• 한국기계가공학회지
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• 제18권8호
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• pp.51-59
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• 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.

• 한국유체기계학회 논문집
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• 제11권2호
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• pp.46-54
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• 2008

This study presents a numerical optimization to optimize an axial flow fan blade to increase the efficiency. The radial basis neural network is used as an optimization method with the numerical analysis by Reynolds-averaged Navier-Stokes equations using SST model as turbulence closure. Four design variables related to airfoil maximum camber, maximum camber location, leading edge radius and trailing edge radius, respectively, are selected, and efficiency is considered as objective function which is to be maximized. Thirty designs are evaluated to get the objective function values of each design used to train the neural network. Optimum shape shows the efficiency increased by 1.0%.

• 대한기계학회논문집
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• 제10권5호
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• pp.706-712
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• 1986

본 연구는 맥동류의 진동 속도가 평균 유속에 비하여 매우 작은 경우로서 Re- ynolbs수가 40 이하 층류유동에 관한 것이다. 부력은 무시하고 비압축성의 점성유체 에 관한 비정상 Navier-Stokes 방정식과 에너지방정식의 선형 섭동방정식을 구하고, 진동성분의 복소진폭을 수치적으로 풀어서 저항력과 함께 열전달 응답의 진폭과 위상 을 구하였다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.327-330
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• 2006

This paper represents the numerical analysis on effects of radius ratio in a concentric annulus with a rotating inner cylinder. The numerical model consisted of two cylinder which inner cylinder is rotating and outer cylinder is fix, and the axial direction is used the cyclic condition because of the length for axial direction is assumed infinite. The diameter of inner cylinder is assumed 86.8mm, the numerical parameters are angular velocity and radius ratio. Also, the whole walls of numerical model have no-slip and the working fluid is used water at $20^{\circ}C$. The numerical analysis is assumed the transient state to observe the flow variations by time and the 3-D cylindrical coordinate system. The calculation grid adopted a non-constant grid for dense arrangement near the wall side of cylinder, the standard $k-{\omega}$ high Reynolds number model to consider the effect of turbulence flow and wall, the fully implicit method for time term and the quick scheme for momentum equation. The numerical method is compared with the experimental results by Wereley and Lueptow, and the results are very good agreement. As the results, TVF isn't appeared when Re is small because of the initial flow instability is disappear by effect of the centrifugal force and viscosity. The vortex size is from 0.8 to 1.1 for TVF at various $\eta$, and the traveling distance for wavy vortex have the critical traveling distance for each case.

• 한국수자원학회논문집
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• 제53권10호
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• pp.861-870
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• 2020

자갈 입자로 구성된 다공성매질에서는 유속이 증가하여 레이놀즈수가 커지게 되면 흐름은 Darcy의 영역을 벗어나게 된다. 본 연구는 인공함양 유역의 소하천에 설치예정인 돌망태 보의 채움재를 통과하는 비선형적인 흐름특성을 규명하기 위하여 자갈칼럼과 돌망태모형을 이용한 투수실험을 수행하였다. 칼럼실험을 통하여 공극유속과 수리경사의 관계식과 계수를 결정하고, 수리평균반경과의 상관관계식을 제안하였다. 제안식으로 부터 계산된 공극유속과 공극유량은 돌망태모형 투수실험의 측정치와 잘 일치하였다.

• 대한교통학회지
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• 제19권2호
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• pp.21-28
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• 2001

본 연구는 다양한 좌회전 곡선반경을 갖고 있는 교차로에서의 좌회전 포화교통류율의 분석을 통하여 좌회전의 직진환산계수를 산정하는 것이다. 한국 도로 용량편람에서는 곡선반경이 약 20m 이상인 곳에서는 좌회전 전용차로에 대하여 직진과 같은 포화교통류율을 보이는 것으로 조사되어 좌회전 보정계수는 없는 것으로 제안하고 있다. 하지만 KHCM은 간선도로 위주로 조사 분석되어 곡선반경이 20m 이하인 교차로가 제외되어 있다. 이에 본 연구에서는 좌회전 전용차로 1개를 갖고 곡선반경이 20m 이하인 교차로 포함하여 다양한 곡선반경 가진 교차로를 대상으로 연구를 수행하였다. 본 연구에서는 포화교통류율을 산출하는데 있어서 분산분석의 후속단계인 다중비교(Multiple comparison)방법중 던컨검정(Duncan's Test)을 이용하였다. 본 연구에서 산정된 좌회전의 직진환산계수는 도로용량편람에서 교차로 분석시 교차로 곡선반경을 반영한 정확한 포화교통류율을 산정할 수 있다. 본 연구의 결과는 좌회전 곡선반경 20m 미만 교차로에서의 좌회전 S는 직진포화교통류율 보다 낮게 결과가 나타났다. 이를 직진환산계수화 시키면 좌회전 곡선반경에 따라서 1.05에서 1.14사이다.

