• 오토저널
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• 제15권1호
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• pp.45-54
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• 1993

The reattachment lengths of the Non-Newtonian fluid are investigated in the sudden expansion pipes whose ratios are 2.316 and 3.368, and the range of the Reynolds numbers is 100-30000. The reattachment lengths for the viscoelastic fluid in the laminar flow region are found to be much shorter than those of the Newtonian fluid, and decrease significantly with the increase of the concentration of viscoelastic fluid is two or three times longer than those of water, and gradually increases with the increase of the concentration of viscoelastic fluid.

• 대한화학회지
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• 제15권6호
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• pp.293-303
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• 1971

The theological properties of aqueous suspensions of Black Hills bentonite were measured by using a Couette-type viscometer. Three kinds of flow units in aqueous bentonite suspension were postulated. Each has a different average relaxation time, one Newtonian. One of the non-Newtonian types is thixotropic, and the other is non-thixotropic. The thixotropic non-Newtonian unit is transformed to a Newtonian unit by shear stress. If the stress is relieved, the transformed unit returns to its original state. Two flow equations were derived by introducing chemical kinetics consideration for such a transition into the generalized theory of viscous flow. One equation describes the "upcurve," a diagram of rate of sheat versus shear stress, obtained by increasing the rate of shear, and the other relates to the "downcurve" obtained by decreasing the shear rate. The equations satisfactorilly describe the experimental thixotropic hysteresis of bentonite suspensions. The equations also were successfully applied to the flow curves of the suspensions containing various amounts of monovalent electrolyte (KCI).

• 한국산학기술학회논문지
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• 제18권3호
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• pp.545-550
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• 2017

대동맥이나 협착된 경동맥에서는 심장수축기에 간헐적으로 난류현상이 발생하고 있으며, 혈액의 점성특성으로 인해 기존 난류모델로는 정확한 해석이 어려운 실정이다. 혈류는 점탄성 유체의 성질을 가지고 있어 유체의 전단 변형률 증가에 따라 점도가 감소하는 점탄성 유체이며, 이러한 점탄성 유체는 난류 유동시 저항 감소 현상이 발생한다. 기존의 난류해석 모델들은 점성변화가 없는 뉴턴 유체에 적합한 모델들이 대부분이기 때문에, 점탄성 유체의 저항 감소 현상을 고려한 비뉴턴 유체 해석에 적합한 난류 모델개발이 필요하다. 본 논문은 난류 모델 가운데 수렴성이 좋고 해석시간이 짧은 표준 $k-{\varepsilon}$ 모델을 기반으로 저항 완충 함수를 이용하여 비뉴턴 유체의 저항감소 현상을 해석할 수 있는 수정된 난류모델을 제시하였으며, 이를 기존 난류모델들과 비교하여 제시된 난류 모델을 검증하였다. 새로 제시된 수정된 난류모델은 벽함수 및 점성저층을 고려하지 않았기 때문에 해석시간이 대폭적으로 감소하였으며, 적은 격자수를 이용하여 효율적으로 비뉴턴 유체의 난류 현상을 해석할 수 있기 때문에 향후 혈류해석 및 점탄성유체 해석에 적용할 예정이다.

• 동력기계공학회지
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• 제13권2호
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• pp.30-35
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• 2009

Numerical Calculations for dimensionless pressure drop (friction factor times Reynolds number) have been obtained for fully developed laminar flow of MPL(Modified Power Law) fluid in isosceles triangle pipes. The solutions are valid for Pseudoplastic fluids over a wide range from Newtonian behavior at low shear rates through transition region to power law behavior at higher shear rates. The analysis identified a dimensionless shear rate parameter which for a given set of operating conditions specifies where in the shear rate range a particular system is operating, i.e., Newtonian, transition or power law region. The numerical calculation data of the dimensionless pressure drop for the Newtonian and power law regions are compared with previously published asymptotic results presenting within 0.16 % in Newtonian region and 2.98 % in power law region.

