• 대한기계학회논문집
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• 제8권6호
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• pp.544-552
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• 1984

본 연구에서는 Chiu et al.의 집단연소이론에 대한 비정상집단연소모델(non- steady group combustion model)을 개발, 정지된 액적군에서 초기 액적들의 분포상태, 즉 초기액적들의 크기, 수밀도 및 액적군의 크기에 따른 연소시간, 연소형태 및 특성 과 화염의 성질등을 비정상 상태하에서 이론적인 모델을 통하여 고찰한다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.585-590
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• 2001

The hemodynamic characteristics were compared using commercial CFD code for the stenosed coronary and abdominal arteries. Numerical calculations were carried out in the axisymmetric arteries over the stenotic diameter ratios ranging from 0.25 to 0.875 (6 cases) employing the typical physiological flow conditions. In case of the coronary artery, there was only one recirculation zone observed distal to the stenosis throat during the major portion of the period. However, in case of the abdominal aorta, there were complex recirculation regions found proximal and distal to stenosis throat. For both models, the wall shear stresses(WSS) increased sharply in the converging stenosis, reaching a peak just upstream of the throat, and became negative or low values in the post-stenotic recirculation region. As the results, the oscillatory shear index(OSI) was abruptly increased at the stenosis throat. For the coronary stenosis model, the second peak in the OSI was observed distal to the stenosis. The distance between the first peak and the second peak was increased as the degree of the stenosis was raised. On the orther hand, the abdominal stenosis model showed a complex oscillatory behavior in the OSI index and did not showed such a strong second peak. As the degree of stenosis was increased, recirculation regions of the both arteries were extended much longer and flow pattern became more complex.

• Geomechanics and Engineering
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• 제8권5호
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• pp.707-726
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• 2015

This paper investigates the time dependent behaviour of Haarajoki test embankment on soft structured clay deposit. Half of the embankment is constructed on an area improved with prefabricated vertical drains, while the other half is constructed on the natural deposit without any ground improvement. To analyse the PVD-improved subsoil, axisymmetric vertical drains were converted into equivalent plane strain conditions using three different approaches. The construction and consolidation of the embankment are analysed with the finite element method using a recently developed anisotropic model for time-dependent behaviour of soft clays. The constitutive model, namely ACM-S accounts for combined effects of plastic anisotropy, interparticle bonding and degradation of bonds and creep. For comparison, the problem is also analysed with isotropic Soft Soil Creep and Modified Cam Clay models. The results of the numerical analyses are compared with the field measurements. The results show that neglecting effects of anisotropy, destructuration and creep may lead to inaccurate predictions of soft clay response. Additionally, the numerical results show that the matching methods accurately predict the consolidation behaviour of the embankment on PVD improved soft clays and provide a useful tool for engineering practice.

• 대한기계학회논문집A
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• 제28권8호
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• pp.1099-1108
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• 2004

In this paper, a study on the development of expert system for Al matrix composite with shape memory alloy fiber is performed to evaluate termomechanical behavior and mechanical properties. Expert system is very useful computer-based analysis system designed to make analysis technique and knowledge conveniently available to a lot of fabricable condition. In the developed system, it is possible to predict termomechanical behavior and mechanical properties for other composite with shape memory alloy fiber. The smartness of the shape memory alloy is given due to the shape memory effect of the TiNi fiber which generates compressive residual stress in the matrix material when heated after being prestrained. For finite element analysis, an analytical model is assumed two dimensional axisymmetric model compared of one fiber and the matrix. To evaluate the strength of composite using FEM, the concept of smart composite was simulated on computer Thus, in this paper, the FEA was carried out at two critical temperature conditions; room temperature and high temperature(363k). The finite element analysis result was compared with the test result for the analysis validity.

• 대한기계학회논문집B
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• 제23권6호
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• pp.778-787
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• 1999

In this study, the autoignition process of liquid fuel, injected into hot and stagnant air in a 2-D axisymmetric confined cylindrical combustor, has been investigated. Eulerian-Lagrangian scheme was adopted to analyze the two-phase flow and combustion. The unsteady conservation equations were used to solve the transition of the gas field. Interactions between two phases were accounted by using the particle source in cell (PSI-Cell) model, which was used for detailed consideration of the finite rates of transports between phases. And infinite conduction model was adopted for the vaporization of droplets. The results have shown that the process of the autoignition consists of heating up of droplets, vaporization, mixing and ignition. The ignition criteria could be determined by the temporal variations of temperature, reaction rate and species mass fraction. And the effects of various parameters on ignition phenomena are examined. These have shown that the increasing the reaction rate and/or the vaporization rate can reduce the ignition delay time.

