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Help on level set method

Posted 28 set 2009, 13:11 GMT-4 5 Replies

PENG LIAN
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Dear Friend:

I'm just starting to learn modeling using COMSOL. My research now involves modeling of liquid/gas two phase flow. So I started with this water droplet formation from a capillary downward. But so far I can not get it converged. Can anyone who is familiar with this area help me take a look at this problem and hopefully give me some advice?

Thank you very much,
Regards,
Peng

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5 Replies Last Post 4 nov 2009, 09:56 GMT-5
Soufiane Oukach
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Posted: 1 decade ago 16 ott 2009, 17:36 GMT-4
Kjetil Birkeland Moe
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Posted: 1 decade ago 30 ott 2009, 06:09 GMT-4
How do you reinitialize at every time step? Isn't this a process being done only at the very beginning? I am trying to do a two-phase phase field case .. but that doesn't converge either.
How do you reinitialize at every time step? Isn't this a process being done only at the very beginning? I am trying to do a two-phase phase field case .. but that doesn't converge either.
Ivar KJELBERG COMSOL Multiphysics(r) fan, retired, former "Senior Expert" at CSEM SA (CH)
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Posted: 1 decade ago 1 nov 2009, 03:56 GMT-5
Hi

I have understood (but I have only followed one training course , hav'nt worked on these solutions extensively) that these kind of problems needs first an "initialisation phase" (short time step) to set up correctly the physics, then you turn on longer time steps analysis.

In your model there is only the initialisation

You can automatise this in the Solver Manager Sequence tab, by first saving a "Transient Initialisation" sequence for a short start up time, save the solution, and then follow by a standard "transient" calculation, but based on the saved values (set up your Solver Parameters correctly for this second phase).

There are a few examples in the doc, and others in the standard models. You need to get aquinted with the solver settings, multiple sequenced solving and the secondary tabs, this takes some training.

It will all be shown in another sequence logic in V4. I'm not sure it will be easier for the new-beginners, but certainly more logical for those of us feeling more familiar with COMSOL and its way to do physics, which is quite different from classical FEM methods limited to a single physics were everything is predefined ready.

Good luck
Ivar
Hi I have understood (but I have only followed one training course , hav'nt worked on these solutions extensively) that these kind of problems needs first an "initialisation phase" (short time step) to set up correctly the physics, then you turn on longer time steps analysis. In your model there is only the initialisation You can automatise this in the Solver Manager Sequence tab, by first saving a "Transient Initialisation" sequence for a short start up time, save the solution, and then follow by a standard "transient" calculation, but based on the saved values (set up your Solver Parameters correctly for this second phase). There are a few examples in the doc, and others in the standard models. You need to get aquinted with the solver settings, multiple sequenced solving and the secondary tabs, this takes some training. It will all be shown in another sequence logic in V4. I'm not sure it will be easier for the new-beginners, but certainly more logical for those of us feeling more familiar with COMSOL and its way to do physics, which is quite different from classical FEM methods limited to a single physics were everything is predefined ready. Good luck Ivar
Kjetil Birkeland Moe
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Posted: 1 decade ago 1 nov 2009, 10:38 GMT-5
Yes, and I have been following these initialization steps closely. I have a uniform grid, and the initialization sesms to work fine - but the simulations simply doesn't converge. And this is a pretty simple 2D-case.

Well, I attach my test-case here. Feel free to have a look - it is a fairly simple two phase inlet-outlet flow with 20% volume fraction gas in. And that's it. Still, it doesn't converge at all ....
Yes, and I have been following these initialization steps closely. I have a uniform grid, and the initialization sesms to work fine - but the simulations simply doesn't converge. And this is a pretty simple 2D-case. Well, I attach my test-case here. Feel free to have a look - it is a fairly simple two phase inlet-outlet flow with 20% volume fraction gas in. And that's it. Still, it doesn't converge at all ....

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Kjetil Birkeland Moe
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Posted: 1 decade ago 4 nov 2009, 09:56 GMT-5
I reply to my own post, after having confronted the Comsol-support desk, and I am now instead using bubbly flow, and I am at least one step closer to getting my 3D-case to work. The phase field does not seem to be the right solver for my case anymore ...
I reply to my own post, after having confronted the Comsol-support desk, and I am now instead using bubbly flow, and I am at least one step closer to getting my 3D-case to work. The phase field does not seem to be the right solver for my case anymore ...

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