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데이터 공학 : 아파치 스쿱을 사용한 하둡의 데이터 적재 성능 영향 요인 분석
( Liu Chen ),고정현 ( Jung Hyun Ko ),여정모 ( Jeong Mo Yeo ) 한국정보처리학회 2015 정보처리학회논문지. 소프트웨어 및 데이터 공학 Vol.4 No.2
빅데이터 기술은 데이터 처리 속도가 빠르다는 면에서 주목을 받고 있다. 그리고 관계형 데이터베이스(Relational Database: RDB)에 저장되어있는 대용량 정형 데이터를 더 빠르게 처리하기 위해서 빅데이터 기술을 활용하는 연구도 진행되고 있다. 다양한 분산 처리 도구들을 사용하여 분석 성능을 측정하는 연구는 많지만 분석하기 전 단계인 정형 데이터 적재의 성능에 관한 연구는 미미하다. 때문에 본 연구에서는 RDB 안에 저장되어있는 정형 데이터를 아파치 스쿱(Apache Sqoop)을 사용하여 분산 처리 플랫폼 하둡(Hadoop)으로 적재하는 성능을 측정하였다. 그리고 적재에 영향을 미치는 요인을 분석하기 위해 여러 가지 영향 요소를 변경해가면서 반복적으로 실험을 수행하였고 RDB 기반으로 구성된 서버 간의 적재 성능과 비교하였다. 실험 환경에서 아파치 스쿱의 적재 속도가 낮았지만 실제 운영하고 있는 대규모하둡 클러스터 환경에서는 더 많은 하드웨어 자원이 확보되기 때문에 훨씬 더 좋은 성능을 기대할 수 있다. 이는 향후 진행할 적재 성능 개선 및 하둡 환경에서 정형 데이터를 분석하는 전체적인 단계의 성능을 향상시킬 수 있는 방법에 대한 연구의 기반이 될 것으로 예상한다. Big Data technology has been attracted much attention in aspect of fast data processing. Research of practicing Big Data technology is also ongoing to process large-scale structured data much faster in Relatioinal Database(RDB). Although there are lots of studies about measuring analyzing performance, studies about structured data loading performance, prior step of analyzing, is very rare. Thus, in this study, structured data in RDB is tested the performance that loads distributed processing platform Hadoop using Apache sqoop. Also in order to analyze the influence factors of data loading, it is tested repeatedly with different options of data loading and compared with data loading performance among RDB based servers. Although data loading performance of Apache Sqoop in test environment was low, but in large-scale Hadoop cluster environment we can expect much better performance because of getting more hardware resources. It is expected to be based on study improving data loading performance and whole steps of performance analyzing structured data in Hadoop Platform.
Energy Efficient Architecture Using Hardware Acceleration for Software Defined Radio Components
Liu, Chen,Granados, Omar,Duarte, Rolando,Andrian, Jean Korea Information Processing Society 2012 Journal of information processing systems Vol.8 No.1
In order to make cognitive radio systems a practical technology to be deployed in real-world scenarios, the core Software Defined Radio (SDR) systems must meet the stringent requirements of the target application, especially in terms of performance and energy consumption for mobile platforms. In this paper we present a feasibility study of hardware acceleration as an energy-efficient implementation for SDR. We identified the amplifier function from the Software Communication Architecture (SCA) for hardware acceleration since it is one of the functions called for most frequently and it requires intensive floating-point computation. Then, we used the Virtex5 Field-Programmable Gate Array (FPGA) to perform a comparison between compiler floating-point support and the on-chip floating-point support. By enabling the on-chip floating-point unit (FPU), we obtained as high as a 2X speedup and 50% of the overall energy reduction. We achieved this with an increase of the power consumption by no more than 0.68%. This demonstrates the feasibility of the proposed approach.
