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Convergence problem with Open Boundary condition - No viscous stress
Posted 06.05.2013, 15:41 GMT-4 5 Replies
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I'm modeling fluid flow through a 2D porous media using Darcy's Law. I intend to estimate fluid flux values across the top boundary of model, however,my desired outputs will be one in which the results obtained at this boundary are dependent on the domain solution.
For my simulations so far, I have observed that the domain solution depends on the prescribed values of the boundary condition, i.e I have to specify Dirichlet boundary conditions of stress, pressure or velocity along the top and bottom boundaries. The Side boundaries are specified as No- flow.
The Comsol user guide suggested that the use of Open Boundaries ( with No viscous stress) might be useful in obtaining solutions in cases where pressure cannot be predicated ahead of time, as such I am trying to run the model using the Brinkman's Interface in order to take advantage of the open boundary physics for the top boundary, along with a specified condition along the bottom of the model. However, I have been unable to get my model to converge with this specification. (The mph file and model diagram file is attached)
I do not understand why this is happening and would appreciate insights/tips into this problem, either under the original Darcy's Law formulation or using the Brinkman's equations.
Thanks.
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I would say it's mainly that it converges slowly, you do not have any "boundary layers (the boundaries are not defined) and when you look at the results when it stops after 25 iterations you see very steep velocity gradients/singularities close to the extreme boundaries, these are probably driving the convergence and slowing down the process.
Try to add correctly the boundary layers and or just use the default physics induced mesh, and you could increase the "maximum number of iterations" entry under the "Solver - ... - Fully coupled" node, Methods and Termination tab
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Good luck
Ivar
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I tried both of the suggestions described, i.e, increasing the maximum number of iterations and making use of the default physics induced mesh but still couldn't get the simulation to converge using the open boundary with no viscous stress boundary condition.
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I have the same problem. Have you ever solved this?
Thanks.
An