• 한국전산유체공학회:학술대회논문집
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• 1995.10a
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• pp.148-153
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• 1995

Three dimensional turbulent flow fields around ships are simulated by a numerical method. Reynolds Averaged Navier-Stokes equations are used where Reynolds stresses are approximated by Baldwin-Lomax and Sub-Grid Scale(SGS) turbulence models. Body-fitted coordinate system is introduced to conform three dimensional ship geometries. The governing equations are discretized by a finite volume method. Temporal derivatives are approximated by the forward differencing and the convection terms are approximated by the QUICK or Kawamura scheme. The 2nd-order centered differencing is used for other spatial derivatives. Pressure and velocity fields are simultaneously iterated by the Highly Simplified Marker-And-Cell method. To verity the numerical method and turbulence models, flow fields around ships are simulated and compared to the experiments.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.191-192
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• 2003

A numerical method for a wave diffraction problem in three-dimensional channels is developed. The physical models are various shapes of channel connected to the open sea. When a ship or an offshore structure is moored in various configurations of channel connected to an open sea, the prediction of the hydrodynamic force exerting on the moored ship could be important for the prediction of its motion. It is assumed that the fluid is inviscid and incompressible and its motion is irrotational. From the continuity equation, the Laplace equation can be obtained as the governing equation. The surface tension at free surface is neglected, and wave amplitude is assumed to be small compared to the wave length. Then the free surface condition can be linearized. The numerical method used here is the localized finite element method based on a variational formulation

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.194-199
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• 2007

IB (immersed boundary) method is one of the prominent tool in computational fluid dynamics for the analysis of flows over complex geometries. The IB technique simplyfies the solution procedure by eliminating the requirement of complex body fitted grids and it is also superior in terms of memory requirement. In this study we have developed numerical code (FOTRAN) for the analysis of 2D flow over a cylinder using IB technique. The code is validated by comparing the wake lengths and separation angles given by Guo et. al. We employed fractional-step procedure for solving the Navier-Stokes equations governing the flow and discrete forcing IB technique for imposing boundary conditions. Also we have developed a 3D code for the backward-facing-step flow and flow over a sphere. The reattachment length in backward-facing-step flow was compared with the one given by Nie and Armaly, which has proven the validity of our code.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.2168-2173
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• 2003

Pressure balancing valve is one of important control devices, which is fully automatic and no manual controls, regulating or adjustments are needed. It is typically used to maintain constant temperature of working fluid in power and chemical plants and domestic water supply systems. Pressure balancing valve is composed of body, cylinder and balancing piston. Therefore, the balancing piston shapes are important design parameters for a pressure balancing valve. In this study, numerical and experimental analyses are carried out with two different balancing piston shapes. Especially, the distribution of static pressure is investigated to calculate the flow coefficient($C_v$). The governing equations are derived from making using of three-dimensional Navier-Stokes equations with standard ${\kappa}-{\varepsilon}$ turbulence model and SIMPLE algorithm. Using commercial code, PHOEIC, the pressure and flow fields in pressure balancing valve are depicted.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.5
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• pp.524-532
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• 2008

This paper presents yaw vibration control performances of railway vehicle featuring controllable magnetorheological damper. A cylindrical type of MR damper is devised and its damping force is evaluated by considering fluid resistance and MR effect. Design parameters are determined to achieve desired damping force level. The MR damper model is then incorporated with the governing equations of motion of the railway vehicle which includes vehicle body, bogie and wheel-set. Subsequently, computer simulation of vibration control via proportional-integral-derivative(PID) controller is performed using Matlab. Various control performances are demonstrated under external excitation by creep force between wheel and rail.

• Journal of Mechanical Science and Technology
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• v.15 no.8
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• pp.1188-1195
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• 2001

A numerical analysis has been carried out to investigate the influences of thermosolutal convection on the heat and mass transfer and solute segregation in crystals grown by the vertical Bridgman technique. The governing equations are solved by a finite-volume method using the power law scheme and the SIMPLE algorithm in which body-fitted coordinate system has been used. A primary convective cell driven by thermal gradients forms in the bulk of the domain, while a secondary convective cell driven by solutal gradients forms near interface. As the solutal Rayleigh number increases, secondary cell becomes to be stronger and has a great influence on the radial concentration along the interface.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.957-962
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• 2008

This paper presents vibration control performances and stability evaluations of railway vehicle featuring controllable magnetorheological (MR) damper. The MR damper model is developed and then incorporated with the governing equations of motion of the railway vehicle which includes vehicle body, bogie and wheel-set. A cylindrical type of MR damper is devised and its damping force is evaluated by considering fluid viscosity and MR effect. Design parameters are determined to achieve desired damping force level applicable to real railway vehicle. Subsequently, computer simulation of vibration control and stability analysis is performed using Matlab Simulink.

• Steel and Composite Structures
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• v.25 no.4
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• pp.497-503
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• 2017

In this paper, nonlinear vibration of multi-degree of freedom systems are studied. It has been tried to develop the mathematical model of systems by second-order nonlinear partial differential equations. The masses are connected with linear and nonlinear springs in series. A great effort has been done to solve the nonlinear governing equations analytically. A new analytical method called Variational Iteration Method (VIM) is proposed and successfully applied to the problem. The linear and nonlinear frequencies are obtained and the results are compared with numerical solutions. The first order of Variational Iteration Method (VIM) leads us to high accurate solution.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.927-939
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• 2007

This paper concerns dynamics of a wheel-axle set on a tangent track which was already published in a book titled "Dynamics of Railway Vehicle Systems" authored by Garg and Dukkipati [1], pointing out several missing terms and erroneous parts in the derived expressions on the conventional governing equations of motion. It is indicated that the x-direction components of normal forces at left and right wheel-rail contact points in the equilibrium axis were missed. Another point is that in deriving the creepages the disturbed velocity components in both x and y directions in the equilibrium axis should not be disregarded in the first term of the numerators. When considering the creepage in the y direction in the body coordinate system, the second term of lateral velocity at the contact point also cannot be neglected. Besides, the hyper-assumptions in the final expressions of vertical components of normal forces at left and right wheel-rail contact points have been recovered in reaching the final stage of analytical model development. Finally it is noteworthy that the process of applying creep theory is deemed to contain a little bit inconsistencies and ambiguities to be clear.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.173-178
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• 1996

A three-dimensional thermo-hydraulic computer code is developed for simulation of incompressible flows in complex geometries. The computer code employs a body-fitted, nonorthogonal grid system in order to efficiently handle the complex geometries encountered in many engineering applications. The finite volume method is used to discretize the governing equations and the convection term is treated by higher-order bounded schemes. The cell-centered, nonstaggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is avoided by use of momentum interpolation practice. The computer code employs the SIMPLE algorithm for pressure and velocity coupling and the k-$\varepsilon$ turbulence for turbulent calculation. The computer code has been tested through application to a variety of test problems and some results are presented in this paper