The Process of Design

Jason M. KeithFuel Cells and Alternative Fuels Enterprise

Michigan Technological UniversityHoughton, MI 49931

Rationale for this Presentation

• Design is usually taught discipline-specific at the end of the undergraduate curriculum

• CM4850 Process Analysis & Design• MEEM4900 Senior Design• EE4900 Design Fundamentals

• One of the most challenging subjects for studentsto learn and practicing engineers to use

• Participants in AFG enterprise have various interests, disciplines, and class standing

• AFG has a new project that requires a significantdesign effort

What do I need? (Crowl, 2005)

To be successful at design you need:• Strong understanding of technical issues (comes

from your core courses)• Methodology of design (focus of this presentation)• “Soft” skills (more of an “art” but best learned by

experience)• Communication• Decision making• Time management• Budget management• Others

“So what is Engineering Design?”

Dym & Little (2000):“The organized, thoughtful development and testingof characteristics of new objects that have a particular configuration or perform some desiredfunction(s) that meets our aims without violatingany special limitations.”There are often additional concerns such as:• No single “correct” solution• Conflicting specifications• Incomplete, extraneous, or incorrect data• Tradeoffs (especially when balancing economics &

environment)

“Can you give me an example?”

Garden Design Project (Crowl, 2005)1. Find garden design resources in library2. Check zoning on gardens; check with neighbors3. Decide where to locate the garden

- accessibility, sun, water drainage issues4. Decide on garden size

- estimate crop yield to determine number ofplants, then use plant spacing tables

5. Sketch layout of garden- dimensions, where plants will be located

6. Determine materials required- seeds, plants, fertilizer, hoses, tools, etc.

“Can you give me an example?”

Garden Design Project (Crowl, 2005)7. Develop planting schedule8. Schedule work for preparation and planting9. Maintain garden10. Harvest crops and replant new ones11. Prepare garden for fall & winter12. Eat (or sell) your vegetables

Real engineering design is like this example exceptthe costs are higher, there is more work, there area lot of people involved, and decisions need to be made

The Prescriptive Model of Design

1. Problem Definition2. Conceptual Design3. Preliminary Design4. Detailed Design5. Design Communication

This model looks sequential but in real design theProcess is not linear!

Real design requires feedback through verification,validation, and iteration

Problem Definition Phase of Design

• Clarify objectives and gather information todevelop an engineering statement of what theclient wants

• Given client statement, clarify objectives forthe design

• Establish user requirements for the design• Identify constraints for the design• Establish functions for the designWe can do this with: objectives tree, pairwisecomparison charts, weighted objectives trees, function-means tree, functional analysis, requirements matrix

Problem Definition Phase of Design

We can do this with the following tools andtechniques: objectives tree, pairwisecomparison charts, weighted objectives trees, function-means tree, functional analysis, requirements matrix

Ways of obtaining useful information include:Literature review, brainstorming, user surveysand questionnaires, structured interviews

Objectives Tree

CombinedTree

Dog on Chair

PairwiseComparison

Charts

Weighted Objectives Tree

Black Box

Transparent Box

Function-Means Tree

Conceptual Design Phase of Design

• Look for different concepts or schemes of candidate designs that can be used to achieveclient objectives

• Address some but not all technical objectives,being sure to maintain a high-level approach

• Establish design specifications• Generate design alternatives that satisfy the

above requirements

Conceptual Design Phase of Design

We can do this with these tools: - performance specification method- quality function deployment- morphological chartUsing: brainstorming, divergent thinking, benchmarking, reverse engineering

A Boy and his Dog

PerformanceSpecification

Curve

Morphological Chart

AnotherMorphChart

Preliminary Design Phase of Design

• Identify principal attributes of the design concept• “Flush out” proposed design schemes• Look at design subsystems and lower level

functions• Use rules of thumb and make final choice from

proposed concepts

Methods: weighted objectives tree, pairwisecomparison chart, numerical evaluation matrix

Means: metrics definition, prototype development,simulation / computer analysis, proof-of-concept

NumericalEvaluation

Matrix

AnotherNumericalEvaluation

Matrix

References

Crowl D. Introduction to Chemical Engineering Design (2005 draft).Dym, C. L. and Little, P. Engineering Design:A Project-Based Introduction, Wiley, New York (2000).