Engineering Design GE121 Finding Answers to the Problem Part V Lecture 13C

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 problem

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

Numerical Evaluation Matrices (continued) Fig. 5.4 p110 (2nd Edition)

Numerical Evaluation Matrices (continued) Fig. 5.5 p111 (2nd Edition)

Weighted Checkmark Method Simpler, Qualitative version of Numerical Evaluation Method High / Medium / Low Priority 3 Checkmarks for High, 2 for Medium, 1 for Low Metrics are taken as 1 if greater than 0.5 and 0 if less than 0.5 Binary Method is susceptible to temptation to ‘Cook’ results to achieve desired outcome

Weighted Checkmark Method (continued) Fig. 5.6 p112 (2nd Edition)

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

Caution on All 3 Methods No excuse for accepting results blindly and uncritically Treat relatively close scores for 2 alternatives as equal If results were unexpected, check expectations/ metrics/ weights Check to see if evaluations were really fair Examine alternatives rejected based on constraints to see if it was really valid

Concept Screening These same processes can be used earlier in the design process (especially weighted checkmark) to do Informal Concept Screening

Activity Continue 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!