• 한국해안해양공학회지
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• 제17권3호
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• pp.158-165
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• 2005

Level Set방법을 사용하여 액체와 기체의 서로 다른 상을 함께 해석하는 연구를 수행하였다. Level Set함수는 상의 경계면에서부터 부호를 갖는 거리함수로 정의되며,계산 격자에서 함수 값의 부호에 따라 각 상을 구분하고 물성치를 부여한다. 본 논문에서는 비압축성 유체의 보존식에 Level Set함수의 이동식을 연계하여 이상유동을 모사하는 지배방정식을 구성하였으며, 이를 pseudo-compressibility 방법으로 함께 풀었다. 이 때 다양한 문제에 적용이 가능하도록 일반 곡선 좌표계에서 식을 유도하였고, 수치해석을 위한 행렬식들을 함께 유도하였다. 개발된 해석 코드를 표면장력이 있는 기포 동역학 문제와 수중익에 의한 파도 발생 문제에 적용하여 타당한 결과를 얻을 수 있었다.

• 한국정보통신학회논문지
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• 제8권7호
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• pp.1453-1463
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• 2004

기존의 레벨셋을 이용한 이미지 분할 방법은 화소값의 기울기를 이용하기 때문에 지역적 형태에 좌우되는 문제점을 지니고 있다. 본 논문에서는 평활한 구동력을 위하여 레벨 셋 함수와 새로운 보상 평활화 함수를 결합시키는 하이브리드 방법을 이용한 방법이 소개된다. 대부분의 경우에 3 교점을 가지고 있지 않다는 가정하에 보상함수를 얻는 방법을 대안으로 고려하였다. 보상함수의 주요 역할은 원보상 함수와 평균 보상함수의 차가 새로운 레벨셋 함수의 합리적인 구동력으로 소개될 수 있다. 본 논문에서 제안한 하이브리드 방법은 기존 레벨셋을 이용한 방법의 단점을 최소화시키는 방법이다.

• 한국멀티미디어학회논문지
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• 제13권8호
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• pp.1142-1153
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• 2010

결막 충혈은 결막염, 각막염, 포도막염 등의 안과질환의 초기 증세로서 정량적으로 평가할 수 있다면 진단과 경과 관찰에 도움이 된다. 충혈의 정량화에서 공막의 크기는 중요한 지표이지만 기존의 공막 분할 방법이 정확하지 않기 때문에 수동으로 분할하고 있다. 본 논문에서는 충혈의 정량화를 위하여 level set 방법을 이용한 공막 분할 알고리즘을 제안한다. Level set의 초기 모델은 Lab 색상 모드와 k-means 알고리즘, 기하학적인 정보를 이용하여 지정된다. 헤이시안(hessian) 분석으로 공막과 피부 사이의 골을 향상시킨 영상에 level set을 적용하였다. 제안 방법의 성능 측정을 위하여 52개의 전안부 영상에 대하여 실험하였다. 실험 결과, 제안 방법이 화소값만 이용하는 region growing이나 level set의 초기 모델로 임의의 원을 이용하는 방법보다 성능이 우수하였다. 이 논문에서 제안한 공막 분할 방법은 객관적인 충혈도 측정에서 중요한 요소 기술의 역할을 할 것이다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.354-359
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• 2007

A new level set based topology optimization employing inner-front creation algorithm is presented. In the conventional level set based topology optimization, the optimum topology strongly depends on the initial level set distribution due to the incapability of inner-front creation during optimization process. In the present work, an inner-front creation algorithm is proposed, in which the sizes, positions, and number of new inner-fronts during the optimization process can be globally and consistently identified. To update the level set function during the optimization process, the least-squares finite element method is employed. As demonstrative examples for the flexibility and usefulness of the proposed method, the level set based topology optimization considering lightweight design of 3D shell structure is carried out.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.10-13
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• 2011

