Evaluation-of-DRed-a-way-of-capturing-and-structuring-engineering-processes

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Cambridge Engineering Design Centre

Department of Engineering Trumpington Street Cambridge CB2 1PZ

E-mail: [email protected] Web: www-edc.eng.cam.ac.uk Tel: +44 (0)1223 332742 Fax: +44 (0)1223 332662

Evaluation of DRed

(Design Rationale editor)

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What is DRed?

DRed is a simple method that captures a design

rationale using a graphical representation of

design elements. The main DRed elements are

issues, answers, pro and con arguments

DRed elements are created, positioned and linked

manually in a workplane consisting of a single

DRed document

Dependencies between elements that belong to

different documents, may be made via tunnel links

As a design proceeds, DRed documents are stored

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DRed document

Mouth of “tunnel” carrying

link into another workplane Issue

Pro argument

Answer

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Aims of the research

• To evaluate how DRed allows the capture of design rationale

• To confirm the perceived benefits of DRed

• To learn more about the design process using the new resources that DRed has made

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Objectives of the research

To determine if DRed:

• is used as instructed in the working practice

guideline

• improves the richness and clarity of the recorded

information

• has a beneficial effect on design behaviour by

prompting design thinking and helping designers

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Methods

To understand if DRed allows the capture of richer information:

• Compare design rationale captured using DRed to that captured using textual representations

To understand if DRed allows the capture of clearer information:

• Compare how a number of subjects interpret design rationale captured using DRed and textual representations

To understand if DRed has a beneficial effect on design behaviour:

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Data set size

• DRed documents data set:

– 7 designers

– 19 DRed folders

– 39 DRed documents

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Research questions

• Q1: Do designers use DRed issues as instructed in the working practice guideline?

• Q2: What problem types do designers address through the questions captured in DRed?

• Q3: What question types do designers capture in DRed?

• Q4: Do designers use DRed syntax as instructed in the working practice guideline?

• Q5: What layout styles do designers use to capture their design processes in DRed?

• Q6: Are more answers per issue and arguments per answers

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Nature category

• Distinguishes an issue element depending on the way it was phrased

Type Description

1 Question Interrogative sentence expressing an inquiry for information

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Nature of issue elements

• DRed working practice guideline: issue elements

should be questions

Type Example % of total

1 Question How could the need for a dust cap be eliminated?

75%

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Research questions

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Problem type category

• Distinguishes a question depending on the problem being addressed by a designer

Type Description

1 Diagnosis The question wants to develop the process to generate a cause to an undesired behaviour in a product 2 Design The question wants to develop the

process to generate a product form from an intended behaviour and other requirements

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Problem types

1 Diagnosis Why did the Trent 800 IPT disc rim design temperature exceed the design value?

10%

2 Design How can I maintain the disc

temperature below design value? 85% 3 Process How to determine the size of the

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Research questions

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Objective category

• Distinguishes a question depending on the intent that a designer pursues when designing

Type Description

1 Information The question wants to obtain information but does not

indicate an objective

2 Confirmation The question wants to establish the truth of a fact, the

occurrence of an event or the existence of a state

3 Comparison The question wants to establish similarities or differences

4 Constructive generation

The question wants to generate a solution: from the generation of creative conceptual solutions to that of detailed features of solutions

5 Explanatory generation

The question wants to generate an explanation: from the generation of explanatory conceptual solution to that of detailed features of solutions

6 Analysis The question wants to establish the consequences of a

solution by carrying out simulation and calculation

7 Evaluation The question wants to establish whether a solution is

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A model of reasoning in design

Intended behaviour Form Predicted behaviour 2 1 3 Ge ne ratio n Evaluation A n a ly sis

How can I improve the oil scavenge

capability in the Trent 900 radial drive shaft to its shroud by 10%?

How much oil does the Trent 900 scavenge if the outer diameter is increased by 2mm?

How does this value compare to

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Objective category

1 Information What material does the Trent 800 use for this part? (from

previous research) 0%

2 Confirmation Are suitable materials available? (from data set) 2% 3 Comparison What are the differences in inspection requirements

between a class 01 and a class 02 forgings? (from previous research)

0%

4 Constructive generation

How can I maintain the disc temperature below design

value? (from data set) 61%

5 Explanatory generation

How does oil scavenge from that side of the chamber?

(from previous research) 0%

6 Analysis How much heat energy can be removed from oil system?

(from data set) 36%

7 Evaluation How does this compare to the potential heat build in today’s

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Examples of issues

• Issue 1:Why did the Trent 800 IPT disc rim

design temperature exceed the design value?

• Issue 2: What are the technical consequences

of the temperature increase?

• Issue 3: How can I maintain the disc

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Examples of issues classification

• Issue 1:Why did the Trent 800 IPT disc rim

design temperature exceed the design value? (diagnosis - generation)

• Issue 2: What are the technical consequences

of the temperature increase? (diagnosis -analysis)

• Issue 3: How can I maintain the disc

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Research questions

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DRed structures

• DRed working practice guideline: the syntax checker should be used to check for logical

structures. The recommended sequences are:

– Issue/Answer/Argument

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DRed syntax

VALID LINK types Frequency of use

1 I I Rarely

2 I A Frequently

3 A AR Very frequently

4 A I Occasionally

5 AR I Rarely

6 I AR Rarely

7 AR AR Rarely

8 AR A Rarely

INVALID LINK type

9 A A Occasionally

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Research questions

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Research questions

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Comparison

Design Definition Report (DDR) generated after the design process

Design Definition Report (DDR) reversed engineered into DRed Design Definition Report (DDR) extracted from a

DRed folder DRed folder

generated during the design process No formal procedure

to capture design rationale during the

design process

Design rationale capture strategy

after DRed (real time)

Design rationale capture strategy

before DRed (retrospective)

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Comparison of DRed and DDR

DRed DDR

Average on 4 folders and 17 doc

Average on 4 folders and 4 doc

Answers per issue 2 1.5

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Conclusions I

• Issue elements are predominantly phrased as

questions to address design problems

• Issue elements are more frequently used to capture

generative questions rather than analytical and evaluative ones

• The most common structure is

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Conclusions II

• The processes captured and and structured in

DRed, compared to those presented in the DDRs

are richer in the number of answers per issue and

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Future work

• Collecting more DRed documents

• Propose to undertake a study with groups of Rolls-Royce trainee designers working in the following conditions:

– carrying out design freely

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Marco Aurisicchio Research Associate

Engineering Design Centre (EDC) Department of Engineering

University of Cambridge Trumpington Street

Cambridge, CB2 1PZ