How is torque calculated in EDEM?

Shinichiro Oshiro

Hi all,

I would like to know about the method for calculating torque of geometry in EDEM.

1. Regarding the radius used in torque calculations, I think it is calculated using the forces and distances acting on each facet of the geometry. For this distance, does EDEM refer to the distance from the rotation axis or the distance from the center of mass of the geometry?

 

2. In the case of simultaneous rotation and translation, is the coordinate movement of the center of mass or rotation axis due to translation considered when calculating torque? At this time, It specify the geometry as a selection during the result export and assume that the Specify Axis is not used.

 

3. If I calculate the motion of the geometry using a mechanism analysis software (Adams) without setting Motion in EDEM and update the geometry position in EDEM, will the coordinate movement of the center of mass or rotation axis due to the geometry movement be considered when calculating torque?

 

Best regards,

Oshiro

Stephen Cole

Hi Oshiro,

Question1:

I'll reply if a few general comments for Q1 just to clarify the torque.  During simulations EDEM calculates the contacts between particles and geometries, we record the positions of these forces and the vector.  There are also some torques calculated during simulation but essentially this is all done in post-processing, as we have the normal force position on the geometry elements.

It's important to differentiate between torque on an element and Torque on the geometry section as a whole, the contact information is all based on element-element contact.  If you colour geometry by torque or export torque 'standard' option this exports the torque on the element not the geometry section.  This is the normal force on the geometry triangle X distance between the contact point and the element centre point.  Really this information isn't that useful as torque on geometry triangles doesn't give us any engineering data, and sum of the torque on the elements does not equal torque on the geometry as the Center of Mass is different.

 

So in the export or graphing tool there is the option of Torque Total (not Standard) and a component (X,Y,Z).

If using component X,Y or Z you can choose 'use CoM' and it will take the particle normal forces on the geometry X distance to axis specified that goes through the CoM.  So if it's a geometry rotating around it's CoM in the Z axis then this would be the query:

However you should check what the CoM is specified as, EDEM makes an approximation based on the geometry volume however if it's an open geometry or has additional components then this may not be calculated as expected.  So it's best to check the Creator  > Geometry Name > Mass  option where it's specified.

The best option in my view is to use the 'Specify Axis' option.  If you choose Torque > Total (the Z axis in the image is grey because it's not used) and the specify axis, EDEM will calculate the distance as the normal between the contact point and the axis and use this in the torque calculation:

 

Question 2:

If the geometry is translating/rotating then the center of mass option has to be used, as the fixed axis option mentioned above won't change.

Question 3

If the geometry is moving the CoM will also move, regardless if it is moved by EDEM or Adams

Regards

Stephen

 

Shinichiro Oshiro

Stephen Cole_21117 said:

Hi Oshiro,

Question1:

I'll reply if a few general comments for Q1 just to clarify the torque.  During simulations EDEM calculates the contacts between particles and geometries, we record the positions of these forces and the vector.  There are also some torques calculated during simulation but essentially this is all done in post-processing, as we have the normal force position on the geometry elements.

It's important to differentiate between torque on an element and Torque on the geometry section as a whole, the contact information is all based on element-element contact.  If you colour geometry by torque or export torque 'standard' option this exports the torque on the element not the geometry section.  This is the normal force on the geometry triangle X distance between the contact point and the element centre point.  Really this information isn't that useful as torque on geometry triangles doesn't give us any engineering data, and sum of the torque on the elements does not equal torque on the geometry as the Center of Mass is different.

 

So in the export or graphing tool there is the option of Torque Total (not Standard) and a component (X,Y,Z).

If using component X,Y or Z you can choose 'use CoM' and it will take the particle normal forces on the geometry X distance to axis specified that goes through the CoM.  So if it's a geometry rotating around it's CoM in the Z axis then this would be the query:

However you should check what the CoM is specified as, EDEM makes an approximation based on the geometry volume however if it's an open geometry or has additional components then this may not be calculated as expected.  So it's best to check the Creator  > Geometry Name > Mass  option where it's specified.

