AN OPTIMAL DESIGN PROCESS FOR AN ADEQUATE PRODUCT?

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1 AN OPTIMAL DESIGN PROCESS FOR AN ADEQUATE PRODUCT? P. J. Clarkson University of Cabridge Departent of Engineering e-ail: Keywords: process odelling, robustness, optiisation Abstract: The optial or best design process ay be the shortest or cheapest process, or the one that leads to a particularly desirable product, or to a reliable and aintainable product, or to a anufacturable product, or soe cobination of all of these. It is likely to satisfy the aspirations of the organisation to invest an appropriate aount of resource in the developent of a specific new arket opportunity, set in the context of longer-ter business goals. This paper describes the progress ade in over ten years of research on process odelling undertaken at the Cabridge Engineering Centre to identify an optial design process with which to develop an adequate product. 1. INTRODUCTION The goal of ost businesses in the odern world is to provide desirable, and ultiately profitable, products and services. This is generally achieved by eeting custoers needs and/or expectations both at the point of purchase of the product or service and during its sustained use. Custoer satisfaction ay range fro delight in acquiring an aesthetically pleasing object (e.g. a lap) or in using a well designed tool (e.g. a good car) to the grudging acceptance of the good value-for-oney of an essential, but poor, service (e.g. telecounications). Business success will depend on the iediate and sustained profitability of a portfolio of products and services, which will in turn depend upon the tiely and cost-effective introduction of new arket offerings. This paper ais to explore the proposition that a significant contribution to business success ight be derived fro the use of an optial design process to develop an adequate product by reflecting on progress ade in over ten years of research on process odelling undertaken at the Cabridge Engineering Centre. It begins by describing the background to this research, then presents soe of the achieveents to date and concludes by describing the research challenges for the future. 2. BACKGROUND The optial or best design process ay be the shortest or cheapest process, or the one that leads to a particularly desirable product, or to a reliable and aintainable product, or to a anufacturable product, or soe cobination of all of these. It is likely to satisfy the aspirations of the organisation to invest an appropriate aount of resource in the developent of a specific new arket opportunity, set in the context of longer-ter business goals. The introduction of a new widget-in-can beer product was driven by the need to deliver an appealing product to arket within ten onths in order to eet the Christas surge in sales. Infringeent of copetitors patents had to be avoided whilst concurrently developing new product, anufacturing and assebly solutions. Developent costs were expected to be significantly less than arketing costs and were ultiately paid back within weeks of a successful launch. The optial design process delivered a good product on tie and rejuvenated an ailing copany. The developent of a prototype fire-fighter training unit (FFTU) for the UK Royal Navy was driven by the need to deonstrate the utility of a novel technological approach to fire-fighter training. The optial design process followed strict quality

2 22 ethods for practice guidelines to deliver a deonstrable syste with robust design and risk docuentation. The developent of the subsequent units was driven by the need to deliver a thirty-year training service. The optial design process in the latter case had to take particular account of the long-ter safety, availability, reliability and aintainability (ARM) requireents for the FFTU in the context of a fixedprice service contract. The supply of an adapted jet engine design as part of an aircraft fleet contract is driven by the need to eet a specified delivery target and to sustain a iniu level of perforance through life. The new design will be based upon previous designs, with the introduction of new technology often contingent on its perforance in test engines. The optial design process will enable as uch exploration and developent of possible designs as is consistent with the need to deliver a product that eets regulatory approval on tie. These exaples highlight the wide range of factors that ay influence the design process, defining both what ay be considered to be adequate as a new product or service and what ight be regarded as optial as a design process. However, since design is a dynaic process that is not easily defined beyond the key stages described in any text books, the optial process ay see ore of an aspiration than a realistic goal. Hence, the following sections describe efforts that have been ade to develop tools that assist in the definition of good design processes for coplex engineering products. The chronology of the actual research is broadly observed and the key research questions at each stage are highlighted. The benefits of a dynaic odel-based approach to design process iproveent are explored through the description of research carried out over a period of ten years on the iproveent of engineering design processes through process odelling and analysis. The research ais to support the design process by capturing, visualising and directing the specific design process required to design a product rather than the official process that designers are supposed to follow. The odelling approach proposed explicitly odels inforation flows within the design process and drives the selection of tasks by the quality of the inforation that is available at any point in tie. 3. CHRONOLOGY The research on began in 1995 with a PhD studentship sponsored by Westland helicopters and continues today with a tea of ore than 10 researchers. In this paper, we explore the dynaic nature of the design process revealed through ten years of epirical studies and through