Learning Forum

[helen.durand]

Hello, I am simulating a coupled transient thermal and transient structural simulation. In the transient thermal simulation, I have an APDL variable representing the amount of heat applied to the surface of the geometry. If I run the thermal simulation with a very small amount of applied heat, this results in a temperatures that are just slightly above the initial temperature.

Then after doing this, improrting the results to transient structural, and running the structural simulation, I get this warning:

 *** WARNING ***                         CP =      42.188   TIME= 12:31:40
 A reference force value times the tolerance is used by the              
 Newton-Raphson method for checking convergence.  The calculated         
 reference FORCE CONVERGENCE VALUE = 1.728813387E-05 is less than a      
 threshold.  This threshold is internally calculated.  You can           
 overwrite it by specifying MINREF on the CNVTOL command.  Check         
 results carefully.    

What does this warning mean?

[John Doyle]

This warning is alerting you that the structural force convergence value used in the Newton-Raphson Procedure is very small. This can happen when applied loads are very small or zero. It is just a warning. If your model convergences successfully, and everything balances, you can probably ignore it. If you are having convergence troubles, the warning is a clue that this might be part of the problem.

The MINREF field of the CNVTOL command is a default minimum value designed to prevent the code from attempting to converge on a nearly zero tolerance.   You can read more about the Newton-Raphson Procedure in Section 14.10 of the MAPDL Theory Manual. Refer also to the online docs for CNVTOL Command in the MAPDL Commands Manual.

[helen.durand]

Thank you!