• Journal of Advanced Marine Engineering and Technology
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• 제26권2호
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• pp.248-255
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• 2002

Miller cycle was studied and analyzed by engine performance simulation to achieve very low fuel consumption and to meet the IMO NOx regulation on a medium speed diesel engine. Based on the performance simulation results the intake valve closing time for HYUNDAI HiMSEN 6H21/32 engine was set at 0deg.ABDC(After Bottom Dead Center). Also, the simulation results indicated that significant NOx reduction could be achieved with low reduction of fuel consumption. The performance simulation investigated the effect of compression ratio and turbocharger on fuel consumption and NOx concentration in combination with Miller cycle. The results indicated a significant reduction of fuel consumption with keeping NOx concentration. The results of performance simulation were compared with measured data to verify simulation results. The comparison showed the maximum error was 2.34% in exhaust temperature. Also, the experimental result showed that improvement in BSFC(Brake Specific Fuel Consumption) was 5.8g/kwh with keeping NOx level similar to simulation result.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2001년도 하계종합학술대회 논문집(5)
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• pp.103-106
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• 2001

In this paper, a soft switching half-bridge converter using secondary switches for output control and conduction loss reduction is proposed. The conventional half-bridge converter must be fixed on duty cycle for soft switching. The proposed converter was consisted of two added switches in series of the secondary rectifier diodes. The main switches with constant duty cycle are operated ZVS. The secondary switches are operated ZV-ZCS. Especially, the primary switches were fixed duty cycle for maximum voltage conversion ratio. Output of converter is controlled by duty cycle or phase-shifted time of secondary switches. The conduction loss of the proposed converter can be reduced by the secondary switches. The operation characteristic, analysis, simulation and experimental results of the proposed converter are presented.

• 대한기계학회논문집
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• 제16권1호
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• pp.77-86
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• 1992

본 연구에서는 사이클은 터빈 출구로 부터 배출되는 폐열을 최대한 회수하여 얻은 증기를 연소기내에 분사시킴으로써 부가적인 압축기 및 비출력의 상향을 기할수 있다.아울러 폐열이용 암모니아 흡수기 냉동기를 구동하여 압축기 입구 온도를 낮 춤에 의해 열효율 및 비출력의 증대는 물론 대기온도 변화에 따른 기관 성능의 변동을 감소시킬 수 있다.

• 한국정보과학회:학술대회논문집
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• 한국정보과학회 2001년도 가을 학술발표논문집 Vol.28 No.2 (3)
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• pp.160-162
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• 2001

Cyclic-Reservation Multiple-Access(CRMA) is an access scheme for high-speed local and metropolitan area networks based on folded-bus or dual-bus configurations. CRMA provides high throughput and fairness independent of the network speed or distance. This paper describes a simulation-based quantitative analysis of the performance gains obtained by introducing slot reuse in CRMA. Generally, a longer cycle length means a longer access delay and a lower throughput. There-fore, it is desirable to develop a scheme such that the cycle length is the shortest. In this paper, we will study the problem of reducing the total number of empty slots generated within every cycle. However, it has been shown that the problem is NP-complete under the constraint that all empty slots used by a station in a cycle are required to be consecutive. We present the algorithm that improves previous novel approach by using previous node information. We compare our slots reuse scheme with several slot reuse algorithms such as region scheme (FMR), address schemes, novel approach in terms of the following two important performance criteria: average cycle length and average slot utilization ratio. As compared with the one proposed in novel algorithm, the new scheme makes the cycle length much shorter. Besides, the resulting slot utilization and the access delay are better than those of the other two schemes.

