[Alhasan]

Hey FOAMers,

I am having a simple 2D airfoil case I have been trying to do mesh dependency test, but with the same boundary conditions I am getting drastically different Cl, Cd for all the cases with different mesh, I have made the mesh with utmost care. Apart from that few cases with reasonably dense meshes are getting stuck without any error at one iteration what could be the reason. It can't be the computer because the cases are on the HPC.

Time = 160052

smoothSolver:  Solving for Ux, Initial residual = 1.14095e-05, Final residual = 7.49989e-09, No Iterations 12
smoothSolver:  Solving for Uy, Initial residual = 1.34364e-05, Final residual = 8.83883e-09, No Iterations 12
GAMG:  Solving for p, Initial residual = 5.67128e-05, Final residual = 9.85634e-08, No Iterations 11
time step continuity errors : sum local = 1.98112e-07, global = 3.63618e-14, cumulative = 1.88178e-12
smoothSolver:  Solving for omega, Initial residual = 3.84661e-07, Final residual = 9.65063e-09, No Iterations 6
smoothSolver:  Solving for k, Initial residual = 1.53943e-05, Final residual = 5.46731e-09, No Iterations 13
ExecutionTime = 1227.14 s  ClockTime = 1561 s

forces output:
    forces(pressure, viscous)((-2.20311e+06 5.95228e+07 1.22269e-14) (-30247.5 2173.54 6.53313e-18))
    moment(pressure, viscous)((-5.75432e-17 -2.17177e-16 -8.19743e+06) (-1.38678e-20 1.70345e-18 -683.179))

forceCoeffs output:
    Cd = -248.151
    Cl = 6613.89
    Cm = -1.19707e-19

Time = 160053

smoothSolver:  Solving for Ux, Initial residual = 1.14094e-05, Final residual = 7.49987e-09, No Iterations 12
smoothSolver:  Solving for Uy, Initial residual = 1.34364e-05, Final residual = 8.83881e-09, No Iterations 12

some cases get stuck forever but some cases after couple of hours move the next time step and get stuck there but still the No iterations of was 11 only moreover i also have

minIter          5;
maxIter          100;

to make sure it is not the no of iterations that is delaying it.

I have no idea why the case is literally getting stuck !!! first time im coming across this problem in 2 years any idea
Thanks for your reply,
Hasan K.J

[Alhasan]

If anybody comes across the same problem the problem is the reltol,

I don't know what I was thinking the cases that were getting stuck that I had said had reltol to 0 it was fv sol,schemes from my old cases in which I had changed the reltol as the case was converging but I had used the same reltol to initiate the case here which caused the slow down and getting stuck

now i have changed the reltol to 0.1 will slowly increase it to 0.01, 0.001 etc as the case converges.

changing the relTol solved my problem

Thanks for your time,
Hasan K.J

[RMacReamoinn]

Hi,

I think I am suffering from the same problem but I am not sure how to rectify it. I am running a simple 2D pimpleFoam simulation with a uniform grid in parallel on a Linux cluster. Initially, I had set the relTol to zero for pressure (p, pFinal) and velocity (UFinal) because I wanted my simulation to converge to the tolerance I had set for each parameter. However, having read the above post, I set the relTol to the same as the tolerance value so that it would still converege to this value. Although I took more iterations before the node hanged, the node did hang. No error file or error message in the output file. The log file stops in the middle of running. The only output I receive occurs when I try to kill the job on the cluster and I get the following message:

qdel: Server could not connect to MOM 43195.scyld.localdomain

I am running the simulation on a single node with 16 processors. There are no other simulations running on this node. I checked the memory available for running the simulation and there is plenty. There is also plenty of storage space available too. I have read elsewhere that this error tends to occur when the stack is full but I am unsure how OF uses the stack in parallel. This is a constantly recurring problem for me and I never know when it is going to surface. If anyone can give me advice on how I should setup my simulation to avoid this occuring I would really appreciate it.

I have attached my OF files for information.

[XJ_Wang]

Hi Reamonn,

Did you solve your problem?

I hope you can see my message after five years....

Bests,
Xiangjie