• 한국해양환경ㆍ에너지학회지
• /
• 제17권3호
• /
• pp.198-204
• /
• 2014

바다를 항해하는 선박은 수면 상부 선체가 공기저항을 받게 된다. 이 공기저항은 수면 상부 선체의 형상, 선속, 풍속 그리고 풍향의 영향을 받는다. 공기저항을 추정하는 실험적인 또는 통계적인 방법은 사고 선박의 예인력을 계산하는 중요한 절차 가운데 하나이다. 본 논문에서는 수면 상부 선체의 투영면적과 선속과 풍속과 풍향을 변수로 사용하여, 실험 또는 통계 분석 방법으로 공기저항을 간편하게 추정하는 방법을 보여주었다. 이 방법들은 기존의 사고선박 예인력 추정을 위한 전산 프로그램에 적용하였다.

• 한국광학회:학술대회논문집
• /
• 한국광학회 2000년도 하계학술발표회
• /
• pp.224-226
• /
• 2000

Consumer electronics is rapidly digitalized invoking the necessity of digital signal transmission. Moreover, even in consumer electronics, occasionally signal speed is over 1Gbps and long distance transmission(over 5 meters) is required. For these requirements, even though optical transmission is ideal, cost problem has blocked up its entrance to consumer market. However, inexpensive and high speed optical devices such as VCSEL, PIN or MSN PD with large detecting area and low capacitance and Plastic Optical Fiber have been developed so that optical solution can be compete with electrical one in consumer electronics.

• 상하수도학회지
• /
• 제26권6호
• /
• pp.851-860
• /
• 2012

In this study, to evaluate the abatement of runoff pollution loads by the road sweeping(cleaning), various investigations are implemented at the sample area of the highway. As the results of evaluating the removal efficiency of pollutants along road cleaning, TSS showed about 78 % of the removal efficiency and COD showed 49 % of removal efficiency through the operation of cleaning vehicle of vacuum suction method. In case of TN and TP, they showed the relatively-lower removal efficiency by 30~35 %. TSS removal efficiency along the number of cleaning appeared about 60 % in case of one time of cleaning and the additional removal effect did not appear though the number of cleaning increased to two times. With running speed of cleaning vehicle, TSS removal ratio is lessened from 60 % to 20 % when cleaning vehicle speed up to 20 km/hr from 6 km/hr. It seems that the reasons why the removal efficiencies are inversely proportional to its speed are related to the lower vacuum efficiencies and the disturbed particles on the road. In the pollutant build-up analysis, it is showed that it takes more time to the critical pollutant build-up in the shoulder than the center of the road. It is also showed that the proper cleaning cycle is recommended as 4~6 dry weather days without rainfall events.

• 한국축산시설환경학회지
• /
• 제15권2호
• /
• pp.99-106
• /
• 2009

방제기 분야에서 전통과 기술력이 인정받고 있는 일본 마루야마사에서 개발한 원거리 고속팬과 비교실험을 하였다. 비교 실험 결과 일본 마루야마사에서 개발한 원거리 팬은 120m 살포를 한 반면 자체 개발한 원거리 방제기 고속팬은 160m 까지 살포가 가능하였다. 지금까지 원거리 방제기는 일본에서 개발된 제품을 수입하여 국내에 보급하였으나 앞으로는 성능, 가격 및 A/S 측면에서 유리한 국산 원거리 방제기가 시장을 점유할 것으로 판단된다. 주요 연구 결과를 살펴보면 다음과 같다. 실험은 시중에서 판매되고 있는 플라스틱컵을 사용하였다. 컵의 배치는 10m 간격으로 종방향 5개, 횡방향 18개 총 90개를 설치한 후 원거리 고속 방제기가 이동하면서 분사한 양을 보고 분포도를 작성하였다. 분무지점에서 분무방향과 수직을 이루는 거리를 5m 간격으로 고정하고, 분무량과 수평을 이루는 지점에 따른 분무량 및 관찰자 4명의 데이터를 이용하여 평균을 구했다. 방제기가 출발하면서 살포한 경우 0m의 경우와 방제기가 정지하면서 살포를 중지한 20m의 경우 살포가 잘 되지 않은 것으로 나타났다. 방제기가 출발하면서 살포한 경우 10m에서 높은 살포량을 나타냈다. 방제기가 15m 이동했을 때 20m 구간에서 가장 높은 살포를 보였다. 실험결과 방제기가 출발하면서 방제한 경우와 방제기가 포착하면서 방제를 정지한 경우를 제외하고 전 구간에서 일본 마루야마사의 방제기 보다 높은 살포량을 보였다.