• Journal of Welding and Joining
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• 제8권2호
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• pp.40-52
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• 1990

Fatigue behavior of the AH, DH and EH grade TMCP(Thermo-Mechanical Control Process) steels was studied. High cycle and low cycle fatigue tests were carried out for the weldment and base metal of each steel. The results showed that the fatigue limit at 2 * $10^6$ cycles was 33 to 37 kg/$mm^2$ for the base metal and 30 to 34 kg/$mm^2$ for the weldment. The ratio of fatigue limit to tensile strength for TMCP steels was 0.65 to 0.71, which was a value close to the upper limit for the ordinary steels. It was also found that the high cycle fatigue behavior of TMCP steels could be affected by the microstructures of base metal. It will be necessary to have fine structure for TMCP steels to increase the fatigue resistance. In low cycle fatigue test, the fatigue lifetime of AH and DH steels accorded well with the ASME best fit curve, while that of EH steel was considerably lower than the fatigue lifetime of the other steels. Fatigue resistance of the weldment made by high heat input(180kJ/cm) welding was not lower than that made by low heat input(80kJ/cm) welding in case of high cycle fatigue, but the high heat input welding decreased the fatigue resistance in case of low cycle fatigue.

• 한국초전도ㆍ저온공학회논문지
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• 제25권4호
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• pp.28-31
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• 2023

This study presents a comprehensive procedure for the low cycle fatigue test of ultrasonically welded (UW) coated conductor (CC) lap-joints. The entire process is examined in detail, from the robust fabrication of the UW REBCO CC joints to the reliability testing under a low number of repeated cycle fatigue conditions. A continuous I_c measurement system enables real-time monitoring of I_c variations throughout the fatigue tests. The study aims to provide a step-by-step procedure that involves joint fabrication, electromechanical property (EMP) tests under uniaxial tension for stress level determination, and subsequent low-cycle fatigue tests. The joints are fabricated using a hybrid method that combines UW with adding In-Sn soldering, achieving a flux-free hybrid welding approach (UW-HW flux-free). The selected conditions for the low cycle fatigue tests include a stress ratio of R=0.1 and a frequency of 0.02 Hz. The results reveal some insights into the fatigue behavior, irreversible changes, and cumulative damage in the CC joints.

• Journal of Advanced Marine Engineering and Technology
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• 제38권4호
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• pp.502-507
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• 2014

본 논문에서는 혼합작동유체를 해양온도차발전에 적용하였을 때에 그에 따른 사이클의 성능특성에 대해 연구를 수행하였다. 다양한 혼합작동유체 중 본 논문에서는 R32/R152a를 해양온도차발전에 적용하였다. 사이클로는 기존의 밀폐형사이클, 암모니아/물 혼합물에 적용하고 있는 칼리나 사이클에 대해 시뮬레이션 해석을 수행하였고, 온열원의 온도는 $26^{\circ}C$, 냉열원의 온도는 $5^{\circ}C$를 적용하였다. R32를 적용한 밀폐사이클의 출력은 22kW, 사이클의 효율은 2.02%를 보였다. 혼합작동유체를 적용하였을 때에 R32/R152a(90%:10%)의 출력은 29.93kW, 사이클 효율은 2.78%로 기존의 단일 냉매보다 36%, 사이클효율은 37%상승함을 확인 하였다. 칼리나 사이클 또한 위와 같은 방법으로 연구를 수행하였다.

• 한국농공학회지
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• 제33권3호
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• pp.51-62
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• 1991

A comprehensive laboratory investigation of the liquefaction characteristics of Jumunjin standard sand. Seoul sand and Hongsung sand was peformed by the undrained cyclic triaxial compression test under different relative densities, confining pressures and cyclic deviator stresses. The results obtained are as follows ; 1. Liquefaction potential was dominated by the stress ratio at a given number of cycle. That is, the number of cycle required to cause initial liquefaction became samller as the stress ratio increased. 2. Liquefaction potential of a sand was infliuenced by initial relative density or void ratio. Under a given relative density. liquefaction potential of Jumunjin standard sand and Seoul sand was smaller than that of Hongsung sand. 3. The pore pressure ratio of Hongsung sand was the smallest three under a given relative density and stress ratio, and it showed higher value when the cyclic stress and the shear strain were high. 4. An excessive pore pressure ratio not found when initial shear was smaller than 0.01%, and the pore pressure ratio started to increase when initial shear became greater than 0.01%. 5. Soil texture is an important factor to cause liquefaction, and liquefaction potential decreased a the mean grain size decreased. however the sand having fine grain such as Hongsung sand showed somewhat higher liquefaction potential. 6. Based on the analysis of the specimens whose number of the cycles to cause liquefaction was 8~12, it was found that the relationship between density and stress ratio was linear. The curves for Hongsung sand was steeper than the other. 7. From the above results and the method suggested by Seed-Idriss, it may be considered that the damages by Hongsung earthquake was not directly caused by liquefaction.

