Vensim software work required for 3 students 3 copies

Dr. Daniel Xing Email: [email protected]

EBUS-504

Operations Modelling and Simulation

Witness Intro

Build your first model in Witness

University of Liverpool

Management School,

UK

Objective of this session

• Understand Witness modelling and simulation foundations;

• Learn the basic Witness functions and elements;

• Build your first Witness model and walk around Witness

Statistics;

• Understand different input rules;

First look of Witness GUI

Standard toolbar

Menu

Witness

toolbar

Simulation space

List of

simulation

elements

Interactive

window Designer elements for

quick built-upSimulation toolbar

Basic elements

✓ Part- representing

materials and products;

✓ Buffers- representing

storage, warehouse, and

queues etc.;

✓ Machine- representing

the machinery resource

which can be used for

processing materials or

serving customers;

✓ Labour- representing

manpower for different

operational purposes.

Element types

• Part types ➢ Active – output from external world, details of its output need to be specified.

➢ Passive – produced internally, no output details is needed.

• Machine types ➢ Single: One in one out;

➢ Batch: X in one out but inputs are not transformed;

➢ Assembly: X in one out and outputs are assembled from the input parts;

➢ Production: One in X out and the output types can be defined.

Elements of a sample model

• Model description

A1 B1 M1

L1

A1

o Arrives every 3 minutes

o First arrival at 2 minutes

o Lot size: 4

o Output: Push to B1

M1

o Input: pull from B1

o Cycle time: 5 minutes

o Setup: L1 spends 2 minutes for

every operation and start from

the first operation

o Output: Push to ship

Elements interactive play

• Input and output rules ❑ Part:

✓ Only active parts has output rules

❑ Machine:

✓ Input rule: wait (passive input rule) or different proactive input rules

✓ Output rule: wait (passive onput rule) or different proactive onput rules

❑ Buffer

✓ No input nor output rule

❑ Conveyor

✓ Same as machine

Define input and output rules

• Method 1 – write your syntax in element detail dialog box

Define input and output rules

• Method 2 – Visual input & output rule

Labour rules

• In setups

Labour rules

• For manual machines

Basic modelling steps

• Step 1: Define Witness elements (use designer elements for

build-up);

• Step 2: Change element graphics if necessary

• Step 3: Detail your elements;

• Step 4: Define your input and output rules;

• Step 5: Simulate, verification and analysis.

Simulate your model

Reset your

simulation

Pause your

simulation

Step run your

simulation

Run your

simulation

Fast forward your simulation

to the defined end time

Current time of your

simulation

Warmup period

Pre-defined simulation

end time

Animated simulation

active/de-active and

speed

Motion speed of your

animation

Statistics

Statistics

Statistics

Statistics