• Wind and Structures
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• 제34권5호
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• pp.451-467
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• 2022

The flow around a high-speed train with three underbody structures in the bogie area is numerically investigated using the improved delayed detached eddy simulation method. The vortex structure, pressure distribution, flow field structure, and unsteady velocity of the wake are analyzed by vortex identification criteria Q, frequency spectral analysis, empirical mode decomposition (EMD), and Hilbert spectral analysis. The results show that the structures of the bogie and its installation cabin reduce the momentum of fluid near the tail car, thus it is easy to induce flow separation and make the fluid no longer adhere to the side surface of the train, then forming vortices. Under the action of the vortices on the side of the tail car, the wake vortices have a trend of spanwise motion. But the deflector structure can prevent the separation on the side of the tail car. Besides, the bogie fairings do not affect the formation process and mechanism of the wake vortices, but the fairings prevent the low-speed fluid in the bogie installation cabin from flowing to the side of the train and reduce the number of the vortices in the wake region.

• 한국추진공학회지
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• 제19권5호
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• pp.31-36
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• 2015

이중 모드 스크램제트 엔진은 미래 가장 촉망받는 시스템 중 하나로, 많은 연구자들에게 각광받고 있다. 이중 모드 스크램제트 엔진 시스템에서 격리부와 관련된 유동 특징들은 중요한 역할을 한다. 본 연구에서 풍동을 가진 이중 모드 스크램제트 엔진을 조사하기 위해 2차원 수치해석을 수행하였다. 계산방법의 타당성을 검증하기 위하여 실험결과와 비교하였으며, 수치해석 결과는 실험값과 비교하여 전체적으로 압력 분포가 잘 일치하였다. 배압은 최대 압력 상승을 분석하기 위해 연구되었다. 그 결과 초음속 흡입구 영역의 압력 분포는 배압에 영향을 받지 않았으며, 배압이 증가함에 따라 Shock train은 상류 쪽으로 밀려나갔다. 격리부의 길이가 증가함에 따라 최대 배압값은 입구 불시동 없이 급격히 증가한 후 일정하게 유지되었으며, 격리부 영역의 최적 길이($L/H_{th}$)는 8.7이다.

• Wind and Structures
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• 제35권4호
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• pp.269-285
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• 2022

The pressure-mitigating effects of a high-speed train passing through a tunnel with a partially reduced cross-section are investigated via the numerical approach. A compressible, three-dimensional RNG k-ε turbulence model and a hybrid mesh strategy are adopted to reproduce that event, which is validated by the moving model test. Three step-like tunnel forms and two additional transitions at the tunnel junction are proposed and their aerodynamic performance is compared and scrutinized with a constant cross-sectional tunnel as the benchmark. The results show that the tunnel step is unrelated to the pressure mitigation effects since the case of a double-step tunnel has no advantage in comparison to a single-step tunnel, but the excavated volume is an essential matter. The pressure peaks are reduced at different levels along with the increase of the excavated earth volume and the peaks are either fitted with power or logarithmic function relationships. In addition, the Arc and Oblique-transitions have very limited gaps, and their pressure curves are identical to each other, whereas the Rec-transition leads to relatively lower pressure peaks in C_Pmax, C_Pmin, and ΔC_P, with 5.2%, 4.0%, and 4.1% relieved compared with Oblique-transition. This study could provide guidance for the design of the novel railway tunnel.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.469-472
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• 2007

Aeroacoustic sound induced from inter-couch spacing is an important contributor to interior noise generation for high speed trains. Especially the open space between mud-flap has significant impact from flow-structure interactions. To understand noise generation mechanism, experiments were performed using the wind tunnel. To find mud-flap parameters for minimal noise generations the various shape of the mud-flap was installed and its effects on the wall-pressure generation were investigated.

• 한국지진공학회논문집
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• 제19권4호
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• pp.145-159
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• 2015

A seismic response analysis method for three-dimensional floating offshore structures due to seaquakes is developed. The hydrodynamic pressure exerted on the structure is calculated taking into account the compressibility of the sea water, the fluid-structure interaction, the energy absorption by the seabed, and the energy radiation into infinity. To validate developed method, the hydrodynamic pressure induced by the vibration of a floating massless rigid circular disk is calculated and compared with an exact analytical solution. The developed method is applied to seismic analysis of a support structure for a floating offshore wind turbine subjected to the hydrodynamic pressures induced from a seaquake. Analysis results show that earthquake response of a floating offshore structure can be greatly influenced by the compressibility of fluid, the depth (natural frequencies) of the fluid domain, and the energy absorption capacity of the seabed.

