1. Modeling and Analysis of Picking Warehouses Using Simio Jeff Smith Industrial and Systems Engineering Auburn University
This chapter replaces chapters 1 & 2 of the standard course for use with experienced simulationists.
Chapter 2 - Introduction to Simio

2. Simio Learning Resources
Videos (
Publications
Introduction to Simio (Included PDF and downloadable seven-part video series)
Joines, J.A. and Roberts, S.D., Simulation Modeling with SIMIO: A Workbook
Kelton, W.D., J.S. Smith, and D.T. Sturrock Simio & Simulation: Modeling, Analysis, Applications
When getting to know Simio, the key place to start is the Support Ribbon.
Resources to learn about Simio, interact with others, and get technical support
Discuss:
SimBits & other Learning Simio Items
Shared Items,
User Forum

3. Key Simio Object Concepts
Defines data, logic, behavior, view, events, and interaction with other objects.
Model:
An object that is executable.
Project:
A collection of models/objects.
A project can be loaded as a library.
Properties:
Static inputs to an object.
States:
Changeable values associated with an object
Events:
Supports communication between objects. Fired when key things happen.
Resource:
Constrains the system. Any object (even an entity) may be a resource.
Entity:
A dynamic object that may move through system
Transporter:
An entity that can “work on” or carry other entities. Vehicles and Workers are entities (and resources).
These concepts are central to understanding Simio’s object model
<click>A project is a collection of 1 or more models which are themselves just objects.
<click>Properties, states, and events, are key characteristics of objects
<click>While Simio’s definition of resource is similar, the concept is much more flexible and useful.
Vehicles and Workers are essentially moveable resources “on steroids” (great capabilities)

4. Simio User Interface Files Menu Ribbons Project Tabs Libraries Project
Current Model
Properties
Facility View
<Open Simio>
<Review UI>
App Menu – Load, Save, Examples, SimBits
Ribbons – switch based on context, extended tool tips, minimize
Project Tabs – for switching between windows associated with the selected project object
Std Library – 1 set of objects, you can build your own
Start Page – Links to valuable resources and your software version
Project Navigation– for switching between the objects you are working on
Properties – describe the objects you are working with
<Support Ribbon>

5. Standard Library Source:
Generate entities of a specified type and arrival pattern.
Sink:
Destroy entities.
Server:
Capacitated process, such as a machine.
Workstation:
Capacitated process, includes setup, process, tear-down.
Combiner:
Batches entities with a parent entity (e.g., pallet).
Separator:
Splits batches or copies entities.
Resource:
Seized/Released by objects.
Vehicle:
Fixed route or on-demand pickups/drop-offs.
Worker:
Moveable resource, for stationary and non-stationary tasks.
BasicNode:
Simple intersection, fixed object input.
TransferNode:
Change destination/get rides, fixed object output.
Connector:
Zero travel time.
Path:
Entities independently move at their own speeds.
TimePath:
Entities complete travel in a specified time.
Conveyor:
Accumulating/non-accumulating conveyor devices.
Most models will be built using these 15 objects.
Each object has basic capabilities and advanced capabilities
Each object can be customized with add-on processes
Each object is open and can be derived from and modified
There are 5 basic grouping of objects:
<click>Entity creation and destruction
<click>Servers (machines)
<click>Resources
<click>Nodes
<click>Links
Chapter 2 - Introduction to Simio

6. Simple Flow Line Server 1 Arrive Server 2 Depart
Let’s now build a simple model to illustrate some of these concepts.
--Open Simio and select New Model.
--Drag and place the Source, two Servers, a Sink, and a ModelEntity
--Double click on the Path object to enter path drawing mode and connect the nodes. Escape in the drawing space to terminate path drawing mode.
--Click on the Run button on the left side of the Run ribbon and you will see your model start executing
The green triangles are entities that represent the customers moving through the system. Note that each server has three green lines representing animations of the queues owned by the server.
You can pause and restart the simulation, or stop the execution of the model. You can also step an entity at a time, fast-forward the run without the animation, or reset the model back to its starting conditions.
You can perform graphical edits such as moving a Server, adding a new path, etc., while the model is running, but you must stop the simulation to change any of the object properties – Properties can’t change value during the simulation run.

7. Object Hierarchy - The Family of “Objects”
Object Runspace
(Realization)
Object Instance
Object Definition
Show the Simio Help – look up “Object Hierarchy” and discuss the details.
(Lots of good stuff in that help topic, plus this illustrates the value of using Help).
Will discuss this again later in the course – I’ve found this topic especially tricky with students.
Definition … Instance … Runspace (Realization) :

8. Simple Flow Line - Details
Server 1
Arrive
Server 2
Depart
Update the model to reflect the tandem queueing model parameters Source: Random.Exponential(2.4) minutes
Server 1: Random.Exponential(2) minutes
Server 2: Random.Exponential(1.71) minutes
Run length: 100 hrs.
Run in Interactive mode. Show Results (pivot grid)
(ρ) Utilization of a server, or of a group of parallel identical servers, the time-average number of individual servers in the group who are busy
(L) Number of entities in system, including in queue plus in service
(W) Time in system, including time in queue plus service time

