• International Journal of Fluid Machinery and Systems
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• 제2권4호
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• pp.315-323
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• 2009

Pressure oscillations triggered by the unstable interaction of dynamic flow features of the hydraulic turbine with the hydraulic plant system - including the electrical design - can at times reach significant levels and could lead to damage of plant components or could reduce component lifetime significantly. Such a problem can arise for overload as well as for part load operation of the turbine. This paper discusses an approach to analyze the overload high pressure oscillation problem using computational fluid dynamic (CFD) modeling of the hydraulic machine combined with a network modeling technique of the hydraulic system. The key factor in this analysis is the determination of the overload vortex rope volume occurring within the turbine under the runner which is acting as an active element in the system. Two different modeling techniques to compute the flow field downstream of the runner will be presented in this paper. As a first approach, single phase flow simulations are used to evaluate the vortex rope volume before moving to more sophisticated modeling which incorporates two phase flow calculations employing cavitation modeling. The influence of these different modeling strategies on the simulated plant behavior will be discussed.

• 멤브레인
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• 제9권2호
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• pp.107-113
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• 1999

상업용 PDMS(polydimethylsiloxiane) 복합막과 플라즈마 처리된 PP(polypropylene)막을 사용하여 투과증발에 의한 알코올 농축을 수행하였고, 공정 조업 변수에 따른 영향을 조사하였다. PDMS막에 대한 부탄올의 친화력과 물의 친화력보다 크기 때문에 공급액의 부탄올 농도가 증가함에 따라 투과량의 선택도가 모두 증가하였다. 조업 온도가 증가함에 따라 고분자 사슬내의 자유 부피)free volume)가 증가하고 막에 대한 알코올과 물의 용해도 및 확산계수도 증가하여 투과량은 증가하였지만, 선택도는 감소하였다. PDMS 막과 용해도 계수(solubility parameter)값의 차가 적은 알코올일수록 높은 투과량과 선택도를 나타내었다. PP막을 메탄올로 플라즈마 처리한 경우 PDMS 복합막과 유사한 분리효율을 나타내면서도 투과량은 6배나 증가하였다. 플라즈마 처리 시간에 따라 투과량과 선택도는 모두 향상되었으나 일정 시간 이후에는 기공의 막힘 현상으로 투과량은 감소하였다.

• 한국도로학회논문집
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• 제16권1호
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• pp.57-62
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• 2014

PURPOSES : Capacity is a main factor of determining the number of lane in highway design or the level of service in road on operation. Previous studies showed that breakdown may occur before capacity is reached, and then it was concluded that capacity is a stochastic value rather than a deterministic one. In general, estimating capacity is based on average over maximum traffic volume observed for capacity state. This method includes the empirical distribution method(EDM) and would underestimate capacity. This study estimated existing empirical methods of estimating stochastic highway capacity. Among the studied methods are the product limit method(PLM) and the selected method(SM). METHODS : Speed and volume data were collected at three freeway bottleneck sites in Cheonan-Nonsan and West Sea Freeway. The data were grouped into a free-flow state or capacity state with speeds observed in the bottlenecks and the upstream. The data were applied to the empirical methods. RESULTS : The results show that the PLM and SM estimated capacity higher than EDM. The reason is that while the EDM is based on capacity observations only, the PLM and SM are based on free-flow high volumes and capacity observations. CONCLUSIONS : The PLM and SM using both free-flow and capacity observations would be improved to enhance the reliability of the capacity estimation.

• Journal of Mechanical Science and Technology
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• 제19권12호
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• pp.2296-2302
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• 2005

This study is focused on the comparison of heat transfer performance of two thermosyphons having 60 straight and helical internal grooves. Distilled water has been used as working fluid. Liquid fill charge ratio defined by the ratio of working fluid volume to total internal volume of thermosyphon, the inclination angle and operating temperature were used as experimental parameters. The heat flux and heat transfer coefficient are estimated from experimental results. The conclusions of this study may be summarized as follows; Liquid fill charge ratio, inclination angle and geometric shape of grooves were very important factors for the operation of thermosyphon. The optimum liquid fill charge ratio for the best heat flux were $30\%$. The heat transfer performance of helically grooved tube was higher than that of straight grooved tube in low inclination angle (less than $30^{\circ}$), but the results were opposite in high inclination angle (more than $30^{\circ}$). As far as optimum inclination angle concerns, range of $25^{\circ}\~30^{\circ}$ for a helically grooved tube and about $40^{\circ}$ for a straight grooved tube are suggested angles for the best results.

