• Title/Summary/Keyword: Implicit Formulation

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Thermal stratification in a horizontal pipe of pressurizer surge line (가압기밀림관의 수평배관내 열성층유동)

  • Jung, I,S,;Kim, Y.;Youm, H.K.;Park, M.H.
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.20 no.4
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    • pp.1449-1457
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    • 1996
  • In this paper, the unsteady two dimensional model for the thermal stratification in the pressurizer surge line of PWR plant has been proposed to numerically investigate the heat transfer and flow characteristics. The dimensionless governing equations are solved by using the Control Volume Formulation and SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The temperature profile of fluids and pipe wall with time are shown when the thermal stratification occurs in the horizontal pipe. The numerical result shows that the maximum dimensionless temperature difference is about O.514 between hot and cold section of pipe wall at dimensionless time 1,632.

Prediction of Earings in the Deep Drawing Processes of a Cylindrical Cup (원통컵 디프드로잉 공정의 귀발생 예측)

  • 이승열;이승열;금영탁;정관수;박진무
    • Transactions of Materials Processing
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    • v.4 no.3
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    • pp.222-232
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    • 1995
  • The planar anisotripic FEM analysis for predicting earing profiles and draw-in amounts in the deep-drawing process is introduced. An implicit, incremental, updated Lagrangian formulation with a rigid-viscoplastic constitutive equation is employed. Contact and friction are considered through the mesh-based unit vector and normal contact pressure. The consistent full set of governing relations, which is comprising euilbrium and geometric constraint equations, is appropriately linearized. Barlat's strain-rate potential is employed, whose in-plane anisotropic properties are taken into account with anisotropic coefficients and potential parameters. The linear triangular membrane elements are used for depicting the formed sheet. In the numerical simulations of deep drawing processes of a flat-top cylindrical cup for 2090-T3 aluminum alloy sheet show good agreement with experiments, although some discrepancies were observed in the directional trend of cup height and thickness strains.

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Finite Element Simulation of Axisymmetric Sheet Hydroforming Processes (축대칭 박판 액압 성형 공정의 유한요소 시뮬레이션)

  • 구본영;김용석;금영탁
    • Transactions of Materials Processing
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    • v.9 no.6
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    • pp.590-597
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    • 2000
  • A finite element formulation lot the simulation of axisymmetric sheet hydroforming is proposed, and an implicit program is coded. In order to describe normal anisotropy of steel sheet, Hill's non-quadratic yield function (Hill, 1979) is employed. Frictional contacts among sheet surface, rigid tool surface, and flexible hydrostatic pressure are considered using mesh normal vectors based on finite element of the sheet. Applied hydraulic pressure is also considered as a function of forming rate and time and treated as an external loading. The complete set of the governing relations comprising equilibrium and interfacial equations is approximately linearized for Newton-Raphson algorithm. In order to verify the validity of the developed finite element formulation, the axisymmetric bulge test is simulated. Simulation results are compared with other FEM results and experimental measurements and showed good agreements. In axisymmetric hydroforming processes of a disk cover, formability changes are observed according to the hydraulic pressure curve changes.

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Finite element analysis of welding process by parallel computation (병렬 처리를 이용한 용접 공정 유한 요소 해석)

  • 임세영;김주완;최강혁;임재혁
    • Proceedings of the KWS Conference
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    • 2003.11a
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    • pp.156-158
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    • 2003
  • An implicit finite element implementation for Leblond's transformation plasticity constitutive equations, which are widely used in welded steel structure is proposed in the framework of parallel computing. The implementation is based upon the multiplicative decomposition of deformation gradient and hyper elastic formulation. We examine the efficiency of parallel computation for the finite element analysis of a welded structure using domain-wise multi-frontal solver.

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Three dimensional finite element analysis of art-welding processor via parallel compuating (아크 용접 공정의 3차원 병렬처리 유한 요소 해석)

  • 임세영;김주완;김현규;조영삼
    • Proceedings of the KWS Conference
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    • 2002.05a
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    • pp.161-163
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    • 2002
  • An implicit finite element implementation for Leblond's transformation plasticity constitutive equations, which are widely used in welded steel structure is proposed in the framework of parallel computing. The implementation is based upon the updated Lagrangian formulation. We examine the efficiency of parallel compuatation for the finite element analysis of a welded structure using multi-frontal solver.

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Finite Element Analysis considering transformation plasticity for a welded structure (변태 소성을 고려한 용접 구조물의 유한 요소 해석)

  • 김주완;임세영
    • Proceedings of the KWS Conference
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    • 2001.10a
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    • pp.116-118
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    • 2001
  • We propose an implicit numerical implementation for Leblond's transformation plasticity constitutive equations , which are widely used in welded steel structure. We apply Euler backward scheme rule to integrate the equations and determine the consistent tangent modulus. The implementation may be used with updated Lagrangian formulation. we test a simple butt-welding process to compare with SYSWELD and discuss the accuracy.

