What exactly is relative veloycity in collision results?

Clemenslischka

Hi,

i need to better understand the mechanics of collisions in EDEM. When i export the results for Particle-Wall "relative velocity" in the Collisions tab. What exactly is this value? Is it the velocity difference of a particle with my specified wall before and after a collision? And if so, how can i know the velocity of my wall after the collision? How can i calculate the energy that is transfered by the geometry to the particles?

Second question: When i export the total energy loss per collision. What is this value? Is it the kinetic energy loss during collision due to the elasticity of the collision (tuned by the restitution coefficient?). And if so, why is the value negative or positive? I would assume energy loss during collision should always be negative, since energy can only be lost in any collision with my wall. Sorry, if i ask such basic questions, but i can not find the answers in the manual.

Thank you

Stephen Cole

Hi Clemens,

The relative velocity is the relative velocity at the contact point, which takes into account the rotation of the particle as well as the velocity at the Centre of Mass.  The difference before and after the collision is averaged to get the relative velocity.

 

Generally I'd look at Contact Force or Geometry Power, the geometry Power calculation is the power required to move the geometry based on the imparted forces.

 

Hopefully I answered the energy loss question in your later post Help with some results regarding the Restitution Coefficient we do see -ve energy losses when a geometry will impart a force to the particle, if a particle was placed on a flat plated and lifted this particle would gain energy from the collision based on the power applied by the geometry (essentially an external source of power) and in the current version energy gained is represented by -ve energy loss.  However as mentioned we are working at updating these calculations to clarify the analysis.

Regards

Stephen