• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.10
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• pp.754-760
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• 2008

Computation of moving interface by the level set method typically requires the reinitialization of level set function. An inaccurate estimation of level set function $\phi$ results in incorrect free-surface capturing and thus errors such as mass gain/loss. Therefore, an accurate and robust reinitialization process is essential to the simulation of free-surface flows. In the present paper, we pursue further development of the reinitialization process, which evaluates level set function directly using a normal vector on the interface without solving there-distancing equation of hyperbolic type. The Taylor-Galerkin approximation and P1P1 splitting/SUPG (Streamline Upwind Petrov-Galerkin) FEM are adopted to discretize advection equation of the level set function and the incompressible Navier-Stokes equation, respectively. Advection equation and re-initialization process of free surface capturing are validated with benchmark problems, i.e., a broken dam flow and timereversed single vortex flow. The simulation results are in good agreement with the existing results.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.60-66
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• 2011

Engineering interests of submerged bodies and turbomachinery has led researchers to study various cavitation models for decades. The governing equations used for the present work are the two-phase Navier-Stokes equations with homogeneous mixture model. The solver employed on implicit dual time preconditioning algorithm in curvilinear coordinates. Three different cavitation models were applied to two axisymmetric cylinders and compared with experiments. It is concluded that the Merkle's new cavitation model has successfully accounted for cavitating flows and well captured the re-entrant jet phenomenon over the 0-caliber cylinder.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.178-181
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• 2011

Recently, micro shock tube is being extensively used in various fields of engineering applications. The flow characteristics occurring in the micro shock tube may be significantly different from that of conventional macro shock tube due to very low Reynolds number and Knudsen number effects which are, in general, manifested in such flows of rarefied gas, solid-gas two-phase, etc. In these situations, Navier-Stokes equations cannot properly predict the micro shock tube flow. In the present study, a two-dimensional CFD method has been applied to simulate the micro shock tube, with slip velocity and temperature jump boundary conditions. The effects of wall thermal conditions on the unsteady flow in the micro shock tube were also investigated. The unsteady behaviors of shock wave and contact discontinuity were, in detail, analyzed. The results obtained show much more attenuation of shock wave, compared with macro-shock tubes.

• Nuclear Engineering and Technology
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• v.43 no.1
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• pp.45-62
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• 2011

The Korean nuclear industry is developing a thermal-hydraulic analysis code for safety analysis of pressurized water reactors (PWRs). The new code is called the Safety and Performance Analysis Code for Nuclear Power Plants (SPACE). The SPACE code adopts advanced physical modeling of two-phase flows, mainly two-fluid three-field models which comprise gas, continuous liquid, and droplet fields and has the capability to simulate 3D effects by the use of structured and/or nonstructured meshes. The programming language for the SPACE code is C++ for object-oriented code architecture. The SPACE code will replace outdated vendor supplied codes and will be used for the safety analysis of operating PWRs and the design of advanced reactors. This paper describes the overall features of the SPACE code and shows the code assessment results for several conceptual and separate effect test problems.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.11a
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• pp.78-81
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• 2008

A numerical study of the unsteady flow in an over-expanded thrust optimized contour and compressed truncated perfect rocket nozzle is carried out in present paper. These rocket nozzles are subject to flow separation in transient phase at engine start-up and/or engine shut-down. The separation flow structures at different pressure ratios are observed. The start-up process exhibits two different shock structures such as FSS (Free Shock Separation) and RSS (Restricted Shock Separation). For a range of pressure ratios, hysteresis phenomenon occurs between these two separation patterns. A three-dimension compressible Navier-Stokes solver is used for the present study. One equation Spalart-Allmaras turbulence model is selected. The computed nozzle wall pressures show a good agreement with the experimental measurements. Present results have shown that present code can be used for the analysis of the transient flows in nozzle.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.3
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• pp.258-266
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• 2017

Numerical simulations of turbulent two phase flows around KCS have been performed to investigate effects of trim conditions on ship resistance of KCS in short waves by utilizing waves2foam. The wave lengths of LPP/2 and LPP/4 with 1m and 2m wave heights were imposed at inlet boundary. The resistance reduction at 2m trim by head and the increase of resistance at trims by stern were observed regardless of wave lengths and wave heights. The hull pressure on fore-and-aft rather than wave patterns around bulbous bows was mainly responsible for the total resistance coefficients of KCS in short waves. A phase diagram of contribution of hull pressure to the total resistance coefficients disclosed that the phase of representing the maximum resistance in time history played an important role in the effect of trim conditions on ship resistance of KCS in short waves.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.494-501
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• 2000

Effectiveness of a 3-pass plate finned-tube heat exchanger is calculated using heat exchangelet method by changing the shape of fin and the arrangement of tubes. The alternative refrigerant R134a is taken in this study. Conduction between neighboring tubes along the fin is taken into account in addition to convection between the fin and the surrounding air. Governing equations are obtained by using energy balance in a small control volume containing a tube and fins. They are numerically solved following the tube. Effect of tube-to-tube conduction is investigated in single-phase and two-phase flows with various fin shapes and arrangements of tubes. Improvement of effectiveness by fin perforation is studied too. The results shows that perforating fins, increasing the number of tubes, and increasing the distance between neighboring tubes at the same fin area enhance the effectiveness.

• Journal of Navigation and Port Research
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• v.32 no.8
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• pp.621-628
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• 2008

Container terminals keenly compete with one another because of the continuous increase of container flows and the appearance of large-sized vessels. Major cargo handling equipment manufacturers are interested in the development of new conceptual equipment to greatly increase its productivity. In this study, a two-phase procedure is suggested for selecting the optimal development alternatives, when various development alternatives for container cranes are given. The first phase removes the alternatives that violate essential requirements and the second phase selects final alternatives by the evaluation of experts and the linear assignment method. Finally, a case applying the procedure is provided.

• The Transactions of the Korean Institute of Power Electronics
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• v.6 no.2
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• pp.209-216
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• 2001

The conventional three-level high frequency phase-shifted dc/dc converter has a disadvantage that a circulating current flows through transformer and switching devices during the freewheeling interval. Due to this circulating current and RMS current stress, conduction losses of transformer and switching devices increases. To alleviate these problems, we propose an improved three-level Zero Voltage and Zero Current Switchig (ZVZCS) dc/dc converter using a tapped inductor, a snubber capacitor and two snubber diodes attached at the secondary side of transformer. The proposed ZVZCS converter is verified on a 7kW, 30kHz experimental prototype.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.339-344
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• 2006

Container terminals compete with other ones because of the continuous increase of container flows and the appearance of large-sized vessels. Major port equipment manufacturers are interested in the development of new conceptual equipment ot greatly increase the productivity. In this study, a two-phase procedure is suggested for selecting the optimal development alternatives, when there are various development alternatives for container cranes, typical equipment in ports. The first phase removes the alternatives that violate essential requirements and the second phase selects find alternatives by using AHP (Analytic Hierarchy Process). Finally and example applying the procedure is provided.