• Title/Summary/Keyword: Flow stress equation

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A Numerical Study on the Blood Flow through a Disc Type Heart Valve (원판형 심장판 주위의 혈액 흐름에 대한 수직 해석)

  • 박영필;이신재
    • Journal of Biomedical Engineering Research
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    • v.2 no.2
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    • pp.89-102
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    • 1981
  • The recirculating flows which occur in the prosthetic heart valve have been known to cause several diseases in the human body. And the recent studies show that the shear stress at the wall of the artery is also very important factor in the formation of thrombus. And many studies knave been devoted in obtaining more information about the blood flow through the prosthetic heart valve. In this Paper, the steady axisymmetric flow through the Disc-Type Heart Valve is studied by using the numerical method. The geometry of the Disc-Type Heart Valve is simplified, and the flow is assumed to be steady axisymmetric flow. The vorticity transport equation derived from the Wavier-Stoke's equation is used as the governing equation, and the explicit finite difference method is used to obtain the steady state solution. The results for several Reynolds numbers show that the recirculating flow becomes large as the Remolds number increases. Furthermore, it can be shown that the magnitudes of the vorticity and the stresses are also increased with the Reynolds number, but there is only a little change in their configurations of distribution and in their positions of maximum values.

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Flow Stress Determination of Johnson-Cook Model of Ti-6Al-4V Material using 3D Printing Technique (3D 프린팅으로 제작한 Ti-6Al-4V 재료의 Johnson-Cook 모델의 유동 응력 결정)

  • Park, Dae-Gyoun;Kim, Tae-Ho;Jeon, Eon-Chan
    • Journal of the Korean Society of Manufacturing Process Engineers
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    • v.17 no.4
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    • pp.64-69
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    • 2018
  • This paper investigates the compressive deformation behavior of direct metal tooling (DMT), processing titanium alloy (Ti-6Al-4V) parts under high strain loading conditions. Split Hopkinson Pressure Bar (SHPB) experiments were performed to determine the flow stress and the coefficients of the Johnson-Cook model. This model is described as a function of strain, strain rate, and temperature. SHPB experiments were performed to characterize the deformation behavior of specimens made with 3D printers, using Ti-6Al-4V material under high temperature and dynamic loading.

The Estimation of Shear Stress in Uniform and Nonuniform Flow by the Entropy Concept (엔트로피 개념을 이용한 개수로에서 등류 및 부등류 흐름의 전단응력 산정)

  • Choo, Yeon Moon;Choo, Tai Ho;Yang, Da Un;Kim, Joong Hoon
    • Journal of Wetlands Research
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    • v.19 no.2
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    • pp.202-210
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    • 2017
  • Shear stress is one of the most important mechanical factors used in various fields and is important for the design of artificial channels. Current shear stresses have been used in the past, but there are factors that are difficult to actually measure or calculate, such as bed shear stress and energy slope in the equation used. In particular, the energy slope is a very difficult factor to estimate, and it is difficult to estimate the slope and flow velocity of the boundary layer although the energy slope can be used to obtain the shear stress distribution. In addition, the bed shear stress among the shear stress distribution is very difficult to measure directly, and the research is somewhat slower than the velocity. In this study, we have studied the simple calculation of the average flow velocity and the shear stress distribution using entropy M without reflecting the energy gradient, and we used existing laboratory data to demonstrate the utility of the applied equation. The stress distribution in the graphs was comparatively analyzed. In the case of the uniform flow and the non-uniform flow, the correlation coefficient was almost identical to 0.930-0.998.

Numerical Simulation of Flow-Induced Birefringence: Comparison of Injection and Injection/Compression Molding

  • Lee, Ho-Sang;Isayev, A.I.
    • International Journal of Precision Engineering and Manufacturing
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    • v.8 no.1
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    • pp.66-72
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    • 2007
  • A computer code was developed to simulate the filling stage of an injection/compression molding process using a finite element method. The constitutive equation was the compressible Leonov model and the PVT relationship was assumed to follow the Tait equation. The flow-induced birefringence was related to the calculated flow stresses through the linear stress-optical law. Simulations of a disk under different processing conditions, including variations of the compression stroke and compression speed, were performed to determine their effects on the flow-induced birefringence. Simulated pressure traces were also compared to those obtained in conventional injection molding and with experimental data from the literature.

