Flow Across a Cross Section

[sachi canning]

Hi all, i am just running some simple tests on an open channel.

For a trapezoidal open channel, is there a way i can get the flow in m3/s at a given cross section in the channel?

Also when you get 'speed' 'stage' 'depth' etc. in the .csv file what unit is the speed in? I have read that is the square root of the total of x-momentum squared plus y-momentum squared (Speed = SQRT((x-momentum)^2 + (y-momentum)^2)), but im not sure what units the x and y momentum is in.

Any help much appreciated

[Vincent Edgewater]

Hi Sachi,

I remember asking this question at some point recently. 

Try the following python code for grabbing the flow:

from anuga.shallow_water.data_manager import get_flow_through_cross_section

flow_line = [ [123.0, 456.0], [789.0, 123.0] ]
# Define a poly-line

model_times, model_q = get_flow_through_cross_section(filename='your_sww_file', polyline=flow_line, verbose=True)

fid = open( "flow_plot_out.csv", "w" )

i = 0

while i < len(model_times):

  fid.write( str(model_times[i]) + ", " + str(model_q[i]) + "\n" )

  i = i + 1

fid.close()

I believe the flow will be in m3/s but don't quote me on that - also i'd have thought the other quanitites you mention will be in SI units. 

speed = (xmomentum**2 + ymomentum**2)**0.5/(stage-elevation+1.e-30)

(don't forget to divide by the depth)

I'm guessing speed should be in m/s

Let me know if anything doesn't make sense. 

Regards,

Vince

[Vincent Edgewater]

PS.  I think the indentation of the code got screwed up

fid.write( str(model_times[i]) + ", " + str(model_q[i]) + "\n" )

and
i = i + 1

should be indented

V

[Ole Nielsen]

Thanks Vincent for replying to Sachi's posting.
I can confirm that flow rates are in m^3/s and speeds in m/s.

Ole

[sachi canning]

Thanks for the reply, I have it working and writing to the csv file. works well