# Some unphysical phenomenon in the calculation example of DamBreak

Hi all,

As you can see in the above picture, there is no water in the area which I have marked out. That is not physical. Relative to the no water region, I think the dam break will also hapeen along the width of the tank(As shown by the arrows).

Why does this unphysical phenomenon happen? I guess maybe the pressure at the free surface is not zero, so the unphysical pressure gradient leads to this unphysical phenomenon. But I cannot be sure of that. Can anyone give some explanations?

• Why is that unphysical?

• Same "unphysical" behaviour can be observed here:

• Because I think that when the water arrive at the Rectangular Cylinder, the water will surround the Rectangular Cylinder rather than leave a no water area behind the Rectangular Cylinder.

• To think that is not a physical proof ;)

The physical information here are the forces used to determine velocities... and both flows that surround the obstacle present high horizontal velocities. Therefore the area after the obstacle can be flooded before or later depending on the dam celerity.

Regards

• edited October 6

It might also be that your perception of nonphysical is biased by the rapidity these processes occur in a small tank? I had posted a video in true time of a dam break simulated with 100M SPH particles here:

I realise the view is at the other side of what you liked better. However, in the real, it would be difficult (although not impossible) for anyone to describe what happens in the lee of the column. (You could put a little floating object and tell!)

For a larger-scale example, we could look at

but then a wave is different from a dam break (owing to the time evolution of the heights of the impacting water to start with, and because the 'floor' is already wet downwave).

Thank you for posting your stimulating question

• Thank you for your explanation.

• Thank you for your attention and share.