As discussed in Under-Relaxation, Ansys Icepak uses under-relaxation to control the update of computed variables at each iteration. This means that all equations solved using Ansys Icepak will have under-relaxation factors associated with them.

You can set the under-relaxation factors in the Advanced solver setup panel (Figure 36.2: The Advanced solver setup Panel).

  Solution settings   Advanced settings

(or Solve Settings Advanced)

The value of the "under-relaxation factor" for each of the equations that Ansys Icepak solves is specified under Under-relaxation in the Advanced solver setup panel. Because of the nonlinearity of the equation set, it is necessary to reduce the change of a variable from one iteration to the next. This is referred to as under-relaxation. For example, if the pressure under-relaxation factor is 0.3, the change in pressure value from one iteration to the next will be restricted to 30% of the difference between the initial value and the newly calculated value.

In Ansys Icepak, the default under-relaxation parameters for all variables are set to values that are near optimal for the largest possible number of cases. These values are suitable for many problems, but for some particularly nonlinear problems (for example, some turbulent flows or high-Rayleigh-number natural-convection problems) it is prudent to reduce the under-relaxation factors initially. If you click Reset in the Basic settings panel (Figure 36.3: The Basic settings Panel), Ansys Icepak adjusts the under-relaxation factors to values that are recommended for the type of problem you are trying to solve.

It is good practice to begin a calculation using the default settings in the Advanced solver setup panel. For most flows, the default under-relaxation factors do not usually require modification. If the solution exhibits unstable or divergent behavior, you may need to modify the under-relaxation factors; however, inappropriate under-relaxation factors may decrease the rate of convergence for your problem. If your solution displays divergent behavior, contact your technical support engineer.