• 대한조선학회논문집
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• 제47권4호
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• pp.508-516
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• 2010

This study aims at investigating the effect of the chamfer on the liquid sloshing in the three-dimensional (3D) rectangular tank. In order to simulate the 3D incompressible viscous two-phase flow in the 3D tank with partially filled liquid, the present study has adopted the volume of fluid (VOF) method based on the finitevolume method which has been well verified by comparing with the results of the relevant previous researches. The effects of the chamfering top corners of the tank on the liquid sloshing characteristics have been investigated. The angle of the chamfering top corners (${\theta}$) has been changed in the range of $0^{\circ}{\leq}{\theta}{\leq}60^{\circ}$(${\Delta}{\theta}=15^{\circ}$) to observe the free surface behavior, and the effect on wall impact load. Generally, as the angle of the chamfering top corners increases, the impact pressure on the upper knuckle point decreases. However it seemed that a critical angle of the chamfering top corners exists to reveal the lowest impact pressure on the wall.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.252-255
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• 2008

In this study, the characteristics of crossing a river of Ground Armored Vehicle (GAV) were evaluated by numerical method and real size tests. 3-D hybrid mesh systems were constructed by 3-D models of the GAV, and a commercial software, FLUENT, was used in numerical analysis. In order to deal with multi-phase problem (air and water), Volume Of Fluid (VOF) method was used, and Moving and Deforming Mesh (MDM) was adapted for unsteady motion of GAV. There were two steps in this research. Firstly, stability of the GAV which cruised a river was evaluated by changing several shapes of water-proof-front-wing of the GAV in steady state, and compared results (free surface shape and drag value in 10km/h) with those of real size tests. Secondly, results of unsteady analysis considering weight and moment of inertia of the GAV were presented. There were showed a maximum velocity with a designed water jet and dynamic stability including pitch, roll, and yaw moment. Based on these results, the optimal shape of water-proof-front-wing of the GAV was determined for a proto-type of the GAV.

• 반도체디스플레이기술학회지
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• 제9권4호
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• pp.19-23
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• 2010

Nanoimprint lithography (NIL) is one of the most versatile and promising technology for micro/nano-patterning due to its simplicity, high throughput and low cost. Recently, one of the major trends of NIL is large-area patterning. Especially, the research of the application of NIL to TFT-LCD field has been increasing. Technical difficulties to keep the uniformity of the residual layer, however, become severer as the imprinting area increases. In this paper we performed a numerical study for a large area NIL (the $2^nd$ generation TFT-LCD glass substrate ($370{\times}470$ mm)) by using finite element method. First, a simple model considering the surrounding wall was established in order to simulate effectively and reduce the computing time. Then, the volume of fluid (VOF) and grid deformation method were utilized to calculate the free surfaces of the resist flow based on an Eulerian grid system. From the simulation, the velocity fields and the imprinting pressure during the filling process in the NIL were analyzed, and the effect of the surrounding wall and the uniformity of residual layer were investigated.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권1호
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• pp.69-84
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• 2018

In order to analyze the characteristics of propeller exciting force, the hybrid grid is adopted and the numerical prediction of KCS ship model is performed for hull-propeller-rudder system by Reynolds-Averaged Navier Stokes (RANS) method and volume of fluid (VOF) model. Firstly, the numerical simulation of hydrodynamics for bare hull at oblique state is carried out. The results show that with the increasing of the drift angle, the coefficients of resistance, side force and yaw moment are constantly increasing, and the bigger the drift angle, the worse the overall uniformity of propeller disk. Then, propeller bearing force for hull-propeller-rudder system in oblique flow is calculated. It is found that the propeller thrust and torque fluctuation coefficient peak in drift angle are greater than that in straight line navigation, and the negative drift angle is greater than the positive. The fluctuation peak variation law of coefficient of side force and bending moment are different due to various causes.

• 대한기계학회논문집B
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• 제30권8호
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• pp.780-787
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• 2006

Several types of different header designs are numerically studied to have uniform distribution of two phase flow in the evaporator header having multi-channels. The different geometries include the inlet tube position into the header and the width of header. In the numerical calculation, two types of two-phase model such as homogeneous model and VOF(Volume Of Fluid) model are employed. In this study, the mal-distribution number, $M_d$, is newly defined to evaluate the averaged level of the flow distribution in the whole passes of the evaporator. As results, two phase flow in the header can be visualized using post-processing of numerical results. Furthermore, the optimum position of the inlet tube into the header and the width of header can be proposed for the better distribution of refrigerant(R-134a) flow.

• 대한기계학회논문집B
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• 제29권5호
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• pp.568-576
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• 2005

A 3-D finite element model combined with a volume tracking method is presented in this work to simulate the mold filling for casting processes. Especially, the analysis involves an adaptive grid method that is created under a criterion of element categorization of filling states and locations in the total region at each time step. By using an adaptive grid wherein the elements, finer than those in internal and external regions, are distributed at the surface region through refinement and coarsening procedures, a more efficient analysis of transient fluid flow with free surface is achieved. Adaptive grid based on VOF method is developed in tetrahedral element system. Through a 3-D analysis of the benchmark test of the casting process, the efficiency of the proposed adaptive grid method is verified. Developed FE code is applied to a typical industrial part of the casting process such as aluminum road wheel.