• 한국자동차공학회논문집
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• 제20권1호
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• pp.131-140
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• 2012

In this study, using the governing equation for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water within engine oil on the performance of high speed journal bearing of a turbocharger. The governing equations are the general equations being able to be applied on the mixture of Newtonian fluid and non- Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing in a turbocharger lubricated with the mixture of two Newtonian fluid, for example, water within engine oil. The results related with the bearing performance are shown that the bearing friction is to decrease and the side leakage and bearing load increase as increasing the water content in an engine oil.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2005년도 춘계학술대회 논문집
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• pp.1757-1760
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• 2005

This paper is concerned with spring back after sheet forming of bulk amorphous alloys in the super cooled liquid state. The temperature-dependence and strain-rate dependence of Newtonian/non-Newtonian viscosities as well as the stress overshoot/undershoot behavior of amorphous alloys are reflected in the thermo-mechanical Finite Element simulations. Hemispherical deep drawing operations are simulated for various forming conditions such as punch velocity, die corner radius, friction, blank holder force, clearance and initial forming temperature. Here, spring back by an instantaneous elastic unloading was followed by thermal deformation during cooling and two modes of spring backs are examined in detail. It could be concluded that the superior sheet formability of an amorphous alloy can be obtained by taking the proper forming conditions for loading/unloading.

• Tribology and Lubricants
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• 제27권4호
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• pp.183-192
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• 2011

In this study, using the governing equations for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water dispersed within engine oil on the performance of high speed journal bearing of a turbocharger. The governing equations are the general equations being able to be applied on the mixture of Newtonian fluid and non-Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing on a turbocharger lubricated with the mixture of two Newtonian fluids, water dispersed within engine oil. The results related with the bearing performance are showed that the friction force and bearing load capacity decrease as increasing the volume percent of water.

• Tribology and Lubricants
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• 제27권2호
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• pp.77-87
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• 2011

In this study, using the governing equation for thermohydrodyamic lubrication involving the homogeneous mixture of incompressible fluid derived by based on the principle of continuum mechanics, it is discussed the effects of water within turbine oil on the performance of high speed journal bearing of a steam turbine shipping engine. The governing equation is the general equation being able to be applied on the mixture of Newtonian fluid and non-Newtonian fluid. Here, the fluid viscosity index, n of power-law non-Newtonian fluid is supposed to be 1 for the application of the journal bearing in a steam turbine shipping engine lubricated with the mixture of two Newtonian fluid, for example, water within turbine oil. The results related with the bearing performance are showed.

• 소성∙가공
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• 제14권9호통권81호
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• pp.751-755
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• 2005

This paper is concerned with spring back after sheet forming of bulk amorphous alloys in the super cooled liquid state. The temperature-dependence and strain-rate dependence of Newtonian/non-Newtonian viscosities as well as the stress overshoot/undershoot behavior of amorphous alloys are reflected in the thermo-mechanical Finite Element simulations. Hemispherical deep drawing operations are simulated for various forming conditions such as punch velocity, die comer radius, friction, blank holder force, clearance and initial funning temperature. Here, spring back by an instantaneous elastic unloading was followed by thermal deformation during cooling, and two modes of spring back are examined in detail. It could be concluded that the superior sheet formability of an amorphous alloy can be obtained by taking the proper forming conditions for loading/unloading.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2004년도 춘계학술대회 논문집
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• pp.265-268
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• 2004

In this present study, mechanical properties of the Zr-Ti-Cu-Ni-Be bulk metallic glass are characterized by compression test over a wide range of temperatures and strain rates. Three different types of deformation behavior have been identified as a result, viz., Newtonian viscous flow, non-Newtonian flow and brittle fracture without plastic deformation. A transition state theory is applicable fur the flow stress - strain rate curve that contains the transition from Newtonian to non-Newtonian flow. Based on the relationship between viscosity and strain rate within undercooled liquid state, we can easily obtain the experimental deformation map and suggest the boundaries among different deformation behavior of this alloy.