Reply To: How joint force is distributed among fem nodes in transient simulation.

[josegegas]

 

 

I would not say stress is “not accurate” in the Ansys simulation results above. “Not accurate” impies at least some accuracy, but to me in this case the stress distribution is plain wrong. Ansys is showing minimum stress in the areas where in reality there would be maximum stress and vice-versa. 

I also think a static structural analysis as descrived would not solve the issue. There will be some problems with this approach. First, a fixed support at one end would show stresses around the fixed nodes or even in other areas of the part, stresses that do not exists in reality. Second, the peak load at the other end may not be correctly distributed among the nodes in the bearing face. The load distribution may not be an accurate representation of how the pin would in reality apply load to the pendulum. This of course depends on the algorithm Ansys uses to distribute load using the “bearing load”. Is there a destription of this algorithm? Another issue with this is that the joint may also exert torque in addition to force. This torque woud have to be applied as a load to the bearing nodes, but how?

I think Ansys may have a better way to do this. Something like what other solvers call “inertia relief”. “Inertia relief” may also be a good description of how the results were obtained with the other software mentioned above. It basically computes the inertial forces for each solid element in the mesh, for each time-step of the MbD simulation, and then does the fem cancelling-out these inertial forces, by applying the “d’Alembert” force to each element. Taken from Wikipedia: “D’Alembert showed that one can transform an accelerating rigid body into an equivalent static system by adding the so-called “inertial force” and “inertial torque” or moment..”

How to do this in Ansys? How to apply “inertia relief”? I assumed Ansys would do this by default when doing transient analysis.