Fuel Cell Systems Engineering

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					 Fuel Cell Systems Engineering

                        Lecture 7
             Quantitative Decision Methods


Fuel Cell Systems Engineering, F06
                                     Topics
• Discussion of individual assignment
• Review questions on OTC solicitation.
• Review Paladin LOA
• Discuss quantitative decision making
  process, Multi-Attribute Utility Theory,
  (MAUT)
• Group activities.

Fuel Cell Systems Engineering, F06
  Questions on OTC Solicitation
• Is methanol as a fuel a design constraint?
• Is 250 W or 300 W the specified output?




Fuel Cell Systems Engineering, F06
    How Do You Decide on a Course
             of Action?
• Let the Boss make the decision
• Take a vote
• Roll the dice
• Consult the Ouija board
                      OR
• Use a quantitative decision making method
  to determine the “Best Technical Approach”

Fuel Cell Systems Engineering, F06
                        The Challenge
• Because the decision variables are many
  and varied, we need a method to
  “normalize” the ratings to some common
  basis.
• Examples: power in watts, mission
  duration in hours, efficiency in %, weight in
  pounds, etc.
• The concept of evaluating the Utility of
  various alternatives allows us to do that.
Fuel Cell Systems Engineering, F06
              Utility of Alternative ai
• The utility of an alternative equals the weighted
  sum of the utilities of individual attributes.

           U(ai)=w1U1(ai)+w2U2(ai)+…+ wnUn(ai)

                                     OR

                                     n

                               U(ai)=ΣwjUj(ai)
                                     j=1



Fuel Cell Systems Engineering, F06
   Multi-Attribute Utility Theory
 Identify Performance Attributes


      Identify Hierarchy of Attributes


           Establish Utility vs. Performance Curves for Attributes


                 Establish Relative Importance Among Attributes


                      Identify Alternatives and Related Performance for Each Attribute


                           Evaluate Multiple Attribute Value Scores


                                 Conduct Sensitivity Analysis




Fuel Cell Systems Engineering, F06
     Identify Performance Attributes
• Select attributes with the highest degree of
  importance
• Include ALL attributes with high
  importance
• Insure attributes are independent (you can
  trade off one for the other) and mutually
  exclusive (one attribute does not include
  another)
Fuel Cell Systems Engineering, F06
        Identify Performance Attributes
               (For Utility Vehicle)

Speed (mph on HLS)                Max Gradeability (degrees)    Fuel Economy (mpg)

                               Side Slope (degrees)        Range (miles)


Acceleration (sec, 0-30 mph)                            Ground Clearance (in)



   Entrance Angle (degrees)                              Exit Angle (degrees)


    Ground Pressure (psi)               Weight (lb)              Payload (lb)


   Fuel Cell Systems Engineering, F06
  Identify Hierarchy of Attributes
• Are there logical groupings of related
  attributes?
• Create a tree of attributes to facilitate
  easier identification of relative importance




Fuel Cell Systems Engineering, F06
         Identify Hierarchy of Attributes
               (For Utility Vehicle)

Off-road Mobility                 Performance                          Weight (lb)

  Entrance Angle (degrees)              Speed (mph on HLS)                Payload (lb)

  Exit Angle (degrees)                  Acceleration (sec, 0-30 mph)

  Side Slope (degrees)                  Max Gradeability (degrees)

  Ground Clearance (in)                 Fuel Economy (mpg)

  Ground Pressure (psi)                 Range (miles)


   Fuel Cell Systems Engineering, F06
   Establish Utility vs. Performance
        Curves for Attributes

                     1                       Typical shapes of
                                             utility curves relate
                                             to level of risk that
                                             the decision maker
      Utility (aj)




                                             is willing to accept.




                     0

                               Performance

Fuel Cell Systems Engineering, F06
                Establish Utility vs. Performance
                     Curves for Attributes

          1.0                                             1.0




                                                Utility
Utility




          0.5                                             0.5




           0                                                0

                10    12     14     16     18                   8     9   10     11    12

                     Ground Clearance (in)                      Acceleration (sec, 0-30 mph)

           Fuel Cell Systems Engineering, F06
      Establish Relative Importance
            Among Attributes
• Methods
    – Survey of potential customers
    – Direction from “the boss”
    – Voting methods
    – Established in user requirements
    – Allocate 100 points




Fuel Cell Systems Engineering, F06
        Establish Relative Importance
              Among Attributes
• Off-road mobility                  (40)
    –   Entrance angle                      .15
    –   Exit angle                          .15
    –   Side slope                          .25
    –   Ground Clearance                    .30
    –   Ground Pressure                     .15
• Performance                        (35)
    –   Speed                               .10
    –   Acceleration                        .30
    –   Gradeability                        .20
    –   Fuel economy                        .15
    –   Range                               .25
• Weight                             (10)
• Payload                            (15)


Fuel Cell Systems Engineering, F06
   Identify Alternatives and Related
    Performance for Each Attribute
• Alternatives should be unique
• Performance levels may be established by
  analysis, testing, system specifications, or
  based on similar systems
• An iterative process




Fuel Cell Systems Engineering, F06
   Evaluate Multiple Attribute Value
               Scores
• U(a1) = W1U1(a1) +W2U2(a1) + ……
• U(a2) = W1U1(a2) +W2U2(a2) + ……
• U(a3) = W1U1(a3) +W2U2(a3) + ……




Fuel Cell Systems Engineering, F06
    Conduct Sensitivity Analysis
• Are overall scores of two or more
  alternatives close?
• Will a slight change in the rating of one
  attribute result in a significant change in
  the relative rankings of alternatives?
• Re-assess ratings scheme and identify
  any additional discrimators.


Fuel Cell Systems Engineering, F06
                  Additional Sources
• Sage & Armstrong, Introduction to
  Systems Engineering, Wiley, 2000




Fuel Cell Systems Engineering, F06

				
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