Oldroyd-A model

The Oldroyd-A model is the lower-convected counterpart of the Oldroyd-B model: its polymeric stress evolves using a lower-convected derivative.

For constant simple shear flow rate $s$, the nonpressure stress in the component-first gradient convention $L_{12}=s$ isThus the first normal-stress difference is $N_1=2(\mu -{\mu }_r)\tau s^2$, while the second is $N_2=-N_1$. Adding the incompressibility pressure changes neither difference.

Put $S={\sigma }^d-2{\mu }_{r}D$ in the Oldroyd-A model. It obeys ${\mathcal{D}}_{l}S+S/\tau =2(\mu -{\mu }_r)D/\tau$. Pulling back as $F^{T}SF$ converts this to an ordinary linear relaxation equation. With decayed remote-past initial memory, its solution isAt a finite initial time, include the homogeneous transported term $e^{-(t-t_0)/\tau }F(t{)}^{-T}F(t_0{)}^{T}S(t_0)F(t_0)F(t{)}^{-1}$. The integral-only law is not equivalent to all arbitrary initial-value solutions without a memory condition.