• Proceedings of the Korean Nuclear Society Conference
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• 2004.10a
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• pp.175-175
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• 2004

• 한국전기화학회:학술대회논문집
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• 2003.10a
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• pp.61-61
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• 2003

• Atmosphere
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• v.26 no.3
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• pp.423-433
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• 2016

In this study, performance of a computational fluid dynamics (CFD) model is assessed from analysis on air flow pattern which is observed in the artificial street canyon. Field observations focusing on flows were conducted at an artificial street canyon in Magok region. For the observation of three-dimensional airflow structures, twelve three-dimensional wind anemometers (hereafter, CSAT3) were installed inside the street canyon. The street canyon was composed of two rectangular buildings with 35-m length, 4-m width, and 7-m height. The street width (distance between the buildings) is 7 m, making the street aspect ratio (defined by the ratio of building height to street width) of 1. For the observation of above-building wind, a CSAT3 was installed above the northwest-side building. Southwesterly, westerly and northwesterly were dominant in the street canyon during the observations. Because wind direction is parallel to the street canyon in the southwesterly case, westerly and northwesterly were selected as inflow directions in numerical simulations using a computational fluid dynamics model developed through the collaborative research project between National Institute of Meteorological Sciences and Seoul National University (CFD_NIMR_SNU). The observations showed that a well-structured vortex flow (skimming flow) and an evidence of a small eddy at the corner of the downwind building and ground appeared. The CFD_NIMR_SNU reproduced both the observed flow patterns reasonably well, although wind speeds inside the street canyon were underestimated.

• Journal of the Society of Naval Architects of Korea
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• v.52 no.6
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• pp.471-477
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• 2015

When a ship sails in a seaway, the resistance on a ship increases due to incident waves and winds. The magnitude of added resistance amounts to about 15–30% of a calm-water resistance. An accurate prediction of added resistance in waves, therefore, is essential to evaluate the performance of a ship in a real sea state and to design an optimum hull form from the viewpoint of the International Maritime Organization (IMO) regulations such as Energy Efficiency Design Index (EEDI) and Energy Efficiency Operational Indicator (EEOI). The present study considers added resistance problem of AFRAMAX-class tankers with the conventional bow and Ax-bow shapes. Added resistance due to waves is successfully calculated using 1) a three-dimensional time-domain seakeeping computations based on a Rankine panel method (three-dimensional panel) and 2) a commercial CFD program (STAR-CCM+). In the hydrodynamic computations of a three-dimensional panel method, geometric nonlinearity is accounted for in Froude-Krylov and restoring forces using simple wave corrections over exact wet hull surface of the tankers. Furthermore, a CFD program is applied by performing fully nonlinear computation without using an analytical formula for added resistance or empirical values for the viscous effect. Numerical computations are validated through four degree-of-freedom model-scale seakeeping experiments in regular head waves at the deep towing tank of Hyundai Heavy Industries.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.488-491
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• 2004

Numerical analysis of the three dimensional turbulent flow field in a complex valve shape is carried out to confirm the flow field whether the designed valve shape is good or not. The simulation of the incompressible flow in a constant flowrate control valve is performed by using the commercial code, FLUENT/UNS 6.0. The results of flow field show the designed valve has some problems, therefore these will be good data for new valve design.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.05a
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• pp.41-44
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• 2003

In spite of many researches made on the supersonic jets until now, detailed three-dimensional structures of supersonic jets are not well hewn. In the current study, the detailed structures of three-dimensional supersonic jets are numerically investigated using a CFD method. The total variation diminishing (TVD) scheme is used to solve the unsteady, three-dimensional, compressible Euler equations. Computational results are visualized to investigate the major features of supersonic jets. The three-dimensional computation results show that the structures of the supersonic jets are significantly different from those of the two-dimensional or axisymmetric supersonic jets.

• Journal of the Korean Society of Combustion
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• v.7 no.1
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• pp.52-57
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• 2002

A numerical investigation using a commercial CFD program of the Inter-Phase Slip Algorithm has been carried out for detail characteristics of particle motions and bubble behaviors in a two dimensional fluidized bed. The bed simulated has been operated with three different distributor geometries, such as bubble cap, nozzle, and perforated plate types. Experiments using a slit-type two-dimensional fluidized bed and a cylinder-type fluidized bed have been performed in order to confirm the simulation model. In addition, the numerical results are compared with the wellknown correlation of bubble sizes and bubble rising velocities by Mori and Wen [1]. The simulation model that we applied is shown to be useful to understand the relation between bubble behaviors and distributor geometries.

• Transactions of the Korean Society of Automotive Engineers
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• v.10 no.5
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• pp.98-106
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• 2002

The airflow characteristics of an air-conditioning duct with multiple diffusers were investigated through one-dimensional analysis, CFD simulation and experimental measurement. One-dimensional program based on Bernoulli's equation and minor loss equations was developed in order to evaluate the air distribution rate at each diffuser. In CFD simulation, three-dimensional flow characteristics inside air-conditioning duct were computed for incompressible viscous flow, adopting the RNG k-$\xi$turbulence model. Also, in an effort to equalize the discharge flow rate at each outlet, the optimization procedure has been performed to obtain the optimum diffuser area. In this process, square of difference between maximum discharge rate and minimum discharge rate is used as an object function. Diffuser area and discharge velocity are established as constraints. After optimization process, determined design variables are applied again in CFD simulation and experiment to validate the optimized result by one-dimensional program. Comparison with the experimental data of airflow rate distribution showed that the developed program seems to be acceptable and can be useful design tool for an automotive air-conditioning duct in an initial design stage.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.228-237
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• 2007

The flow characteristics around a horn-type rudder behind an operating propeller of a high-speed large container carrier are studied through a numerical method in fully wetted and cavitating flow conditions. The computations are carried out in a small scale ratio of 10.00(gap space=5mm) to consider the gap effects. The Reynolds averaged Navier-Stokes equation for a mixed fluid and vapor transport equation applying cavitation model are solved. The axisymmetry body-force distribution technique is utilized to simulate the flow behind an operating propeller. The gap flow, the three-dimensional flow separation, and the cavitation are the flow characteristics of a horn-type rudder. The pattern of three-dimensional flow separation is analyzed utilizing a topological rule. The various cavity positions predicted by CFD were shown to be very similar to rudder erosion positions in real ship rudder. The effect of a preventing cavitation device, a horizontal guide plate, is also investigated.

• International Journal of Naval Architecture and Ocean Engineering
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• v.3 no.1
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• pp.65-71
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• 2011

Seakeeping analysis has progressed from the linear frequency-domain 2D strip method to the nonlinear timedomain 3D panel method. Nevertheless, the violent free surface flows such as slamming and green water on deck are beyond the scope of traditional panel methods based on potential theory. Recently, Computational Fluid Dynamics (CFD) has become an attractive numerical tool that can effectively deal with the violent free surface flows. ABS, as a classification society, is putting forth a significant amount of effort to implement the CFD technology to the advanced strength assessment of modern commercial ships and high-speed naval craft. The main objective of this study is to validate the CFD technology as a seakeeping tool for ship design considering fully nonlinear three-dimensional slamming and green water on deck. The structural loads on a large container carrier were successfully calculated from the CFD analysis and validated with segmented model test measurements.