• 대한조선학회논문집
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• 제53권4호
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• pp.300-306
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• 2016

The gas ventilated by supercavitation splits into smaller bubbles and follows the water passage of the cavitation tunnel. The bubbles quickly return to the test section by rather high speed flow, and interrupt the observation of the supercavitation. To secure clear observation in the test section, the bubble collecting section(settling chamber) of large volume is prepared to collect bubbles in the water passage ahead of the test section. The bubble collecting section should provide enough buoyancy effect to the bubbles for proper bubble collecting. However, rather high-speed oncoming flow produces non-uniform velocity distribution and deteriorates buoyancy effect in the bubble collecting section. In the present study, the bubble collecting space and three porous plates are designed and analyzed through numerical methods, and the bubble collecting function is experimentally validated by 1/10-scaled model in terms of the formation of uniformly low velocity distribution in the bubble collecting section.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2010년도 춘계학술대회 논문집
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• pp.133-138
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• 2010

This paper describes on aerodynamic characteristics of pantograph system for Next generation high speed train(HEMU-400). The pantograph which supports electric power is located on the roof. Because of this, it generate high drag, severe acoustic noise and vibration which induced unstable flow due to complex configuration. Therefore, the design of high efficient pantograph needs to increase operational speed. In this research, wind tunnel tests were performed to design a high efficient pantograph system using 1/4 scaled model which were KTX-II pantograph, single arm pantograph and periscope type pantograph with square cylinder shape panhead and optimized shape panhead. For real operational condition, flow directions were adapted by rotation of pantograph. From this results of wind tunnel, it is checked that the pantograph with optimized panhead and single arm type or periscope type has better aerodynamic performance. In addition, lift control device and spoiler in pantograph were tested to investigate the validity of application.

• Wind and Structures
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• 제31권4호
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• pp.351-362
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• 2020

In this study, the impact of roof slope on the flow characteristics over low-sloped gable roofs was investigated using steady computational fluid dynamics (CFD) simulations based on a k-ω SST turbulence model. A measurement database of the flow field over a scaled model of 15° was created using particle image velocimetry (PIV). Sensitivity analyses for the grid resolutions and turbulence models were performed. Among the three common Reynolds-averaged Navier-Stokes equations (RANS) models, the k-ω SST model exhibited a better performance, followed by the RNG model and then the realizable k-ε model. Next, the flow properties over the differently sloped (0° to 25°) building models were determined. It was found that the effect of roof slope on the flow characteristics was identified by changing the position and size of the separation bubbles, 15° was found to be approximately the sensitive slope at which the distribution of the separation bubbles changed significantly. Additionally, it is suggested additional attention focused on the distributions of the negative pressure on the windward surfaces (especially 5° and 10° roofs) and the possible snow redistribution on the leeward surfaces.

• Wind and Structures
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• 제22권2호
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• pp.161-184
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• 2016

Long-span suspension bridges have evolved through the years and with them, the bridge girder decks improved as well, changing their shapes from standard box-deck girders to twin box and multi-box decks sections. The aerodynamic characteristics of the new generation of twin and multiple-decks are investigated nowadays, to provide the best design wind speeds and the optimum dimensions such bridges could achieve. The multi-box Megane bridge deck is one of the new generation bridge decks, consisting of two side decks for traffic lanes and two middle decks for railways, linked between them with connecting beams. Three-dimensional CFD simulations were performed by employing the Large Eddy Simulation (LES) algorithm with a standard Smagorinsky subgrid-scale model, for $Re=9.3{\times}10^7$ and angles of attack ${\alpha}=-4^{\circ}$, $-2^{\circ}$, $0^{\circ}$, $2^{\circ}$ and $4^{\circ}$. Also, a wind tunnel experiment was performed for a scaled model, 1:80 of the Megane bridge deck section, for $Re=5.1{\times}10^5$ and the aerodynamic static coefficients were found to be in good agreement with the results obtained from the CFD-LES model. However the aerodynamic coefficients determined individually, from the CFD-LES model, for each of the traffic and railway decks of the Megane bridge, varied significantly, especially for the downstream traffic deck. Also the pressure distribution and the effect of the spacing between the connecting beams, on the wind speed profiles showed a slight increase in turbulence above the downstream traffic and railway decks.

• Journal of Advanced Marine Engineering and Technology
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• 제35권5호
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• pp.608-615
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• 2011

The objective of this study is to investigate the flow characteristics of polluted air behavior in rectangular tunnels using a PIV system and a commercial CFD program. The PIV experiments are simulated by using the olive oil as the tracer particles in scaled rectangular tunnels. Each model has one of four different outlet vents, each dimensionless L/H ratio of which is 0, 0.375, 0.75 and 1.125, respectively as the locations of each outlet are away from the vertical centerline through the inlet. A commercial CFD program, ANSYS CFX, was used to examine the velocity fields and the pressure distributions in numerical simulations. The kinematic viscosity of the air flow of $1.51{\times}10^{-5}m^2/s$ and the flow velocity of 0.3 m/s at the inlet are given under the same conditions in order to analyze the polluted air flow characteristics experimentally and computationally. This study is considered to examine the effect of the outlet locations in the naturally ventilated tunnel models.

