The Design Rationale Editor (Dred)

INTRODUCING THE CAPTURE OF ARGUMENTATION-BASED DESIGN RATIONALE INTO INDUSTRIAL PRACTISE

Rob Bracewell Ken Wallace

Cambridge Engineering Design Centre Department of Engineering E-mail: [email protected] Trumpington Street Web: www-edc.eng.cam.ac.uk Cambridge Tel: +44 (0)1223 332742 CB2 1PZ Fax: +44 (0)1223 332662 The Design Rationale editor (DRed)

• What is DRed? • Where did it come from? • How was it researched, implemented and introduced? • Why do designers seem to find it a help rather than a hindrance?

2 What is DRed?

• DR capture tool used by aerospace designers on live tasks from v0.1 onward – just 3 weeks’ software development in v0.1 • Example: Dave Williams, July 2002 – ANTLE Internal Gear Box – Issue: how to improve scavenge while avoiding oil leaks? – Rationale shown in recent DRed, but was originally captured with crude early version

3 Issue: Open

Start with an open issue Note “traffic light” statuses

4 No hidden information, easy to scan and browse

5 Proposed answers: Open

Pro argument Con argument (qualified)

Development of answers and arguments

6 Argument declared to be false

All elements have alternative statuses, easily changed

7 Answer rejected in response to dominant con

Changes of status capture decisions Follow arrows for knock-on effects Rejection decisions captured

8 Mouth of “tunnel” carrying link into a new file

Tunnel links enable large, connected rationales to be distributed legibly

9 Far end of tunnel

10 Back to previous graph

11 Where did it come from?

KCSR Project: Socio-Technical Approach to Engineering KM

Individual Other Designers System

Design Product Rationale world Manager Communities of Practice

Expertise Design review Finder Process meetings world Other System TECHNICAL SYSTEM

12 Where did it come from?

KCSR Project: Socio-Technical Approach to Engineering KM

Individual Other Designers System

Design Product Rationale world Manager Communities of Practice

Expertise Design review Finder Process meetings world Other System TECHNICAL SYSTEM

13 Need for Design Rationale Capture

• By 2001, rationale capture had become moribund topic in design research community – Full text search of proceedings of premier annual design research conference (ASME DETC) revealed just 3 citations of IBIS or derivative work in 4 years – IBIS community had shifted focus toward facilitated capture of real or virtual meetings

14 Example of gIBIS

Figure 3: an Example of gIBIS [Buckingham Shum, 1991]

15 DRL: a rather complex notation

Figure 11: DRL notation [Buckingham Shum, 91]

16 Commercial Tool (2001): QuestMap

17 Commercial Tool (2001): DRAMA

18 Rolls-Royce Design Definition Report

19 Design Definition Report Study

•Objectives – Inform development of the KCSR project Design Rationale Manager – Explore the potential uses and benefits of simple graph-based design rationale notations in design processes. – Explore the best structure for textual design reports • Use of “Graphlet” graph layout & editing tool – produced by University of Passau – efficient, robust, underlying graph processing library (C++) with flexible scripted GUI (Tcl/Tk)

20 Design Definition Report Structure

•1. Summary • 2. Problem Analysis/ Requirements Specification –2.1 … • 3. Alternative Solutions –3.1 … • 4. Final Solution Description –4.1 …

21 Initial DR Notation

• Directed graph of these elements:

22 23 24 25 26 27 28 DKC118351: Problem 1

• During strip of the Trent 500 development engine 70003/2 is was found that two anti score plate tangs with balance weights were missing of the HPT rotor assembly

29 30 DKC118351: Problem 2

• Problems were experienced during the build of the HPT rotor for development engine 70004/1 during the straight line build procedure (RTS81338). Swash and runout measurements were not repeatable once the main tooling bolts were removed from the assembly and the coverplate was only held on by the set screws

31 32 Conclusions of DDR study

• Subjective impression favourable, in that: – use of notation not difficult, feels natural – improves structure of DR captured compared to textual design definition reports – graphical portrayal easier to interpret than original structured text document – may help in structuring, representing and reviewing designers’ thought processes • Promising enough to be tested by designers on live problems

