• Asian Journal of Atmospheric Environment
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• 제11권4호
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• pp.270-282
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• 2017

To evaluate the deposition amount on a ground surface, mesoscale numerical models coupled with atmospheric chemistry are widely used for larger horizontal domains ranging from a few to several hundreds of kilometers; however, these models are rarely applied to high-resolution simulations. In this study, the performance of a dry and wet deposition model is investigated to estimate the amount of deposition via computational fluid dynamics (CFD) models with high grid resolution. Reynolds-averaged Navier-Stokes (RANS) simulations are implemented for a cone and a two-dimensional ridge to estimate the dry deposition rate, and a constant deposition velocity is used to obtain the dry deposition flux. The results show that the dry deposition rate of RANS generally corresponds to that observed in wind-tunnel experiments. For the wet deposition model, the transport equation of a new scalar concentration scavenged by rain droplets is developed and used instead of the scalar concentration scavenged by raindrops falling to the ground surface just below the scavenging point, which is normally used in mesoscale numerical models. A sensitivity analysis of the proposed wet deposition procedure is implemented. The result indicates the applicability of RANS for high-resolution grids considering the effect of terrains on the wet deposition.

• 한국항공우주학회지
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• 제38권2호
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• pp.99-110
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• 2010

강한 압축성을 갖는 유동의 DES 해석에서, 일반적인 경험상수 $C_{DES}$ 값 0.65를 사용할 경우 경계층 내에서 인위적으로 LES 모드로 수행된다. 본 연구에서는 S-A DES 모델에서 RANS 모드 보호를 위하여 사용되는 난류 길이와 벽거리 비의 분포 함수를 이용한 $C_{DES}$의 동적 결정 방법을 제시하였다. 동적 $C_{DES}$ 결정식을 초음속 기저 유동장에 적용한 결과 다른 모델 상수를 사용한 기존의 연구 결과에 비하여 우수한 예측을 보여주었다.

• 대한조선학회논문집
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• 제43권4호
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• pp.460-466
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• 2006

The three-dimensional RANS equations were applied to analyze the flow field of a submarine. To validate the code, the DARPA SUBOFF bare hull and an eliipsoid at angles of attack of $10^{\circ}\;and\;30^{\circ}$ were simulated and good agreement with experiments was obtained. After the code validation, the flows over the full configuration of DARPA SUBOFF model having a fairwater and four stern appendages were simulated at four angles of attack $(0^{\circ},\;10^{\circ},\;20^{\circ},\;30^{\circ})$ and three yaw angles $(10^{\circ},\;20^{\circ},\;30^{\circ})$ Specifically, the pressure contours and streamlines of fairwater and stern appendage were compared as the angle of attack and yaw angle changed. The variations of hydrodynamic forces were also calculated.

• 대한조선학회논문집
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• 제41권6호
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• pp.8-14
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• 2004

The numerical analysis of a waterjet propulsion system was performed to provide detail understanding of complicated flow phenomena including interactions of intake duct, rotor, stator, and contracted discharge nozzle. The incompressible RANS equations were solved on moving multiblocked grid system. To handle interface boundary between rotor and stator, the sliding multiblock method was applied. The numerical results were compared with experiments and good agreement was obtained. The complicated viscous flow features of the waterjet, such as secondary flow inside the intake duct, the recovery of axial flow by the role of the stator, and tip and hub vortex, etc. were well analyzed by the present simulation. The performance of thrust and torque was also predicted.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권4호
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• pp.502-512
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• 2013

Simulations of cavitation flow and hull pressure fluctuation for a marine propeller operating behind a hull using the unsteady Reynolds-Averaged Navier-Stokes equations (RANS) are presented. A full hull body submerged under the free surface is modeled in the computational domain to simulate directly the wake field of the ship at the propeller plane. Simulations are performed in design and ballast draught conditions to study the effect of cavitation number. And two propellers with slightly different geometry are simulated to validate the detectability of the numerical simulation. All simulations are performed using a commercial CFD software FLUENT. Cavitation patterns of the simulations show good agreement with the experimental results carried out in Samsung CAvitation Tunnel (SCAT). The simulation results for the hull pressure fluctuation induced by a propeller are also compared with the experimental results showing good agreement in the tendency and amplitude, especially, for the first blade frequency.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 춘계학술대회 논문집
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• pp.133-137
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• 2009