literature. We describe research using the Signposting approach to odel dynaic process behaviour. This research includes the developent of a syste to guide the adaptive design of a helicopter blade; a real-tie process anageent syste which supports the integration of proprietary copressor design codes; and a odel-based approach to support ning practice in collaborative design projects (Figure 1). Identify possible tasks Identify best policy Execute best task Identify best Execute best policy Identify robust Execute best Fig.1. The developent of Signposting Identify optial Execute robust Execute optial IDENTIFYING POSSIBLE TASKS Early attepts at capturing design processes within a nuber of organisations found that current off-theshelf approaches were lacking in their ability to capture coplex engineering design processes. This led directly to the developent of a new approach to process apping A passive paraeter-driven odel Westlands are recognised as world-leaders in the developent of helicopter rotor-blades and developed the burp-tip rotor blade to iprove the aerodynaic perforance and hence lift and loadcapacity of their aircraft. They had tried to capture the rotor-blade design process theselves and found that the highly iterative process could not be adequately described with conventional stage-based process odels [1]. Through a series of interviews and onths of observations it becoe clear that rotor blade design process was data-driven and consisted of repeating the sae or siilar tasks with ever ore accurate input data [2]. Subsequently, a tool (known as Signposting) was developed (see Figure 2 for notation) that provided designers with a list of tasks that they could carry out at any point in the design process, given the availability of appropriate inforation [1]. if and then at least ediu confidence at least ediu confidence in transfer atrix at ost high confidence if rigid-body test positive blade-loads Rigid-body transfer atr blade-loads h l Confidence apping l Inputs Output task not appropriate if and then tie at least ediu confidence at least low confidence in transfer atrix at ost ediu confidence if rigid-body test positive Fig.2. The basic eleent of a Signposting odel A subsequent tool (Figure 3) was successfully evaluated in Westlands.

3 PART I General approaches to the design process 23 notion of probabilistic task failure, where each task can either succeed and advance the design, fail in its execution without changing the design or produce results that reduce the designer s confidence in the design [4]. 3. Finalise geoetry 2. Refine geoetry 1. Sketch geoetry loadsl h geoetry loads stress conc. loads stress conc. l bulk stress l h stress conc bulk stress geoetry l h l bulk stress geoetry h l geoetry h l 6. Siulate loads 5. Analyse geoetry loads 4. Estiate geoetry loads loadsl geoetry loads stress lconc. loads stress conc. x bulk stress stress conc bulk stress loads h l bulk stress loads h l loads h l Fig.3. An early Signposting tool 4.2. An active paraeter-driven odel In 1997 the sae core idea was applied to the conceptual design of stea-turbine copressor blades. It soon becoe clear that turbine blade design was a lengthy process, not only because it was highly iterative, but also because designers had to use any separate coputational tools, anually transferring inforation between the. A subsequent version of the Signposting tool (Figure 4) integrated these disparate analysis tools and provided real-tie data anageent for early conceptual design, incorporating a sensitivity analysis to identify the ost appropriate task to advance the design towards its perforance goals [3]. Again interviews and observation provided understanding and data for the study. Manageent Software 9. Initial FE analysis 8. St Venant s geoetry loads 7. Visual geoetry check l stress conc. geoetry loads l bulk stress loads stress conc. l bulk stress stress conc. Stress conc h l bulk stress stress conc. h l stress conc h l 12. Final FE analysis 11. Stress analysis geoetry loads h 10. Initial geoetry check l stress conc. h geoetry loads l bulk stress loads stress conc. l bulk stress bulk stress Stress conc l h l bulk stress bulk stress h l bulk stress h l Fig.5. A siple 12-task odel Much effort was also spent in visualising networks of alternate paths through a given set of tasks as a eans to articulate the best policy [5]. Figure 6 shows the best policy for the tasks shown in Figure 5. Policies could also be represented as soft dependencies in the Signposting odel in contrast to the hard dependencies defined by critical data flows. The research was infored by a study on design process ning within a sports car anufacturer, by undertaking interviews with 18 engineers and design anagers regarding how design processes were ned and what functions the resulting s carried out [6]. This was copleented by a further 17 interviews carried out in an autootive consultancy. Preliinary Throughflow 2D Blade 3D Blade Hierarchical Inforation Store Fig.4. A fraework for a dynaic Signposting tool Paraeter States 5. IDENTIFYING THE BEST POLICY Identifying tasks that will progress a design provides an instantaneous view of the design process that takes no account of the relative risk incurred in choosing a particular option. A better approach would be to select a task based on soe knowledge of process risk Risk-based route finding Identification of the best route through the design process was addressed in a theoretical research project on route ning which utilised Markow chains to identify policies for navigating the design process (Figure 5). This research introduced the Steps Fig.6. Best policies (in bold) for the 12-task odel 5.2. Siulation-based route finding processes are full of uncertainty and, as a result, it is difficult to identify all the tasks, and their ordering, at the beginning of a process and assue that this process will be followed. anagers are interested in the risk associated with alternative design routes, which ay be estiated through siulations of the design process (Figure 7).

