• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.25-32
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• 1999

In the present paper, we theoretically analyze the flow of magnetic fluids in a circular pipe with a vertical magnetic field and investigate the magnetic response by the external magnetic field. Theoretical study through the governing equation derived by Siliomis is carried out with numerical analysis by the Gauss Elimination Method. Using polar and magnetic effect parameters, theoretical equations and distributions for the velocity, vorticity, internal angular momentum and induced magnetization as the magnetic response are shown. Especially, in the region of strong magnetic field the specific property is appeared by finding a critical magnetic effect parameter for a polar effect parameter.

• Journal of the Korean Magnetics Society
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• v.10 no.1
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• pp.42-47
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• 2000

In the present work, we analyze theoretically the flow of magnetic fluids in a circular pipe with longitudinal magnetic field. We used governing equations induced Shliomis and Polar theory of Eringen. Using theoretical equations and distributions for the velocity, vorticity and angular velocity as the magnetic response, it is shown that magnetic fluid flow is non-Newtonian fluid. We investigate dynamic characteristic of magnetic fluid by comparing longitudinal magnetic field with transverse magnetic field. And, the limits, influence magnetic fluid, of the intensity of the magnetic field with polar, size and magnetic effect parameters are shown.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.3
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• pp.38-46
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• 1990

A numerical solution method of the boundary integral equation for axisymmetric potential flows is presented. Those are represented by ring source and ring vorticity distribution. Strengths of ring source and ring vorticity are approximated by linear functions of a parameter $\zeta$ on a segment. The geometry of the body is represented by a cubic B-spline. Limiting integral expressions as the field point tends to the surface having ring source and ring vorticity distribution are derived upto the order of ${\zeta}ln{\zeta}$. In numerical calculations, the principal value integrals over the adjacent segments cancel each other exactly. Thus the singular part proportional to $\(\frac{1}{\zeta}\)$ can be subtracted off in the calculation of the induced velocity by singularities. And the terms proportional to $ln{\zeta}$ and ${\zeta}ln{\zeta}$ can be integrated analytically. Thus those are subtracted off in the numerical calculations and the numerical value obtained from the analytic integrations for $ln{\zeta}$ and ${\zeta}ln{\zeta}$ are added to the induced velocity. The four point Gaussian Quadrature formula was used to evaluate the higher order terms than ${\zeta}ln{\zeta}$ in the integration over the adjacent segments to the field points and the integral over the segments off the field points. The root mean square errors, $E_2$, are examined as a function of the number of nodes to determine convergence rates. The convergence rate of this method approaches 2.

• Journal of Ocean Engineering and Technology
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• v.36 no.5
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• pp.326-339
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• 2022

Recently, not only Korea but also the world has been suffering from problems related to coastal erosion. The hard defense method has been primarily used as a countermeasure against erosion. However, this method is expensive and has environmental implications. Hence, interest in other alternative methods, such as the eco-friendly vegetation method, is increasing. In this study, we aim to analyze the hydraulic characteristic of submerged rigid vegetation according to the cross-sectional change through a hydraulic experiment and numerical simulation. From the hydraulic experiment, the reflection coefficient, transmission coefficient, and energy dissipation coefficient were analyzed according to the density, width, and multi-row arrangement of the vegetation zone. From numerical simulations, the flow field, vorticity distribution, turbulence distribution, and wave distribution around the vegetation zone were analyzed according to the crest depth, width, density, and multi-row arrangement distance of the vegetation zone. The hydraulic experiment results suggest that the transmission coefficient decreased as the density and width of the vegetation zone increased, and the multi-row arrangement condition did not affect the hydraulic characteristics significantly. Moreover, the numerical simulations showed that as the crest depth decreased, the width and density of vegetation increased along with vorticity and turbulence intensity, resulting in increased wave height attenuation performance. Additionally, there was no significant difference in vorticity, turbulence intensity, and wave height attenuation performance based on the multi-row arrangement distance. Overall, in the case of submerged rigid vegetation, the wave energy attenuation performance increased as the density and width of the vegetation zone increased and crest depth decreased. However, the multi-row arrangement condition did not affect the wave energy attenuation performance significantly.

