• Korea-Australia Rheology Journal
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• v.20 no.4
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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.

• Journal of The Korean Astronomical Society
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• v.21 no.2
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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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.

• Journal of computational fluids engineering
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• v.20 no.2
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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.

• Korean Security Journal
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• no.10
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• pp.355-385
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• 2005

As the system of autonomous police that has been debated for long time is fixed to be introduced by the program of participatory government, this treatise intends to analyze main contents and review controversial items in order to present supplementary measures. The program of participatory government to introduce autonomous police in Korea focuses on converting the autonomous police of Korea from centralized police administration in order to provide 'customized security service' that is appropriate to the regional environment. Thus, if relevant city, county or district considers that it is required to introduce the system autonomous police, the assembly may enforce the decision by enacting ordinance. For enforcement, organization in the unit of section will be established in the line of mayor, county headman and district office. The main role will be security service that is closely related to the life of inhabitants such as crime prevention, patrol, traffic crackdown, etc. as well as public health, sanitation and environmental control which are being performed by autonomous organization at present. However some expected controversial items may be summarized in the following 3 points on the premise of accepting the program of government. First, the point at issue related to the basic function of police. The basic function of police is generally understood as order keeping function such as anterior and preventive job and law enforcing function such as posterior and suppressing job. By the way, the program of government does not endow the autonomous police with investigation right for general crime, thereby raising the controversy that our autonomous police is nothing but the assistant of police. Furthermore, the present national police also expresses its dissatisfaction to the transfer of authority. Second, the issue of balance of security service between self-governing bodies may be raised. The security environment is different between self-governing bodies and thus demand of security is different. Therefore, the security service of autonomous police will reveal difference in qualitative aspect for each self-governing body. Moreover, it can be easily anticipated that the quality of security service may be different as per the financial independence degree. Third, the point at issue anticipated with the operation funded by the budget of self-governing body. As autonomous police is operated by the budget of self-governing body, the following problems may be raised; (1) since police administration is subordinated to general administration, the concentration may be weakened (2) the cooperation between policy agencies may be impeded (3) owing to the difficult in possessing spare police, the mobility of police may be somewhat reduced.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.2
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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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• 2001.05a
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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.

• Journal of computational fluids engineering
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• v.6 no.3
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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.

• International Journal of Aeronautical and Space Sciences
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• v.17 no.2
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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.

• Proceedings of the KSR Conference
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• 2007.11a
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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.