• Title/Summary/Keyword: Incompressibility

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A Comparative Study of the Incompressibility Constraint on the Rigid Plastic Finite Element Method (강소성 유한요소법에서 비압축성조건의 비교 연구)

  • 이상재;조종래;배원병
    • Transactions of Materials Processing
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    • v.8 no.1
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    • pp.47-56
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    • 1999
  • The governing functional in plastic deformation has to satisfy the incompressibility constraint. This incompressibility constraint imposed on velocity fields can be removed by introducing either Lagrange multiplier or the penalty constant into the functional. In this study, two-dimensional rigid plastic FEM programs using these schemes were developed. These two programs and DEFORM were applied in a cylinder upsetting and a closed die forging to compare the values of load, local mean stress and volume loss. As the results, the program using Lagrange multiplier obtained a more exact and stable solution, but it took more computational time than the program using the penalty constant. Therefore, according to user's need, one of these two programs can be chosen to simulate a metal forming processes.

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Incompatible Three-Dimensional Hexagonal Finite Elements by Multivariable Method (다변수 변분해법에 의한 비적합 8절점 육면체 요소)

  • Ju, Sang-Baek;Sin, Hyo-Chol
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.7
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    • pp.2078-2086
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    • 1996
  • This paper introduces two three-dimensional eight-node hexagonal elements obtained by using multivariable variational mehtod. Both of them are based on the modified hellinger-reissner principle to employ incompatible displacements and assumed stresses of assumed strains. The internal functions of element are introduced to as element formulation through two different methods : the first one uses the functions determined directly from the element boundary condition of the incompatible displacements ; while the second, being a kind of B-bar mehtod, employs the modification technique of strain-displacement matrix to pass the patch test. The elements are evaluated on the selective problems of bending and material incompressibility with regular and distorted meshes. The results show that the new elements perform with good accuracy in both of deformation and stress calculation and they are insensitive to distorted geometry of element.

Incompatible finite Elements for Axisymmetric Structure with Assumed Strains (가상 변형률을 갖는 비적합 4절점 축대칭 요소)

  • 주상백;신효철
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.19 no.2
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    • pp.486-494
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    • 1995
  • This paper introduces two kinds of new four-node quadrilateral axisymmetric elements with independently-assumed strains. They are formulated by the modified Hellinger-Reissner principle so as to employ incompatible displacements and assumed strains. In one of the present elements, the strains from incompatible displacements are corrected to pass the constant strain patch test. The other contains incompatible functions that are obtained from the element boundary condition. The elements are evaluated on the several problems of bending and material incompressibility with regular and distorted meshes. The results show that the new element performs excellently in deformation and stress calculation.

The Development of Incompatible Finite Elements for Plane Stress/Strain Using Multivariable Variational formulation (다변수 변분해법에 의한 비적합 4절점 사각형 평면응력 및 평면변형률 요소의 개발)

  • 주상백;신효철
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.18 no.11
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    • pp.2871-2882
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    • 1994
  • Two kinds of 4-node plane stress/strain finite elements are presented in this work. They are derived from the modified Hellinger-Reissner variational principle so as to employ the internal incompatible displacement and independent stress fields, or the incompatible displacement and strain fields. The introduced incompatible functions are selected to satisfy the constant strain condition. The elements are evaluated on several problems of bending and material incompressibility with regular and distorted elements. The results show that the new elements perform excellently in the calculation of deformation and stresses.

Analysis of fiber-reinforced elastomeric isolators under pure "warping"

  • Pinarbasi, Seval;Mengi, Yalcin
    • Structural Engineering and Mechanics
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    • v.61 no.1
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    • pp.31-47
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    • 2017
  • As a relatively new type of multi-layered rubber-based seismic isolators, fiber-reinforced elastomeric isolators (FREIs) are composed of several thin rubber layers reinforced with flexible fiber sheets. Limited analytical studies in literature have pointed out that "warping" (distortion) of reinforcing sheets has significant influence on buckling behavior of FREIs. However, none of these studies, to the best knowledge of authors, has investigated their warping behavior, thoroughly. This study aims to investigate, in detail, the warping behavior of strip-shaped FREIs by deriving advanced analytical solutions without utilizing the commonly used "pressure", incompressibility, inextensibility and the "linear axial displacement variation through the thickness" assumptions. Studies show that the warping behavior of FREIs mainly depends on the (i) aspect ratio (shape factor) of the interior elastomer layers, (ii) Poisson's ratio of the elastomer and (iii) extensibility of the fiber sheets. The basic assumptions of the "pressure" method as well as the commonly used incompressibility assumption are valid only for isolators with relatively large shape factors, strictly incompressible elastomeric material and nearly inextensible fiber reinforcement.

