• Journal of the Korean Society of Marine Environment & Safety
• /
• v.22 no.7
• /
• pp.900-905
• /
• 2016

The field of power system harmonics has been receiving a great deal of attention recently. This is primarily due to the fact that non-linear (or harmonic-producing) loads comprise an ever-increasing portion of what is handled at a typical industrial plant. The incidence rate of harmonic-related problems is low, but awareness of harmonic issues can still help increase offshore power plant system reliability. On the rare occasion that harmonics become a problem, this is either due to the magnitude of harmonics produced or power system resonance. This harmonic study used an electrical configuration for the offloading scenario of a Floating LNG (FLNG) unit, considering power load. This electrical network configuration is visible in the electrical network load flow study part of the project. This study has been carried out to evaluate the performance of an electric power system, focusing on the harmonic efficiency of an electrically driven motor system to ensure offshore plant safety. In addition, the design part of this study analyzed the electric power system of an FLNG unit to improve the safety of operation and maintenance.

• KIPS Transactions on Computer and Communication Systems
• /
• v.4 no.6
• /
• pp.185-196
• /
• 2015

Energy aware server clusters aim to reduce power consumption at maximum while keeping QoS(Quality of Service) compared to energy non-aware server clusters. They adjust the power mode of each server in a fixed or variable time interval to let only the minimum number of servers needed to handle current user requests ON. Previous studies on energy aware server cluster put efforts to reduce power consumption further or to keep QoS, but they do not consider energy efficiency well. In this paper, we propose an energy efficient cluster management based on autonomous learning for energy aware server clusters. Using parameters optimized through autonomous learning, our method adjusts server power mode to achieve maximum performance with respect to power consumption. Our method repeats the following procedure for adjusting the power modes of servers. Firstly, according to the current load and traffic pattern, it classifies current workload pattern type in a predetermined way. Secondly, it searches learning table to check whether learning has been performed for the classified workload pattern type in the past. If yes, it uses the already-stored parameters. Otherwise, it performs learning for the classified workload pattern type to find the best parameters in terms of energy efficiency and stores the optimized parameters. Thirdly, it adjusts server power mode with the parameters. We implemented the proposed method and performed experiments with a cluster of 16 servers using three different kinds of load patterns. Experimental results show that the proposed method is better than the existing methods in terms of energy efficiency: the numbers of good response per unit power consumed in the proposed method are 99.8%, 107.5% and 141.8% of those in the existing static method, 102.0%, 107.0% and 106.8% of those in the existing prediction method for banking load pattern, real load pattern, and virtual load pattern, respectively.

• Proceedings of the Korean Society for Agricultural Machinery Conference
• /
• 2017.04a
• /
• pp.71-71
• /
• 2017

농용트랙터의 운전자는 작업, 주행으로 인한 유해한 저주파 진동에 장시간 노출된다. 이에 따라 운전자에게 전달되는 노면 진동을 감소시켜주기 위한 전방차축 현가장치의 역할이 커지고 있다. 트랙터의 전방차축 현가장치는 주로 유압식으로 설계되어 있으며 이를 구성하는 유압요소 선정이 현가장치의 성능에 중요한 영향을 미친다. 하지만, 실제와 유사한 조건에서 트랙터 차체 무게만큼 큰 부하를 제공하여 유압회로의 성능을 실험하는 것은 비용과 시간 측면에서 비효율적이다. 본 연구에서는 이를 대체하기 위하여 개별 유압요소의 성능을 테스트 할 수 있는 현가장치 유압회로 요인 시험기를 설계제작 하였다. 이를 이용하여 개별 부품의 성능곡선을 센서를 이용 측정하였고 얻은 특성값을, 구성한 유압 시뮬레이션 모델에 반영하여 실제조건의 유압특성을 얻을 수 있는 유효한 시뮬레이션 모델 개발에 활용하였다. 또한, 실험실 환경에서 유압식 현가장치를 간소화 시킨 형태로 유압회로의 성능을 예비시험해 볼 수 있도록 다양한 센서를 장착 데이터를 취득할 수 있도록 하였다. 개발한 요인 시험기는 하부에 설치된 가진 실린더를 이용하여 상부에 설치된 현가장치 실린더의 스트로크 변위와 속도에 따른 힘을 측정할 수 있도록 구성하였다. 이를 위해 현가장치 실린더의 헤드부와 로드부에 각각 압력센서를 설치하였으며 헤드부, 로드부의 압력 차이와 로드셀을 이용해 측정한 가진 실린더의 힘의 관계를 확인하였다. 상부의 현가 실린더 장치는 복동 형태로 제작되어 헤드부, 로드부 양쪽 방향으로 유량이 흐를 수 있도록 설계되었다. 이를 이용해 헤드부와 로드부 사이에 어큐뮬레이터, 가변 오리피스, 릴리프 밸브 등으로 유압회로를 구성하였으며 어큐뮬레이터 용량에 따른 힘의 변화, 가변 오리피스의 개도량에 따라서 전달되는 힘의 크기 등을 측정하였다. 하부의 가진 실린더는 사인파, 삼각파, 계단 입력, DC 레벨 등의 신호를 발생시킬 수 있도록 제작되었다. 신호의 주파수는 0~4Hz, 범위에서 사용자가 조절할 수 있도록 설정되었으며 계단응답 성능 측정 시험을 평가한 결과 정상상태오차는 0.470mm~0.536mm, 입상시간은 0.194초~0.202초, 정착시간은 0.230초~0.421초로 나타났다.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.6B
• /
• pp.595-604
• /
• 2009

