• 제목/요약/키워드: Fractional-Step Method

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Identification of Fractional-derivative-model Parameters of Viscoelastic Materials Using an Optimization Technique (최적화 기법을 이용한 점탄성물질의 분수차 미분모델 물성계수 추정)

  • Kim, Sun-Yong;Lee, Doo-Ho
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • 제16권12호
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    • pp.1192-1200
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    • 2006
  • Viscoelastic damping materials are widely used to reduce noise and vibration because of its low cost and easy implementation, for examples, on the body structure of passenger cars, air planes, electric appliances and ships. To design the damped structures, the material property such as elastic modulus and loss factor is essential information. The four-parameter fractional derivative model well describes the dynamic characteristics of the viscoelastic damping materials with respect to both frequency and temperature. However, the identification procedure of the four-parameter is very time-consuming one. In this study a new identification procedure of the four-parameters is proposed by using an FE model and a gradient-based numerical search algorithm. The identification procedure goes two sequential steps to make measured frequency response functions(FRF) coincident with simulated FRFs: the first one is a peak alignment step and the second one is an amplitude adjustment step. A numerical example shows that the proposed method is useful in identifying the viscoelastic material parameters of fractional derivative model.

Analysis of Salinity Dispersion in Estuaries by an X-Y Numerical Model (X-Y 수치모형에 의한 하구의 염도확산 분석)

  • 강주환;이길성
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • 제3권4호
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    • pp.197-208
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    • 1991
  • A depth-averaged X-Y numerical model with transformed coordinates is developed to analyze the salinity dispersion in estuaries. Simulation of intertidal zones, residual current and closed boundary condition are examined. Especially. the improvements in stability and accuracy of the numerical algorithm are made by adopting fractional step method for the dispersion term of the governing equation. The model being applied to the Keum River Esturary, velocity fields and salinity fields are reproduced satisfactorily and the estimation of the dispersion coefficient with respect to the flow fold is also studied.

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Turbulent Flow Analysis around Circular Cylinder and Airfoil by Large Eddy Simulation with Smagorinsky Model (Smagorinsky model을 이용한 실린더 및 익형 주위의 LES 난류유동해석)

  • 박금성;구본국;박원규;전호환
    • Journal of the Society of Naval Architects of Korea
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    • 제41권4호
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    • pp.1-8
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    • 2004
  • As a computer has been continuously progressed to reduce R&D time and cost, the study of the flow physics has been significantly relied on the numerical method. Recently, Large Eddy Simulation(LES) has been widely used in CFD community to accurately capture the turbulent flows. The LES code requires high accuracy in time, as well as in space. Also, it should have strong robustness to ensure the convergence in various complicated flows. The objective of the present work is to develop a base code for LES simulation, having 2$^{nd}$ order accuracy in time and 4$^{th}$ order accuracy in space. To achieve the present objective, the four-step fractional step method was enhanced by adopting compact Pade'scheme. The standard Smagorinsky model was implemented for the first stage of the present code development. The flows over a cylinder and an airfoil were successfully simulated. and an airfoil were successfully simulated.

FLUID-BODY INTERACTION ANALYSIS OF FLOATING BODY IN THREE DIMENSIONS (3차원 부유체의 유체-물체 연성해석)

  • Go, G.S.;Ahn, H.T.
    • Journal of computational fluids engineering
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    • 제20권2호
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    • pp.103-108
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    • 2015
  • Fluid-body interaction analysis of floating body with six degree-of-freedom motion is presented. In this study, three-dimensional incompressible Navier-Stokes equations are employed as a governing equation. The numerical method is based on a finite-volume approach on a cartesian grid together with a fractional-step method. To represent the body motion, the immersed boundary method for direct forcing is employed. In order to simulate the coupled six degree-of-freedom motion, Euler's equations based on rigid body dynamics are utilized. To represent the complex body shape, level-set based algorithm is utilized. In order to describe the free surface motion, the volume of fluid method utilizing the tangent of hyperbola for interface capturing scheme is employed. This study showed three different continuums(air, water and body) are simultaneously simulated by newly developed code. To demonstrate the applicability of the current approach, two different problems(dam-breaking with stationary obstacle and water entry) are simulated and all results are validated.

