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ExtendSim Models
by John Michl 08/13/2010
ExtendSim Models
by John Michl
1. Model Building Steps
1.1. Determine goals
1.2. Understand process to be modeled
1.3. Draw a block diagram of process
1.4. Specifiy parameter values
1.5. Define logic of model and connections
1.6. Validate the model
1.7. Add data collection and graphical analysis
1.8. Analyze output and draw conclusions
2. Block types
2.1. model activities
2.2. model resources
2.3. model routing
2.4. collect data
2.5. calculate stats
2.6. display output
3. Models share certain concepts
3.1. Selection of time units
3.2. Length of a run
3.3. Number of runs
3.4. Model verification
3.5. Model validation
4. Items
4.1. Import block
4.1.1. generates arrivals
4.1.2. specify arrival pattern
4.1.3. specify amount per arrival
4.1.4. alternative would be Generator block
4.2. Input Data block
4.2.1. changing arrival rate based on exponential distribution
4.3. Program block
4.3.1. schedule specific arrivals at specific times
4.4. Attributes
4.4.1. set via
4.4.1.1. Input block
4.4.1.1.1. easiest
4.4.1.2. Operation block
4.4.1.3. Repository block
4.4.1.4. Labor Pool block
4.4.1.5. Program block
4.4.1.6. Set Attribute blocks
4.4.2. carry through entire process
4.5. Prioritizing items
4.5.1. Stack block
4.5.1.1. choose type of stack
4.5.2. other methods?
4.6. Repository block
4.6.1. holding area (think inbox)
4.6.2. can start with some items
4.6.3. assign attribute and priority as they leave
4.6.4. can't measure wait time; use Stack block instead
4.6.5. items leave FIFO
4.7. Export block
4.8. Operations block
4.8.1. simulates an activity
4.8.2. delays item passing through
4.8.3. delay time constant unless Input Random Number is attached
4.9. Transaction block
4.9.1. alternative to Operations for modeling parallel servers
4.9.2. also used to model multiple simultaneous activities
5. Queuing
5.1. blocks
5.1.1. Stack block
5.1.1.1. like Repository but with Q stats and custom routing
5.2. reneging option
5.2.1. leaves the queue because wait is too long
5.2.2. set in Queue tab of Stack block
5.2.3. adjust time with R connector
5.3. balking
5.3.1. never enters queue because line too long
5.3.2. Decision block
5.3.2.1. used to model balking
5.4. blocking
5.4.1. item finished but can't move forward; held in queue
5.5. priority queues
5.5.1. attributes tab of Input block - set priority
5.5.2. use Select DE Output block
6. Routing
6.1. Decision block
6.1.1. yes/no or binary paths
6.2. Decision(5) block
6.2.1. up to five paths
6.3. Select DE (discrete event) block
6.3.1. use for probabilistic section of paths
6.3.2. check Do Not Use Connector and select Route Items by Probability
6.4. Merge block
6.4.1. combine up to three streams into one
6.4.2. doesn't process or hold; just combine
7. Processing Time
8. Batching
8.1. Operation block
8.2. Batch block
8.2.1. batch up to three items into a single output
8.3. Unbatch block
8.3.1. separate up to three item
8.3.2. used to separate resource from the item so item can go forward and resource back to pool
8.3.3. when batch/unbatch, check Preserve Uniqueness
9. Resources
9.1. Labor Pool block
9.1.1. defines attributes of resource including availability and usage
9.1.2. use to determine staffing needs based on performance measures such as queue length, waiting time, resource utilization
10. Cycle Time Analysis
10.1. Timer block
11. Measures
11.1. wait time
11.1.1. queue modeling blocks
11.2. utilization
11.2.1. resource blocks
11.3. Count Items block
11.3.1. number of items that route through a certain path
11.4. various statistics blocks
11.4.1. don't need to be connected; just present
11.4.2. collect data from blocks that have a delay or processing time (Operation, Stack, etc.)
11.4.3. Queue Stats block
11.4.3.1. from DE lib
11.4.3.2. ave queue length, max Q length, ave wait, max wait time
11.4.4. Resource Stats block
11.4.4.1. from DE lib
11.4.4.2. collects from resource-type blocks like Repository, Labor Pool
11.4.4.3. resource utilization
11.4.5. Costs Stats block
11.4.5.1. from DE lib
11.4.5.2. info on costing blocks like Operations
11.4.5.3. cost per item, cost per unit of time, total cost
11.4.6. Cost by Item block
11.4.6.1. from DE lib
11.4.6.2. cost info for every block that passes through the block (must be connected)
11.4.6.3. cost of each item
11.4.6.4. connectors
11.4.6.4.1. average cost
11.4.6.4.2. current cost
11.4.6.4.3. total cost
11.4.7. Mean & Variance block
11.4.7.1. calcs average and std dev for the simulation
11.4.7.2. connect to plotter to see ave over time
11.4.8. Activity Stats
11.5. Plotters
11.5.1. Plotter, DE block
11.5.1.1. four inputs on discrete events
11.5.1.2. value
11.5.1.3. time value (when it happened)
11.5.1.4. use Show Instantaneous Length option if connected to L on Stack
11.5.2. Histogram
11.5.2.1. connect L from Stack
11.5.2.1.1. Length column is length of queue
11.5.2.2. adjust bins; often 6
