Fine Tuning DEM Inputs

HelixChute2 gives you the tools to build a model of the transfer station, but it's up to you to adjust the input data until the model represents a realistic flow of particles. The calculation engine applies the physical laws of motion, collision and impulse, but the actual flow of material depends on many factors beyond gravity and Newton's laws alone.

Coefficient of restitution, coefficient of friction, face and particle stiffness, particle size and mass, belt speed and more all affect flow, and these differ not only between materials but for the same material under different conditions (e.g. moisture content).

General rules for adjusting DEM inputs

Set Particle Stiffness so particles overlap only slightly. Too low and they overlap a lot; too high and they spring apart too violently, especially at the discharge pulley. Re-tune it whenever you change particle density or size.
Set Face Stiffness so particles penetrate the belt surface a little, but don't bleed through it and aren't shot into the air.

These settings depend on the calculation time step dt, particle density and particle diameter, so there's no universal setting, but as a starting point for iron ore:

time step = 0.005 s
density = 3200 kg/m³
particle diameter = 70 mm
particle stiffness = 300
face stiffness = 5000
vertical chute face friction = 0.1, e = 0.6
curved impact plates e = 0.2

Adjusting speed on a sloping surface

Adjust the speed at which particles slide down a sloping face using the layer's friction and co-efficient of restitution e (on the Chute Faces tabsheet, select the layer):

To increase speed – reduce friction and increase e.
To reduce speed – increase friction and reduce e.

Both friction and e must be between 0 and 1.

Overall, the best way to fine-tune these inputs is to model an existing chute, observe the real material flow on site, and adjust the inputs until the model matches. You'll then have values you can trust for designing new transfer stations – see Calibrating the DEM Model.