• Journal of the KSME
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• v.48 no.12
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• pp.55-58
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• 2008

• Journal of Korean Port Research
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• v.12 no.1
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• pp.87-93
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• 1998

For the calculation of the free-surface elevation, a new finite difference scheme is studied where the third derivative term for the wave elevation is artificially added in the Eulerian expression of the free-surface boundary condition. The paper presents a comparative analysis with simulations performed by the classical MAC method. More schematic computations are carried out by changing the submergence-depth and angle-of-attack. The present study shows that this new method is very efficient for the simulation of free-surface elevation around the trailing edge.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.6
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• pp.617-624
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• 2011

The two-dimensional sloshing problem in a rigid rectangular tank with a free surface is considered. The flow is generated by a container in harmonic motion in time along the horizontal axis, i.e., a container excited by u=Asin($2{\pi}ft$) where u denotes the container velocity imposed externally, A is the amplitude of the oscillation velocity, and f is the frequency of oscillation. Experimental apparatus is arranged to investigate the large-amplitude sloshing flows in off-resonant conditions, where the large amplitude means that A~O(1), and the distance, S, is comparable to the breadth, L, of the container, i.e., L/S~O(1). Comprehensive particle image velocimetry (PIV) data are obtained, which show that the flow physics of the nonlinear off-resonant sloshing problem can be characterized into three peculiar free surface motions: standing-wave motions similar to those of linear sloshing, a run-up phenomenon along the vertical sidewall at the moment of turn-over of the container, and gradually propagating bore motion from the sidewall to the interior fluid region, like a hydraulic jump.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.33-42
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• 2003

This paper deals with the FEM analysis of nonlinear sloshing of incompressible, invicid and irrotational flow in two dimensional rectangular tank. We use laplace equation based on potential theory as governing equation. For large amplitude sloshing motion, kinematic and dynamic free surface conditions derived from Bernoulli equation are applied. This problem is solved by FEM using 9-node elements. For the time integration and accurate velocity calculation, we introduce predictor-corrector time marching scheme and least square method. Also, numerical stability in tracking of free surface is obtained by direct calculation of free surface location to time variation. Numerical results of sloshing induced by harmonic excitations, while comparing with those of linear theory and references, prove the accuracy and stability. After verification of our program, we analyze sloshing response characteristics to the fluid height and the excitation amplitude.

• Journal of the Society of Naval Architects of Korea
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• v.30 no.3
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• pp.29-40
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• 1993

The fundamental characteristics of nonlinear free-surface waves generated by a shallowly submerged 3-dimensional hydrofoil are investigated. The fluid is assumed inviscid, incompressible and its motion irrotational. The surface tension on the free-surface is neglected. The hydrofoil is represented by a horseshoe vortex system whose shape is assumed fixed. Also the strengths of vortices are assumed given. The exact problem for the wave potential due to the horseshoe vortex system is formulated by the variational principle based on the classical Hamilton's principle. The localized finite element method is used in the numerical computations. In order to increase the numerical efficiency, an intermediate nonlinear-to-linear transition buffer subdomain for a smooth matching is introduced between the fully nonlinear computation subdomain and the truncated linear infinite subdomain. Also used is the modal analysis to reduce the computation tome drastically. The effect of inflow velocity, submergence depth of the hydrofoil and the shape of circulation distribution on the wave profiles are thoroughly examined. Especially it was possible to investigate the nonlinear influence of the free vortex on the free vortex. The nonlinear free-surface effect on the induced forces on the hydrofoil is also investigated.

• Elastomers and Composites
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• v.35 no.2
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• pp.98-105
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• 2000

Using FT-IR and contact angle measurements it is observed that the chemical surface treatments on virgin carbon blacks lead to a change of the surface properties, including surface functionality and surface free energy It is found that the developments of surface functional groups on acidically and basically treated (ACB and BCB in this study, respectively) carbon blacks are largely correlated with the specific component of surface free energy of the carbon blacks. However, a significant advantage of compounding composites is gained by BCB or NCB (nonpolar chemical treatment) specimens, resulting in improving the hardness, elongation at break, and tensile strength. Particularly, it is seen that the tensile strength of the composites are greatly depended on the London dispersive component of surface free energy determined from the contact angle measurements. It is then concluded that the London dispersion component of carbon blacks plays an important role in an organic rubbers-based compounding composite system.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.37-44
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• 2000

