• 대한조선학회논문집
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• 제39권1호
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• pp.16-27
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• 2002

이유체 비압축성 점성 유동장내에서의 이차원 기포의 운동과 변형을 레벨셋 방법을 도입하여 해석하였다. 지배방정식은 유한체적법을 사용하여 해석하였다. 본 방법의 수치계산결과는 발표된 실험결과와 계산결과의 비교를 통해 검증하였다. 수치계산에서는 초기상태에 유동장 내에 두 유체의 비교란 자유표면이 존재할 때 단일 및 다수의 기포의 운동과 변형을 해석하였다. 해석을 통해 표면장력의 변화와 밀도비의 변화에 따른 기포거동의 변화를 살펴볼 수 있었다. 자유표면은 기포가 자유표면으로 상승할 때 기포의 거동에 큰 영향을 끼친다. 레벨셋법을 사용하여 계산된 본 연구의 결과들을 통해서 기포거동의 특성을 살펴볼 수 있었다.

• 대한기계학회논문집B
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• 제29권10호
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• pp.1111-1118
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• 2005

In this study, a unified numerical investigation has been performed on the evolution of weld pool and key-hole geometry during low-power and high-power density laser welding. Unsteady phase-change heat transfer and fluid flow with the surface tension are examined. The one-dimensional vaporization model is introduced to model the overheated surface temperature and recoil pressure during high-power density laser welding. It is shown that Marangoni convection in the weld pool is dominant at low-power density laser welding, and the keyhole with thin liquid layer and the hump are visible at high-power density laser welding. It is also shown that the transition from conduction welding to penetration welding fur iron plate exists when the laser power density is about $10^6W/Cm^2$.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.54-57
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• 2011

In this paper we present an algorithm about how to simulate two dimensional dam breaking with lattice Boltzmann method (LBM). LBM considers a typical volume element of fluid to be composed of a collection of particles that represented by a particle velocity distribution function for each fluid component at each grid point. We use the modified Lattice Boltzmann Method for incompressible fluid. This paper will represent detailed information on single phase flow which considers only the water instead of both air and water. Interface treatment and conservation of mass are the most important things in simulating free surface where the Interface is treated by mass exchange with the water region. We consider the surface tension on the interface and also bounce back boundary condition for the treatment of solid obstacles. We will compare the results of the simulation with some methods and experimental results.

• 한국고분자학회:학술대회논문집
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• 한국고분자학회 2006년도 IUPAC International Symposium on Advanced Polymers for Emerging Technologies
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• pp.135-136
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• 2006

The shear flow properties have been reported in many cases by manufactures and fabricators. Only this characteristic is sometimes insufficient for the processings to provide a complete picture of the relationship between the processability and the flow behavior when underwent free-surface processes in which the shape and thickness of the extrudate are determined by the rheological properties of the melt, the die dimensions etc. In this paper the methodology of control of elongational flow is discussed in terms of relaxation time control of the polymer melts.

• 한국물환경학회지
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• 제26권5호
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• pp.781-788
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• 2010

A pilot study was performed to examine the feasibility of multiple stage of constructed wetland (CW) for nutrient removal. The system is composed of six wetland cells connected with water-ways. The hydraulic of wetland cells is designed as free water surface flow. The treatment capacity was $25m^3d^{-1}$ at HRT of about one day for each cell. The magnitude of nutrient removal was related with the length of wetlands and plant density. Total N and P removal rates were 1353 and $246mg\;m^{-2}d^{-1}$ respectively. The pilot-scale reactor was model as continuous flow system containing contribution of CSTR and PFR typed-reactors. The $k-C^*$ model equation was applied to predict N and P reduction. The result indicated the equation was well guided to estimate reduction of $NO_3-N$ and $PO_4-P$.

