Posted Tue, 18 Sep 2007 06:40:24 GMT by Denim Umeshkumar Anajwala
[b][size=10pt]Hi.. Feflower...

This is simple question. If I do not prescribe any boundary conditions on the boundary, does it mean that the boundary is impervious?

To check this, I made simple model and ran the model but the boundary (on which no boudary conditions) nodes show the some normal velocity vector. I think it is somewhat strange.

You can also check this problem by using DYNAMIC_RIVER.FEM which is included in the folder ../feflow5.1/demo/examples/femdata. This FEM file has boundary conditions only in left side as a transfer type (type 3 B.C.). But if you run the model, you can see many vectors on other boundary has the normal component.

As far as I known, if no coditions meas the impervious boundary, there should be no vertical (or normal) component in that boundary.

Please let me know this more clear.

Thanks     8) 8) 8)

PS : Direct contact by using my e-mail, <>, is surely welcomed and acknowledged. [/size] [/b]
Posted Tue, 18 Sep 2007 14:50:23 GMT by Thierry

it means only that you have no flow through the boundary. the in the model you flow is parallel to the boudary (included vertical flow). 

For the rest of your question, I don't know, it's necessary to visualize something, but may be it's a question of representation of the vectors. The vector seems to cross the boundary, but in reality it's not the case.

hope this would help you
best regards
Posted Wed, 19 Sep 2007 16:05:39 GMT by Denim Umeshkumar Anajwala
[size=10pt][b]Thank you so much, Thierry.

I think that you mean that no boundary condition is no flow, i.e. impervious boundary and the vector cross the boundary is just fictitious. Is it right ?

In my question, the VERTICAL means just crossing boundary NOT UP and Down...and I just used 2-D model to test the no boundary condition setting. I am still confused because of the resulting vectors in the boundary which has no boudary conditions.

The sample FEM file (Dynamic_river.fem) has no boundary conditions in left, up and down sides but the boundaries have initial head conditions. Is there any possibility the initial head condition make the boundary as a 1st kind boudary condition ?

Also, if I use the FLUX ANALYZER (in POSTPROCESSOR MENU) to check the in or out flux flow, there are values still in the boundary which was not applied any boundary condition.  I do not understand yet this problem.....Please help me if you (anybody also) know further about this. [/b][/size]

Posted Thu, 20 Sep 2007 16:06:35 GMT by Boris Lyssenko
Setting no condition, the boundary is impermeable. The vectors, however, might show a normal component still. The reason for this is that the velocity field is calculated on a nodal basis, which includes some kind of mapping of the velocities to the nodes. For example, if there's some flow component towards the border which is then 'bended' to flow along the border, the component towards the border would lead to avelocity vectors slightly pointing out of the model.
Posted Fri, 21 Sep 2007 01:16:17 GMT by Denim Umeshkumar Anajwala
[b]Thank you so much Peter

I understood the problem. That comes from the nodal basis calcuation in FEM.
Because I have interests in potential (i.e. head) in many cases. I did not check and think the FEM procedure.

Thank you again [/b] :D :D :D

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