# slow down the velocity

edited November 2017
Hi,

I am modelling a box of mud running from a plane slope and stops in the horizontal ground. The mud runs too fast and stop too far away comparing to the experiment. I try to increase the parameter of "Visco" to 0.5 and the parameter of "ViscoBoundFactor" to 25, and the mud stops a little closer but still too far. If I continue to increase these values, the mud will “fly” into the air from the slope plane at the beginning of the simulation, and some particles are ejected from the mud. It seems that the interacting force between the mud and the slope is too high. I kindly want to ask:
(1) Is there some way to slow down the velocity of the mud and not let it “fly”? Or is there something I can do to increase the “friction” between the mud and the slope? Or if I should model the slope plane using the DEM? ( I have already read the paper of “Integration of UAV photogrammetry and SPH modelling of fluids to study runoff on real terrains.”)
(2) Then I try to model the mud using the sediment model just like in the example of “Two-phase liquid-sediment implementation in DualSPHysics”, because it seems that the mud is similar to the sediment. I find that the parameter of "Coh_0" (Cohesion coefficient of the phase) has no effect on the result at all. But a very high value of "Coh_0" should imply that the mud is quite stiff, and the final shape of the mud should be different. I want to ask is there some effect of "Coh_0" and "PhiF_0" in my case?
(3) What is the maximum of DEM particle in DualSPHysics? If I create 5000 sphere DEM particle to model the mud, can it run? Many thanks to your guide!

• This should be the reason for the interaction between the boundary conditions and the fluid. I also have the same problem.
• About question (1)... you have not explained in detail what are you using to simulate mud... floatings? DEM? multiphase?

For questions related with multiphase code (soil-water) please write to Dr Fourtakas (georgios.fourtakas@manchester.ac.uk)

New v4.2 that will be released in 1-2 months will include the possibility of creating much more than 65,000 floatings, so that 65,000 different "mk" set of particles.

Regards
• hi