• 전기학회논문지
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• 제63권11호
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• pp.1575-1581
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• 2014

In this paper, eddy current loss, iron loss and heat transfer of PMSG with 2,000kW capacities were analyzed for wind turbine. The PMSG with 3 split magnet was analyzed using ansoft maxwell commercial program and, generator was tested by Back to Back converter with no load condition at laboratory. Rotor surface temperature was measured by Pt100 sensors for investigating heat transfer from rotor to atmosphere. The simulation results shows 27.4kW eddy current loss in no load condition and 50.2kW eddy current loss in rated load condition with 3 split magnet, and also shows 4.3kW iron loss in no load condition and 7.3kW iron loss rated load condition. The heat transfer coefficient of convection between rotor surface and atmosphere was investigated by $9.6W/m^2{\cdot}K$. Therefore the heat transfer from rotor to atmosphere was about 17kW(54%) and from rotor to air-gap was about 14.6kW(46%) in no load condition. It is identified that the cooling system for stator have to include the 46% of iron loss, and heat dissipation structure of rotor surface have to be suggested and designed for efficiency improvement of generator.

• 한국농공학회논문집
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• 제59권6호
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• pp.1-8
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• 2017

The purpose of this study was to provide basic data for development of environmental design technology for greenhouses constructed in reclaimed lands. We analyzed the climatic conditions around seven major reclaimed land areas in Korea, which have a plan to install advanced horticultural complexes. The characteristics of heating load through the thermal environment measurement of the greenhouse in Saemangeum were analyzed. The part to be applied to the environmental design of the greenhouses in reclaimed lands were reviewed. The overall heat transfer coefficient of the experimental greenhouse with the aluminum screen and multi-layer thermal curtain averaged $3.79W/m^2^{\circ}C$. It represents a 44 % heat savings rate compared with plastic greenhouses with a single covering, which was significantly lower than that of the common greenhouses with 2-layer thermal curtains. This is because the experimental greenhouse was installed on reclaimed land and wind was stronger than the inland area. Among the total heating load, the transmission heat loss accounted for 96.4~99.9 %, and the infiltration loss and the ground heat exchange were low. Therefore, it is necessary to take countermeasures to minimize the transmission heat loss for greenhouses constructed in reclaimed lands. As the reclaimed land is located on the seaside, the wind is stronger than the inland area, and the fog is frequent. Especially, Saemangeum area has 2.6 times stronger wind speed and 3.4 times longer fog duration than the inland area. In designing the heating systems for greenhouses in reclaimed lands, it is considered that the maximum heating load should be calculated by applying the wind coefficient larger than the inland area. It is reasonable to estimate the operation cost of the heating system by applying the adjustment factor 10 % larger than the average in calculating the seasonal heating load.

• Tribology and Lubricants
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• 제39권2호
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• pp.81-85
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• 2023

This study presents an experimental investigation of the effects of surface roughness on gas foil thrust bearing (GFTB) performance. A high-speed motor with the maximum speed of 80 krpm rotates a thrust runner and a pneumatic cylinder applies static loads to the test GFTB. When the motor speed increases and reaches a specific speed at which a hydrodynamic film pressure generated within the gap between the thrust runner and test GFTB is enough to support the applied static load, the thrust runner lifts off from the test GFTB and the friction mechanism changes from the boundary lubrication to the hydrodynamic lubrication. The experiment shows a series of lift-off test and load-carrying capacity test for two thrust runners with different surface roughnesses. For a constant static load of 15 N, thrust runner A with its lower surface roughness exhibits a higher start-up torque but lower lift-off torque than thrust runner B with a higher surface roughness. The load capacity test at a rotor speed of 60 krpm reveals that runner A results in a higher maximum load capacity than runner B. Runner A also shows a lower drag torque, friction coefficient, and bearing temperature than runner B at constant static loads. The results imply that maintaining a consistent surface roughness for a thrust runner may improve its static GFTB performance.

• 대한환경공학회지
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• 제39권12호
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• pp.714-722
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• 2017

수질오염총량관리제도(이하 총량제)는 하천의 목표수질을 달성하기 위해 유역에서 배출되는 오염물질의 총량을 관리하는 제도이다. 유역에서 배출되는 오염물질의 허용총량은 수질모델을 활용하여 산정하며, 이과정에서 오염부하량은 발생, 배출, 유달부하량으로 구분할 수 있다. 유달부하량은 배출부하량과 유달율의 곱으로 계산되며 유달율은 유역에서 배출된 오염물질이 하천의 특정지점에 도달하는 비율로 정의된다. 본 연구에서는 Hwang(2016) 등이 제시한 기준유량 조건의 유달율 추정방법을 영강유역에 적용하고 QUALKO2 수질모델의 수질 입력자료를 생성하여 기준유량 조건의 유달율 산정방법(식 (3))과 평균 개념의 유달율 산정 방법(식 (2))의 비교분석을 통해 유달율 추정방법에 대한 검증 연구를 수행하였다. 연구결과, 유달율 함수식은 식 (2)와 식 (3) 모두 사용 가능하나, 배출계수 적용에 따라 방법론을 달리할 필요가 있다. 식 (2)를 사용할 경우는 배출계수를 저수량, 평수량 구분없이 1로 동일하게 사용해야 하며, 식 (3)을 사용할 경우는 기술지침에서 정한 배출계수(저수량 0.15, 평수량 0.5)를 적용해야 할 것으로 판단된다.

