# chaos moving of fluid particles in 3d model

edited March 10
hi i simulate a tank of water in 3d model in case DEM but when i run case and see my simulation the fluid particles have chaos movement & i dont know why!
i working in 3D model recently and i cant realize this problem. i use laminar+sps viscosity in my model.

1.PNG 52.7K
2.PNG 136.7K

• It is because you have not activated delta-SPH scheme. Because of this you get some density fluctuations which lead to chaotic movement and finally unstability. If you want to know more read Dalrymple 2004.

Kind regards
• Dear @Asalih3d in my simulation DELTASPH=0.1 and when i use artificial viscosity this problem would be solved but when use laminar+sps and v=0.000001 problem occur. are you sure this problem relevant to deltasph term?
Best Regards
• In my case, delta-SPH has played a huge role in stabilizing SPS-LES simulations since they handle the artificial density increase due to SPS-LES. Another parameter would be the number of particles, what happens if you decrease and increase the amount of particles?

A good test is always to try the artifical scheme and see if it is stable in that and then try fine tuning the laminar+sps scheme afterwards.

Kind regards
• Laminar viscosity + SPS turbulence model should be used only in the case of simulating a laminar flow and with a very high resolution... If not, it is recommend to use artificial viscosity where you can obtain more stable simulations.
Alpha=0.01 is recommended for wave tanks.

Regards
• @Asalih3d Thanks For Your Advice I try your Idea.
best Regards
• edited March 11
Dear @Alex What do you mean about High Resolution? Because The Size Of Domain Relevent To Dp and When Create Small Domain actually use smaller dp. in my simulation dp=0.005 and size of domain x=0.5 m y=0.040 z=0.06? and when run 2D simulation with Laminar+SPS this chaotic movement very decrease!!! Why?

• Dear @Alex I Increase The Y direction(double of last simulation -> y=0.080) & this problem is fix, is there any relation between this problem and resolution?
• SPS means Sub-Particle Scale model so that this model only solves turbulence at a very small scale
• @Alex Thanks Dear Professor