Hi fellow Abaqus users,

I'm running a dynamic (explicit) simulation in Abaqus CAE to analyze the reaction forces on a vertical shaft supported by two bearings. The shaft is impacted axially by a rod at the top, while the bottom rests on the ground. I've set up parts, assembly, boundary conditions, meshing, contacts, and interactions, and I'm using an explicit step with mass scaling (percentage change in mass is below 10%).

However, when I analyze the reaction forces in the Y direction and compare them with hand calculations, I noticed that there is differences between results of simulation and hand-calculations. For example, in Y direction, reaction force is approaching 200 kN at the end of the simulation, For that we would expect only a gravitation force of ~ 0.8 kN.

Additionally, after a certain time, the total energy decreases and even becomes negative.

I've used Linear "reduced integration" element meshes, and enhanced Hourglass controlling. Is there be an issue with my setup? What might be causing the negative total energy and differences in reaction forces?"

I need to mention that I am running for 2 seconds, I know it is too much for dynamic analysis, but since its a metal deformation process, I need to see the reaction forces between shaft and bearings for this period, because for a short time, the process would not be completed.
I ran the simulation for a shorter time like 0.2 Seconds but still negative energy happened!

Thanks in advance,