Numerical prediction of switching gurney flap effects on straight bladed VAWT power performance
Liu Chen,Jun Xu,Ren Dai 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.12
Based on the lift mechanism of the Gurney flap (GF) applied on isolated airfoil trailing edge, an active GF was designed to vary its height with the rotation of VAWT blades. The active GF extrudes over the blade when the blade is in the upwind area and retreats into the blades in the downwind area. The VAWT performance was studied by two-dimensional CFD numerical simulation for varied tip speed ratios. Results show that the VAWT power coefficients with active GFs increased over all tip speed ratios. The relative increase of power coefficient was 5.14 % at the operation condition of maximum power coefficient. Proper orthogonal decomposition analysis reveals the small-scale coherent vortex structure in the wake of the VAWT, which exists in the high order modes. It spreads in the rotating domain of the impeller and generates major energy loss. Active GF limits the vortex strength of the 5th order structures during the blade rotation.
Q-learning Algorithm Based Multi-Agent Coordinated Control Method for Microgrids
Yuanyuan Xi,Liuchen Chang,Meiqin Mao,Peng Jin,Nikos Hatziargyriou,Haibo Xu 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6
This paper proposes a Q-learning algorithm (Q-LA) based multi-agent coordinated control method for microgrids. By the method, Q-LA is adopted to calculate the power to be regulated, which is called the microgrid regulation error (MRE), in secondary control for real-time operation. And the generation schedule of distributed generators (DGs) as well as batteries is modified in real time with the MRE by the fuzzy theory and particle swarm optimization method, taking the economy and environmental benefits into consideration together. The simulation platform of Q-LA based multi-agent hybrid energy management system for microgrid (HEMS-MG) is established in C++ Builder. The simulation results verify the effectiveness and feasibility of the proposed method.
Development of a Current-Sensorless Multi-Loop Control for Standalone PWM Inverters
Yuan Yisheng,Liuchen Chang,Song Pinggang 전력전자학회 2007 ICPE(ISPE)논문집 Vol.- No.-
A current-sensorless multi-loop control method that estimates the capacitor current is proposed for standalone inverter applications. The theory of the control loop is given, and a mathematical model is analyzed. The effect of capacitor parameter mismatch on system characteristics was emphasized and discussed through modeling and simulation. Finally, experimental results comparing the characteristics of the output voltage under parameter mismatch conditions verified the operation and merits of the proposed controller.
Improved SVM for High Gain Tri-state CSI to Reduce DC Side Inductor Current Ripple
Chufeng Li,Liuchen Chang,Meiqin Mao 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5
Extending our previous work proposing a high gain tri-state current source inverter (CSI), in this paper, an improved space vector modulation (SVM) method is proposed in order to reduce the DC side inductor current ripple. By the proposed SVM method, the active state time is divided into four equal segments and the shoot-through state time is divided into six equal segments and inserted into the four equal active state segments, respectively. Theoretically, the maximum ripple can be obtained to 1/3 of that compared with the traditional SVM mode. The proposed improved SVM method is compared with the traditional SVM method. Simulation and experimental results verify the effectiveness of the proposed strategy.
Multi-Agent Based Simulation for Microgrid Energy Management
Mao Meiqin,Dong Wei,Liuchen Chang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
This paper presents a general multi-agent based model for the hierarchical and distributed energy control of a Microgrid. In this model, the agents under three different levels are classified and defined in detail. And based on the model, a novel simulation platform for the energy management system of the Microgrid (EMS-MG) is designed in terms of Client-Server and implemented under C++ Builder environment. Taking the generation automatic control for example and by the proposed model and implemented EMS-MG, a simulation result is shown to illustrate the operation process of the simulation platform and present the benefits of the proposed method.
Economic Analysis of the Microgrid with Multi-energy and Electric Vehicles
Mao Meiqin,Sun Shujuan,Liuchen Chang 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Electric vehicles (EVs) may play dual roles when they plug in a microgrid. They appear as loads during charging, meanwhile they may also be used as storage units to supply energy to the rest loads in the microgrid if the batteries have the sufficient spare energy. Considering the characteristic of bidirectional energy flow of EVs in a microgrid, this paper proposes the energy dispatch model and strategies for the microgrid including Wind generators, Photovoltaic systems, Battery storages, EVs and other local loads to analyze the impact of incorporating vehicles within and without microgrid on the economic operation of the microgrid. The simulation results indicate that incorporating EVs within the microgrid can not only minimize the capital cost of storages and reduce operation cost of the microgrid’s operator, but also save the cost of EVs’s owners.