10.3 – Arrival-Related Techniques
10.3.1 – Constant Supply of Entities
An arrival that supplies entities to the attached activity whenever that activity has the capacity to take more entities (any input queue capacity is ignored).
Suggested Technique
1. Create the entity and the activity at which it will arrive.
2. Create an arrival connection to the new activity from the entity.
3. On the arrival connection’s properties sheet, select Continuous from the Type pull-down box.
Example: The beginning of an assembly line has a constant supply of Part_A . Whenever the first assembly station ( Assembly_1 ) has a need for Part_A , it’s there.
TO DO: In the arrival connection’s properties sheet, select Continuous from the Type pull-down box. (This is the default connection type.)
10.3.2 – Fixed Interval Arrivals
Arrivals in which one or more entities arrive at fixed time intervals.
Suggested Technique
1. Create the entity and the activity at which it will arrive.
2. Create an arrival connection to the new activity from the entity.
3. On the arrival connection’s properties sheet, select Periodic from the Type pull-down box.
4. Enter the time interval and select the time unit.
5. Enter the quantity of entities to arrive at each interval.
Example: A tour group convenes in the lobby of a museum every hour to start a tour. The size of the tour group is 25.
TO DO: Place the entity and activity in the model. Connect the entity and activity and select Periodic from the Type pull-down box. Enter the 60 min in the Repeat every field and 25 in the Quantity per arrival field.
10.3.3 – Random Interval Arrivals
An average number of entities arrive randomly throughout a specified period. Useful in modeling situations where no specific pattern seems to exist.
Suggested Technique
1. Connect the entity to the storage or activity.
2. Select the connection and choose Periodic from the Type pull-down box.
3. Enter a distribution to create randomness in the Repeat every field. (The exponential distribution is recommended, e.g., E(10) would yield a random time period with an average of ten minutes.)
4. Enter the number of entities to arrive during the period. (This is usually left at the default of 1 .)
Example: A car wash gets an average of ten customers per hour arriving at random intervals. (This can be reduced to one customer about every six minutes.)
TO DO: Connect the Customer entity to the Line storage (where customers wait in line) and select Periodic from the Type pull-down box. Enter a distribution of E(6) to create an arrival about every six minutes.
10.3.4 – Appointment Scheduling
Arrivals occurring at specifically scheduled times such as office appointment schedules.
Suggested Technique
1. On the arrival connection’s properties sheet, select Scheduled from the Type pull-down box.
2. Click on the Define Schedule… button.
3. Use the Scheduled Arrivals dialog to define the appointment schedule (see example below).
Example: A dentist wants to model his office procedures including the appointment schedule to decrease patient waiting time. The appointment schedule is modeled using a Scheduled arrival with one patient arriving every half hour except during the noon hour.
TO DO: Create the Scheduled arrival connection. Click the Define Schedule button and create a schedule. Click the New button for each scheduled arrival. (Any changes to the edit fields are updated when you press the New button.)
You can define action logic for each scheduled arrival entry. This is done in the lower half of the Scheduled Arrivals dialog. This is mainly useful to assign specific attribute values such as patient type.