• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2005년도 춘계 학술대회논문집
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• pp.169-172
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• 2005

A numerical analysis was made In investigate the pressure diminution of a silencer with baffles for high pressure blast flow fields. Reynolds-Averaged Navier-Stokes equations were solved for an axisymmetric computational domain constructed by multi block Chimera grids. A blast flow field was calculated for the silencers that are with one and three baffles. The evolution of high pressure blast flow fields was observed by depicting calculated contours of pressure. It was found that the tested silencer could achieve 97.7 percent pressure diminution.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.586-592
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• 2000

터보머신 태부에 존재하는 정익 - 동익의 상호작용 유동현상을 수치모사 하는 코드를 병렬화 하였다 정익 - 동익의 상호작용을 해석하는 데에 편리하도륵 Multi-Block Grid System을 도입하여 계산영역을 형성하였고, 동익의 움직임으로 인해 발생하는 Sliding Interface부분은 Patched 알고리즘을 적용하여 해석하였다. 정익과 동익의 수를 1대 1로 단순화시켜 수치모사한 결과와 정익과 동익의 수를 실제 조건과 더 비슷하게 설정한 3대 4의 비율로 맞추어 수치모사한 결과를 비교하였다. 또한, 병렬컴퓨팅으로 인해 단축된 계산시간을 다른 연구에서의 계산시간들과 서로 비교하였다. 2차원 비정상 압축성 Navier-Stokes 방정식이 이용되었고, 난류모델링에는 K-w SST 모델링이 적응되었다. Roe의 FDS 기법을 사용하여 플럭스를 계산하였고, MUSCL 기법을 적용하여 3차의 공간정확도를 갖도록 하였다. 시간적분에는 이보성의 DP-SGS를 사용하였다. 해석결과의 분석에는 Time-averaged pressure distribution과 Pressure amplitude distribution 데이터를 사용했다.

• 대한기계학회논문집B
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• 제31권3호
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• pp.217-224
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• 2007

A numerical analysis for a silencer with three baffles of 120mm tank gun has been performed. The Reynolds-Averaged Wavier-Stokes equations with Baldwin-Lomax turbulence model were employed to compute unsteady, compressible flow inside the tank gun and the silencer. An axisymmetric computational domain was constructed by using 12 multi block chimera grids. The resolution of flow field is observed by depicting calculated pressure and muzzle brake force. The peak blast pressure and noise through the silencer reduced approximately 99% and 41dB in comparison to the tank gun without the silencer at near filed.

• 한국해양공학회지
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• 제21권3호
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• pp.16-25
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• 2007

A comparative study on the turbulent flaw simulation and the potential flaw analysis has been performed. A law Mach number preconditioned Navier-Stokes solver, using the multi-block grid method and a panel method based on the velocity potential, have been developed and validated by comparison to the experimental data. The present numerical analysis methods are applied to the ground effect problem around the NACA 4412 airfoil. It has been confirmed that the potential flaw analysis on the ground effect, using the image method, is consistent, to some degree, with the viscous calculations for high Reynolds number flows.

• Nuclear Engineering and Technology
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• 제41권7호
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• pp.893-906
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• 2009

The present work presents the development of a Large Eddy Simulation (LES) methodology viable for complex geometries and suitable for the simulation of rod-bundles. The use of LES and Direct Numerical Simulation (DNS) allows for a deeper analysis of the flow field and the use of stochastical tools in order to obtain additional insight into rod-bundle hydrodynamics. Moreover, traditional steady-state CFD simulations fail to accurately predict distributions of velocity and temperature in rod-bundles when the pitch (P) to diameter (D) ratio P/D is smaller than 1.1 for triangular lattices of cylindrical pins. This deficiency is considered to be due to the failure to predict large-scale coherent structures in the region of the gap. The main features of the code include multi-block capability and the use of the fractional step algorithm. As a Sub-Grid-Scale (SGS) model, a Dynamic Smagorinsky model has been used. The code has been tested on plane channel flow and the flow in annular ducts. The results are in excellent agreement with experiments and previous calculations.

• 산업기술연구
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• 제20권B호
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• pp.55-62
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• 2000

The purpose of this research is to find out how the inlet angle of secondary air affects the formation of recirculation zone inside a small incinerator. A commercial code, PHOENICS, is used to simulate the flow field of an incinerator. The computational grid system is constructed by Multi-Block technique. Numerical experiments are done with the five different angles of secondary air inlet. The formation of recirculation zone is evaluated by checking velocity fields. The computational results show that recirculation zone is clearly formed from 60 degree of inlet angle and the zone of recirculation is widen as angle of recirculation is increased to $75^{\circ}$.

