# Boundary conditions

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 January 16, 2013, 17:20 Boundary conditions #1 Member   mahdi Join Date: Jan 2013 Posts: 43 Rep Power: 6 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.

 January 24, 2013, 05:37 #2 New Member   Join Date: Nov 2012 Posts: 8 Rep Power: 6 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.

January 24, 2013, 07:06
#3
Member

mahdi
Join Date: Jan 2013
Posts: 43
Rep Power: 6
Quote:
 Originally Posted by burbur 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).

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

 January 24, 2013, 10:41 #4 New Member   Join Date: Nov 2012 Posts: 8 Rep Power: 6 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.

February 9, 2013, 07:39
#5
Member

mahdi
Join Date: Jan 2013
Posts: 43
Rep Power: 6
Quote:
 Originally Posted by burbur 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

 February 9, 2013, 14:17 #6 New Member   Join Date: Nov 2012 Posts: 8 Rep Power: 6 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.

February 13, 2013, 11:02
#7
Member

mahdi
Join Date: Jan 2013
Posts: 43
Rep Power: 6
Quote:
 Originally Posted by burbur 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?

 February 16, 2013, 09:27 #8 New Member   Join Date: Nov 2012 Posts: 8 Rep Power: 6 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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