• 한국유체기계학회 논문집
• /
• 제10권4호
• /
• pp.21-28
• /
• 2007

The ratio of disk friction loss in a centrifugal pump is very large for the total pump loss in the range of very low specific speed. Therefore, impeller radius should be shortened to increase the pump efficiency because the disk friction loss is proportional to the fifth power of impeller radius. In order to compensate the decreased head by the shortened impeller radius, vane angle at impeller outlet should be increased. However, as the vane angle at impeller outlet becomes larger, performance instability occurs at low flow rate regions. In this study, J-Groove is adopted to suppress the performance instability and detailed examination is performed for the influence of the J-Groove on the pump performance. The results show that J-Groove gives good effect on the suppression of performance instability. Moreover, as J-Groove increases pump head considerably, the pump size can be smaller for head requirements.

• 드라이브 ㆍ 컨트롤
• /
• 제11권4호
• /
• pp.25-31
• /
• 2014

This paper details application of a DLC(Diamond Like Carbon)-coating to the swash plate and the ball joint of pistons that make sliding contact with the piston shoes of an axial piston pump. This process, aimed to reduce the frictional and leakage power losses of the hydrostatic piston shoe bearings at the low speed range. At lower speeds than 100rpm, the positive effects of the DLC-coating on the power loss reduction of the hydrostatic piston shoe bearings could be confirmed. These effects resulted in little improvement in volumetric efficiency of the test pump, but the mechanical efficiency could be raised by up to 5% at 100rpm; here, the DLC-coated swash plate played a more dominant role than the DLC-coated ball joint.

• KSTLE International Journal
• /
• 제3권1호
• /
• pp.1-6
• /
• 2002

The purpose of this paper is to investigate the effects of design parameters on the friction loss in piston skirt. An analytical model to describe the friction characteristics of piston skirt has been presented, which is based on the secondary motion of piston and mixed lubrication theory, It could be shown that the skirt friction closely depends on the side force acted on the piston pin. The side force is inf1uenced by cylinder pressure at low engine speed, but by inertia force at high engine speed. The usage of extensive skirt area and low weight piston is effective to reduce the friction loss at high speed. The low viscosity oil considerably decreases viscous friction as engine speed increases, but it increases boundary friction at low engine speed. From the parametric study, it is found that the skirt axial profile is the most important design parameter related to the reduction of skirt friction.

• 열처리공학회지
• /
• 제5권2호
• /
• pp.122-132
• /
• 1992

This study has been performed to investigate into some effects of the power density and traverse speed of laser beam on the optical microstructure, hardness and wear characteristics of medium carbon low alloy steel treated by laser surface hardening technique. The results obtained from the experiment are summarized as follows : (1) Optical micrograph has shown that finer lath martensite is formed and the amount of undissolved complex carbides increases as the traverse speed increases under the condition of a given power density, whereas the coarsening of lath martensite and the reduction of undissolved complex carbides occur with increasing the power density at a given traverse speed. (2) Hardness measurements have revealed that as the traverse speed increases, hardness values of outermost surface layer more of less decrease under low power densities, but are uniformly distributed under high power densities, also showing that they are uniformly distributed at low traverse speeds and more or less decrease at high traverse speeds with increasing the power density. (3) The effective case depth has been found to decrease from 0.26 mm to 0.17 mm with increasing the traverse speed from 1.5 m/min to 3.0 m/min at a given power density of $25.48{\times}10^3w/cm^2$ and to increase from 0.20 mm to 0.36 mm with increasing the power density from $19.11{\times}10^3w/cm^2$ to $38.22{\times}10^3w/cm^2$ at a given traverse speed of 2.0 m/min. (4) Wear test has exhibited that the amount of weight loss of laser surface hardened specimen with respect to sliding distance at a given load increases with increasing traverse speed at a given power density and decreses with increasing power density at a given traverse speed.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2009년도 춘계학술대회 논문집 전기설비전문위원
• /
• pp.10-12
• /
• 2009

Electromagnetic Interference(EMI) in electric railway operation has become increasingly important. The components within very high power electronic, and the circuits for treating low-level signals, comprise complex system that must coexist and be highly reliable. To study it, It were included how much the HEMU-400X generates EMI and it has an effect on the power conversion units which resulted from Power Line Disturbance (PLD) phenomenon by contact loss during its running. In this study, the dynamic characteristic of a contact wire and pantograph suppling electrical power to high-speed trains are investigated. The analysis of the loss of contact based on Power Simulator program software is performed to develop power line disturbance model suitable for high speed operation. It is confirmed that a contact wire and pantograph model are necessary for studying the dynamic behavior of the pantograph system.