FLUID SIMULATION METHODS FOR COMPUTER GRAPHICS SPECIAL EFFECTS (컴퓨터 그래픽스 특수효과를 위한 유체시뮬레이션 기법들)

  • Jung, Moon-Ryul
    • 한국전산유체공학회:학술대회논문집
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    • 2009.11a
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    • pp.1-1
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    • 2009
  • In this presentation, I talk about various fluid simulation methods that have been developed for computer graphics special effects since 1996. They are all based on CFD but sacrifice physical reality for visual plausability and time. But as the speed of computer increases rapidly and the capability of GPU (graphics processing unit) improves, methods for more physical realism have been tried. In this talk, I will focus on four aspects of fluid simulation methods for computer graphics: (1) particle level-set methods, (2) particle-based simulation, (3) methods for exact satisfaction of incompressibility constraint, and (4) GPU-based simulation. (1) Particle level-set methods evolve the surface of fluid by means of the zero-level set and a band of massless marker particles on both sides of it. The evolution of the zero-level set captures the surface in an approximate manner and the evolution of marker particles captures the fine details of the surface, and the zero-level set is modified based on the particle positions in each step of evolution. (2) Recently the particle-based Lagrangian approach to fluid simulation gains some popularity, because it automatically respects mass conservation and the difficulty of tracking the surface geometry has been somewhat addressed. (3) Until recently fluid simulation algorithm was dominated by approximate fractional step methods. They split the Navier-Stoke equation into two, so that the first one solves the equation without considering the incompressibility constraint and the second finds the pressure which satisfies the constraint. In this approach, the first step introduces error inevitably, producing numerical diffusion in solution. But recently exact fractional step methods without error have been developed by fluid mechanics scholars), and another method was introduced which satisfies the incompressibility constraint by formulating fluid in terms of vorticity field rather than velocity field (by computer graphics scholars). (4) Finally, I want to mention GPU implementation of fluid simulation, which takes advantage of the fact that discrete fluid equations can be solved in parallel.

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A NONCONFORMING PRIMAL MIXED FINITE ELEMENT METHOD FOR THE STOKES EQUATIONS

  • Cho, Sungmin;Park, Eun-Jae
    • Bulletin of the Korean Mathematical Society
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    • v.51 no.6
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    • pp.1655-1668
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    • 2014
  • In this article, we propose and analyze a new nonconforming primal mixed finite element method for the stationary Stokes equations. The approximation is based on the pseudostress-velocity formulation. The incompressibility condition is used to eliminate the pressure variable in terms of trace-free pseudostress. The pressure is then computed from a simple post-processing technique. Unique solvability and optimal convergence are proved. Numerical examples are given to illustrate the performance of the method.

Steady Stokes flow analysis using Axial Green's Function Formulation (축그린함수법을 이용한 정상상태의 스톡스유동해석)

  • Kim, D.W.
    • 한국전산유체공학회:학술대회논문집
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    • 2011.05a
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    • pp.256-258
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    • 2011
  • Using the axial Green's function method for Steady Stokes flows, we introduce a new pressure correction formula to satisfy the incompressibility condition, in which the pressure is related to the integral of the second order derivatives of the velocity. Based on this formula, we propose the iterative method for solving the Stokes flows in complicated domains. Even if the domain is complex, this method maintains the second order of convergence for the velocity.

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A Comparative Study for Incompressibility of Rigid Plastic Finite Element Method (강소성 유한요소법에서 비압축성조건에 관한 비교 연구)

  • 이상재;조종래;배원병;김영호
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1997.10a
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    • pp.40-44
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    • 1997
  • The governing functional in plastic deformation has to satisfy the incompressible condition. This incompressible condition imposed on the velocity fields can be removed by introducing either the Langrange multiplier or the penalty function into the functional. In the study two-dimensional rigid plastic FEM programs using by Lagrange multiplier and penalty function are developed. A compression of cylinder and a spike forging are simulated to compare the data of loads, local mean stresses and reductions of volume.

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A Comparative Study for Incompressibility of Rigid Plastic Finite Element Method (강소성 유한요소법에서 비압축성조건에 관한 비교 연구)

  • 이상재;조종래;배원병;김영호
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 1997.10a
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    • pp.57-61
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    • 1997
  • The governing functional in plastic deformation has to satisfy the incompressible condition. This incompressible condition imposed on the velocity fields can be removed by introducing either the Langrange multiplier or the penalty function into the functional. In this study two-dimensional rigid plastic FEM programs using by Langrange multiplier and penalty function are developed. A compression of cylinder and a spike forging are simulated to compare the data of loads, local mean stresses and reductions of volume.

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