• 한국분무공학회지
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• 제24권4호
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• pp.185-193
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• 2019

The effervescent atomizer is one of twin-fluid atomizers that aeration gas enters into bulk liquid and two-phase flow is formed in the mixing section. The effervescent atomizer requires low injection pressure and small amount of aeration gas, as compared to other twin-fluid atomizers. In this study, cold flow test was conducted to investigate the spray characteristics of aerated impinging jets. The present effervescent impinging atomizers were composed of the aerator device and like-on-like doublet impinging atomizer which had different impinging angles. To analyze the spray characteristics such as breakup length and droplet size distribution, the image processing technique was adopted by using instantaneous images at each flow condition. Non-dimensional parameters, induced by the homogeneous flow model, were used to predict the breakup length. The breakup length was decreased with the mixture Reynolds number and impinging angle increasing. The result of droplets showed that the size distribution was axisymmetric about the center of the injector and their diameter tended to decrease with increasing GLR.

• International Journal of Fluid Machinery and Systems
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• 제2권2호
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• pp.147-155
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• 2009

Dynamic characteristics of the clearance flow between an axially oscillating rotational disk and a stationary disk were examined by experiments and computations based on a bulk flow model. In the case without pressure fluctuations at the inlet and outlet of the clearance, parallel and contracting flow paths had an effect to stabilize the axial oscillation of the rotating disk. The enlarged flow path had an effect to destabilize the axial oscillation due to the negative damping and stiffness for outward and inward flows, respectively. It was shown that the fluid force can be decomposed into the component caused by the inlet or outlet pressure fluctuation without the axial oscillation and that due to the axial oscillation without the inlet or outlet pressure fluctuation. A method to predict the stiffness and damping coefficients is proposed for general cases when the device is combined with an arbitrary flow system.

• 대한조선학회논문집
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• 제29권4호
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• pp.132-145
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• 1992

추진 효율 향상을 위한 대칭형 전류 고정날개-프로펠러 추진시스템의 설계, 이론성능해석 및 모형시험 과정을 정리하였다. 프로펠러 후류에서의 회전방향 운동에너지 회수를 통한 추진효율 향상을 도모하기 위하여 프로펠러 전방에 반대방향의 회전 속도를 주기 위한 고정날개를 설치하였다. 모형시험 결과 대칭형 전류 고정날개 추진시스템이 단독프로펠러에 비하여 3%정도 추진효율의 향상이 있음을 확인하였다. 실선 장착시에는 선체 반류에서의 난류 강도증가 및 레이놀드수 증가에 따른 고정날개 표면에서의 박리현상 감소에 의하여 고정날개 항력계수가 감소할 것으로 추정되며 그에 따라 본 추진시스템의 추진효율 증가량이 더욱 커지리라 판단된다.

• Smart Structures and Systems
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• 제26권6호
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• pp.809-817
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• 2020

In cells, the microtubules are surrounded by viscoelastic medium. Microtubules, though very small in size, perform a vital role in transportation of protein and in maintaining the cell shape. During performing these functions waves propagate and this propagation of waves has been investigated using nonlocal elastic theory. But the effect of surrounding medium was not taken into account. To fill this gap, this study considers the viscoelastic medium along with nonlocal elastic theory. The analytical formulas of the velocity of waves, and the results reveal that the presence of medium reduces the velocity. The axisymmetric and nonaxisymmetric waves are separately discussed. Furthermore, the results are compared with the results gained from the studies of free microtubules. The presence of medium around microtubules results in the increase of the flexural rigidity causing a significant decrease in radial wave velocity as compared to axial and circumferential wave velocities. The effect of viscoelastic medium is more obvious on radial wave velocity, to a lesser extent on torsional wave velocity and least on longitudinal wave velocity.

• KEPCO Journal on Electric Power and Energy
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• 제7권2호
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• pp.285-293
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• 2021

The construction of underground structures such as power supply lines, communication lines, utility tunnels has significantly increased worldwide for improving urban aesthetics ensuring citizen safety, and efficient use of underground space. Those underground structures are usually constructed along with vertical cylindrical shafts to facilitate their construction and maintenance. When constructing a vertical shaft through the open-cut method, the walls are mostly designed to be flexible, allowing a certain level of displacement. The earth pressure applied to the flexible walls acts as an external force and its accurate estimation is essential for reasonable and economical structure design. The earth pressure applied to the flexible wall is closely interrelated to the displacement of the surrounding ground. This study simulated stepwise excavation for constructing a cylindrical vertical shaft through a centrifugal model experiment. One quadrant of the axisymmetric vertical shaft and the ground were modeled, and ground excavation was simulated by shrinking the vertical shaft. The deformation occurring on the entire ground during the excavation was continuously evaluated through digital image analysis. The digital image analysis evaluated complex ground deformation which varied with wall displacement, distance from the wall, and ground depth. When the ground deformation data accumulate through the method used in this study, they can be used for developing shaft wall models in future for analyzing the earth pressure acting on them.