4 24 ethods for practice Fig.7. Typical process siulation output This research drew on coplexity theory and involved the analysis of any design project s in the autootive consultancy. An evaluation odel was built of an in-house process of a jet engine coponent design cobined with four interviews with design experts in the copany [7]. Fig.9. A DSM for the process in Figure 8 This tool has subsequently been developed further to support a variety of explicit definitions of process iteration. These range fro the original Signposting forulation to descriptions that show a specific nuber of iterations or a probability of task success. 6. IDENTIFYING THE BEST PLAN The best policy provides support in selecting the best next task during execution of a design process. A ore pragatic approach would be to select the best route or before the process coences. This is the ain tenet of process ning process capture To introduce process risk assessent techniques in industry it is vital that designers and design anagers can build knowledge-rich process odels and benefit fro the process of odel building itself. Based on experiences gained through a seven onth secondent to Rolls-Royce, a tool was developed that enables designers to capture detailed hierarchical design process odels [8]. These odels can be viewed as flowcharts (Figure 8) or DSMs (Figure 9) and, using the siulation approached developed earlier, translated into Gantt charts (Figure 10). Fig.10. A Gantt chart for the process in Figure 8 The tool also supports the attachent of ebedded task definitions allowing active task execution Characteristics of good processes Copanies need to ake trade-offs between process tie and product quality and are therefore interested in trading off product and process risk. A detailed study in an off-road diesel engine anufacturer involved one onths observation over a period of 6 onths and about 40 interviews with designers, anagers and support staff, led to an inclusion of product quality easures into the process odels. The sae study also ade it clear that it is difficult to evaluate objectively the structural properties of design processes odels, i.e. to identify those process constructs that coonly succeed (or fail), using real industrial odels. Therefore a odel generator was developed that creates and perturbs odels to investigate the relative robustness of odels of different characteristic types. Fig.8. A hierarchical process capture tool

5 PART I General approaches to the design process IDENTIFYING A ROBUST PLAN Process odels based on flow-charts derived fro designers are typically over-constrained when copared to the earlier Signposting odels. They are likely to contain dependencies between tasks that are a reflection of the designer s preference rather than the absolute need to pass data between tasks. This allows the possibility of identifying better s for a given process. Any given, if executed any ties, is likely to show a variation in perforance, as easured in ters of process or product perforance (Figure 11a, curve I). If that variation can be reduced the process will becoe ore iune to external disturbances (Figure 11b, curve II), i.e. ore robust. It is possible that further iproveents in robustness ay be achieved if soe of the designer s preferences (Figure 11c, curve I) can be relaxed. This should lead to a greater nuber of design process possibilities (Figure 11c, curve III) within which a better perforing subset of s ay be found (Figure 11c, curve II). cost, of the process itself. However, as entioned earlier, it is also iportant to consider the ipact of the process on the easurable perforance of the product, for exaple its weight or reliability. Future research will focus on attributing product perforance to specific process tasks, hence enabling the investigation of product perforance variance against process. This is turn leads to the possibility of adopting ulti-objective ulticriteria optiisation techniques to identify the tradeoffs between product and process perforance. 