= Phan-Thien-Tanner fluid
{c}
= PTT fluid
{c}
{synonym}
The affine linear PTT fluid considered here uses a symmetric dimensionless tensor $A$ with $\overset\nabla A+(1+\alpha\operatorname{tr}A)A/\tau=2E$ and polymer <stress> $G_0A$. Here $\overset\nabla A$ is the <upper-convected derivative>, $G_0,\tau>0$ and the nonlinear relaxation parameter $\alpha$ is usually positive. Linearizing about rest gives the <Maxwell fluid> <relaxation modulus> $G(s)=G_0e^{-s/\tau}$. The PTT family also admits other relaxation functions and nonaffine derivatives; their nonlinear predictions need not equal those of this specified version.
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