• 한국유체기계학회 논문집
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• 제7권1호
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• pp.51-57
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• 2004

The waterhammer has recently become more important because the pumping stations were big and the systems conveying the fluid through the large and long transmission pipelines were complex. When the pumps are started or stopped for the operation or tripped due to the power failure, the hydraulic transients occur as a result of the sudden change in velocity As the pressure waves are propagating between the pumping station and the distributing reservoir, the pressure inside the pipe drops to the liquid vapor pressure with the pipeline profile, at which time a vapor cavity forms, and finally the column separation occurs. If the pressure in the pipe is less than the atmospheric pressure, the pipe can be collapsed and destroyed after the water columns separated by the vapor cavity rejoin. During the reverse flow, the pressure is so abnormally increased at the pumping station that the accident of flooding may happen due to the failure of system. In this paper, the field tests on the waterhammer by the startup, stoppage, and power failure of a centrifugal pump were carried out for Yongma transmission pumping station in Seoul. The experimental results were compared with that of the numerical calculations, in which results the procedure of controlled pump normal shut-down and the two-step closing mode of controlling the ball valve for pump emergency stop are proposed to reduce the pressure surge.

• Current Optics and Photonics
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• 제5권3호
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• pp.220-228
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• 2021

To improve the measurement accuracy of a solar-radiation observer instrument, aiming at the problem of multiorder-stray-light interference caused by the diffraction of the flat-field concave grating in the spectroscopic system, straylight suppression methods for different forms of optical traps are studied. According to the grating surface-scattering distribution-function model, the bidirectional scattering distribution function (BSDF) of a dust-polluted surface and the flat-field concave grating's transition area of the spectroscopic system is calculated, and a Lyot stop with blade baffle is designed to suppress this kind of stray light. For diffraction multiorder stray light, based on the theory of light-energy transmission, a design for precise positioning of the trench optical trap is proposed. The superiority of the method is verified through simulation and actual measurement. The simulation results show that in a spectroscopic system approximately 160 mm × 140 mm × 80 mm in size, the energy of the stray light is reduced by one order of magnitude by means of the trench optical trap and Lyot stop, and the number of beams is reduced from 5664 to 1040. The actual measurements show that the stray-light-suppression efficiency is about 69.4%, which is effective reduction of the amount of stray light.

• 대한교통학회지
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• 제6권1호
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• pp.55-64
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• 1988

Prior to using any computer model, the program-embedded palameters showing significant differences from real world should be calibrated. This is especially true when the model is expected to be used fro various roadway and traffic condition. The calibration of TRANSYT model was conducted for the parameters of start-up delay, and lag, stop penalty(K), platoon dispersion factor, and saturation flow rate. The values of the parameters were obtained by theoretical methods from actual field measurements for discharging and arrival pattern. The sites elected for the study was an intersection of Dongil-Ro and Hwarang-Ro, and a 334 meter downstrean section from the intersection stop line on westbound Hwarang-Ro. The study results showed that the start-up delay was 2.6 sec, end lag was 1.0 sec, saturation flow rate was 2287 pcphgpl, platoon dispersion factor was 0.2-03, and stop penalty(K) was 32. However, since these parameters re apt to depend on traffic and roadway condition, it is doubtful whether the obtained values will be applicable to the area-wide situation other than this particular site.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1697-1702
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• 2004

The waterhammer has recently become more important because the pumping stations were big and the systems conveying the fluid through the large and long transmission pipelines were complex. When the pumps are started or stopped for the operation or tripped due to the power failure. the hydraulic transients occur as a result of the sudden change in velocity. In this paper, the field tests on the waterhammer by the startup, stoppage, and power failure of a centrifugal pump were carried out for Yongma transmission pumping station in Seoul. The experimental results were compared with that of the numerical calculations. in which results the procedure of controlled pump normal shut-down and the two-step closing mode of controlling the ball valve for pump emergency stop are proposed to reduce the pressure surge.

• 한국안전학회지
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• 제18권2호
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• pp.22-27
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• 2003

The roller machines installed in the industrial field are operated under hazardous conditions due to no safety devices available, human error during operation, defective safety devices, and inadequate regulation even in case that safety devices are provided. Up to now, most roller machines installed in domestic field are provides with band breaking system as a safety device. In this study, the emergency stop distance is measured within the limit of domestic regulation but violates a foreign regulation(EN1417). Consequently, it is concluded that the roller machines with a band breaking system have high possibility of death or serious injury of the operator and the system should be improved with the introduction of additional safety devices. This thesis suggests the safety measures suitable for the roller machines with different drive systems based on the experiment results. The use of the newly developed safety system has been tested on many cases.

