• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.144-149
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• 2011

A study to determine the optimal jet conditions for maximizing altitude of the sounding rocket is conducted. The behavior of a simplified linear momentum equation including aerodynamic drag is investigated. The analytic solutions are obtained and compared with numerical solutions. It is shown that there are the optimal jet conditions for maximizing altitude of a sounding rocket according to the rocket mass ratio.

• Kyungpook Mathematical Journal
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• v.58 no.2
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• pp.361-375
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• 2018

The object of the present paper is to study super quasi-Einstein manifolds. Some geometric properties of super quasi-Einstein manifolds have been studied. We also discuss $S(QE)_4$ spacetime with space-matter tensor and some properties related to it. Finally, we construct an example of a super quasi-Einstein spacetime.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05d
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• pp.413-418
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• 1996

To derive the optimimum antenna launching condition for fast wave current drive, the propagation and absorption of the ion cyclotron range of frequencies waves are studied in a KT-2 tokamak plasma. We sove the kinetic wave equation in one dimensional slab geometry with the phase-shifted antenna array to inject the toroidal momentum to electrons. The accessibility conditions and the guidelines of the optimum antenna design for the efficient current drive are derived. The dependence of the current drive efficiency on launching conditions such as the phase and spacing Is presented.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2696-2701
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• 2007

For the analysis of a two-phase flow, the interaction between two phases such as the interfacial momentum or heat transfer is proportional to the interfacial area. So the interfacial area concentration (IAC) is one of the most important parameters governing the behavior of each phase. This study focuses on the development of a computational fluid dynamics (CFD) code for investigating a boiling flow with a one-group IAC transport equation. It was based on the two-fluid model and governing equations were calculated by SMAC algorithm. For checking the robustness of the developed code, the experiment of a subcooled boiling in a vertical annulus channel was analyzed to validate the capability of the IAC transport equation. As the results, the developed code was confirmed to have the capability in predicting multi-dimensional phenomena of vapor generation and propagation in a subcooled boiling.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.7-13
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• 2011

A comparative analysis of thermal models in the lattice Boltzmann method(LBM) for the simulation of laminar natural convection in a square cavity is presented. A HYBRID method, in which the thermal equation is solved by the Navier-Stokes equation method while the mass and momentum conservation are resolved by the lattice Boltzmann method, is introduced and its merits are explained. All the governing equations are discretized on a cell-centered, non-uniform grid using the finite-volume method. The convection terms are treated by a second-order central-difference scheme with a deferred correction method to ensure stability of the solutions. The HYBRID method and the double-population method are applied to the simulation of natural convection in a square cavity and the predicted results are compared with the benchmark solutions given in the literatures. The predicted results are also compared with those by the conventional Navier-Stokes equation method. In general, the present HYBRID method is as accurate as the Navier-Stokes equation method and the double-population method. The HYBRID method shows better convergence and stability than the double-population method. These observations indicate that this HYBRID method is an efficient and economic method for the simulation of incompressible fluid flow and heat transfer problem with the LBM.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.10
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• pp.1368-1379
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• 2000

A numerical study on swirling pulverized coal combustion in an axisymmetric enclosure is carried out by applying the 2-phase weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eulerian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard and RNG k-${\varepsilon}$ turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step and two-step first-order reaction model for the devolatilization process for coal. Special attention is given to establish the thermal boundary conditions on radiative transfer equation By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide an alternative for simulating the radiative transfer.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.56 no.1
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• pp.1-5
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• 2007

Study on the electron transport coefficient in mixtures of CF4 and Ar, have been analyzed over a range of the reduced electric field strength between 0.1 and 350[Td] by the two-term approximation of the Boltzmann equation (BEq.) method and the Monte Carlo simulation (MCS). The calculations of electron swarm parameters require the knowledge of several collision cross-sections of electron beam. Thus, published momentum transfer, ionization, vibration, attachment, electronic excitation, and dissociation cross-sections of electrons for $CF_4$ and Ar, were used. The differences of the transport coefficients of electrons in $CF_4$ mixtures of Ar, have been explained by the deduced energy distribution functions for electrons and the complete collision cross-sections for electrons. The results of the Boltzmann equation and the Monte Carlo simulation have been compared with the data presented by several workers. The deduced transport coefficients for electrons agree reasonably well with the experimental and simulation data obtained by Nakamura and Hayashi. The energy distribution function of electrons in $CF_4-Ar$ mixtures shows the Maxwellian distribution for energy. That is, $f({\varepsilon})$ has the symmetrical shape whose axis of symmetry is a most probably energy. The proposed theoretical simulation techniques in this work will be useful to predict the fundamental process of charged particles and the breakdown properties of gas mixtures. A two-term approximation of the Boltzmann equation analysis and Monte Carlo simulation have been used to study electron transport coefficients.

• 한국기계연구소 소보
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• s.9
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• pp.141-151
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• 1982

An iterative procedure for the calculation of the thick axisymmetric boundary layer and wake near the stern of a body of revolution is presented. Procedure consists of the potential flow calculation by a method of the integral equation of first kind and the calculation of boundary layer and wake by a differential me¬thod of the boundary layer theory. Additionally, higher order terms are included in the conventional momentum equations and continuity equation for the consider¬ation of the characteristics of axisymmetric flow different from the one of two dimentional flow and the thick boundary layer. These solutions are matched at the edge of boundary layer and wake. The results obtained by the present me¬thod are compared with the experimental data and it is found that the nominal wake distribution at the propeller plane of a axisymmetric body is in good agree¬ment with the experiment.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1404-1406
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• 1995

In this paper, argon gas was used for numerical analysis of an arc in a cutting plasma torch driven by constant current. We established nozzle-constricting type torch domain and calculated steady state characteristics of argon arc plasma using the control volume method(CVM). For simplicity, we assumed that the flow field is laminar and the local thermodynamic equilibrium(LTE) prevails in all domain regions. We also neglected cathode-fall and anode-fall effects. Considering magnetic pinch effect and viscosity effect, we solved the momentum equation. Voltage drop in the arc column due to input current was calculated from the temperature field obtained by the energy balance equation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.451-462
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• 1996

In this study, which focuses on ice storage, a fundamental study in cooling and solidification was performed, including the interesting phenomena of density inversion, supercooling and dendritic ice. A numerical study was performed for natural convection and ice formation considering existence of subcooling and dendritic ice were analyzed numerically by using finite difference method and boundary fixing method. In the mesh, the solid fraction was introduced with adding as a term to the energy conservation equation. A flow in the dendrite was modelled as a flow in a porous medium, and the momentum conservation equation was modified to incorporate resistance forces involved in flows through porous media. A numerical solution of the time dependencies of dendrite area and dense ice front was successfully obtained, and the numerical results were good agreement with experimental results. Based on this methodology, a discussion was made of phenomena and characteristics of cooling and freezing processes under various conditions.