Packages arrive with interarrival times distributed as EXPO(0.47) minutes to an unloading facility. There are f ve different types of packages, each equally likely to arrive, and each with its own unload station (see following f gure). The unloading stations are located around a loop conveyor that has room for only two packages in the queue at each unload station. Arriving packages enter an inf nite-capacity queue to wait for space on the loop conveyor, and 2 feet of conveyor space is required per package. Upon entering the loop conveyor, the package is conveyed to its unload station. If there is room in the queue at its unload station, the package is automatically diverted to the queue, which takes no time. The package then waits for a dedicated unloader (dedicated to this unload station, not to this package) to be unloaded, which takes time distributed as EXPO(2) minutes. If a package arrives at its station and f nds the queue full, it is automatically conveyed around the loop and tries the next time. Each station is located 10 feet from the next, and the conveyor speed is 12 feet per minute. Animate your model.

(a) Run the simulation for 500 minutes, collecting statistics on the time in system (all package types together, not separated out by package type), and the number of packages in queue at the package-arrival station.

(b) Which will have more impact on average time in system: increasing the conveyor speed to 15 feet per minute or increasing each unloading-queue capacity to 4? kel01315_ch09_379-422.indd 416 05/12/13 3:21 PM A Sampler of Further Modeling Issues and Techniques 417