• 한국경영과학회지
• /
• 제23권1호
• /
• pp.97-107
• /
• 1998

This paper is concerned with a parallel system that sustains a time-independent load and consists of n components with exponential lifetimes. It is assumed that the total load is shared by the working components and the failures of components increase higher failure rates in the surviving components according to the relationship between the load and the fialure rates. The power rule model among several load-failure rate relationships is considered. We consider the system efficiency meausre as the expected profit earned by the system per unit time. The high load causes high gain but it also occurs frequent system failures. The expected profit per unit time is used as criterion to evaluate the system efficiency. The goal of system engineer is to determine the optimal load and redundant units maximizing the expected profit per unit time. First, the system reliability function is obtained and the optimization problem of the load-sharing parallel system is considered. Given the redundant units, the existence of the optimal load can be proved analytically and given the load, the optimal redundant units can be solved also analytically. The optimal load and redundant units are obtained simultaneously by numerical computation. Some numerical examples are studied.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2012년도 추계학술대회 논문집
• /
• pp.663-664
• /
• 2012

• Journal of Electrical Engineering and Technology
• /
• 제11권5호
• /
• pp.1274-1281
• /
• 2016

• Journal of Communications and Networks
• /
• 제12권5호
• /
• pp.510-517
• /
• 2010

In this paper, an adaptive MAC protocol (variable load adaptive (VLA)-MAC) is proposed for wireless sensor networks. This protocol can achieve high energy efficiency and provide low latency under variable-traffic-load conditions. In the case of VLA-MAC, traffic load is measured online and used for adaptive adjustment. Sensor nodes transmit packets in bursts under high load conditions to alleviate packet accumulation and reduce latency. This also removes unnecessary listen action and decreases energy consumption in low load conditions. Simulation results show that the energy efficiency, latency, and throughput achieved by VLA-MAC are higher than those achieved by some traditional approaches.

• Journal of Power Electronics
• /
• 제16권1호
• /
• pp.102-110
• /
• 2016

Contactless power transfer technology is gaining increasing attention in city transportation applications because of its high mobility and flexibility in charging and its commensurate power level with conductive power transfer method. In this study, an inductively coupled contactless charging system for a 48 V light electric vehicle is proposed. Although this study does not focus on system efficiency, the generic problems in an inductively coupled contactless power transfer system without ferromagnetic structure are discussed. An active load matching method is also proposed to control the power transfer on the receiving side through a load matching converter. Small signal modeling and linear control technology are applied to the load matching converter for port voltage regulation, which effectively controls the power flow into the load. A prototype is built, and experiments are conducted to reveal the intrinsic characteristics of a series-series resonant inductive power charger in terms of frequency, air gap length, power flow control, coil misalignment, and efficiency issues.

• Journal of Biosystems Engineering
• /
• 제31권1호
• /
• pp.16-23
• /
• 2006

Depth and working load control is one of the most important technique in control system for tractor rotary implement automation. Keeping the depth consistent is critical to bring along crops and to improve the efficiency and quality of the following operations. Keeping the load of engine consistent is an essential factor for the efficiency of operation and engine protection of tractor. In this study we investigated the possibility of application of depth and working load control system for tractor using a proportional valve through field tests. Depth control was implemented by the ascent and descent of 3 point linkage for the change of setting depth. There were 4 mm and 5.2 mm control deviations for setting depths of 50mm and 100mm, respectively. Load control was operated appropriately by the ascent and of descent of 3 point link for the change of setting working load. The standard deviations between setting load and engine load were 171 rpm at 1.3 km/h and 164 rpm at 2.3 km/h tractor travel velocity. The results of experiment showed that the characteristics of response was sufficient to be used as the implement depth and working load control system for tractor using proportional valve.