• 한국자동차공학회논문집
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• 제2권2호
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• pp.103-116
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• 1994

In this study the behavior of engine cooling loss and overall heat transfer coefficient were studied experimentally using naturally aspirated engine and turbo charged engine. Using turbo charging, heat dissipation was increased because of the density of the mixture was increased with increment of inlet air flow rate. Therefore, cooling loss of turbo charged engine is larger than naturally aspirated engine. As taking the measurement of surface temperature of combustion chamber, gas heat transfer coefficient was calculated and found that it has greatly affected to overall heat transfer coefficient. The empirical formula of overall heat transfer coefficient established in order to predict of engine cooling loss and express only as a function of mean piston velocity.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2001년도 춘계학술대회 논문집
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• pp.28-31
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• 2001

Friction for sheet metal forming affects improvement of deep drawing formability. The deep drawing is affected by many process variables, such as lubricant, blank shapes, shape radius and so on. Especially, lubrication is very important formability factor. In this study, in order to investigate fraction coefficient of sheet metal forming, we examined friction test about three conditions, such as non-lubrication, full lubrication and film lubrication. We measured friction coefficient according to pin load under the conditions like deep drawing die. Mean friction coefficient for film lubrication condition would be very useful value to improve drawability.

• 소성∙가공
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• 제13권6호
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• pp.528-534
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• 2004

In order to find the effect of lubricant viscosity, tool geometry, forming speed, and sheet material properties on the friction in the sheet metal forming, friction tests were performed. Friction test results show that as the lubricant viscosity becomes lower, the friction coefficient is higher. When surface roughness is extremely low or high, the friction coefficient is high. The bigger die corner radii and punch speed are, the smaller is the friction coefficient. From the experimental observation, the friction model which is the mathematical expression of friction coefficient in terms of lubricant viscosity, roughness and hardness of sheet surface, punch corner radius, and punch speed is constructed. By comparing the punch load found by FEM using the proposed friction model with that obtained from the experiment in 2-D stretch forming, the validity and accuracy of the friction model are demonstrated.

• 한국농공학회논문집
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• 제54권6호
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• pp.77-87
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• 2012

Recently, Load and Resistance Factor Design (LRFD) based on reliability analysis has become a global trend for economical and rational design. In order to implement the LRFD, quantification of uncertainty for load and resistance should be done. The reliability of result relies on input variable, and therefore, it is important to obtain exact uncertainty properties of load and resistance. Since soil stress is the main reason causing the settlement or deformation of ground and load on the underground structure, it is essential to clarify the uncertainty of soil stress distribution for accurately predict the uncertainty of load in LRFD. In this study, laboratory model test on silty sand bed under probabilistic load is performed to observe propagation of upper load uncertainty. The results show that the coefficient of variation (COV) of soil stress are varied depending on location due to non-linear relationship between upper load increment and soil pressure increment. In addition, when the load uncertainty is transmitted through ground, COV is decreased by damping effect.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1391-1397
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• 2012

하이포 트로코이드 기반의 CRG(Cam ring gear) 시스템은 핀 또는 롤러 치형을 가지는 기어와 공액인 캠 링기어로 구성된 내접기어 시스템이다. 본 논문에서는 CRG 시스템의 엄밀 치형설계를 바탕으로 기어 치면에서의 접촉특성을 분석하였으며 형상설계변수인 치형수정계수에 따른 기어의 내구수명을 검토하였다. 결과적으로 치형수정계수의 증가를 통해 기 설계된 CRG 시스템에 영향을 미치지 않으면서 기어의 접촉 피로수명을 향상시킬 수 있다.

• 한국농공학회논문집
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• 제53권6호
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• pp.137-144
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• 2011

We have examined the pollutant load of combined sewer in dry days. Two monitoring sites (C-1, C-2) were equipped with an flowmeter. Monitoring was conducted from September 2004 to April 2006 for 20 months during dry days. Flowrate and concentration of pollutants are lowest from 3 to 6 o'clock, and it is high at 9, 12 and 21 o'clock. Most of organic matters exist in the dissolved state. The results show that pollution loads in C-2 area were 4.5-7.2 times higher than in C-1. Pollutant loads were high on Saturdays. Pollutant loads (kg/ha/day) of C-2 were 1.1-3.1 times higher those of C-1. However there was no significant difference in winter. Analysis of correlation coefficient of water quality parameter indicates that besides of flowrate all items in C-1 site have tight relationship respectively (p<0.01). In C-2 site, correlation coefficient of TP-SS, TP-TN, TP-flowrate, BOD-flowrate, BOD-SS and TN-TP are statistically significant (p<0.01).