A level set method is proposed to simulate the incompressible two-phase flow considering the effect of surface tension. For reinitialization of level set junction, a direct approach method is employed, instead of solving hyperbolic type equation. A mixed element is adopted, so that the continuity mid Navier-Stokes equations are solved by using the quadratic elements (six-node triangular element mid nine-node quadrilateral element), mid the level set function is solved by using the linear elements (three-node triangular element mid four-node quadrilateral element). In order to verify the accuracy mid robustness of the codes, the present methods are applied to a few benchmark problems. It is confirmed that the present results are in good qualitative mid quantitative agreements with the existing studies.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 춘계학술대회논문집
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• pp.568-571
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• 2008

The computation of moving interface by the level set method typically requires reinitializations of level set function. An inaccurate estimation of level set function ${\phi}$ results in incorrect free-surface capturing and thus errors such as mass gain/loss. Therefore, accurate and robust reinitialization process is essential to the free-surface flows. In the present paper, we pursue further development of the reinitialization process, which evaluates directly level set function ${\phi}$ using a normal vector in the interface without solving the re-distancing equation of hyperbolic type. The Taylor-Galerkin approximation and P1P1splitting FEM are adopted to discretize advection equation of the level set function and the Navier-Stokes equation, respectively. Advection equation of free surface and re-initialization process are validated with benchmark problems, i.e., a broken dam flow and time-reversed single vortex flow. The simulation results are in good agreement with the existing results.

• 대한기계학회논문집B
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• 제32권10호
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• pp.754-760
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• 2008

Computation of moving interface by the level set method typically requires the reinitialization of level set function. An inaccurate estimation of level set function $\phi$ results in incorrect free-surface capturing and thus errors such as mass gain/loss. Therefore, an accurate and robust reinitialization process is essential to the simulation of free-surface flows. In the present paper, we pursue further development of the reinitialization process, which evaluates level set function directly using a normal vector on the interface without solving there-distancing equation of hyperbolic type. The Taylor-Galerkin approximation and P1P1 splitting/SUPG (Streamline Upwind Petrov-Galerkin) FEM are adopted to discretize advection equation of the level set function and the incompressible Navier-Stokes equation, respectively. Advection equation and re-initialization process of free surface capturing are validated with benchmark problems, i.e., a broken dam flow and timereversed single vortex flow. The simulation results are in good agreement with the existing results.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집E
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• pp.113-118
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• 2001

We present a new interface tracking method for computing two-phase flow. This method is based on VOF method coupled with Level set method. The method is verified to calculate an interfacial curvature accurately as well as to achieve volume conservation during the whole computation period. We apply the present method to calculate a falling drop. The calculated shape and terminal velocity of the falling drop showed good agreement with the data reported in the literature. Also, the present method was proven to be applicable to drop-wall collision phenomenon.

• 대한기계학회논문집B
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• 제27권6호
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• pp.744-752
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• 2003

A level set method is combined with the volume-of-fluid method so that the coupled method can not only calculate an interfacial curvature accurately but also can achieve mass conservation well. The coupled level set and volume-of-fluid(CLSVOF) method is efficiently implemented by employing an interface reconstruction algorithm which is based on the explicit relationship between the interface configuration and the fluid volume function. The CLSVOF method is applied for numerical simulation of droplet impact on solid surfaces with variable contact angles. The numerical results are found to preserve mass conservation and to be in good agreement with the data reported in the literature. Also, the present method proved to be applicable to the complex phenomena such as breakup and rebound of a droplet.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2011년 춘계학술대회논문집
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• pp.259-260
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• 2011

Using modern techniques from scientific computing and numerical analysis, natural phenomena or scientific experiment can be simulated effectively with a computer and used for computer graphics, for example as special effects for the film industry, manufacturing the thin film, multi-phase simulation and image processing. The Level Set method can make those things happen without a lot of difficulties. This method was devised by Osher and Sethian(1988) to represent dynamically moving interfaces as the zero level set of a scalar function that evolves in time. Since then, many researchers have worked on many applications using a Level Set Method. I will give a talk about the applications of the Level Set Method.