Create a sub-task for the simplified viscoelastic flow problem.

  Create a sub-task

1. Select the appropriate problem from the Create a sub-task menu.

     Simplified viscoelastic isothermal flow problem

   or

     Simplified viscoelastic non-isothermal flow problem

2. When prompted, specify a name for the sub-task.

Specify the region where the sub-task applies.

  Domain of the sub-task

Define the material properties.

  Material data

1. Define the shear rate dependence of the viscosity.

   See the corresponding step 3.(a) in General Procedure for the definition of the shear rate dependence of the viscosity.

2. For nonisothermal flows, define the temperature dependence of the viscosity.

   See the corresponding step 3.(b) in General Procedure for the definition of the temperature dependence of the viscosity.

3. If inertia, heat convection, or natural convection are to be taken into account in the calculation, define the density, inertia terms, and gravity.

   See the corresponding step 3.(c) in General Procedure for the definition of density, inertia terms, and gravity.

4. Set any other relevant material properties (such as thermal conductivity, heat capacity, or the thermal expansion coefficient).

   See the corresponding step 3. in General Procedure for the definition of nonisothermal parameters.

5. Define the simplified viscoelastic model.

     Simplified viscoelastic model

   1. Define the first normal viscosity.

        First normal viscosity

      By default, the first normal viscosity is described with the same function as the shear viscosity, and involves the same parameters. Select Switch to “Not linked to shear rate viscosity" if you want to specify another function for the normal viscosity, and select the required function with the numerical parameters accordingly.

   2. Define the weighting coefficient.

        Weighting coefficient

      It may be appropriate to apply an evolution strategy on the weighting coefficient (which can be positive or zero). A ramp function can be a good choice.

   3. Define the shear rate dependence of the relaxation time.

        Shear rate dependence of relaxation time

      By default, the relaxation time is vanishing. A Bird-Carreau or a power law can be selected for describing the shear rate dependence. For flow simulations involving the prediction of extrudate, you should consider a Bird-Carreau law, as it is bounded at vanishing shear rates.

   4. Specify the temperature dependence for the relaxation time.

        Switch to H(T) applied on relaxation time

      By default, the relaxation time does not depend on the temperature for nonisothermal flows. Select Switch to “H(T) applied on relaxation time" if you want the same temperature dependence as defined for the shear and normal viscosities.

Define the flow boundary conditions.

  Flow boundary conditions

See Boundary Conditions for details, and Using Evolution to Compute Generalized Newtonian Flow for suggestions about using evolution on boundary conditions.

For nonisothermal flows, define the thermal boundary conditions.

  Thermal boundary conditions

See Boundary Conditions and Problem Setup for details.

For free surface flows, define the remeshing method.

  Global remeshing

See Free Surfaces and Extrusion for details.

Define the interpolation.

  Interpolation

The motivation for using the simplified viscoelastic model is to quickly provide (qualitative) results on extrudate swelling, for both 2D and 3D flow simulations. Hence it is reasonable to select the most computationally inexpensive interpolation for the calculated fields (velocity, pressure, viscoelastic variable, temperature). By default, linear interpolation is used for the velocity and the viscoelastic variable within the context of the simplified viscoelastic model. While other interpolations are available and can be invoked, they will lead to an increase in the calculation time.