• Journal of Advanced Marine Engineering and Technology
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• 제37권4호
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• pp.404-408
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• 2013

본 연구에서는, 대형 증기유량이 요구되는 플랜트에서 정밀한 압력제어의 요구를 충족시키기 위한 다른 방법으로 3단계의 다중 제어밸브 구조를 이용하여 압력을 제어하는 제어기를 설계하는 내용이다. 본 연구의 핵심은 전기 유압시스템 외부에 별도의 PID 제어기를 이용하여 제어밸브의 위치를 정확하게 제어하는 것이다. 시뮬레이션 및 실험을 통해 제어기의 성능을 검증한다.

• 드라이브 ㆍ 컨트롤
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• 제17권4호
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• pp.46-53
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• 2020

In this paper, the development of a manually and continuously variable impact force control mechanism for hydraulic breakers was studied. Generally, a hydraulic breaker has one or two piston strokes. Hydraulic breakers, which have two strokes, have two valve-switching ports and make short and long piston strokes. The piston stroke valve controls the piston stroke by opening and closing a short stroke-switching port. The short piston stroke mode is used to break soft rock, concrete, or asphalt. This stroke control valve system is not popular for small hydraulic breakers mounted on 1 to 14-ton excavators. To preserve the carrier-like excavator, proper breaking force is needed, and it can be easily controlled by multiple piston stroke control valves. The easiest way to control these breakers is to use several switching ports and valves but they are not easy to install in small hydraulic breakers and are expensive. To use only one switching port and valve, a method can be used to change the open area of the switching port to delay valve switching. This method provides multiple piston strokes.

• 설비공학논문집
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• 제18권2호
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• pp.163-171
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• 2006

In order to control multi-zone temperatures, a multi-type air-conditioning system may be used. In this study, control algorithms for the compressor and the electronic expansion valve of a multi-type air-conditioning system were developed by using fuzzy logics. The compressor control algorithm was composed of a compressor pressure setpoint algorithm, a compressor pressure setpoint reset algorithm, and a compressor frequency setpoint algorithm. The electronic expansion valve control algorithm was composed of an indoor temperature control algorithm, and a superheat control algorithm. These algorithms were applied to a multi-type air-conditioning system. Test showed good results for the control of a multi-type air-conditioning system.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.675-680
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• 2006

Capacities of a tandem-type air-conditioner may be modulated by turning on and off of multiple compressors, and adjusting the position of a electronic expansion valve. In this study, control algorithms for compressors and a electronic expansion valve were developed by using fuzzy logics. The pressure control algorithm was also developed for the safe operation of compressors. There algorithms were implemented in a test lab and proved to be effective for the control of indoor air temperature and superheat temperature,

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.469-473
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• 2005

Capacities of a tandom-type air-conditioner may be modulated by turning on/off multiple compressors and adjusting positions of a electronic expansion valve. In this study. control algorithms for compressors and a electronic expansion valve were developed by using fuzzy’ logics. There algorithms were implemented in a test lab and proved to be effective for the control of indoor air temperature and superheat temperature.

• 한국산업융합학회 논문집
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• 제23권2_2호
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• pp.199-207
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• 2020

These days, many different types of valves are developed in the industrial area according to their use purpose. Multiple kinds of valves are installed to control a flow and pressure of the pipe conveying fluid. Valves serve as critical roles in land plants such as power plants. The performance of equipment varies depending on valve characteristics. In this study, the internal flow analysis on Cone-type valve is conducted to analyze flow field and secure a value of the flow coefficient Cv. According to the internal flow analysis, when the flow distribution of the middle cross-section of valve was open 100%, flow field was relatively and smoothly taken out. If it was open 50%, flow recirculation region increased and a little complex flow field occurred. Unlike ball valve or butterfly valve, this valve had flow recirculation in its outlet depending on a valve opening amount. Therefore, it was found that there was no flow recirculation in the outlet of Cone-type valve.