• 한국광학회지
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• 제32권1호
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• pp.9-14
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• 2021

본 논문에서는 인공위성용 비축 삼반사 망원경의 조리개 위치에 따른 광학계 연구를 진행하였다. 인공위성 광학 탑재체로 주로 사용되는 비축 삼반사 망원경은 높은 해상도와 넓은 화각을 가져야 한다. 또한, 광학계가 구조적으로 비축상에 위치하여 조립이 어려우므로 넓은 공차범위를 가져야 한다. 그러나 조리개의 위치 선정에 따라 광학계의 성능 차이 이외에도 민감도의 차이가 있어, 사용 목적에 따른 적합한 조리개의 위치 선정이 중요하다. 따라서 본 논문에서는 조리개 위치가 각각 다른 비축 삼반사 망원경을 설계하고 성능 및 민감도 분석을 진행하여 적합한 조리개의 위치를 제시하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.396-401
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• 2008

The disc-pad brake system is an important part of automobile safety system. During braking, the kinetic energy and potential energies of a moving vehicle are converted into the thermal energy through frictional heat between the brake disc and the pads. Most of the thermal energy dissipated through the brake disc. The temperature could be exceed the critical value for a given material, which leads to undesirable effects, such as the brake fade, premature wear, brake fluid vaporization, bearing failure, thermal cracks, and thermallyexcited vibration. The object of the present study is to investigate temperature field and temperature variation of brake disc and pad during single brake. The brake disc is decelerated at the initial speed with constant acceleration, until the disc comes to stop. The pad-disc brake assembly is built by 3D model with the appropriate boundary condition. In the simulation process, the mechanical loads are applied to the thermomechanical coupling analysis in order to simulate the process of heat produced by friction.

• Journal of the Optical Society of Korea
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• 제16권4호
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• pp.343-348
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• 2012

This paper described an off-axis five-mirror-anastigmatic telescope. It is composed of three aspheric surfaces and one spherical surface while the third mirror and fifth mirror have the same parameters at the same place. This configuration is useful for having wide field of view. The strip full field of view for the near infrared telescope is $20^{\circ}{\times}0.2^{\circ}$. The entrance pupil is located in front of the first mirror. There is an intermediate image between the second mirror and the third mirror. The entrance pupil diameter is 100 mm and the effective focal length is 250 mm. The spectral range is $0.85-1.75{\mu}m$. The pixel pitch is $15{\mu}m$. The image quality is near the diffraction limit. Some methods were used to restrain the stray light such as a field stop near the intermediate image, the baffle, the narrow-band pass filter and a stop in front of the focal plane.

• 대한교통학회지
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• 제18권3호
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• pp.29-39
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• 2000

본 논문은 교차로 좌회전 궤적에 따른 정지선의 위치결정에 관한 연구로서 현행 교차로를 설계하는데 있어 좌회전 차량의 운행특성을 고려하지 못하는 불합리한 점을 지적하고, 좌회전 궤적을 고려한 차량정지선의 위치를 결정하는 기준을 제시하는데 그 목적이 있다. 면적이 한정되어 있는 교차로상에서 좌회전궤적을 고려하여 이를 수용하려면 정지선의 형태가 일자형이 아닌 계단형의 모양을 보이게 되는데, 이때 후퇴하게 되는 정지선의 길이를 산정함에 있어 차종을 3가지로 분류하였고 그에 따른 설치곡선반경을 12m, 15m, 23m로 제시하였다. 그리고 교차로 연석선상을 기준으로 개별 차로의 폭 차로수의 조합을 고려하였다. 따라서 본 논문은 후퇴되는 차량정지선의 길이뿐 아니라 곡선반경의 설치방법을 제시함으로서 설계된 곡선반경을 노면상에 표시하는데 도움이 될 것이다. 좌회전 궤적의 영향에 대한 연구는 교통류율과 안전성에 관계되는 것으로 불합리하게 설계된 좌회전 이동류에 대한 곡선반경은 좌회전 용량감소의 원인으로 작용할 뿐만 아니라 운전자로 하여금 죄회전시에 불안정함을 느리게 하여 인근차로를 침범하게 되는 상충발생을 증가시키게 된다.

• 한국전기전자재료학회논문지
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• 제30권3호
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• pp.148-151
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• 2017

This research concerns field rings for 3.3kV planar gate power insulated-gate bipolar transistors (IGBTs). We design an optimal field ring for a 3.3kV power IGBT and analyze its electrical characteristics according to field ring parameters. Based on this background, we obtained 3.3kV high breakdown voltage and a 2.9V on state voltage drop. To obtain high breakdown voltage, we confirmed that the field ring count was 23, and we obtained optimal parameters. The gap distance between field rings $13{\mu}m$ and the field ring width was $5{\mu}m$. This design technology will be adapted to field stop IGBTs and super junction IGBTs. The thyristor device for a power conversion switch will be replaced with a super high voltage power IGBT.