Operations Management National Cranberry - Lecture 5 (Chapter 5)

Dr. Ursula G. Kraus

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Review • • • • Flow Time Analysis Capacity Analysis Kristen’s Cookie Company Resource Pools 2/12

Review: Process Flow Measures   

Flow Time

(T): The

average

time a job spends in the process

Inventory

(I): The

average

number of jobs accumulated in the process

Throughput

, or Flow Rate (R): The

average

rate at which jobs flow through a process

Little’s Law I = R x T

Source: Managing Business Process Flows (1999) 3/12

Agenda • National Cranberry Coop • The Effect of Variability 5/12

Critical Assumptions from National Cranberry  Truck

arrivals

are constant, evenly spaced over the 11 (12) hour period  The

mix

70/30 between wet and dry berries is constant at  No variation in

processing time

processing stages at the individual 6/12

Agenda • National Cranberry Coop • The Effect of Variability 7/12

Post Office: Why Do Queues form?

• Average inter-arrival time is 4 minutes • Average processing time 3 minutes We are processing customers faster than they arrive so what's the problem?

Source: Managing Business Process Flows (1999) 8/12

Post Office: Customer processing

Customer # Time Time

Source: Prof. K. Gue, Winter 03 9/12

Post Office: With constant processing time

Customer # Time Time

Source: Prof. K. Gue, Winter 03 10/12

Post Office: … and constant interarrival time

Customer # Time Time

Source: Prof. K. Gue, Winter 03 11/12

Reasons Why Queues form 

Variability:

– interarrival times – processing times – server availability

Call #

10 9 8 3 2 1 0 7 6 5 4 0 20 

(System) Utilization:

 = throughput/capacity Source: Managing Business Process Flows (1999)

Inventory (# of calls in system)

5 4 3 2 1 0 0 20 40

TIME

60 40

TIME

60 80 80 100 100 12/12