• 천문학회보
• /
• 제38권2호
• /
• pp.33-33
• /
• 2013

We are developing empirical space weather (solar flare, solar proton event, and geomagnetic storm) forecast models based on solar data. In this talk we will review our main results and recent progress. First, we have examined solar flare (R) occurrence probability depending on sunspot McIntosh classification, its area, and its area change. We find that sunspot area and its increase (a proxy of flux emergence) greatly enhance solar flare occurrence rates for several sunspot classes. Second, a solar proton event (S) forecast model depending on flare parameters (flare strength, duration, and longitude) as well as CME parameters (speed and angular width) has been developed. We find that solar proton event probability strongly depends on these parameters and CME speed is well correlated with solar proton flux for disk events. Third, we have developed an empirical storm (G) forecast model to predict probability and strength of a storm using halo CME - Dst storm data. For this we use storm probability maps depending on CME parameters such as speed, location, and earthward direction. We are also looking for geoeffective CME parameters such as cone model parameters and magnetic field orientation. We find that all superstorms (less than -200 nT) occurred in the western hemisphere with southward field orientations. We have a plan to set up a storm forecast method with a three-stage approach, which will make a prediction within four hours after the solar coronagraph data become available. We expect that this study will enable us to forecast the onset and strength of a geomagnetic storm a few days in advance using only CME parameters and the WSA-ENLIL model. Finally, we discuss several ongoing works for space weather applications.

• Tribology and Lubricants
• /
• 제13권4호
• /
• pp.47-52
• /
• 1997

Friction torques, electrical contact resistances and bearing temperatures were measured on high speed angular contact ball beatings for the spindle of machine tools. The test bearings ran with oil-air lubrication at the thrust loads from 320 N to 1920 N and at the rotational speed of up to 12000 rpm. Electrical contact resistances between balls and races were measured to evaluate the formation of the lubricant film in the contact area. The test results with sufficient lubrication showed that the variations of friction torques were sensitive to the thrust loads and the rotational speeds, and that the friction torques were higher than those with insufficient lubrication. With insufficient lubrication and high thrust loads, the collapse of the lubricant film was detected even at a high rotational speed. It was concluded that these high speed beatings to run in condition of fluid lubrication should require monitoring not only the temperature increase of the bearing but also the lubricant film formation in contact areas resulting from the change in the applied load and the lubricant amount.

• Tribology and Lubricants
• /
• 제32권4호
• /
• pp.125-131
• /
• 2016

In recent years, thick ta-C coating has attracted considerable interest owing to its existing and potential commercial importance in applications such as automobile accessories, drills, and gears. The thickness of the ta-C coating is an important parameter in these applications. However, the biggest problems are achieving efficient coating and uniformity over a large area with high-speed deposition. Feasibility is confirmed for the ta-C coating thickness of up to 9.0 µm (coating speed: 3.0 µm/h, fixed substrate) using a single FCVA cathode. The thickness was determined using multiple coating cycles that were controlled using substrate temperature and residual stresses. In the present research, we have designed a coating system using FCVA plasma and produced enhanced thick ta-C coating. The system uses a specialized magnetic field configuration with stabilized DC arc plasma discharge during deposition. To achieve quality that is acceptable for use in automobile accessories, the magnetic field, T-type filters, and 10 pieces of a multi-cathode are used to demonstrate the deposition of the thick ta-C coating. The results of coating performance indicate that uniformity is ±7.6 , deposited area is 400 mm, and the thickness of the ta-C coating is up to 5.0 µm (coating speed: 0.3 µm/h, revolution and rotation). The hardness of the coating ranges from 30 to 59 GPa, and the adhesion strength level (HF1) ranges from 20 to 60 N, depending on the ta-C coating.

