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Hi,

I am trying to simulate a simple channel flow, originally, I prescribed both flowrate and elevation at both ends of teh channel, however when I ran the simulation, the steady state velocity in the channel was too low for the flow rate to be correct as I had defined it in the steering file. So my first question is, why is the correct flow velocity at the channel inlet and outlet not occuring so that the flowrate I and elevation I want in the channel is not occuring?

Secondly, I tried to edit the boundary conditions by defining a flowrate and elevation at the inlet, but only a flowrate at the outlet, however when I try to run the simulation, an error message comes up saying that more prescribed elevations are required in the parameter file at least 2 must be given. So why must 2 prescribed elevations be defined even when I only define one elevation in the .cli file?

I have included the .cli and steering files for both runs.

Any help would be much appreciated.

Cheers

Danny

Hello,

The correct way of prescribing the boundary conditions in a simple channel is discharge imposed at the entrance, depth free at the entrance, depth imposed at the exit, velocity free at the exit. The prescribed values are given per liquid boundary, so prescribing a discharge of 100 m3/s at the entrance is written:

PRESCRIBED DISCHARGES : 0. ; 100.

if the entrance is boundary 2. You can look at the examples, e.g. pildepon, to see how it is done.

With best regards,

Jean-Michel Hervouet

Hi Jean-Michel,

Thanks, however there are still a couple of things that dont make sense to me...

1. When you say I must define a discharge at the entrance, do you mean a flowrate? If I put PRESCRIBED DISCHARGES: 0.;0.069 into the steering file as the only bondary condition at the entrance of the channel, I get an error saying uncontroled error from python:: KeyError('PRESCRIBED DISCHARGES',).

2. When I define a Flowrate at the entrance and an elevation at the exit of the channel, the steady state flow velocity is still too low, why is this?

3. I have looked at the files in the pildepon but there is no steering file that I could see, which file is the one that can help me with this?

I have attached my new steering file.

Cheers

Danny

Hello,

Yes sorry, it is PRESCRIBED FLOWRATES...

"The velocity is still too low" : If you give the flowrate at the entrance and the elevation at the exit, mass conservation will give at the exit a velocity such that U*section=flowrate, so in some sense you give the velocity.

Use the keyword CONTINUITY CORRECTION = YES to get exact flowrates at the exit in your listing.

I also notice that you use a Nikuradse friction law (5) with friction coefficient 1.23 (grain size ??), is it really what you want, this must be a lot of friction...

With best regards,

Jean-Michel Hervouet