• 설비공학논문집
• /
• 제20권2호
• /
• pp.87-96
• /
• 2008

Flow condensation heat transfer coefficients(HTCs) of R123 and R245fa are measured in a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 9.52 mm outside diameter and 530 mm length. The refrigerant is cooled by passing cold water through an annulus surrounding the test section. Tests are performed at a fixed saturation temperature of $50\;{\pm}\;0.2\;^{\circ}C$ with mass fluxes of 50, 100, $150\;kg/m^2s$ and heat flux of $7.3{\sim}7.7\;kW/m^2$. Heat transfer data are obtained in the vapor quality range of $10{\sim}90%$. Test results show that the flow condensation HTCs of R245fa are overall 7.9% higher than those of R123 at all mass fluxes. The pressure drop of R245fa is smaller than that of R123 at the same heat flux. In conclusion, R245fa is a good candidate to replace ozone depleting R123 currently used in chillers from the view point heat transfer and environmental properties.

• 설비공학논문집
• /
• 제14권2호
• /
• pp.175-183
• /
• 2002

Flow Condensation heat transfer coefficients (HTCs) of Rl2, R22, R32, Rl23, Rl25, R134a, R142b were measured experimentally on a horizontal plain tube. The experi- mental apparatus was composed of three main parts; a refrigerant loop, a water loop and a water-glycol loop. The test section in a refrigerant loop was made of a copper tube of 8.8 mm inner diameter and 1000 mm length respectively. The refrigerant was cooled by passing cold water through an annulus surrounding the test section. All tests were performed at a filed refrigerant saturation temperature of 4$0^{\circ}C$ with mass fluxes of 100, 200, 300 kg/$m^2$s. The experimental result showed that flow condensation HTCs increase as the quality, mass flux, and latent heat of condensation increase. At the same mass flux, the HTCs of R32 and R142b were higher than those of R22 by 35~45% and 7~14% respectively while HTCs of R134a and Rl23 were similar to those of R22. On the other hand, HTCs of Rl25 and Rl2 were lower than those of R22 by 28 ~30% and 15 ~25% respectively Finally, a new correlation for flow condensation HTCs was developed by modifying Dobson and Chato's correlation with the latent heat of condensation considered. The correlaton showed an average deviation of 13.1% for all pure fluids data indicating an excellent agreement.

• 설비공학논문집
• /
• 제18권12호
• /
• pp.984-991
• /
• 2006

The applications of multi air-conditioners into multiplex and high-rise buildings have been increased by replacing central air-conditioning systems. The pipe length and altitude difference between the indoor and outdoor units can be increased based on installation conditions, which may increase the possibility of flash gas generation at the expansion device inlet. The flash gas generation causes rapid reduction of refrigerant flow rate passing through the expansion device, yielding lower system efficiency. Accumulator heat exchangers have been widely used in multi air-conditioners in order to minimize flash gas generation and obtain system reliability. However, the studies on the heat transfer characteristics and pressure drops of accumulator heat exchangers are very limited in open literature. In this study, the heat transfer rates and pressure drops of accumulator heat exchangers were measured with refrigerant flow rate and operating conditions by using R-22. The heat transfer rate increased with the increase of refrigerant flow rate, while subcooling decreased. The heat transfer rate enhanced with the reduction of inlet superheat and subcooling due to the increased temperature difference between the accumulator and inner heat exchanger.

• 한국해양공학회:학술대회논문집
• /
• 한국해양공학회 2004년도 학술대회지
• /
• pp.166-172
• /
• 2004

An underwater motion measurement system was constructed for applications to the model basin. A commercial motion capture system, FALCON of Motion Analysis Corp., which corrects automatically the distortion caused by refraction of the light passing through water and air, was adopted for underwater motion measurement. The modifications of FALCON system were performed: waterproofing camera housings, markers, connectors, and a new blue ring lighter. the accuracy of the motion measurement was obtained within the calibration error of 0.87mm in average and 0.89mm in standard deviation for the distance of 500mm between two markers on the calibration device. the volume of $2100mm(length)\times2100mm(breadth)\times2300mm(Height)$ was covered with 4 cameras of the underwater motion measurement system. For the performance verification, motion measurement test of a vertical mooring chain model excited at the top end was carried out. The 3D motions of mooring model were measured with variable amplitude and period of the forced excitation. Higher order motions of the mooring model were observed as the excitation period decreases. the performance of the system was verified by successfully measuring 3D motion of mooring model.

• 센서학회지
• /
• 제5권6호
• /
• pp.1-6
• /
• 1996

외부 침입자를 감지하기 위한 높은 감도의 실질적인 매설형 광섬유 센서의 제작에 관하여 논의하였으며, 광섬유로 구성된 마이켈슨 간섭계 센서를 이용하려 본 실험을 수행하였다. 외부에서 인가된 무게와 위상변화 사이의 관계는 선형적이었고, 감지 아암을 모래 표면으로부터 8 인치 아래로 매설하였을 때, 센서 출력파형의 위상이 반주기가 이동하는데 필요한 압력과 길이의 곱은 약 $1.09\;kPa{\cdot}m$이였다. 본 실험으로부터 광섬유 센서의 감도는 매설된 광섬유 위를 걸어가는 사람과 그 위를 지나가는 수레 등을 감지하기에 충분히 높은 감도를 가진다는 결론을 얻을 수 있었다.

