Discussion Forum

Hi

The best response you will get from COMSOL support, so I would advice you to contact them directly. I'm just a user, but from my simulations done with two phase flow (level set and phase fields) air + liquid droplet falling by gravity and interacting bouncing back) with a flat surface depending on the surface contact angle settings, indicates for me that COMSOL have everything to simulate your case. An even with the easy to add your own physics.

So for me there is no better tool (that I know about ;)

Nevertheless, you have a complex study to perform, it's a difficult domain with many physics and phenomena, and for "small scale" objects, where our usual understanding of the physics are put to challenge. But it's very interesting, so my only advice, start simple one physics at the time, then couple 2, three ... and be sure you master each physics separately, by exercising several of the Model/Application library cases from COMSOL, then I'm sure you will manage and learn a lot

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Good luck
Ivar

Hi Ivar
Thanks for your reply.
I asked my question for collision of droplet and particle from COMSOL support and here is their response:

"The type of simulation you want to perform is currently falls beyond the
standard usage of COMSOL. We have not confirmed the usage of COMSOL for
such simulations. While it may be possible to set up such a simulation,
this would require an in-depth expertise in the usage of COMSOL and the
contact mechanics between the particle and the droplet, which is not an
in-built functionality such cases. It would therefore require user
expertise in equation based modeling to come up with your own expressions
and modeling strategy for such problems.

In summary, no, this type of problem cannot be readily set up with in-built
capabilities of the software. If you do have any other simulation needs,
please let us know the details.

Best regards,
Chandan Kumar,
COMSOL Applications"

I'd like to know your opinion about this and thanks in advance:
Based on my understanding so far, if I want to simulate this with Comsol, I can use currently available standard features for some parts, but I should also introduce my own equations for others. While I'm not a numeric man, do you think that for those parts that I should adjust Comsol myself, if I read some available Comsol models and also get related equations that I need from literature, then would I be able to come up with a satisfactory model for this case? (also if it's possible for me to get some technical helps from Comsol support in some points as well). Do you think that this way is doable for building an appropriate simulation?

I am know doubting whether it's better to choose Comsol OR another commercial software/code like Fluent or OpenFoam.

Thanks again for your helpful comments,
Sayed

Hi

Certainly the designers of COMSOL know best their limits, and I must probably correct my statement above to something less optimistic, if support has told you that ;)

What is sure COMSOL is best to adapt to most situation, but some models might be very though to implement, when it recalls to customizing the equations.

Yes you will need to know the details of how COMSOL works and understand well the particular physics involved, this will require several months of training I suspect, certainly if you are a new-beginner with this tool, but thereafter you will become an expert :)

But if you are to model such a case I would rather try with COMSOL, than start from scratch with i.e. Matlab and writing code. Because with COMSOL you work at "physics" level of perception, with Matlab, you are first of all in the math coding (noting wrong with that, it's just that you might drown in the coding before coming to the physics ;)

Why not start with a try: a 2D axi case with a rectangle and 2 smaller half circles, one is the fluid "sphere" i.e. the top one, the other your fixed body, the surrounding is air, and you let them interact, by giving a downwards velocity to the fluid "sphere" (velocities are relative at least at low speed, you can always stop one item and simply correct the velocity of the other item to have the same relative velocity between the two items, no ?) And then see how the fluid behaves. You will need to use the 2 phase flow, not sure which to select first, need some tests here, and be careful with the mesh to ensure correct conservation of the mass.
I'm not saying this IS the solution to your demand, but its something you can do with current built-in features. Thereafter you need to knit in your additional equations, one by one.

At least this is how I interpret your demand, but I might have missed an important point, to find out I would need to do the job myself, and sorry that is outside what I can afford of my time. But you have a nice and challenging subject there !

I must also admit I'm become somewhat biased with time, as I have dropped most other FEM tools and do all my simulations in COMSOL as so far I have not yet hit a limit ! something that happened with our older tools, about a decade ago

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Good luck
Ivar