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Schiller Neuman SLIP Velocity Mixture Model V3.5a

Posted 15 juin 2011, 14:39 UTC−4 Fluid & Heat, Computational Fluid Dynamics (CFD), Studies & Solvers Version 4.0a, Version 5.2 6 Replies

Rui Silva
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Hi folks.

I have trying to use the Schiller Neuman Slip velocity model for a few days but no success.

I am successful in using the Hadamard-Rybczynski but I need to use the Schiller Model for comparison
purposes.

However I get the error 7248 - Undefined value found.

But I can not understand why...

The reason I am using V3.5a is because Helpdesk have said to me that the Schiller model will only work
in version V4.2.

Hope someone can help, because I am really stuck.

The file is attached.

Cheers.

Attachments:

6 Replies Last Post 5 avr. 2017, 10:58 UTC−4
COMSOL Moderator

Hello Rui Silva

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Cathal Cummins
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Posted: 1 decade ago 12 août 2011, 10:56 UTC−4
Hi there,


I am running a mixture model in comsol 4.0a.

* laminar
* low gas concentration
* no slip on all walls except top gas vent, which has slip
* gravity

the particle Reynolds number is about 3 and the sedimenting dispersed phase are about 100 microns diameter. Hence, while the Hadamard-Rybczynski model gives reasonable results, it is far from ideal. I had the model working fine with this drag model however, I feel that a Schiller-Naumann model would suit better. This means solving an implicit equation for u_slip which is okay but comsol tells me that it can't evaluate Jacobian:

Failed to evaluate variable Jacobian.
- Variable: mod1.mm.udz
- Geometry: 1
- Boundary: 3

Boundary 3 is the top of the geometry. However, it works fine for other drag models.

The initial conditions are 5% void fraction, zero velocity everywhere both gas and liquid. My question is, when you choose SN drag, is there anything else you need to specify to help it solve the implicit equation?
Hi there, I am running a mixture model in comsol 4.0a. * laminar * low gas concentration * no slip on all walls except top gas vent, which has slip * gravity the particle Reynolds number is about 3 and the sedimenting dispersed phase are about 100 microns diameter. Hence, while the Hadamard-Rybczynski model gives reasonable results, it is far from ideal. I had the model working fine with this drag model however, I feel that a Schiller-Naumann model would suit better. This means solving an implicit equation for u_slip which is okay but comsol tells me that it can't evaluate Jacobian: Failed to evaluate variable Jacobian. - Variable: mod1.mm.udz - Geometry: 1 - Boundary: 3 Boundary 3 is the top of the geometry. However, it works fine for other drag models. The initial conditions are 5% void fraction, zero velocity everywhere both gas and liquid. My question is, when you choose SN drag, is there anything else you need to specify to help it solve the implicit equation?

Attachments:

Cathal Cummins
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Posted: 1 decade ago 12 août 2011, 17:40 UTC−4
According to support there's a bug in the slip velocity model in 4.0a?

Could this be the reason why the Schiller-Naumann model wasn't working?

Cheers,
According to support there's a bug in the slip velocity model in 4.0a? Could this be the reason why the Schiller-Naumann model wasn't working? Cheers,
Cathal Cummins
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Posted: 1 decade ago 15 août 2011, 14:17 UTC−4
Hi,

Just in case anyone has the same problem, my problem was simply a badly defined initial pressure distribution. I figured a zero pressure ic would suffice but it didn't. Specifying the hydrostatic pressure p(z)=rho g (H-z) avoided the singularity in the slip velocity which happens when p is identically zero everywhere.

Hope this helps!
Hi, Just in case anyone has the same problem, my problem was simply a badly defined initial pressure distribution. I figured a zero pressure ic would suffice but it didn't. Specifying the hydrostatic pressure p(z)=rho g (H-z) avoided the singularity in the slip velocity which happens when p is identically zero everywhere. Hope this helps!
Rui Silva
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Posted: 1 decade ago 15 août 2011, 19:27 UTC−4
Hi Cathal,

sorry it took me so long to reply but I have been away on vacation.

To me the problem was solved using version 4.2 and using an estimative for the slip
velocity using the terminal velocity expression.

I don't have the references with me but If you need them I will gladly provide them.

Hope this helps.

Cheers!
Hi Cathal, sorry it took me so long to reply but I have been away on vacation. To me the problem was solved using version 4.2 and using an estimative for the slip velocity using the terminal velocity expression. I don't have the references with me but If you need them I will gladly provide them. Hope this helps. Cheers!
Cathal Cummins
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Posted: 1 decade ago 16 août 2011, 02:39 UTC−4
Thank you for your help Rui. As per the last post, it was actually the initial condition for the pressure (also the slip squared velocity) which was causing me the problems.

Initially I ran the H-R model which, since the slip velocity vector is directly proportional to the pressure gradient, could handle p_{t=0}=0 everywhere this doesn't carry over to the S-N. In any case, as you say there is a bug in the older versions of comsol.

Thanks again!
Thank you for your help Rui. As per the last post, it was actually the initial condition for the pressure (also the slip squared velocity) which was causing me the problems. Initially I ran the H-R model which, since the slip velocity vector is directly proportional to the pressure gradient, could handle p_{t=0}=0 everywhere this doesn't carry over to the S-N. In any case, as you say there is a bug in the older versions of comsol. Thanks again!
Andres Arevalo
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Posted: 8 years ago 5 avr. 2017, 10:58 UTC−4
Hi,
I´m using the machinery rotating, mixture model and I have a problem with Schiller-Naumann slip model, When I use Schiller-Naumann slip velocity in the model, the program produce a error.

"Failed to find consistent initial values"

What happen? I had changed the initial value for pressure and squared slip velocity and nothing! How can I fix this problem?

Thanks for help me!
Hi, I´m using the machinery rotating, mixture model and I have a problem with Schiller-Naumann slip model, When I use Schiller-Naumann slip velocity in the model, the program produce a error. "Failed to find consistent initial values" What happen? I had changed the initial value for pressure and squared slip velocity and nothing! How can I fix this problem? Thanks for help me!

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