• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2009년도 춘계 학술발표회
• /
• pp.1100-1106
• /
• 2009

A debris flow is known as that flood and landslide of water cause much physical human damages worldwide to complex natural disaster that happen combining and happy event is happening mainly in urgent mountains area in domestic. Because happen about debris flow that happen from each place every year and is drift, mechanism of accumulation definitely make clear and great many damage is not running out. Must grasp actual conditions of priority debris flow to need debris flow prevention countermeasure and lay countermeasure to take away damage by debris flow. Because collecting actual conditions of debris flow that happen by objective investigation methods and accuracy, proposed about investigation calamity investigation method so that can calculate debris flow damage and prepare in subsequentness damage.

• 반도체디스플레이기술학회지
• /
• 제19권4호
• /
• pp.51-58
• /
• 2020

Many types of optical plastic films are essential in optoelectronics display unit fabrication and it is important to develop high precision laser cutting methods of optical films with extremely low level of film surface contamination by fume particles. This study investigates the effects of suction and blowing air motions with air flow misalignment in removing fume particles from laser cut line by employing random particle trajectory simulation and probabilistic particle generation model. The computational results show fume particle dispersion behaviors on optical film under suction and blowing air flow conditions. It is found that suction air flow motion is more advantageous to blowing air motion in reducing film surface contamination outside designated target margin from laser cut line. While air flow misalignment adversely affects particle dispersion in blowing air flows, its effects become much more complicated in suction air flows by showing different particle dispersion patterns around laser cut line. It is required to have more careful air flow alignment in fume particle removal under suction air flow conditions.

• 대한기계학회논문집B
• /
• 제22권1호
• /
• pp.25-33
• /
• 1998

An experimental study has been carried out to obtain optimal conditions for turbulent mixing of two fluid streams at various angle branches by a flow visualization method. The main purpose of this study is the utilization of flow visualization method as a fast and efficient way to find the optimal mixing conditions when several flow control parameters are superimposed. It is verified that the optimal conditions estimated by flow visualization method have good agreement with the concentration field measurements. The results demonstrate that the diameter ratio is mainly attributed to the mixing phenomena than the branch pipe angle and the Reynolds number. The most striking fact is that there exists the best diameter ratio, d/D.ident. O.17, which requires the minimum momentum ratio in the range of the present experiment. The velocity ratio for the optimal mixing condition has a value within 2 to 16 according to the different flow parameters.

• 한국해양공학회지
• /
• 제28권6호
• /
• pp.500-507
• /
• 2014

This study aimed at conducting a flow analysis of the pressure distribution, discharge flow rate, and consequent thrust force according to the rotational speed of a three-dimensional screw propeller, and then investigating the effect of the rotational speed on the characteristics of the screw propeller by varying the relevant speed (3200, 2400, 1600, 800 rpm). In particular, the computational domain was considered by the analysis in the blades and outlet chamber, using boundary conditions. The difference between the minimum and maximum pressures was 5.5 MPa under the given conditions. The discharge flow rate at this pressure difference was on the level of 1956.67 kg/s, as a thrust force of 47083.7 T(N) was obtained. This study showed that the discharge flow rate linearly increased with the rotational speed, proportional to the RPM, while the thrust force was gradually and steadily increased with the relevant speed. In addition, it was proved that the occurrence of cavitation under the given conditions was closely related to the decrease in the durability of the screw propeller because the thrust force depends on the speed.

• 마이크로전자및패키징학회지
• /
• 제8권4호
• /
• pp.67-72
• /
• 2001

반도체 칩 캡슐화성형시 칩 캐비티에서의 유동을 보다 엄밀하게 모델링하고 해석하기 위한 연구가 이루어졌다. 리드프레임에서의 구멍부위를 통과하는 유동의 모델링을 시도하였고 리드프레임에서의 열 경계조건을 정확하게 취급하였다. 유동의 이론적 해석을 위해 헬레쇼오 모델을 채택하였고 리드프레임에 의해 아래 위로 분리된 각각의 캐비티로 가정하여 해석하였다. 리드프레임에서 구멍부위를 통과하는 유동은 헬레쇼오 모델링시에 질량 소스(source) 항으로 삽입되었다. 유동해석 프로그램과 콤플렉스 방법에 기반을 둔 최적화 프로그램을 연계하여 미성형 방지를 위한 최적 공정조건을 성공적으로 정확하게 얻어낼 수 있었다.