• 대한환경공학회지
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• 제39권12호
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• pp.679-684
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• 2017

고속열차의 설계 및 운행기술이 발전하면서 고속철도의 운행속도가 빠르게 증속되고 있다. 반면 증속 시 발생하는 소음으로 인해 고속철도 연변의 주거지역 등에서는 많은 소음문제가 발생하고 있으며, 고속철도 소음에 대한 민원도 지속적인 증가추세에 있다. 향후 고속철도가 원활히 설계속도대로 운행되기 위해서는 고속철도의 방사소음특성에 적합한 소음예측기술 및 저감기술이 개발되어야 한다. 이와 같은 요구에 부합하기 위해, 400 km/h 고속철도 인프라 연구가 수년에 걸쳐 진행되었다. 이 연구를 통해 신뢰성을 갖는 고속철도 소음예측평가 기술이 개발되었고, 현재 소음저감기술의 단점을 극복하기 위한 핵심방음장치가 개발되었다. 본 연구의 궁극적인 목적은 고속철도 환경소음을 줄이기 위해 개발된 선로 변 벽체 상단에 설치되는 상단장치의 소음성능평가 및 풍압안전성 검증에 관한 것이다.

• 한국전산유체공학회지
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• 제20권2호
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• pp.61-66
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• 2015

In this study, an aero-acoustic analysis around pantograph of a high speed train is performed. Computational technique and grid system is validated with wind tunnel test result and unsteady acoustic pressure data are used for analyzing noise level of each part of pantograph. FLUENT is used for flow analysis and LES(Large Eddy Simulation) is applied for analyzing turbulent flow. For acoustic analysis, Ffowcs Williams-Hawkings(FW-H) acoustics model is used and it bring the aero-acoustic characteristic of pantograph. As the result, contact strip, knee, substructure of pantograph is confirmed as a main source of aero-acoustic noise and it is dealt in various frequencies. The result is expected to help building improved grid system.

• 한국도시철도학회논문집
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• 제6권4호
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• pp.249-257
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• 2018

교통사상사고 원인 중 선로근접 및 무단통행으로 인한 사고가 많이 발생하고 있다. 운행선 근접공사 시 열차운행에 지장을 주지 않고, 작업자의 안전확보 및 작업효율을 높이기 위해 철도선로용 안전펜스가 사용되고 있다. 하지만 철도선로에 적용되는 레일저부형 안전펜스는 열차주행 시 안전펜스의 간섭여부를 확인할 필요가 있다. 본 연구에서는 철도선로용 안전펜스의 열차운행 시 지장여부를 확인하기 위하여 국내에서 운행되고 있는 열차들과 안전펜스 설치 시 이격간격을 분석하였다. 또한, 국내 열차종류별 열차 풍압에 대한 횡방향 하중조건을 산정하여 철도선로용 안전펜스의 설치간격에 따른 수치해석을 수행하였다. 본 연구를 통하여 철도선로용 안전펜스의 적정 이격거리는 차량한계로부터 200mm 이상을 확보하고, 열차풍압을 고려한 철도선로용 안전펜스의 적정 설치간격을 산정할 필요가 있음을 확인하였다.

• 한국지진공학회논문집
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• 제18권6호
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• pp.279-289
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• 2014

Considering a rigorously fluid-structure interaction, a method for an earthquake response analysis of a floating offshore structure subjected to vertical ground motion from a seaquake is developed. Mass, damping, stiffness, and hydrostatic stiffness matrices of the floating offshore structure are obtained from a finite-element model. The sea water is assumed to be a compressible, nonviscous, ideal fluid. Hydrodynamic pressure, which is applied to the structure, from the sea water is assessed using its finite elements and transmitting boundary. Considering the fluid-structure interaction, added mass and force from the hydrodynamic pressure is obtained, which will be combined with the numerical model for the structure. Hydrodynamic pressure in a free field subjected to vertical ground motion and due to harmonic vibration of a floating massless rigid circular plate are calculated and compared with analytical solutions for verification. Using the developed method, the earthquake responses of a floating offshore structure subjected to a vertical ground motion from the seaquake is obtained. It is concluded that the earthquake responses of a floating offshore structure to vertical ground motion is severely influenced by the compressibility of sea water.

• 한국입자에어로졸학회지
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• 제12권1호
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• pp.11-20
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• 2016

A large amount of wear dust generated during train operation is a major dust source in urban railway tunnels. To check possibility of a louver dust collector for the removal of dust in the railway tunnel, five louver dust collector models were designed and their performance was tested in a wind tunnel. JIS Z 8901 Class 8 dust was used as a test dust. Pressure drop and particle collection efficiency were evaluated with the face velocity ranging from 1 m/s to 4 m/s. At this low velocity range, particle collection efficiency of the louver dust collector was found to be insensitive to air velocity and design parameters. Pressure drop was under 40 Pa, and $PM_{10}$ and $PM_{2.5}$ collection efficiencies were approximately 50% and 30%, respectively.