• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• 제16권1호
• /
• pp.65-84
• /
• 2012

We present an application of the variational multiscale methodology to the computation of concentric annular pipe flow. Isogeometric analysis is utilized for higher order approximation of the solution using Non-Uniform Rational B-Splines (NURBS) functions. The ability of NURBS to exactly represent curved geometries makes NURBS-based isogeometric analysis attractive for the application to the flow through the curved channel.

• Coupled systems mechanics
• /
• 제2권2호
• /
• pp.191-214
• /
• 2013

The unsteady flow past a circular cylinder which starts rotating or rotary oscillating impulsively from rest in a viscous fluid is investigated for Reynolds numbers Re=200 and 1000, rectilinear speed ratios ${\alpha}$ between 0.5 and 5.0, and forced oscillating frequencies $f_s$ between 0.1 and 2.0. Numerical solutions of the Navier-Stokes equations are obtained by using a finite volume method on an unstructured colocated grid. The objective of the study is to examine the effect of the rotating and rotary oscillating circular cylinder on the flow patterns and dynamics loads. The numerical results reveal that the $K\acute{a}rm\acute{a}n$ vortex street vanishes entirely behind the rotating cylinder when the ratio ${\alpha}$ exceeds the critical value, and the vortex shedding behind the rotary oscillating cylinder undergoes mainly three modes named 'synchronization', 'competition' and 'natural shedding' with the increase of $f_s$. Based on the amplitude spectra analysis of the lift coefficients, the regions of the classification of flow structure modes are presented, which provide important references for the flow control in the ocean engineering.

• 한국유체기계학회 논문집
• /
• 제19권1호
• /
• pp.37-44
• /
• 2016

In this study, a parametric study of a centrifugal pump with double volute has been performed numerically using three-dimensional Reynolds-averaged Navier-Stokes equations. The shear stress transport model was selected as turbulence closure through turbulence model test. The finite volume method and unstructured grid system were used for the numerical analysis. The optimal grid system in the computational domain was determined through a grid dependency test. The expansion coefficient, circumferential and radial starting positions and length of divider were selected as the geometric parameters to be tested. And, the hydraulic efficiency and the radial thrust coefficient were considered as performance parameters. It was found that the radial thrust and hydrualic efficiency are more sensitive to the expansion angle and circumferential starting position of the divider than the other geometrical parameters.

• 한국수소및신에너지학회논문집
• /
• 제31권1호
• /
• pp.151-159
• /
• 2020

This study aimed to investigate the performance characteristics of vertical axis turbine of tidal energy convertor. Three-dimensional Reynolds-averaged Navier-Stokes equation with shear stress transport turbulence model has been solved to analyze the fluid flow of the vertical axis turbine. The hexahedral grids have been used to construct the computational domain and the grid dependency test has been performed to find the optimum grid system. Four steps have been carried out to design the vertical axis turbine of the 100 kW class tidal energy convertor.

• 한국유체기계학회 논문집
• /
• 제5권3호
• /
• pp.40-45
• /
• 2002

Since the previous cut-and-try design algorithm requires much cost and time, the automated design technique with the CFD and optimum design algorithm has recently been concerned. In this work, the Navier-Stokes equation was solved to gain more detailed viscous flow information of cascade with rotor-stator interactions. The H-grid embedded by O-grid was generated to obtain more accurate solution by eliminating the branch cut of H-grid near airfoil surface. To handle the relative motion of the rotor to the stationary stator, the sliding multiblock method was applied and the cubic-spline interpolation was used on the block interface boundary. To validate present procedure, the time-averaged aerodynamic loads were compared with experimeatal data. A good agreement was obtained. The Modified Method of Feasible Direction (MMFD) was used to carry out the sensitivity analysis of the change of aerodynamic performance by the changes of the cascade geometry. The present optimization of the cascade gave a dramatic reduction of the drag while the lift maintains at the value within the user-specified tolerance.

• 대한기계학회논문집B
• /
• 제31권8호
• /
• pp.663-671
• /
• 2007

In this work, shape optimization of a wire-wrapped fuel assembly in a liquid metal reactor has been carried out by combining a three-dimensional Reynolds-averaged Navier-Stokes analysis with the radial basis neural network method, a well known surrogate modeling technique for optimization. Sequential Quadratic Programming is used to search the optimal point from the constructed surrogate. Two geometric design variables are selected for the optimization and design space is sampled using Latin Hypercube Sampling. The optimization problem has been defined as a maximization of the objective function, which is as a linear combination of heat transfer and friction loss related terms with a weighing factor. The objective function value is more sensitive to the ratio of the wire spacer diameter to the fuel rod diameter than to the ratio of the wire wrap pitch to the fuel rod diameter. The optimal values of the design variables are obtained by varying the weighting factor.

