• 한국항공우주학회지
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• 제33권10호
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• pp.17-25
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• 2005

중첩격자계와 접합격자계를 이용한 적응격자 기법이 개발되었다. 유동장은 물체와 근접한 영역과 떨어진 영역으로 구분된다. 근접한 영역은 곡선 격자계로 채워지며 중첩격자기법으로 영역이 연결되고 떨어진 영역은 다양한 적응 단계를 가진 직교 격자계로 채워지며 접합격자기법으로 연결된다. 본 적응격자기법은 격자생성에 있어서의 유연성과 효과적인 격자적응 기능을 보여준다. 2차원 스토어 분리 해석을 포함하는 몇 가지 수치해석을 통해 본 적응격자기법의 성능을 검증하였다.

• International Journal of Aeronautical and Space Sciences
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• 제3권1호
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• pp.74-85
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• 2002

The numerical experiment has been conducted to investigate the unsteady shock wave reflecting phenomena. The cell-vertex finite-volume, Roe's upwind flux difference splitting method with unstructured grid is implemented to solve unsteady Euler equations. The $4^{th}$-order Runge-Kutta method is applied for time integration. A linear reconstruction of the flux vector using the least-square method is applied to obtain the $2^{nd}$-order accuracy for the spatial derivatives. For a better resolution of the shock wave and slipline, the dynamic grid adaptation technique is adopted. The new concept of grid adaptation technique, which is much simpler than that of conventional techniques, is introduced for the current study. Three error indicators (divergence and curl of velocity, and gradient of density) are used for the grid adaptation procedure. Considering the quality of the solution and the numerical efficiency, the grid adaptation procedure was updated up to $2^{nd}$ level at every 20 time steps. For the convenience of comparison with other experimental and analytical results, the case of interaction between the straight incoming shock wave and a sharp wedge is simulated for various flow conditions. The numerical results show good agreement with other experimental and analytical results, in the shock wave reflecting structure, slipline, and the trajectory of the triple points. Some critical cases show disagreement with the analytical results, but these cases also have been proven to show hysteresis phenomena.

• 한국자동차공학회논문집
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• 제4권4호
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• pp.179-189
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• 1996

An unstructured grid finite-volume method has been applied to predict the linear and nonlinear attenuation characteristics of the expansion chamber silencer system. In order to achieve a grid flexibility and a solution adaptation for geometrically silencer system. In order to achieve a grid flexibility and a solution adaptation for geometrically complex flow regions associated with the actual silencers, the unstructured mesh algorithm in context with the node-centered finite volume method has been employed. The present numerical model has been validated by comparison with the analytical solutions and the experimental data for the acoustic field of the concentric expansion chamber with and without pulsating flows, as well as the axisymmetric blast flowfield with open end. Effects of the chamber geometry on the nonlinear wave attenuation characteristics is discussed in detail.

• Water Engineering Research
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• 제1권3호
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• pp.187-197
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• 2000

This paper describes an adaptive quadtree-based 2DH wave-current interaction model which is able to predict wave breaking, shoaling, refraction, diffraction, wave-current interaction, set-up and set-down, mixing processes (turbulent diffusion), bottom frictional effects, and movement of the land-water interface at the shoreline. The wave period-and depth-averaged governing equations are discretised explictly by means of an Adams-Bashforth second-order finite difference technaique on adaptive hierarchical staggered quadtree grids. Grid adaptation is achieved through seeding points distributed according to flow criteria(e.g. local current gradients). Results are presented for nearshore circulation at a sinusoidal beach. Enrichment permits refined modelling of important localised flow features.

• 대한기계학회논문집
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• 제17권1호
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• pp.182-189
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• 1993

본 연구에서는 한곳에 적응효과가 중복되는 것을 피하고 해의 변화율이 상대 적으로 큰 곳에 대해 대등한 격자 적응효과를 주는 방법을 연구하였다. 전 유동장에 서 해의 변화율을 계산하여 하한값(threshold) 보다 큰 값을 갖는 cell에 대해 같은 크기의 가중함수(weight function) 값을 갖게 한다. 하한값(threshold)은 전체 cell 수에 대해 상위의 변화율을 갖는 cell의 백분율(percentage)로부터 구한다. 이 방법 은 하한값을 직접 대입해야 한다는 단점은 있으나 변황율이 상대적으로 큰 영역에 대 해 고른 격자 적응 효과를 줌으로 해서 격자 적응의 회수를 줄일 수 있으며 해의 발달 에 긍정적인 격자를 생성할 수 있다.

• 대한기계학회논문집
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• 제11권2호
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• pp.234-242
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• 1987

본 논문에서는 변분법으로 유도한 최적조건을 수치계산에 적용키 위해 영역적 응법이 사용되었으며 불규칙한 형상의 방지에는 격자 적응법이 제시되었다. 설계 문 제로는 '국부 응력치의 일정 한도내에서 구조물 무게의 최소화' 또는 대등한 문제로 '제한된 구조물의 무게한도내에서 최대 국부응력치의 최소화'를 다루었다.

• 한국전산유체공학회지
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• 제1권1호
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• pp.19-25
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• 1996

A multiblock grid generation has been developed to be reliably used for a Navier-Stokes simulation of the turbomachinery flow-fields A multiblock structure simplifies the creation of structured H-grids about complex turbomachinery geometries and facilitate the creation of a grid in the tip flow region. The numerical algorithm adopts the combination of the algebraic and elliptic method to create the internal grids efficiently and quickly. The grid refinement process is enhanced by developing strategies to utilized Bezier curves and splines along with weighted transfinite interpolation technique and by formulating the grid-imbedding method for the viscous boundary-layer meshes. For purposes of illustration, the grid generator is applied to the high turning turbine rotor blades. Two different types of computational grids are provided to be compared with respect to the grid adaptation to the flow simulations. Extension to three-dimensions was done to show the possibility of its application to the tip-flow simulations. The grid quality of the multiblock structure is good in the passages, with gloval orthogonality and adequate smoothness.

• 한국전산유체공학회지
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• 제21권2호
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• pp.62-69
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• 2016

It has been highly demanded to improve the accuracy of CFD(Computational Fluid Dynamics) methods for the assessment of the hydrodynamic performance of marine propellers in cavitating and non-cavitating flows. This paper presents a validation study on the numerical simulation of the tip vortex flow of a non-cavitating marine propeller SVA VP1304. The calculations are carried out by using the Reynolds averaged Navier-Stokes(RANS) approach, where the Reynolds Stress Model(RSM) is used for turbulence closure. The present paper contains a grid dependence test for the propeller open water simulations and a special emphasis is placed on conducting a local grid adaptation on the blade tip and in the tip vortex to reasonably reproduce the velocity and the pressure in the tip vortex flow field. The numerical results are compared with the experimental validation data, which are published in the second International Symposium on Marine Propulsors 2011(SMP'11). The present numerical results show a reasonable agreement with the experiments.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.85.2-85.2
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• 2005

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 12th Asian Congress of Fluid Mechanics
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• pp.75.3-75.3
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• 2008