• Title/Summary/Keyword: Visco-elastic model

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DEVELOPMIN OF A MODIFIED $k-{\varepsilon}$ TURBULENCE MODEL FOR VISCO-ELASTIC FLUID AND ITS APPLICATION TO HEMODYNAMICS (점탄성 유체의 난류 해석을 위한 수정된 $k-{\varepsilon}$ 난류모델 개발 및 혈류역학에의 적용)

  • Ro, K.C.;Ryou, H.S.
    • 한국전산유체공학회:학술대회논문집
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    • 2010.05a
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    • pp.214-220
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    • 2010
  • This article described that a high Reynolds number version of a turbulence model was modified by using drag reduction to analyze the turbulent flows of non-Newtonian fluid with visco-elastic viscosity and it was applied hemodynamics which was representative of visco-elastic fluid. The turbulence characteristics of visco-elastic fluid was expanded viscous sublayer region and buffer layer region by drag reduction phenomenon and also Newtonian turbulence models does not predict because viscosity was related with shear rate of fluid flow. Hence numerical simulation using a modified turbulence model was conducted under the same conditions that were applied to obtain the experiment results and previous turbulence models and then the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body.

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A FINITE-VISCOELASTIC CONTINUUM MODEL FOR RUBBER AND ITS FINITE ELEMENT ANALYSIS

  • Kim, Seung-Jo;Kim, Kyeong-Su;Cho, Jin-Yeon
    • Journal of Theoretical and Applied Mechanics
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    • v.1 no.1
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    • pp.97-109
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    • 1995
  • In this paper, a finite viscoelastic continuum model for rubber and its finite element analysis are presented. This finite viscoelatic model based on continuum mechanics is an extended model of Johnson and Wuigley's 1-D model. In this extended model, continuum based kinematic measures are rigorously defied and by using this kinematic measures, elastic stage law and flow rule are introduced. In kinematics, three configuration are introduced. In kinematics, three configuration are introduced. They are reference, current and virtual visco configurations. In elastic state law, it is assumed that at a certain time, there exists an elastic potential which describes the recoverable elastic energy. From this elastic potential, elastic state law is derived. The proposed flow rule is based on phenomenological observation. The flow rule gives precise relaxation response. In finite element approximation, mixed Lagrangian description is used, where total and similar method of updated Lagrangian descriptions are used together. This approach reduces the numerical job and gives simple nonlinear syatem of equations. To satisfy the incompressible condition, penalty-type modified Mooney-Rivlin energy function is adopted. By this method nearly incompressible condition is obtain the virtual visco configuration. For verification, uniaxial stretch tests are simulated for various stretch rates. The simulated results show good agreement with experiments. As a practical experiments. As a preactical example, pressurized rubber plate is simulated. The result shows finite viscoelastic effects clearly.

Development of Analysis Model for Underwater Acoustic Performance of Multi-Layered Coatings Containing Visco-Elastic Composites (점탄성 복합재가 포함된 다층구조 코팅재의 수중음향성능 해석모델 개발)

  • Kim, Jae Ho
    • Journal of the Korea Institute of Military Science and Technology
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    • v.21 no.1
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    • pp.25-39
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    • 2018
  • In this paper, an integrated analysis model for evaluating the underwater acoustic performance of the multilayered acoustic coatings containing visco-elastic composite layers with hollow glass microspheres is described. The model uses the effective medium theory considering the acoustic scattering and resonance effects of the inclusions. Also, the model incorporates the compressive deformation mechanism associated with hydrostatic pressure. The technique developed in this work was used as the acoustic layer design and performance analysis tools for the practical hull coatings and acoustic baffles in Korean next generation submarines.

Structural analysis of liquid rocket thrust chamber regenerative cooling channel using visco-plastic model (점소성 모델을 이용한 액체로켓 연소기 재생냉각 채널 구조해석)

  • Ryu Chul-Sung;Choi Hwan-Seok
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2006.05a
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    • pp.151-155
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    • 2006
  • Elastic-viscoplastic structural analysis is performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was also conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plsstic model was incorporated into finite element program, Marc, by means of user subroutine. The structural analysis results indicate that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under operating condition.

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Vibration Reaponse Analysis of frames with energy absober installed in Beams (보 제진 프레임의 진동응답해석)

  • Lee, Ho
    • Proceedings of the Earthquake Engineering Society of Korea Conference
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    • 1997.10a
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    • pp.159-166
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    • 1997
  • The purpose of this thesis is to derive a theoretical model of the hysteretic resistance of the visco-elastic damper based on test results of harmonic excitation and to investigate of the basis of theory and experiment the effect of vibration control and response characteristics of portal frames degree vibration systems provided with the damper. The behaviour of a visco-elastic degree under dynamic loading is idealized by a model of the theory of visco-elasticity, i.e. a four-parameter model formed as a parallel combination of Maxwell fluid and Kelvin-Voigh models and its constitutive equation is derived. The model parameters are determined for a tested damper from the datas of harmonic excitation tests. The theoretical model of the damper is incorporated in equation fo motion of single degree of freedom. A computer program for solving the equation is written using Runge-kuttas's numerical integration scheme. Using this analysis program test cases of the earthquake excitation are simulated and the results of the simulation are the results of the simulation are the results of the simulation are compared with the test results.

