• Title/Summary/Keyword: level-set function

Search Result 462, Processing Time 0.026 seconds

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
    • /
    • v.25 no.6
    • /
    • pp.559-567
    • /
    • 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 SIMULATION OF MULTIPHASE FLOW USING LEVEL CONTOUR RECONSTRUCTION METHOD (Level Contour Reconstruction 방법을 이용한 다상유동 수치해석)

  • Shin, Seung-Won
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2009.11a
    • /
    • pp.193-200
    • /
    • 2009
  • Recently, there have been efforts to construct hybrids among the existing methodologies for multiphase flow such as VOF, Level Set, and Front Tracking with the intention of facilitating simulations of general three-dimensional problems. As one of the hybrid method, we have developed the Level Contour Reconstruction Method (LCRM) for general three-dimensional multiphase flows including phase change. The main idea was focused on simplicity and a robust algorithm especially for the three-dimensional case. It combines characteristics of both Front Tracking and Level Set methods. While retaining an explicitly tracked interface using interfacial elements, the calculation of a vector distance function plays a crucial role in the periodic reconstruction of the interface elements in the LCRM method to maintain excellent mass conservation and interface fidelity. In addition, compact curvature formulation is incorporated for the calculation of the surface tension force thereby reducing parasitic currents to a negligible level.

  • PDF

A Study of Accuracy Improvement of an Analysis of Flow around Arbitrary Bodies by Using an Eulerian-Lagrangian Method (Eulerian-Lagrangian 방법을 사용한 임의 물체주위 유동해석의 정도 향상을 위한 연구)

  • Park I. R.;Chun H. H.
    • Journal of computational fluids engineering
    • /
    • v.6 no.3
    • /
    • pp.19-26
    • /
    • 2001
  • An Eulerian-Lagrangian method, so called immersed boundary method, is used for analysing viscous flow around arbitrary bodies, where governing equations are discretized on a regular grid by using a finite volume method. To improve the accuracy of flow near body boundaries, a second-order accurate interpolation scheme is used and a level-set based grid deformation method is presented to construct the adaptive grids around body boundaries. The present scheme is used to simulate steady flow around a semicircular cylinder mounted on the bottom of flow domain and calculated results are validated by results of a body fitted grid method. Finally, present method is applied to a complex flow around multi body and the usefulness is checked by investigating calculated results.

  • PDF

Numerical Study on a Sliding Bubble During Nucleate Boiling

  • Son, Gihun
    • Journal of Mechanical Science and Technology
    • /
    • v.15 no.7
    • /
    • pp.931-940
    • /
    • 2001
  • A numerical method for simulating bubble motion during nucleate boiling is presented. The vapor-liquid interface is captured by a level set method which can easily handle breaking and merging of the interface and can calculate an interfacial curvature more accurately than the VOF method using a step function. The level set method is modified to include the effects of phase change at the interface and contact angle at the wall as well as to achieve mass conservation during the whole calculation procedure. Also, a simplified model to predict the heat flux in a thin liquid microlayer is developed. The method is applied for simulation of a sliding bubble on a vertical surface to further understand the physics of partial boiling. Based on the computed results, the effects of contact angle, wall superheat and phase change on a sliding bubble are quantified.

  • PDF

Numerical Simulation of a Taylor Bubble Rising in a Vertical Tube (수직관에서 상승하는 Taylor 기포의 수치해석)

  • Son, Gi-Heon
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.3
    • /
    • pp.373-380
    • /
    • 2001
  • In this study, a single Taylor bubble and a train of Taylor bubbles rising in a vertical tube were simulated numerically. A finite difference method was used to solve the mass and momentum equations for the liquid-gas region. The liquid-gas interface was captured by a level set function which is defined a signed distance from the interface. For a train of Taylor bubbles repeated periodically in space, the periodic conditions were imposed at the boundaries normal to the gravitational direction and the pressure boundary conditions were iteratively determined so that the computed flow rate should be equal to a given flow rate. Based on the numerical simulation, the calculated shape and rise velocity of a Taylor bubble were found to be in good agreement with the experimental data reported in the literature.

Hybrid of topological derivative-based level set method and isogeometric analysis for structural topology optimization

  • Roodsarabi, Mehdi;Khatibinia, Mohsen;Sarafrazi, Seyyed R.
    • Steel and Composite Structures
    • /
    • v.21 no.6
    • /
    • pp.1389-1410
    • /
    • 2016
  • This paper proposes a hybrid of topological derivative-based level set method (LSM) and isogeometric analysis (IGA) for structural topology optimization. In topology optimization a significant drawback of the conventional LSM is that it cannot create new holes in the design domain. In this study, the topological derivative approach is used to create new holes in appropriate places of the design domain, and alleviate the strong dependency of the optimal topology on the initial design. Furthermore, the values of the gradient vector in Hamilton-Jacobi equation in the conventional LSM are replaced with a Delta function. In the topology optimization procedure IGA based on Non-Uniform Rational B-Spline (NURBS) functions is utilized to overcome the drawbacks in the conventional finite element method (FEM) based topology optimization approaches. Several numerical examples are provided to confirm the computational efficiency and robustness of the proposed method in comparison with derivative-based LSM and FEM.