The best option in my view is to use the 'Specify Axis' option.  If you choose Torque > Total (the Z axis in the image is grey because it's not used) and the specify axis, EDEM will calculate the distance as the normal between the contact point and the axis and use this in the torque calculation:

 

Question 2:

If the geometry is translating/rotating then the center of mass option has to be used, as the fixed axis option mentioned above won't change.

Question 3

If the geometry is moving the CoM will also move, regardless if it is moved by EDEM or Adams

Regards

Stephen

 

Hi Stephen,

Thank you for your thoughtful response.

I understand that the element torque output from the Standard option and the geometry torque output from the Total option are different.

Specifically, I would like to know how the torque calculated using the "Total" option in EDEM, without specifying a direction, is derived for a screw auger subjected to both translational and rotational motion in Adams.

I apologize for the additional questions, but could you please clarify the following two points?

1.When selecting the "Total" option and not specifying a direction (Magnitude), what reference point (e.g., CoM) is used for the torque calculation?

2.When moving geometry using external software such as Adams, if the CoM of the geometry is specified (check out Auto Calculation) in EDEM's Creator, will the movement of the object be reflected in the torque calculations?

Thank you for your assistance.

Best regards,
Oshiro

Stephen Cole

Shinichiro Oshiro said:

Hi Stephen,

Thank you for your thoughtful response.

I understand that the element torque output from the Standard option and the geometry torque output from the Total option are different.

Specifically, I would like to know how the torque calculated using the "Total" option in EDEM, without specifying a direction, is derived for a screw auger subjected to both translational and rotational motion in Adams.

I apologize for the additional questions, but could you please clarify the following two points?

1.When selecting the "Total" option and not specifying a direction (Magnitude), what reference point (e.g., CoM) is used for the torque calculation?

2.When moving geometry using external software such as Adams, if the CoM of the geometry is specified (check out Auto Calculation) in EDEM's Creator, will the movement of the object be reflected in the torque calculations?

Thank you for your assistance.

Best regards,
Oshiro

Hi Oshiro,

If using Total without specifying an axis EDEM will take the torque around the X , Y and Z axis that passes through the geometry CoM and take the magnitude of the 3 values.  However I'd recommend exporting X,Y or Z rather than Magnitude.

The CoM should always move with the geometry, even if the geometry section is moved via an external coupling.  If you switch to displaying the Centre of Mass via the Global reference space you should see this is different at different time-steps if the geometry is moving.

Regards

Stephen

 

Shinichiro Oshiro

Stephen Cole_21117 said:

Hi Oshiro,

If using Total without specifying an axis EDEM will take the torque around the X , Y and Z axis that passes through the geometry CoM and take the magnitude of the 3 values.  However I'd recommend exporting X,Y or Z rather than Magnitude.

The CoM should always move with the geometry, even if the geometry section is moved via an external coupling.  If you switch to displaying the Centre of Mass via the Global reference space you should see this is different at different time-steps if the geometry is moving.

Regards

Stephen

 

Thank you for your response. I apologize for the delay in getting back to you.

Why export the torque of each axis rather than Magnitude?

Additionally, how can I calculate the total torque applied to the geometry from the torque of each axis?

I appreciate your assistance and look forward to your reply.

Best regards,

Oshiro

Stephen Cole

Shinichiro Oshiro said:

Thank you for your response. I apologize for the delay in getting back to you.

Why export the torque of each axis rather than Magnitude?

Additionally, how can I calculate the total torque applied to the geometry from the torque of each axis?

I appreciate your assistance and look forward to your reply.

Best regards,

Oshiro

Hi Oshiro,

You can use magnitude but typically the application where EDEM uses torque is a mixer or drum and often this is limited to rotate in 1 axis, so it's best to get the torque only in the axis of rotation as the motion is restricted anyway in the other axis.  The total torque would just be the magnitude of the individual values.

 

Regards

Stephen