Design activity requires engineering designers to ask questions and find ... have a greater problem space from which to create solutions and to recognize design ..... A period can be observed from N1 until N4 where the designer understands the .... the Engineering and Physical Sciences Research Council. (EPSRC) and ...
CONNECTED 2007 INTERNATIONAL CONFERENCE ON DESIGN EDUCATION 9 – 12 JULY 2007, UNIVERSITY OF NEW SOUTH WALES, SYDNEY, AUSTRALIA
Understanding Engineering Design Activity through Questioning Saeema Ahmed1 and Marco Aurisicchio2 1
DEPARTMENT OF MECHANICAL ENGINEERING, TECHNICAL UNIVERSITY OF DENMARK, LYNGBY, DENMARK 2
DEPARTMENT OF ENGINEERING, UNIVERSITY OF CAMBRIDGE, CAMBRIDGE, UNITED KINGDOM
ABSTRACT This research describes an understanding of design activity through design questions. From a number of previous studies two types of questions have been identified: 1) reasoning questions; and 2) strategic questions. Strategic questions are part of an experienced designers approach to solving a design task. The paper describes how designers progress their tasks by asking questions at both a reasoning and strategic level. Transcripts of protocol analysis have been examined to identify both strategic questions and reasoning questions. These are discussed together with their relation to a problem solving model. An example of aerospace engineering design is used to illustrate the argument. The research contributes to an understanding of design activity. I. INTRODUCTION Design activity requires engineering designers to ask questions and find satisfactory answers. Recent research to understand design behavior has shown that the questions asked by designers can be used to describe the progress made in problem solving as well as the application of different strategies (Eris, 2002; Aurisicchio et al, 2006; Ahmed, 2003). The questions asked at a problem solving and strategic level are different and have always been researched independently. However, they are both critical to the development of new designs. Hence, the aim of this research is to bring together these two bodies of research to: (1) understand the relation between reasoning and strategic questions; (2) understand if questions allow a detailed description of design activity to be obtained; and (3) develop new understanding on the design activity. II. BACKGROUND A. Models of design expertise A number of empirical studies in engineering design have focused upon understanding how experienced designers approach design tasks. The insight gained from such research can assist in understanding how designers generate concepts. Novice designers tend to reason backwards and to use a deductive approach. In contrast experienced designers tend to reason forwards, and, when solving more complex problems, to
alternate between forward and backward reasoning (Ericsson, 1997; Zeitz, 1997; Jong, 1986; Waldron, 1987). Lawson has examined the role of design conversation to understand the design process and states that references made during conversation point to huge chunks of information (Lawson, 2003). Conversations between experienced designers reveal that they have shared expectations with a common language. De Groot states that experienced chess players rarely analyze a chess situation but recognize a situation (De Groot, 1978). Lawson translates this finding to the ill-defined area of design as the use of precedents, where the designers can recognize similar design situations (Lawson, 2003). Christiaans found that a designer’s problem space increased with experience (Christiaans, 1992). Hence, experienced designers have a greater problem space from which to create solutions and to recognize design solutions due to their experience. Short-term memory is limited by the number of chunks rather than the quantity of information it can hold, so the ability to recall increases with experience (Miller, 1956). Research carried out by Waldron and Waldron found that experienced designers hold larger amounts of information in a single chunk (Waldron, 1996). The number of issues that a designer is aware of as relevant to their design problem also increases with experience (Ahmed, 2005). One of the explanations for this may lie in the experienced designers ability to make associations between issues, and hence create ‘chunks’. Cross has conducted protocol analysis with outstanding designers from different domains (Cross, 2003). The common characteristics of these designers was the use of first principles within their respected domains. These designers were also able to frame their problem and to view the problem in a broad view rather than accepting narrow criteria or requirements. One of the characteristics of experienced designers, is that they formulate strategies to approach a design task (Ahmed, 2003; Kavakli, 2001; Cross, 2004). Cross explains the ability of the designers to frame the problem through the use of strategic knowledge. Kavalki suggests that the experienced designers use strategic knowledge but does not identify what this strategic knowledge is. Ahmed’s observations of experienced and novice designers led to the identification of a number of strategies that were used when approaching a design task (these are described in section IV-C).
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B. Question-asking in design The first wave of research into the questions asked by engineering designers has been driven by the need to understand how to develop intelligent CAD tools, design rationale tools and information management tools for indexing, modeling and retrieving design information (Kuffner and Ullman, 1991; Gruber and Russell, 1992; Baya, 1996). Subsequent research has been driven by the need to understand how designers approach design activities (Eris, 2002). Baya, investigating the information handling behavior of designers (Baya, 1996), observed that designers: (1) do not form questions randomly; (2) do not carry out design with a predefined set of questions; and (3) form new questions after reflecting on information received in answer to previous questions. Eris, exploring the nature of questions asked when designing, identified a set of questions conceptually closer to the intention of the questioner (Eris, 2002). These classes are divided into two groups termed Deep Reasoning Questions (DRQs) and Generative Design Questions (GDQs). If DRQs aim at understanding facts, GDQs aim at creating possibilities from facts. More so, DRQs are described as characteristic of a convergent thinking process, whereas GDQs of divergent inquiry. Dym et al identified the need to teach divergent query in the concept domain and suggested recommendations on how to incorporate a question centric thinking process as a tool to raise student awareness of the effective query in the design process (Dym et al, 2005).