The HCCA reserves the channel resources based on the mean data rate in IEEE 802.11e. It may cause either the waste of channel resource or the increase of transmission delay at MAC layer if the frame size is rapidly varied when a compressed mode video codec such as MPEG video is used. To solve these problems, it is developed that the packet scheduler allocates the wireless resource adaptation by according to the packet size. However, it is difficult to perform the admission control because of the difficulty with calculating the available resources. In this paper, we propose a CAC mechanism to solve the problem that may not satisfy the QoS by increasing traffic load in case of using EDCA. Especially, the proposed CAC mechanism calculates the EB of TSs using the traffic information transmitted by the application layer and the number of average transmission according to the wireless channel environment, and then determines the admission of the TS based on the EB. According to the simulation results of the proposed CAC mechanism, it admitted the TSs under the loads which are satisfied within the delay bound. Therefore, the proposed mechanism guarantees QoS of streaming services effectively.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.15 no.2
• /
• pp.103-110
• /
• 2010

In this paper, a new mode changeable asymmetric full bridge dc/dc converter is proposed to solve the freewheeling current problem of the conventional zero voltage switching(ZVS) phase shift full bridge(PSFB) dc/dc converter of low output voltage and high output current applications. The proposed converter is operated as an asymmetric full bridge converter when the duty cycle is less than 50% and active clamp full bridge converter when the duty cycle is greater than 50%. As a result, since its freewheeling current is eliminated, the conduction loss is lower than that of the conventional ZVS PSFB dc/dc converter. Moreover, ZVS of all power switches can be ensured along a wide load ranges and output current ripple is very small. Therefore, high efficiency of the proposed converter can be achieved. Especially since its operation mode is changed to the active clamp full bridge converter during hold up time and can be operated with 50~100% duty ratio, it can produce the stable output voltage along wide input voltage range. The operational principles, theoretical analysis and design considerations are presented. To confirm the operation, validity and features of the proposed converter, experimental results from a 1.2kW($400V_{dc}/12V_{dc}$) prototype are presented.

• Journal of the Institute of Electronics Engineers of Korea SD
• /
• v.47 no.3
• /
• pp.28-34
• /
• 2010

In this paper, the transceiver for RFID reader using 13.56MHz as a carrier frequency and meeting International Standard ISO 14443 type A, 14443 type B and 15693 is presented. The receiver is composed of envelope detector, VGA(Variable Gain Amplifier), filter, comparator to recovery the received signal. The proposed automatic reference voltage generator, positive peak detector, negative peak detector, and data slicer circuit can adjust the decision level of reference voltage over the received signal amplitudes. The transmitter is designed to drive high voltage and current to meet the 15693 specification. By using inductor loading circuit which can swing more than power supply and drive large current even under low impedance condition, it can control modulation rate from 30 percent to 5 percent, 100 perccnt and drive the output currents from 5 mA to 240 mA depending on standards. The 13.56 MHZ RFID reader is implemented in $0.18\;{\mu}m$ CM08 technology at 3.3V single supply. The chip area excluding pads is $1.5mm\;{\times}\;1.5mm$.

• The Journal of the Acoustical Society of Korea
• /
• v.14 no.4
• /
• pp.29-37
• /
• 1995

A resonant frequency of piezoelectric transducer depends remarkably on the electric impedance connected to the vibrator. In this paper, using this effect of frequency controllable two layered PZT ultrasonic transducer is designed and its acoustic characteristics are analyzed by a new transmission model equivalent circuit. The theoretical and the experimental results of the electric impedance effect on the resonant frequency variation were compared and both results showed a good consistency each other. The resonant frequency has been controlled continuously in the wide frequency range of 180kHz~580kHz and the effective attenuations were less than 7dB in the frequency range of 330kHz~470kHz.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.11 no.3
• /
• pp.258-265
• /
• 2006

In this paper, an active clamping sepic-flyback converter has been proposed, which is suitable for a fuel cell based power generation system. The proposed converter is superposition of sepic converter mode and flyback mode. It has outstanding high boosting output voltage, component utilization and high efficiency characteristics under the inherently severe low output voltage of the fuel cell generator. In this paper, the validity of the proposed converter has been verified by the informative simulation and experimental results that make used of the PEMFC.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.20 no.2
• /
• pp.167-173
• /
• 2009

This paper proposes an electronically beam steering array antenna, consisting of single fed active element and 4 parasitic elements, operating in 5.8 GHz ISM band. Beam steering can be achieved by controlling the reactance of the variable reactance control circuit connected to the load of the parasitic elements without using the high cost phase shifters. The proposed antenna realizes ${\pm}30^{\circ}$ beam scanning of E-plane and H-plane with the below -10 dB return loss in ISM band. The gain of the $6.18{\sim}7.53\;dBi$ in E-plane and $7.022{\sim}7.779\;dBi$ in H-plane is shown in the scanning range.

• Journal of Advanced Marine Engineering and Technology
• /
• v.35 no.8
• /
• pp.1009-1015
• /
• 2011

In this study, in the high expansion cycle was conduced by variable valve timing system composition to close intake valve late, and in the intake air reduction on the low compression was solved by supercharging pressure. In this wise, by constituting Diesel-Atkinson cycle, this study looked into a possibility of thermal efficiency improvement. As a result, there was improvement in thermal efficiency and output in a whole range of closing timing from ABDC $40^{\circ}$ to ABDC $80^{\circ}$. However, after ABDC $70^{\circ}$ of closing timing, the thermal efficiency increase was getting smaller. As the result of the study, the optimum intake valve closing timing was about ABDC $70^{\circ}$, high loading territory of engine was more effective than low loading territory, and engine operation in middle loading territory was stable. At this time, brake thermal efficiency was 12.5% higher than ordinary engine on average.