• The Bulletin of The Korean Astronomical Society
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• v.33 no.2
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• pp.33.2-33.2
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• 2008

• 한국전산유체공학회:학술대회논문집
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• 1999.05a
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• pp.48-57
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• 1999

This paper deals with the numerical simulation of the behavior of single bubble rising near the free surface. Volume fraction of fluid (VOF) method with continuum surface force (CSF) model, the well known method for two phase flow simulation is adopted. A bubble of spherical shape positioned beneath the free surface is assumed at the initial stage. The difference according to the fluid properties of surrounding medium is examined. Simulation results are depicted and explained with the time history of bubble shape, velocity field and vorticity distribution.

• Journal of Ocean Engineering and Technology
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• v.13 no.1 s.31
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• pp.105-112
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• 1999

This research is an experimental investigation of the region of the Biased Flow. This experiment was carried out in a circulating water channel, and the results are analyzed by using the PIV technique. The results are presented in velocity vector field, velocity contour and vorticity contour. The results were compared with those of Zdravkovich which were carried out in a wind tunnel. These results will be very useful to verify numerical codes.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.516-523
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• 2009

The artificial compressibility (AC) method for the incompressible Navier-Stokes equations in the generalized curvilinear coordinates using the primitive form is implemented. The main advantage of the AC approach is that the resulting system of equations resembles the system of compressible N-S equations and can thus be integrated in time using standard, well-established time-marching methods. The errors, which are the odd-even oscillation, for pressure field in using the artificial compressibility can be eliminated by using the $4^{th}$ order artificial dissipation term which is explicitly included. Even though this paper focuses exclusively on 2D laminar flows to validate and assess the performance of this solver, this numerical method is general enough so that it can be readily extended to carry out 3D URANS simulation of engineering flows. This algorithm yields practically identical velocity profiles and primary vortex and secondary vortices that are in excellent overall agreement with the results of the vorticity-stream function formulation (Ghia et al., 1982). However, the grid resolution have to be required to be large enough to express the various vortices.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.3135-3147
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• 1993

A numerical method is presented which can solve the steady flow and heat transfer from a rotating and heated circular cylinder in a uniform flow for a range of Reynolds number form 5 to 100. The steady response of the flow and heat transfer is simulated for various spin parameter. The effects on the flow field and heat transfer characteristics known as lift, drag and heat transfer coefficient are analyzed and the streamlines, velocity vectors, vorticity, temperature distributions around it were scrutinized numerically. As spin parameter increases the region of separation vortex becomes smaller than upper one and the lower region will vanish. The lift force, a large part is due to the pressure force, increases as the Reynolds number and it increases linearly as spin parameter increases. The pressure coefficient changes rapidly with spin parameter on the lower surface of the cylinder and the vorticity is sensitive to the spin parameter near separation region. As spin parameter increases the maximum heat coefficient and the thin thermal layer on front region are moved to direction of rotation. However, with balance between the local increase and decrease, the overal heat transfer coefficient is almost unaffected by rotation.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.2
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• pp.267-277
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• 1993

A finite element method(FEM) is presented and applied to the two-dimensional bottom turbulent boundary layer. The time-dependent incompressible motion of a viscous fluid is formulated by using the well-known Navier-Stokes equations and vorticity equation in terms of the velocity and pressure fields. The general numerical formulation is based on Galerkin method and solved by introducing the mixing length theory of Prandtl for eddy kinematic viscosity of a turbulent flow field. Numerical computations of the transport of sediment on an arbitrary sea-bed due to wave motion in the turbulent boundary layer are carried out. The results obtained by the FEM made clear the difference in characteristic features between the boundary layer due to oscillatory flow and the boundary layer due to wave motion.