• 오토저널
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• 제6권4호
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• pp.54-61
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• 1984

Numerical calculation of the flow field past a passenger car was carried out by using a panel method with a small computer of 5Mbyte memory size. The shape of car body was simplified and reconstructed by 2180 panels on which a constant strength sink (or source) was distributed. The separation of flow from the surface and the wake flow were not considered in the calculation because of the computer memory limitation. All of the results of calculation were presented by using a 3-dimensional computer graphics. In spite of small memory size of computer, generally good agreements were obtained, except the separated region, from the comparison of pressure distribution between numerical analysis and wind tunnel experiment with 1/5 scaled model.

• Wind and Structures
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• 제17권6호
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• pp.629-646
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• 2013

One of the most common solutions adopted to reduce vibrations of skyscrapers due to wind or earthquake action is to add external damping devices to these structures, such as a TMD (Tuned Mass Damper) or TLCD (Tuned Liquid Column Damper). It is well known that a TLCD device introduces on the structure a nonlinear damping force whose effect decreases when the amplitude of its motion increases. The main objective of this paper is to describe a Hardware-in-the-Loop test able to validate the effectiveness of the TLCD by simulating the real behavior of a tower subjected to the combined action of wind and a TLCD, considering also the nonlinear effects associated with the damping device behavior. Within this test procedure a scaled TLCD physical model represents the hardware component while the building dynamics are reproduced using a numerical model based on a modal approach. Thanks to the Politecnico di Milano wind tunnel, wind forces acting on the building were calculated from the pressure distributions measured on a scale model. In addition, in the first part of the paper, a new method for evaluating the dissipating characteristics of a TLCD based on an energy approach is presented. This new methodology allows direct linking of the TLCD to be directly linked to the increased damping acting on the structure, facilitating the preliminary design of these devices.

• Wind and Structures
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• 제29권3호
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• pp.177-194
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• 2019

While establishing adequate load paths in the light-frame wood structures is critical to maintain the overall structural integrity and avoid significant damage under extreme wind events, the understanding of the load paths is limited by the high redundant nature of this building type. The objective of the current study is to evaluate the system effects and investigate the load paths in the wood structures especially the older buildings for a better performance assessment of the existing building stock under high winds, which will provide guidance for building constructions in the future. This is done by developing building models with configurations that are suspicious to induce failure per post damage reconnaissance. The effect of each configuration to the structural integrity is evaluated by the first failure wind speed, amajor indicator beyond the linear to the nonlinear range. A 3D finite-element (FE) building model is adopted as a control case that is modeled using a validated methodology in a highly-detailed fashion where the nonlinearity of connections is explicitly simulated. This model is then altered systematically to analyze the effects of configuration variations in the model such as the gable end sheathing continuity and the gable end truss stiffness, etc. The resolution of the wind loads from scaled wind tunnel tests is also discussed by comparing the effects to wind loads derived from large-scale wind tests.

• 한국항공우주학회지
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• 제41권9호
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• pp.714-719
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• 2013

본 연구 대상 터보 프롭 항공기는 주어진 항공기 임무 수행을 위해 결빙 조건하에서도 운용이 가능하여야 한다. 동 연구에 적용된 터보 항공기의 공기 흡입구 계통은 정상 비행조건하에서 엔진 입구에 최대 전압력을 공급할 수 있도록 설계 및 검증이 되어야 할 뿐만 아니라 결빙조건하에서 생길 수 있는 얼음과 같은 입자가 엔진 흡입구 망으로 들어가서 엔진 화염꺼짐이나 엔진에 심각한 손상을 주지 않도록 하기 위한 관성분리기를 포함하도록 개발이 되어야 한다. 따라서 결빙 조건하에서 형상이 변하는 가변형상의 공기흡입구 조립체를 설계하고 설계 결과 확인을 위해 조립체에 대한 전산 유동 및 구조해석을 수행하였다. 이후 35% 축소형 모델을 제작하여 풍동시험을 수행하였다. 동 논문에서는 흡입구 조립체 개발과정에서 요구되는 공기역학적 설계, 잔산 유동/구조 해석 및 풍동 시험평가 결과를 기술하였다.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1272-1278
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• 2014

본 최근 성장하고 있는 해상 풍력의 실험연구에서 풍동시험이 수직형 횡류 풍력발전시스템의 성능을 조사하기 위해 실시되었다. 풍동의 시험 부분은 제한된 크기로 인해 실제 풍력 발전의 입구 안내 베인을 약 1/5로 축소시켰고, 터빈 임펠러의 지름을 모형 임펠러의 1/2로 감소시켰다. 임펠러 블레이드 갯수는 풍력 발전 시스템의 출력에 대한 또 다른 중요한 변수이기 때문에 8개와 16개로 변경하여 시험하였다. 실험 분석 결과, 모형 풍력 터빈의 출력 제동력은 정격 풍속 12m/s에서 블레이드 갯수가 8개 보다 16개일 때 82% 출력이 증가된 278와트로 측정되었고, 정격 제동력은 정격 작동 조건에서 3.9kW로 계산되었다.