• 대한기계학회논문집B
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• 제29권9호
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• pp.997-1005
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• 2005

The extinction characteristics of low strain rate normal gravity (1-g) nonpremixed methane-air flames were studied numerically and experimentally. A time-dependent axisymmetric two-dimensional (2D) model considering buoyancy effects and radiative heat transfer was developed to capture the structure and extinction limits of 1-g flames. One-dimensional (1D) computations were also conducted to provide information on 0-g flames. A 3-step global reaction mechanism was used in both the 1D and 2D computations to predict the measured extinction limit and flame temperature. A specific maximum heat release rate was introduced to quantify the local flame strength and to elucidate the extinction mechanism. Overall fractional contribution by each term in the energy equation to the heat release was evaluated to investigate the multi-dimensional structure and radiative extinction of 1-g flames. Images of flames were taken for comparison with the model calculation undergoing extinction. The two-dimensional numerical model was validated by comparing flame temperature profiles and extinction limits with experiments and ID computation results. The 2D computations yielded insight into the extinction mode and flame structure of 1-g flames. Two combustion regimes depending on the extinction mode were identified. Lateral heat loss effects and multi-dimensional flame structure were also found. At low strain rates of 1-g flame ('Regime A'), the flame is extinguished from the weak outer flame edge, which is attributed to multi-dimensional flame structure and flow field. At high strain rates, ('Regime B'), the flame extinction initiates near the flame centerline due to an increased diluent concentration in reaction zone, which is the same as the extinction mode of 1D flame. These two extinction modes could be clearly explained with the specific maximum heat release rate.

• 한국화재소방학회논문지
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• 제27권6호
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• pp.64-69
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• 2013

본 연구에서는 엔진 나셀 화재를 모사하고 이전의 실험결과를 보충하기위해 이차원 둔각물체 주위의 반응유동장에 대하여 수치해석을 수행하였다. Direct numerical simulation (DNS) 기반의 fire dynamic simulator (FDS)를 이용하여 반응유동장의 특성을 조사하였고, 실험결과와의 비교를 통해 화학반응식을 결정하였다. 산화제는 공기를 사용하였고, 연료는 메탄을 사용하였다. 동축류와 대향류 분사 모두의 경우에 화염의 안정성이나 모양은 둔각물체 주위의 와 강도와 크기에 크게 영향을 받았다. 동축류 분사의 경우 계산에 통한 화염소화한계를 결정하였는데 연료유속이 커질수록 공기의 유속 또한 커지는 경향이 있었고, 그 속도들 또한 기존의 실험결과와 잘 일치함을 볼 수 있었다. 유동장 특성에 대한 화학반응의 효과를 고찰하기 위해 반응이 없는 경우를 계산하여 비교하였다. 모든 경우에 비반응 유동장에 비해 반응 유동장의 후류와는 크기도 감소하고 세기도 감소함을 볼 수 있었는데 이는 반응에 의한 후류의 온도증가가 유체의 밀도 및 모멘텀을 감소시켰기 때문으로 판단된다.

• 한국수산과학회지
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• 제27권6호
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• pp.754-770
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• 1994

미국 북캐롤라이나의 동해안에 위치하는 뉴우스강 하구를 대상으로 1988년 2월부터 1989년 2월까지 매월 부유퇴적물의 분포와 유속 및 염분을 조사하여, 최대혼탁수의 형성과 물리적 환경요인(담수유출량, 풍향 및 풍속, 조석 등)에 따른 시간적, 공간적 변화를 조사하였다. 대부분의 조사기간동안, 염하구 순환과 관련된 미약한 최대혼탁수의 형성이 염수 침입한계 근처에서 관측되었으며, 염수 침입한계의 연중 이동과 수반하여 강 상류의 약 20 km 지역에 걸쳐 이동하면서 분포하였다. 이 지역 계절풍의 주된 풍향(북동-남서)과 Pamlico Sound의 지형적 방향성의 일치로 인하여, 염분 성충구조와 염하구 순환의 발달정도는 바람의 영향을 크게 받으며, 따라서 최대혼탁수의 형성과 변동 양상도 조석의 영향보다는 담수유출량과 바람의 영향을 뚜렷이 나타내었다.

