• Journal of Advanced Marine Engineering and Technology
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• v.19 no.3
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• pp.33-41
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• 1995

본 연구는 터보 과급기 부착 디젤 기관의 급가속 운전시 기관과 과급기의 과도 응답 성능을 규명하고 이를 개선하기 위한 실험을 수행하였다. 과도 응답 성능 구명은 일정한 회전 속도로 정상 운전중인 기관의 연료 펌프 랙을 10%에서 40%까지 일정 시간동안 급가속하였을 경우에 대하여 수행하였으며, 이때의 과급기 응답 지연 현상을 개선하기 위한 실험은 급가속과 동시에 압축기 출구의 흡기메니폴드 내에 일정한 압력의 공기를 추가 분사하는 방법을 이용하였다. 그리고 공기 분사 압력, 공기분사 기간, 가속률, 가속 시간 등이 압축기 출구의 압력과 온도, 터빈 입구의 압력과 온도, 실린더 압력, 기관과 과급기 회전 속도 등의 응답 성능에 미치는 영향을 가속전 정상 상태의 기관 회전 속도와 적용부하의 변화에 따라 시간의 함수로 나타내었다.

• Journal of the KSME
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• v.23 no.6
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• pp.427-433
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• 1983

내연기관의 성능은 실린더에서 연료의 화학에너지가 열에너지로 얼마만큼 빠르고 완전하게 변화하느냐에 좌우된다. 이를 위해서는 실린더 내에서 뜨거운 압축공기와 연료의 혼합 및 증기화가 요구된다. 엔진의 출력은 매 사이클당 흡입.압축할 수 있는 공기량에 좌우되므로 연소의 해석을 위해서는 실린더 내의 공기유동, 연료의 분무 및 연소과정을 이해 해야한다. 배기와 엔진효율의 요구성때문에 희박 혼합기 또는 EGR (exhaust gas recirculation)이 필요하게 된다. 그러나 희석이 크면 낮은 연소온도, 낮은 층류흐름속도와 화염전면의 낮은 난류강도 때문에 연소기간이 증대하게 된다. 실제로 희박의 증가는 실화 또는 긴 연소 지연기간, 사이클 마다의 연소맥동현상, HC배기의 증가등을 초래하게 된다. 이러한 저온연소의 단점들은 연소상태를 안정시키고 연소량을 증대시키는 공기의 유동을 이용해서 해결 될 수 있다. 최근에는 선회류와 난류의 강도를 증가시켜서 빠른연소(fast burning)를 이루고 있다. 선회류와 난류의 강도를 증대시키는 가장 중요한 2가지 방법은 흡입포트(port), 매니홀드(manifold)설계이다.

• Journal of the Korean Society for Railway
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• v.15 no.6
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• pp.662-669
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• 2012

In 2004, KTX operated in Korea on the 5th in the world. But there are various factor on planed schedule delay of Big National Construction Project like Seoul-Busan High Speed Rail Project(Seoul-Busan HSR). For example, Often change of government policy, project management control problem of design and construction, conflict of interested party like environmental organization/resident are the main delay factors. The suggestions for improvement of the construction schedule through the Seoul-Busan HSR will help to make a new leap forward in rail construction.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.383-387
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• 2003

Construction project has many problem such as delay of the appointed date delivery, over budget, wether and site conditions. When several activities are influenced by the same factor, their duration may be delayed. This paper deals with the problem of construction duration estimating and schedule variation on the construction project. The theory of constraints technique for project management is referred to 'Critical Chain' technique. This paper shows optimal scheduling plan and time management technique, used probability construction duration estimating and scheduling buffer based on the critical chain project management.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.4 no.2
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• pp.175-180
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• 2001

Purpose: The advantages of air reduction are the ease of performing the procedure, reduced radiation time and lower morbidity rate if perforation occurs. But, patients who fail air reduction undergo a laparotomy at which 10% have spontaneously reduced. The first enema decreases the edema and venous congestion of bowel wall, thus repeated reduction may succeed. The aim of this study is to evaluate the efficacy of delayed repeated pneumatic reduction of intussusception in patients with failure of an initial attempt. Methods: Between January 1998 and December 1999, 21 patients with proven intussusception received repeated delayed reduction 1 to 3 hours following the first failed attempt. These patients were in stable condition and did not have peritonitis, shock or toxic sign. Results: Before reduction, the patients had symptoms and signs for 6 to 48 hours (median 24 hr). The interval from the first reduction to the repeated was 1 to 3 hours (median 2.2 hr). The success rate of repeated reductions was 76.2% (16 of 21 patients), and 23.8% (5 of 21 patients) required surgery. Four of 5 patients requiring surgery were manually reduced and 1 spontaneously reduced in the operating room. Conclusion: We recommended a repeated reduction in patients with intussusception who are in stable clinical condition after an unsuccessful initial reduction attempt.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.3D
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• pp.363-369
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• 2008

