Hi,
Yes, use tabular loads in Mechanical APDL. Might be easiest to define the pressure outside of ansys and then read it in using the *TREAD-command. I normally use Octave, Scilab or OO Calc to define tables. Make sure to format it adequately for the *TREAD-command.
Define your pressures in a table containing the corresponding spatial coordinates, this is well documented in the help if you search for tabular loads.
Define a local cylindrical csys lined up with the axis of the drum. Make sure that you have your local csys active when you apply your tabular load.
HTH
petb