Learning Forum

[wakai.kaiki.q2]

Hello. I am using Autodyn to study space debris and shield damage.

We are analyzing a sphere like the one in the photo that collides vertically with two aluminum plates with a gap between them at 7 km/s. The two plates are located at the top and the bottom of the sphere.The two aluminum plates are fixed at the top and bottom under the condition of zero velocity.

 The attached figure shows the energy transition, and there is a term labeled 'Work done.' What exactly is doing work on what? Since the figure displays the energy transition for all particles, if one particle does work, another particle receives an equal amount of work, so the total work should sum to zero. However, the graph shows a non-zero value. Why is this the case?

[Chris Quan]

The  Work Done in the Energy Plot includes the work done by displacement constraints, loads, body forces, and contact penalty forces. It also includes the Energy removed from system by element erosion.

 

It is true that when one particle impacts the other particle, the contact force are equal on each particle but are in opposite directions. Thus the total contact force on these two particles are zero so equlibrium is reached. But the work is not zero. The work done by the contact force is equal to the contact force mulitiplies the contact penetration that the contact force has removed or increased during that time step (cycle).

 

If contact force has removed the contact penetration, both contact force and contact penetrations are in the same direction, the work done by contact force is positive. If contact force has not removed any contact penetration or contact penetration increases during that time step (cycle), contact force and contact penetration are in the opposite direction, the work done by contact force may be zero or negative.