• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.159-162
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• 2007

The numerical efforts are presented for investigation of irregular waves passing a slit cassion and a warock block breakwater. In the numerical model, the Reynolds equations are solved by a finite difference method and $k-\varepsilon$ model is employed for the turbulence analysis. To track the free surface displacement, the volume of fluid method(VOF) is employed. Numerical predictions of reflection and transmission coefficients are compared with those of the warock block breakwater with the slit caisson. Energy dissipation and seawater exchange rates of the slit caisson are better than those of the warock block breakwater.

• 한국해안해양공학회지
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• 제14권2호
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• pp.171-181
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• 2002

최근, 구조물에 의한 쇄파를 수반한 다양한 파랑변형 해석법중에 자유수면의 추적기법인 VOF법을 이용한 수치해석기법이 각광을 받고 있다. 본 연구는 수중투과성구조물(잠제)에 의한 파랑변형 및 유속장의 해석을 위해 조파를 위한 line-source와 파의 재반사를 방지하기 위한 부가감쇠영역이 설치된 2차원수치파동수조에 잠제를 설치하고 구조물에 의한 파랑변형의 자유수면 추적을 위해 VOF법을 적용하였다. 2차원수치파동수조를 이용한 본 연구의 수치해석수법의 타당성 검증을 위해 수리실험을 실시하였으며 그 결과 본 수치해석결과와 잘 일치하였다. 일열잠제와 이열잠제에 대한 수치해석을 통해 잠제 주변 유속장 해석으로부터 일열잠제의 경우 배후에서 와가 발생하고 이열잠제의 경우 잠제사이와 잠제배후에서 와가 발생함을 확인하였으며 잠제의 천단상에서는 강한 비선형성분파가 발생하고 투과층내의 유속방향은 자유수면의 형상에 의해 좌우됨을 확인하였다

• 대한조선학회논문집
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• 제48권4호
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• pp.317-324
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• 2011

When a ship proceeds in confined water, like canal, the water ahead of ship is pushed by hull. This pushed water returns to the side and under the hull, and this returned water will make fluid velocity higher at the side and under the hull, compared to the case in the infinite water depth. Due to the higher velocity, the pressure under the hull will decrease, resulting in the ship drop. This phenomenon is called "ship squat" and ship squat will result in various marine accidents. In this paper, for predicting ship squat, numerical calculation was carried out using commercial CFD code, FLUENT. To confirm wave pattern profile around the ship, VOF(Volume of Fluid) method was applied. The calculated results were compared with other paper's results and empirical methods.

• International Journal of Ocean System Engineering
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• 제1권3호
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• pp.136-143
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• 2011

In this paper, three-dimensional free-surface flows are simulated by using two different numerical methods, the constrained interpolation profile (CIP)-based and finite volume (FV)-based methods. In the CIP-based method, the governing equations are solved on stationary staggered Cartesian grids by a finite difference method, and an immersed boundary technique is applied to deal with wave-body interactions. In the FV-based method, the governing equations are solved by applying collocated finite volume discretization, and body-fitted meshes are used. A free-surface boundary is considered as the interface of the multi-phase flow with air and water, and a volumeof-fluid (VOF) approach is applied to trace the free surface. Among many variations of the VOF-type method, the tangent of hyperbola for interface capturing (THINC) and the compressive interface capturing scheme for arbitrary meshes (CICSAM) techniques are used in the CIP-based method and FV-based method, respectively. Numerical simulations have been carried out for dam-breaking and wave-body interaction problems. The computational results of the two methods are compared with experimental data and their differences are observed.

• 한국해양공학회지
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• 제21권2호
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• pp.12-21
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• 2007

As the economy grows and the population increases, we need to develop our coastal area and make use of it for various purposes. Specifically, investigation of the wave interactions on and around the vertical cylinders is very important in the design of the offshore or coastal structures. The nonlinear potential analysis developed so far, although very useful, has been found to be limited in application, as strong nonlinear waves generated by the interference between multilayered cylinders and wave impact forces by breaking waves can hardly be estimated. In this study, using a 3-Dimensional volume tracking method VOF(Volume of Fluid), based on Namer-Stokes equations, was developed to simulate highly nonlinear effects, such as breaking waves at the interface or complicated interference waves among structures. A numerical method for nonlinear interaction wave and vertical cylinders is newly proposed. The wave forces and wave transformations computed by the newly proposed numerical simulation method were compared to the other researcher's experimental results, and the results agree well. Based on the validation of this study, this numerical method is applied to the two vertical cylinders to discuss their nonlinear wave forces and wave transformations, according to the variations of separate distance of vertical cylinders.