Bleed 영역이 있는 흡입구 주위의 초음속 유동에 대한 수치 모사를 수행하였다. 이를 위하여 RANS(Reynolds Averaged Navier-Stokes) 방정식과 2-방정식 난류 모델 방정식을 기반으로 한 기존의 코드를 축대칭형으로 변환하고 bleed 경계 조건을 적용하였다. 본 논문에서는 개발한 코드를 검증하기 위해 범프(bump)와 경사충격파와 bleed 영역이 있는 평판 주위에서의 흐름에 대해 실험치 및 타 수치 해석 결과와 비교하였다. 개발한 코드를 이용하여 bleed 장치가 장착된 축대칭 초음속 흡입구 주변의 유동에 대한 수치 모사를 수행하였다.

• 한국해양공학회지
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• 제26권1호
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• pp.9-16
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• 2012

This paper presents the numerical results of a simulation of the free surface flow around a blunt bow ship model and focuses on the validation of the proposed method with a brief investigation of the relation between the resistance and free surface behavior. A finite volume method based on the Reynolds Averaged Navier-Stokes (RANS) approach is used to solve the governing flow equations, where the free surface, including wave breaking,is captured by using a two-phase Level-Set (LS) method. For turbulence closure, a two equation k-${\varepsilon}$ model with the standard wall function technique is used. Finally, the numerical results are compared with the available experimental data, showing good agreement.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 춘계학술대회 논문집
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• pp.68-75
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• 2009

In this study, aeroelastic response analyses have been conducted for a 3D wind turbine blade model. Advanced computational analysis system based on computational fluid dynamics(CFD) and computational structural dynamics(CSD) has been developed in order to investigate detailed dynamic responsed of wind turbine blade. Vibration analyses of rotating wind-turbine blade have been conducted using the general nonlinear finite element program, SAMCEF (Ver.6.3). Reynolds-averaged Navier-Stokes (RANS)equations with spalart-allmaras turbulence model are solved for unsteady flow problems of the rotating turbine blade model. A fully implicit time marching scheme based on the Newmark direct integration method is used for computing the coupled aeroelastic governing equations of the 3D turbine blade for fluid-structure interaction (FSI) problems. Detailed dynamic responses and instantaneous Mach contour on the blade surfaces considering flow-separation effects are presented to show the multi-physical phenomenon of the rotating wind-turbine blade model.

• 한국항해항만학회지
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• 제44권2호
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• pp.53-64
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• 2020

This paper discusses the hydrodynamic characteristics of a catamaran at low speed. In this study, the Delft 372 catamaran model was selected as the target hull to analyze the hydrodynamic characteristics by using the RANS (Reynold-Averaged Navier-Stokes) numerical method. First, the turbulence study and mesh independent study were conducted to select the appropriate method for numerical calculation. The numerical method for the CFD (Computational Fluid Dynamic) calculation was verified by comparing the hydrodynamic force with that obtained experimentally at high speed condition and it rendered a good agreement. Second, the virtual captive model test for a catamaran at low speed was conducted using the verified method. The drift test with drift angle 0-180 degrees was performed and the resulting hydrodynamic forces were compared with the trends of other ship types. Also, the pure rotating test and yaw rotating test proposed by Takashina, (1986) were conducted. The Fourier coefficients obtained from the measured hydrodynamic force were compared with those of other ship types. Conversely, pure sway test and pure yaw test also were simulated to obtain added mass coefficients. By analyzing these results, the hydrodynamic coefficients of the catamaran at low speed were estimated. Finally, the maneuvering simulation in low speed conditions was performed by using the estimated hydrodynamic coefficients.

• 한국전산유체공학회지
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• 제11권4호
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• pp.32-38
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• 2006

The objective of this study is to evaluate the prediction accuracy of development large eddy simulation(LES) program for turbulent flow behind a bluff-body. The LES solver was implemented on parallel computer consisting 16 processors. To verify the capability of LES code, the results were compared with those of Reynolds Averaged Navier-Stokes(RANS) using standard ${\kappa}-{\varepsilon}$ model as well as experimental data. The results showed that the LES and RANS qualitatively well predicted the experimental results, such as mean axial, radial velocities and turbulent kinetic energy. In the quantitative analysis, however, the LES showed a better prediction performance than RANS. Specially, the LES well described characteristics of the recirculation zones, such as air stagnation point and jet stagnation point. Finally, the unsteady phenomena on the Bluff-body, such as the transition of recirculation region and vorticity, was examined with LES methodology.