• 환경영향평가
• /
• 제20권4호
• /
• pp.539-555
• /
• 2011

Newly constructed, high-rise dense building areas by urban development can cause changes in local wind fields. Wind fields were analyzed to assess the impact on the local meteorology due to the land use changes during the urban redevelopment called "Eunpyeong new town" in north-western Seoul using CFD_NIMR_SNU (Computational Fluid Dynamics, National Institute of Meteorological Research, Seoul National University) model. Initial value of wind speed and direction use analysis value of AWS (Automatic Weather Station) data during 5 years. In the case of the pre-construction with low rise built-up area, it was simulated that the spatial distribution of horizontal wind fields depends on the topography and wind direction of initial inflow. But, in the case of the post-construction with high rise built-up area, it was analyzed that the wind field was affected by high rise buildings as well as terrain. High-rise buildings can generate new circulations among buildings. In addition, small size vortexes were newly generated by terrain and high rise buildings after the construction. As high-rise buildings act as a barrier, we found that the horizontal wind flow was separated and wind speed was reduced behind the buildings. CFD_NIMR_SNU was able to analyze the impact of high-rise buildings during the urban development. With the support of high power computing, it will be more common to utilize sophisticated numerical analysis models such as CFD_NIMR_SNU in evaluating the impact of urban development on wind flow or channel.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2001년도 추계학술대회 논문집 전기기기 및 에너지변환시스템부문
• /
• pp.161-164
• /
• 2001

This paper presents a digital speed sensorless control system for Reluctance Synchronous Motor (RSM) drives with direct torque control (DTC). The system consist of stator flux observer, rotor speed estimator, torque estimator two hysteresis band controllers, an optimal switching look-up table. IGBT voltage source inverter, and TMS320C31DSP controller by using fully integrated control software. The stator flux observer is based on the combined voltage and current model with stator flux feedback adaptive control that inputs are current and voltage sensing of motor terminal with estimated rotor angle for wide speed range. The rotor speed is estimated by the observed stator flux-linkage space vector. The estimated rotor speed can be determinated by differentiation of the rotor position used only in the current model part of the flux observer for a low speed operating area. In order to prove the suggested speed sensorless control algorithm. There are some simulation and testing at actual experimental system. The developed digitally high- performance speed sensorless control system are shown a good speed control response characteristic results and high Performance features using 1.0Kw RSM.

• JSTS:Journal of Semiconductor Technology and Science
• /
• 제17권4호
• /
• pp.561-567
• /
• 2017

This paper presents a 4-channel common-cathode VCSEL driver array operating up to 6.25 Gb/s per channel for the applications of HDMI 2.0 active optical cables. The proposed VCSEL driver consists of an input buffer, a modified Cherry-Hooper amplifier as a pre-driver, and a main driver with pre-emphasis to drive a common-cathode VCSEL diode at high-speed full switching operations. Particularly, the input buffer merges a linear equalizer not only to broaden the bandwidth, but to reduce power consumption simultaneously. Measured results of the proposed 4-channel VCSEL driver array implemented in a $0.13-{\mu}m$ CMOS process demonstrate wide and clean eye-diagrams for up to 6.25-Gb/s operation speed with the bias current 2.0 mA and the modulation currents of $3.1mA_{PP}$. Chip core occupies the area of $0.15{\times}0.1{\mu}m^2$ and dissipate 22.8 mW per channel.