Simulation

Prepared by: Hussein Khaled ZahranMaha Moustafa El ZiadyMustafa Sherif IbrahimAhmad Majed Ashraf

ModelModeling is the process of producing a model; a model is a representation of the construction and working of some system of interest.A model is similar to but simpler than the system it represents. One purpose of a model is to enable the analyst to predict the effect of changes to the system. On the one hand, a model should be a close approximation to the real system and incorporate most of its salient features. A good model is a judicious tradeoff between realism and simplicity.

Simulation Simulation is the imitation of the operation of a real-world process or system over time. The act of simulating something first requires that a model be developed; this model represents the key characteristics or behaviors/functions of the selected physical or abstract system or process. The model represents the system itself, whereas the simulation represents the operation of the system over time.

Simulation

Computer simulationA computer simulation (or "sim") is an attempt to model a real-life or hypothetical situation on a computer so that it can be studied to see how the system works. By changing variables in the simulation, predictions may be made about the behavior of the system. It is a tool to virtually investigate the behavior of the system under study.

Introduction 7

LANGUAGES USED FOR SIMULATION

FORTRAN– Probably more models than any other language.

PASCAL– Not as universal as FORTRAN

MODULA– Many improvements over PASCAL

ADA– Department of Defense attempt at standardization

C, C++– Object-oriented programming language

Main stepsThe steps involved in developing a simulation model, designing a simulation experiment, and performing simulation analysis are:

• Step 1. Identify the problem.• Step 2. Formulate the problem.• Step 3. Collect and process real system data.• Step 4. Formulate and develop a model.• Step 5. Validate the model.• Step 6. Document model for future use.• Step 7. Select appropriate experimental design.• Step 8. Establish experimental conditions for runs.• Step 9. Perform simulation runs.• Step 10. Interpret and present results.• Step 11. Recommend further course of action.

Simulation in education and training

Simulation is often used in the training of civilian and military personnel. This usually occurs when it is prohibitively expensive or simply too dangerous to allow trainees to use the real equipment in the real world. In such situations they will spend time learning valuable lessons in a "safe" virtual environment yet living a lifelike experience (or at least it is the goal). Often the convenience is to permit mistakes during training for a safety-critical system. There is a distinction, though, between simulations used for training and industrial simulation

Virtual simulation input hardware

• Body tracking • Physical controllers• Voice/sound recognition

Digital lifecycle simulationSimulation solutions are being increasingly integrated with CAx (CAD, CAM, CAE....) solutions and processes. The use of simulation throughout the product lifecycle, especially at the earlier concept and design stages, has the potential of providing substantial benefits. These benefits range from direct cost issues such as reduced prototyping and shorter time-to-market, to better performing products and higher margins. However, for some companies, simulation has not provided the expected benefits.

Simulation and manufacturing• Throughput under average and peak loads;• System cycle time (how long it take to

produce one part);• Utilization of resource, labor, and

machines;• Bottlenecks and choke points;• Queuing at work locations;• Queuing and delays caused by material-

handling devices and systems;• WIP storages needs;• Staffing requirements;• Effectiveness of scheduling systems;• Effectiveness of control systems.

Advantages, Disadvantages & Pitfalls

• Advantages– Simulation allows great flexibility in modeling complex systems,

so simulation models can be highly valid– Easy to compare alternatives– Control experimental conditions– Can study system with a very long time frame

• Disadvantages– Stochastic simulations produce only estimates – with noise– Simulation models can be expensive to develop– Simulations usually produce large volumes of output – need to

summarize, statistically analyze appropriately• Pitfalls– Failure to identify objectives clearly up front– In appropriate level of detail (both ways)– Inadequate design and analysis of simulation experiments– Inadequate education, training

FLEXSIM CASE STUDY

Problem

• We will look at the process of testing three products coming off a manufacturing line.

• There are three different flowitem itemtypes that will arrive based on a normal distribution.

• Itemtypes will be uniformly distributed between itemtypes 1, 2, and 3.

• As flowitems arrive they will be placed in a queue and wait to be tested.

Problem

• Three testers will be available for testing. One tester will be used for itemtype 1, another for itemtype 2, and the third for itemtype 3.

• Once the flowitem is tested it will be placed on a conveyor.

• At the end of the conveyor the flowitem will be sent to a sink where it will exit the model.

Conceptual Model

Model Data

• Source arrival rate: normal(20,2) seconds• Queue maximum size: 25 flowitems• Testing time: exponential(0,30) seconds• Conveyor speed: 1 meter per second• Flowitem routing: Itemtype 1 to Tester 1,

Itemtype 2 to Tester 2, Itemtype 3 to Tester 3.

Layout

Statistics

• After 5 minutes of running the system.

Q&A’s

• What is simulation?• Simulation is the imitation of the operation of

a real-world process or system over time.

Q&A’s

• How can simulation be used in our real life?• 1) simulation can be used in education and

training :This usually occurs when it is prohibitively expensive or simply too dangerous to allow trainees to use the real equipment in the real world.

• 2) body tracking : this includes videos games.• 3) simulation in manufacturing: Queuing at work

locations,Staffing requirements,Effectiveness of scheduling systems; Effectiveness of control systems.

Q&A’s

• State some languages used for simulation.• FORTRAN• PASCAL• MODULA• ADA• C,C++

Q&A’s• State the main steps involved in simulation.• Step 1. Identify the problem.• Step 2. Formulate the problem.• Step 3. Collect and process real system data.• Step 4. Formulate and develop a model.• Step 5. Validate the model.• Step 6. Document model for future use.• Step 7. Select appropriate experimental design.• Step 8. Establish experimental conditions for runs.• Step 9. Perform simulation runs.• Step 10. Interpret and present results.• Step 11. Recommend further course of action.

Q&A’s

• What are the advantages and disadvantages of simulation?

• Advantages– Simulation allows great flexibility in modeling complex

systems, so simulation models can be highly valid– Easy to compare alternatives– Control experimental conditions– Can study system with a very long time frame

• Disadvantages– Stochastic simulations produce only estimates – with

noise– Simulation models can be expensive to develop– Simulations usually produce large volumes of output –

need to summarize, statistically analyze appropriately