Particle Packing changes the moment the coupled model activated ??

Submitted by Luton on Wed, 01/03/2018 - 11:54

Hello everyone,

I am running the coupled model with multi-sphere particles by creating a very loose packing density (%80 void fraction) inside a cylinder, where the air flows between the two ends of the cylinder.

I am using both friction and cohesion models in order to keep the particle as far as possible from each other to create such loose packing.

Each of my multi-sphere particle consists of one large particle in the middle and six particles with half large particle radius on the top of large particle (No overlaping).

I am trying to study the permeability of this packing by initiating an air flow with very small velocity through the cylinder, but the moment I run the coupled model the particles packing collapse down and the void fraction goes up to about %70 .

I also tested the model by setting both the velocity and the pressure to zero, but I noticed that some values for velocity and pressure appeared randomly in the beginning of the simulation and my particle packing was collapsing again even with zero input values.

I am not sure exactly what causes this problem, is it related to the coupled model or multi-sphere model? Any hints or advice would be very appreciated.

Thanks in advance,

Luton

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alice's picture

alice | Mon, 01/08/2018 - 11:16

Hello Luton,

I assume that you packing is stable when you run a pure LIGGGHTS simulation and that the collision is not gravity-driven?

Of course an air-stream could re-arrange the packing and thus cause the collapse, but with zero velocity this should of course not happen.

For starters you could also freeze the packing (apply a fix freeze on the liggghts side or stop integrating the multispheres)  and see how the pressure developes.

Cheers,

Alice