Missing water particles when simulating a complex floating object

kavsole · May 2023

Dear DualSPHysics developers/users

I have a problem with simulating a ship structure with complex geometry. First, I simulated the wave generation in the flume and everything was Ok. However, when I placed the ship inside the tank, some strange and large gaps were created near the boundaries. There was no difference between the two XML files unless in the second case, I just inserted the ship inside the tank. Can anyone help me with this particular problem?

TPouzol · May 2023

Hello,

Are you using mDBC ?

Regards

kavsole · May 2023

Dear @TPouzol

In this simulation, I used the traditional dynamic boundary condition (not MDBC) to simulate the motion behavior of a DTC ship in beam seas, U=0 kn. As far as I know, the mdbc capability for floating bodies is just available in the newest version released in early May. Hence, I don't master this capability for floating bodies. However, I tied to simulate this problem with mdbc and as I can remember, I got the following message: The number of faces is too large. Then, following the instructions made in Mesh Decimating - FreeCAD Documentation, I reduced the number of faces. However, I got the same error again. Actually, I don't know if the reason is the complex geometry of the considered ship or not.

Anyway, I simulated this phenomenon by importing some solid walls near those boundaries with no numerical error or particle out. Although the heave motion was simulated with acceptable accuracy, the Sway and Roll motions results were too far from the experimental data. For example, in the experimental data sets, the sway motion of the ship is almost sinusoidal, however, my data shows that the ship moves progressively instead of being sinusoidal, or as shown in the attached figure, the ship experiences severe roll motions that are not evident in the experimental study.

Hence, I think that to get more accurate simulation results, I have to solve this particular problem by removing those solid walls and implementing periodic boundary conditions at these two boundaries to lessen the possible wave reflection.

Regards

TPouzol · May 2023

Hello,

I'm not competent in wave and ship modelling, so I can't help you there.

Implementing periodic boundaries is easy (see examples).

Regarding the strange gap, it is the result of the boundaries formulation DBC (see https://dual.sphysics.org/faq/#Q_13)

Regards

kavsole · May 2023

Dear @TPouzol

Thanks for your help. The problem is solved now. I had made a mistake in applying and scaling the stl geometry in my XML file:

<!-- <scale x="0.9333" y="0.9333" z="0.9333" />

--> <drawfilestl file="Ship.stl">

</drawfilestl>

By removing "<scale x="0.9333" y="0.9333" z="0.9333" />" this issue was solved.

Regards

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Missing water particles when simulating a complex floating object

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