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
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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 = RxT
Source: Managing Business Process Flows (1999)
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Agenda
• National Cranberry Coop
• The Effect of Variability
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Critical Assumptions
from National Cranberry
 Truck arrivals are constant, evenly spaced over the
11 (12) hour period
 The mix between wet and dry berries is constant at
70/30
 No variation in processing time at the individual
processing stages
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Agenda
• National Cranberry Coop
• The Effect of Variability
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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)
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Post Office: Customer processing
Customer #
Time
Time
Source: Prof. K. Gue, Winter 03
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Post Office: With constant processing time
Customer #
Time
Time
Source: Prof. K. Gue, Winter 03
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Post Office: … and constant interarrival time
Customer #
Time
Time
Source: Prof. K. Gue, Winter 03
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Reasons Why Queues form
Call #
 Variability:
– interarrival times
– processing times
– server availability
10
9
8
7
6
5
4
3
2
1
0
0
20
40
60
80
100
TIME
 (System) Utilization:
 = throughput/capacity
Inventory (# of calls in system)
5
4
3
2
1
0
0
Source: Managing Business Process Flows (1999)
20
40
60
TIME
80
100
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