• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2005년도 추계학술대회 논문집
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• pp.103-106
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• 2005

Lattice Boltzmann method is a new numerical method of investigating the fluid flow which have been solved by Navier-Stokes equation recently. It is known that making the single and parallel algorithms of the Lattice Boltzmann equation is easier than those of Navier-Stokes equations. Also, we can simulate the two phase flow using either the 'Interaction Potential model ' introduced by Shan and Chen. In this paper, we first compared the 3D cavity results of Lattice Boltzmann method with other numerical results for validation and showed the 3D phase transition and its simple application by using the ' Interaction Potential model'

• Korea-Australia Rheology Journal
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• 제14권4호
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• pp.161-174
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• 2002

A new technique for numerical calculation of viscoelastic flow based on the combination of Neural Net-works (NN) and Brownian Dynamics simulation or Stochastic Simulation Technique (SST) is presented in this paper. This method uses a "universal approximator" based on neural network methodology in combination with the kinetic theory of polymeric liquid in which the stress is computed from the molecular configuration rather than from closed form constitutive equations. Thus the new method obviates not only the need for a rheological constitutive equation to describe the fluid (as in the original Calculation Of Non-Newtonian Flows: Finite Elements St Stochastic Simulation Techniques (CONNFFESSIT) idea) but also any kind of finite element-type discretisation of the domain and its boundary for numerical solution of the governing PDE's. As an illustration of the method, the time development of the planar Couette flow is studied for two molecular kinetic models with finite extensibility, namely the Finitely Extensible Nonlinear Elastic (FENE) and FENE-Peterlin (FENE-P) models.P) models.

• 한국정밀공학회지
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• 제18권9호
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• pp.156-164
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• 2001

Two-dimensional solidification analysis during rheology forming process of semi-solid aluminum alloy has been studied. Two-phase fluid flow model to investigate the velocity field and temperature distribution is proposed. The proposed mathematical model is applied to the die shape of the two types. To calculate the velocity and temperature fields during rheology forming process, the earth governing equation correspondent to the liquid and solid region are adapted. Therefore, each numerical models considering the solid and liquid region existing within the semi-solid material have been developed to predict the deflect of rheology forming gnarls. The Arbitrary Boundary Maker And Cell (ABMAC) method is employed to solve the two-phase flow model of the Navier-Stokes equation. Theoretical model on the basis of the two-phase flow model is the mixture rule of solid and liquid phases. This approach is based on the liquid and solid viscosity. The liquid viscosity is pure liquid state value, however solid viscosity is considered as a function of the shear rate, solid fraction and power law curves.

• Nuclear Engineering and Technology
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• 제55권7호
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• pp.2697-2711
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• 2023

In this study, the validity of reducing the number of gas turbine stages designed for a nitrogen Brayton cycle coupled to a sodium-cooled fast reactor was assessed. The turbine performance was evaluated through computational fluid dynamics (CFD) simulations under different off-design conditions controlled by a reduced flow rate and reduced rotational speed. Two different multistage gas turbines designed to extract almost the same specific work were selected: two- and three-stage turbines (mid-span stage loading coefficient: 1.23 and 1.0, respectively). Real gas properties were considered in the CFD simulation in accordance with the Peng-Robinson's equation of state. According to the CFD results, the off-design performance of the two-stage turbine is comparable to that of the three-stage turbine. Moreover, compared to the three-stage turbine, the two-stage turbine generates less entropy across the shock wave. The results indicate that under both design and off-design conditions, increasing the stage loading coefficient for a fewer number of turbine stages is effective in terms of performance and size. Furthermore, the Ellipse law can be used to assess off-design performance and increasing exponent of the expansion ratio term better predicts the off-design performance with a few stages (two or three).

• 한국지진공학회논문집
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• 제27권4호
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• pp.163-170
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• 2023

In the fluid-structure interaction analysis, the finite element formulation is performed for the wave equation for dynamic fluid pressure, and the dynamic pressure is defined as a degree of freedom at the fluid nodes. Therefore, to connect the fluid to the structure, it is necessary to connect the degree of freedom of fluid dynamic pressure and the degree of freedom of structure displacement through an interface element derived from the relationship between dynamic pressure and displacement. The previously proposed fluid-structure interface elements use conformal finite element meshes in which the fluid and structure match. However, it is challenging to construct conformal meshes when complex models, such as water purification plants and wastewater treatment facilities, are models. Therefore, to increase modeling convenience, a method is required to model the fluid and structure domains by independent finite element meshes and then connect them. In this study, two fluid-structure interface elements, one based on constraints and the other based on the integration of nonsmooth functions, are proposed in nonconformal finite element meshes for structures and fluids, and their accuracy is verified.

