• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.3-3
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• 2000

Limit cycle analysis of attitude control system using gas jet thrusters is performed. Schmitt-Trigger and PD control laws are applied and solenoid valve time delay is considered. Phase plane method is used for calculation of characteristics of limit cycle. Important characteristics of resultant limit cycle such as frequency, amplitude, maximum rate, and duty ratio could be expressed analytically by proposed method.

• 한국자동차공학회논문집
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• 제13권5호
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• pp.188-194
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• 2005

The direct injection diesel engine is one of the most efficient thermal engines. For this reason DI diesel engines are widely used for heavy-duty applications. But the world is faced with very serious problems related to the air pollution due to the exhaust emissions of diesel engine. So, that is air pollution related to exhaust gas resulted from explosive combustion should be improved. Exhaust Gas Recirculation(EGR) is a proven method to reduce NOx emissions. In this study, the experiments were performed at various engine loads while the EGR rates were set from $0\%$ to $30\%.$ The emissions trade-off and combustion of diesel engine are investigated. The brake specific fuel consumption rate is very slightly fluctuated with EGR in the range of experimental conditions. The ignition delay increased with increasing EGR rate. The maximum value of premixed combustion for the rate of heat release is increased with increasing EGR rate. NOx emissions are decreased with increasing EGR rate at high load and high speed. It was found that the exhaust emissions with the EGR system resulted in a very large reduction in oxides of nitrogen at the expense of higher smoke emissions.

• 전자공학회논문지T
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• 제36T권3호
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• pp.56-63
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• 1999

본 논문에서는 BF 컨버터의 Active PFC 시스템을 구성하고, 전력 변환시 입력 전류를 전원 전압과 동상인 정현파로 제어하며 직류 출력 전압을 제어하기 위한 PWM-PFM 제어 기법을 사용하여 역률을 개선하였다. FET와 IGBT를 이용하여 본 논문에서 제시한 Boost 컨버터와 인버터 회로를 구성하였고, 제안된 Boost 컨버터의 제어 회로는 마이크로프로세서 80C196으로 구성하였다. 또한 입력 전압이 30V이고, Boost 인덕터가 1.1 mH일 때 정격 출력은 전압 50V, 전류 IA, 듀티비 (Duty Ratio) 0.5 이상으로 하였다. 부하 저항의 변화에 따른 전압 변화를 PWM-PFM 제어 기법을 이용하여 제어하였고, 전류 성형 기법을 이용하여 역률이 0.96 가지 개선됨을 실험으로써 입증하였다.

• Journal of Nutrition and Health
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• 제35권2호
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• pp.263-271
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• 2002

The purpose of this study was to determine the standard work time of dietetic staff through work sampling methodology in school flood service systems. Work measurement through work sampling methodology was conducted in five conventional, five commissary and five joint management flood service systems over two consecutive weeks in October 1999. Statistical analysis was performed on the SAS/Win 6.12 package program for Kruskal-Wallis test and multiple comparison. Observed data were satisfied with a confidence level of 95% and a confidence interval of $\pm$ 0.05. The results of this study can be summarized as follows. The actual time spent by dietetic staff members in conventional, commissary, joint-management flood servile systems was 2,394, 2,521 and 2,110 minutes per week, respectively. Transportation time of each flood service systeml and ILO allowance rate (11%) was applied. Thus, the standard work time per week of dietetic staff members in conventional, commissary, joint-management flood service systems was 2,746.14, 2,861.58 and 2,520.81 minutes, respectively. The standardized index was 1.04, 1.08 and 0.95 men in conventional, commissary, and joint-management flood service systems, respectively. Regardless of the school flood service system, those with "the duty of cooking and distribution management" had the longest labor time, while those with "duty of nutritional education" had the shortest labor time.

• Environmental Engineering Research
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• 제20권4호
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• pp.397-402
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• 2015

SCR has been popularly approved as one of the most effective means for NOx emission control in heavy-duty and medium-duty vehicles currently. However, high urea dosing would lead to ammonia slip. And $NH_3$ sensor for vehicle emission applications has not been popularly used in real applications. This paper presents experimental studies on the diesel engine urea-SCR system by using a double NOx sensor system that is arranged in the downstream of the SCR catalyst based on ammonia cross-sensitivity. It was shown that the NOx conversion efficiency rised as $NH_3/NOx$ increases and the ammonia slip started from the $NH_3/NOx$ equal to 1.4. The increase of temperature caused high improvement of the SCR reaction rate while the space velocity had no obvious change. The ammonia slip was in advance as catalyst temperature or space velocity increase and the ammonia storage reduced as catalyst temperature or space velocity increase. The NOx real-time conversion efficiency rised as the ammonia accumulative storage increase and reached the maximum value gradually.