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Thermal load analysis in an incompressible linear visco-elastic cylinder bonded to an elastic shell (非壓縮 粘彈性 圓筒體의 熱荷重 解析)

  • 이영신;최용규
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.205-213
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    • 1987
  • A linear thermoviscoelastic material model, whose basis is on incremental constitutive equation that takes complete strain and temperature histories into account, is derived and computerized in the finite element code. The thermoviscoelastic F.E.M. code which is intended primarily to analyze the cylinder model during the cool-down period, embodies the assumption of linearly elastic bulk and visco-elastic shear responses, thermo-rheologically simple response to temperature change and isotropic thermal expansion. The verification of computer program is accomplished by first testing it against a closed form solution of A.M. Freudenthal & M. Shinozuka's. The stress and strain analyses of five cylindrical models are presented and compared with experimental results. Analytical results are good agreement with experimental results. Margins of safety are evaluated and its allowable ranges are presented.

Dynamic response of a linear two d.o.f system visco-elastically coupled with a rigid block

  • Di Egidio, Angelo;Pagliaro, Stefano;Fabrizio, Cristiano;de Leo, Andrea M.
    • Coupled systems mechanics
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    • v.8 no.4
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    • pp.351-375
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    • 2019
  • The present work investigates the use of a rigid rocking block as a tool to reduce vibrations in a frame structure. The study is based on a simplified model composed by a 2-DOF linear system, meant to represent a general M-DOF frame structure, coupled with a rocking rigid block through a linear visco-elastic device, which connects only the lower part of the 2-DOF system. The possibility to restrain the block directly to the ground, by means of a second visco-elastic device, is investigated as well. The dynamic response of the model under an harmonic base excitation is then analysed in order to evaluate the effectiveness of the coupling in reducing the displacements and the drift of the 2-DOF system. The nonlinear equations of motion of the coupled assemblage 2-DOF-block are obtained by a Lagrangian approach and then numerically integrated considering some reference mechanical and geometrical quantities as variable parameters. It follows an extensive parametric analysis, whose results are summarized through behaviour maps, which portray the ratio between the maximum displacements and drifts of the system, with and without the coupling with the rigid block, for several combinations of system's parameters. When the ratio of the displacements is less than unity, the coupling is considered effective. Results show that the presence of the rocking rigid block improves the dynamics of the system in large ranges of the characterizing parameters.

Structural Analysis of Liquid Rocket Thrust Chamber Regenerative Cooling Channel using Bodner-Partom Viscoplastic Model (Bodner-Partom 점소성 모델을 이용한 액체로켓 연소기 재생냉각 채널 구조해석)

  • Ryu, Chul-Sung;Baek, Un-Bong;Choi, Hwan-Seok
    • Journal of the Korean Society of Propulsion Engineers
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    • v.10 no.4
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    • pp.69-76
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    • 2006
  • Elastic-viscoplastic structural analysis has been performed for regenerative cooling chamber of liquid rocket thrust chamber using Bodner-Partom visco-plastic model. Strain rate test was conducted for a copper alloy at various temperatures in order to get material constants of visco-plastic model used in the structural analysis. Material constants of visco-plastic model were obtained from strain rate test results and visco-plastic model was incorporated into finite element program, Marc, by means of a user subroutine. The structural analysis results indicated that the deformation of cooling channel is mostly caused by thermal loading rather than pressure loading and confirmed structural stability of the cooling channel under the operating condition.

Dynamic analyses for an axially-loaded pile in a transverse-isotropic, fluid-filled, poro-visco-elastic soil underlain by rigid base

  • Zhang, Shiping;Zhang, Junhui;Zeng, Ling;Yu, Cheng;Zheng, Yun
    • Geomechanics and Engineering
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    • v.29 no.1
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    • pp.53-63
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    • 2022
  • Simplified analytical solutions are developed for the dynamic analyses of an axially loaded pile foundation embedded in a transverse-isotropic, fluid-filled, poro-visco-elastic soil with rigid substratum. The pile is modeled as a viscoelastic Rayleigh-Love rod, while the surrounding soil is regarded as a transversely isotropic, liquid-saturated, viscoelastic, porous medium of which the mechanical behavior is represented by the Boer's poroelastic media model and the fractional derivative model. Upon the separation of variables, the frequency-domain responses for the impedance function of the pile top, and the vertical displacement and the axial force along the pile shaft are gained. Then by virtue of the convolution theorem and the inverse Fourier transform, the time-domain velocity response of the pile head is derived. The presented solutions are validated, compared to the existing solution, the finite element model (FEM) results, and the field test data. Parametric analyses are made to show the effect of the soil anisotropy and the excitation frequency on the pile-soil dynamic responses.

Analyzing consolidation data to obtain elastic viscoplastic parameters of clay

  • Le, Thu M.;Fatahi, Behzad;Disfani, Mahdi;Khabbaz, Hadi
    • Geomechanics and Engineering
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    • v.8 no.4
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    • pp.559-594
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    • 2015
  • A nonlinear creep function incorporated into the elastic visco-plastic model may describe the long-term soil deformation more accurately. However, by applying the conventional procedure, there are challenges to determine the model parameters due to limitation of suitable data points. This paper presents a numerical solution to obtain several parameters simultaneously for a nonlinear elastic visco-plastic (EVP) model using the available consolidation data. The finite difference scheme using the Crank-Nicolson procedure is applied to solve a set of coupled partial differential equations of the time dependent strain and pore water pressure dissipation. The model parameters are determined by applying the algorithm of trust-region reflective optimisation in conjunction with the finite difference solution. The proposed method utilises all available consolidation data during dissipation of the excess pore water pressure to determine the required model parameters. Moreover, the reference time in the elastic visco-plastic model can readily be adopted as a unit of time; denoting creep is included in the numerical predictions explicitly from the very first time steps. In this paper, the settlement predictions of thick soft clay layers are presented and discussed to evaluate and compare the accuracy and reliability of the proposed method against the graphical procedure to obtain the model parameters. In addition, comparison of the available experimental results to the numerical predictions confirms the accuracy of the numerical procedure.