• Journal of Radiation Protection and Research
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• v.32 no.1
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• pp.15-20
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• 2007

An empirical formula fur the neutron dose equivalent at the maze entrance of medical accelerator treatment rooms was derived on the basis of a Monte Carlo simulation. The simulated neutron dose equivalents around the Varian medical accelerator by the MCNPX code were employed. Two cases of target rotational planes were considered: parallel and perpendicular to maze walls. Most of the maximum neutron dose equivalents at the doorway were found when the target rotational planes were parallel to maze walls and the beams were directed to the inner maze entrances. The neutron dose equivalents at the outer maze entrances were calculated for about 698 medical accelerator facilities which were generated from the geometry configurations of running treatment rooms, based on such gantry rotation that produces the maximum neutron dose at the doorway. The results calculated with the empirical formula in this study were compared with those calculated by the Kersey method for 7 operating facilities. It was found that the maximum disagreement between the calculation of this study and that of the Kersey method was a factor of 8.54 with the value calculated by the Kersey method exceeding that of this study. It was concluded that the kersey method estimated the neutron dose equivalent at the doorway computed by MCNPX more conservatively than this study technique.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.5
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• pp.499-508
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• 2004

An efficient method of moments(MoM), which can lead to the analytical evaluation of the matrix elements, is proposed to analyze microstrip structures. The present method is formulated in conjunction with use of a new closed-form spatial-domain Green's functions which are derived by use of the integral formula for semi-infinite integrals of Bessel functions. It is observed that the computational efficiency such as the amount of calculation and computation speed has been improved due to the present MoM scheme by a factor of about 4 in comparison with the previous method. To validate the proposed method, several numerical examples are presented.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.253-254
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• 2003

Computations of the mean and turbulence flows over three-dimensional hill of conical shape have implemented. Beside the standard ${\kappa}-{\varepsilon}$ , two other modifications proposed by Detering & Etling and Duynkerke for atmospheric applications were also considered. These predictions were compared with the data of a wind tunnel experiment. From the comparison, it was concluded that all three models predict the mean flow velocities equally well while only the Duynkerke's model accurately predicts the turbulence data statistics. It also concluded that there are large discrepancies between model predictions and the measurements near the ground surface. The flow field, which was obtained by using the Duynkerke's modification, was used to simulate gas dispersion from an upwind source. The calculation results are verified based on the measurement data. Modifications of the turbulent Schmidt number were carried out in order to match the measured results. The code was used to investigate the influence of the recirculation zone behind a building of cubical shape on the transport and dispersion of pollutant. For a stack behind and near the obstacle, some conclusions about the effect of the stack height and stack location were derived.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.335-340
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• 2010

In this paper development of an automatic grid generation program for flow field calculation around 3D wing is described and its application is also introduced. The program is developed by using JAVA programming language and a graphic library, JOGL, and it can be usee either as an application program on a local computer or as a applet in the network environment. Currently, The program provides NACA series 4-digit airfoils as the wing cross-section shape and it offers a non-complicated GUI program which can easily generate structured grids for wings based on user's parameter input. Grid generated by the program can be selected as one of two types; O-type and C-type. In this research advancing layer method(ALM) augmented by elliptic smoothing method is used for the FLUENT. It is shown that by using current program high-quality structured grids around 3D wings can be easily generated, and typical grid generation results and flow solutions are demonstrated. Study on effects of geometric parameters on flow field is also tried by changing major wing parameters such as incidence angle type of wing-tip and sweepback angle.

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.263-270
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• 2010

In this study, an air cleaner is considered to improve comfort, safety, and health of automobile passengers. The performance and installation conditions of the air cleaner have been studied to investigate their effects on the air quality in the cabin room using numerical analysis. A five-passenger sedan and a seven-passenger minivan that have comparatively large indoor volume have been considered. The distributions of the local mean age and the volume averaged age of indoor air are calculated according to the variation of the placement and the air flow of the air cleaner. In addition, a decrease of contamination concentration, especially VOCs(volatile organic compounds), by the air cleaner is numerically analyzed with time-accurate unsteady calculation to quantify the effect of the air cleaner on the indoor air quality. As a result, the effective installation and operation conditions of the air cleaner for the automobile cabin room could be suggested.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.687-693
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• 2007

It has been known that one of the main obstacles of improving the performance of positive displacement hydraulic turbine is pressure pulsation which occurs at the regions upstream and downstream of the turbine. In order to suppress the pressure pulsation. occurrence reason of the pressure pulsation should be understood in detail Therefore. this study aims to establish a CFD analysis method by which the phenomena of unsteady pressure pulsation can be examined with high accuracy. Internal flow field of the turbine is modeled simply to generalize the relation between the pressure pulsation and internal flow. The results show that the Present CFD method adopting unsteady calculation can be applied successfully to the analysis of the Phenomena of Pressure Pulsation. Occurrence of the Pressure pulsation is due to the difference of the rotational speed of turbine rotors When driving rotor rotates by uniform speed and fellowing rotor rotates by variable speed, very large Pressure pulsation occurs within the turbine periodically.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.34 no.2
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• pp.191-201
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• 2010

This paper presents a new global optimization algorithm based on the branch-and-bound principle using Bspline approximation techniques. It describes the algorithmic components and details on their implementation. The key components include the subdivision of a design space into mutually disjoint subspaces and the bound calculation of the subspaces, which are all established by a real-valued B-spline volume model. The proposed approach was demonstrated with various test problems to reveal computational performances such as the solution accuracy, number of function evaluations, running time, memory usage, and algorithm convergence. The results showed that the proposed algorithm is complete without using heuristics and has a good possibility for application in large-scale NP-hard optimization.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.177-180
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• 2004

The development of a tilting train with construction of electric line on the conventional railway is required for speed-up on the conventional railway with many curving sections. For development of tilting train, the study and development of the tilting system and tilting bogie having the different mechanism with a general high speed train will play a main role for improving the technology in the field of Korean railway The study and development of the pantograph tilting mechanism in order to keep a good contact behavior between a pantograph and a contact wire by tilting a pantograph on the opposite direction of the vehicle tilting direction. In this study, we analyzed the aerodynamic characteristic of a developing pantograph on the tilting train and obtained the contact force with catenary by aerodynamic lift force by the aerodynamic analysis. We also performed the numerical analysis for design the device controlling lift force on a pantograph. From the aerodynamic simulation and parameter study for a device to control the lift force, we will suggest the various shape and the optimal shape of it corresponding to a developing tilting pantograph. The Fluent software is used for the calculation of flow profile in this study.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.95-99
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• 2004

The developing Smart UAV in KARI supposes high speed flight as like a conventional plane, as well as vertical takeoff and landing as like a helicopter. Therefore, the air intake system should be designed to provide the sufficient air flow to the engine and the maximum possible total pressure recovery at the engine intake screen over a wide range of flight conditions. For this purpose, we designed the intake system using a pilot type intake model and plenum chamber In this paper, we designed the intake model and analyzed the performance of designed intake system using the general-purpose commercial CFD code, CFD-ACE+ For 3-D calculation, we generated mesh using the unstructured gird and used $\kappa-\epsilon$ turbulence model. The analysis results of the total pressure variation and the velocity distribution was illustrated in this paper. The pressure recovery and distortion coefficient at a plane coincident with the compressor inlet were calculated and streamline variation through the intake system was investigated at the worst condition as well as the standard flight condition.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.181-184
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• 2006

High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation and reattachment, shock and expansion waves. The general cavity flow phenomena include the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity' flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions, The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio(L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyized and compared with the results of Rossiter's Eq.