• Korea-Australia Rheology Journal
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• 제20권4호
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• pp.189-196
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• 2008

The pulsatile flow of blood through a stenosed artery under the influence of external periodic body acceleration is studied. The effect of non-Newtonian nature of blood in small blood vessels has been taken into account by modeling blood as a Casson fluid. The non-linear coupled equations governing the flow are solved using perturbation analysis assuming that the Womersley frequency parameter is small which is valid for physiological situations in small blood vessels. The effect of pulsatility, stenosis, body acceleration, yield stress of the fluid and pressure gradient on the yield plane locations, velocity distribution, flow rate, shear stress and frictional resistance are investigated. It is noticed that the effect of yield stress and stenosis is to reduce flow rate and increase flow resistance. The impact of body acceleration is to enhance the flow rate and reduces resistance to flow.

• 천문학회지
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• 제21권2호
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• pp.97-104
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• 1988

This study presents the specific rule governing the image configurations of an extended source for micro lensing of the two body gravitational lens system developed by Chang and Refsdal (1979). Various topological situations of a source are considered in relation to the regions bounded by the so-called critical curves.

• 설비공학논문집
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• 제3권4호
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• pp.241-249
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• 1991

A quasi-three dimensional calculation method is presented on the basis of Wu's idea using finite element methods. In B-B flow the governing equations are cast into a single equation to overcome the restriction of the type of turbomachinery, and Kutta condition is exactly assured by introducing a combination of two kinds of stream functions. In H-S flow a dissipative force which is assumed to be opposed to the relative velocity is added to the governing equation for a consistent loss model. The entropy change along each streamline is then calculated by assuming that the dissipative force may be a force coming from laminar viscous stresses with inviscid velocity distributions. Both the flow solvers are combined to build a three-dimensional flow field through a few iterations. For an effect of the distortion of H-S flow surface the body forces are computed after each B-B flow calculation is finished. Mizuki's centrifugal impellers are tested numerically. The reliability of the numerical solution compared with experimental data is guaranteed.

• 한국전산유체공학회지
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• 제20권2호
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• pp.103-108
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• 2015

Fluid-body interaction analysis of floating body with six degree-of-freedom motion is presented. In this study, three-dimensional incompressible Navier-Stokes equations are employed as a governing equation. The numerical method is based on a finite-volume approach on a cartesian grid together with a fractional-step method. To represent the body motion, the immersed boundary method for direct forcing is employed. In order to simulate the coupled six degree-of-freedom motion, Euler's equations based on rigid body dynamics are utilized. To represent the complex body shape, level-set based algorithm is utilized. In order to describe the free surface motion, the volume of fluid method utilizing the tangent of hyperbola for interface capturing scheme is employed. This study showed three different continuums(air, water and body) are simultaneously simulated by newly developed code. To demonstrate the applicability of the current approach, two different problems(dam-breaking with stationary obstacle and water entry) are simulated and all results are validated.

• 시큐리티연구
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• 제10호
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• pp.355-385
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• 2005

본 논문은 오랫동안 논의되어 왔던 자치경찰제의 도입방안에 대한 참여정부의 도입안이 확정됨에 따라 주요내용을 분석하고 쟁점사항을 검토하여 보완책을 제시하는데 목적이 있다. 참여정부의 자치경찰 구성은 해당 시${\cdot}$군${\cdot}$구가 자치경찰제 도입의 필요성이 있다고 판단되면 의회에서 조례를 제정하여 실시할 수 있도록 했으며, 시장, 군수, 구청 조직에 과단위의 기구로 운영되도록 한다는 것이다. 주요 업무는 방범, 순찰, 교통단속 등 주민생활과 밀접한 치안서비스와 현재 자치단체가 벌이고 있는 보건, 위생, 환경단속의 업무를 수행하게 된다. 그러나 정부안의 수용을 전제로, 예상되는 몇 가지 쟁점사항을 정리하면 다음의 세가지로 요약할 수 있다. 첫째, 경찰의 기본기능과 관련된 논점이다. 정부안에는 자치경찰에게 일반범죄에 대한 수사권을 주지 않고 있어 ‘경찰의 보조원’에 불과한 것이 아닌가, 하는 것이 논점이 되고 있다. 둘째, 지자체간의 치안서비스의 균형성 논란이 제기될 수 있다. 지방 자치단체간에는 치안환경이 상이하고, 따라서 치안수요도 각기 다르다. 그러기에 자치경찰의 치안서비스는 지자체에 따라 질적인 면에서 차이를 보이게 될 것이다. 셋째, 자치단체 예산으로 운영됨으로서 예상되는 논점이다. 자치경찰이 지자체의 예산으로 운영된다는 점에서, (1) 경찰행정이 일반행정의 하위에 놓여 집행력이 약화 될 수 있다. (2) 경찰기관 간에 협조가 원활하게 이루어지지 않을 수 있다. (3) 예비경찰 보유의 어려움으로 인해 경찰의 기동성(機動性)이 다소 떨어질 수도 있다.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.149-156
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• 2016