• 대한기계학회논문집B
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• 제30권10호
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• pp.1003-1011
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• 2006

Droplets are ejected onto a substrate through a nozzle by pushing liquids in flow channels of drop-on-demand devices. The behavior of ejection and formation of droplets is investigated to enhance the physical understanding of the hydrodynamics involved in inkjet printing. The free surface phenomenon of a droplet is described using $CFD-ACE^{TM}$ which employs the volume-of-fluid (VOF) method with the piecewise linear interface construction (PLIC). Droplet formation characteristics are analyzed in various flow regimes with different Ohnesorge numbers. The computational results show that the droplet formations are strongly dependent on the physical properties of working fluids and the inlet flow conditions. In addition, the wetting characteristics of working fluids on a nozzle influence the volume and velocity of a droplet produced in the device. This study may provide an insight into how a liquid droplet is formed and ejected in a piezoelectric inkjet printing device.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권4호
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• pp.1024-1040
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• 2014

The theoretical background and a numerical solution procedure for a time domain hydroelastic code are presented in this paper. The code combines a VOF-based free surface flow solver with a flexible body motion solver where the body linear elastic deformation is described by a modal superposition of dry mode shapes expressed in a local floating frame of reference. These mode shapes can be obtained from any finite element code. The floating frame undergoes a pseudo rigid-body motion which allows for a large rigid body translation and rotation and fully preserves the coupling with the local structural deformation. The formulation relies on the ability of the flow solver to provide the total fluid action on the body including e.g. the viscous forces, hydrostatic and hydrodynamic forces, slamming forces and the fluid damping. A numerical simulation of a flexible barge is provided and compared to experiments to show that the VOF-based flow solver has this ability and the code has the potential to predict the global hydroelastic responses accurately.

• 한국전산유체공학회지
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• 제14권2호
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• pp.68-76
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• 2009

The sloshing tank causes the instability of the fluid flows and the fluctuation of the impact pressure by the liquid on the tank. These flow characteristics inside the sloshing tank can generate the uncomfortable sloshing noise. In the present study, a numerical analysis for the reduction of a fuel tank sloshing noise was performed. To simulate the flow characteristics in a sloshing tank with partially filled liquid, a VOF method was used for interfacial flows by applying a momentum source term for the sloshing motion in a non-inertial reference frame. This numerical method was verified by comparing its results with the available experimental data. For the reduction of the sloshing noise, the horizontal and vertical baffles and porous media inside a sloshing tank were considered and numerically analyzed in the present study. For various installations of these baffles and porous media, the characteristics of the liquid behavior in the sloshing tank were obtained along with the impact pressure on the wall and the height of the free surface along the wall. These basic results can be used for the design of the actual vehicular fuel tank with the reduced sloshing noise.

• 한국해양공학회지
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• 제14권3호
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• pp.41-45
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• 2000

In solving the unsteady potential flow problem of the ship in waves with the panel method, in general one can consider the basic flow as the free stream or double body solution. For the double body solution, the body boundary condition has the 2nd derivatives of the velocity potential. Low order panel methods are known to suffer from the significant error in the 2nd derivatives computed at the body surface. This paper analyzes the numerical error in the 2nd derivatives for a 2-D cylinder and a 3-D sphere problem, and an extrapolation method to obtain the correct derivatives on the body surface is suggested.

• 대한조선학회논문집
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• 제33권2호
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• pp.13-29
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• 1996

이 논문은 자유표면을 포함하는 시리즈 60($C_B=0.6$)선형 주위 유동장에 대한 계산결과를 보여준다. 지배 방정식으로는 3차원 Navier-Stokes 방정식을 사용하고, 높은 레이놀즈수에서의 난류 유동장을 계산하기 위하여 Baldwin-Lomax난류모형을 채용하였으며 계산시간을 줄이기 위해 물체 표면에서는 벽법칙을 채용하였다. 지배 방정식은 유한 차분법에 의해 차분화 되었으며, 음해법[1]에 의해, 압력 Poisson방정식은 완화법(successive-over-relaxation method)에 의해 프로그램을 구성하였다. 자유표면 유동을 정확히 계산하기 위해서는, 동역학적 자유표면 경계조건식의 수치해법이 매우 중요하다. 이 논문에서는 세 가지의 수치해법을 채용하여 그 결과를 실험결과와 비교하였다. 결론적으로, 계산된 저항계수($C_F,\;C_P$와 파형은 실험 값과 잘 일치하고 있다.