open channel boundary condition

pa8001 · January 27, 2015, 19:56

hello
I am trying to simulate openn channel flow 2D. I know the exact velocities at the inlet and the outlet. Can I impose constant velocities to the inlet and outlet during the transiant simulation? I dont want the velocity at the outlet change during the simulation.

Any suggestions would be greatly appreciated.

edoan · February 5, 2015, 14:07

What is transient about the simulation if your BC velocity is fixed?

pa8001 · February 8, 2015, 09:43

thank you for answering!
I am trying to simulate a hydraulic jump just by imposing the depths of upstream and down stream.
acctually I want a uniform flow with a constant speed at time 0 and then the velocity at upstream BC increases to 5m/s but I want to keep downstream flow subciritical to have a hydraulic jump somewhere in between. but I dont know how to do so.

Ema40 · April 18, 2015, 05:34

Hi. Try with these three ways:

Steady simulations:
1) fix both the water depths already at the beginning of the simulations and run the simulations up to the convergence (also try different initialization methods, both NONE and FLAT, which are initialization methods for open channel flow)

Unsteady simulation
2) as 1)
3) Fix only the upstream depth

Let me know if you success in this and the more appropriate solution!
Bye bye

pa8001 · April 20, 2015, 12:35

Thank you ema!
What i did, is running the simulation in transient. I set the depth of downstream BC at the begining, but the model wont maintain it fix. In the other word, I want to tell the model to change the velocity not the depth! But it wont understand.

I want to know if there is any way to have a fix depth of water in the downstream in a transient simulatin? Because as i mentioned, i want to produce a hydraulic jump.

Any help would be greatly appreciated.

Ema40 · April 20, 2015, 14:00

Hi...I don't know....probably the water depth that you set is wrong. Or maybe the changes that it undergoes are very small and they are only numerical oscillations..

But you fixed both the downstream and the upstream water depth?
Try fixing the mass flow at the outlet and the other methods that I said you..

Let me know

Bye

January 27, 2015, 19:56	open channel boundary condition	#1
pa8001 New Member pouyan Join Date: Jan 2015 Posts: 7 Rep Power: 11	hello I am trying to simulate openn channel flow 2D. I know the exact velocities at the inlet and the outlet. Can I impose constant velocities to the inlet and outlet during the transiant simulation? I dont want the velocity at the outlet change during the simulation. Any suggestions would be greatly appreciated.

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February 5, 2015, 14:07		#2
edoan Member Ethan Doan Join Date: Oct 2012 Location: Canada Posts: 90 Rep Power: 14	What is transient about the simulation if your BC velocity is fixed?

February 8, 2015, 09:43		#3
pa8001 New Member pouyan Join Date: Jan 2015 Posts: 7 Rep Power: 11	thank you for answering! I am trying to simulate a hydraulic jump just by imposing the depths of upstream and down stream. acctually I want a uniform flow with a constant speed at time 0 and then the velocity at upstream BC increases to 5m/s but I want to keep downstream flow subciritical to have a hydraulic jump somewhere in between. but I dont know how to do so.

April 18, 2015, 05:34		#4
Ema40 Senior Member Join Date: Oct 2014 Posts: 124 Rep Power: 12	Hi. Try with these three ways: Steady simulations: 1) fix both the water depths already at the beginning of the simulations and run the simulations up to the convergence (also try different initialization methods, both NONE and FLAT, which are initialization methods for open channel flow) Unsteady simulation 2) as 1) 3) Fix only the upstream depth Let me know if you success in this and the more appropriate solution! Bye bye

April 20, 2015, 12:35		#5
pa8001 New Member pouyan Join Date: Jan 2015 Posts: 7 Rep Power: 11	Thank you ema! What i did, is running the simulation in transient. I set the depth of downstream BC at the begining, but the model wont maintain it fix. In the other word, I want to tell the model to change the velocity not the depth! But it wont understand. I want to know if there is any way to have a fix depth of water in the downstream in a transient simulatin? Because as i mentioned, i want to produce a hydraulic jump. Any help would be greatly appreciated.

April 20, 2015, 14:00		#6
Ema40 Senior Member Join Date: Oct 2014 Posts: 124 Rep Power: 12	Hi...I don't know....probably the water depth that you set is wrong. Or maybe the changes that it undergoes are very small and they are only numerical oscillations.. But you fixed both the downstream and the upstream water depth? Try fixing the mass flow at the outlet and the other methods that I said you.. Let me know Bye