The hypersonic flow on the stagnation streamline of a blunt body is analyzed with quasi one-dimensional (1-D) Navier-Stokes equations approximated by adopting the local similarity to the two-dimensional (2-D)/axisymmetric Navier-Stokes equations. The governing equations are solved using the implicit finite volume method. The computational domain is confined from the stagnation point to the shock wave, and the shock fitting method is used to find the shock position. We propose a boundary condition at the shock, which employs the shock wave angle in the vicinity of the stagnation streamline using the shock shape correlation. As a result of numerical computation conducted for the hypersonic flow over a sphere, the proposed boundary condition is shown to improve the accuracy of the prediction of the shock standoff distance. The quasi 1-D Navier-Stokes code is efficient in computing time and is reliable for the flow analysis along the stagnation streamline and the prediction of heat flux at the stagnation point in the hypersonic blunt body flow.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권2호
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• pp.206-218
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• 2014

The wave attenuation by floating breakwaters in high amplitude waves, which can lead to wave overtopping and breaking, is examined by numerical simulations. The governing equations, the Navier-Stokes equations and the continuity equation, are calculated in a fixed Cartesian grid system. The body boundaries are defined by the line segment connecting the points where the grid line and body surface meet. No-slip and divergence free conditions are satisfied at the body boundary cell. The nonlinear waves near the moving body is defined using the modified marker-density method. To verify the present numerical method, vortex induced vibration on an elastically mounted cylinder and free roll decay are numerically simulated and the results are compared with those reported in the literature. Using the present numerical method, the wave attenuations by three kinds of floating breakwaters are simulated numerically in a regular wave to compare the performance.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.105-110
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• 2001

An Eulerian-Lagrangian method, so called immersed boundary method, is used for analysing viscous flow around arbitrary bodies, where governing equations are discretized on a regular grid by using a finite volume method. To improve the accuracy of flow near body boundaries, a second-order accurate interpolation scheme is used and a level-set based grid deformation method is presented to construct the adaptive grids around body boundaries. The present scheme is used to simulate steady flow around a semicircular cylinder mounted on the bottom of flow domain and calculated results are validated by results of a body fitted grid method. Finally, present method is applied to a complex flow around multi body and the usefulness is checked by investigating calculated results.

• 한국전산유체공학회지
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• 제6권3호
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• pp.19-26
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• 2001

An Eulerian-Lagrangian method, so called immersed boundary method, is used for analysing viscous flow around arbitrary bodies, where governing equations are discretized on a regular grid by using a finite volume method. To improve the accuracy of flow near body boundaries, a second-order accurate interpolation scheme is used and a level-set based grid deformation method is presented to construct the adaptive grids around body boundaries. The present scheme is used to simulate steady flow around a semicircular cylinder mounted on the bottom of flow domain and calculated results are validated by results of a body fitted grid method. Finally, present method is applied to a complex flow around multi body and the usefulness is checked by investigating calculated results.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2007년도 추계학술대회 논문집
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• pp.940-952
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• 2007

It is found that there are many serious errors in deriving the existing governing equations of motion for a wheel-axle set negotiating an arbitrarily changing radius curve by Vijay K. Garg and Rao V. Dukkipati. Among other things, despite the hypothesis on arbitrarily changing radius of curve, there had been no taking a time derivative of the radius R in the first half of the derivation. Even if the D'lambert force arising from the centrifugal acceleration of vehicle body or bogie was appropriately taken into account while calculating cant deficiency, it is unnecessarily duplicated in the force vectors of governing equations. The graphical model given in Fig. 5.15 is not enough to follow those developed expressions from both physical and structural points of view. Besides, there are some blunders in assigning plus or minus sign not to be regarded as simple typographic ones and similar mistakes are committed in deriving creep force expressions as in the case of a wheel-axle set on a tangent track.