Rahul
Ansys Employee

Hello 

Ensure that your participant solution solved alone works well before coupling.

If the coupled run fails:
‐ Find out which solver failed first – look at all the output files to determine where the error started
‐ Check the mapping
‐ If MAPDL, were reasonable forces / thermal loads received?
‐ If Fluent, were reasonable displacements / thermal loads received?
‐ Were the individual field solvers converging?
‐ If a run fails in the first few time steps, re-run for a limited number of time steps and/or with a limited 
number of Coupling Iterations so that you can generate results files and examine the result

Also, refer to: Building a Coupled FSI Analysis from Decoupled Participant Problems (ansys.com)

Improving the Accuracy of Transient Analyses (ansys.com)

Improving Coupled Analysis Stability (ansys.com)