Change is inevitable and is a reality of construction projects. Change adjustment includes the cost associated with materials, labor, etc. However, the actions of a contractor can cause a loss of productivity and furthermore can result in disruption of the whole project because of a cumulative or ripple effect. Because of its complicated nature, it becomes a complex issue to determine the cumulative impact (ripple effect) caused by single or multiple change orders. Furthermore, owners and contractors do not always agree on the adjusted contract price for the cumulative impact of the changes. What is needed is a reliable method to identify and quantify the loss of productivity caused by cumulative impact of change orders. This study survey the change orders data in domestic area for public construction and analyze to quantify change order impact. This study developed concepts of "%CO", "%Delta", "%T" to capture change order effect on project and search the relationships between them. Finally, this study find strong relationship between change order and loss.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.43 no.6
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• pp.841-849
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• 2023

Construction projects have risks due to various factors such as construction delays and construction accidents. Based on these construction risks, the method of calculating the construction period of the construction project is mainly made by subjective judgment that relies on supervisor experience. In addition, unreasonable shortening construction to meet construction project schedules delayed by construction delays and construction disasters causes negative consequences such as poor construction, and economic losses are caused by the absence of infrastructure due to delayed schedules. Data-based scientific approaches and statistical analysis are needed to solve the risks of such construction projects. Data collected in actual construction projects is stored in unstructured text, so to apply data-based risks, data pre-processing involves a lot of manpower and cost, so basic data through a data classification model using text mining is required. Therefore, in this study, a document-based data generation classification model for risk management was developed through a data classification model based on SVM (Support Vector Machine) by collecting construction project documents and utilizing text mining. Through quantitative analysis through future research results, it is expected that risk management will be possible by being used as efficient and objective basic data for construction project process management.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.92-95
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• 2005

The present work has been developed the type of non-electric and delay explosive bolt which does not need power supply device and has the delay function in the operation of the explosive bolt. Separation device system could be minimized because of non-electric power supply system. In order to prove the mechanism of operation, the present work used to ignite the initiator the power of air resistance caused front aviation object. we can be founded from the present work that the changes in the operation load influence directly the ignition of the initiator. The design of non-electric and delay explosive bolt is the most suitable the separation system necessary to reduce the velocity of aviation object and safe landing of parachute system.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.3
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• pp.60-65
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• 2005

The present work has developed non-electric and delay-type explosive bolt that does not need electric power supply device and has the delay function in the operation. Non-electric power supply system enables separation device system to be minimized. In order to prove the mechanism of the operation, the power of air resistance caused from aviation object used to ignite the initiator. we can be founded from the present work that the changes in the operation load influence directly the ignition of the initiator. The design of non-electric and delay type of explosive bolt is the most suitable for the separation system that is necessary to reduce the velocity of aviation object and safe landing of parachute system.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.10
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• pp.1025-1031
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• 2011

Autoignition characteristic is an important parameter for designing diesel or PCCI engines. In particular, diesel spray flames are lifted from the nozzle and the initial flame is formed by an autoignition phenomenon. The lifted nature of diesel spray flames influences soot formation, since air will be entrained into the spray core by the entrainment of air between the nozzle region and the lifted flame base. The objective of the present study was to identify the effect of heat loss on the ignition delay time by adopting a coflow jet as a model problem. Methane ($CH_4$), ethylene ($C_2H_4$), ethane ($C_2H_6$), propene ($C_3H_6$), propane ($C_3H_8$), and normal butane (n-$C_4H_{10}$) fuels were injected into high temperature air, and the liftoff height was measured experimentally. As the result, a correlation was determined between the liftoff height of the autoignited lifted flame and the ignition delay time considering the heat loss to the atmosphere.