• 한국수자원학회논문집
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• 제48권10호
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• pp.869-877
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• 2015

해수침투 방지나 대수층 인공함양을 위하여 다수의 관정을 통하여 대수층으로 물을 주입하는 공법이 있다. 이러한 공법의 경우 소기의 목적을 달성하기 위해서는 관정의 위치와 주입량, 그리고 결과되는 관정의 지하수위 등이 별도의 지하수 모델링을 통하여 결정된다. 주입수는 통상 관망을 통하여 관정으로 공급되는 데 이 때 관망에는 관정별 주입량을 조절하기 위한 밸브가 설치된다. 본 연구에서는 다수의 주입 관정이 연결된 관망에서 사전에 산정된 주입량 분포를 준수하기 위한 밸브 개도와 주입관망 가동에 필요한 펌프 최소 소요양정 산정방안을 제시하였다. 본 연구결과는 주입군정 운영의 정밀도를 향상시키는 데 기여할 수 있다.

• 한국초전도ㆍ저온공학회논문지
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• 제18권2호
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• pp.42-47
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• 2016

A free-piston reciprocating expander is a device which operates without any mechanical linkage to a stationary part. Since the motion of the floating piston is only controlled by the pressure difference at two ends of the piston, this kind of expander may indispensably require a sophisticated active control system equipped with multiple valves and reservoirs. In this paper, we have suggested a novel design that can further reduce complexity of the previously developed cryogenic free-piston expander configuration. It is a simple replacement of both multiple valves and reservoirs by a combination of an orifice valve and a reservoir. The functional characteristic of the integrated orifice-reservoir configuration is similar to that of a phase controller applied in a pulse tube refrigerator so that we designate the one as a phase controller. Depending on the orifice valve size in the phase controller, the different PV work which affects the expander performance is generated. The numerical model of this unique free-piston reciprocating expander utilizing a phase controller is established to understand and analyze quantitatively the performance variation of the expander under different valve timing and orifice valve size. The room temperature experiments are carried out to examine the performance of this newly developed cryogenic expander.

• Journal of Chest Surgery
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• 제20권1호
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• pp.48-54
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• 1987

This report provides follow-up data on 557 patients [73 aortic, 357 mitral, and 127 multiple valve replacements] undergone lonescu-Shiley pericardial Xenograft valve replacement at Seoul National University Hospital between January, 1979 and December, 1985. There were 35 early death [6.3%] and 522 operative survivors were observed, and the cumulative follow-up is 1,140 patient-years [mean: 2.18 years per patient] The thromboembolic complications occurred in 34 cases [3.0% per patient-year] and the rate was 2.1% per patient-year for mitral and 0.3% per patient-year for aortic valve replacement in the presence of anticoagulation therapy. Among the 34 embolic episodes, 9 patients were dead [0.8% per patient-year] and the cause of death were 5 cerebral thromboembolism, 2 pulmonary embolism, and 2 intracerebral hemorrhage due to inappropriate anticoagulation after thromboembolic episode. Actuarial probability [+ SEM] of remaining free of thromboembolism for AVR is 88.1 x 11.1% at 5 years, for MVR 79.1 a 13.4% at 7 years and for multiple valve replacement 77.2 e 5.21% at 7 years. The incidence rate of thromboembolic complications after AVR is not less than that of MVR [0.3 Among the potential thromboembolic risk factors, atrial fibrillation is possible risk factor to increase the thromboembolic complication [0.05 < P < 0.1], but the importance of other factors, such as atrial clot, large left atrial size, mitral position, NYHA functional class, and age is less definite. A careful follow-up and the proper control of anticoagulation without omission, poor control, and arbitrary withdrawal is important for the successful management of the thromboembolic complications and the anticoagulation-related morbidity and mortality.

• International Journal of Control, Automation, and Systems
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• 제6권4호
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• pp.468-476
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• 2008

This paper presents a novel approach to economic dispatch (ED) with nonconvex fuel cost function as combinatorial optimization problems (COP) while most of the conventional researches have been developed as function optimization problems (FOP). One nonconvex fuel cost function can be divided into several convex fuel cost functions, and each convex function can be regarded as a generation type (G-type). In that case, ED with nonconvex fuel cost function can be considered as COP finding the best case among all feasible combinations of G-types. In this paper, a genetic algorithm is applied to solve the COP, and the $\lambda$-P table method is used to calculate ED for the fitness function of GA. The $\lambda$-P table method is reviewed briefly and the GA procedure for COP is explained in detail. This paper deals with three kinds of ED problems, namely ED considering valve-point effects (EDVP), ED with multiple fuel units (EDMF), and ED with prohibited operating zones (EDPOZ). The proposed method is tested for all three ED problems, and the test results show an improvement in solution cost compared to the results obtained from conventional algorithms.