• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.531-536
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• 2012

This study presents a result on aero-acoustic characteristics of pantograph panheads. To analyze the fluid flow around the panhead and resulting sound radiation, simple models of panhead were used in the numerical simulations called Lattice-Boltzmann method. The simulation results were verified using the wind tunnel test. The main aerodynamic noise was generated from the vortex shedding which is characterized by the Strouhal number, flow speed and geometry. The reduction in the radiated noise with simultaneously achieving increased lifting force was implemented for the simple rectangular geometry used in this study. Also, it was shown that the radiated sound power was significantly reduced by minimizing vortex shedding using through-holes or streamline shapes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.10a
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• pp.308-308
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• 2010

본 논문에서는 판토그라프의 공력소음 발생 특성을 규명하기 위하여 단순 모델을 이용하여 그 특성을 분석하였다. 단순 모델은 실제 팬헤드의 사이즈를 고려하여 선정하였고, 이를 통해 음압 해석 알고리즘을 구축하고 소음 발생 메커니즘을 분석하였다. 단순 모델을 선정하여 이를 Lattice Boltzmann Method 를 기반으로 한 전산 유체 해석을 통한 결과를 이용하여 음압 레벨과 음압의 방사형태를 계산하고, 풍동 실험을 통해 이를 검증한다. 풍동 실험에서는 단순 모델을 제작하여 100 km/h 의 속도 환경에서 항력, 양력과 소음을 측정하였다. 단면의 형상에 따른 변화 추이를 검토하였으며 해석결과를 단일 수치로도 정량화하여 제시한다. 최종적으로 정립된 알고리즘을 기반으로 팬헤드의 3 차원 모델을 시뮬레이션 한 결과를 제시한다.

• Proceeding of EDISON Challenge
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• 2014.03a
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• pp.579-584
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• 2014

고속 열차의 속도가 점점 빨라짐에 따라 고속 열차 주행 시 발생하는 여러 공력적인 문제가 대두되고 있다. 그 중 고속 열차와 전력선을 이어주는 판토그래프에서의 소음 발생과 압상력 불안정 문제가 중요시 되어왔고 이에 대한 여러 선행연구가 진행되고 있다. 지금까지의 선행 연구는 원형, 사각형, 에어포일과 같이 기본적인 형상을 이용한 판토그래프 팬헤드의 최적 단면 형상을 찾는 데에 초점을 맞추고 있다. 본 연구는 이러한 주류의 접근 방식에서 벗어나 팬헤드에 구멍을 추가하여 그 효과를 보는 다양한 시도를 해보았고 구멍이 소음 발생과 압상력 불안정에 미치는 영향에 대하여 연구하였다.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.367-372
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• 2001

The paper presents an improved way of aerodynamic quality in Korean Very High Speed Railway, The pantograph model being under development dissatisfies the required grade of aerodynamic lift force. So the present work proposes modified configurations of panheads to maintain consistent aerodynamic characteristics. Analysis has been performed using commercial CFD program. Simulation based analysis has been conducted with two different models. One is to attach the thin plate on the crossbar and the other is the use of trapezoidal cross section in contact strip. Various length of thin plate is simulated for flow velocity and acceptable value of plate length is selected which satisfy the necessary average lift force. Aerodynamic variation on the panheads strip is studied.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.569-575
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• 2011

Since the high heat generation of LED chips can cause a reduction in lifetime, degradation of luminous efficiency, and variation of color temperature, studies have been carried out on the optimization of LED packaging and heat sinks. Recently, LED packages have been applied to high-power lights such as car headlamps or street lights, and it is known that cooling using only free convection is not at all efficient. Thus, in this study, a heat pipe with forced convection was examined for the optimization of the cooling performance in high-power LED lights. In addition, optimal on-off control of a fan was adopted to increase the fan lifetime, since the lifetime of the fan is generally shorter than that of the LEDs.

• The KSFM Journal of Fluid Machinery
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• v.20 no.1
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• pp.35-40
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• 2017

In order to investigate the change of contact force of pantograph pan head due to the change of aerodynamic force, three dimensional flow around the pan head were calculated. For this, the aerodynamic modeling of pan head of CX pantograph was performed and the standard deviation of the contact force of the simulation results were compared with those of the experimental results of wind tunnel tests. From the comparison, it was confirmed that the current grid system and the numerical methodologies can be utilized to calculate the aerodynamic characteristics of the pantograph pan head. By using these grid system and the methodologies, the standard deviations of the contact force of pan head were calculated with velocities as 200, 250, 300, 350, and 400 km/h. The maximum standard deviation of the aerodynamic contact force of pan head was 92 N at 400 km/h and statistical minimum contact force was more than 0 N. Therefore, it was confirmed that and the pan head of CX pantograph was statistically contacted with the catenary system with the train speed of 350 km/h though the aerodynamic contact force was changed.

• Journal of the Korean Society for Railway
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• v.7 no.3
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• pp.232-238
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• 2004

The dynamic characteristics of the current collection process of the high-speed railway are investigated through signals acquired during a test run. The signals are obtained from accelerometers, load cells, and strain gauges attached to various positions of the pantograph, and they are processed in time-and frequency-domains to obtain the dynamic characteristics. The main natural frequency of the pantograph is found to be 8.5Hz. There also are components at low frequencies varying linearly with the train speed. The contact frequency components above 20Hz is attenuated as they pass through the secondary suspension. The main frequency component of the load cell signal is found to be related with the rolling motion of the panhead generated by the stagger in the catenary.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1223-1228
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• 2001

We have been developing the pantograph for Korean High Speed Train for the last five years. To fulfil the following requirements at designed speed of 350km/h ： 1) contact loss less than 1 ％, 2) aerodynamic noise less than 91dB, 3) average uplift force less than 200N, the pantograph has been modified two times since the first prototype pantograph was manufactured, By means of the following up characteristic test, low speed wind tunnel test, and high speed wind tunnel test for the prototype pantographs, we found that the aerodynamic uplift force did not exceed l60N at speed up to 350km/h and the aerodynamic noise was less than 88dB, that the following up characteristics of the prototype pantograph was excellent.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.17-23
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• 2011

The turbulent flow and vortex shedding phenomena around pantograph panhead of high speed train were investigated and compared with available experimental data and other simulations. The pantograph head was simplified to be a square-cross-section pillar and assumed to be no interference with other bodies. The Reynolds number (Re) was 22,000. The LES(large eddy simulation) of FDS code was applied to solve the momentum equations and the Wener-Wengle wall model was employed to solve the near wall turbulent flow. Smagorinsky model($C_s$=0.2) was used as SGS(subgrid scale) model. The total grid numbers were about 9 millions and the analyzed domain was divided into 12 multi blocks which were communicated with each other by MPI. The time-averaged mainstream flows were calculated and well compared with experimental data. The phased-averaged quantities had also a good agreement with experimental data. The near-wall turbulence should be carefully treated by wall function or direct resolution to get successful application of LES methods.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.33 no.12
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• pp.947-951
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• 2009

LED has the merits of high reliability, semi-permanent life, rapid-response and its small size for use as light source of head lamp. But the dependence of its performance and life on temperature affect on its practical use. Which dependence makes problem when the LED is heated up to a higher temperature level by self-generation of heat, due to "highly integration" to get enough quantity of light. To solve this problem, effective cooling system is needed that consider conduction, convection and radiation. This study points out the limits of natural convection cooling system and propose of forced convection with heat sink. Also, it describes a correlation between heat sink area and fluid velocity using numerical analysis to optimize the cooling system.