How to solve an implicit equation for non-newtonian fluid viscosity. An algebraic equation can not be applied here, as the solver processes the following steps when evaluating an expression for viscosity:

1. Solver recognises, that viscoity is needed as variable to solve the expression.
2. The solver calls getvar.
3. getvar looks for the viscosity.
4. Recognizes that there is no viscosity to put into the expression.
5. Solver looks into the material properties and finds the expression for the viscosity. Now, Solver proceeds with step 1. and comes into a circle.

The viscosity of the old iteration has to be provided to the solver. Therefore the viscosity of the last iteration has to be stored in the MMS to mask the circularity which would occur by getvar.

A junction box, which writes the actual values of the viscosity into the MMS at the end of the coefficient loop
A user cel routine, which reads the viscosity values out of the MMS and stores it into an Additional Variable (AV).
This AV is used as viscosity of the old iteration in the expression for the viscosity.

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