Numerical Simulation of Flow-Induced Birefringence in Injection/Compression Molding (사출압축성형에서의 유동에 의한 복굴절 해석)

  • Lee H.-S.;Isayev A.I.
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2004.10a
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    • pp.65-69
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    • 2004
  • A computer code was developed to simulate the filling stage of the injection/compression molding process by a finite element method. The constitutive equation used here was the compressible Leonov model. The PVT relationship was assumed to follow the Tait equation. The flow-induced birefringence was related to the calculated flow stresses through the linear stress-optical law. Simulations of a disk part under different processing conditions including the variation of compression stroke and compression speed were carried out to understand their effects on flow-induced birefringence. The simulated results were also compared with those by conventional injection molding and with experimental data from literature.

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The Non Newtonian Flow Mechanism and Rheological Properties of Polyurethane Melts (용융 폴리우레탄의 비 뉴톤 유동 메카니즘과 유변학적인 성질)

  • Kim, Nam-Jeong
    • Elastomers and Composites
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    • v.44 no.4
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    • pp.423-428
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    • 2009
  • The non-Newtonian flow curves of polyurethane melts were obtained by using a Physica cone-plate rheometer at various temperatures. The rheological parameters were obtained by applying non-Newtonian flow equation to the flow curves for polyurethane samples. When the polyurethane samples are under increasing-decreasing shear rate modes, the hysteresis loop and thixotropic behavior were shown. Polyurethane melts behave as strong gels when they are subjected to shear flow, but when the applied stress surpasses the yield stress, they exhibit non-linear viscoelasticity. Upon decreasing shear rate, its shear stress remains smaller than the values measured in the increasing shear rate mode, because of broken of its structure.

A Reynolds Stress Model for Low-Reynolds-Number Turbulence (저레이놀즈수 난류에 대한 레이놀즈 응력모델)

  • 김광용
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.17 no.6
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    • pp.1541-1546
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    • 1993
  • To extend the widely used Gibson and Launder's second order closure model to the low-Reynolds-number region near a wall, modifications have been made for velocity pressure-gradient interaction and dissipation terms in the stress equations, and also for the dissipation rate equation. From the computation of fully developed plane channel flow, it is found that the results with present model agree well with the data of direct numerical simulation in the predictions of stress components. And, the computed mean velocity profile coincides with the universal velocity law.

Changes in the Rheological Characteristics by Various Concentrations and Temperatures of Korean white Gruel (농도와 온도에 따른 흰죽의 리올로지 특성 변화)

  • Lee, Chang-Ho;Han, Ouk
    • Korean journal of food and cookery science
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    • v.11 no.5
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    • pp.552-556
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    • 1995
  • The rheological properties of Korean white gruel at various concentrations (4-7%) and temperatures (30-60$^{\circ}C$) were investigated. The rheological behavior of Korean white gruel was evaluated by Herschel-Bulkley equation and showed typical Bingham psedoplastic behavior with yield stress. Flow behavior index was increased at over 5% of rice content. Consistency index was increased by the increase of concentration of rice. But, measuring temperature was not effected in the flow behavior index and consistency index. Yield stress was increased by the incerase of concentration of rice and the decrease of measuring temperature. The activation energy of flow of Korean gruel increased from 7.646 to 32.949${\times}$10/Sup 6/ J/Kg$.$ mole by increasing concentration from 4% to 7%. As the temperature increased from 30$^{\circ}C$ to 60$^{\circ}C$, B-value decresed from 1.214 to 0.947 Flow behavior index and consistency index was reduced during storage.

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Modeling of Turbulent Heat Transfer in an Axially Rotating Pipe Flow (축을 중심으로 회전하는 관유동에서 난류열전달의 모형화)

  • Shin, Jong-Keun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.9
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    • pp.741-753
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    • 2007
  • The elliptic conceptual second moment model for turbulent heat fluxes, which was proposed on the basis of elliptic-relaxation equation, was applied to calculate the turbulent heat transfer in an axially rotating pipe flow. The model was closely linked to the elliptic blending model which was used for the prediction of Reynolds stress. The effects of rotation on the turbulent characteristics including the mean velocity, the Reynolds stress tensor, the mean temperature and the turbulent heat flux vector were examined by the model. The numerical results by the present model were directly compared to the DNS as well as the experimental results to assess the performance of the model predictions and showed that the behaviors of the turbulent heat transfer in the axially rotating pipe flow were satisfactorily captured by the present models.