• 전력전자학회논문지
• /
• 제21권5호
• /
• pp.381-387
• /
• 2016

Many efforts have focused on the improvement of power density and efficiency by downsizing the motor and inverter. Recently, Toyota, Honda, and GM realized that the compact-sized motor uses the hairpin structure with increased space factor. Reducing the maximum torque from high-speed technique also makes it possible to design the high-power density model. Toyota and Honda used the newly developed power semiconductor IGBT to decrease conduction loss for high-efficiency inverter. In particular, Toyota used the boost converter to increase the DC link voltage for high efficiency in low-torque high-speed region. Toyota and GM also used the double-sided cooling structure for miniaturization of inverter for high-power density.

• 동력기계공학회지
• /
• 제18권4호
• /
• pp.11-16
• /
• 2014

Although smoke emitted from ships is not included in IMO(International Maritime Organiztion) regulation yet, it is one of the substance what is polluting mainly the air. Especially, its concentration is very high when an engine is started and a load is rapidly changed. This is caused by unburned fuel what is injected more than necessary quantity after combustion period. It is possible to decrease smoke concentration emitted at starting engine by controlling fuel injection quantity, but it is concerned that time to rated speed must be spent. Then a governor what can reduce the smoke concentration without a loss of time to rated speed is needed. We adopted a electro-hydraulic governor what can control dual fuel start limit function and achieved very low level of smoke concentration without greater the loss of time to rated speed.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1990년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 26-27 Oct. 1990
• /
• pp.681-686
• /
• 1990

The existing Swash Plate Type Axial Piston Motor rapidly drops efficiency at high speed in comparison with low speed. This is the reason why the motor was designed only in a viewpoint of minimum of power supply. But, in this paper, the motor which was optimally designed in a veiwpoint not only power supply but also load capacitancy, flow loss volume, axial stiffness and tilting stiffness keeps up high efficiency at high speed.

• 정보처리학회논문지A
• /
• 제16A권1호
• /
• pp.27-34
• /
• 2009

최근 디지털 시스템 응용의 복잡성이 증가하면서, 고성능화와 전력 소모 절감은 중요한 문제로 대두되고 있다. 전력 소모를 줄이기 위한 방법으로, 프로세서의 저 전력화 또한 미세 공정의 개발과 함께 다양하게 접근되고 있으며, 이러한 결과 모바일 시스템의 시장 확대가 이루어지고 있다. 본 논문은 이러한 프로세서에서 소모되는 전력 중 데이터 캐시의 전력 손실을 줄이기 위하여 데이터 캐시의 웨이 중 필요로 하는 부분을 예측하여 선택적으로 프리자치 하도록 하는 전력 소모 개선 방법을 제안하였으며, 접근하는 웨이에 대한 예측이 성공했을 경우에는 에너지를 절감하면서 지연이 발생하지 않는 빠른 접근이 이루어지게 하고, 실패하였을 경우에도 최소한의 시간 지연으로 해당되는 웨이의 접근이 이루어지게 하였다. 시뮬레이션을 통한 검증 결과 웨이 예측 기법만을 사용한 경우에 대비하여 평균 10.2% 의 전력을 절감할 수 있었으며, 일반적 캐시에 비하여는 평균 56.4%의 전력을 절감할 수 있었다.

• 한국태양에너지학회 논문집
• /
• 제36권1호
• /
• pp.49-61
• /
• 2016

The power production using hub height wind speed tends to be overestimated than actual power production. It is because the hub height wind speed cannot represent vertical wind shear and blade tip loss that aerodynamics characteristic on the wind turbine. The commercial CFD model WindSim is used to compare and analyze each power production. A classification of atmospheric stability is accomplished by Monin-Obukhov length. The concentric wind speed constantly represents low value than horizontal equivalent wind speed or hub height wind speed, and also relevant to power production. The difference between hub height wind speed and concentric equivalent wind speed is higher in nighttime than daytime. Under the strongly convective state, power production is lower than under the stable state, especially using the concentric equivalent wind speed. Using the concentric equivalent wind speed considering vertical wind shear and blade tip loss is well estimated to decide suitable area for constructing wind farm.