ATS timestep debugging

[Lijing Wang]

Hi Ethan, 

I would like to ask a general perspective on the timestep. I am doing cold spin-up and each timestep is around 0.01. I understand that a better practice might be from the 0.1 to 1. But I have a hard time finding where is wrong and what physics that I can improve. 

I am mostly facing converging error for the overland flow. But it seems that after reducing the timestep to the 0.5 of the last step, it converges. Therefore, I would say the physics is ok. 

But still for the model I run (smaller scale), the timestep seems to be very small. What would be a great practice of choosing the timestep? 

Thanks! And thank you for making this great tool available to the community. I really appreciate it! 

Best,

Lijing. 

[Amanzi-ATS Users]

Hi Lijin,

The answer depends completely upon the physics you're solving, along with boundary and initial conditions and parameters.  It sounds like this is on surface+subsurface flow only?  Is this a 3D run or else what is your geometry?  What boundary and initial conditions are you using?  What are the min and max values of permeability and porosity?  All of these (and more) will affect the performance of the code.

Ethan

[Lijing Wang]

Thanks Ethan! I now have a better idea where there is no single rule for the timesteps. I will debug with the boundary/initial condition, mesh complexity and flow PKs. 

Best,

Lijing. 

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Lijing Wang

Postdoc Fellow @ EESA, Berkeley Lab

Ph.D., Stanford University, lijingwang.github.io