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Dr. Daniel Xing Email: [email protected]

EBUS-504

Operations Modelling and Simulation

Lecture 3

Bottleneck analysis

University of Liverpool

Management School,

Key learning outcomes

1. Understand what is a “bottleneck” to a simulation;

2. Use of bottleneck for different analysis;

Building a Simulation Model

3. STRUCTURED

WALK-THROUGH

2. DATA AND

MODEL DEFINITION

1. PROBLEM

FORMULATION

6. VALIDATE

MODEL

5. PERFORM

PILOT RUNS

4. BUILD MODEL

AND VERIFY

10. DOCUMENT AND

IMPLEMENT RESULTS

9. ANALYSE OUTPUT

DATA

8. MAKE PRODUCTION

RUNS

7. DESIGN

EXPERIMENTS

Bottleneck

The term Bottleneck is used to describe “a point of congestion in any

system from computer networks to a factory assembly line. In such a

system, there is always some process, task, machine, etc. that is the

limiting factor preventing a greater throughput and thus determines the

capacity of the entire system.” (Goldratt and Cox, 1984)

Bottleneck is critical

1. It determines the throughput of the entire system, i.e. the production

pace;

2. Most effective way to improve the entire system;

3. It constrains the utilisation and performance of other resources.

2mins 1min 8mins 4mins

Finding bottleneck is not always straightforward

Examples:

1. The production of product A requires a sequential processes and their

operation time is 3mins, 5mins and 7mins respectively;

2. Product A is assembled by 4 components (2Bs, 1C and 1D) with 2mins.

Each type of component requires a pre-processing operation with

machine time 3mins, 5mins, and 4mins respectively.

3. A supermarket has three tills to serve its customers. Each till needs

2mins on average to finish the service and customers arrive the store

every 1min.

4. A line production is comprised by 3 machines with operation time

6mins, 8mins and 4mins respectively. Every machine needs a 2mins

setup by L1 (there is only one labour available) and part arrives every

2mins.

Analytical-based methods Input rate vs. output rate

Bottleneck of your system is always identified when input rate is faster than

output rate

The busiest resource (capacity analysis)

Filter out the entity in the system which takes the longest time to complete a job

The most congested place (throughput analysis)

The place where a part takes the longest time to enter and leave it.

Product production lifecycle analysis

From raw material(s) until the completion of an end-product, analysing how

much time in percentage that each component needs to be operated with.

How do we find the bottleneck?

How can we use the aforementioned techniques to locate your bottleneck?

Use Gantt chart for a solution!!

2min 1mins 8mins 4mins P1

arrives

every 2

mins

Why bottleneck is so important?

1. It defines the maximal throughput rate of your system.

2. It helps modellers quickly locate queues

3. It helps you identify the total outputs at a certain point. (How do you

calculate it?)

4. It defines the maximal utilisation rate for each entity of your system.

(How do you calculate it?)

5. Most importantly, it provides further improvement directions. (Why and

how will you anticipate your improvement?)

Bottleneck and simple queues

1. Where will you build up queues?

2. How do we interpret different queues?

1min 2mins 8mins 4mins P1

arrives

every

1min

Bottleneck and simple queues

1. Where will you build up queues?

2. How do we know the waiting time for the 10th part? 50th part? Or the nth

part?

3. How do we know the queue size at minute 50? Or minute 100? Or the

nth minute?

2mins 1min 8mins 4mins

Intro for next week – steady state analysis

Recall the example and think the following questions:

1. What is the difference between the first output and any future outputs?

2. Why do we need to exclude warm-up period?

3. What if some rates are uncertain?