• Title, Summary, Keyword: 유체점성

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비뉴우튼유체의 유동현상

  • 유정열
    • Journal of the KSME
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    • v.25 no.4
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    • pp.312-319
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    • 1985
  • 유탁액(emulsion), 현탁액(suspension), 고분자용액(polymer solution) 및 고분자 용식물(polymer melt) 등의 유동에 대하여는 응력과 속도구배 사이에 선형적인 관계가 성립되지 않는다. 이런 유체들은 뉴우튼유체들의 경우와는 달리 단한번의 점성계수 측정만으로는 완전한 유변학 적(rheological) 특징을 파악할 수 없으므로 이들을 통털어서 비뉴우튼유체(non-Newtonian fluid )라고 한다. 이들의 응력과 속도구배 사이의 비선형적인 관계를 고찰하는 비뉴우튼유체역학은 최근에 빠르게 발전하고 있는 유체역학의 한 분야이며, 고분자 공정, 식품, 생물공학 및 유전등의 여러 산업부문에서 많은 관심의 대상이 되고 있다. 여기서는 뉴우튼유체에서 관찰될 수 없는 비뉴우튼유체의 독특한 유동 현상에 대한 이해를 증진시킴으로써, 비뉴우튼유체역학의 여러 문 제들을 취급하는데 필요한 기본지식을 제공하고자 한다.

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Rheological Properties of Konjac Glucomannan Dispersons (구약감자 Glucomannan 현탁액의 유동특성)

  • Ji, Soo-Kyung;Kim, Nam-Soo
    • Korean Journal of Food Science and Technology
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    • v.27 no.2
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    • pp.246-250
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    • 1995
  • Konjac(Amorphophallus konjac) glucomannan dispersions were prepared from konjac flour, pretreated konjac flour and purified glucomannan. Konjac glucomannan dispersions showed non-Newtonian fluid behavior without yield stress and higher shear stress at fixed shear rate than the dispersions of gum xanthan, gum carrageenan and sodium alginate. While temperature increased, shear stress at fixed shear rate of konjac glucomannan dispersion steadily decreased. The apparent viscosity of konjac glucomannan dispersion was in its maximum at pH 7, whereas decreased on the outskirts of pH 7. The change in apparent viscosity was not found up to 1% sodium chloride addition in case of konjac glucomannan dispersion. However, the apparent viscosity of konjac glucomannan dispersion decreased up to sugar addition of 10%, afterwards increased.

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Electro-Magnetic Field Analysis for Optimal design of Magneto-Rheological Fluid Damper Core (자기점서유체 댐퍼 코어의 최적화 설계를 위한 전자기장 해석)

  • Song, June-Han;Son, Sung-Wan;Chun, Chong-Keun;Kwon, Young-Chul;Ma, Yang-Soo
    • Journal of the Korea Academia-Industrial cooperation Society
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    • v.9 no.6
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    • pp.1511-1517
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    • 2008
  • The magneto-rheological fluid expresses different cohesiveness according to the strength of the external electric current. The magneto-rheological fluid damper, which uses such characteristics of the fluid, generates shear force due to the fluid's cohesiveness. The core can be said to determine the magneto-rheological fluid damper's performance. This study uses the finite element analysis to compare the performance of different electromagnetic forces, which are affected by the shapes of the coil, and thus to find the optimum design for the core. In addition, as a step to construct a high-efficient damper, we suggest a type of damper that can control multiple coils and compares the performance of this damper and that of the standard damper by comparing the performance of their electro-magnetic fields.

A Study on the Ultraprecision Polishing of Single Crystal Silicon using Electrorheolgical Fluids. (전기점성유체를 이용한 단결정 실리콘의 초정밀 연마에 관한 연구)

  • 박성준;이성재;김욱배;이상조
    • Journal of the Korean Society for Precision Engineering
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    • v.20 no.6
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    • pp.27-36
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    • 2003
  • The Electro-Rheological (ER) fluid has been used to the ultraprecision polishing of single crystal silicon as new polishing slurry whose properties such as yield stress and particle structure changed with the application of an electric field. In this work, it is aimed to find the effective parameters in the ER fluid on material removal in the polishing system whose structure is similar to that of the simple hydrodynamic bearing. The generated pressure in the gap between a moving wall and a workpiece, as well as the electric field-induced stress of the mixture of ER fluid-abrasives, is evaluated experimentally, and their influence on the polishing of single crystal silicon is analyzed. Moreover, the behavior of abrasive and ER particles is described.