• 한국환경보건학회지
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• 제22권2호
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• pp.43-57
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• 1996

To characterize worker's exposure to glass fibers, to find the correlation between airborne total dust concentrations and fiber concentrations and to recommend an appropriate evaluation method for worker's exposure to fibrous dusts in glass wool industry, we carried out this study. Average respirable fiber levels at five factories were 0.013-0.056 f/cc, and fairly below the OSHA PEL, 1 f/cc. A factory showed the lowest airborne fiber level, 0.013 f/cc, which was different significantly from those of other factories of which average fiber concentration was 0.046 f/cc. The cutting and grinding operations of insulation products resulted in higher airborne fiber cocentrations than any other processes(p<0.05). To characterize airborne fiber dimension, fiber length and diamter were determined using phase contrast microscope. The geometric means of airborne fiber lengths were $42-105 \mu m$. One factory had airborne fibers whose length distribution(GM = $105 \mu m$) was different from those of other factories(GM = $42-50 \mu m$). The percentages of respirable fibers less thinner than 3 gm were 38.9-90.9% at four factories, and two factories of them had the higher percentages than others. The findings explain for variation of airborne fiber diameters between factories. On the other hand, between the processes were the difference of fiber-length distributions observed. The cutting and grinding operations showed shorter fiber-length distributions than the fiber forming one. However, fiber-diameter distributions or respirable fiber contents were similar in all processes. The airborne fiber concentrations and the dust concentrations had relatively weak correlation(r=0.25), thus number of fibers couldn't be expected reliably from dust amount. Fiber count is appropriate for assessing accurate exposures and health effects caused by fibrous dusts including glass fibers. Ministry of Labor have established occupational exposure limit to glass fibers as nuisiance dust, but should establish it on the basis of respirable fiber concentration to provide adequate protection for worker's health

• International Journal of Automotive Technology
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• 제8권3호
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• pp.269-274
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• 2007

A prior fundamental study was executed using a constant volume chamber (CVC) to improve the burning characteristics of lean pre-mixture by the injection of active radicals generated in the sub-chamber of the CVC. The Radical ignition (RI) technique shows remarkable progress in the burning velocity and combustible lean limit compared with the results of the spark ignition (SI) technique. The optimum design value of the sub-chamber geometry is near $0.11cm^{-1}$ for the ratio of the total area of the holes to the sub-chamber volume $(A_h/V_s)$. In this study, based on the former experimental results, the additional works have been performed to examine the effects of the geometry change in the number $(N_h)$, the total section area $(A_h)$, and diameter $(D_h)$ of the passage holes on the combustion characteristics in the CVC. Also ambient conditions such as the initial temperature and the initial pressure of the mixture were selected as experimental parameters and the effects of residual gas at the chamber on the combustion characteristics were investigated. As a result, the correlation between the passage hole number and overall passage hole area was grasped. The effects of the initial temperature were significant, but on the other hand, those of the initial pressure were weak. A more detailed analysis on the residual gas is required in the future.

• 대한물리치료과학회지
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• 제9권2호
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• pp.17-26
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• 2002

This study is aimed to compare the effect of visuo-perceptual biofeedback sitting balance training and conventional sitting balance training using Balance Master on stroke patients with that of program in order to analyze the effect it has on dynamic postural balance. The subjects are twenty-four stroke patients who are receiving physical therapy in Ilsan Paik Hospital and can maintain sitting posture by themselves. These patients were divided to control group and experimental group randomly. In order to compare to control and experimental group before and after the balance training, they were tested with Mann-Whitney U test and in order to compared the changes before and after the balance training, they were tested with Wilcoxon signed-ranks test. The results are as follows: we measured the ability of dynamic posture balance control with limit of stability(LOS) test and rhythmic weight shift test. There was an increasing improvement in the ability of dynamic posture balance control of the experimental group that had visuo-perceptual biofeedback sitting balance control training using the Balance Master(p<0.05, p<0.01). According to the results from above, compared to conventional sitting balance training programs, visuo-perceptual biofeedback sitting balance control training using the Balance Master is considered to be a more valuable therapy in balance control improvement and physical function improvement. It is considered that if the weak points are made up, the training with Balance Master will give help to stroke patients and to patients with balance control disabilities and will further more contribute to successful rehabilitation therapy.

• 한국콘텐츠학회:학술대회논문집
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• 한국콘텐츠학회 2006년도 춘계 종합학술대회 논문집
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• pp.317-321
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• 2006

현재의 우리 사회는 21세기를 맞이하여 범죄예방 및 진압 등에 새로운 치안수요가 국민적인 관심을 불러일으키고 있다. 사회의 안전을 담당하는 것은 근본적으로 경찰의 책임이나 시대가 복잡해지고 치안수요가 다양해지면서 그 모든 것을 경찰력만으로 해결하는 것은 한계가 있다고 하겠다. 이에 따라 등장한 것이 민간경비이며, 오늘의 우리사회에서 더욱 요청되고 있는 분야이기도 하다. 민간경비의 수요 증가로 인한 역할증대에도 불구하고 우리나라 민간경비 산업의 발전을 위해서는 많은 과제를 안고 있다. 우리나라의 민간경비 수준은 미국이나 일본의 경우와 비교해 볼 때 아직 미흡한 수준이며 취약점이 있어 이에 대한 법 제도적 개선이 필요하다. 먼저 국가 공인 민간경비자격증제도를 도입하여 이러한 전문 자격증을 갖춘 사람을 채용하는 것도 경비인력의 자질향상을 위한 하나의 해결책이 될 것이다. 또한 2001년 4월에 전문 개정된 경비업법에 의하면 경비업자는 경비업법에 의한 경비업 외의 영업을 하여서는 안 되도록 규정되었다. 이러한 경비업자의 겸업금지조항은 헌법상 기본권인 직업의 자유를 침해하는 조항으로 겸업금지로 보호하려는 공익보다 기본권침해의 강도가 지나치게 크므로 과잉금지의 원칙에 위배되는 것으로 판단된다. 청원경찰법 제8조에 의하면 청원경찰은 직무수행을 위하여 필요하다고 인정할 때에는 청원주의 신청에 의하여 총기를 휴대할 수 있다. 그러나 청원경찰은 시설보호 및 방범적 차원의 업무수행을 하기 때문에 소지할 수 있는 무기 중에서 위험성이 높은 총기는 제외하는 것이 더 바람직하다.

