Smaller Dp Results in Noise in the Force on the Seawall

barrybarry
in DualSPHysics v4.4

Hi all!

Greetings. I am modeling a 2D-Wave-on-seawall type of problem.

The model setup can be seen in the following picture where I have an inlet-zone to generate 2nd order regular wave and a trapezoidal seawall seated on a slope. The water depth in front of the wall is around 5.4m.

Wave height is 3.6m and wave period is 3.6s.

Setup.png

The time-steping algorithm implemented is Symplectic while two choices of dp results in quite different result for the force on the seawall obtained by ComputeForce :

Force.png

The result of dp=0.3 is quite smooth and is without the overshoots while dp =0.15 seems unstable and is with "noises".

Given the conditon, I expect that the wave does not break and as a result no breaking-wave force is exerted on the wall, and even if there exists impulsive force, it can only account for the "ups" but not the "downs" in the time history if I am not mistaken.

So I think the result may come from the numerical part. From a PDE point of view, for smaller dp, we need smaller dt but I think this is guaranteed because we use CFL number to calculate dt.

And I also check the free surface elevation at x =30, and the result is quite similar and smooth (does this mean that the time integration is stable ?). Probably it's due to my BC settings or other parameters but I am not sure. I am wondering how to explain/resolve this and I am sincerely thankful for all of your insights.


Best,

Barry

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