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A dissipative family of eigen-based integration methods for nonlinear dynamic analysis

  • Chang, Shuenn-Yih
    • Structural Engineering and Mechanics
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    • v.75 no.5
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    • pp.541-557
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    • 2020
  • A novel family of controllable, dissipative structure-dependent integration methods is derived from an eigen-based theory, where the concept of the eigenmode can give a solid theoretical basis for the feasibility of this type of integration methods. In fact, the concepts of eigen-decomposition and modal superposition are involved in solving a multiple degree of freedom system. The total solution of a coupled equation of motion consists of each modal solution of the uncoupled equation of motion. Hence, an eigen-dependent integration method is proposed to solve each modal equation of motion and an approximate solution can be yielded via modal superposition with only the first few modes of interest for inertial problems. All the eigen-dependent integration methods combine to form a structure-dependent integration method. Some key assumptions and new techniques are combined to successfully develop this family of integration methods. In addition, this family of integration methods can be either explicitly or implicitly implemented. Except for stability property, both explicit and implicit implementations have almost the same numerical properties. An explicit implementation is more computationally efficient than for an implicit implementation since it can combine unconditional stability and explicit formulation simultaneously. As a result, an explicit implementation is preferred over an implicit implementation. This family of integration methods can have the same numerical properties as those of the WBZ-α method for linear elastic systems. Besides, its stability and accuracy performance for solving nonlinear systems is also almost the same as those of the WBZ-α method. It is evident from numerical experiments that an explicit implementation of this family of integration methods can save many computational efforts when compared to conventional implicit methods, such as the WBZ-α method.

Implicit Numerical Integration of Two-surface Plasticity Model for Coarse-grained Soils (Implicit 수치적분 방법을 이용한 조립토에 관한 구성방정식의 수행)

  • Choi, Chang-Ho
    • Journal of the Korean Geotechnical Society
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    • v.22 no.9
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    • pp.45-59
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    • 2006
  • The successful performance of any numerical geotechnical simulation depends on the accuracy and efficiency of the numerical implementation of constitutive model used to simulate the stress-strain (constitutive) response of the soil. The corner stone of the numerical implementation of constitutive models is the numerical integration of the incremental form of soil-plasticity constitutive equations over a discrete sequence of time steps. In this paper a well known two-surface soil plasticity model is implemented using a generalized implicit return mapping algorithm to arbitrary convex yield surfaces referred to as the Closest-Point-Projection method (CPPM). The two-surface model describes the nonlinear behavior of coarse-grained materials by incorporating a bounding surface concept together with isotropic and kinematic hardening as well as fabric formulation to account for the effect of fabric formation on the unloading response. In the course of investigating the performance of the CPPM integration method, it is proven that the algorithm is an accurate, robust, and efficient integration technique useful in finite element contexts. It is also shown that the algorithm produces a consistent tangent operator $\frac{d\sigma}{d\varepsilon}$ during the iterative process with quadratic convergence rate of the global iteration process.

A Jacobian Update-Free Newton's Method for Efficient Real-Time Vehicle Simulation (효율적인 실시간 차량 시뮬레이션을 위한 자코비안 갱신이 불필요한 뉴턴 적분방법)

  • Kang, Jong Su;Lim, Jun Hyun;Bae, Dae Sung
    • Journal of the Korean Society of Manufacturing Technology Engineers
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    • v.23 no.4
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    • pp.337-344
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    • 2014
  • While implicit integration methods such as Newton's method have excellent stability for the analysis of stiff and constrained mechanical systems, they have the drawback that the evaluation and LU-factorization of the system Jacobian matrix required at every time step are time-consuming. This paper proposes a Jacobian update-free Newton's method in order to overcome these defects. Because the motions of all bodies in a vehicle model are limited with respect to the chassis body, the equations are formulated with respect to the moving chassis-body reference frame instead of the fixed inertial reference frame. This makes the system Jacobian remain nearly constant, and thus allows the Newton's method to be free from the Jacobian update. Consequently, the proposed method significantly decreases the computational cost of the vehicle dynamic simulation. This paper provides detailed generalized formulation procedures for the equations of motion, constraint equations, and generalized forces of the proposed method.

Numerical Study on Performance of Horizontal Axis (Propeller) Tidal Turbine

  • Kim, Kyuhan;Cahyono, Joni
    • Proceedings of the Korea Water Resources Association Conference
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    • 2015.05a
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    • pp.296-296
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    • 2015
  • The aim of this paper is to numerically explore the feasibility of designing a Mini-Hydro turbine. The interest for this kind of horizontal axis turbine relies on its versatility. For instance, in the field of renewable energy, this kind of turbine may be considered for different applications, such as: tidal power, run-of-the-river hydroelectricity, wave energy conversion. It is fundamental to improve the turbine performance and to decrease the equipment costs for achievement of "environmental friendly" solutions and maximization of the "cost-advantage". In the present work, the commercial CFD code ANSYS is used to perform 3D simulations, solving the incompressible Unsteady Reynolds-Averaged Navier-Stokes (U-RANS) equations discretized by means of a finite volume approach. The implicit segregated version of the solver is employed. The pressure-velocity coupling is achieved by means of the SIMPLE algorithm. The convective terms are discretized using a second order accurate upwind scheme, and pressure and viscous terms are discretized by a second-order-accurate centered scheme. A second order implicit time formulation is also used. Turbulence closure is provided by the realizable k - turbulence model. In this study, a mini hydro turbine (3kW) has been considered for utilization of horizontal axis impeller. The turbine performance and flow behavior have been evaluated by means of numerical simulations. Moreover, the performance of the impeller varied in the pressure distribution, torque, rotational speed and power generated by the different number of blades and angles. The model has been validated, comparing numerical results with available experimental data.

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