CFD Online Discussion Forums

CFD Online Discussion Forums (http://www.cfd-online.com/Forums/)
-   CFX (http://www.cfd-online.com/Forums/cfx/)
-   -   CFX-10 - Adaptive Time Stepping (http://www.cfd-online.com/Forums/cfx/21653-cfx-10-adaptive-time-stepping.html)

James Date September 28, 2005 06:22

CFX-10 - Adaptive Time Stepping
 
Can anyone explain how the adaptive time stepping control values work. I've had a play but they don't seem to be doing what i expect! I assume the relaxation factors are meant to relax the time steps from one iteration to another? This doesn't seem to be happening in my simulation by the factors specified! Any answers guys?

SIMULATION TYPE:

Option = Transient

INITIAL TIME:

Option = Automatic with Value

Time = 0 [s]

END

TIME DURATION:

Option = Total Time

Total Time = 1.25 [s]

END

TIME STEPS:

First Update Time = 0.0 [s]

Initial Timestep = 0.005 [s]

Option = Adaptive

Timestep Update Frequency = 1

TIMESTEP ADAPTION:

Courant Number = 0.75

Decreasing Relaxation Factor = 1.0

Increasing Relaxation Factor = 0.5

Maximum Timestep = 0.01 [s]

Minimum Timestep = 0.00001 [s]

Option = MAX Courant Number

END

END

END


Ribeiro September 28, 2005 08:52

Re: CFX-10 - Adaptive Time Stepping
 
Hi James,

These relaxation factors work like other relaxation factors. The solver will try to reach the timestep which satisfy the Courant Number condition (in your case, 0.75 MAX) but the solver will do this finding a increasing (or decreasing) factor. This factor is multiplied by the relaxation factor in order to obtain a more conservative factor. That's the idea.

Regards,

banjara kotresha September 29, 2005 05:16

Re: CFX-10 - Adaptive Time Stepping *NM*
 

Neale October 17, 2005 22:15

Re: CFX-10 - Adaptive Time Stepping
 
With this setup the solver will reduce the timestep without under realaxtion, but increase it with under relaxation of 0.5.

The raw deltat (for the next timestep) is obtained by multiplying the old deltat by the the factor (target courant number)/(last courant number) to force the deltat used for the next timestep to give your specified target.

Neale


All times are GMT -4. The time now is 16:38.