Hi!
A. The difference between the results is resulting from the lack of
convergence. Since you have specified your real time step a hundred
times larger than your pseudo time step, it is unlikely that 20
iterations (your max) would be sufficient to converge each pseudo steady
state (that is each real time step).
B. Dual time stepping can be used as an acceleration method when used
together with a fast steady state solver. It was added to accommodate
for instance the method of artificial compressibility (incompressible
Navier-Stokes), which is included in the next release.
Best regards,
Niki
On 24/01/17 15:03, CatDog wrote:
Hi, everyone.
I just tested the dual time stepping for euler vortex case in the
examples using following *.ini configuration:
|
[solver-time-integrator]
formulation =dual
scheme =bdf2
pseudo-scheme =tvd-rk3
tstart =0.0
tend =100.0
dt =1
pseudo-dt =0.01
controller =none
pseudo-niters-max =20
pseudo-niters-min =5
pseudo-aresid =1e-5
pseudo-rresid =1e-5
|
It is really fast (4s) comparing with standard time integrator (39s).
|
100.00/100.00ela:00:00:04rem:00:00:00
|
However, the result is different from default setting. The vortex goes
lower in the dual-time stepping case.
dual:<https://lh3.googleusercontent.com/-GXzvC5V4K6c/WIdrpyT6amI/AAAAAAAAFu8/8dQSDiN4E4YQFPtucrVm8J6OqPne_UQcwCLcB/s1600/dual.png>
std:<https://lh3.googleusercontent.com/-lgNIR1Ly9uU/WIdrNLuC0sI/AAAAAAAAFu4/maBfcsazhS08NsErlyoZwd6Qj7RpkGx_ACLcB/s1600/std.png>
I also tried to use pseudo-dt = 0.05 and 0.1 but it resulted in NaN
error. My question is:
a. What is wrong with this euler-vortex case using dual time stepping?
b. What can I expect from using dual-stepping?
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