Error: No Convergence in Nonlinear Thermal Simulation

What Happened?

The nonlinear thermal solver was not able to achieve convergence of the numerical solution.

What Could Be the Possible Reason?

When solving the nonlinear thermal problem, the solver was not able to find a converging solution under the given conditions of maximum allowed residual and time step size. In other words, there was a temperature change at some point that is too large to be captured in the given time step within the allowed relative change. Possible reasons could be:

1. Invalid or nonphysical boundary conditions
2. Invalid material model.
3. Maximum allowed residual is too small.
4. Time step is too large.

What Can I Do Now?

In order to try and achieve convergence in the nonlinear thermal simulation, and according to the stated possible reasons above, please implement the following actions:

1. Review all the boundary conditions and material properties for the magnitude of parameters, consistency of units, physical validity, and confirm that all values are realistic.
2. Increase the value of Tolerance under Numerics. Turning on ‘Thermal line search‘ can also help in this case. See Figure 1 below.
3. If performing a nonlinear transient thermal simulation, decrease the value of Time step length (see Figure 2 below). Bear in mind the times of changes in the boundary conditions, and choose a time step small enough to capture those changes.