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### Modeling and Simulationin Engineering

Chris Paredis

G.W. Woodruff School of Mechanical Engineering

Georgia Institute of Technology

Lecture Overview

- Objective:
- Define what a model is
- Illustrate why models are important in engineering
- Topics:
- What is a model?
- What are some properties of models?
- How does one create a new model?
- How are models used in engineering?

What is a Model?

- Examples of Models…
- What do these examples have in common?

Noise, Vibration,

and Harshness

Thermal

Crash Testing

Examples of Models in Vehicle DesignComputational Fluid Dynamics

Stress Analysis

All models are 'wrong'.

Some are useful.

Attributed to George Box

What is a Model?- Definition (based on Marvin Minsky's definition) :
- A model (M) for a system (S) and an experiment (E) is anything to which E can be applied in order to answer questions about S
- A model is an abstraction of reality

Who has created a new model today?

How Do We Create Models?

- Gather data about real system
- Postulate hypotheses about the relationships in the data
- Formalize these hypotheses in models
- Validate models by performing simulations
- If necessary, modify the hypotheses and models until valid

(Adapted from F. Cellier)

Models can never be proven correct – only falsified.

(Adapted from Karl Popper)

A Quick Aside:When is a Model Valid?Is this model valid?

f(x)

x

Simulator

Simulator

Simulator

Simulator

System

Model

System

Model

System

Model

System

Model

Why are Models Important in Engineering?Initial

Guess

Satisficing

Solution

Decision

Solver

Predict theOutcome of Engineering Design Decisions

DesignAlternative

Evaluation ofDesign Alternative

When are Models Most Useful?

- When the system is not available
- When the physical experiments cannot be performed
- When the cost of experimentation is too high
- When the time scale of the system is not compatible with those of the experimenter
- Under controlled circumstance (e.g. no disturbances)

Noise, Vibration,

and Harshness

Thermal

Crash Testing

Examples of Models in EngineeringComputational Fluid Dynamics

Stress Analysis

Manufacturing Simulation

- DFM – DFA – DFX
- Take life cycle cost into account at the design stage

Training Simulators

- Use the previously developed simulation models for training
- Train operators before prototypes are built
- Test whether user interface is user-friendly

Immersive Environments

- Allow user to interact with models through
- 3-dimensional vision
- Touch (tactile interface)
- Complete virtual prototype

Crash TestingIf a picture is worth 1000 words,how about a simulation?

Summary

- We all create and use models all the time
- Models should be validated
- In engineering, models are used for predicting the outcome of decisions, but also for training or documentation.
- In this class you will use models to solve engineering problems

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