• 한국습지학회지
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• 제19권1호
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• pp.16-29
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• 2017

북한에서는 1990년대 이후 경제실패로 인해 대규모의 산림파괴가 이루어 진 것으로 알려져 있으며, 이는 결과적으로 수문순환의 특성을 크게 변화시켰을 것으로 예측되고 있다. 본 연구에서는 이를 확인하기 위해 지표수문해석모형인 VIC 모형을 이용하여 한반도 전역을 대상으로 1981년부터 2013년까지 약 30여년의 기간에 대해 수문순환모의를 수행하였다. 모의 결과를 요약하면 다음과 같다. 먼저, 유출률의 경우, 남한에서는 55%~70%, 북한에서는 38%~56% 정도인 것으로 나타났다. 특히 유출률 자체가 작음에도 불구하고 그 변동폭은 남한의 15% 보다 큰 28% 정도임에 주목할 필요가 있다. 증발산률은 북한이 남한보다 크게 나타났다. 즉, 남한에서는 증발산률이 20~35%, 북한에서는 25%~46%로 나타났다. 그러나 그 변동폭은 북한의 경우가 21%로 남한의 15%에 비해 다소 크게 나타났다. 셋째, 토양수분량의 경우 남한의 평균이 34%, 북한의 평균은 27%로 남한이 높은 것으로 나타났다. 그러나 유출률과 증발산률의 모의 결과와는 달리 토양수분은 전 기간에 걸쳐 남한과 북한이 변동성 차이가 8% 내외로 유사한 것으로 나타났다. 이상과 같은 결과를 통해 특히 북한의 산림파괴가 본격적으로 이루어진 1990년대 이후 남한과 북한의 수문순환 특성의 차이가 확대되었음을 확인할 수 있었다. 남한의 경우에는 유역별 수문순환 특성의 차이가 미미한데 비해, 북한의 경우에는 확연히 다른 차이를 보여주고 있는데, 이 역시 산림파괴의 영향 차이가 반영된 결과로 추측된다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 추계학술대회 논문집 전력기술부문
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• pp.145-147
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• 2005

This paper presents a methodology for satisfying the thermal comfort of Indoor environment and reducing the summer peak demand power by minimizing the power consumption for an Air-conditioner within a space. KEPCO(Korea Electric Power Corporation) use the fixed duty cycle control method regardless of the indoor thermal environment. This method has disadvantages that energy saying depends on the set-point value of the Air-Conditioner and DLC has no net effects on Air-conditioners if the appliance has a lower operating cycle than the fixed duty cycle. A variable duty cycle estimates the PMV(Predict Mean Vote) at the next step with a predicted temperature and humidity coming from the back propagation neural network model. It is possible to reduce the energy consumption by maintaining the Air-conditioner's OFF state when the PMV lies in the thermal comfort range. The proposed methodology uses the historical real data of Sep. 7th, 2001 from a classroom in seoul to verify the effectiveness of the variable duty cycle method comparing with fixed duty cycle. The result shows that the variable duty cycle reduces the peak demand to 2.6times more than fixed duty cycle and increases the load control ratio by 8% more. Based on the variable duty cycle control algorithm, the effectiveness of DLC is much more improved as compared with the fixed duty cycle.