Hi all,
I'm trying to simulate an initially laminar jet flow and getting it to show
unsteady behavior is proving a bit problematic. Specifically it arises
while adding awgn initial boundary conditions while simataneously trying to
run this case in parallel.
I have attached my xml file for the case but in brief the problem lies with
the initial conditions, which are as follows:
<FUNCTION NAME="InitialConditions">
<E VAR="u" VALUE="1 + 0.0001*awgn(1.0)" />
<E VAR="v" VALUE="0.0001*awgn(1.0)" />
<E VAR="p" VALUE="0.0001*awgn(1.0)" />
</FUNCTION>
When I try to run this upto 10 cpus, the solver works fine and produces the
required output as expected.
However, when I try to run this on greater than 10 cores the case crashes
instantly.
*=======================================================================
EquationType: UnsteadyNavierStokes Session Name:
2d_jet_final_Re_4632 Spatial Dim.: 2 Max SEM Exp. Order:
5 Num. Processes: 20 Expansion Dim.: 2 Projection
Type: Continuous Galerkin Advection: explicit
Diffusion: implicit Time Step: 0.0001 No. of
Steps: 150000 Checkpoints (steps): 1000 Integration Type:
IMEXOrder2 Splitting Scheme: Velocity correction (strong press.
form) Smoothing: SVV (spectral/hp SVV (cut-off = 0.75, diff
coeff =
0.10000000000000001)=======================================================================Initial
Conditions: - Field u: 1 + 0.0001*awgn(1.0) - Field v: 0.0001*awgn(1.0)
- Field p: 0.0001*awgn(1.0)Writing: "2d_jet_final_Re_4632_0.chk"
(0.0232423s, XML)CG iterations made = 5001 using tolerance of 1e-06 (error
= -nan, rhs_mag = 1.6679)Fatal : Level 0 assertion violationExceeded
maximum number of
iterations-------------------------------------------------------Primary
job terminated normally, but 1 process returneda non-zero exit code. Per
user-direction, the job has been
aborted.-------------------------------------------------------*
It seems as if the solver diverges very quickly. What I cannot understand
is why it should fail instantly on running with more processors,
particularly as it seems unconditionally stable for 10 processors. If the
solution were to blow up shouldnt it do so after at least a few iterations?
As you can see, I have also included the SVV option to stabilise the
solution but this seems not to make any appreciable difference.
I'd appreciate some insight into the matter.
--
*Amitvikram Dutta*
Graduate Research Assistant
Fluid Mechanics Research Lab
Multi-Physics Interaction Lab
University of Waterloo