engineering design ge121 finding answers to the problem part v
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Connecting Concepts to Objectives: Selecting the BEST Designs Can be done by many different approaches Some Formal and Rigorous Others are simple – Example: Simply the alternative that the team likes the best! Use Objectives (and Constraints) to compare Process usually begins by examining alternatives in terms of Constraints Alternatives that don’t satisfy ALL constraints can be immediately rejected Different clients have different Values (weights on objectives) May end up choosing different designs for same problemTRANSCRIPT
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GE 121 – Engineering Design - 2009
Engineering DesignGE121
Finding Answers to the Problem
Part V
Lecture 13C
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GE 121 – Engineering Design - 2009
Connecting Concepts to Objectives:Selecting the BEST Designs
Can be done by many different approachesSome Formal and RigorousOthers are simple – Example: Simply the alternative that
the team likes the best!Use Objectives (and Constraints) to compareProcess usually begins by examining alternatives
in terms of ConstraintsAlternatives that don’t satisfy ALL constraints can be
immediately rejectedDifferent clients have different Values (weights on
objectives)May end up choosing different designs for same
problem
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GE 121 – Engineering Design - 2009
Numerical Evaluation Matrices
Following Examples show Numerical Evaluation Matrices for two different clients
Notice that calculated Weights (importance of each objective) are different for each – possibly due to different corporate values
Constraints dictate that two options are eliminated - Glass bottle with twist-off cap, and Aluminum can with pull-tab (don’t meet constraints)
Compare / Contrast for your own benefit
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GE 121 – Engineering Design - 2009
Numerical Evaluation Matrices (continued)
Fig. 5.4 p110 (2nd Edition)
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GE 121 – Engineering Design - 2009
Numerical Evaluation Matrices (continued)
Fig. 5.5 p111 (2nd Edition)
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GE 121 – Engineering Design - 2009
Weighted Checkmark MethodSimpler, Qualitative version of Numerical
Evaluation MethodHigh / Medium / Low Priority
3 Checkmarks for High, 2 for Medium, 1 for Low
Metrics are taken as 1 if greater than 0.5and 0 if less than 0.5Binary Method is susceptible to temptation to
‘Cook’ results to achieve desired outcome
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GE 121 – Engineering Design - 2009
Weighted Checkmark Method (continued)
Fig. 5.6 p112 (2nd Edition)
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GE 121 – Engineering Design - 2009
Best of Class Chart
Rank each alternative for how it meets the objective, with 1 being the best down to 5 for the worst (assuming 5 alternatives)
Ties allowed, but split rankings (two alternatives tied for 1st would each get (1+2)/2 = 1.5)
Lowest score is best, unless used with previous weighting scheme (then use 5 as best and 1 as worst for ranking, and Highest score wins)
Advantages – Ranks alternatives rather than just binary, and is easy
Disadvantages – Opinion-based, may also be tempted to ‘fudge’ results
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GE 121 – Engineering Design - 2009
Caution on All 3 MethodsNo excuse for accepting results blindly and
uncriticallyTreat relatively close scores for 2
alternatives as equalIf results were unexpected, check
expectations/ metrics/ weightsCheck to see if evaluations were really fairExamine alternatives rejected based on
constraints to see if it was really valid
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GE 121 – Engineering Design - 2009
Concept Screening
These same processes can be used earlier in the design process (especially weighted checkmark) to do Informal Concept Screening
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GE 121 – Engineering Design - 2009
ActivityContinue working on your 4 (or 3 if you’re a
group of 3) design concepts (all 4 must meet all constraints)
Make sure that you have Metrics and Weighting factors ready to go for ALL of your Objectives – you will need them next week to make a decision as to which design is best
Continue to work on your Final Report and your Presentation weekly as you cover each step of the process!