Schröder–Hipparchus number: Difference between revisions

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en>David Eppstein
Related sequences: I think Row vector is a better choice, because we're not imposing an artificial basis on a space that doesn't already have one
 
en>David Eppstein
m link more journals while I'm at it
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The '''Oldroyd-B model''' is a constitutive model used to describe the flow of [[viscoelastic]] fluids.
This model can be regarded as an extension of the [[Upper Convected Maxwell model]] and is equivalent to a fluid filled with elastic bead and spring dumbbells.
The model is named after its creator [[James G. Oldroyd]].


The model can be written as:
:<math> \mathbf{T} + \lambda_1 \stackrel{\nabla}{\mathbf{T}} = 2\eta_0 (\mathbf{D} + \lambda_2 \stackrel{\nabla}{\mathbf{D}}) </math>
where:
* <math>\mathbf{T}</math> is the [[Stress (physics)|stress]] [[tensor]];
* <math>\lambda_1</math> is the relaxation time;
* <math>\lambda_2</math> is the retardation time = <math> \frac{\eta_s}{\eta_0}\lambda_1 </math>;
* <math> \stackrel{\nabla}{\mathbf{T}} </math> is the [[Upper convected time derivative]] of stress tensor:
:<math> \stackrel{\nabla}{\mathbf{T}} = \frac{\partial}{\partial t} \mathbf{T} + \mathbf{v} \cdot \nabla \mathbf{T} -( (\nabla \mathbf{v})^T \cdot \mathbf{T} + \mathbf{T} \cdot (\nabla \mathbf{v})) </math>;
*<math>\mathbf{v}</math> is the fluid velocity;
*<math>\eta_0</math> is the total [[viscosity]] composed of solvent and polymer components, <math> \eta_0= \eta_s + \eta_p </math>;
*<math>\mathbf {D}</math> is the deformation rate tensor or rate of strain tensor, <math>\mathbf{D} = \frac{1}{2}\left[\boldsymbol\nabla \mathbf{v} + (\boldsymbol\nabla \mathbf{v})^T\right]</math>.


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The model can also be written split into polymeric (viscoelastic) part separately from the solvent part:
<math> \mathbf{T} = 2\eta_s \mathbf{D} + \mathbf{\tau} </math>.
 
where
:<math> \mathbf{\tau} + \lambda_1 \stackrel{\nabla}{\mathbf{\tau}} = 2\eta_p \mathbf{D} </math>
 
 
 
 
Whilst the model gives good approximations of viscoelastic fluids in shear flow, it has an unphysical singularity in extensional flow, where the dumbbells are infinitely stretched;
If the solvent viscosity is zero then the Oldroyd-B becomes the [[Upper Convected Maxwell model]].
 
 
==References==
* {{cite journal|last=Oldroyd|first=James|title=On the Formulation of Rheological Equations of State|journal=Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences|year=1950|month=Feb|volume=200|issue=1063|pages=523–541}}
 
* {{cite book | author=Owens, R. G.,Phillips, T. N.| title=Computational Rheology.| publisher=Imperial College Press | year=2002 | isbn=978-1-86094-186-3}}
 
[[Category:Non-Newtonian fluids]]

Revision as of 07:05, 23 October 2013

The Oldroyd-B model is a constitutive model used to describe the flow of viscoelastic fluids. This model can be regarded as an extension of the Upper Convected Maxwell model and is equivalent to a fluid filled with elastic bead and spring dumbbells. The model is named after its creator James G. Oldroyd.

The model can be written as:

T+λ1T=2η0(D+λ2D)

where:

T=tT+vT((v)TT+T(v));

The model can also be written split into polymeric (viscoelastic) part separately from the solvent part: T=2ηsD+τ.

where

τ+λ1τ=2ηpD



Whilst the model gives good approximations of viscoelastic fluids in shear flow, it has an unphysical singularity in extensional flow, where the dumbbells are infinitely stretched; If the solvent viscosity is zero then the Oldroyd-B becomes the Upper Convected Maxwell model.


References

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