• 한국전산유체공학회지
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• 제15권4호
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• pp.25-31
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• 2010

Interface tracking of two phase is significant to analyze multi-phase phenomena. The VOF(Volume of Fluid) and level set are well known interface tracking method. However, they have limitations to solve compressible flow and incompressible flow at the same time. CIP(Cubic Interpolate Propagation) method is appropriate for considering compressible and incompressible flow at once by solving the governing equation which is divided up into advection and non-advection term. In this article, we analyze the droplet impingement according to various We number using improved CIP method which treats nonlinear term once more comparison with original CIP method. Furthermore, we compare spread radius after droplet impingement on the wall with the experimental data and original CIP method. The result using improved CIP method shows the better result of the experiments, comparison with result of original CIP method, and it reduces the mass conservation error which is generated in the numerical analysis comparison with original CIP method.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2015년도 학술발표회
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• pp.42-42
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• 2015

사행수로에서의 원심력은 비선형적인 압력분포를 야기하여 이차류, 편수위 등과 같은 불규칙하고 복잡한 흐름을 발생시킨다. 일반적으로 이들 흐름은 난류이고 매우 3차원적이며 자유수면과의 상호작용이 중요한 역할을 할 수도 있다. 환경, 유사이동, 지형 변화와 관련된 환경 수리학적 관점에서 사행수로에서의 흐름을 이해하고 설계하기 위해서는 이러한 복잡한 3차원 흐름을 정확하게 계산하는 것이 매우 중요하다. 이 연구에서는 유한차분법에 근거한 3차원 흐름해석 모형을 이용하여 사행수로에서의 난류 흐름을 모의하고자 한다. 지배방정식은 3차원 비정상 RANS(Reynolds averaged Navier-Stokes) 방정식이며, 난류 해석을 위해서 공학적으로 널리 이용되고 있는 난류 모형 중 k-omega 모형을 이용한다. 수치모형은 시간과 공간에 대해서 2차 정확도의 이산화 기법을 적용한다. 자유수면의 변동은 이상(two-phase) VOF (volume of fluid) 기법을 이용하여 계산한다. 수치모형의 적용 대상은 기존 문헌에서 제시되어 있는 키노시타 사인곡선을 이용하여 만든 폭 60cm의 사행수로에서 후르드수 0.23 그리고 레이놀즈수 41,700의 조건에서 발생시킨 난류 흐름이다. 적용한 난류모형들을 이용하여 해석한 결과들을 유속벡터분포와 수위의 항으로 비교분석하여 사행수로에서 발생되는 이차류와 편수위 변화 재현에 대한 수치모형의 적용성을 평가하고 각 난류모형들의 특성을 제시한다.

• 대한토목학회논문집
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• 제28권3B호
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• pp.323-334
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• 2008

본 연구는 유체장에 대한 Navier-Stokes방정식과 자유수면을 효과적으로 추적할 수 있는 VOF법을 지배방정식으로 사용하는 수치파동수로를 적용하여 고립파(지진해일)에 대한 이열투과성수중방파제의 파랑제어기능을 수치적으로 검토한다. 고립파의 조파는 수치파동수로의 계산영역내에 설치된 수치조파기(내부조파소스)를 이용하였으며, 구조물에 의한 고립파의 파랑변형을 논한 기존의 연구결과와 본 해석결과를 비교함으로써 본 연구의 타당성을 확인하였다. 이로부터 일렬 및 이열의 투과성수중방파제에 의한 고립파의 파랑변형, 전달율, 반사율 및 에너지플럭스를 포함한 파동장의 변화를 수치시뮬레이션하였다. 비록 한정된 범위의 연구결과이지만, $h_0/h=0.925$($h_0$는 수중방파제의 천단고, h는 수심)를 갖는 이열수중방파제의 경우에 수중방파제 배치간격 $l/L_{eff}>0.4$(여기서, $L_{eff}$는 고립파의 유효거리)의 범위에서 입사파랑의 파고는 이열수중방파제에 의해 약 60%까지 감쇠되는 것을 알 수 있었으며, 일렬수중방파제에 비해 반사율이 약 47%정도로 증가하고, 전달율은 약 18%로 감소하였다. 따라서, 본 연구에서 고립파의 제어를 위해 처음으로 도입되는 투과성이열수중방파제는 일렬의 경우와 대비하여 경제적으로, 그리고 보다 효과적으로 고립파를 제어하는 것을 알 수 있었다.

• 대한토목학회논문집
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• 제29권3B호
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• pp.289-301
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• 2009

본 연구에서는 Navier-Stokes방정식과 자유수면추적을 위해 도입한 VOF함수의 이류방정식에 기초하고 있는 CADMAS-SURF(CDIT, 2001)에 Fenton(1972)의 3차근사고립파이론에 의한 조파이론을 새롭게 도입한 수치파동수로로부터 직립호안상에서 지진해일(고립파)의 처오름 및 작용파력을 해석한다. 기존의 연구결과와 대비하여 본 수치해석결과의 적용성을 논의하며, 최소자승법에 기초하여 직립호안상에서 최대처오름과 최대파력을 합리적으로 추정할 수 있는 회귀식을 제안한다. 또한, 육상구조물에 작용하는 지진해일(tsunami wave)의 파력산정에 CADMAS-SURF(CDIT, 2001)의 적용을 시도한다. 육상에서 지진해일의 수위변동, 유속 및 파력변동의 특성으로부터 육상구조물에 미치는 지진해일의 직접적인 영향을 추론할 수 있을것이다.