33 Initial Development of DRed tool

• Simplified version of Graphlet, customised for DR by Tcl/Tk scripting • Standalone, file based, Win98/NT/2000 platforms • Export DR graphs to .wmf for Word/PowerPoint • First version delivered in under a month to interested parties at RR for trials of the DR notation • Research ideas, user suggestions and feedback on problems rapidly transformed into working software • 8 releases to core evaluation team in 8 months

34 Questionnaire of users in Rolls-Royce after 6 month trial

• Found to be easy to use – 14 out of 19 responses found easy or very easy • Some immediate improvements to design process: – 10 out of 10 found improved or slightly improved overall view of design process – 7 out of 10 found improved or slightly improved keeping track of design process – 6 out of 10 found improved or slightly improved evaluating and deciding between concepts –No(!) negative feedback, 0 out of 10 said hindered/slightly hindered design process • Designers perceive future benefits. Main benefits: – communicating to others 11 out of 14 designers – monitoring progress 9 out of 14 designers

35 Examples of use in Rolls-Royce

• Encouraging clear and rigorous thinking – Industrial Trent 60 dual fuel A “eureka” moment resulting from a DRed analysis caused the team to change design concept to “a rationalised, cost effective layout where liquid manifolds are protected from radiation, and are clear of the flame break-out region”; Allan Salt, Preliminary Design, Ansty – JSF passive valve/rear casing clash and JSF Z ring design; both Martin Cullen, Bristol –iRB211 Dual Fuel DLE Deletion of Central Diffusion Gas Circuit “DRed was used to clearly identify the problem, the various solutions and their advantages and disadvantages. … was successful due to its: clarity, rapidity [and] colour coded visual symbols”; Yasmine Ghaly & Richard Hamby, Montreal

36 Examples of use in Rolls-Royce

• Structuring and clarifying complex problems – Design combines problem understanding and solution creation…

– Edelweiss failure investigation and subsequent design; Ian Merryfield & Paul Brooks, Derby “An added … bonus was that [DRed] provided an admirable diagnostic tool which has been used successfully to understand Civil Aerospace fleet events.” Geoff Kirk, Chief Design Engineer – Adour LPT blade rubs root cause; Keith Nurney, Bristol

37 Examples of use in Rolls-Royce

• Communicating in reviews – JSF mandates DRed use in Scheme Reviews Andy Haasz – Submarines Main Coolant Pump rundown problem in review with the Navy, Andy Storer – 1) Solution to EJ200 bearing stub shaft damage on LPT installation. 2) Assessment of squeeze film options to reduce EJ200 vibration - both examples Volker Herzog, Bristol “Volker used DRed in a DDRAM presentation to good effect. It gave a very clear picture of the thought processes and reasons for choosing the final solution. For the CDE, it provided a visible route map which aided discussion of alternative solutions and agreement of the chosen solution.” Graham Slack D(A)

38 Examples of use in Rolls-Royce

• Communicating to the team, focussing effort – Trent 500 fir tree cracking; Richard Corran – Trent 1000 combustor design; Giles Harvey, APSD • Saves effort in creating reports – Accepted by the Design Practices Committee – Trent 1000 IP/HP Coupling & presentation to ANA “DRed proved to be a powerful tool when considering the complex issues surrounding the many concept options…. It … enabled rational down select of the leading designs. This has proven to be a valuable reference pack throughout the design evolution” Andy Swift, APSD • Use by supply chain and to support review of designs done for R-R – Use of DRed in India by Quest

39 40 41 Why is DRed an effective design tool?

• Simplicity, low training requirements • No database management system required – Tunnel linked DRed files live in the project folder – Simple to deploy DRed and create a browsable and searchable archive of completed project folders • Easy to produce comprehensive hardcopy identical to view on screen – no hidden information • Traffic-light statuses of all elements • Anchor links to locations in graphical elements • Tunnel linking more effective for expressing design dependencies than transclusion?