About Multiple Resource Simulation

Multiple Resource Simulation enables users to select tasks associated with more than one resource (e.g., multiple robots or multiple manikins) and simulate those tasks simultaneously, even though the tasks run sequentially in the process document.
  Multiple Resource Simulation serves as a lead-in to Process Simulation .
  Once you invoke the Multiple Resource Simulation , you get the Multi Resource Simulation dialog box.

  The dialog box lists all the resources in the PPR tree that have tasks associated with them.  Use the list to select the tasks you want to see run simultaneously.  (Remember that None is an option for the list associated with each resource.)  Once you select the tasks and click OK, you see the toolbars associated with Process Simulation
See Running the Process Simulation for more information.