• Title, Summary, Keyword: 레벨셋 기법

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Morphing Technique using Scanned Data and Level-Set Method (스캔 데이터와 레벨셋 방법을 이용한 몰핑 기법)

  • Lee, Tae-Ho;Lee, Seung-Wook;Cho, Seon-Ho
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.565-568
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    • 2011
  • NURBS는 매개변수를 이용하여 3차원에서 곡면을 표현한 방법으로서 노트벡터, 조정점, 가중치로 구성된다. 레벨셋은 공간을 음함수로 정의된 장으로 형성하여 음함수의 일정한 값을 추적하여 곡면을 표현한 방법이다. 본 논문에서는 스캔 데이터를 NURBS 형태로 추출한 뒤 이를 정밀한 레벨셋 모델로 변환하였다. 레벨셋 모델을 구성하기 위해서 형성된 음함수는 부호를 갖는 거리함수를 사용하였고, 거리함수를 정밀하게 나타내기 위해 Newton 순환법을 이용하였다. 변환된 레벨셋 모델을 이용하여 형상의 몰핑을 수행하였다. 몰핑은 초기 형상을 목표 형상으로 변화시켜 나가는 과정으로서 레벨셋 모델을 이용한 몰핑은 용이성과 질적인 측면에서 우수하다. 수치 예제에서는 스캔 데이터의 레벨셋 모델 변환과 변환된 형상이 자연스럽게 목표형상으로 변화하는지를 확인한다.

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Level Set Based Topological Shape Optimization of Hyper-elastic Nonlinear Structures using Topological Derivatives (위상 민감도를 이용한 초탄성 비선형 구조의 레벨셋 기반 위상 및 형상 최적설계)

  • Kim, Min-Geun;Ha, Seung-Hyun;Cho, Seonho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.25 no.6
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    • pp.559-567
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    • 2012
  • A level set based topological shape optimization method for nonlinear structure considering hyper-elastic problems is developed. To relieve significant convergence difficulty in topology optimization of nonlinear structure due to inaccurate tangent stiffness which comes from material penalization of whole domain, explicit boundary for exact tangent stiffness is used by taking advantage of level set function for arbitrary boundary shape. For given arbitrary boundary which is represented by level set function, a Delaunay triangulation scheme is used for current structure discretization instead of using implicit fixed grid. The required velocity field in the actual domain to update the level set equation is determined from the descent direction of Lagrangian derived from optimality conditions. The velocity field outside the actual domain is determined through a velocity extension scheme based on the method suggested by Adalsteinsson and Sethian(1999). The topological derivatives are incorporated into the level set based framework to enable to create holes whenever and wherever necessary during the optimization.

NUMERICAL ANALYSIS OF DYNAMIC CONTACT ANGLE PROBLEMS IN ELECTROWETTING WITH LEVEL SET METHOD (레벨셋 기법을 이용한 전기습윤 현상의 동적 접촉각 문제에 대한 수치해석)

  • Park, J.K.;Kang, K.H.
    • 한국전산유체공학회:학술대회논문집
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    • pp.155-158
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    • 2009
  • We developed a numerical method to analyze the contact-line problems, incorporating a dynamic contact angle model. We used level set method to capture free surface. The method is applied to the analysis of dynamic behavior of a droplet in DC electrowetting. The result is compared with an experimental data and result of perturbation method.

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Level Set based Shape Optimization Using Extended B-spline Bases (확장 B-스플라인 기저함수를 이용한 레벨셋 기반의 형상 최적설계)

  • Kim, Min-Geun;Cho, Seon-Ho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.21 no.3
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    • pp.239-245
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    • 2008
  • A level set based topological shape optimization using extended B-spline basis functions is developed for steady-state heat conduction problems. The only inside of complicated domain identified by the level set functions is taken into account in computation, so we can remove the effects of domain outside parts in heat conduction problem. The solution of Hamilton-Jacobi equation leads to an optimal shape according to the normal velocity field determined from the sensitivity analysis, minimizing a thermal compliance while satisfying a volume constraint. To obtain exact shape sensitivity, the precise normal and curvature of geometry need to be determined using the level set and B-spline basis functions. Using topological derivative concept, the nucleation of holes for topological changes can be made whenever and wherever necessary during the optimization.

Color image segmentation by level set method (레벨셋 기법을 이용한 컬러 이미지 분할)

  • Yoo, Ju-Han;Jung, Moon-Ryul
    • Journal of The Korea Computer Graphics Society
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    • v.18 no.2
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    • pp.9-15
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    • 2012
  • In this paper, we propose a method to segment a color image into several meaningful regions. We suppose that the meaningful region has a set of colors with high frequency in the color image. To find these colors, the color image is represented as several sets of color points in RGB space. And when we use the density of points defined in this method, color belonging to a dense region of color points in RGB space refers to the color that appeared frequently in the image. Eventually, we can find meaningful regions by looking for regions with high density of color points using our level set function in RGB space. However, if a meaningful region does not have a contiguous region of the sufficient size in the image, this is not a meaningful region but meaningless region. Thus, the pixels in the meaningless region are assigned to the biggest meaningful region belonging to its neighboring pixels in the color image. Our method divides the color image into meaningful regions by applying the density of color points to level set function in RGB space. This is different from the existing level set method that is defined only in 2D image.

