User Forum of Software BASEMENT

basemind

User

Registered: 2015-10-28

Posts: 15

Water rushing from outflow condition into the model

Hi,

I have a model up and running with 2 inflows at the model boundary, 1 gate of constant height (=1 inflow & 1 outflow) and 1 outflow at the model boundary. As initial condition I set the river area to contain 1m of not-moving water.

For the first seconds, the simulation runs smooth - the water I filled into the river area is flowing down the bank into the channel. After ~2seconds one of the elements situated at the model boundary and the outflow is starting to misbehave - it starts to distribute water with absurd velocities - topped at the predefined 200m/s and completely messing up my simulation. Do you have any idea what could be the case?

The element doesn't look suspicious at all - all heights are correct, the strdef is defined correctly.

The model's initial condition:

Detail of the culprit area:

Initial flowing of water:

Suspicious element starting to act suspicious:

Total mess:

The mesh in 3D:

maarnold

Advanced_User

Registered: 2014-09-13

Posts: 30

Re: Water rushing from outflow condition into the model

Have you tried to start from dry conditions?

basemind

User

Registered: 2015-10-28

Posts: 15

Re: Water rushing from outflow condition into the model

With dry conditions the calculation will take longer until it reaches its final state (it is a steady-state model), it seems to work though (it takes the water a while to reach the critical point).

Could it be that the zero gradient outflow condition amplifies itself due to the initial negative velocity (water flowing backwards in the channel due to the banks being inclined against the flow direction)?

If this is the case I could always just leave a little space between my inital water level and the outflow boundary to ensure the velocity is positive (out of the model); it is strange nonetheless.

I prepared my model this way (with a little gap between the initial water level and the outflow boundary), it seems to work now - yet another note in my Basement manual!

Last edited by basemind (2015-12-03 14:00:26)