Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.
Discussion Closed This discussion was created more than 6 months ago and has been closed. To start a new discussion with a link back to this one, click here.
Iteration in COMSOL
Posted Sep 14, 2012, 6:35 p.m. EDT Version 4.3 1 Reply
Please login with a confirmed email address before reporting spam
Hello,
I have a problem here. I want to use COMSOL for one of my problems. In this model, I want to find the viscosity and velocity in a geometry which I have both soil and water. So I should use Darcy's law. In this law velocity is dependent to viscosity. However, the viscosity which I need to find at the end is also dependent to Darcy's law velocity. Hence my fluid is non-Newtonian fluid.
When I add Darcy's law to my physics. It asked for fluid and matrix properties. For matrix properties I have no problems, but for fluid properties it asked for viscosity, which I should write in that spot a function of Darcy's law velocity ( f(darcy's law velocity) ). When I run this model the error is : ''circular variable dependency detected'. So I used the iterative solver instead of direct one. Still the same error. Can anyone please help me here. Can COMSOL solve this problem?
Thanks,
Negin
I have a problem here. I want to use COMSOL for one of my problems. In this model, I want to find the viscosity and velocity in a geometry which I have both soil and water. So I should use Darcy's law. In this law velocity is dependent to viscosity. However, the viscosity which I need to find at the end is also dependent to Darcy's law velocity. Hence my fluid is non-Newtonian fluid.
When I add Darcy's law to my physics. It asked for fluid and matrix properties. For matrix properties I have no problems, but for fluid properties it asked for viscosity, which I should write in that spot a function of Darcy's law velocity ( f(darcy's law velocity) ). When I run this model the error is : ''circular variable dependency detected'. So I used the iterative solver instead of direct one. Still the same error. Can anyone please help me here. Can COMSOL solve this problem?
Thanks,
Negin
1 Reply Last Post Sep 25, 2012, 4:46 a.m. EDT
Please login with a confirmed email address before reporting spam
Posted:
1 decade ago
Hello Negin,
It is most likely that COMSOL can solve your problem, one way or the other. The first thing I would try is adding a separate equation for the viscosity (use a Distributed ODE interface from the Mathematics branch in the model navigator). The viscosity then becomes a dependent variable which you can use in Darcy's law.
The new system of equations can be solved either using a coupled or a segregated solver. In the former case, make sure that you set non-zero initial value on the viscosity variable, and in the latter, I think you should solve the viscosity variable in the first group and the pressure in the second group.
best regards
Nils Malm
COMSOL AB
It is most likely that COMSOL can solve your problem, one way or the other. The first thing I would try is adding a separate equation for the viscosity (use a Distributed ODE interface from the Mathematics branch in the model navigator). The viscosity then becomes a dependent variable which you can use in Darcy's law.
The new system of equations can be solved either using a coupled or a segregated solver. In the former case, make sure that you set non-zero initial value on the viscosity variable, and in the latter, I think you should solve the viscosity variable in the first group and the pressure in the second group.
best regards
Nils Malm
COMSOL AB