• 한국습지학회지
• /
• 제17권4호
• /
• pp.414-420
• /
• 2015

질소는 수계 부영양화를 유발하는 주요 원인이며, 수계 보호를 위해 반드시 처리해야 하는 오염물질이다. 본 연구에서는 고농도 질소를 처리하여 하수처리장 운전 효율 증대를 위한 방안을 연구하고자 하였다. 약 250일간 하수처리장 농축조상징액을 이용하여 실험실 규모 반응조를 운전하였다. 실험실 반응조 운전은 안정적인 아질산화 반응을 유도하고, 관련 운전 인자 영향을 분석하고자 하였다. 연구 결과 체류시간 조절을 통해 인위적으로 아질산화 반응이 유도가능한 것을 확인하였으며, 안정적인 아질산화 반응이 유도되는 구간을 파악하였다. 특히, 체류시간 1일 조건에서는 90%에 가까운 고효율의 아질산화율을 보이는 것을 확인하였다. 특히 ammonium nitrogen load는 암모니아성 질소 제거율과 아질산화율에 영향을 미치는 것으로 나타났다. 높은 ammonium nitrogen load 조건에서는 아질산화율과 암모니아성 질소 효율이 감소하였다. 반면, 낮은 ammonium nitrogen load 조건에서는 아질산화율이 감소하는 것으로 나타났다. 이는 아질산화 반응을 위해 암모니아성질소 농도 및 체류시간의 조절이 필요하다는 것을 의미한다. 농축조 상징액과 같은 슬러지 처리 공정 내 고농도 질소를 함유한 폐수는 아질산화 반응을 적용할 수 있으며, 이는 하수처리장 개조 방안으로 제안 될 수 있을 것으로 판단된다.

• 한국도로학회논문집
• /
• 제16권3호
• /
• pp.9-20
• /
• 2014

PURPOSES : This study is to compare load transfer efficiency of key joint and dowel joint for airport concrete pavement. METHODS : As AC150/5320-6D of FAA's [Advisory Circular] was changed into AC150/5320-6E, Key joint type of rigid pavement were excluded from Construction Joints. LTE(Load Transfer Efficiency) of dowel joint and key joint were compared by times and seasons through pavement temperature measurement, ocular investigation and HWD measurement. RESULTS : For the joint performance grade of No. 2(The second) runway of airport, 12% of poor rate was observed in key joint and 2% of poor rate in dowel joint. Poor rate of key joint was increased to 17%, if only No. 3~No. 6 slabs, which are mostly loaded from the airplanes, were applied for the study. In apron area, LTE poor rate of key joint was high in winter, and LTE poor rate of dowel joint was at least above 'Fair' grade. In summer, 'Fair' for key joint, 'Acceptable' for dowel joint appeared. CONCLUSIONS : As results, dowel joint was superior than key joint for LTE. Deviations of seasons and times were smaller in dowel joint's result. And LTE in winter was lower than LTE in summer.

• Journal of Electrical Engineering and Technology
• /
• 제12권3호
• /
• pp.1195-1202
• /
• 2017

Induction motors often reach their maximum efficiency at the nominal load. In most applications, the machine load is not equal to the nominal load, thus reduces the motor efficiency and turns a greater percent of power into loss. In this paper, the induction motor control problem has been investigated to reduce the system losses. The Field Oriented Control method (FOC) has been employed in this paper. In this research, the mathematical equations related to system losses are calculated in relation to torque and speed, and then the q- and d-axis are summarized according to the current components. After that, the proposed method is applied along with d- and q-axis. In the recent three decades, many techniques have been suggested to improve the induction motor performance using smart and non-smart methods. In this paper, a new PSO-Fuzzy method have used in real time. The fuzzy logic method serves as speed controller in q-axis and PSO algorithm controls the optimum flux in d-axis. It will be proved that the use of this combined method will lead to a significant improvement in motor efficiency.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1991년도 추계학술대회 논문집 학회본부
• /
• pp.137-139
• /
• 1991

This paper proposes a minimum power factor control for maximum efficiency operation of an induction motor, under low load condition. Minimum input or maximum efficiency operation is achived by properly adjusting the amplitude of the stator voltage, with the three phase AC voltage controller. Through the simulation, the relationships between the delay angle and input power under various load conditions are examined. Experimental results are also given, which show good coincidence with the simulation results.