Level Set Based Shape Optimization of Linear Structures using Topological Derivatives (위상민감도를 이용한 선형구조물의 레벨셋 기반 형상 최적설계)

  • Yoon, Minho;Ha, Seung-Hyun;Kim, Min-Geun;Cho, Seonho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.27 no.1
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    • pp.9-16
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    • 2014
  • Using a level set method and topological derivatives, a topological shape optimization method that is independent of an initial design is developed for linearly elastic structures. In the level set method, the initial domain is kept fixed and its boundary is represented by an implicit moving boundary embedded in the level set function, which facilitates to handle complicated topological shape changes. The "Hamilton-Jacobi(H-J)" equation and computationally robust numerical technique of "up-wind scheme" lead the initial implicit boundary to an optimal one according to the normal velocity field while minimizing the objective function of compliance and satisfying the constraint of allowable volume. Based on the asymptotic regularization concept, the topological derivative is considered as the limit of shape derivative as the radius of hole approaches to zero. The required velocity field to update the H-J equation is determined from the descent direction of Lagrangian derived from optimality conditions. It turns out that the initial holes are not required to get the optimal result since the developed method can create holes whenever and wherever necessary using indicators obtained from the topological derivatives. It is demonstrated that the proper choice of control parameters for nucleation is crucial for efficient optimization process.

An Adaptive FLIP-Levelset Hybrid Method for Efficient Fluid Simulation (효율적인 유체 시뮬레이션을 위한 FLIP과 레벨셋의 적응형 혼합 기법)

  • Lim, Jae-Gwang;Kim, Bong-Jun;Hong, Jeong-Mo
    • Journal of The Korea Computer Graphics Society
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    • v.19 no.3
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    • pp.1-11
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    • 2013
  • Fluid Implicit Particle (FLIP) method is used in Visual Effect(VFX) industries frequently because FLIP based simulation show high performance with good visual quality. However in large-scale fluid simulations, the efficiency of FLIP method is low because it requires many particles to represent large volume of water. In this papers, we propose a novel hybrid method of simulating fluids to supplement this drawback. To improve the performance of the FLIP method by reducing the number of particles, particles are deployed inside thin layers of the inner surface of water volume only. The coupling between less-disspative solutions of FLIP method and viscosity solution of level set method is achieved by introducing a new surface reconstruction method motivated by surface reconstruction method[1] and moving least squares(MLS) method[2]. Our hybrid method can generate high quality of water simulations efficiently with various multiscale features.

Level Set Based Topological Shape Optimization Combined with Meshfree Method (레벨셋과 무요소법을 결합한 위상 및 형상 최적설계)

  • Ahn, Seung-Ho;Ha, Seung-Hyun;Cho, Seonho
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.27 no.1
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    • pp.1-8
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    • 2014
  • Using the level set and the meshfree methods, we develop a topological shape optimization method applied to linear elasticity problems. Design gradients are computed using an efficient adjoint design sensitivity analysis(DSA) method. The boundaries are represented by an implicit moving boundary(IMB) embedded in the level set function obtainable from the "Hamilton-Jacobi type" equation with the "Up-wind scheme". Then, using the implicit function, explicit boundaries are generated to obtain the response and sensitivity of the structures. Global nodal shape function derived on a basis of the reproducing kernel(RK) method is employed to discretize the displacement field in the governing continuum equation. Thus, the material points can be located everywhere in the continuum domain, which enables to generate the explicit boundaries and leads to a precise design result. The developed method defines a Lagrangian functional for the constrained optimization. It minimizes the compliance, satisfying the constraint of allowable volume through the variations of boundary. During the optimization, the velocity to integrate the Hamilton-Jacobi equation is obtained from the optimality condition for the Lagrangian functional. Compared with the conventional shape optimization method, the developed one can easily represent the topological shape variations.

ASSESSMENT OF PROPERTY INTERPOLATION METHODS IN LEVEL SET METHOD (레벨셋 기법의 물성 보간 방법에 대한 고찰)

  • Park, J.K.;Oh, J.M.;Kang, K.H.
    • 한국전산유체공학회:학술대회논문집
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    • pp.283-289
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    • 2009
  • In level set method, material properties are made to change smoothly across an interface of two materials with different properties by introducing an interpolation or smoothing scheme. So far, the weighted arithmetic mean (WAM) method has been exclusively adopted in level set method, without complete assessment for its validity. We showed here that the weighted harmonic mean (WHM) method for rate constants of various rate processes, including viscosity, thermal conductivity, electrical conductivity, and permittivity, gives much more accurate results than the WAM method. The selection of interpolation scheme is particularly important in multi-phase electrohydrodynamic problems in which driving force for fluid flow is electrical force exerted on the phase interface. Our analysis also showed that WHM method for both electrical conductivity and permittivity gives not only more accurate, but also more physically realistic distribution of electrical force at the interface. Our arguments are confirmed by numerical simulations of drop deformation under DC electric field.

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ANALYSIS OF ELECTROWETTING DYNAMICS WITH CONSERVATIVE LEVEL SET METHOD (레벨셋 기법을 이용한 전기습윤 현상의 동적 거동에 대한 해석)

  • Park, J.K.;Hong, J.W.;Kang, K.H.
    • 한국전산유체공학회:학술대회논문집
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    • pp.84-87
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    • 2009
  • Electrowetting is a versatile tool to handle tiny droplets and forms a backbone of digital microfluidics. Numerical analysis is necessary to fully understand the dynamics of electrowetting, especially in designing electrowetting-based devices, such as liquid lenses and reflective displays. We developed a numerical method to analyze the general contact-line problems, incorporating dynamic contact angle models. The method is based on the conservative level set method to capture the interface of two fluids without loss of mass. We applied the method to the analysis of spreading process of a sessile droplet for step input voltages and oscillation of the droplet for alternating input voltages in electrowetting. The result was compared with experimental data. It is shown that contact line friction significantly affects the contact line motion and the oscillation amplitude. The pinning process of contact line was well represented by including the hysteresis effect in the contact angle models.

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