An experimental study has been carried out at circulating water channel to investigate the viscous flow around breaking waves generated by a submerged hydrofoil(NACA0012). Detailed flow measurements were made at several critical points including an incipient wave-breaking point and a fully-developed wave breaker. Particle Image Velocimetry(PIV) was employed to visualize the flow field very close to the breaker as well as at the near- and far-wake of the breaker. Generation, development and decay of the wave breaker have been investigated. It is found that PIV technique could be well applied to the complex flow field, including the vortical structures near the free surface as well as the wake of the hydrofoil.

• Journal of the Korean Ceramic Society
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• v.11 no.2
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• pp.38-49
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• 1974

운모기판에 증착한 비정형 셀레니움 박막의 결정성장의 형태와 그 변태속도에 대하여 연구하였다 열처리된 박막에서 비정질성분은 CS2에 용해되나 결정질은 아무 변화없이 남아 있으므로 쉽게 현미경을 이용하여 그 모양을 조사할 수 있다. 결정은 (30$^{\circ}$~10$0^{\circ}C$ 온도 범위에서) 박막과 운모기관의 경계면을 따라서 원형상(구상 결정의 이차원 적 모양) 중심으로 부터 일정 속도로 자란다. 또한 필라멘트 형태의 결정이 원형상 결정의 비 규칙적인 부분에서 박막을 뚫고 위로 자란다. 이들 필라멘트형 결정은 자유표면에 도달하여 새로이 자유표면을 따라서 원형상으로 자라게 된다. 경계에 있는 원형상 결정의 두께는 약 500$\AA$정도이고 이것이 비정질 세레니움 박막에서 보이는 "어두어 지는" 현상의 원인이 되고 있음이 밝혀졌다. 원형상 결정은 아주 조그마한 결정 "도메인"으로 구성되어 있으며 이들 "도메인"의 축 방향은 경계면과 나란하고 반경방향에 수직으로 되어 있다. 고온처리에서 얻어지는 규칙적인 결정은 이들 "도메인"이 모여서 "라멜라"를 형성하여 중심부에서부터 뻗어나가고 이들 "라멜라"간의 공간은 불규칙적으로 나열된 "도메인"으로 연결되어 있으며, 고분자 결정에 비하여 훨씬 두껍다. 반경 방향으로의 결정성장 속도는 아주 순도가 높은 박막에서는 시간에 따라 일정하고 주어진 온도에서 재현성이 아주 좋다. 이 실험에서 측정된 성장속도는 지금까지 발표된 어느 실험에서 관측된 것보다 빠르고 또 자유표면에서 자라는 속도에 비해서 약 백 여배나 빠르다. 결장 성장의 온도 의존은 u=6$\times$1015 exp[-32.7(kcal/mol)/RT] cm/sec로 표시할 수 있다.

• 한국전산유체공학회:학술대회논문집
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• 2004.10a
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• pp.15-18
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• 2004

A numerical method for simulating two-phase flows including surface force is presented. The method is based on fractional step method of finite volume formulation and the interface is tracked with PLIC VOF method. In the CSF model, as color function, f, representing the location of interface varies steeply in the interface region, we need to use smoothed function f to get accurate unit normal and the curvature. Peskin kernel is used to get smoothed function f. A spherical drop in static equilibrium and three-dimensional merging of gas bubble are tested, resulting in the validation of this method

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.304-307
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• 2008

Two-dimensional Stokes flow due to the line source and line sink of same strength in semi-infinite flow region with free surface is analysed using complex variable theory and conformal mapping. Surface tension effects are included while gravity is neglected. From the results of analysis, flow pattern and free surface shape are obtained and velocity distribution on the free surface is determined with 2 independent parameters Ca (capillary number) and h (non-dimensionalized distance between source and sink). When the location of the sink is above the source, velocity on the free surface converges and a cusp occurs on the free surface for the value of Ca above some critical capillary number.