As discussed in Using Evolution to Compute Integral Viscoelastic Flow, it is strongly recommended that you define your
viscoelastic flow problem using an evolution scheme. In addition, due to the use of
an uncoupled formulation for the viscoelastic extra stresses and the velocity and
pressure variables, a typical 
step will generally require a larger number of iterations than for
a Newton-Raphson coupled scheme. In order to minimize the CPU time, which can be
quite large for integral viscoelastic simulations (especially if the problem
involves recirculation zones), some modifications to the numerical scheme parameters
are recommended.
It is generally not necessary to perform many iterations with a very small
convergence criterion for a given value of 
. Since many 
steps are required, and the intermediate steps are not physically
meaningful, it is more economical to require a strict convergence tolerance only
when 
reaches its final value. A convergence criterion of 0.01 with 5
iterations is usually used for the intermediate 
steps.
The convergence criterion and the number of iterations can be set in the Numerical parameters menu. See Using the Solver for details.
At the end of the evolution scheme, additional iterations of the integral problem
should be performed in steady-state mode with a lower value for the convergence
criterion. Typically, in order to reach a converged final solution, you should
perform additional iterations with a convergence criterion of 0.001 or 0.0001. You
can accomplish this by executing an additional task after the original task, or by
continuing the Ansys Polyflow calculation starting from the solution obtained at
. This task is referred to as a post-convergence task.
For free surface or moving interface problems, improved numerical stability can be obtained if you decouple the velocity and pressure (and temperature, for nonisothermal flows) variables from the position variables, as described below.
The items in the Numerical integration menu allow you to fine-tune the integration method. These items are not recommended for general use.
In order to solve an integral viscoelastic problem that includes one or more free surfaces or moving interfaces, the following procedure is recommended:
Start the integral viscoelastic task in evolution mode with upwinding on the free surfaces, and use an uncoupled scheme for the moving boundaries. Set the convergence criterion to 0.01, in order to reduce the number of iterations performed.
Solve the post-convergence task by defining the same integral problem in steady-state mode, with upwinding on the free surfaces and an uncoupled scheme for the moving boundaries. Set the convergence criterion to 0.001 to obtain an accurate solution.
In the decoupled approach, Ansys Polyflow computes the velocity and the pressure fields on a fixed domain. Then, based on the fixed velocity and pressure fields, the position of the free surface or moving interface is updated.