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Continuous vs interrupted simulation

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Old   November 3, 2008, 08:46
Default Hello World. I made a stran
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Sebastian Gatzka
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Hello World.

I made a strange experience some days ago.
I started a two-phase-flow simulation not knowing how long it will take so reach its final equilibrium state.

My first, second and third guesses of the simulation time were too short.
In all cases I restarted the calculation by putting the latest time into the startTime entry.

Due to insufficient disc space I had to recalculate the simulation on another system.
As a matter of fact I knew the correct simulation time and simulated straight from 0 to the final timestep.

I compared a characteristic value of the two simulations (magU in this case) and found that they differ over time!

Interrupted simulation:



Continuous simulation:



Strange to me are the tree peaks at the interrupted simulation plot.
They are not exactly at but following a short time after the three interruption-times.

What went wrong? Did I made something wrong?
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Old   November 3, 2008, 10:18
Default did you write your data as asc
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did you write your data as ascii or binary?
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Old   November 3, 2008, 12:49
Default Ascii in both cases.
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Ascii in both cases.
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Old   November 3, 2008, 14:27
Default Use binary, and run in double
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Use binary, and run in double precision.
Your restart will behave much better!
I guess this is what Niklas was thinking of...

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Old   November 3, 2008, 15:29
Default It is http://www.cfd-online.co
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It is

restarting in ascii files is nasty business.
You lose alot of the accuracy, which you just have witnessed I guess.

I still remember the trouble I faced when I was implementing the spray and saved the data in ascii...

If a drop is close to a face it might actually end up in another cell when you do a restart, because of the round-off errors.

would be nice to see what you got when you use binary.
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