A technique for capturing structural crack geometry in numerical simulation based on the invariant level set method

  • Tao Wang;Shangtao Hu;Menggang Yang;Shujun Fang
    • Structural Engineering and Mechanics
    • /
    • v.87 no.3
    • /
    • pp.243-254
    • /
    • 2023
  • Engineering structures usually suffer from cracks. The crack geometry has an influence on the structural mechanical properties and subsequent crack propagations. However, as an extensively utilized method in fracture analysis, the extended finite element method provided by Abaqus fails to output the specific location and dimensions of fractures. In this study, a technique to capture the crack geometry is proposed. The technique is based on the invariant level set method (I-LSM), which can avoid updating the level set function during crack development. The solution is achieved by an open-source plug-in programmed by Python. Three examples were performed to verify the effectiveness and robustness of the program. The result shows that the developed program can accurately output the crack geometry in both the 2D and 3D models. The open-source plug-in codes are included as supplementary material.

Color Object Segmentation using Distance Regularized Level Set (거리정규화 레벨셋을 이용한 칼라객체분할)

  • Anh, Nguyen Tran Lan;Lee, Guee-Sang
    • Journal of Internet Computing and Services
    • /
    • v.13 no.4
    • /
    • pp.53-62
    • /
    • 2012
  • Object segmentation is a demanding research area and not a trivial problem of image processing and computer vision. Tremendous segmentation algorithms were addressed on gray-scale (or biomedical) images that rely on numerous image features as well as their strategies. These works in practice cannot apply to natural color images because of their negative effects to color values due to the use of gray-scale gradient information. In this paper, we proposed a new approach for color object segmentation by modifying a geometric active contour model named distance regularized level set evolution (DRLSE). Its speed function will be designed to exploit as much as possible color gradient information of images. Finally, we provide experiments to show performance of our method with respect to its accuracy and time efficiency using various color images.

Particle Swarm Optimization for Redundancy Allocation of Multi-level System considering Alternative Units (대안 부품을 고려한 다계층 시스템의 중복 할당을 위한 입자 군집 최적화)

  • Chung, Il Han
    • Journal of Korean Society for Quality Management
    • /
    • v.47 no.4
    • /
    • pp.701-711
    • /
    • 2019
  • Purpose: The problem of optimizing redundancy allocation in multi-level systems is considered when each item in a multi-level system has alternative items with the same function. The number of redundancy of multi-level system is allocated to maximize the reliability of the system under path set and cost limitation constraints. Methods: Based on cost limitation and path set constraints, a mathematical model is established to maximize system reliability. Particle swarm optimization is employed for redundant allocation and verified by numerical experiments. Results: Comparing the particle swarm optimization method and the memetic algorithm for the 3 and 4 level systems, the particle swarm optimization method showed better performance for solution quality and search time. Particularly, the particle swarm optimization showed much less than the memetic algorithm for variation of results. Conclusion: The proposed particle swarm optimization considerably shortens the time to search for a feasible solution in MRAP with path set constraints. PS optimization is expected to reduce search time and propose the better solution for various problems related to MRAP.

A Novel Instruction Set for Packet Processing of Network ASIP (패킷 프로세싱을 위한 새로운 명령어 셋에 관한 연구)

  • Chung, Won-Young;Lee, Jung-Hee;Lee, Yong-Surk
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.34 no.9B
    • /
    • pp.939-946
    • /
    • 2009
  • In this paper, we propose a new network ASIP(Application Specific Instruction-set Processor) which was designed for simulation models by a machine descriptions language LISA(Language for Instruction Set Architecture). This network ASIP is aimed for an exclusive engine undertaking packet processing in a router. To achieve the purpose, we added a new necessary instruction set for processing a general ASIP based on MIPS(Microprocessor without Interlock Pipeline Stages) architecture in high speed. The new instructions can be divided into two groups: a classification instruction group and a modification instruction group, and each group is to be processed by its own functional unit in an execution stage. The functional unit was optimized for area and speed through Verilog HDL, and the result after synthesis was compared with the area and operation delay time. Moreownr, it was allocated to the Macro function ana low-level standardized programming language C using CKF(Compiler Known Function). Consequently, we verified performance improvement achieved by analysis and comparison of execution cycles of application programs.