• Journal of the korean society of oceanography
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• v.37 no.1
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• pp.20-26
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• 2002

The offshore extension of the East Korean Warm Current (EKWC) mostly turns anti-cyclonically around the Ulleung Warm Eddy (UWE). This fact needs to be dynamically explained because a rectilinear stream past a circular cylinder is normally expected to have a flow pattern symmetric about the stream axis. For this purpose, a simple analytical model is presented in this paper. This model shows that the EKWC's tendency to be anti-cyclonic around the UWE is due to the anti cyclonic circulation generated around the UWE. This tendency results from the geostrophic adjustment between the UWE and the ambient EKWC water. As the strength of the UWE decreases, relative to the EKWC, this model shows that the flow pattern gradually changes from circular to rectilinear.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.10 s.241
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• pp.1156-1162
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• 2005

In this study, a noble method is proposed to prevent the edge overcoating (EOC) that may develop near the edge of the steel strip in the gas wiping process of continuous hot-dip galvanizing. In our past study (Trans. of the KSME (B), Vol. 27, No. 8, pp. $1105\~1113$), it was found that EOC is caused by the alternating vortices which are generated by the collision of two opposed jets in the region outside the steel strip. When the two opposed jets collide at an angle much less than $180^{o}$, non-alternating stable vortices are established symmetrically outside the steel strip, which lead to nearly uniform pressure on the strip surface. In order to deflect both jets downward by a certain angle, a cylinder with small diameter is installed tangentially to the exit of the lower lip of the two-dimensional jet. In order to find an optimum cylinder diameter, the three dimensional flow field is analysed numerically by using the commercial code, STAR-CD. And the coating thickness is calculated by using an integral analysis method to solve the boundary layer momentum equation. In order to compare the present noble method with the conventional baffle plate method to prevent the EOC, the flow field with a baffle plate is also calculated. The calculation results show that the tangentially installed cylinder at the bottom lip of the jet exit is more effective than the baffle plate to prevent EOC.

• Journal of the Korean Society of Marine Environment & Safety
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• v.26 no.4
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• pp.419-428
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• 2020

The flow past a wall mounted square cylinder, a typical and basic shape of building, bridge or offshore structure, was simulated using URANS computation through adoption of three turbulence models, namely, the k-ε model, k-ω model, and the v²-f model. It is well known that this flow is naturally unstable due to the Karman vortex shedding and exhibits a complex flow structure in the wake region. The mean flow field including velocity profiles and the dominant frequency of flow oscillation that was from the simulations discussed earlier were compared with the experimental data observed by Wang et al. (2004; 2006). Based on these comparisons it was found that the v²-f model is most accurate for the URANS simulation; moreover, the k-ω model is also acceptable. However, the k-ε model was found to be unsuitable in this case. Therefore, v²-f model is proved to be an excellent choice for the analysis of flow with massive separation. Therefore, it is expected to be used in future by studies aiming to control the flow separation.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.12
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• pp.1624-1634
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• 1997

A numerical study on two-dimensional unsteady transonic cascade flow has been performed by adopting dual time stepping and the k-.omega. turbulence model. An explicit 4 stage Runge-Kutta scheme for the compressible Navier-Stokes equations and an implicit Gauss-Seidel iteration scheme for the k-.omega. turbulence model are proposed for fictitious time stepping. This mixed time stepping scheme ensures the stability of numerical computation and exhibits a good convergence property with less computation time. Typical steady-state convergence accelerating schemes such as local time stepping, residual smoothing and multigrid combined with dual time stepping shows good convergence properties. Numerical results are presented for unsteady laminar flow past a cylinder and turbulent shock buffeting problem for bicircular arc cascade flow is discussed.

• Journal of Advanced Research in Ocean Engineering
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• v.3 no.4
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• pp.165-173
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• 2017

This study aims at validating simulations of the forced and freely vibrating cylinders at Reynolds number of approximately 500 in order to identify the capability of the CFD code, and to establish the analysis process of the vortex-induced vibration (VIV). The direct numerical and large eddy simulations were employed to resolve the various length scales of the vortices, and the morphing technique was used to consider a motion of the circular cylinder. For the forced vibration case, both in- and anti-phase VIV processes were observed regarding the frequency ratio. Namely, when the frequency ratio approaches to unity, the synchronization/lock-in process occurs, leading to substantial increases in drag and lift coefficients. This is strongly linked with the switch in timing of the vortex formation, and this physical tendency is consistent with that of Blackburn and Henderson (J. Fluid Mech., 1999, 385, 255-286) as well as force coefficients. For the free oscillation case, the mass and damping ratio of 50.8 and 0.0024 were considered based on the study of Blackburn et al. (J. Fluid Struct., 2000, 15, 481-488) to allow the direct comparison of simulation results. The simulation results for a peak amplitude of the cylinder and a shedding mode are reasonably comparable to that of Blackburn et al. (2000). Consequently, based on aforementioned results, it can be concluded that numerical methods were successfully validated and the calculation procedure was well established for VIV analysis with reasonable results.

• Advances in nano research
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• v.10 no.3
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• pp.221-234
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• 2021

During the previous few years, phenomenon of bioconvection along with the use of nanoparticles showed large number of applications in technological and industrial field. This paper analyzed the bioconvection phenomenon in magnetohydrodynamic boundary layer flow of a Powell-Eyring nanoliquid past a stretchable cylinder with Cattaneo-Christov heat flux. In addition, the impacts of chemical reaction and heat generation/absorption parameter are considered. By the use of appropriate transformation, the governing PDEs (nonlinear) have been transformed and formulated into nonlinear ODEs. The resulting nonlinear ODEs subjected to relevant boundary conditions are solved analytically through homotopy analysis method which is programmed in Mathematica software. Graphical and numerical results versus physical quantities like velocity, temperature, concentration and motile microorganism are investigated under the impact of physical parameters. It is noted that velocity profile enhances as the curvature parameter A and Eyring-Powell fluid parameter M increases but a decline manner for large values of buoyancy ratio parameter Nr and bio-convection Rayleigh number Rb. In the presence of Prandtl number Pr, Eyring-Powell fluid parameter M and heat absorption parameter ��, temperature profile decreases. Nano particle concentration profile increases for increasing values of magnetic parameter Ha and thermophoresis parameter Nt. The motile density profile has revealed a decrement pattern for higher values of bio-convection Lewis number Lb and bio-convection peclet number Pe. This study may find uses in bio-nano coolant systems, advance nanomechanical bio-convection energy conversion equipment's, etc.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.4
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• pp.876-891
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• 1988

This study was carried out to investigate the mixing flow of a turbulent cross jet in a cylindrical chamber. A study on the turbulent mixing flow of a cross jet at 45.deg. with respect to each other in the free atmospheric condition was conducted before this study and has given us some fundamental experimental results. Present data have been analyzed and compared with semi-empirical equations for a round and a plane jets. Interests on this kind of cross jets (flows) have been increasing during the past several years for the purpose of the analysis of mixing flows and their applications. In this study, a turbulent cross jet of air in a cylindrical chamber has been conducted and the turbulent characteristics in the mixing region have been analyzed experimentally. The experimental data were discussed by comparing with the semi-empirical equations of Hinze and Gortler. From the experimental curve, the semi-empirical equations of mean velocities and Reynolds stresses have been derived. Three dimensional data acquisitions and the statistical treatments of turbulence characteristics were carried out by on-line computer measurement system connected with the constant temperature type 2-channel hot-wire anemometer system.