• Nuclear Engineering and Technology
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• 제55권8호
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• pp.2823-2834
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• 2023

Austenitic stainless steel welds (ASSWs) of nuclear components undergo aging-related degradations caused by high temperature and neutron radiation. Since irradiation leads to the change of material characteristics, relevant quantification is important for long-term operation, but limitations exist. Although ion irradiation is utilized to emulate neutron irradiation, its penetration depth is too shallow to measure bulk properties. In this study, a systematic approach was suggested to estimate mechanical properties of ion irradiated 308 ASSW. First of all, weld specimens were irradiated by 2 MeV proton to 1 and 10 dpa. Microstructure evolutions due to irradiation in δ-ferrite and austenite phases were characterized and micropillar compression tests were performed. In succession, dislocation density based stress-strain (S-S) relationships and quantification models of irradiation defects were adopted to define phases in finite element analyses. Resultant microscopic S-S curves were compared to verify material parameters. Finally, macroscopic behaviors were calculated by multiscale simulations using real microstructure based representative volume element (RVE). Validity of the approach was verified for the unirradiated specimens such that the estimated S-S curves and 0.2% offset yield strengths (YSs) which was 363.14 MPa were in 10% agreement with test. For irradiated specimens, the estimated YS were 917.41 MPa in 9% agreement.

• Archives of Plastic Surgery
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• 제37권5호
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• pp.626-632
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• 2010

Purpose: Nasal bone fractures are often classified as minor injury. However, the incidence of posttraumatic nasal deformity remains alarmingly high. It is because of unnoticed septal fracture. This study was conducted to determine the necessity of septoplasty for patients with nasal bone fracture accompanying grade I septal fractures. Methods: Among 105 patients with nasal bone fractures, 52 who had grade I septal fracture were diagnosed based on physical examination and computed tomography. Patients' age ranged from 14 to 65 years (mean 29.25 years), and 35 were male and 17 female. Patients were divided into 2 groups according to surgical treatment methods: patients who underwent closed reduction only (group 1, n=28) and those who underwent simultaneous closed reduction and septoplasty (group 2, n=24). The treatment outcomes were evaluated by comparing changes in nasal airway volume measured by acoustic rhinometry before the surgery, 3 months and 6 months after the surgery according to the timing of surgical repair and surgical treatment methods. Results: Nasal airway volume increased after the surgery by 17.8% in 3 months after the surgery, 25.2% in 6 months in group 1 and by 22.7% in 3 months, 35.8% in 6 months in group 2. The increase in airway volume after the surgery by 26.3% in 3 months after the surgery, 34.2% in 6 months after the surgery in operation within 1 week after trauma and by 12.1% in 3 months, 22.2% in 6 months after the operation later 1 week after trauma. The difference was statistically significant. Three patients in group 1 complained of intermittent nasal obstruction, two of whom showed a decrease in nasal airway volume by acoustic rhinometry. Conclusion: Most patients with nasal bone fractures accompanying grade I septal fractures have been treated with closed reduction in clinical settings. However, the results of this study suggest that septoplasty be performed after a correct diagnosis of septal fracture is made through comprehensive physical examination and computed tomography. Septoplasty is important to obtain more favorable outcomes and reduce complication.

• 대한토목학회논문집
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• 제38권6호
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• pp.925-932
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• 2018

