ESI4523 Exam 1
Resource Module
mange resources used in a simulation model; set queue capacity and patter of failure
Simulation
method to mimic real systems under virtual environment
Steps in Simulation
1. Problem Formulation 2. Set Objective 3. Model Conceptualization and Data Collection 4. Model Translation 5. Verify and Validate 6. Experimental Design 7. Production Runs and Analysis 8. Documentation and Reporting 9. Implementation
NR
number of busy resources
NQ
number of entities in the queue
Event Calendar
place where future events are stored; Arena places newly scheduled events to event calendar in increasing order of event times
Verification
process to check whether the model works properly
Decide Module
provides branch points by condition or by chance
Sample Path
record of time depended behavior of the system
Process Module
represents the processes such as machine drilling; resources, queues, entity delay time defined
MR
resource capacity
Resources
seized and released by entities; entities compete with eachother for service from resources
Route/Station Transfer
send an entity from one station to another without direct connection
Entity Module
sets different types of entities in simulation model
P-value
significance level at which we can reject the null hypothesis; large p-value = good fit, small p-value = bad fit If p-value is smaller than alpha reject the null
Events
something that happens at an instant of time that might change a system state
Dispose Module
terminates entities; records entity stats
Stopping Rule
time or number of parts produced; stops simulation from running forever
When to Use Simulations?
to evaluate the behavior of the system under different sets of conditions. Dynamic, complex, and uncertain systems need simulation.
Event Routine
updates system state and statistical counters
Station Module
used as an entry point to sections of model logic. It provides location information of entities to simulation logic.
Statistical Accumulators
used to estimate desired performance measures
Resource Failures
used to model unplanned, random downtimes; can be time-based or count-based
Resource Schedules
vary capacity of a resource over time; can be idle, busy, inactive or failed
Dynamic Plots
visualize states of system, trace variables or queues as simulation runs, disappear after run ends
Scheduled Utilization
∫B(t)dt/∫M(t)dt B(t)-busy resources M(t)-schedule resources
Instantaneous Utilization
∫U(t)dt/t U(t) = B(t)/M(t) B(t)-busy resources M(t)-schedule resources
Continuous Function
CONT(CDF value, X value,....)
Chi Square Test
Chi Square = sum(nj -ej)^2/ej If Chi Square is small then it is a good fit
Continuous vs Discrete Simulation
Continuous - state of the system changes continuously over time Discrete - state of the system changes only at discrete points
Komolgrov-Smirnov Test
D=greatest vertical distance between empirical distribution and theoretical distribution
Discrete Function
DISC(CDF value, X value,...)
Deterministic vs Stochastic Simulation
Deterministic - No probabilistic components Stochastic - random behavior on components
Little's Law
Length of queue = arrival rate * wait time
Normal Distribution
NORM(mean,standard deviation)
Static vs Dynamic Simulation
Static- at a particular time or time plays no role Dynamic - evolves over time
Tradeoff between System and Model
Systems are more costly and complex, but they have a higher fidelity. Whereas models are less costly and simpler but have a lower fidelity.
Triangular Function
TRIA(Min,Mode,Max)
Uniform Distribution
UNIF(min,max)
Linear Congruential Method
Zi = (aZi-1 + c) mod m Ui = Zi/m Full period if m = period
Queues
a place where entities can wait when no resource is available
Record Module
able to collect and report various kinds of statistics(e.g., user defined statistics)from within model run as entities pass through it.
Counter Statistics
accumulated sums of something; accumulation of number that are not all 1; total production
Assign Module
assigns certain characteristics to different entities
Schedule Rule - Wait
capacity decrease waits until entity releases the resource; full break but may start and end late
Schedule Rule - Ignore
capacity goes down immediately for stat collection, but work goes on until finished; could shorten break
Schedule Rule - Preempt
capacity goes down immediately; processing is interrupted and break starts immediately
Time-persistent Statistics
continuous time statistics; statistics obtained from trajectory of system state over time; utilization of a machine
TNOW
current simulation time
Timing Routine
determines the next event type and advances the simulation clock
Tally Statistics
discrete time statistics; taking average, minimum, maximum; average waiting time, max waiting time
Entities
dynamic objects in the system; something moving throughout the system
TFIN
final simulation time
Create Module
generates entities
Storage Module
holds a non-ordered set of entities that are waiting for an event to occur the conclusion of a predefined delay time and arrival of a requested transporter that is en route.
Variables
information that reflects some characteristics of the system
Simulation clock
keeps track of the current value of simulated time
Attributes
local variable characterizing entities