• 생태와환경
• /
• 제42권4호
• /
• pp.487-494
• /
• 2009

We compared spatial and temporal variations of water chemistry between high-flow year ($HF_y$) and low-flow year ($LF_y$) in an artificial lentic ecosystem of Daechung Reservoir. The differences in the rainfall distributions explained the variation of the annual inflow and determined flow characteristics and water residence time and modified chemical and biological conditions, based on TP, suspended solids, and chlorophylla, resulting in changes of ecological functions. The intense rainfall and inflow from the watershed resulted in partial disruption of thermal structure in the metalimnion depth, ionic dilution, high TP, and high suspended solids. This condition produced a reduced chlorophyll-a in the headwaters due to low light availability and rapid flushing. In contrast, reduced inflow and low rainfall by drought resulted in strong thermal difference between the epilimnion and hypolimnion, low inorganic solids, high total dissolved solids, and low phosphorus in the ambient water. The riverine conditions dominated the hydrology in the monsoon of $HF_y$ and lacustrine conditions dominated in the $HF_y$. Overall data suggest that effective managements of the flow from the watershed may have an important role in the eutrophication processes.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
• /
• pp.357-364
• /
• 2004

A computational study on the supersonic flow around the lateral jet controlled missile has been performed. Case studies have been performed by comparing the normal force coefficient and the moment coefficient of a missile body for several different jet flow conditions, angle of attacks, circumferential jet locations, and spouting jet angles. For the several different jet flow conditions, which include the jet pressure, the jet Mach number, and the corresponding jet mass flow rate, the results show that the normal force coefficient is almost proportional to the jet thrust but the moment coefficient is not. Distinctly different flow phenomena can be noticed as the pressure ratio and the jet Mach number increase. By investigating the angle of attack effect to the normal force and the pitching moment, it has been identified that the normal force and the pitching moment show nonlinearity with respect to the angle of attack. From the detailed flow field analyses with respect to the jet flow conditions and the angle of attacks, it is verified that most of the normal force loss and the pitching moment generation are taken place at the low-pressure region behind the jet nozzle. Furthermore, the normal force and the pitching moment characteristics of the missile have been identified by comparing different circumferential jet locations and spouting jet angles.

• 한국기계가공학회지
• /
• 제18권8호
• /
• pp.51-59
• /
• 2019

Flow forming is an eco-friendly and high-efficiency plastic deformation process with fewer chips during a process which is specifically used to manufacture seamless tubular products like tire wheels, rocket motor cases etc. On the development of mortar barrel using Inconel718 tube, some flow formed products had dimensional errors on their thickness. In this study, our purpose is to optimize the process conditions with the smallest dimensional error. In order to find an optimum process condition, 2D axisymmetric FEM simulation analyses with Taguchi method were conducted. Geometric variables (attack angle, flatting angle, roller nose radius) and operating parameters (depth of forming, feed rate) are considered as control factors. Forward flow forming with single roller was first analyzed to determine the effective factors using AFDEX software and attack angle of the roller was identified as the most influential factor. Also, the nose radius of the rollers was confirmed as a significant factor in multi-rollers flow forming system. The effect of rollers offset values are also studied and finally, we proposed optimal conditions to improve the accuracy of flow forming process with Inconel718 tube for mortar barrel manufacturing.

• 한국재료학회지
• /
• 제30권12호
• /
• pp.693-700
• /
• 2020

Direct water quenching technique can be used in hot stamping process to obtain higher cooling rate compared to that of the normal die cooling method. In the direct water quenching process, setting proper water flow rate in consideration of material thickness and the size of the area directly cooled in the component is important to ensure uniform microstructure and mechanical properties. In this study, to derive proper water flow rate conditions that can achieve uniform microstructure and mechanical properties, microstructure and hardness distribution in various water flow rate conditions are measured for 3.2 mm thick boron steel sheet. Hardness distribution is uniform under the flow condition of 1.5 L/min or higher. However, due to the lower cooling rate in that area, the lower flow conditions result in a drastic decrease in hardness in some areas in the hot-stamped part, resulting in low martensite fraction. From these results, it is found that the selection of proper water flow rate is an important factor in hot stamping with direct water quenching process to ensure uniform mechanical properties.

• 한국산업융합학회 논문집
• /
• 제26권6_2호
• /
• pp.1109-1115
• /
• 2023

The shell and tube-type heat exchanger was the most utilized in industrial field because of its simple structure and wide operation conditions and so on. This study was performed to investigate the characteristics of behavior of thermal flow according to operation condition of small-sized shell and tube-type heat exchanger. The operation conditions, here, were set up to flow rate of hot air with temperature of 100℃, number of baffle and cut rate of baffle(BCR) using numerical analysis. As the results, both mean relative pressure and relative pressure drop was increased with quadratic curve in case of less than BCR 25%, however, decreased linearly in case of more than BCR 25%. The collision with first baffle by flow velocity and temperature, of hot air, respectively, was depended on BCR. Further it showed that the behaviors between flow velocity and temperature were almost similar.