Department of Mechanical & Marine Engineering, University of Plymouth1

Formulating the Design Envelope

The Role of Reflective Practice*

Professor M Neil James

*RS Adams, J Turns and CJ Atman (2003) Educating effective engineering designers: the role of reflective practice, Design Studies 24 275-294.

Department of Mechanical & Marine Engineering, University of Plymouth2

What is the Design Envelope ?

It is a means of describing the following aspects of the design:

• The various possible interactions between the design concept and the totality of its external environment – these:

Define design parameters

Constrain possible solutions

Affect material choice

Influence geometry and shape

Department of Mechanical & Marine Engineering, University of Plymouth3

What is the Design Envelope ?

It is a means of describing the following aspects of the design:

• The relationships among, and between, its various parts or components – these:

Influence function

Influence form and aesthetics

Confer operating characteristics

Department of Mechanical & Marine Engineering, University of Plymouth4

What is the Design Envelope ?

• This description will contain text-based, graphical and numerical parts

• Through achieving inclusivity, it allows clearer identification of potential areas of innovation

• It forms the basis for rational choice between potential solutions

• It is performed for the overall concept and for sub-systems

• It allows for iteration between later and earlier stages in the design process

Department of Mechanical & Marine Engineering, University of Plymouth5

What is the Design Envelope ?

In simple terms a design envelope summarises:

• Requirements

Attributes that the solution must have to satisfy external or internal parameters

The more specific these become, reflecting better quantification of aspects of the problem, the better the potential solution choice and problem understanding

e.g. “it must not be too heavy”, cf “it should weight less than 25 kg to meet COSH lifting guidelines

Department of Mechanical & Marine Engineering, University of Plymouth6

What is the Design Envelope ?

In simple terms a design envelope summarises:

• Constraints

Limitations on design characteristics imposed by external or internal parameters

The more specific these become, reflecting better quantification of aspects of the problem, the better the potential solution choice and problem understanding

e.g. “it must operate quickly”, cf “it should have a response time of 10 s” (power implications etc)

Department of Mechanical & Marine Engineering, University of Plymouth7

What is the Design Envelope ?

In simple terms a design envelope summarises:

• Criteria

Critical design characteristics imposed by external or internal parameters

These are used to assess optimality of proposed solutions - very specific identification of these will assist greatly in choosing between various proposals

e.g. “it must be failsafe in use”, cf “it must cut electrical power in 100ms if a short circuit occurs”

Department of Mechanical & Marine Engineering, University of Plymouth8

What is the Design Envelope ?

Requirements, constraints and criteria are interchangeable depending on the details of the design solution specification

• e.g. “it must operate quickly”

Could be a requirement of a design parameter

Could be a constraint on performance

Could be a criterion of paramount importance

• Careful thought as to the most appropriate category will amplify knowledge of the design ‘space’

Department of Mechanical & Marine Engineering, University of Plymouth9

Formulating a Design Envelope

Obtaining a fully specified design envelope is more involved than may initially be thought

• There are significant potential benefits

A good specification may enable greater innovation/cost savings

Advances in function

Advances in materials engineering

A more elegant solution may result

Better form/ergonomics; simpler operation

Department of Mechanical & Marine Engineering, University of Plymouth10

Formulating a Design Envelope

Obtaining a fully specified design envelope is more involved than may initially be thought

• It is a high level engineering skill

Innate embodiment of sum of knowledge

Achieved through ‘reflective practice’

Can be inculcated through understanding of reflective practice in design and project work

• It leads to ‘spider web’ linkages between design attributes

Department of Mechanical & Marine Engineering, University of Plymouth11

Reflective Practice in Engineering Design

Realising an engineering design encompasses 3 key stages:

• NEEDNEED – all design begins with a clearly defined need• VISIONVISION – all designs arise from a creative response to a need• DELIVERYDELIVERY – all designs result in a system, product or project that meets the need

Department of Mechanical & Marine Engineering, University of Plymouth12

Reflective Practice in Engineering Design

Consider the systems approach to design:

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Reflective Practice in Engineering Design

Systems approach involves:

• ‘Deconstructing’ a particular problem in a sequential way into components, systems and actions prior to ‘constructing’ various potential solutions

• It also involves cross-linking and integrative processes between the various sub-sets of design activity

• This is done in a ‘virtual’ iterative and reflective way prior to prototype or final design production

Department of Mechanical & Marine Engineering, University of Plymouth14

Reflective Practice in Engineering Design

Another way of showing this reflective process in design activity terms is via an ‘iterative transition diagram’ – e.g. design of a playground

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Reflective Practice in Engineering Design

The ‘iterative transition diagram’ is a model of the design process and summarises the key issues in reflective practice:

• Interactive framing of the problem

• Reflection on the outcome on these moves

• Inexperienced designers show a low level of iteration across design activities

Particularly the case later in the design activity sequence

Less willing to revisit earlier decisions

Department of Mechanical & Marine Engineering, University of Plymouth16

Reflective Practice in Engineering Design

What does reflective design practice entail ?

• Emphasis on problem-setting activities, as well as problem solving activities

• Reasoning about the problem

Experimentation with ideas/solutions

A variety of graphical and textual representations of problem aspects

Department of Mechanical & Marine Engineering, University of Plymouth17

Reflective Practice in Engineering Design

What does reflective design practice entail ?

• Interactive problem framing

• Iterative generation of ‘moves’ towards a solution

• Reflection on outcomes of this problem and solution framing

Department of Mechanical & Marine Engineering, University of Plymouth18

Reflective Practice in Engineering Design

Important features of this model of the design process are:

• Unpredictability (of final solution)

• Consequent surprise in the design process

Leads to innovation, novelty, uniqueness

• Reflection

Unpredictability of complex design situations encourages ‘back-talk’

Department of Mechanical & Marine Engineering, University of Plymouth19

Reflective Practice in Engineering Design

‘Back-talk’ is reflective interaction with aspects of the design and potential materials

• Aids in developing a deeper understanding of the design problem

• Experiment with solution to push boundaries

Irregularities in solution suggest further areas of clarification

• Iterative transitions between design activities represent such ‘back-talk’

Department of Mechanical & Marine Engineering, University of Plymouth20

Reflective Practice in Engineering Design

Iteration triggered by specific activities:

• Self-monitoring

Reviewing and evaluating progress

Checking understanding of problem

Searching for and being open to potential solution short-comings

• Clarifying

Interpret meaning of ambiguities or important criteria

Department of Mechanical & Marine Engineering, University of Plymouth21

Reflective Practice in Engineering Design

Iteration triggered by specific activities:

• Examining

Efforts to understand solution behaviour

Determine solution feasibility

Iteration likely to result in:

• Redefining problem elements

More detail in design envelope

• Coupled revision to problem understanding and potential solutions

Department of Mechanical & Marine Engineering, University of Plymouth22

Reflective Practice in Engineering Design

Complex and ambiguous (open-ended) design tasks involve a paradox:

• Information cannot be gathered meaningfully unless the problem is understood

• Cannot understand the problem without gathering detailed information about it

Iteration and reflection are essential to effective design practice