User Forum of Software BASEMENT

Matteo Facchini

Developer

From: Trento

Registered: 2014-09-05

Posts: 286

Very high velocities at boundary

I would like to post something that I discovered in these days, just to share it with the community and maybe get some feedbacks.

I was running a simulation with a very steep boundary condition (10%) and I noticed very high (unrealistic) values of flow velocities in the flood_tracking_v output.

After some reasoning and tests, I realized that the problem was linked to:

• dry initial conditions

• minimum water depth

Changing the initial conditions to continue or region defined solved the problem.

What I realized is that starting from dry initial conditions, in the first time steps the water depth was increasing but it was still below the minimum water depth, so there was no flux from the first cells to the rest of the domain. In one time step the water increased from far below (1.7E-4 m) to far above (0.5 m) the minimum water depth (0.05 m). This was caused something like a dam break, I suppose, hence the high velocity values.

Do you think I came to the right conclusion, or could it be something else?

Last edited by Matteo Facchini (2023-04-18 13:39:17)

Matthias Bürgler

Developer

From: Zürich

Registered: 2019-04-04

Posts: 175

Re: Very high velocities at boundary

Hi Matteo

Thank you for sharing this observation. The described behaviour could definitely be the reason for the high velocities in the flood tracking.

I recently also noticed that the initial conditions can influence the flow at a uniform inflow boundary. For a straight channel and starting from dry initial conditions, the uniform inflow boundary resulted in supercritical flow directly downstream of the boundary, followed by a hydraulic jump. But when starting with region-defined initial conditions imposing supersubcritical (edit: 10.12.2024) flow from the beginning, the hydraulic jump did not occur and the flow always remained subcritical.

Last edited by Matthias Bürgler (2024-12-10 20:07:04)

Giampietro

User

Registered: 2021-06-25

Posts: 5

Re: Very high velocities at boundary

Hi Matthias,

I read your replay.
At the end you write:" remained subcritical". Did you mean supercritial?
Otherwise, coud you please explain me better?

In essence, how does the flow remain subcritical by requiring it to be supercritical at the beginning without hydraulic jump?

Thank you!

Last edited by Giampietro (2024-07-29 20:45:26)

Matthias Bürgler

Developer

From: Zürich

Registered: 2019-04-04

Posts: 175

Re: Very high velocities at boundary

Thanks for the correction, I meant subcritical conditions (see edit).