• 산업기술연구
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• 제20권B호
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• pp.63-70
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• 2000

One aims to find out how the operation condition of secondary inlet angle effects the temperature distribution inside a small incinerator. A finite volume commercial code, PHONICS, is used to simulate the temperature field in an incinerator. The computational grid system is constructed by Multi-Block technique. The governing equations based on the curvilinear coordinates are used. Numerical experiments are done with the five variations of secondary air inlet. The temperature distribution is quantified by the statistical deviation of temperature in an incinerator. The computational analysis says that the certain angle of secondary air inlet could improve the uniformity of temperature distribution in an incinerator.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1999년도 춘계 학술대회논문집
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• pp.186-191
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• 1999

An Euler solver is developed to predict accurate aerodynamic data such as lift coefficient, drag coefficient, and moment coefficient. The conservation law form of the compressible Euler equations are used in the generalized curvilinear coordinates system. The Euler solver uses a finite volume method and the second order Roe's flux difference splitting scheme with min-mod flux limiter to calculate the fluxes accurately. An implicit scheme which includes the boundary conditions is implemented to accelerate the convergence rate. The multi-block grid is integrated into the flow solver for complex geometry. The flowfields are analyzed around NACA 0012 airfoil in the cases of $M_{\infty}=0.75,\;\alpha=2.0\;and\;M_{\infty}=0.80,\;\alpha=1.25$. The numerical results are compared with other numerical results from the literature. The final goal of this research is to prepare a robust and an efficient Navier-Stokes solver eventually.

• 정보처리학회논문지B
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• 제16B권2호
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• pp.123-130
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• 2009

움직임 추정은 동영상 압축에서 영상 화질과 인코더 속도에 대하여 중요한 역할을 하지만, 많은 수행 시간을 요구한다. H.264/AVC에서 움직임 추정에 소요되는 수행 시간을 줄이면서 화질을 유지하기 위하여 본 논문에서는 정화소와 부화소 움직임 추정 기법을 제안하였다. 본 논문에서는 정화소 움직임 추정을 위하여 계층적인 탐색 기법을 사용하였고, 정확한 움직임 추정을 위하여 블록 크기에 따라 부화소 움직임 추정 패턴을 적응적으로 결정하였다. 제안한 정화소 움직임 추정 탐색 기법은 대칭적 십자가-엑스 탐색 패턴, 다중 사각형 탐색 패턴, 다이아몬드 탐색 패턴들로 이루어져 있다. 이 탐색 패턴들은 블록 움직임이 수직으로 크거나 블록 움직임이 크면서 규칙적인 영상에서 국부적 최소화 문제를 해결하고 움직임 추정에 소요되는 시간을 줄이기 위하여 탐색 영역 내에 탐색 점들을 규칙적, 대칭적으로 배치하였다. 제안한 부화소 움직임 추정 탐색 기법은 부화소 움직임 추정을 위하여 기존의 전역 부화소 탐색 패턴, 중앙 편향적 부화소 탐색 패턴과 제안한 부화소 움직임 탐색패턴들을 사용한다. 그리고 블록의 크기에 따라 3가지의 부화소 탐색 패턴들 중 한 패턴이 부화소 움직임 추정을 위해 적응적으로 결정된다. 블록의 크기에 따라 적응적으로 부화소 탐색 패턴이 결정되므로 보다 정확하게 부화소 움직임 추정을 수행할 수 있다. 제안한 기법을 전역 탐색 기법과 비교하였을 때 약 5.2배의 속도 향상을 가져왔으며, 영상 화질에 있어서 약 0.01 (dB)정도 성능 저하를 보였다. 반면에, 비대칭 다중육각형 탐색 기법과 비교하였을 때 움직임 추정 속도와 화질에 있어서 각각 약 1.2배와 약 0.02 (dB)정도 향상을 보였다.

• 한국유체기계학회 논문집
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• 제15권5호
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• pp.60-66
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• 2012

One of commonly physical phenomena encountered in pump sump systems in which its significant influence to the hydraulic performance of pump system plays an important role in the field of fluid engineering, is the appearance of free surface and submerged vortices. In this paper, a study of the vortices behavior and their formative mechanism of asymmetry is considered in this paper by using numerical approach. The Reynolds-Averaged Navier-Stokes (RANS) equations and k-omega Shear Stress Transport turbulence model used to describe the properties of turbulent flows, in company with VOF multiphase model, are implemented by Fluent code with multi-block structured grid system. In the numerical simulation, the calculated elevation of air-water interface and vortex core contours are used to classify visually surface vortices as well as submerged vortices. It is shown that the free surface vortex is identified by the concavity of liquid region from the free surface and swirling flow at that own plane. To investigate the distinctive behavior of these vortices corresponding to each given flow rate at the same water level, some numerical testing of them are considered here in such a manner that the flow pattern of surface vortex are obtained similarly to the obtained results from experiment. Furthermore, the influence due to the change of grid refinement and the variation of depth of the concavity are also considered in this paper. From that, these influential factors will be implemented to design a good pump sump with higher performance in the future.