Instantaneous Dam-break

[simone minesso]

Hi there,
I’m trying to perform the follows laboratory experiment:

“The experimental setup consisted of a reservoir connected with a channel through a
pneumatically actuated gate. The reservoir was initially filled with water and
the channel was occluded on the other end. The experimental runs started with
the quasi-instantaneous opening of the gate. Bridges were placed in the channel,
close to the gate, where they got hit by the dam-break wave.”

I have collocated the gate into an embankment and represented the gate opening type as a sluice one. I have set the gate opening law to be as already full opened at the initial time (00:00), because otherwise I would have set the full opening at 00:01 minute (lowest data time interval is 1 minute), that consists in a condition really far from the quasi-instantaneous opening one.
By operating in this manner the wave at the zero time has already moved a bit down from the reservoir into the channel and this fact bad affects the solution.

So I have tried to represent the experiment in another way, as an instantaneous dam break. I did it by removing the gate and by setting a breach progression in this way (time fraction 0; breach fraction 1); (1;1) but I have had stability problem.

Any advices how to solve problems? Or in setting the gate opening time interval lower than 1 minute, or in performing an instantaneous dam break?

Thanks in advance

[Anonymous]

The instantaneous dam break is the easiest way since, as you point out, the gate opening takes at least a minute. (An alternative would be to use the “advanced rules” and this would allow the gate to be fully opened in a single time step. But it would be a bit more complicated.)

Stability is likely to be an issue. If you haven’t already, you might try turning on the “Mixed Flow Regime” on the main Unsteady flow run editor. Also, from the run editor, go to Options, Unsteady Computation Options and set the Inline Structure (or Lateral Structure if you are using a Lateral Structure) “flow stability factor” to the maximum value of 3. This might help a bit with stability.

[Author]

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