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Velocity of deformable droplet

Posted 13 sept. 2017, 06:05 UTC−4 Computational Fluid Dynamics (CFD), Microfluidics, Results & Visualization 3 Replies

Akshay Tiwari
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Hello, I'm building a unsteady computational model of 'Motion and deformation of droplet through minichannel using Level set method'. I ant to plot a graph between droplet velocity and the time scale. How can I do it when droplet is itself deforming and interface is changing with time.? Kindly help me.

         Regards,
         Akshay Tiwari
3 Replies Last Post 14 sept. 2017, 16:18 UTC−4
Eric Favre COMSOL Employee

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Posted: 7 years ago 14 sept. 2017, 08:24 UTC−4
Updated: 7 years ago 14 sept. 2017, 08:41 UTC−4

You can probably integrate over the whole domain with integration coupling variable, intop1() will be the default name. Define as variables :
vol1 = intop1(ls.Vf1)
xc = intop1(x * ls.Vf1)/vol1
yc = intop1(y * ls.Vf1)/vol1
this is simply the definition of the center of mass that only takes into account your fluid. ls.Vf1 is the volumic fraction of fluid 1 (perhaps this is fluid 2 in your case!) available with the levelset physics interface, that give 1 in fluid 1 and 0 in fluid 2. xc and yc can be ploted wrt time easily.

Best regards, Eric Favre COMSOL France

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Eric Favre
COMSOL France
You can probably integrate over the whole domain with integration coupling variable, intop1() will be the default name. Define as variables : vol1 = intop1(ls.Vf1) xc = intop1(x * ls.Vf1)/vol1 yc = intop1(y * ls.Vf1)/vol1 this is simply the definition of the center of mass that only takes into account your fluid. ls.Vf1 is the volumic fraction of fluid 1 (perhaps this is fluid 2 in your case!) available with the levelset physics interface, that give 1 in fluid 1 and 0 in fluid 2. xc and yc can be ploted wrt time easily. Best regards, Eric Favre COMSOL France
Akshay Tiwari
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Posted: 7 years ago 14 sept. 2017, 11:03 UTC−4

Thanks Eric, But I wanted a plot between Velocity of Deformable droplet and Time. For that, Can I do use the Surface Integration operation (Result>Derived Values>Surface Integration) and then Intergrating the variable Velocity Magnitude, U over the Domain of the droplet to get the Single Velocity that will represent the Velocity of whole droplet and hence plot this with timescale? If no, Then what does this signify?

Regards, Akshay Tiwari

Thanks Eric, But I wanted a plot between Velocity of Deformable droplet and Time. For that, Can I do use the Surface Integration operation (Result>Derived Values>Surface Integration) and then Intergrating the variable Velocity Magnitude, U over the Domain of the droplet to get the Single Velocity that will represent the Velocity of whole droplet and hence plot this with timescale? If no, Then what does this signify? Regards, Akshay Tiwari
Eric Favre COMSOL Employee

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Posted: 7 years ago 14 sept. 2017, 16:18 UTC−4

Hello Akshay,
based on my first indication, you can simply derive xc and yc in time : d(xc,t) will give you the velocity along x. Yes, you can integrate u instead of x for getting the velocity directly without having to derive in time (since integration and derivative can permute). You can probably define everything in the Results section but this is often easier to refer to variables instead. In most of the cases this is the user's choice. To access in Results those variables that you would define after having performed a possibly very long simulation without recomputing all, press F5 (study : update solution).
You can integrate u instead of x for getting the velocity directly without having to derive in time. However, you cannot simply integrate the magnitude U. You need to compute both velocity components (uc and vc) and then take sqrt(uc^2+vc^2) to get the magnitude (you cannot permute integration with non linear operator like sqrt).

Hope this helps, best regards, Eric Favre

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Eric Favre
COMSOL France
Hello Akshay, based on my first indication, you can simply derive xc and yc in time : d(xc,t) will give you the velocity along x. Yes, you can integrate u instead of x for getting the velocity directly without having to derive in time (since integration and derivative can permute). You can probably define everything in the Results section but this is often easier to refer to variables instead. In most of the cases this is the user's choice. To access in Results those variables that you would define after having performed a possibly very long simulation without recomputing all, press F5 (study : update solution). You can integrate u instead of x for getting the velocity directly without having to derive in time. However, you cannot simply integrate the magnitude U. You need to compute both velocity components (uc and vc) and then take sqrt(uc^2+vc^2) to get the magnitude (you cannot permute integration with non linear operator like sqrt). Hope this helps, best regards, Eric Favre

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