• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.189-193
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• 2010

RMA-2, Telemac-2D, River2D 등 기존의 대부분 국내외 상용모형에서는 내부 경계인 하천구조물과 외부 경계인 측벽에서의 경계조건을 활동조건(slip condition)으로 가정하여 흐름장을 계산하였다. 그러나 실제로 벽면에서는 마찰력에 의해 흐름이 존재하지 않는 무활조건(no slip condition)이 물리적으로 타당하다. 따라서 본 연구에서는 내부구조물인 교각이 존재하는 영역에서의 수평 2차원 유속분포를 구하기 위해 천수방정식을 Galerkin법과 Newton-Raphson법에 의해 이산화한 수치모형을 개발하였다. Yulistiyanto 등(1998)이 수치모의 및 수리실험에 사용한 조건을 채택하여 벽면에서의 접선방향 유속이 존재하는 활동조건과 벽면에서 유속이 없는 무활조건을 부여하고 교각을 포함한 수로에서 유속, 수위 및 전단분포를 해석하였다. 활동경계조건을 적용한 경우 교각 표면을 따라 큰 유속이 분포하고 후면에서도 관성력에 의해 흐름방향 유속이 두드러지게 나타났으나 무활조건을 적용한 경우 교각 후면에서 와가 형성되고 후류현상이 두드러지게 나타났다. 무활조건을 적용한 경우 교각 전면부에서는 선수파(bow wave)가 4 cm정도 높게 나타났으며 교각 측면부에서는 2 cm 높게 나타났다. 반면 교각 후면에서는 후류의 영향으로 수면이 2 cm 낮게 분포하였다. 교각부에 작용하는 전단력을 분석한 결과 무활조건을 적용한 경우가 활동조건을 적용한 경우에 비해 최대 6배 높은 전단력이 나타났다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.8
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• pp.2468-2479
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• 1996

An upper bound solution is obtained to perform the process analysis of hot strip rolling process. The material flows within the roll bite at various geometries and frictional conditions are obtained from finite element analysis and the typical flow pattern which is necessary to determine the kinematically admissible velocity field is assumed. From the kinematically admissible velocity field, the upper bound energy is calculated and the rolling load, angle of neutral point and forward slip ratio at various operational conditions are obtained from upper bound energy. The process analysis of above mentioned parameters at various operational conditions have provided valuable information which is hard to obtain during rolling operation and the predicted ranges of quantitive values from these analyses lie whthin the bound of actual operational data.

• Computers and Concrete
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• v.30 no.2
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• pp.143-150
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• 2022

In this paper, the non-linear mathematical problem is solved via numerical scheme by utilizing shooting method. Brownian diffusion and thermophoresis along mass and heat transfer are accounted for. Non-linear expression is reduced via non-dimensional variables. The simplified ordinary differential equations are tackled by shooting technique. Behavior of distinct influential parameters is investigated graphically and analyzed for temperature and concentration profile. Our finding indicates that temperature profile is enhanced for the thermophoresis, Brownian motion coefficient, Prandtl number, Eckert number and temperature slip parameter. Comparison of numerical technique with the extant literature is made and an acceptable agreement is attained. Graphs are plotted to examine the influence of these parameters.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.6
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• pp.652-658
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• 2004

In this paper, we report the numerical and experimental solutions of the axi-symmetric flows in the axial plane driven by an impingement of fluid from the bottom wall of a circular cylinder. We managed to visualize successfully the flow pattern shown on the vertical plane through the container axis. The numerical results are shown to compare well with the experimental results for the case of infinity Rossby number. The satisfactory agreement between the two results was possible when in the numerics the free surface was treated as a solid wall so that a no-slip condition was applied on the surface. The numerical solutions reveal that inertial oscillation plays an important role at small Rossby numbers, or at a larger background rotation.

