Learning Forum

[M. Namaki]

I'm currently working on a simulation in ANSYS AQWA (2023 R2) and have encountered a persistent issues that I’d like to better understand and resolve.

I receive the warning:

"JACOBI: Failed to Converge."

This appears during the simulation, but the documentation does not provide much context. I would appreciate any insight into what causes this issue and how to resolve it. 

I need to add that the simulation involves multiple hydrodynamically interacting structures. the project completes successfully despite the warnings, but I would prefer to clean up these issues for better accuracy because I do not trust the results. 

Any advice or suggestions from experienced users would be greatly appreciated.

[Mike Pettit]

Hello,

What type of analysis are you running when this warning occurs? Is this in Hydrodynamic Diffraction, or one of the Hydrodynamic Response calculations?

Mike

[M. Namaki]

Hello Mike,

I encounter this issue during the hydrodynamic response calculations. My setup includes several hydrodynamic bodies, each connected to a single main body through individual joints.

Thank you very much for your assistance.

[Mike Pettit]

Hello,

Generally there are a few places during the solution where we try to find the eigenvalues/eigenvectors of a matrix, which we do using a Jacobi iteration method. Please can you clarify exactly when the JACOBI warning appears? Is this during a Stability Analysis, Frequency Response Analysis or Time Response Analysis? Do you notice anything unusual or unrealistic about the results?

Mike

[M. Namaki]

Hello,

I encounter this error during Time Response Analysis. I am trying to find the response of a platform under regular wave loading but the result is much bigger than usual and beyond the reasonable amounts.

[Mike Pettit]

Thank you. Can I also ask how many Wave Frequencies you have included in the Hydrodynamic Diffraction analysis? If the number of frequencies in the hydrodynamic database is relatively small, then the simulation will generally be improved by increasing this, though I can't say for sure that this will fix the JACOBI warnings.

Regarding the motion response of the platform, please bear in mind that Aqwa does not directly account for viscous effects in the solution. This means that damping is usually underestimated, and it is therefore a good idea to introduce some additional damping - this can be linear (e.g. Additional Damping matrix, which is included in the Hydrodynamic Diffraction analysis) or nonlinear (e.g. Morison Hull Drag coefficients, which are only included in Hydrodynamic Response analyses).

Mike

[M. Namaki]

  

[M. Namaki]

Thank you for your response. Even with the maximum number of frequencies (98), I still encounter the same warning and the issue remains unresolved. Are there any alternative ways to address my motion response problem? I would prefer not to use additional damping, as I am unsure of the appropriate damping values for a realistic case.

I believe that solving this issue, along with another one I previously mentioned in this linked discussion (for which I have not yet found a suitable solution), could help resolve the problem.