Reply To: Problem during restarting of System Coupling

[sampathsrikanth1999]

Thanks for the reply. My case details are as follows:

Fluent starts to converge after coupling iteration 8. It takes approximately 60 iteration to converge which goes down with the succeding coupling iterations

I have a residual control as 1e-4. Fluent runs for 100 iterations max. The maximum number of coupling iteration is 30.

My major problem is the fsi data transfer to structural. I have set an rms of 0.001 for data transfer. Even after 30 iterations the residual limit is not met.(In some time steps, it is achieved in as low as 12 coupling iterations).  The following is an example at last coupling iteration

                           COUPLING ITERATION = 30                           |
+-----------------------------------------------------------------------------+
| Transient Structural                |                                       |
|   Interface: interface-1            |                                       |
|     Data Transfer                   |         Not yet converged             |
|       RMS Change                    |     6.85E-04          6.54E-03        |
|       Sum x                         |     1.22E-01          1.16E-01        |
|       Sum y                         |     2.65E-01          2.59E-01        |
|       Sum z                         |     4.09E-01          3.89E-01        |
+-----------------------------------------------------------------------------+
| Fluid Flow (Fluent)                 |                                       |
|   Interface: interface-1            |                                       |
|     Data Transfer 2                 |             Converged                 |
|       RMS Change                    |     1.04E-04          1.20E-04        |
|       Weighted Average x            |     4.14E-05          4.14E-05        |
|       Weighted Average y            |     2.15E-04          2.14E-04        |
|       Weighted Average z            |     2.35E-04          2.35E-04        |
+-----------------------------------------------------------------------------+
| Participant solution status         |                                       |
|   Transient Structural              |             Converged                 |
|   Fluid Flow (Fluent)               |             Converged                 |

I think the data transfer is where the problem occurs. I use Quasi-newton stabilzation (0.01) (based on a similar thread in the forum regarding simulation of arteries) and I am ramping up the load to structural with URF 0.5. Without ramping, the structural elements gets highly distorted. Thanks in advance