• Korea-Australia Rheology Journal
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• 제21권4호
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• pp.213-223
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• 2009

Taylor-Couette flow (i.e., flow between concentric, rotating cylinders) has long served as a paradigm for studies of hydrodynamic stability. For Newtonian fluids, the rich cascade of transitions from laminar, Couette flow to turbulent flow occurs through a set of well-characterized flow states (Taylor Vortex Flow, wavy Taylor vortices, modulated wavy vortices, etc.) that depend on the Reynolds numbers of both the inner and outer cylinders ($Re_i$ and $Re_o$). While extensive work has been done on (a) the effects of weak viscoelasticity on the first few transitions for $Re_o=0$ and (b) the effects of strong viscoelasticity in the limit of vanishing inertia ($Re_i$ and $Re_o$ both vanishing), the viscoelastic Taylor-Couette problem presents an enormous parameter space, much of which remains completely unexplored. Here we describe our recent experimental efforts to examine the effects of drag reducing polymers on the complete range of flow states observed in the Taylor-Couette problem. Of particular importance in the present work is 1) the rheological characterization of the test solutions via both shear and extensional (CaBER) rheometry, 2) the wide range of parameters examined, including $Re_i$, $Re_o$ and Elasticity number E1, and 3) the use of a consistent, conservative protocol for accessing flow states. We hope that by examining the stability changes for each flow state, we may gain insights into the importance of particular coherent structures in drag reduction, identify simple ways of screening new drag reducing additives, and improve our understanding of the mechanism of drag reduction.

• 한국사회복지학
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• 제62권4호
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• pp.249-274
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• 2010

본 연구는 한국복지패널 1~3차년도 자료를 이용하여 우울과 국민기초생활보장제도 수급지위 변화의 관계를 분석하였다. 분석 결과는 다음과 같다. 첫째, 수급진입은 우울수준을 증가시킨다. 이는 주로 빈곤진입을 동반한 수급진입이 경제적 스트레스를 증가시켰기 때문으로 판단된다. 둘째, 수급탈출은 우울수준을 감소시키지 않는다. 하지만 수급탈출 중에서도 탈빈곤을 동반한 수급탈출의 경우에는 우울수준을 감소시킨다. 셋째, 높은 우울수준이 수급진입확률을 증가시킨다. 넷째, 높은 우울수준이 수급탈출 확률을 감소시키지 않는다. 수급탈출을 나누어 보면, 높은 우울수준은 탈출 후에도 여전히 빈곤한 수급탈출(탈락)의 가능성을 증가시킨다.

• Structural Engineering and Mechanics
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• 제57권3호
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• pp.507-528
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• 2016

Reduced beam section (RBS) moment resisting connections are among the most economical and practical rigid steel connections developed in the aftermath of the 1994 Northridge and the 1995 Kobe earthquakes. Although the performance of RBS connection has been widely studied, this connection has not been subject to in the skewed conditions. In this study, the seismic performance of dogbone connection was investigated at different angles. The Commercial ABAQUS software was used to simulate the samples. The numerical results are first compared with experimental results to verify the accuracy. Nonlinear static analysis with von Mises yield criterion materials and the finite elements method were used to analyze the behavior of the samples The selected Hardening Strain of materials at cyclic loading and monotonic loading were kinematics and isotropic respectively The results show that in addition to reverse twisting of columns, change in beam angle relative to the central axis of the column has little impact on hysteresis response of samples. Any increase in the angle, leads to increased non-elastic resistance. As for Weak panel zone, with increase of the angle between the beam and the column, the initial submission will take place at a later time and at a larger rotation angle in the panel zone and this represents reduced amount of perpendicular force exerted on the column flange. In balanced and strong panel zones, with increase in the angle between the beam and the central axis of the column, the reduced beam section (RBS), reaches the failure limit faster and at a lower rotation angle. In connection of skewed beam, balanced panel zone, due to its good performance in disposition of plasticity process away from connection points and high energy absorption, is the best choice for panel zone. The ratio of maximum moment developed on the column was found to be within 0.84 to 1 plastic anchor point, which shows prevention of brittle fracture in connections.