• Tribology and Lubricants
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• 제28권2호
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• pp.81-92
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• 2012

To product multi-grade oil like engine oil, a sort of mineral base oil is mixed with a fundamental additive liquid package and a polymer liquid as viscosity index improver in order to improve the lubricating property of oil. That is, engine oil is the mixture of more than two fluids. In this paper, it will be systematically organized the governing equation describing non-Newtonian thermo-hydrodynamic lubrication related with the mixture of incompressible fluids based on the principle of continuum mechanics. Then, in order to find how the thermal analysis effect on the bearing performance lubricated with the mixture of multi-fluids, it will be compared to the performances between the mixture of each liquid to be blended and multi-grade engine oil as a single fluid in a high speed journal bearing. It is found that, in the case of lower viscosity oil, the difference of pressure distribution between the above two cases turns out to be existed, even if the load capacity is same level.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.164-169
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• 2009

Study on swimming of microorganisms like, sperm motility, cilia beating, bacterial flagellar propulsion has found immense significance in the field of biological fluiddynamics. Because of the complexity involved, it is challenging for the researchers to model such problems. Immersed boundary method has proved its efficacy in the field of biological fluiddynamics, The present work aims at performing a numerical study on the microorganism locomotion using the immersed boundary method proposed by Peskin[1]. A two-dimensional model of the microorganism is modeled as thin elastic filament described as a sine wave. The neutrally buoyant organism undergoing deformations is immersed in a viscous and incompressible fluid. The fluid quantities are described using Eulerian coordinates and the immersed body is represented by Lagrangian coordinates. The Eulerian and Lagrangian variables are connected by the Dirac delta function. The Navier-Stokes equations governing the fluid flow are solved using the fractional step method on a staggered Cartesian grid system. The developed numerical code in FORTRAN will be validated by comparing the numerical results with the available results.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.215-222
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• 2009

In the present study, a numerical analysis on the sloshing in a tank with the harmonic motion was investigated. A VOF method was used for two-phase flows inside the sloshing tank and a source term of the momentum equation was applied for the harmonic motion. This numerical method was verified by comparing its results with the available experimental data. The sloshing in a tank causes the instability of the fluid flows and the fluctuation of the impact pressure on the tank. By these phenomena of the tank sloshing, the sloshing problems such as the failure and the noise of system can be generated. For the reduction of these sloshing problems, the various baffles such as the horizontal/vertical plate baffles and the porous baffles inside the tank are installed. With the installations of these baffles, the characteristics of the liquid behavior in the sloshing tank, the impact pressure on the wall, the amplitude of the free surface near the wall and the sloshing noise were numerically analyzed.

• 한국항공우주학회지
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• 제36권1호
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• pp.72-78
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• 2008

본 연구에서는 블레이드 구조 변형 효과를 고려하여 스테이터-로터 상호간섭 케스케이드 모델의 성능평가를 위한 유체-구조 연계해석 시스템을 개발하였다. 고정된 스테이터와 회전하는 로터는 상호간섭 영향이 유동해석에 고려되었으며, 레이놀즈-평균화 난류 방정식인 Spalart-Allmaras 모델과 k-ω SST 난류 모델이 압축성 유동박리 효과를 고려한 유동하중을 예측하기 위해 적용되었다. 정적인 유체-구조 연계해석과 수렴율 증진을 효과적으로 수행하기 위하여 큰 인공 감쇠를 가지는 연계 Newmark 시간적분 기법을 적용하였다. 수치실험을 통해 탄성축 위치에 따른 구조변형 효과가 케스케이드 성능에 미치는 영향을 파악하였다. 구조변형 효과가 고려된 경우 일반적인 강체 블레이드 모델에 대한 성능예측 결과와 다소 차이가 유발될 수 있음을 보였으며 공력탄성학적 영향을 고찰하였다.

• 대한토목학회논문집
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• 제14권5호
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• pp.1033-1042
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• 1994

2차원 경계요소-유한요소 연계법을 사용하여 구형 수조구조물의 동적거동 특성을 파악하였다. 비점성, 비압축성 이상유체의 운동은 경계요소법으로 모델링하였으며 구조물의 운동은 유한요소법으로 모델링하였다. 경계요소법의 적용시 Singularity를 소거한 경계적분식을 사용하였다. 유체와 구조물의 경계면에서 적합조건과 평형조건을 만족시킴으로써 경계요소와 유한요소를 연계하였다. 유체-구조물 상호작용의 영향은 유체의 부가질량행렬과 유체 유동에 의한 강성행렬로 연계된 유체-구조물계에 반영된다. 연계된 유체-구조물계의 고유치 문제로부터 수조구조물의 고유진동수외 고유모드를 구하였으며 수평 및 수직 자바운동에 의하여 수조구조물에 발생하는 유체동압력과 자유수면의 유동도 산출하였다.