{"id":364692,"date":"2024-04-29T13:07:33","date_gmt":"2024-04-29T13:07:33","guid":{"rendered":"\/forum\/?post_type=topic&p=364692"},"modified":"2024-04-29T13:07:44","modified_gmt":"2024-04-29T13:07:44","slug":"diverging-amg-solver-in-fluent2024-r1-but-not-in-2019-r2","status":"closed","type":"topic","link":"https:\/\/innovationspace.ansys.com\/forum\/forums\/topic\/diverging-amg-solver-in-fluent2024-r1-but-not-in-2019-r2\/","title":{"rendered":"Diverging AMG Solver in Fluent2024 R1 but not in 2019 R2"},"content":{"rendered":"

Dear Ansys-Forum,<\/p>\n

I have a 2D simulation of a horizontal pipe with a porous zone acting as a catalyst vertically in it. There, a bunch of exothermic reactions (gas species reacting to gas species) are happening, which are solved using the Stiff Chemistry Solver + ISAT.<\/p>\n

The model was initially constructed in Fluent 2019 R2 and is running and converging there without any problems. Now I want to migrate the model into Fluent 2024 R1 and when I do that, I first get the following message:<\/p>\n

Warning: Zero number of gas phase reactions.<\/span><\/em>
Please disable the (gas phase) Stiff Chemistry Solver.<\/em><\/pre>\n
 <\/p>\n
and after around 5 to 60 iterations, the first messages of:<\/p>\n

Integrating chemistry on fluid zone 196 ...<\/em><\/pre>\n
Stabilizing species-1 to enhance linear solver robustness.<\/em>
Stabilizing species-1 using GMRES to enhance linear solver robustness.<\/em><\/pre>\n
 <\/em><\/p>\n
appear only to crash the simulation afterward with the message:<\/p>\n
 <\/p>\n
Divergence detected in AMG solver: species-1
<\/em><\/pre>\n
Error at host: floating point exception<\/em>
Error: floating point exception<\/em>
Error Object: ()<\/em><\/pre>\n
Error at Node 2: floating point exception<\/em><\/pre>\n
 <\/p>\n
Note here: The same message appears for each species, but for simplification, I only copied it of species-1.<\/p>\n
The simulations are both run the same way with the same initialization.<\/p>\n
 <\/p>\n
I played around first with the solution controls relaxation factors for the species, ranging from 1 to 0.1, but this did not help. Additionally, I had a go at the advanced solution controls, but no other cycle-type or stabilization method helped (values of 2019R2 added as pictures; I did not touch the algebraic multigrid controls yet). Furthermore, I tried every species solution method from first order to third with no success. I also switched from ISAT to direct integration with no success.<\/p>\n
The case runs without any problems if I turn off the species transport model. I also tried to load the converged 2019 R2 solution and calculate from there, but here the crash appeared nevertheless.<\/p>\n
Do you guys have any other Idea what could help this case and\/or what changed with the AMG Solver that could lead to such a problem?<\/p>\n
Greetings and thank you.<\/p>\n
<\/p>\n","protected":false},"template":"","class_list":["post-364692","topic","type-topic","status-closed","hentry","topic-tag-2019-r2-1","topic-tag-amg-divergence","topic-tag-ansys-fluent","topic-tag-divergencedetectedinamgsolver-1","topic-tag-divergence-in-amg-solver"],"aioseo_notices":[],"aioseo_head":"\n\t\t\n\t\n\t\n\t\n\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t\n\t\t