• 한국전산유체공학회지
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• 제15권4호
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• pp.99-108
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• 2010

Fractional Step Methods(FSM) are popular in simulation of unsteady incompressible flow. In this study, we demonstrate that FSM, combined with a Volume-Of-Fluid method, can be further applied to simulation of multiphase flow. The interface between the fluids is constructed by the effective least squares volume-of-fluid interface reconstruction algorithm and advected by the velocity using the operator split advection algorithm. To verify our numerical methodology, our results are compared with other authors' numerical and experimental results for the benchmark problems, revealing excellent agreement. The present FSM sheds light on accurate simulation of turbulent multiphase flow which is found in many engineering applications.

• Macromolecular Research
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• 제15권6호
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• pp.491-497
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• 2007

NPT Monte Carlo simulations were performed to calculate the molecular properties of syndiotactic poly(vinyl chloride) (PVC) and syndiotactic poly(vinyl alcohol) (PVA) melts using the configurational bias Monte Carlo move, concerted rotation, reptation, and volume fluctuation. The density, mean square backbone end-to-end distance, mean square radius of gyration, fractional free-volume distribution, distribution of torsional angles, small molecule solubility constant, and radial distribution function of PVC at 0.1 MPa and above the glass transition temperature were calculated/measured, and those of PVA were calculated. The calculated results were compared with the corresponding experimental data and discussed. The calculated densities of PVC and PVA were smaller than the experimental values, probably due to the very low molecular weight of the model polymer used in the simulation. The fractional free-volume distribution and radial distribution function for PVC and PVA were nearly independent of temperature.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1555-1569
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• 2000

Numerical simulation of fluid flow with moving free surface has been carried out. For the free surface flow, a VOF(Volume of Fluid)-based algorithm utilizing a fixed grid system has been investigated. In order to reduce numerical smearing at the free surface represented on a fixed grid system, a new free surface tracking algorithm based on the donor-acceptor scheme has been presented. Novel features of the proposed algorithm are characterized as two numerical tools; the orientation vector to represent the free surface orientation in each cell and the baby-cell to determine the fluid volume flux at each cell boundary. The proposed algorithm can be easily implemented in any irregular non-uniform grid systems that are usual in finite element method (FEM). Moreover, the proposed algorithm can be extended and applied to the 3-D free surface flow problem without additional efforts. For computation of unsteady incompressible flow, a finite element approximation based on the explicit fractional step method has been adopted. In addition, the SUPG(streamline upwind/Petrov-Galerkin) method has been implemented to deal with convection dominated flows. Combination of the proposed free surface tracking scheme and explicit fractional step formulation resulted in an efficient solution algorithm. Validity of the present solution algorithm was demonstrated from its application to the broken dam and the solitary wave propagation problems.

• 멤브레인
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• 제29권4호
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• pp.191-201
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• 2019

산업 응용에 적용할 수 있는 중합체 막의 상용화 전에, 고성능 중합체가 실질적인 도전, 즉 연장된 서비스 시간에 대한 장기 안정성을 극복해야하는 과제가 남아있다. 매우 높은 분수 자유 부피(fractional free volume) 및 높은 투과성을 나타내는 고유한 미세 다공성 중합체(polymers of intrinsic microporosity)는 비효율적 무작위 패킹에 의해 생성된 여분의 부피가 물질의 부피적 평형에서 멀어짐과 동시에, 다시 부피적 평형 상태로 복귀하려는 특성, 즉 자유 부피를 줄여가는 특정으로 인해 투과성을 감소시키는 물리적 노화에 영향을 받기 쉽다. 본 논문에서 우리는 미세 다공성 고분자의 물리적 노화를 재검토하고 PIM에서 물리적 노화를 완화하려는 가장 두드러진 시도 중 일부를 논의할 것이다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 추계 학술대회논문집
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• pp.9-10
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• 2006

A numerical method for simulating tree surface flows including the surface tension is presented. Numerical scheme is based an a fractional-step method with a finite volume formulation and the interface between liquid and gas is tracked by Volume of Fluid (VOF) method. Piecewise Linear Interface Calculation (PLIC) method is used to reconstruct the interface and the surface tension is considered using a Continuum Surface Force (CSF) model. Several free surface flow phenomena were simulated to show its effectiveness to find such phenomena.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.910-915
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• 2003

A Navier-Stokes equation solver for incompressible viscous flows with free surface is developed and tested. This is based upon a fractional time step method and a non-staggered finite volume formulation for unstructured meshes. For time advancement scheme, Adams -Bashforth method for convective term and Crank-Nicolson method for diffusive term are applied. The interface between two fluids with different fluid properties is tracked with Piecewise Linear Interface Calculation(PLIC) Volume-of-Fluid(VOF) methods. Computational results are presented for some test problems: the broken dam, the sloshing in a rectangular tank, the filling of a cylindrical tank.

