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Surface tension effects on a free boundary

Posted Nov 21, 2012, 7:48 p.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD) Version 4.3a 4 Replies

Shawn.F
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Dear all,

In COMSOL website, there is a model for "Square Droplet Oscillations under Surface Tension". In this model, instead of two phase flow modeling, ALE and single phase flow have been combined, and the effects of surface tension has been introduced in a weak form. the model has been developed in COMSOL3.5 in 2D axi-symmetric.

The surface tension effects are introduced over the free surfaces of the droplet for "u" and "v" components of the velocity in weak form as:

for "u" (r direction) => -(surface_tension)*(r*test(uTr)+test(u))
for "v" (z direction) => -(surface_tension)*r*test(vTz)

Now, I would like to do the same thing in COMSOL4.3, But the problem is that I have no idea how to define directional weak forms. When I add a boundary weak contribution it asks for just one expression regardless of any direction, and unfortunately I am not expert in weak form equations.

Could anyone give me any hint about this, it would be highly appreciated.

Regards,

Shawn
4 Replies Last Post Nov 27, 2012, 12:15 p.m. EST
Daniel Smith COMSOL Employee

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Posted: 1 decade ago Nov 26, 2012, 10:10 a.m. EST
The Microfluidics Module contains a ready made interface which uses the ALE method to model two-phase flows. Free surfaces can exist on interior or exterior boundaries. I recommend you use the Microfluidics Module to solve the type of problem you describe:

www.comsol.com/products/microfluidics/
The Microfluidics Module contains a ready made interface which uses the ALE method to model two-phase flows. Free surfaces can exist on interior or exterior boundaries. I recommend you use the Microfluidics Module to solve the type of problem you describe: http://www.comsol.com/products/microfluidics/
Shawn.F
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Posted: 1 decade ago Nov 26, 2012, 2:15 p.m. EST

Daniel, thank you for the hint.

But, I cannot find microluidics module in my COMSOL Do I have to purchase an extra license for that module? Or It should be implemented indirectly?
--
Shawn
Daniel, thank you for the hint. But, I cannot find microluidics module in my COMSOL Do I have to purchase an extra license for that module? Or It should be implemented indirectly? -- Shawn
Daniel Smith COMSOL Employee

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Posted: 1 decade ago Nov 26, 2012, 5:00 p.m. EST
Hi Shawn, you will need to purchase the Microfluidics module for your license. Implementation of the boundary condition yourself would be practically impossible so I would recommend you add the Microfluidics module to your license. There are some example models which use this interface here:

www.comsol.com/showroom/documentation/model/4650/

Please be aware that the Two-Phase Flow, Moving Mesh interface cannot handle topological changes in the fluid.
Hi Shawn, you will need to purchase the Microfluidics module for your license. Implementation of the boundary condition yourself would be practically impossible so I would recommend you add the Microfluidics module to your license. There are some example models which use this interface here: http://www.comsol.com/showroom/documentation/model/4650/ Please be aware that the Two-Phase Flow, Moving Mesh interface cannot handle topological changes in the fluid.
Shawn.F
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Posted: 1 decade ago Nov 27, 2012, 12:15 p.m. EST
Daniel,

Thank you very much. I will go for this module.

Regards,

Shawn
Daniel, Thank you very much. I will go for this module. Regards, Shawn

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