• International Journal of Aeronautical and Space Sciences
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• 제13권3호
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• pp.386-397
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• 2012

The stability and structure of bluff-body stabilized hydrogen flames were investigated numerically and experimentally. The velocity of coflowing air was varied from subsonic velocity to a supersonic velocity of Mach 1.8. OH PLIF images and Schlieren images were used for analysis. Flame regimes were used to classify the characteristic flame modes according to the variation of the fuel-air velocity ratio, into jet-like flame, central-jet-dominated flame, and recirculation zone flame. Stability curves were drawn to find the blowout regimes and to show the improvement in flame stability with increasing lip thickness of the fuel tube, which acts as a bluff-body. These curves collapse to a single line when the blowout curves are normalized by the size of the bluff-body. The variation of flame length with the increase in air flow rate was also investigated. In the subsonic coflow condition, the flame length decreased significantly, but in the supersonic coflow condition, the flame length increased slowly and finally reached a near-constant value. This phenomenon is attributed to the air-entrainment of subsonic flow and the compressibility effect of supersonic flow. The closed-tip recirculation zone flames in supersonic coflow had a reacting core in the partially premixed zone, where the fuel jet lost its momentum due to the high-pressure zone and followed the recirculation zone; this behavior resulted in the long characteristic time for the fuel-air mixing.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.7-8
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• 2006

The governing equations for high-speed lateral atomizing injector nozzle flow based on the LES-VOF model in conjunction with the CSF model are presented, and then an integrated parallel computation are performed to clarify the detailed atomization process of a high speed nozzle flow and to acquire data which is difficult to confirm by experiment such as atomization length, liquid core shapes, droplets size distributions, spray angle and droplets velocity profiles. According to the present analysis, it is found that the atomization rate and the droplets-gas two-phase flow characteristics are controlled by the turbulence perturbation upstream of the injector nozzle, hydrodynamic instabilities at the gas-liquid interface, shear stresses between liquid core and periphery of the jet. Furthermore, stable and a high-resolution computation can be attained in the high density ratio (pl/ pg = 554) conditions conditions by using our numerical method.

• 한국의류산업학회지
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• 제1권2호
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• pp.154-159
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• 1999

In this study, for different test methods of the performance of sewing threads were used to evaluate the sewability of 10 different industrial threads. Sewability evaluations related to the breakage of thread during sewing operation were investigated by seam length and fabric thickness method (Test 1), thread tension method (Test 2), strength retention method (Test 3), and backward sewing method(Test 4), and discussed. Two of the methods, Test 1 and Test 2, simulated very harsh sewing conditions which each thread could accept as an evaluation of its sewability. Core spun thread ranked with the best sewability generally and followed by air jet textured (ATY) thread. Spun thread was superior to the filament thread in sewing thread type. In general, there was a high degree of correlation in the results of Test 1 and Test 2. The order of sewing thread by sewability test 1 was polyester spun thread, cotton thread, and p/c core spun thread. The order of sewing thread by test 2 was polyester spun thread, and p/c core spun thread. Cotton threads and cotton blended threads performed better in Test 3, and ATY threads and core spun threads in Test 4.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1442-1450
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• 2017

In liquid metal fast breeder reactors, postulated failures of the plant protection system may lead to serious unprotected accidental consequences. Unprotected transients are generically categorized as transient overpower accidents and transient under cooling accidents. In both cases, core meltdown may occur and this can lead to a molten fuel coolant interaction (MFCI). The understanding of MFCI phenomena is essential for study of debris coolability and characteristics during post-accident heat removal. Sodium is used as coolant in liquid metal fast breeder reactors. Viewing inside sodium at elevated temperature is impossible because of its opaqueness. In the present study, a methodology to depict MFCI phenomena using a flat panel detector based imaging system (i.e., real time radiography) is brought out using a woods metal-water experimental facility which simulates the $UO_2-Na$ interaction. The developed imaging system can capture attributes of the MFCI process like jet breakup length, jet front velocity, fragmented particle size, and a profile of the debris bed using digital image processing methods like image filtering, segmentation, and edge detection. This paper describes the MFCI process and developed imaging methodology to capture MFCI attributes which are directly related to the safe aspects of a sodium fast reactor.

• 대한토목학회논문집
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• 제5권1호
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• pp.75-81
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• 1985

정지상태의 수역에서 연직상향으로 방류(放流)되는 평면부력(平面浮力)?의 발달과정(發達過程)흐름영역(領域)의 거동이 질량(質量), 운동량(運動量) 및 추적물보존(追跡物保存)의 적분방정식(積分方程式)에 의하여 해석된다. 이 해석은 밀도(密度)후르드수(數)와 핵(核)에 대한 퍼짐비 및 발달과정(發達過程)흐름영역(領域)의 길이를 포함한다. 발달과정(發達過程)흐름영역(領域)의 끝에서 중심선속도(中心線速度)는 특히 낮은 밀도(密度)후르드수(數)에서 부력(浮力)의 영향을 크게 받는다. 이 결과는 발달(發達)된 흐름영역(領域)의 해석(解析)에 필요한 초기조건(初期條件)을 제공한다.

• 한국추진공학회지
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• 제6권1호
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• pp.63-70
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• 2002

본 연구에서는 초음속 및 음속 마이크로 제트 유동의 특성을 파악하기 위해서 2차원 축대칭 압축성 Navier-Stokes 방정식을 이용한 수치해석을 수행하였다. 수치해석에서는 여러 형태의 난류모델을 적용하여 실험결과와 비교하였으며, 부족팽창과 과팽창 상태를 얻기 위하여 노즐 출구의 압력비 $P_b/P_e$를 0.2~l.25로 변화시켰다. 또, 레이놀즈 수 Re를 약 600~40000까지의 범위에서 변화시켜, $P_b/P_e$와 Re가 마이크로 제트 유동장에 미치는 영향을 조사하였다. 본 연구로부터 층류 제트의 특성은 난류 제트와는 달리 레이놀즈 수의 의존성이 크다는 것을 알았다.

• 대한기계학회논문집
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• 제13권1호
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• pp.140-152
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• 1989

본 논문에서는 소형 고속 디젤 분무의 반경 방향의 연류 농도 분포를 고려한 비균질 분무의 분무 선단 도달 거리에 대한 관계식을 유도하고, 비정상 분무인 디젤 분무의 분사 차압-시간 곡선을 입력시킴으로써, 분사 초기 뿐 아니라 전 분사 기간의 분무 선단 도달 거리를 예측할 수 있는 새로운 모델을 제안하여 실험치와 비교 분석하였다. 그리고 분사각과 분열장의 무차원 실험식을 도출하여 계산에 사용하였고 분무 선단 도달 거리의 천이점과 분열장에 대하여 고찰하였다.