Learning Forum

[ivan.beltracchi]

Hi everyone, 

I'm doing some DEM analyses in Rocky (by using the CFD results from a VOF analysis with air and concrete) with a certain amount of fibers, which are generated from a surface inside the domain. These fibers could be subjected to drag forces from the flow of concrete (generated from an inlet) to fill the volume showed in the pic. 

After an initial phase in which a certain generated number of them fall and settle on the bottom in a physically acceptable way, it seems that many of them are lifting upwards (while the domain is filling with concrete) and they are dissappearing and they are not accumulating within the domain, as concrete does. 
As also showed in the plots, the number of particles count and the particles Enabled are lower than the number of particle released.

I don't know if maybe there could be an imposed limit of the particles or there could be something else which prevents the accumulation of them in the correct amount or in a physical acceptable way, as concrete does. Could someone help me?

 

 

[Jackson Gomes]

Hi ivan.beltracch.

The DEM time step size can significantly impact simulation stability. If the DEM time step is too large, it may cause divergence issues, especially when calculating drag forces on particles. Adjusting the Rocky time step and maintaining a controlled ratio with the Fluent time step can help prevent force calculation errors and improve simulation accuracy. To achieve precise results in complex interactions, such as particles being dragged by concrete flow, optimizing the CFD mesh resolution and employing semi-resolved model can improve simulation fidelity for particle behavior under flow conditions​. 

Double-check the domain bounds to make sure it is correct defined.

Best regards.