9. Editing Object Properties
Displayed in Properties Window
Defined by object builder
Integers, Booleans, rules, expressions, …
Expression editor (down arrow at right):
Whenever you select an object in the facility (by clicking on it) the properties of the selected object are displayed for editing in the Property window in the Browse panel on the right.
The properties for an object are defined by the designer of that object. The properties may be different types such as strings, numbers, selections from a list, and expressions. For example the Ranking Rule for the Server is selected from a drop down list and the Processing Time is specified as an expression.
For expression fields an expression builder simplifies the process of entering complex expressions. When you click in an expression field a small button with a down arrow appears on the right. Clicking on this button opens the expression builder.
Random distributions, Math Functions
Object functions may also be referenced by function name. A function is a value that is internally maintained or computed by Simio and can be used in an expression but cannot be assigned by the user. For example all objects have function named ID that returns a unique integer for all active objects in the model. Note that in the case of dynamic entities the ID numbers are reused to avoid generating very large numbers for an ID.
If you type an invalid entry into a property field the field turns a salmon color and the error window will automatically open at the bottom. If you double-click on the error in the error window it will then automatically take you to the property field where the error exists. Once you correct the error the error window will automatically close.

10. “Top 10” Expressions X (a number – integer or real)
Random.Exponential(mean)
Random.Triangular(min, mode, max)
Random.Uniform(min, max)
ServerName.Capacity.ScheduledUtilization
ServerName.InputBuffer.Contents
DefaultEntity.Population.TimeInSystem.Average
DefaultEntity.Population.NumberInSystem.Average
SinkName.InputBuffer.NumberEntered
SinkName.TimeInSystem.Average

11. Simple Flow Line – Expressions
Source1
Interarrival Time: Random.Exponential(2.4)
Server1
Processing Time: Random.Exponential(2)
Server2
Processing Time: Random.Exponential(1.7)

12. Simple Flow Line - Experiment
Server 1
Arrive
Server 2
Depart
Run the model interactively, discuss, show the pivot grid
Create an experiment, discuss, run 10 replications, show the pivot grid
Create a View called Base
Filter:
Data item: Number in System, Time in System, Scheduled Utilization
Statistic: Average, Average (Hrs), Percent
Point out and discuss the two observations of Time in System (the Model Entity population and the Sink)
Create a ‘View’ of the filtered pivot grid. Remove the filters and illustrate going back to the view.

13. Simple Flow Line – Responses
Server 1
Arrive
Server 2
Depart
A Response is an expression that is evaluated (and displayed) at the end of each replication.
The pivot grid (object name, category and data item) is a good source of information
Create responses for UtilS1, UtilS2, NIS, TIS and run the experiment
--Server1.Capacity.ScheduledUtilization
--Server2.Capacity.ScheduledUtilization
--DefaultEntity.Population.NumberInSystem.Average
--Sink1.TimeInSystem.Average (Unit Type: Time, Units: Hours)

14. Simple Flow Line – SMORE Plots
Server 1
Arrive
Server 2
Depart
Simio Measure Of Risk and Error
Demonstrate the options on 10 reps.
Run for 100 or so reps and watch the SMORE plot.

15. Simple Flow Line – Throughput Response
Server 1
Arrive
Server 2
Depart
Create a response to measure throughput. First step, define exactly what we mean by throughput.
Throughput === number of customers that leave the system / unit time

16. Buffers and Referenced Properties
Server 1
Arrive
Server 2
Depart
Convert the paths to connectors (just a convenience – the paths act as buffers and we don’t want that yet).
Set the all buffer capacities to 0
Run the experiment, update the property values, see the effect on throughput …

17. Buffers and Referenced Properties
Server 1
Arrive
Server 2
Depart
Create referenced properties for the two input buffer capacities.
Show the Control properties for the model.
Update experiment with multiple scenarios – different control values.

18. Buffers and Referenced Properties
Server 1
Arrive
Server 2
Depart
Create referenced properties for the two buffer capacities.
Set objectives for Thput and TIS – use Subset Selection.
Mention that OptQuest is there and we’ll come back to it ….
Depending on the audience, add referenced properties for the server processing times (model-03) – Good time for a “lab/exercise” using different Simio distributions for the processing time properties: Help : Expression Editor, Functions, and Distributions : Distributions

19. Simple Picking Warehouse

20. Pickers Fork Lift Walk speed: 1 meter/sec
Pick time: Uniform(10, 20) sec
Pack time: Triangular(.5, 2, 3.5) min
Fork Lift
Travel speed: 1.5 meters/sec
Load time: Uniform(5, 10) sec
Unload time: Uniform(20, 30) sec

21. Racks
45 m
30 pick positions in each rack (approximate using 15 evenly spaced locations)
Decisions:
Number of pickers
Number of pack stations
Number of forklifts