Class 4_2

• Today’s topic: Engineering the details• Questions about DP?

Reminder: The first part of your design report is due Tues. Include: cover page, problem statement, specs, alt. designs, and WOT

Questions about DP?

Don’t forget to read the design requirement clarifications that are

posted on our website.

Critical…I know I was quite critical in my review of your alternative designs!This is not personal. My goal is to help you get to a good design outcome. In engineering design that sometimes (most times) requires a highly challenging look at the design proposals.

Critical…This is a learning process.

You will get there!

Define the problem

Specify product requirements

Invent alternatives

Evaluate the alternatives

Engineer the details / analyze performance

Test prototypes

Report complete product description

Model of the Design Process

Engineer the details

• Difficult to generalize• The stage of the design process where most

work is done and time spent• Requires technical knowledge that you are

learning in many of your engineering courses

Your assignmentBuild an analytical model to predict the

performance of your design.

Your work will be part of your final design report. It is a major part of the grade.

It should be done now, at this stage of the design process…don’t procrastinate!

What it should be when done:1. Defines the purpose by posing questions to

be answered2. Derives the analysis from first principles3. Implements the analysis using a MatLab

program4. Provides information that is useful in

designing the details of your device

I know you will find this difficult.It is probably new for you.But I think you will agree that it is a vital skill to develop if you want to be a design engineer.When it is done I think you will appreciate how much it helped you with your design project and take great satisfaction in doing some real engineering.

Use the power of the force, Luke!

Do not take a cut-and-paste or trial-and-error approach to designing your device.

This approach is unlikely to give you satisfactory results.

Use the power of analysis to guide your design!

You will be glad you did.

Engineering analysis has several characteristics

• It is quantitative (math, numbers, units)• It uses science & engineering theories,

engineering experience, test data• It is always recognized as an approximation

to reality• It typically breaks a complicated problem

into smaller pieces• It delivers an answer within the limitations

of time, money, and knowledge available.

Let’s do some analysis to help us design a rubber band powered rope climber.• The problem: design a device to

ascend as far as possible up a rope in SC360 using only 5, #16 rubber bands.

• Analysis question: What is the upper limit for the weight of my device?

Did you just do an engineering analysis?

• Was it quantitative (math, numbers, units)?• Did it use science & engineering theories,

engineering experience, test data?• Is it recognized as an approximation to reality?• Did it break a complicated problem into smaller

pieces?• Did it deliver an answer within the limitations of

time, money, and knowledge available?

How could the analysis be improved?

• Since we recognize that all engineering analysis is an approximation, there is always room for improvement. How could our estimate be improved?

• One of the benefits of doing an engineering analysis is that it helps make clear the things that you do not understand. This can point you in the right direction for further work...

All engineering analyses are essentially

Models

What is a model?

• A purposeful representation of some part of the real world.

Real system

Model

Computer

Modeling Simulation

Why build models?

• To predict how a system will behave.– Lets us design the system, practice using the

system, and make decisions about what to do.• To help test our understanding of a system.

– Can compare predictions to experiments.

Examples....

• Design: Solar heating for a house• Make decisions: Deer population• Practice: Flight simulators• Test understanding: Climate prediction

Many type of models• Physical (ex. Clay mock-up of an auto

body)• Static or dynamic (ex. Ball-and stick model

of a molecule-static, wind tunnel model airplane-dynamic)

• Deterministic or probabilistic (also called stochastic)

• Analogic (ex. Flow of electricity like flow of water)

Types of models, cont.

• Symbolic (ex. Prediction of the size of beams needed in new building.)– Empirical (based on data)– Theoretical (based on ideas)

• Many others...

What are we going to do in this course?

• Start to learn how to build engineering models by doing it—your computer modeling assignment portion of your design project.

• Model building is as much art as it is science...must be learned by practice.

• We will use the computer as a tool. (I hope you will see what a powerful tool it can be in conjunction with your analysis capabilities.)

Computers are powerfulmodeling tools

• These days computers are helping engineers (and most other problem solvers!) develop powerful models.

• Caution: the model is still only as good as the understanding that goes into making it!

• GIGO (garbage in…garbage out)

Reminder

Design report, Part 1, is due Tuesday.