• 한국구조물진단유지관리공학회 논문집
• /
• 제4권2호
• /
• pp.103-111
• /
• 2000

The objectives of the study are to know the strain distribution and modal dynamic behaviour of steel bridge girders by actual traffic load. The live load effect depends on many parameters including the span length, gross vehicle weight, axle weight, axle configuration so on. For the estimation of static and dynamic characteristic, strain data caused by moving loads and traffic characteristics of passing vehicle under actual traffic load have measured using Bridge Weigh in Motion. To confirm the reliability of BWIM system, strain data measured using the $120{\Omega}$ strain gauge under the same condition. It is considered that the data acquired from BWIM system have reliability through the analysis and comparison between stress measured by strain data from BWIM and computed by FEM. Additionally according to the measured strain data of up-line and down-line on the highway, the up-line bridge grows more faster than the down-line bridge and girder 4 and 5 carry more load when vehicles pass the inner line and girder 2 and 3 does when vehicles pass the outer line as this case(the bridge composed with 5 girders).

• 한국지능시스템학회논문지
• /
• 제6권3호
• /
• pp.51-62
• /
• 1996

전자감응식 교통신호시스템은 승용차환산계수를 고려하지 않음으로서 과포화상태에서 출발지연시간 및 승용차 대기시간을 유발하고 있다. 본 논문에서는 전처리로,우선 신경망을 이용하여, 하위 교차로의 승용차환산계수를 생성한다. 그러나, 간혹 차량의 무게, 속도가 틀리기때문에 최적주기신호를 부정확하게 산출할 수 있다. 그러므로 후처리로 상위교차로의 포화상태비율에 의한 Feed-Back된 데이터를 이용한 퍼지제어를 함으로서, 과포화시에 승용차대기 시간 및 출발지연시간을 감소기키는 연구이다. 뿐만아니라, 과포화상태에서 앞막힘현상을 예방제어하기 위해서 포화상태비율, 도로길이, 도로경사도, 도로폭등이 같지 않은 상위교차로에서도 앞막힘현상을 예방제어 할 수 있도록 하였다.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 1999년도 추계학술대회 논문집
• /
• pp.333-343
• /
• 1999

When a high speed train enters a tunnel, wind speed passing through the train in a tunnel section becomes higher due to the reverse flow to the direction of the train. The higher wind speed gives more aerodynamic forces to the pantograph on the train. Therefore, it is necessary to perform aerodynamic and dynamic analyses in order to check whether the current collection of the high speed train, entering the tunnel, still remain permissible or not. In this paper, the aerodynamic analysis has been performed under the assumption that a high speed train at 300 km/h enters a tunnel whose cross sectional area Is 107/㎡ and length is 1000m. In consideration of the aerodynamic analysis results, the dynamic analysis has been performed based on the catenary and pantograph dynamic models in SEOUL-PUSAN high speed rail, using the GASENDO developed by RTRI. In addition, the fatigue life of the contact wire has been reviewed using the Goodman diagram. Based on the analysis results, it is concluded that the increase of the aerodynamic forces on the pantograph in the tunnel section shall not affect characteristics of current collection adversely except that motions of the pantograph may be constrained by bump-stops.

• 풍력에너지저널
• /
• 제9권4호
• /
• pp.57-64
• /
• 2018

To maximize power generation and reduce the construction cost of a commercial utility-grade wind turbine, the size of the wind turbine should be large. The initial design of the 12 MW University of Ulsan(UOU) Floating Offshore Wind Turbine(FOWT) was carried out based on the 5 MW National Renewable Energy Laboratory(NREL) offshore wind turbine model. The existing 5 MW NREL offshore wind turbines have been expanded to 12 MW UOU FOWT using the geometric law of similarity and then redesigned for each factor. The resonance of the tower is the most important dynamic responses of a wind turbine, and it should be designed by avoiding resonance due to cyclic load during turbine operations. The natural frequency of the tower needs to avoid being within the frequency range corresponding to the rotational speed of the blades, 1P, and the blade passing frequency, 3P. To avoid resonance, vibration can be reduced by modifying the stiffness or mass. The direct expansion of the 5 MW wind turbine support structure caused a resonance problem with the tower of the 12 MW FOWT and the tower length and diameter was adjusted to avoid a match of the first natural frequency and 3P excitation of the tower.

• 한국방송∙미디어공학회:학술대회논문집
• /
• 한국방송∙미디어공학회 2022년도 하계학술대회
• /
• pp.1249-1252
• /
• 2022

In this paper, we propose a conceptual framework that identifies video frames in motion containing the movement of people and vehicles in traffic videos. The automatic selection of video frames in motion is an important topic in security and surveillance video because the number of videos to be monitored simultaneously is simply too large due to limited human resources. The conventional method to identify the areas in motion is to compute the differences over consecutive video frames, which has been costly because of its high computational complexity. In this paper, we reduced the overall complexity by examining only the keyframes (or I-frames). The basic assumption is that the time period between I-frames is rather shorter (e.g., 1/10 ~ 3 secs) than the usual length of objects in motion in video (i.e., pedestrian walking, automobile passing, etc.). The proposed method estimates the possibility of videos containing motion between I-frames by evaluating the difference of consecutive I-frames with the long-time statistics of the previously decoded I-frames of the same video. The experimental results showed that the proposed method showed more than 80% accuracy in short surveillance videos obtained from different locations while keeping the computational complexity as low as 20 % compared to the HM decoder.