9. SUMMARY The research presented in this paper reflects the Cabridge Engineering Centre s preferred approach to cobining the developent of applied solutions for industry with theoretical research. We wish to understand how design processes work in industry and how we can support their ning and execution through coputer tools that capture, visualise, optiise and anage the design process. The intended outcoe of the research is a suite of robust industrial software tools. The research originally arose fro the practical needs of copanies to understand and iprove their processes. Interestingly, a coon observation has been that even the ost successful copanies often struggle to describe the very processes by which the products that bring the success are generated. There would appear to be roo for iproveent. The research has continued to involve close collaboration with industry, both to ground it in the needs of industry and to gain iediate feedback on the tools under developent. Our current research approach ay be suarised as a continual cycle of odelling, siulation, iproveent and application. (Figure 12). Fig.11. Searching for a ore robust process This approach sounds fine in theory, but in practice it is not clear how better, ore robust, s can be identified. In addition, it is not at all clear how a single project can be derived that represents the characteristics of a set of siilar s, i.e. how can the distribution shown as curve II in Figure 11c be represented by a single Gantt chart? 8. IDENTIFYING AN OPTIMAL PLAN Most of the research to date has focused on iproving the perforance of the design process in ters of easurable characteristics, such as tie and Fig.12. A fraework for process iproveent Process odelling represents the critical starting point of the iproveent cycle. Good odels are essential and research efforts reain focussed on understanding how best to odel the intended design process, balancing the desire to build an inforation-rich odel suitable for siulation, with

6 26 ethods for practice the cost of data collection. Graphical elicitation techniques are iportant as they find favour with designers and design anagers alike. Process siulation is generally straightforward. However, the challenge reains to choose which process paraeters to vary and to identify soe basis for the range and type of variation. Again, sophistication has to be traded against accuracy and the cost of data collection. Siulation is unlikely to produce results with absolute accuracy, but can be very effective at identifying links between process perforance and process attributes, such as task ordering, and design resource capability. Process iproveent reains a challenging task. There is still uch research required to explore the link between process siulation and process iproveent. In particular, there is a need to understand how to identify robust processes, both in ters or design process perforance and subsequent product perforance. Finally, it is iportant to identify practical eans by which robust processes ay be described to designers and design anagers. It is likely that traditional Gantt and PERT charts will continue to have significant influence is this area, but research will also focus on identifying alternative descriptions. Coon to all of these steps is a desire to provide designers with practical, easy-to-use tools that allow the to capture, visualise and anage the design process. In suary, the Cabridge Engineering Centre is coitted to developing practical process iproveent tools that will challenge current ning approaches. Acknowledgeents: the work presented in this papers represents the efforts of the author s any PhD students and Research Associates who have contributed to the developent of the Signposting concept over the past 10 years. The research has also been infored throughout by studies in six copanies: a ajor aeroengine anufacturer; a anufacturer of diesel engines for power generation and off-road vehicle applications; an industrial cheicals anufacturer; an autootive engineering copany; an autootive consultancy within a steel copany; and a large European aircraft anufacturer. References [1] Clarkson P.J., Hailton J.R., Signposting: a paraeter-driven task-based odel of the design process, Research in Engineering 12(1) pp , [2] Hailton J.R., The Capture and Representation of Knowledge to Support Aerospace, PhD thesis, University of Cabridge, [3] Jarrett J.P., Technology or ethodology? An approach to designing better turboachinery, PhD thesis, University of Cabridge, [4] Melo A.F., A State-Action Model for Process Planning, PhD thesis, University of Cabridge, [5] Clarkson P.J., Melo A.F., Eckert C.M., Visualization Techniques to Assist Process Planning. ICED 01, Glasgow, Scotland, [6] Eckert C.M., Clarkson P.J., The Reality of Process Planning, ICED03, Stockhol, Sweden, [7] O Donovan B.D., Modelling and Siulating Processes, PhD thesis, University of Cabridge Departent of Engineering, (2004). [8] Wynn D.C., Clarkson P.J., Eckert C.M., A Modelbased approach to iprove ning practice in collaborative aerospace design, Proceedings of ASME IDETC/CIE, Long Beach, California, USA, 2005.