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-   -   Boundary conditions (http://www.cfd-online.com/Forums/flow-3d/111858-boundary-conditions.html)

mahdi1 January 16, 2013 17:20

Boundary conditions
 
Hello
I want to simulate a channel with vegetation by flow-3D code. As far as the length of channel is high and thickness of rigid elements is very small, I want to run the software for a part of channel (for example 2 m) with uniform conditions.
my problem is in specifying boundary condition. If I choose periodic boundary for inlet and outlet, How and where can I insert flow depth, velocity or discharge for this part of channel in the software exactly.

I would be thankful, if anybody can help me.

burbur January 24, 2013 05:37

Hi,
I was trying to use the same bc, and i saw that, periodic bc uses your initial depth as the normal depth of the channel and solves for discharge by using roughness and the slope you entered. The initial velocity does not have an effect it is just an initial but the initial depth is important as the program takes it as a fixed input.

mahdi1 January 24, 2013 07:06

Quote:

Originally Posted by burbur (Post 403721)
Hi,
I was trying to use the same bc, and i saw that, periodic bc uses your initial depth as the normal depth of the channel and solves for discharge by using roughness and the slope you entered. The initial velocity does not have an effect it is just an initial but the initial depth is important as the program takes it as a fixed input.

Hello
Did you choose a free surface or no sharp interface in your work?
I think that, If we choose no sharp interface, depth of channel equals to normal depth (According to technical note 60).
What's your opinion?


Also do you have experience to simulate a channel with horizontal slope? Because I think that Period boundary condition is correct when there is a slope in channel.

Regards

burbur January 24, 2013 10:41

I didnt choose them either, i am not sure where do Flow-3d use it.
Also i did solve problems with slope, i personally think if a flow would be in a horizontal slope, there should be a driving force other than gravity, and that force should be inserted to the program.

mahdi1 February 9, 2013 07:39

Quote:

Originally Posted by burbur (Post 403721)
Hi,
I was trying to use the same bc, and i saw that, periodic bc uses your initial depth as the normal depth of the channel and solves for discharge by using roughness and the slope you entered. The initial velocity does not have an effect it is just an initial but the initial depth is important as the program takes it as a fixed input.

Hello

Did you choose Free surface or No sharp interface?
Could you please send me a description (text file) about your study that you worked before about period boundary condition?

Thanks

burbur February 9, 2013 14:17

Hello, I chose free-surface flow, I used periodic bc to get a fully developed flow to feed my original simulation. I give the slope, surface roughness and the initial fluid region as input and as I said earlier depth of the initial fluid region is taken as the normal depth of the channel. And developed flow is obtained.

mahdi1 February 13, 2013 11:02

Quote:

Originally Posted by burbur (Post 406903)
Hello, I chose free-surface flow, I used periodic bc to get a fully developed flow to feed my original simulation. I give the slope, surface roughness and the initial fluid region as input and as I said earlier depth of the initial fluid region is taken as the normal depth of the channel. And developed flow is obtained.

Hello again

Is the length of channel important or not?

burbur February 16, 2013 09:27

length plays a role like simulation time i.e. 10 m channel with 100 seconds simulation time = (approximately) 100 m channel with 10 seconds simulation time


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