1. ME 481 Engineering Modeling
Prof. Clark Radcliffe Mechanical Engineering

2. Why do Modeling? Design is a Problem Solving Process
Key to the Process is Problem Definition
Design Problem Definition states Specifications of Desired Performance
Models Predict Performance
The Goal: To predict design performance for comparison against definition specifications

3. Why do Modeling?
Engineering Designs are Typically Systems of Many Components
Each Component Needs a Separate Subdesign
Each Subdesign has Separate “Roll down” of Performance Specifications to Meet
Predicting Performance of Components Predicts Performance of the System
Then Check: Does System meet Specifications?

4. Model Types Cost: Money and Time
Safety: Pinch Points, Impact, Crush, Ingestion, Temperature, etc …
Geometry: Size, Connections, Aesthetics, …
Speed: Response Time, Production, …
Energy and Power: Operating, Supply, …
Reliability: MTBF, Service Life, Strength, …
And Many others …

5. How to Start Sketches are a great start
One of the earliest creative artifacts
Break up system into components
Identify Component Connections
“Roll Down” System Specifications to Component Specifications
Identify Inputs and Outputs at Connections
Block Diagrams can be useful here
Select a Model that Predicts The Performance Required for each Specification

6. Some Example Models Scale Models: Graphical Models:
Useful to evaluate geometry
Graphical Models:
Now replacing some scale models
Mathematical Models:
A basis for quantitative performance prediction
Physical Models use power and energy
Prototype Models:
To test performance of near final design
THE most expensive model

7. System Modeling Break up System into subsystems
Vehicle System
Body and Structure
Interior and Controls
Drivetrain

8. Break up Subsystems into Components
System Modeling
Break up Subsystems into Components
Drivetrain Subsystem
Wheels and Tires
Engine
Transmission

9. Drivetrain Example Build Subsystem from Components
Drivetrain components linked to show connectivity
Drivetrain
Transmission
Engine
Wheels and Tires
Drivetrain

10. System Modeling System is connected subsystems (connections define model type)
Vehicle
Interior and Controls
Body and Structure
Drivetrain

11. System Conceptual Model
Shows Components, connections and Systems
Organizes Information, Expertise …
SAE Formula Car project does it … you can too
Provides Information Interfaces
where critical connections are defined
Helps Identify Critical Parts and Paths

12. Model Individual Components
What design performance specification do you need to evaluate?
Develop a model to predict that performance,
Put together a subsystem model, and
Build a system performance model.
Finally predict system performance and Compare with specification.

13. Modeling Question: What’s the maximum vehicle acceleration?
Start with Components…
Parameter: Tire Diameter D
Wheels and Tires

14. Modeling Question: What’s the maximum vehicle acceleration?
Assemble Subsystem Models…
Parameters: Tire Diameter D, Gear Ratio N
Drivetrain
Transmission
Engine
Wheels and Tires
Engine Torque Map

15. Modeling Question: What’s the maximum vehicle acceleration?
Assemble System Model…
Parameters: Body mass mbody, Interior mass mint , Drag fdrag(vveh)
Interior and Controls
Body and Structure
Drivetrain
Vehicle

16. System Modeling Form System from subsystems
Result is a system model to be solved either analytically or numerically
Iterate on vehicle velocity to find max accel
Vehicle

17. Engineering Modeling involves:
Identifying a complex physical process
Breaking it up into simple physical component processes
Representing the simple physical processes by equations
Assembling components into system model
Predicting performance for the system

18. ME 481 Examples Motor Cycle Oil Change Adapter
Refrigerator Thermal Storage System 18

19. Motor Cycle Oil Change Adapter
Frame plus motorcycle components
Need forces at components connections
Write force balances for components
assume weights
Assemble system force balance equations
Solve for connection forces
Pipe beam calculation to determine wall thickness of structural components
Calculate weights
Iterate to solution convergence
Calculate weight & cost 19

20. Thermal Storage System
Assume amount of phase change material (PCM)
Use thermal circuit to determine heat gain
Use latent heat with heat gain to find required mass of PCM
Iterate to solution convergence 20

21. Iteration is common Tools: Excel’s Solver
Loaded from Distribution or Internet
Matlab Optimization Functions
Built in and ready in DECS labs

22. Sources of Help Books Notes The Web (but be careful) Experts
Faculty, other students, Professional Advisor, Staff