[aspect-devel] Prescribed stokes flow and the time step

[Harsha Lokavarapu]

Hi all,

I am a junior specialist at CIG and recently, we have accumulated solution data (VTU format) for a 2-D domain of 4root(2) by 1 at a Rayleigh number of 1e7 on Stampede.
This was ten days worth of computational time on 256 processors totaling approximately 3 TBs of solution data. Given the data, we reran aspect using 
the prescribed stokes plugin starting with the solution data at the 80,000th time step number all the way to the 90,000th time step number of the run on Stampede with a layer of uniformly placed particles in the top three percent of the domain. After examining the output, we immediately saw that the flow and particles were not synced. We have narrowed the problem down to the difference in the time step (or delta T between two consecutive time step numbers) between the original and the second run.
One attempt at a solution was to set the start time of the second run to the same value as that of the time at the 80,000th time step number in the statistics file of the first run. Although initially there was little to no deviation in time step between the two runs, by the 200th time step number, it was clear that this wasn’t viable. The other thought we are contemplating is to read in an ascii file that consists of the time step at each time step number as part of the prescribed stokes plugin. By then setting the start time as well and adding the time steps for each time step number, we are certain that the displacement of particles at each time step number will be correct even if we begin at any time step of the original run. Is this the right method of solving this problem?  Does such functionality already exist within ASPECT? If not, I could really use another perspective on this.

Thanks for reading,
-Harsha

P.s.

Also, another thread I am investigating is using the VTK library to extract the time from each solution.pvtu file. All I have found are meta data with "modified time” field being the closest to what I am looking for. Do you have experience with using the VTK library?