ENGR 107: Engineering ENGR 107: Engineering FundamentalsFundamentals

Lecture 7:

The Engineering Design Process:

Making Design Decisions Using Tradeoff Analyses

C. Schaefer

September 29, 2003

September 29, 2003 Egnineering Fundamentals 107 2

StuffStuffReview Project 1Yacht design handoutsYacht diagram:

– http://www.cnn.com/interactive/sailing/yacht.diagram/

Lecture

September 29, 2003 Egnineering Fundamentals 107 3

Project 2 Begins!!Project 2 Begins!!

For each Team, all functional groups shall provide cost ROM’s, Bills of Material, and a list of required tools to the Systems Engineering Group and to me by next Monday.

Systems Engineering group: preliminary schedule and budget due next Wednesday.

Design and Manufacturing Groups: begin conceptual and preliminary design of your respective systems.

Handout $$ and radios on Wednesday.

September 29, 2003 Egnineering Fundamentals 107 4

Engineering DecisionsEngineering Decisions Engineering decision – selecting a specific

solution to a design problem from a set of alternative solutions

Trade-off analysis – an analysis technique in which the performance of various design alternatives are evaluated by varying different design parameters within a design space defined by parameter boundaries or design constraints.

Payoff function – a mathematical model that relates system performance to various design parameters that the designer can control.

September 29, 2003 Egnineering Fundamentals 107 5

Analyze Potential SolutionsAnalyze Potential Solutions

Narrow the ideas generated during the brainstorming phase to several realistic alternatives.

Analytical techniques to narrow choice:– Estimation (“back of the envelope” calculations).– Common sense.– Economic analysis.– Engineering analysis.– Computer analysis.

September 29, 2003 Egnineering Fundamentals 107 6

Using Models in the Decision Using Models in the Decision Making ProcessMaking Process

Mathematical models.Computer models.

– CAD (computer aided design)– Simulink

Scale models.– Wind tunnel models– Mockups

Diagrams or graphs.– Free body diagrams

Math models oftenimplemented ascomputer models.

September 29, 2003 Egnineering Fundamentals 107 7

Model FeaturesModel Features Should represent the dynamics of the system being

represented. Good fidelity: simple to understand and manipulate but

good enough to generate believable results. Should address the most important design parameters.

Ignore higher order terms. Should be repeatable. Should be of modest complexity: complexity often a

function of time and budget constraints on design process. Easily modified.

September 29, 2003 Egnineering Fundamentals 107 8

Mathematical ModelsMathematical Models Uncovers relations between the various aspects of

the problem that may not be apparent in verbal descriptions.

Enables comparisons of many possible solutions. Illustrates cause-and-effect relationships. Defines the type of data required to solve the

problem. Can be used for prediction and forecasting. Aids in identifying areas of risk and uncertainty.

September 29, 2003 Egnineering Fundamentals 107 9

Mathematical Model Example:Mathematical Model Example:Yacht Rating Measurement Yacht Rating Measurement

FormulaFormula

68.230124

253

D

SALSAL

September 29, 2003 Egnineering Fundamentals 107 10

Payoff Function:Payoff Function:Length = Length = f f (Sail Area, Displacement)(Sail Area, Displacement)

3 3031

72.110

D

SA

SAL

September 29, 2003 Egnineering Fundamentals 107 11

Excel Spreadsheet SolutionExcel Spreadsheet Solution

Sail Area (square inches) 4 4.5 5 5.5 6 6.5 7 7.5 8300 43.0 43.9 44.7 45.5 46.1 46.8 47.3 47.9 48.4350 40.6 41.5 42.3 43.0 43.7 44.3 44.9 45.4 45.9400 38.5 39.4 40.2 40.9 41.6 42.2 42.7 43.2 43.7450 36.7 37.6 38.4 39.1 39.7 40.3 40.8 41.3 41.8500 35.2 36.0 36.7 37.4 38.0 38.6 39.2 39.7 40.1550 33.7 34.5 35.3 35.9 36.6 37.1 37.7 38.1 38.6600 32.4 33.2 34.0 34.6 35.2 35.8 36.3 36.8 37.2650 31.3 32.0 32.8 33.4 34.0 34.5 35.0 35.5 36.0700 30.2 31.0 31.6 32.3 32.9 33.4 33.9 34.4 34.8750 29.2 30.0 30.6 31.2 31.8 32.3 32.8 33.3 33.7800 28.3 29.0 29.7 30.3 30.8 31.4 31.8 32.3 32.7850 27.4 28.1 28.8 29.4 29.9 30.4 30.9 31.4 31.8900 26.6 27.3 28.0 28.6 29.1 29.6 30.1 30.5 30.9

Displacement (in pounds)

Yacht Length (in inches)

September 29, 2003 Egnineering Fundamentals 107 12

Parametric AnalysisParametric Analysis

Length vs. Sail Area (Displacement Constant)

25.0

30.0

35.0

40.0

45.0

50.0

200 300 400 500 600 700 800 900 1000

Sail Area (square inches)

Ya

ch

t L

en

gth

(in

ch

es

)