• 대한기계학회논문집B
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• 제24권12호
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• pp.1570-1579
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• 2000

Finite element analysis of fluid flow with moving free surface has been carried out in two and tree dimensions. The new VOF-based numerical algorithm that has been proposed by the present authors was applied to several 2-D and 3-D free surface flow problems. The proposed free surface tracking scheme is based on two numerical tools that have been newly introduced by the present authots; 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 numerical algorithm has been applied to 2-D and 3-D cavity filling and sloshing problems, which demonstrated versatility and effectiveness of the new free surface tracking scheme as well as the overall solution procedure. The proposed numerical algorithm resolved successfully the interacting free surface with each other. The simulated results demonstrated the applicability of proposed numerical algorithm to the practical problems of large free surface motion. Also, it has been demonstrated that the proposed free surface tracking scheme can be easily implemented in any irregular non-uniform grid systems and can be extended to the 3-D free surface flow problem without additional efforts.

• 한국추진공학회지
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• 제21권3호
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• pp.61-67
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• 2017

본 연구에서는 VOF 기법을 이용하여 3D 그레인 형상의 연소표면적을 계산하는 프로그램을 개발하고 연소표면적 결과를 이용하여 내탄도 성능해석을 수행하였다. 연소표면적 계산 수행 시 격자 크기, 난류화염속도, 단위 계산시간을 기초로 한 매개변수의 의존성을 확인하고, 상용 3D 모델링 소프트웨어를 이용하여 산출한 면적 결과와 비교하였다. 개발 프로그램으로 산출한 연소표면적 결과를 바탕으로 고체로켓모터의 내탄도 해석을 수행하였다. 임의의 추진제 조성으로 화학평형을 계산하고 시간에 따른 연소표면적 및 모터 내부 압력을 예측하였다. 웹(web) 연소 동안 평균 압력은 5.34 MPa 으로 기존 연구 결과와 약 20%의 차이를 보였다.

• 대한기계학회논문집B
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• 제38권6호
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• pp.513-523
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• 2014

유체이송 기술은 최근 마이크로 유체시스템 개발에서 핵심문제로 인식되고 있다. 본 연구에서는 최근 저자가 제안한 외부동력을 사용하지 않고 액적을 이송시킬 수 있는 새로운 개념인 친수성/소수성 수평 표면에서의 액적이송을 자체개발 코드(PowerCFD)를 사용하여 수치해석하였다. 수치해석에 사용된 코드는 보존적인 압력기반 유한체적방법에 기초한 비정렬 셀 중심 방법 및 VOF 방법에 체적포착법인 CICSAM을 채용하고 있다. 액적 내 및 주위의 속도벡터, 압력분포 및 전체운동에너지와 같은 수치해석 결과를 제시하고 이 결과들을 통해 액적이송 메커니즘을 규명하였다.

• 대한기계학회논문집B
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• 제39권4호
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• pp.359-370
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• 2015

본 연구는 다양한 조건하에서 모세관력 불균형에 의해 구동되는 수평 표면 위의 액적 거동을 수치해석적으로 연구한 것이다. 액적 거동은 자체개발 코드(PowerCFD)를 사용하여 수치해석하였다. 수치해석에 사용된 코드는 보존적인 압력기반 유한체적방법에 기초한 비정렬 셀 중심 방법 및 VOF 방법에 체적포착법인 CICSAM을 채용하고 있다. 상세한 액적 거동이 다양한 초기 액적형상, 접촉각 및 표면장력(또는 Bond 수)의 조건하에서 얻어졌다. 또한 액적 이송 메커니즘이 액적 형상에 대한 수치해석 결과로부터 검토되었다.

• 대한조선학회논문집
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• 제47권3호
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• pp.377-387
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• 2010

In this study, the turbulent free surface around KVLCC1 employed in the circular motion test simulation is numerically calculated using a commercial CFD(Computational Fluid Dynamics) code, FLUENT. Also, hydrodynamic forces and yaw moments around a ship model are calculated during the steady turning. Numerical simulations of the turbulent flows with free surface around KVLCC1 have been carried out by use of RANS equation based on calculation of hydrodynamic forces and yaw moments exerted upon the ship hull. Wave elevation is simulated by using the VOF method. VOF method is known as one of the most effective numerical techniques handling two-fluid domains of different density simultaneously. Boundary layer thickness and wake field are changed various yaw velocities of ship model during the steady turning. The calculated hydrodynamic forces are compared with those obtained by model tests.