• 대한기계학회논문집B
• /
• 제38권7호
• /
• pp.557-570
• /
• 2014

본 연구에서는 삼차원 RANS 방정식을 이용하여 냉각 유로 내에 부착하는 새로운 핀휜의 다양한 부채꼴 형상에 대해 열전달, 압력강하, 열성능을 평가하였다. 레이놀즈수가 5,000부터 100,000인 경우에 대하여 수치해석을 수행하였으며, 난류모델로는 Low-Re SST 모델을 사용하였다. 수치해석의 정당성을 확보하기 위하여 실험과 동일한 조건에서 면적 평균 누셀트수에 대한 실험값과 계산값을 비교하였다. 앞전 각도와 뒷전 각도를 매개변수로 하여 세 종류의 부채꼴 핀휜의 형상 변화에 따른 열성능을 평가하였다.

• 한국항공우주학회지
• /
• 제34권11호
• /
• pp.1-8
• /
• 2006

축대칭 발사체의 동적 감쇠계수를 계산하기 위한 정상 예측 방법을 제안한다. 관성좌표계에서 영스핀 코닝 운동을 사용한 정상 해법을 적용하기 위해서는 점성유동 해석이 필수적으로 이루어져야 한다. 제안된 방법을 회전발사체에 적용하여 피칭모멘트와 피치감쇠 모멘트계수를 계산하였다. 결과는 포물형 Navier-Stokes 예측 결과, 실험결과, 비정상 예측 결과와 잘 일치함을 확인하였다. 또한, secant-ogive-cylinder 계열 발사체에 대한 정적 및 동적 계수의 축방향 생성과정을 살펴봄으로써 후방동체의 형상으로 인한 유동 변화가 동적 안정성에 미치는 영향을 고찰하였다.

• 대한토목학회논문집
• /
• 제36권4호
• /
• pp.645-650
• /
• 2016

본 연구에서는 기존의 수리모형실험에서 나타나는 파랑-흐름 상호작용에 의한 파고감쇠현상을 분석하기 위하여 Navier-Stokes Solver를 이용한 수치시뮬레이션을 수행하였다. 파랑과 흐름이 만날 경우, 유속의 난류성분이 증가하여 난류강도가 커지는 것을 확인하였다. 이것으로부터 파랑이 전파될수록 난류의 영향으로 파랑에너지가 감소하고, 파고가 줄어드는 현상을 이해할 수 있었다. 그리고 흐름의 유속이 증가할수록 난류강도가 증가함으로 파고감쇠효과가 크게 나타났다. 또한 파랑이 동일한 거리를 전파할 때에 파고가 작을수록, 주기가 짧을수록 파고감쇠현상이 심화되는 것을 확인할 수 있었다.

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2007년도 춘계학술대회논문집
• /
• pp.247-250
• /
• 2007

Flexible media such as the paper, the film, etc. are thin, light and very flexible. They behave in geometrically nonlinear. Any of small force makes large deformation. So we must including aerodynamic effect when its behavior is predicted. Thus, it becomes fully coupled fluid-structure interaction(FSI) problem. In FSI problems, where the fluid mesh near the structure undergoes large deformations and becomes unacceptably distorted, which drive the time step to a very small value for explicit calculations, the arbitrary Lagrangian-Eulerian(ALE) methods or rezoning are used to create a new undistorted mesh for the fluid domain, which allows the calculations to continue. In this paper, FE sheet model considering geometric nonlinearity is formulated to simulate the behavior of the flexible media. Aerodynamic force to the media by surrounding air is calculated by solving the incompressible Navier-Stokes equations. Q2Q1(Taylor-Hood) element which means biquadratic for velocity and bilinear for pressure is used for fluid domain. Q2Q1 element satisfies LBB condition and any stabilization technique is not needed. In this paper, cantilevered sheet in the viscous incompressible Navier-Stokes flow is simulated to check the mesh motion and numerical integration scheme, and then falling paper in the air is simulated and the effects of some representative parameters are investigated.