이 연구는 특수형 회전교차로 중 터보형 회전교차로를 다루고 있다. 최근 많은 회전교차로가 국내에 건설되고 있으나, 회전교차로의 효과는 총 진입교통량과 용지면적에 달려 있다. 이 연구의 목적은 부도로 교통량이 매우 작은 신호교차로를 터보형 회전교차로로 전환함에 따른 운영 및 사고감소 효과를 분석하는데 있다. 주요 연구결과는 다음과 같다. 첫째, 주도로의 교통량 비율이 높고, 부도로의 교통량이 10~15% 이하인 경우나 좌회전 비율이 30% 이하로 적을 경우 1차로형 및 2차로형 회전교차로 보다는 터보형 회전교차로로 전환할 경우 개선효과가 있는 것으로 분석되었다. 둘째, 1차로형 회전교차로에 비해 터보형 회전교차로는 지체감소효과가 매우 높고, 2차로형 회전교차로에 비해 용지 면적이 적어 도로용량의 증대에도 더욱 효율적인 것으로 판단된다. 셋째, 터보형 회전교차로 전환설치 후 교통사고 건수는 45.9%, 부상자수는 76.5%가 감소하였고, 사고유형별로 차대사람 사고가 2.3명에서 2명(14.3%), 차대차 사고가 14.3명에서 0명(100%), 차량단독 사고가 0.3명에서 사상자가 0명(100%)으로 분석되었다. 마지막으로 이용자 만족도 조사 결과 긍정적인 평가는 60.4%에서 터보형 회전교차로 전환설치 후 76.8%로 약 16.4%가 향상되어 안전성, 접근성, 편의성 등에 대한 개선효과가 높은 것으로 분석되었다.

• 한국추진공학회지
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• 제26권1호
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• pp.28-37
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• 2022

밀폐용기(Closed Bomb)시험을 통해 고압에서 작동하는 고체 추진제의 연소속도를 추정하는 방법을 연구하였다. CEA를 이용하여 연소가스의 조성을 계산였으며 밀폐용기 내부의 고온, 고압의 환경을 묘사하기 위해 Noble-Abel 상태방정식을 적용하였다. 분자의 부피를 고려한 분자 간의 충돌을 묘사하는 인자인 Covolume을 분자의 LJ potential을 이용하여 모델링하였다. 또한 추진제의 부피 변화율을 고려하기 위해 3차 형상함수(Cubic form function)를 적용하였다. 각 모델을 사용하여 고압용기에서 측정된 5개의 압력-시간 선도로부터 연소속도를 계산하고 이를 BRLCB 결과와 비교 검증하였다. 각 실험에서 약 6% 이내의 최대 오차를 갖는 연소속도를 추정함으로써 초고압 환경에서의 연소속도 추정 방법을 정립하였다.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권5호
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• pp.253-259
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• 2005

Magnetic encoder with relatively low pulse per rotation is generally used for detecting speed of the high-speed rotating machine. It is due to the fact of the mechanical problems of vibration and bearing stiffness and also the limit of maximum output pulse of the mounted encoder. The magnetic encoder is divided into two types, that is, toothed gear-wheel method and magnetic wheel method according to the shape of the rotation disk. In case of detecting speed by the tooth gear-wheel, the encoder itself can be acted as the additional inertia where the number of tooth determining the output pulse and the width of the wheel detecting the change of the magnetic flux density are relatively enough large considering the volume of the rotating machine. While the magnetic wheel method has the limit of the magnetizing number of the ring magnet, there is relatively few, if nv, the influence of inertia on the machine. In this paper, it is proposed a simple magnetic wheel encoder suited for the high speed rotating machine and the method of signal processing and the output characteristics are examined through the V/F operation of max 48,000(rpm) and 2.4(KW) spindle motor.

• 한국응용과학기술학회지
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• 제28권4호
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• pp.455-463
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• 2011

The average sulfur content of crude oil is 2.2%. Coal is about 0.3 to 4.0 percent of the sulfur gases or particles being discharged into the atmosphere through the chimney as 1 to 2% $SO_3$(Sulfur trioxide) and about 95% of the $SO_2$ is reported. $SO_3$ gas, which has many different causes of, as the combustion of sulfur containing fuel during the air due to the excess $SO_2$ gas is oxidized to $SO_3$ gas. Sulfur trioxide emitted from high sulfur heavy oil fired boiler caused white plume in stack and high temperature and cold end corrosion of facilities. So, in order to control sulfur trioxide concentration of Fuel gas in boiler, various of additives are used in other foreign. They are injected to Fuel Oil and consumed in boiler and reduce ash and the conversion rate of sulfur trioxide. In domestic, MgO compounds are used as additives but the total volume of them are made from other foreign company. In this study, MgO compounds were developed with liquid MgO compounds and field application was accomplished. The effect of newly developed chemicals and process were nearly equal to foreign products. In Consequent, the chemicals and process produced by newly developed technology can be substituted for foreign products and reduce the cost of plant operation.