• 한국자동차공학회논문집
• /
• 제10권2호
• /
• pp.1-8
• /
• 2002

The flow and combustion patterns have been investigated inside the gasoline engine cylinder with the swirl or tumble flow, whereas the air flow characteristics, which are generated in the part of intake system before entering into the intake manifold, have not been known completely. It is necessary to analyze the flow field in the intake system consisting of air rater, throttle valve and intake manifold. The throttle valve, used to control the intake air flow rate, is important because it makes various mass flow rate and flow patterns. Three-dimen-sional How characteristics such as velocities, turbulent intensities and Reynolds shear stresses are measured by the hot wire anemometer at the exit of the throttle valve with the variation in the valve opening angle($15^{\circ}$, $45^{\circ}$, $75^{\circ}$ and $90^{\circ}$) and the Reynolds numbers (45000, 70000 and 140000). There are a lot of changes in flow characteristics at $75^{\circ}$ due to the large recirculation flow comparing with those of the other cases, and the streamwise velocity is especially enforced strongly below the valve shaft. The other component velocities are relatively large near the centerline parallel to the valve shaft. The effects of the Reynolds number on the flow field are not severe.

• 설비공학논문집
• /
• 제5권1호
• /
• pp.10-17
• /
• 1993

This paper describes the boiling heat transfer phenomena to be divided into three regions, nonboiling, nucleate boiling and burn-out in the impinging subcooled water jet system. In the nonboiling region, Nusselt number is a function of Prandtl number, Reynolds number and ${\Delta}T_{sub}/T_{ast}$ In the nucleate boiling region, the heat flux increases with increment of the nozzle exit velocity. But the degree of liquid subcooling does not affect the shape of the nucleate boilng curve. The dimensionless correlations can be expressed in the form of $q{\ell}/K_f{\Delta}T_{ast}=C(Bo{\cdot}C_p{\cdot}{\Delta}T_{sat}/Vo^2)^m{\cdot}(Re/We)^n$. The burn-out heat flux increases linearly with increment of the nozzle exit velocity, but independs of degree of subcooling and the supplementary water height.

• 한국수소및신에너지학회논문집
• /
• 제22권6호
• /
• pp.878-883
• /
• 2011

Effect of flow uniformity on the reaction characteristics of a catalytic combustor for high temperature fuel cell system has been experimentally investigated in the present study. One of the most important factor in designing catalytic combustion is to avoid hot spot in catalysts. In this regard, it is very important to secure flow uniformity of combustor inlet. A couple of perforated plates were applied at the front of catalyst region as flow uniformity device with minimal pressure drop. Results show that the velocity and temperature profile became more uniform when applying the flow uniformity device. CO and $CH_4$ emissions at the combustor exit were decreased and the average exit temperature was slightly increased with the flow uniformity device.

• Journal of Advanced Marine Engineering and Technology
• /
• 제25권4호
• /
• pp.817-824
• /
• 2001

In the present study, flow characteristics of turbulent oscillatory flows in the exit region connected to the square-sectional $180^{\circ}$curved duct was investigated experimentally. The experimental study for air flows was conducted to measure velocity profiles, shear stress distributions by using the Laser Doppler Velocimetry(L.D.V) system with the data acquisition and processing system of Rotating Machinery Resolver(R.M.R) and PHASE software. The results obtained from the experimentation were summarized as follows : The critical Reynolds number for a change from transitional oscillatory flow to turbulent oscillatory flow was about 75,000 in the 90 region of dimensionless axial position (x/Dh) which was considered as a fully developed flow region. In the turbulent oscillatory flow, velocity profiles of the inflow period in the entrance region were gradually developed, but those of the outflow period were not changed nearly. Shear stress distributions of turbulent oscillatory flow was gradually increased as the flow proceeds to downstream.

• Journal of Mechanical Science and Technology
• /
• 제20권2호
• /
• pp.286-294
• /
• 2006

Flows in a ramjet inlet is simulated for the study of the rocket-ramjet transition. The flow is unsteady, two-dimensional axisymmetric, compressible and turbulent. Double time marching method is used for the unsteady calculation and HLLC method is used as a higher order MUSCL method. As for turbulent calculation, $\kappa-\omega$ SST model is used for more accurate viscous calculations. Sinusoidal pressure perturbation is given at the exit and the flow fields at the inlet is studied. The cruise condition as well as the ground test condition are considered. The pressure level for the ground test condition is relatively low and the effect of the pressure perturbation at the combustion chamber is small. The normal shock at the cruise condition is very sensitive to the pressure perturbation and can be easily detached from the cowl when the exit pressure is relatively high. The sudden decrease in the mass flux is observed when the inlet flow becomes subcritical, which can make the inlet incapable. The amplitude of travelling pressure waves becomes larger as the downstream pressure increases, and the wavelength becomes shorter as Mach number increases. The phase difference of the travelling perturbed pressure wave in space is 180 degree.

