recent heuristic search method is proposed as an effective method for improving the search efficiency for unknown parameters. To verify the performance of the proposed RPSO algorithm, it is compared with a basic particle swarm optimization(PSO) algorithm and a hybrid genetic algorithm(HGA) for the inverse radiation problem with estimating the wall emissivities in a two-dimensional irregular medium when the measured temperatures are given at only four data positions. A finite-volume method is applied to solve the radiative transfer equation of a direct problem to obtain measured temperatures.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.3467-3472
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• 2007

The effects of the wall geometry on the spray-wall impingement process of a hollow-cone fuel spray emerging from a high-pressure swirl injector of the Gasoline Direct Injection (GDI) engine were investigated by means of a numerical method. The ized Instability Sheet Atomization (LISA) & Aerodynamically Progressed Taylor Analogy Breakup (APTAB) model for spray atomization process and the Gosman model were applied to model the atomization and wall impingement process of the spray. The calculation results of spray characteristics, such as a spray development process and a radial distance after wall impingement, compared with the experimental ones by the Laser Induced Exciplex Fluorescence (LIEF) technique. It was found that the radial distance of the cavity angle of 90$^{circ]$ after wall impingement was the shortest and the ring shaped vortex was generated near the wall after spray-wall impingement process.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.10
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• pp.1516-1523
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• 2003

An inverse radiation analysis is presented for the estimation of the boundary emissivities for an absorbing, emitting, and scattering media with diffusely emitting and reflecting opaque boundaries. The finite-volume method is employed to solve the radiative transfer equation for a two-dimensional irregular geometry. A hybrid genetic algorithm is proposed for improving the efficiency of the genetic algorithm and reducing the effects of genetic parameters on the performance of the genetic algorithm. After verifying the performance of the proposed hybrid genetic algorithm, it is applied to inverse radiation analysis in estimating the wall emissivities in a two-dimensional irregular medium when the measured temperatures are given at only four data positions. The effect of measurement errors on the estimation accuracy is examined.

• Proceedings of the Acoustical Society of Korea Conference
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• 1993.06a
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• pp.3-5
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• 1993

실내 음향특성의 컴퓨터 씨뮬레이션 기법은 모형실험 기법과 더불어 건축물의 음향설계 분야에서 널리 사용되는 도구이다. 본 연구에서는 건축물의 음향특성을 설계단계에 예측하기 위해 영상법에 기초한 실내음향 해석 소프트웨어를 개발하였다. 개발된 소프트웨어는 건축물의 3차원 형상모델, 벽면등 반사체의 흡음특성, 음원과 수음점의 위치 등의 데이터를 입력하면, 음선의 전파경로, 수음위치에서의 반사음 패턴, 실내 음향 특성의 평가척 (음의 명료도, 잔향시간 등)을 산출하여 출력하는 기능을 지니고 있다. 기존의 씨뮬레이션 기법이 소요 장비나 비용, 시간적 제약으로 널리 실용화되기 어려웠던 점을 고려하여 PC급에서 간편하게 활용할 수 있도록 개발하였고 음선 전차경로의 그래픽 표현, 반사음 패턴의 분석등, 건축물의 음향 설계를 위한 기능을 부여하는데 중점을 두었다.

• Transactions of the Korean Society of Mechanical Engineers
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• v.6 no.2
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• pp.147-159
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• 1982

내부에 정방형, 외부에 원형인 두 정온동심수평관으로 이루어진 폐쇄공간에서 열부력으로 야기된 대류열전달 현상을 연구하였다. 주어진 비정규적 형상에서의 층류 정상 Boussinesq 유동을 해 석하기 위하여, 지구중력방향에 대하여 가능한 두 개의 대칭형 위치에 관하여, Galerkin 유한요 소법을 사용하였다. 이론의 결과를 확증하기 위하여 실험적으로도 온도측정과 유선의 가시화를 수행하였다. 정방형내관의 직각인 선단은 국소 및 총체열전달에 있어서 소극적인 역할을 하지만, 이들로 인한 경계층 유동의 박리는 발생하지 아니함을 보였다. 이 내관의 상부 수평면상에서는 유동속도와 온도구배가 낮기는 하나 확연한 대칭형의 열상승류(Plume)가 가능하였다. 내관의 벽면들이 지구중력방향에 관하여 .+-.45.deg.의 각을 이룰 경우 과류의 중심부가, Rayleigh수가 6.5*$10^{4}$보다 작을 때는 4개, 이보다 클때는 2개가 폐쇄공간 안에서 발생하였다.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1996.10b
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• pp.181-189
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• 1996

회전열파이크는 전기모터, 고온가스터빈 등의 냉각에 이용함으로써 성능개선을 얻을 수 있다는 점에서 지난 20년 동안 많은 연구가 이루어져왔다. 그동안 내부벽면형상개발은 Taper를 설치하거나, 계단식 단면변화 또는 Impeller설치와 같은 기술들이 연구되었다. 본 연구는 회전 열파이프 용기내벽에 Coil Insert를 설치하여 응축액막 유동효과에 대한 가시화실험 및 열전달 성능실험을 통하여 그 특성을 검토하였고 아래와 같은 결과를 얻을 수 있었다. 1) Pool 영역에서는 Coil Insert에 의한 축방향 펌프효과가 매우 크며, 그 효과는 나선각이 클수록 크게 나타난다. 2) Coil Insert는 Pool에서 환상류로 천이를 촉진시키며, 나선각이 클수록 그 효과가 크게 나타난다. 3) Coil insert 열파이프의 열저항에 미치는 효과는 크지 않은 것으로 보인다. 4) Coil Insert에 의해 Dry-out한계의 증가가 예상되지만, 실험장치의 열부하한계에 의해 확인할 수 없었다.