CFX-10 - Adaptive Time Stepping

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 September 28, 2005, 06:22 CFX-10 - Adaptive Time Stepping #1 James Date Guest   Posts: n/a Sponsored Links 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
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 September 28, 2005, 08:52 Re: CFX-10 - Adaptive Time Stepping #2 Ribeiro Guest   Posts: n/a 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,

 September 29, 2005, 05:16 Re: CFX-10 - Adaptive Time Stepping *NM* #3 banjara kotresha Guest   Posts: n/a

 October 17, 2005, 22:15 Re: CFX-10 - Adaptive Time Stepping #4 Neale Guest   Posts: n/a 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

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