• 한국수처리학회지
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• 제26권6호
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• pp.3-12
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• 2018

The objective of this study was to evaluate the radius of influence of effluent of water treatment system developed for the purpose of improvement of reservoir water quality using fluorescent dye (Rhodamine-WT) tracer experiment and 3-D numerical model. The tracer experiment was carried out in a medium-sized agricultural reservoir with a storage capacity of $227,000m^3$ and an average depth of 1.6 m. A guideline with a total length of 160 m was installed at intervals of 10 m in the horizontal direction from the discharge part, and a Rhodamine measurement sensor (YSI 6130, measurement range $0-200{\mu}g/L$) was used to measure concentration changes in time, distance, and depth. Experimental design was established in advance through Jet theory and the diffusion process was simulated using ELCOM, a three dimensional hydraulic dynamics model. As a result of the study, the direct effect radius of the jet emitted from the applied water treatment system was about 50-70 m, and the radius of physical effect by the advection diffusion was judged to be 100-120 m. The numerical simulations of effluent advection-diffusion of the water treatment system using ELCOM showed very similar results to those of the impact radius analysis using the tracer experiment and jet flow empirical equations. The results provide valuable information on the spatial extent of the water quality improvement devices installed in the reservoir and the facility layout design.

• 한국연소학회지
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• 제20권3호
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• pp.1-7
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• 2015

The laminar lifted jet flames for methane diluted with helium and nitrogen in co-flow air have been investigated experimentally. Such jet flames could be lifted in both buoyancy-dominated and jet momentum dominated regimes (even at nozzle exit velocities much higher than stoichiometric laminar flame speed) despite the Schmidt number less than unity. Chemiluminescence intensities of $OH^*$ radical (good indicators of heat release rate) and the radius of curvature for tri-brachial flame were measured using an intensified charge coupled device (ICCD) camera and digital video camera at various conditions. It was shown that, an increase in $OH^*$ concentration causes increase of edge flame speed via enhanced chemical reaction in buoyancy dominated regime. In jet momentum dominated regime, an increase in radius of curvature in addition to the increased $OH^*$ concentration stabilizes such lifted flames. Stabilization of such lifted flames is discussed based on the stabilization mechanism.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.367-370
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• 2007

Present study examines detonation wave propagation characteristics in annular channel. A normalized value of channel width to the annular radius was considered as a geometric parameter. A parametric study was carried out for a various regimes of detonation waves from weakly unstable to highly unstable detonation waves. Numerical approaches that used in the previous study of numerical requirements of the simulation of detonation wave propagations in 2D and 3D channel were used also for the present study with OpenMP parallization for multi-core SMP machines. The major effect of the curved geometry on the detonation wave propagation seems to be a flow compression effect, regardless of the detonation regimes. The flow compression behind the detonation wave by the curved geometry of the circular channel pushes the detonation wave front and results in the overdriven detonation waves with increased detonation speed beyond the Chapmann-Jouguet speed. This effect gets stronger as the normalized radius smaller, as expected. The effect seems to be negligible beyond the normalized radius of 10.

• Tribology and Lubricants
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• 제30권5호
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• pp.265-270
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• 2014

Frictional heat greatly influences the friction behaviors during clutch engagement. Therefore, the engagement of a wet or dry clutch is frequently not under control by the frictional heat. In a wet clutch, the frictional temperature also specially needs to be controlled, and in many cases, the clutch material is selected to prevent a temperature rise from the friction between friction pad and separator. However, only the selection of the clutch material cannot ensure sufficient control of the temperature rise by the friction. The groove pattern on a friction pad is designed for more flow rates of transmission fluid between the contact gap of clutch pad and separator for the cooling effect. In this work, grove patterns are designed for more flow rates out of the contact gap between friction pad and separator plate. Selected groove design shows the improvement flow rates of transmission fluid through both inner and outer radius, where most of the transmission fluid flows through the outer radius when the clutch is engaged due to the centrifugal force in conventional wet clutch groove. Several comparisons of the amounts of frictional heat generated on clutch pads are made in order to verify the decrease of the temperature rise according to the flow rates along the groove patterns.