# Fundamentals of Forecasting Using Excel by myh14608

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```									ENGR 107: Engineering
Fundamentals
Lecture 7:
The Engineering Design Process:
Making Design Decisions Using

C. Schaefer
September 25, 2002
Stuff
 Reading assignment: section 2.9 in Eide, et
al.
 Yacht design handouts
 Yacht diagram:
– http://www.cnn.com/interactive/sailing/yacht.diagram/

 Lecture
 Meeting with test and evaluation group

September 25, 2002    Egnineering Fundamentals 107             2
Engineering 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 25, 2002   Egnineering Fundamentals 107   3
Analyze 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 25, 2002     Egnineering Fundamentals 107        4
Using Models in the Decision
Making Process
 Mathematical models.                              Math models often
 Computer models.                                  implemented as
computer models.
   Scale models.
– Wind tunnel models
– Mockups
   Diagrams or graphs.
– Free body diagrams

September 25, 2002   Egnineering Fundamentals 107                 5
Model 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 25, 2002     Egnineering Fundamentals 107            6
Mathematical 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 25, 2002       Egnineering Fundamentals 107    7
Mathematical Model Example:
Yacht Rating Measurement
Formula

L  SA   L SA
25          3       2.68
4    12 30 D

September 25, 2002   Egnineering Fundamentals 107   8
Payoff Function:
Length = f (Sail Area, Displacement)

L
110.72     SA                     
    SA 
1       
 33 30 D 
         
September 25, 2002      Egnineering Fundamentals 107       9
Yacht Length (in inches)
Displacement (in pounds)
Sail Area (square inches)    4      4.5      5        5.5      6          6.5    7      7.5         8
300            43.0   43.9     44.7     45.5     46.1       46.8   47.3   47.9        48.4
350            40.6   41.5     42.3     43.0     43.7       44.3   44.9   45.4        45.9
400            38.5   39.4     40.2     40.9     41.6       42.2   42.7   43.2        43.7
450            36.7   37.6     38.4     39.1     39.7       40.3   40.8   41.3        41.8
500            35.2   36.0     36.7     37.4     38.0       38.6   39.2   39.7        40.1
550            33.7   34.5     35.3     35.9     36.6       37.1   37.7   38.1        38.6
600            32.4   33.2     34.0     34.6     35.2       35.8   36.3   36.8        37.2
650            31.3   32.0     32.8     33.4     34.0       34.5   35.0   35.5        36.0
700            30.2   31.0     31.6     32.3     32.9       33.4   33.9   34.4        34.8
750            29.2   30.0     30.6     31.2     31.8       32.3   32.8   33.3        33.7
800            28.3   29.0     29.7     30.3     30.8       31.4   31.8   32.3        32.7
850            27.4   28.1     28.8     29.4     29.9       30.4   30.9   31.4        31.8
900            26.6   27.3     28.0     28.6     29.1       29.6   30.1   30.5        30.9

September 25, 2002             Egnineering Fundamentals 107                            10
Parametric Analysis
Length vs. Sail Area (Displacement Constant)

50.0

45.0
Yacht Length (inches)

4
4.5
40.0                                                                          5
5.5
6
6.5
35.0                                                                          7
7.5
8

30.0

25.0
200   300        400     500       600       700      800   900   1000

Sail Area (square inches)

September 25, 2002                       Egnineering Fundamentals 107                      11
Parametric Analysis
Length vs. Sail Area (Displacement Constant)

50.0

Invalid Design Space

45.0
Yacht Length (inches)

Length Constraint = 36 inches               4
Invalid Design Space                                                                           4.5
40.0                                                                                                     5
5.5
6
6.5
35.0                                                                                                     7
7.5
8
Invalid Design Space

30.0

Valid Design Space
25.0
200           300            400     500        600       700         800       900      1000

Sail Area (square inches)

September 25, 2002                                      Egnineering Fundamentals 107                                 12
Parametric Analysis

September 25, 2002       Egnineering Fundamentals 107   13
Payoff Function:
Sail Area = f (Length, Displacement)

2
            
 110.72  L 
SA              
1     L 
 3 30 D 
     3

September 25, 2002      Egnineering Fundamentals 107       14
Sail Area (square inches)
Displacement (in pounds)
Length (inches)      4       4.5      5          5.5       6         6.5     7       7.5          8
25           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

September 25, 2002            Egnineering Fundamentals 107                            15
Parametric Analysis
Sail Area vs. Yacht Length (Constant Displacement)

1,400

1,300

1,200
Sail Area (square inches)

1,100
4
4.5
1,000                                                                       5
5.5
900                                                                        6
6.5
800                                                                        7
7.5
8
700

600

500

400
24      26        28          30           32     34      36

Yacht Length (inches)

September 25, 2002                      Egnineering Fundamentals 107                16
Payoff Function:
Displacement = f (Sail Area, Length)

3
        L SA          
                      
D  332.16  3( L  SA ) 
30

September 25, 2002      Egnineering Fundamentals 107       17
Displacement (in pounds)
Length (in inches)
Sail Area (square inches)    28    29          30        31         32          33     34     35          36
300             0.5   0.6         0.7       0.8        0.9         1.0   1.2    1.4          1.6
350             0.7   0.8         0.9       1.1        1.2         1.4   1.6    1.9          2.1
400             0.9   1.0         1.2       1.4        1.6         1.8   2.1    2.4          2.8
450             1.1   1.3         1.5       1.8        2.0         2.3   2.7    3.1          3.6
500             1.4   1.6         1.9       2.2        2.5         2.9   3.4    3.9          4.5
550             1.7   2.0         2.3       2.7        3.1         3.6   4.1    4.8          5.5
600             2.0   2.4         2.8       3.2        3.7         4.3   5.0    5.8          6.7
650             2.4   2.8         3.3       3.8        4.4         5.2   6.0    6.9          8.0
700             2.8   3.3         3.9       4.5        5.2         6.1   7.1    8.2          9.5
750             3.3   3.9         4.5       5.3        6.1         7.1   8.3    9.6         11.2
800             3.8   4.5         5.2       6.1        7.1         8.3   9.7    11.2        13.0
850             4.4   5.1         6.0       7.0        8.2         9.6   11.2   13.0        15.1
900             5.0   5.9         6.9       8.1        9.4       11.0    12.8   15.0        17.4

September 25, 2002               Egnineering Fundamentals 107                               18
Parametric Analysis
Displacement vs. Sail Area (Length Constant)

18.0

16.0

14.0
Displacement (pounds)

12.0                                                                           28
29
30
10.0                                                                           31
32
8.0                                                                           33
34
35
6.0                                                                           36

4.0

2.0

0.0
250   350      450         550         650          750   850   950

Sail Area (square inches)

September 25, 2002             Egnineering Fundamentals 107                     19
How Important are the Criteria in the Decision
Process?
Working               Points Avail.       #1                    #2   #3
Criteria
Cost                  20                  10                    15   18
Prod. Difficulty      15                  8                     12   14
Size, Weight,         5                   5                     4    4
Strength
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

September 25, 2002              Egnineering Fundamentals 107        20

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