• Journal of Ocean Engineering and Technology
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• v.6 no.1
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• pp.29-42
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• 1992

자유표면하에 잠긴 복잡한 3차원 물체 주위의 흐름을 해소하기 위한 수치계산법이 TUMMAC(Tokyo Univ. Modified Marker And Cell)법을 기초로 하여 개발되었다. 임의물체의 no-slip 3차원 물체표면조건을 보다 간단히 처리하기 위하여 "porosity"라는 개념이 도입되었으며, 담수성에 잠겨 있는 해저돌출물 주위의 유동을 계산하여 그 응용성을 검토하였다. 돌출물 후방의 복잡한 와동들의 상호간섭이 잘 시뮬레이션 되었다.시뮬레이션 되었다.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1992.03a
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• pp.159-176
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• 1992

Limit analysis has been rendered versatile in many problems such as structural problems and metal forming problems. In metal forming analysis, a slip-line method and an upper bound method approach to limit solutions is considered as the most challenging areas. In the present work, a general algorithm for limit solutions of plastic flow is developed with the use of finite element limit analysis. The algorithm deals with a generalized Holder inequality, a duality theorem, and a combined smoothing and successive approximation in addition to a general procedure for finite element analysis. The algorithm is robust such that from any initial trial solution, the first iteration falls into a convex set which contains the exact solution(s) of the problem. The idea of the algorithm for limit solution is extended from rigid/perfectly-plastic materials to work-hardening materials by the nature of the limit formulation, which is also robust with numerically stable convergence and highly efficient computing time.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.652-657
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• 2002

It is addressed that the turbulent broadband sound power from a sirocco fan can be modeled by the trailing edge noise. The trailing edge noise is usually influenced by inflow turbulence, separation and boundary layer on the blade. The design parameters such as solidity(c/s) and stagger angle are specified to predict performance and noise level because the separation and slip velocity are strongly affected by them along with the flow coefficient. This paper reports the effects of the stagger angle upon the trailing edge noise for various trailing edge shapes. It is believed that the serrated trailing edge provides break-up mechanism for organized convecting vortices, thereby reduce the overall noise level.

• Journal of Mechanical Science and Technology
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• v.18 no.11
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• pp.2021-2031
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• 2004

A new nondimensional method for predicting the windmilling performance of centrifugal -flow turbojet engines in flight has been developed. The method incorporates loss correlations to estimate the performance of major engine components. Given basic engine geometry, flight Mach number, and ambient conditions, this method predicts transient and steady-state windmilling performance. Thus, this method can be used during the preliminary design stage when detailed hardware geometry and component performance data are not yet available. A nondimensional time parameter is newly defined, and using this parameter, the transient performance of different types of turbojets (e.g. centrifugal vs. axial) is compared. In addition, the predictions' sensitivity to loss correlations, slip factors, and inlet ambient temperatures are analyzed.

• The KSFM Journal of Fluid Machinery
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• v.4 no.4 s.13
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• pp.7-15
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• 2001

Flow analysis was carried out for a double-suction centrifugal pump. Impeller-only models and a full pump model were used to simulate the velocity field and the pressure field of the pump. Heads and efficiencies were calculated with flow rates in order to obtain general performance of the pump. The calculation results were compared to the experimental data, and satisfactory results were obtained. Thus, it may be said that the CFD serves as a useful tool for pump designs.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.349-352
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• 2002

The time-development of the wake vortices of the unsteady viscous flow past a semicircular cylinder is simulated using the vortex particle methods for direct numerical simulations(DNS). The early wake behaviour of the flow behind an impulsively started a semicircualr cylinder is evaluated for a range of Reynolds numbers between 60 and 200 with opposite body configurations respectively. The diffusion scheme based on the particle strength exchange(PSE) is used to account far the viscous effect accurately. And the vorticity generation algorithm to enforce the no-slip boundary conditions is employed. In order to redistribute particles efficiently on the distorted Lagrangian grid the particle distribution technique is adaptively revised, while maintaining the uniform resolution. The results of the simulations are compared to other experimental results.