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

  • Jung, Moon-Ryul
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2009년 추계학술대회논문집
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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 Study on Analysis of Polymer Extruder Process Using Finite Element Method (유한요소법을 이용한 폴리머 압출 공정해석에 관한 연구)

  • Ye Youngsoo;Kim Hongbum;Lee Jaewook;Kim Naksoo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • 제29권1호
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    • pp.145-155
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    • 2005
  • In this study, a finite element method program code which can be accomodate boundary conditions on the complex surfaces has been developed to simulate polymer extruder processes. The analysis method includes the fractional 4-step method for efficient computation time and compact usage of memory storage to solve the velocities and the pressure values from the Navier-Stokes equation. By using the developed program which was verified with simple Poiseuille flow mixture phenomena in single-and twin-screw extruder are analyzed. It is concluded that the proposed method resulte Poiseuille Poiseuille d in fair agreement with the exact solution of simple flow and the back flow near the entrance happens in single-screw model. It is identified that the location and values of maximum pressure in the twin screw extruder model. It is expected that the Velocity field found can be used to predict the degree of mixture in the extruder barrel.

Stability analysis in BWRs with double subdiffusion effects: Reduced order fractional model (DS-F-ROM)

  • Gilberto Espinosa-Paredes;Ricardo I. Cazares-Ramirez;Vishwesh A. Vyawahare;Erick-G. Espinosa-Martinez
    • Nuclear Engineering and Technology
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    • 제56권4호
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    • pp.1296-1309
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    • 2024
  • The aim of this work is to explore the effect of the double subdiffusion on the stability in BWRs. A BWR novel reduced order model with double subdiffusion effects: reduced order fractional model (DS-F-ROM) to describe the neutron and heat transfer processes was proposed for this study. The double subdiffusion was developed with a fractional-order two-equation model, and with different fractional-orders and relaxation times. The stability analysis was carried out using the root-locus method and change from the s to the W domain and were confirmed using the time-domain evolution of neutron flux for a unit step change in reactivity. The results obtained using the reduced fractional-order model are presented for different anomalous diffusion coefficient values. Results are compared with normal diffusion and P1 equations, which are obtained straightforwardly with DS-ROM when relaxation time tends to zero, and when the anomalous diffusion coefficient tends to one, respectively.

Finite Element Analysis of Fluid Flows with Moving Boundary

  • Cha, Kyung-Se;Park, Jong-Wook;Park, Chan-Guk
    • Journal of Mechanical Science and Technology
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    • 제16권5호
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    • pp.683-695
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    • 2002
  • The objective of the present study is to analyze the fluid flow with moving boundary using a finite element method. The algorithm uses a fractional step approach that can be used to solve low-speed flow with large density changes due to intense temperature gradients. The explicit Lax-Wendroff scheme is applied to nonlinear convective terms in the momentum equations to prevent checkerboard pressure oscillations. The ALE (Arbitrary Lagrangian Eulerian) method is adopted for moving grids. The numerical algorithm in the present study is validated for two-dimensional unsteady flow in a driven cavity and a natural convection problem. To extend the present numerical method to engine simulations, a piston-driven intake flow with moving boundary is also simulated. The density, temperature and axial velocity profiles are calculated for the three-dimensional unsteady piston-driven intake flow with density changes due to high inlet fluid temperatures using the present algorithm. The calculated results are in good agreement with other numerical and experimental ones.

BARRIER OPTIONS UNDER THE MFBM WITH JUMPS : APPLICATION OF THE BDF2 METHOD

  • Choi, Heungsu;Lee, Younhee
    • Journal of the Chungcheong Mathematical Society
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    • 제33권1호
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    • pp.165-171
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    • 2020
  • In this paper we consider a mixed fractional Brownian motion (mfBm) with jumps. The prices of European barrier options can be evaluated by solving a partial integro-differential equation (PIDE) with variable coefficients, which is derived from the mfBm with jumps. The 2-step backward differentiation formula (BDF2 method) proposed in [6] is applied with the second-order convergence rate in the time and spatial variables. Numerical simulations are carried out to observe the convergence behaviors of the BDF2 method under the mfBm with the Kou model.

A Study on the Flow with Interfacial Phenomena Using VOF Method

  • Baek, J.H.
    • 한국전산유체공학회:학술대회논문집
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    • 한국전산유체공학회 2006년도 추계 학술대회논문집
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    • pp.9-10
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    • 2006
  • A numerical method for simulating tree surface flows including the surface tension is presented. Numerical scheme is based an a fractional-step method with a finite volume formulation and the interface between liquid and gas is tracked by Volume of Fluid (VOF) method. Piecewise Linear Interface Calculation (PLIC) method is used to reconstruct the interface and the surface tension is considered using a Continuum Surface Force (CSF) model. Several free surface flow phenomena were simulated to show its effectiveness to find such phenomena.

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