results discussion

[Dongxueyang]

Hi everyone:

These days I am simualting a flood routing model. I set an inlet boundary at upper reaches of river and the water can flow into the domain according to a flow-time curve.
When I finished the simulation I output a flow curve of one section at downstream of river.
Compared to the actual discharge of this section, the simulation results is lower and it reached this section about ten hours later than actual situation.

So I want to know is there any factors will have an effect on the simulaiton？ The resolution of topograph ？ the friction (manning coefficient)？ Or any other parameters?

Hope for help and any suggestion.

Best wishes
dong

[Dongxueyang]

@stoiver

[stoiver]

Hi Dong,

First I would suggest you submit questions like this to the anuga mailing list https://lists.sourceforge.net/lists/listinfo/anuga-user Will get more access to users of anuga that way.

But there are a number of possible things to look at. Look at the flows and see if there is ponding or excessive over bank flows in flat areas. So would be useful to see a plot of the flow.

If you have a coarse resolution it is possible that the mesh is creating numerical dams, which need to be filled before flowing downstream. Fine meshes should alleviate this, but also a judicious use of breaklines along rivers can help a lot. Getting a good coarse mesh is almost always the most time consuming part of the model setup.

If there are parts of the domain which are very flat and so large areas of low froude flow, the default numerical algorithm can tend to be too diffusive. This tends to create excessive over bank flooding.

If is is your case then you can tweak the flow algorithm by doing

domain.set_low_froude(1)

after you create your domain.

I would be interested if this is the case as we are looking for test cases for the low_froude tweak.

Cheers
Steve

[Dongxueyang]

@stoiver
I have tried to change the froude number. And I am testing.
And I want to know if there are more factors and parameters about fluid and flow, such as friction and froude number.
Because I do not find any other clarification about these parameters except for friction.
Is there any files or materials can you send me ? So that I can test the sensitivity of these parameters.

Best regards
Dong

[stoiver]

@Dongxueyang
Froude number is a property of the flow, measured as u/sqrt(gh) where u is the speed, g is the gravitational acceleration (9.81) and h is the depth of water. The command

domain.set_low_froude(1)

tweaks the flow algorithm to deal with very flat regions.

The friction quantity is used to specify the mannings friction coefficient over the terrain. A fairly standard value is 0.03 (eg for flow down a concrete culvert or a road).

A large value of mannings friction can slow the flow markedly.

[Dongxueyang]

@stoiver
Now I am interested in the effection of mesh on simulation.
I generated a mesh with different area of element. I set the maximum_area_triangle=1000 and 1500.
And I get mesh like this:
element_area = 1500

element_area = 1000

Obviously, the smaller the element is the more accurate the results is . But the numeric_dams often appear and it will have bad effection on simulation. Even there so many numeric_dams along the river .
So is there any other ways to improve the simulation and decrease the effection of numeric_dams .

best regards
dong

[rudyvandrie]

As steve has mentioned this site is for CODE Development rather than new users issues in learning tto use ANUGA. I would suggest you submit questions like this to the anuga mailing list https://lists.sourceforge.net/lists/listinfo/anuga-user Will get more access to users of anuga that way.