터널내를 주행하는 열차의 공기역학적 해석(II)-2열차의 공기역학-

김희동,Kim, Hui-Dong 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.8

As a high-speed train enters a tunnel, a compression wave is generated ahead of it due to the piston action of train. The compression waves propagate along the tunnel and reflect backward at the exit of tunnel. A complex wave phenomenon appears in the tunnel, because of the successive reflections of the pressure waves at the exit and entrance of tunnel. The pressure waves can give rise to large pressure transients which impose the fluctuating loads on the running train. It is highly needed that the pressure transients should be predicted to design the train body and to improve the comfort for the passengers in the train. In the present study, the pressure transients and aerodynamic drag for two-trains running in a tunnel were calculated numerically for a wide range of train speed, and compared with the results of the previous tunnel tests and calculations for one train. The present calculation results agreed with ones of the tunnel tests, and the mechanism of pressure transients was made clear.

다공벽을 전파하는 압축파에 관한 수치해석적 연구

김희동,Kim, Hui-Dong,Setoguchi, Toshiaki 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.11

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates through the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study calculated the effect of porous walls on the compression wave propagating into a model tunnel. Two-dimensional unsteady compressible equations were differenced by using a Piecewise Linear Method. Calculation results show that the cavity/porous wall system is very effective for a compression wave with a large nonlinear effect. The porosity of 30% is most effective for the reduction of the maximum pressure gradient of the compression wave front. The present calculation results are in a good agreement with experimental ones obtained previously.

두 연속 터널을 전파하는 압축파의 실험적 연구

김희동,허남건,Kim, Hui-Dong,Heo, Nam-Geon,Setoguchi, Toshiaki 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.10

For the purpose of investigating the impulsive noise at the exit of high-speed railway tunnel and the pressure transients inside the tunnel, experiments were carried out using a shock tube with an open end. A great deal of experimental data were obtained and explored to analyze the peak pressures and maximum pressure gradients in the pressure waves. The effects of the distance and cross-sectional area ratio between two-continuous tunnels on the characteristics of the pressure waves were investigated. The peak pressure inside the second tunnel decreases for the distance and cross-sectional area ratio between two tunnels to increase. Also the peak pressure and maximum pressure gradient of the pressure wave inside the second tunnel increase as the maximum pressure gradient of initial compression wave increases.

초음속 노즐을 통하는 부족팽창 제트에 관한 수치계산적 연구 (2)

김희동,신형승,Kim, Hui-Dong,Sin, Hyeong-Seung 대한기계학회 1996 大韓機械學會論文集B Vol.20 No.6

Numerical calculation was applied to supersonic under-expanded jets, and compared with the results of a linear theory and other experiments. TVD difference scheme was employed to solve 2-dimensional and axisymmetric inviscid Euler equation. This paper aims to explore the effects of angle of divergence and design Mach number of nozzle on the structure of under-expanded jets. The angle of divergence was varied from 0 to 20 deg. The results show that the length of the first cell of the under-expanded jets decreases and Mach disk generates at lower nozzle pressure ratio, if the angle of divergence or design Mach number of nozzle increases. The distance from the nozzle exit to Mach disk in 2-dimensional jets becomes much larger than that of axisymmetric jets, and the widths of the jet boundary and the barrel shock wave are also larger than that of axisymmetric jets. Calculation results indicate that the configuration of the under-expanded jets is strongly dependent on the nozzle pressure ratio.

급축소관을 전파하는 압축파에 관한 이론적 연구

김희동,김태호,Kim, Hui-Dong,Kim, Tae-Ho 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.1

Compression waves propagating in a high speed railway tunnel impose large pressure fluctuations on the train body or tunnel structures. The pressure fluctuations can cause ear discomfort for the passengers and increase the aerodynamic resistance of trains. As a fundamental research to resolve the pressure wave phenomenon in the tunnel, a steady theory of Chester-Chisnell- Whitham was applied to a simple shock tube with a sudden cross-sectional area reduction to model trains inside the tunnel. The results of the present theoretical analysis were compared with the experiments of the shock tube. The results show that the reflected compression wave from the model becomes stronger as the strength of incident compression wave and the blockage ratio increase. However, the compression wave passing through the model is not strongly dependent on the blockage ratio. The theoretical results are in good agreement with the experiments.

음속/초음속 이젝터 유동에 관한 실험적 연구

김희동,최보규,권오식,Kim, Hui-Dong,Choe, Bo-Gyu,Gwon, O-Sik 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.5

An experimental investigation or the sonic and supersonic air ejector systems has beer conducted to develop design and prediction programs for practical ejector system. Five different primary nozzles have been employed to operate the ejector systems in the ranges of low and moderate operating pressure ratios. The ejector operating pressure ratio for the secondary chamber pressure to be minimized has a strong influence of the ejector throat ratio. The pressure inside the ejector diffuser is not dependent on the primary nozzle configurations employed but only a function of the ejector operating pressure ratio. Experimental results show that a supersonic ejector system is more desirable for obtaining high vacuum pressure of the secondary chamber than a sonic ejector system.

가스터빈 발전기 건전성 평가기술

김희동,Kim, Hui-Dong 한국열병합발전협회 2011 열병합발전 Vol.81 No.-

대용량 발전기 및 고압전동기 진단기술

김희동,공태식,Kim, Hui-Dong,Gong, Tae-Sik 한국전기전자재료학회 2013 전기전자재료 Vol.26 No.5

수직갱을 이용한 터널내 비정상 압축파의 피동제어

김희동,Kim, Hui-Dong,Setoguchi, Toshiaki 대한기계학회 1997 大韓機械學會論文集B Vol.21 No.9

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates along the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. For the purpose of the impulsive noise reduction, the present study investigated the effect of a vertical bleed duct on the compression wave propagating into a model tunnel. Numerical results were obtained using a Piecewise Linear Method and testified by experiment of shock tube with an open end. The results showed that the vertical bleed duct reduces the maximum pressure gradient of compression wave front by about 30 percent, compared with the straight tunnel without the bleed duct. As the width of the vertical bleed duct becomes larger, reduction of the impulsive noise is expected to be greater. However the impulsive noise is independent of the height of the vertical bleed duct.

고압전동기 및 발전기 운전 중 부분방전 감시기술

김희동,Kim, Hui-Dong 한국열병합발전협회 2005 열병합발전 Vol.48 No.-