• 한국해안·해양공학회논문집
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• 제23권3호
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• pp.248-257
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• 2011

본 연구에서는 규칙파동장에 있어서 인장계류된 원형부유체의 파랑응답해석에 2차원 Navier-Stokes solver에 기초한 새로운 수치파동수조모델을 제안하였다. 본 수치파동수조모델에서는 이동구조물과 유체와의 상호작용을 해석하기 위하여 직각좌표계에서 임의형상의 불투과경계를 갖는 구조물과 유체와의 연성해석이 가능한 IBM(Immersed Boundary Method)과 자유수면 추적을 위한 VOF(Volume of Fluid)법을 결합하였다. 부유체운동에 대한 수치결과를 기존의 FAVOR(Fractional Area Volume Obstacle Representation)법에 의한 계산결과 및 수리실험과 비교하였다. 게다가, 수치모델의 보다 자세한 검증을 위하여 원형부유체의 동요 및 자유수면변동에 관한 수리모형을 추가로 실시하였고, 제안된 수치모델의 범용성과 타당성을 검증하기 위하여 직사각형부유체에 대한 수치 및 수리실험도 병행하였다. 이로부터 추정된 수치계산결과는 실험결과를 잘 재현하고 있는 것으로 판단되었다.

• 공업화학
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• 제10권7호
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• pp.1041-1045
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• 1999

세 가지 종류의 방향족 다이안하이드라이드(6FDA, BTDA, PMDA)와 polydimethylsiloxane(SIDA, 평균 분자량 800)을 단독 다이아민으로 하여 축중합반응에 의하여 폴리실록산이미드(PSI) 막을 제조하였다. 이들은 모두 실록산 30~40 wt % 함유하고 있는 고무상의 고분자로서 낮은 밀도, 높은 비자유부피, 그리고 낮은 표면에너지를 가지고 있었다. 제조된 PSI막을 0.05 wt %의 4가지 혼합용매(ethyl acetate, methylene chloride, trichloroethylene, toluene)에 대해 투과증발 특성을 알아본 결과 이들은 유기용매의 소수성 경향이 증가할수록 높은 선택도와 투과도를 보였다.

• 한국전산유체공학회지
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• 제20권2호
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• pp.103-108
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• 2015

Fluid-body interaction analysis of floating body with six degree-of-freedom motion is presented. In this study, three-dimensional incompressible Navier-Stokes equations are employed as a governing equation. The numerical method is based on a finite-volume approach on a cartesian grid together with a fractional-step method. To represent the body motion, the immersed boundary method for direct forcing is employed. In order to simulate the coupled six degree-of-freedom motion, Euler's equations based on rigid body dynamics are utilized. To represent the complex body shape, level-set based algorithm is utilized. In order to describe the free surface motion, the volume of fluid method utilizing the tangent of hyperbola for interface capturing scheme is employed. This study showed three different continuums(air, water and body) are simultaneously simulated by newly developed code. To demonstrate the applicability of the current approach, two different problems(dam-breaking with stationary obstacle and water entry) are simulated and all results are validated.

• Journal of Mechanical Science and Technology
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• 제16권5호
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• pp.720-731
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• 2002

Flow with moving free surfaces is analyzed with an the Eulerian coordinate system. This study proposes a semi-implicit filling algorithm using VOF in which the PLIC (Piecewise Linear Interface Calculation) -type interface reconstruction method and the donor-acceptor-type front advancing scheme are adopted. Also, a new scheme using extrapolation of the stream function is proposed to find the velocity of the node that newly enters the computational domain. The effect of wall boundary conditions on the flow field and temperature field is examined by numerically solving a two-dimensional casting process.