• 한국조리학회지
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• 제10권3호
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• pp.32-50
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• 2004

The purpose of this study was to examine what caused bakery employees at tourist hotel to leave their job. It's basically meant to lay the foundation for increasing personnel management efficiency and reducing turnover rate, as an attempt to prevent workers from quiting their jobs would be a successful way to take advantage of human resources more efficiently. Both theoretical and experimental approaches were utilized to serve the purpose of this study. First, concerning salaries, their turnover intention was under the influence of whether they were properly paid or gained a sufficient living. Second, as for environmental factors, their turnover intention was affected by performance appraisal and interpersonal trust with colleagues. Third, regarding job-related factors, their turnover intention was impacted by whether their job was clearly defined, how much they were satisfied with their job and whether their posts were suitable. Forth, the change of job was subjected to the influence of the desire for job in another region, job in another company and another kind of job. And there should be a clear distinction between sales and other works, and they should carefully be treated so that they could find their job more satisfactory.

• 한국자동차공학회논문집
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• 제8권5호
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• pp.1-11
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• 2000

This study is aimed to develop a proto-type LPG engine for medium-duty commercial vehicles in order to substitute for conventional diesel engine. Recently, it is recognized that diesel engines are main cause for smoke pollution in urban site. So, it is expected to reduce this environmental emission by developing and substituting LPG engine which has the advantage of practical use in a short development period in aspects of infrastructures. For that, after analysing the specifications and performance characteristics of a base diesel engine, parts of combustion chamber, intake system, fuel supply and ignition systems suitable for LPG combustion were re-designed and manufactured. And and engine controller for fuel supply and ignition distributions was matched by feedback mapping based on the speed-load conditions. The torque and power of LPG engine were increased by 6∼12% on the overall driving conditions compared to the base diesel engine, and fuel consumption rate marked the similar level based on the fuel price. Exhaust emissions such as THC, CO, NOx recorded the same order with conventional LPG engine for passenger car.

• Journal of Welding and Joining
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• 제25권5호
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• pp.64-71
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• 2007

The aim of this paper is to investigate the effects of welding parameters on the weld shape in seal-welding of STS304L capsule for manufacturing a radioisotope source which is widely used in nondestructive testing of metal structures using gamma ray. Pulsed gas tungsten arc (Pulsed GTA) welding is performed for thin cross sectional area of the capsule. Seven welding parameters including current waveform parameters and arc length etc. are selected as main process parameters using design of experiment. The weld shape such as bead width, penetration depth, weld area, aspect ratio and area rate is investigated to assess the effects of welding parameters. As results, the combination of pulse duty/welding speed largely affects on bead width, penetration depth, area and aspect ratio. Finally, it is concluded that the key parameters are the combination of pulse duty/welding speed, base current and arc length, and their optimal conditions are 50%/1.77mm/s, 6.4A and 1 mm.

• 한국생산제조학회지
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• 제9권6호
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• pp.49-56
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• 2000

Due to the rapid increase of long-distance transportation, particular attentions have been paid to truck tires, especially to their dynamic characteristics. In this research, experimental modal analysis on two kinds of light-duty truck tires, i.e., radial tire and bias tire, are performed by using GRFP(global rational fraction polynomial) method to investigate differences of the dynamic behavior of the two tires. The test results have shown that the modal frequencies of bias tire are much higher than the corresponding values of radial tire with a similar mode shape, which is in accordance with the fact that the radial rigidity of bias tire is higher than that of radial tire. And most of the modal decay rates of bias tire are larger than those of radial tire within the scope of this experiment. In the frequency domain range of test, the bias tire has extra modes, which do not occur in the radial tire. This difference is based on the fact that the circumferential rigidity of the bias tire is quire low whereas that of radial tire is so high that the frequencies of the corresponding modes are out of the frequency range of test.

• 한국환경보건학회지
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• 제33권1호
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• pp.36-42
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• 2007

Diesel PM can be controlled using Diesel Particulate Filter, which can effectively reduce the level of soot emissions to ambient background levels. In the Heavy Duty Diesel area, the Continuously Regeneration trap has been widely applied in the retrofit market. As the Special act for the improvement of air quality in the capital area, the retrofit program for DPF to used diesel vehicle has progressed favorably and there are currently over 1,000 of these DPF in use in retrofit applications in korea. These DPF comprise a specially formulated Diesel Oxidation Catalyst upstream of a DPF. The $NO_2$ generated by the DOC is used to combust the carbon collected in the DPF at low temperature. To certificate DPF device that is suitable to domestic circumstances, it is necessary to evaluate exactly the DPF devices according to the regulation of DPF certificate test procedure for retrofit(ministry of environment(MOE) announcement NO. 2005-16). To do so the understand of that regulation like the standard of PM reduction rate is needed. In this study the test procedure including test cycle and BPT test condition was examined and also the test result for specific DPF was analyzed. In every test like field test, PM reduction efficiency test and seoul-10 mode test, no defect could be showed.