• Journal of Sport and Applied Science
• /
• 제5권1호
• /
• pp.11-15
• /
• 2021

Purpose: Swimming industry is improving faster than the other types of sport industries and populations of participating swimming are promptly increasing. Lack of recognition of fire safety in swimming facilities is issues related-studies has only recently begun to pay attention. This study is to review and extract fire safety factors for managing swimming pool. Research design, data, and methodology: The study reviewed related-ordinances, governmental documents, and studies discussing safety management of sport facility. Given the literature review, the study produced an initial construct presenting items and factors including fire safety elements and experts' review were conducted to ensure conceptual validity. Finally, the study generated the final factors and subitems representing fire safety elements for swimming pool management. Results: The study confirms factors and elements as follows: the study identifies fire safety equipments as first factors presenting fire extinguisher' place, its proper run, check list and so forth, Second factor is warning system including fire warning equipment, its proper operation, sprinkler and its proper operation, switch and lamp of emergency panel and their proper run and so on. Third factor is evacuation system including a fire exit, exit sign, broadcasting equipment, and their proper operation, and so on. The other factors are an electronic equipment and its subelements, gas management including safety management of LPG, gas valve, pipe, and fire prevention facility including a fire door and its proper operating. Conclusions: Regarding safety management of swimming pool, further discussions and implications were made, and future directions for related-studies were discussed.

• 한국안광학회지
• /
• 제7권2호
• /
• pp.197-202
• /
• 2002

본 논문에서는 telecentric 렌즈에 대하여 간략하게 그 성질을 알아보고 기존에 설계된 profile projection lens를 선택하여 광학적 성능을 조사하여 봄으로서 telecentric에 관한 이해를 도모하고자 하였다. 분석한 광학계는 F-no가 2.8이고, 첫 번째 렌즈를-렌즈로 사용하여 물측 초점의 위치를 광학계 안쪽에 위치시킴으로서 aperture stop을 광학계 내부에 설치하게 하여 광학계를 보다 compact하게 하려 하였음을 알 수가 있었다. 시야는 $21^{\circ}$ 정도를 유지하며, entrance pupil이 물측 초점의 위치(FFL)에 놓여짐으로써 exit pupil은 -49404.1mm로 물측 공간쪽으로 무한대로 놓여지게 됨을 확인할 수가 있다. 이로서 본 광학계는 '상측이 텔레센트릭계(image space telecentricity)'의 한 형태라고 할 수 있다.

• 한국사회복지학
• /
• 제37권
• /
• pp.1-31
• /
• 1999

실직자의 재취업 실태 및 실업기간에 관한 실증연구는 지난 수 십년간 실업(고용)보험의 연구에 있어 중요한 부분을 차지하여 왔지만, 우리나라에서는 이러한 주제에 관한 체계적 실증 연구가 매우 부족한 실정이다. 본 연구는 1996년 7월부터 1997턴 12월까지 18개월간 총 60,141명의 실업급여 수급권자 중 1997년 6월까지의 실업급여 수급권자 40,175명을 대상으로 생존분석의 Life table 분석과 Accelerated Failure Time 모델분석을 실시하여, 실직자 및 실업급여 관련 변수들이 실업탈피 기대기간(expected unemployment period)에 미치는 영향력을 측정 분석하였다. 생존분석결과 최장 실직기간까지 실업상태로 남아있는 수급권자들의 비율(누적생존율)이 64.83%나 되었다. Accelerated Failure Time 모델 중 Log-Normal Model에 의한 분석결과 교육수준과 상시근로자수를 제외한 대부분의 독립변수들이 재취업까지의 기대기간에 통계적으로 유의미한 영향력을 미치는 것으로 나타났다. 이러한 실종분석 결과를 바탕으로 고학력, 고임금을 받던 화이트칼라 노동자들에 대한 적극적 노동시장정책의 필요성과 지역 및 업종의 재취업여건 차이를 감안한 실업대책의 필요성을 제언하였으며, 실업급여의 제도적 변수가 나타내는 순수한 효과를 파악하기 위한 다각적인 후속연구의 필요성을 제기하였다.

• 한국자동차공학회논문집
• /
• 제16권5호
• /
• pp.49-59
• /
• 2008

The effects of design parameters on the pellet transport rate in the ejector system which is widely used in the production processes of automotive parts were investigated experimentally. The primary nozzle geometry, the area ratio (R) of nozzle exit cross-sectional area to mixing chamber cross-sectional area and the distance (S) from primary nozzle exit to mixing chamber entrance were considered as the design parameters. The area ratios of the primary nozzle were varied from R=0.10 to R=0.25, 0.30, 0.40 and 0.55. The primary nozzle was positioned at the non-dimensional distance (S/D) of 1.30, 1.87, 2.44, 3.00 and 3.75, normalized using the mixing chamber diameter (D). The design parameters were determined to run with high efficiency by measuring the pellets transport rate. The geometry and the area ratio (R) of the primary nozzle had an effect on the pellet transport rate of the ejector system, and the area ratio of R=0.3 was carefully selected after taking the minimum fluidization velocity and transport rate of applied pellets into account. The higher pellet transport rate with the variation of the distance (S/D) was observed at S/D of 2.44.

• 한국정보디스플레이학회:학술대회논문집
• /
• 한국정보디스플레이학회 2007년도 7th International Meeting on Information Display 제7권2호
• /
• pp.1749-1752
• /
• 2007

The Near to Eye Display (NED) solves the problem of having a display larger than a small portable device. The virtual image of the NED is created using a microdisplay and imaging optics. It is important that the optics does not interfere with the human visual system and that the device is light, compact and easy to wear. In this paper the principles of a biocular NED, which is based on a novel diffractive Exit Pupil Expander (EPE), are presented. The optical system is compact and intrinsically free from distortions and misalignments.