Discussion Forum

Steve-

One solution would be to divide your problem into two time-dependent steps in separate studies:

1) Study 1 - Step 1 - Solve for 0 to 1 sec
2) Study 2 - Step 1 - Solve for 1 to 2 sec (using solution from Study 1 as "Initial values of variables solved for")

Compute both studies in series.

Then, you are free to clear the solutions from Study 1 while retaining results in Study 2 for post-processing.

You may also consider reducing the number of Times requested for ranges you will not be post-processing -- this is another simple way of reducing file sizes. For example, use this as the Times request:

0 range(1,0.1,2)

This will only store the solution for 0 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 and 2 sec.

With this method, accuracy will not be affected unless you are relying on Strict or Intermediate time stepping to govern the error. By default, the absolute and relative tolerances will force the solver to solve at finer time steps -- even though you are not storing the solution at these increments.

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Best regards,
Josh Thomas
AltaSim Technologies

Thanks, Josh

I first implemented it as two studies, but these results are used to compute flows for a subsequent mass transport step, which was also two studies. Four studies seemed a bit unwieldy and a lot of interaction, hence the question. It is a large 3D FSI problem that takes about 20 hours to solve. By using a single study, I can solve with two steps (flow and mass transport) in the single study with no interaction. I apologize for not describing the full project, but I was aiming for simplicity.

I also thought about your approach of limiting the time studies in the first half, but I need a full set of results from all of the flow steps in order to properly calculate the mass transport. I also looked at solving flow and mass transport simultaneously which would let me use the approach of reducing the time steps, but this greatly extended the solution time.

For ease of interaction I'll probably just keep the single step and live with a large dataset. I did reduce my storage requirements some by only storing those field variables i really needed to post-process. This reduced storage requirements by 30%.

Thanks for your time!

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Steven Conrad, MD PhD
LSU Health

Steve-

Glad to hear you have found an acceptable solution -- albeit maybe not an ideal one.

A side issue perhaps but...

In terms of running multiple studies automatically, have you seen the Study Reference feature? For example, if you have two studies in a model you would like to run sequentially -- you can add a third study and then add two "Study Reference" nodes that reference Study 1 and Study 2 in sequence. Then, when you click "Compute" on Study 3 it will execute Study 1 and Study 2 in sequence automatically with no additional user interaction required. (See attached image).

This technique may re-open the door for the double-study option being useful for you.

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Best regards,
Josh Thomas
AltaSim Technologies

Hi,

Note that for many models you can reduce the file size significantly by a couple of changes in the Time-Dependent Solver node:

In the Output section, you can clear 'Store reaction forces' and 'Store time derivatives' (assuming that you do not need these results). Not storing the time derivatives will often reduce the file size by 40 to 60%.

Regards,
Henrik

Thanks, Josh, I had just come across the Study Reference feature. I've been using COMSOL since FEMLAB 2.3, but I overlooked this addition when it was introduced, or perhaps I saw it and didn't know how I might use it. I've added a 5th study to calculate a parabolic flow profile over a non-planar boundary for one of my boundary conditions.

Thanks, Henrik, I don't need the reaction forces or derivatives stored, so that would be a good complementary way to reduce storage further. I wasn't aware of this option.

I'll be presenting this work at COMSOL Boston (if my abstract gets accepted), so thanks again for the help.

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Steven Conrad, MD PhD
LSU Health

Good luck! See you in Boston!

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Best regards,
Josh Thomas
AltaSim Technologies