4

4.5

5

5.5

6

6.5

7

7.5

8

September 29, 2003 Egnineering Fundamentals 107 13

Parametric AnalysisParametric AnalysisLength vs. Sail Area (Displacement Constant)

25.0

30.0

35.0

40.0

45.0

50.0

200 300 400 500 600 700 800 900 1000

Sail Area (square inches)

Ya

ch

t L

en

gth

(in

ch

es

)

4

4.5

5

5.5

6

6.5

7

7.5

8

Length Constraint = 36 inches

Valid Design Space

Invalid Design Space

Invalid Design Space

Invalid Design Space

September 29, 2003 Egnineering Fundamentals 107 14

Parametric AnalysisParametric AnalysisLength vs. Sail Area (Displacement Constant)

25.0

30.0

35.0

40.0

45.0

50.0

200 300 400 500 600 700 800 900 1000

Sail Area (square inches)

Ya

ch

t L

en

gth

(in

ch

es

)

4

4.5

5

5.5

6

6.5

7

7.5

8

Valid Design Space

Invalid Design Space

September 29, 2003 Egnineering Fundamentals 107 15

Payoff Function:Payoff Function:Sail Area = Sail Area = f f (Length, Displacement)(Length, Displacement)

2

3 3031

72.110

D

LL

SA

September 29, 2003 Egnineering Fundamentals 107 16

Excel Spreadsheet SolutionExcel Spreadsheet Solution

Length (inches) 4 4.5 5 5.5 6 6.5 7 7.5 825 1,014 1,065 1,112 1,155 1,196 1,235 1,271 1,305 1,338 26 942 990 1,035 1,076 1,115 1,151 1,185 1,218 1,249 27 877 922 964 1,003 1,039 1,074 1,106 1,137 1,167 28 816 859 899 935 970 1,003 1,034 1,063 1,091 29 761 801 838 873 906 937 966 994 1,020 30 709 747 783 816 847 876 904 930 955 31 662 698 731 762 792 819 846 870 894 32 618 652 684 713 741 767 792 815 838 33 578 610 639 667 693 718 742 764 785 34 540 570 598 625 649 673 695 716 736 35 505 534 560 585 608 631 652 672 691 36 473 500 525 548 570 591 611 630 648

Sail Area (square inches)

Displacement (in pounds)

September 29, 2003 Egnineering Fundamentals 107 17

Parametric AnalysisParametric AnalysisSail Area vs. Yacht Length (Constant Displacement)

400

500

600

700

800

900

1,000

1,100

1,200

1,300

1,400

24 26 28 30 32 34 36

Yacht Length (inches)

Sa

il A

rea

(s

qu

are

in

ch

es

)

4

4.5

5

5.5

6

6.5

7

7.5

8

September 29, 2003 Egnineering Fundamentals 107 18

Payoff Function:Payoff Function:Displacement = Displacement = ff (Sail Area, Length) (Sail Area, Length)

30

)(316.332

3

SAL

SAL

D

September 29, 2003 Egnineering Fundamentals 107 19

Excel Spreadsheet SolutionExcel Spreadsheet Solution

Sail Area (square inches) 28 29 30 31 32 33 34 35 36300 0.5 0.6 0.7 0.8 0.9 1.0 1.2 1.4 1.6350 0.7 0.8 0.9 1.1 1.2 1.4 1.6 1.9 2.1400 0.9 1.0 1.2 1.4 1.6 1.8 2.1 2.4 2.8450 1.1 1.3 1.5 1.8 2.0 2.3 2.7 3.1 3.6500 1.4 1.6 1.9 2.2 2.5 2.9 3.4 3.9 4.5550 1.7 2.0 2.3 2.7 3.1 3.6 4.1 4.8 5.5600 2.0 2.4 2.8 3.2 3.7 4.3 5.0 5.8 6.7650 2.4 2.8 3.3 3.8 4.4 5.2 6.0 6.9 8.0700 2.8 3.3 3.9 4.5 5.2 6.1 7.1 8.2 9.5750 3.3 3.9 4.5 5.3 6.1 7.1 8.3 9.6 11.2800 3.8 4.5 5.2 6.1 7.1 8.3 9.7 11.2 13.0850 4.4 5.1 6.0 7.0 8.2 9.6 11.2 13.0 15.1900 5.0 5.9 6.9 8.1 9.4 11.0 12.8 15.0 17.4

Displacement (in pounds)

Length (in inches)

September 29, 2003 Egnineering Fundamentals 107 20

Parametric AnalysisParametric AnalysisDisplacement vs. Sail Area (Length Constant)

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

250 350 450 550 650 750 850 950

Sail Area (square inches)

Dis

pla

ce

me

nt

(po

un

ds

)

28

29

30

31

32

33

34

35

36

September 29, 2003 Egnineering Fundamentals 107 21

How Important are the Criteria in the Decision Process?

Working Criteria

Points Avail. #1 #2 #3

Cost 20 10 15 18Prod. Difficulty 15 8 12 14Size, Weight, Strength

5 5 4 4

Appearance 10 7 6 8

Convenience 5 3 4 4

Safety 10 8 7 8

Legal 5 4 4 4

Reliability 15 7 9 11

Recyclability 5 4 3 4

Appeal 10 7 8 9

TOTAL 100 63 72 84