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Dear all,

I'm calibrating on a velocity profile for an open channel with changing bathymetry and bend, using a FOTRAN file with subroutines CONDIM and VEL_PROF_Z (I may also try bord3.f). It's heavily based on the canal example.

The idea is to let the model work out the velocity profile down the stream after prescribing at the inlet.

My main issue is that I don't seem to get an outflow. Both are open boundaries but the water seems to 'rebound'. My BC are set to prescribed UV and tracer at the inlet, and prescribed H at the outlet. I assume it might be because H is higher than the modeled height but the problem persists even when changing the BC.

Second to that my velocities are negative! I'm unsure as to why this is.

I've attached my .cas file just in case.

Thanks,
Simon

Hello,

What you are doing at the exit is not clear, I see no prescribed elevation, should it be 0.73 (assuming the bottom at 0...) ? We would need to see the boundary conditions file, normally with an horizontal canal boundary 1 is on the right, the exit, and you seem to prescribe the discharge at the exit, this would explain the negative velocities...

Regards,

JMH

Hello,

Thanks for your reply.

Apologies, the incorrect *.cas file was attached. Please see attached.
I've also attached my boundary conditions *.bc2 and *.cli file (i.e. inlet: prescribed UV & tracer; outlet: prescribed H & free tracer).

To clarify: the problem is that the flow seems to result from the downstream, with the "rebound" occurring as it approaches the upstream. Inverting the prescribed velocities/elevation results in zero flow.

The negative values were just a symptom of my fiddling about!

Thanks for looking at this.

Regards,
Simon

The *.cas and *.bc2 didn't seem to be added.

Hello,

You are now asking for a CONSTANT ELEVATION as initial conditions, but you do not give the keyword 'INITIAL ELEVATION' which by default is equal to 0., is it what you want or are you missing:

INITIAL ELEVATION : 0.65

in your steering file?

Regards,

JMH

You're correct, thanks for catching that. The flow is now going in the right direction!

The problem with the "rebound" still persists however.

Apologies if this is a stupid question, but does the fact that the depth values have been given as all positive values result in no water in the channel at the beginning? Currently I have to flush the water through and I'm not sure if there's a reason for this. Currently I'm using 2D continuation for initial conditions.

Regards,
Simon

Hello,

This is not linked, it must be due to what is in your previous coputation file; With the constant elevation as initial conditions you should have water everywhere in the domain.

Regards,

JMH