2/1/12

1

ME 481 Mechanical Engineering

Design Projects

Week 4

More Week 2 Quiz Comments

•  Typical Problem Definition models use Conservation of Energy, Power, … and Forces but NOT Design Details

•  Your Problem Definition Should not Change after Approval by Your Sponsor – Caution Them

•  When Do You Know When You Are Done Defining the Problem? When You Have Enough…

•  How Many Models do We Need? Enough to Develop Sufficient Performance Specifications?

•  What Kind of Pictures are Needed Group-FA-PA? You need to get Group, then PA, then FA.

•  Submit 1st Progress Report, including Gannt Chart & Budget Report (Today, 1/30, ME Office)

•  Prepare and Give 1st Presentation (Monday, 2/6)

•  Pictures for Synopsis (Wed, 2/22) •  ME481 Design Team Folders

•  smb://filer1.egr.msu.edu/courses/ME/481

This Week •  Lecture: Jason Heist,

Harness Dickey & Pierce “Patent Law and Intellectual Property”

•  Develop Synopsis (Picture + Description) •  Create & Evaluate Conceptual Designs

•  Model the Alternatives

•  Revise Gantt Chart

Next Week

Prof. Clark Radcliffe Mechanical Engineering

ME 481 Engineering Modeling

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

2/1/12

2

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?

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 …

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

Some Example Models •  Scale 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

System Modeling Break up System into subsystems

Interior and Controls

Drivetrain

Body and Structure

Vehicle System

System Modeling Break up Subsystems into Components

Drivetrain Subsystem

Transmission

Wheels and Tires Engine

2/1/12

3

Drivetrain Example

Drivetrain

Transmission Engine Wheels and Tires

Build Subsystem from Components Drivetrain components linked to show connectivity

Drivetrain

System Modeling System is connected subsystems

(connections define model type)

Vehicle

Interior and Controls Body and Structure Drivetrain

Vehicle

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

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.

Modeling Question: •  What’s the maximum vehicle acceleration? •  Start with Components…

•  Parameter: Tire Diameter D

Wheels and Tires

! transfdrive

vveh ! trans

fdrive =! transD

(N)

! trans =vvehD

(rad/s)

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! transfdrive

vveh ! trans ! engine

fdrive =N! engineD

(N), ! engine = ! engine " engine( ), " engine = NvvehD (rad/s)Engine Torque Map

2/1/12

4

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

fdrive

vvehvveh

fint

aveh = !vveh =

1mbody + mint( ) fdrive vveh( ) + fint vveh( ) ! fdrag vveh( )

"# $% (m/s2 )

aveh = !vveh = !vveh vveh( ) (m/s2 )

System Modeling Form System from subsystems

Vehicle

•  Result is a system model to be solved either analytically or numerically

•  Iterate on vehicle velocity to find max accel

aveh = !vveh = !vveh vveh( ) (m/s2 )Parameters: D, N, mint ,mbody

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

ME 481 Examples

•  Motor Cycle Oil Change Adapter •  Refrigerator Thermal Storage System

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

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

2/1/12

5

Iteration is common

•  Tools: – Excel’s Solver

•  Loaded from Distribution or Internet

– Matlab Optimization Functions •  Built in and ready in DECS labs

Sources of Help •  Books •  Notes

•  The Web (but be careful) •  Experts

– Faculty, other students, Professional Advisor, Staff