There are several descriptions of how to calculate wear in Ansys Help using Mechanical APDL Contact elements.
To read these, first open Ansys Help, then copy/paste the following URLs into the Ansys Help address bar.

The first link is to a technology guide using Workbench, the second link is the guide for Mechanical APDL and the third link is to the material reference.

The example is a simple and well controlled configuration of two parts. Your question involves many stones that contact the shell and each other. That is not a good fit for using MAPDL contact to evaluate wear since there are too many contact pairs and they would overwhelm the contact algorithm.

Explicit Dynamics or LS-DYNA are solvers that can easily solve multibody random contact such as you have described, but they can't use the MAPDL Archard Wear Model. Instead you could model many very thin layers of elements that would be removed due to damage caused by impact and sliding. However, the run time of these solvers is a function of the element size, so this would create a model that would need to run for months or years. The SPH method of these solvers may be an area to investigate. The SPH method creates parts using small spheres that are held together until applied forces pry them apart. I have no experience with the SPH method, so you will have to do some research but I believe the number of spheres that are small enough to model wear will also create a model that is too big to run except on a supercomputer.

I believe the best method is an experimental approach. Build the drum, run it with stones and measure the wear.