The Calculation of Three-Dimensional Viscous Flow in a Transonic, Multi-Stage Axial Compressor (다단축류압축기내의 천음속 점성유동에 대한 삼차원 수치해석)

  • Yi H. W.;Kim K. Y.
    • 한국전산유체공학회:학술대회논문집
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    • pp.181-189
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    • 1998
  • A numerical study based on the three-dimensional Reynolds averaged Navier-Stokes equations is presented to analyze the transonic flowfield through two-stage axial compressor. Explicit four-step Runge-Kutta scheme is used for solution algorithm, and local time step and implicit residual averaging are introduced for enhancing the convergency. Artificial dissipation model is adopted to assure the stability of solution. The solver is coupled with Baldwin-Lomax model to describe turbulence. To avoid calculating the unsteady flow, a mixing process is modeled at a station between rotating and stationary blade rows. Results show a variety of important physical phenomena. Comparison of the flowfields with and without tip clearance shows that the effect is considerable in this flowfield. Comparisons with experimental data carried out to validate the calculational results show reasonable agreements. Some remedies are also suggested to improve the revealed problems.

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INFLUENCE OF EDDY VISCOSITY COEFFICIENT ON ${\kappa}-{\varepsilon}$ TURBULENCE MODEL FOR SUPERSONIC BASE FLOW (초음속 기저부 유동에서 ${\kappa}-{\varepsilon}$ 난류 모델에 대한 와점성 계수의 영향)

  • Park, Soo-Hyung;Sa, Jeong-Hwan;Kim, Jee-Woong;Kwon, Jang-Hyuk;Kim, Chang-Joo
    • Journal of computational fluids engineering
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    • v.13 no.3
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    • pp.1-7
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    • 2008
  • A supersonic base flow is computed to investigate the effect of the eddy viscosity coefficient to the linear ${\kappa}-{\varepsilon}$ turbulence models. Slight modifications to the eddy viscosity coefficient, which are based on the realizability condition, are given to the Launder-Sharma turbulence model so that present models satisfy the realizability condition. Numerical results for supersonic base flow show that turbulence models with the weaky-nonlinear eddy viscosity coefficient can lead to reasonable enhancements in the prediction of the velocity and turbulent kinetic energy profiles.

EFFECTS OF TURBULENCE MODEL AND EDDY VISCOSITY IN SHOCK-WAVE / BOUNDARY LAYER INTERACTION (충격파 경계층 상호작용에서 난류모델 및 난류점성의 효과)

  • Jeon, Sang Eon;Park, Soo Hyung;Byun, Yung Hwan
    • Journal of computational fluids engineering
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    • v.18 no.2
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    • pp.56-65
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    • 2013
  • Two compression ramp problems and an impinging shock problem are computed to investigate influence of turbulence models and eddy viscosity on the shock-wave / boundary layer interaction. A Navier-Stokes boundary layer generation code was applied to the generation of inflow boundary conditions. Computational results are validated well with the experimental data and effects of turbulence models are investigated. It is shown that the behavior of turbulence (eddy) viscosity directly affects both the extent of the separation and shock-wave positions over the separation.

Numerical Analysis on Hydrodynamic Forces Acting on Side-by-Side Arranged Two-Dimensional Floating Bodies in Viscous Flows (점성유동장에 병렬배치된 2차원 부유체에 작용하는 유체력에 관한 수치해석)

  • Heo, Jae-Kyung;Park, Jong-Chun
    • Journal of the Society of Naval Architects of Korea
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    • v.49 no.5
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    • pp.425-432
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    • 2012
  • Viscous flow fields of side-by-side arranged two-dimensional floating bodies are numerically simulated by a Navier-Stokes equation solver. Two identical bodies with a narrow gap are forced to heave and sway motions. Square and rounded bilge hull forms are compared to find out the effects of vortex shedding on damping force. Wave height, force RAOs, added mass and damping coefficients including non-diagonal cross coefficients are calculated and a similarity between the wave height and force RAOs is discussed. CFD which can take into account of viscous damping and vortex shedding shows better results than linear potential theory.

Influence of Design Parameters of Grout Injection in Rock Mass using Numerical Analysis (암반 그라우팅 주입 설계변수가 주입성능에 미치는 영향의 수치해석적 평가)

  • Lee, Jong Won;Kim, Hyung Mok;Yazdani, Mahmoud;Park, Eui-Seob
    • Tunnel and Underground Space
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    • v.27 no.5
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    • pp.324-332
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    • 2017
  • In this paper, a numerical analysis of one-dimensional viscous fluid flow in a rock joint using UDEC code is performed to evaluate the effect of design parameters on injection performance. We consider injection pressure, fluid compressibility, time dependence of yield strength and viscosity of injected grout fluid, and mechanical deformation of joint as the design parameters, and penetration length and flow rate of injection are investigated as the injection performance. Numerical estimations of penetration length and flow rate were compared to analytical solution and were well comparable with each other. We showed that cumulative injection volume can be over-estimated by 1.2 times than the case that the time-dependent viscosity evolution is not considered. We also carried out a coupled fluid flow and mechanical deformation analysis and demonstrated that injection-induced joint opening may result in the increment of cumulative volume by 4.4 times of that from the flow only analysis in which joint aperture is kept constant.