Ethnographic participation, diary study participation, observation with shadowing, questions from rational capture tool
Interviews, Protocol analysis, Discourse Analysis
Data Collection Analyse to understand experience in design
Analyse to understand information acquisition
Strategic Questions
Re-analyse transcripts. Examination of questions in relation to each other, and in the sequence of design activity.
The aim of this research was to integrate reasoning and strategic questions. Hence transcripts generated after the observation of six expert designers were reanalysed to: (1) identify reasoning questions; (2) understand the relation between reasoning and strategic questions. In particular, fragments of the design discourse that showed a progression in problem solving were identified and converted into reasoning questions.
Research Method
Figure 1. Research approach
IV. FOUNDATION This research is based on a model of design activity and the findings from two independent studies to characterise reasoning and strategic questions. The reasoning questions focus primarily upon the progression of the design whereas the strategic questions apply also to the process. The model of design activity and the findings from the two studies are described in the following sections. A. A model of designing
III. RESEARCH METHODOLOGY A number of empirical studies provide the data and foundation of the research described. The aims of the initial studies were to understand: 1) how designers acquire and process information to establish how to manage design knowledge and how designers design with the support of a tool to record design rationale (reasoning questions); and 2) how designers design to establish the role of expertise in design (strategic questions). These studies indicated that designers ask different types of questions; and that designers adopt numerous different strategies when designing. The data collection method employed for these two initial studies and a description of the research methodology for this research is presented in Figure 1.
Individual Results
Reasoning Questions
The model represents designing using nodes and arcs, see Figure 2. The nodes describe different states of the developing design through three classes of variables: • Form variables: describe the components of an artifact and their relationships; • Behavior variables: describe the whole complex of transformations that occur to an artifact and its context during its use; • X variables: describe any additional issue driving the design process, e.g. manufacture, cost or assembly. F
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NODES F: Form IB: Intended Behaviour PB: Predicted Behaviour X: Any additional driver in the design process
2
ARCS : Trasfromation : Comparison 1: Generation 2: Analysis 3: Evaluation
IB(X)
3
PB(X)
Figure 2. A model of design
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The arcs describe a set of processes linking form, behavior and X. The three processes are briefly outlined below: • Generation transforms an intended behavior (IB(X)) into a form (F); • Analysis derives a predicted behavior (PB(X)) from a form (F); • Evaluation compares a predicted behavior (PB(X)) to the intended behavior (IB(X)). In this representation the term intended behavior is used to mean function. This model is in line with the findings by March and Gero (March, 1984; Gero, 1990). B. Reasoning questions Recent research into questions aimed at understanding how designers acquire and process information in the design process (Aurisicchio et al, 2005). Two main observations were made as to the nature of the questions asked when designing: • O1: design questions indicate different objectives (intents). These objectives sit at least at two different levels. At the lower level there are questions without an objective and questions with objectives like confirmation and comparison. At the higher level there are questions with objectives characteristic of problem solving, i.e. generation, analysis and evaluation. • O2: design questions indicate that different response processes (cognitive processes) are required to answer them. These response processes sit at three different levels. At the lower level, there are questions that are answered by retrieval-recognition. At the intermediate level, there are questions that are answered by reasoning, i.e. making an inference from an initial proposition (IP) to a final proposition (FP). At the higher level, there are questions that are answered by deliberation. In the model of designing in Figure 2, each of the three processes has an initial proposition (IP) and a final proposition (FP). For example, the generation process has IB(X) as IP and F as FP, see Figure 2. Observation O2 stated that reasoning questions aim at making an inference from an IP to a FP. Hence, reasoning questions were analyzed to find out if these could be used to describe the processes detailed in the model. In particular, the interest was in identifying reasoning questions that had the same IP and FP as the three processes in Figure 2. The example of the design of the oil jet nozzle for the low pressure front roller bearing (FRB) of an aero engine gas turbine is now considered to show how reasoning questions were identified that describe the three processes in the model of designing. The function to be realized is providing the FRB with oil for lubrication and cooling purposes at a low cost. The embodiment of this function required asking the three reasoning questions in Figure 3.
Side oil jet nozzle
How can we adequately lubricate and cool the FRB at a 1 low cost?
Lubricate and cool the FRB at a low cost
What oil quantity and angle cone does the use of a side oil jet nozzle allow 2 us to obtain?
3 Do these values for the oil quantity and oil jet angle cone meet our lubrication and cooling requirements?
x oil quantity and y angle cone
Figure 3. Example of three reasoning questions asked when designing
C. Strategic questions The strategic questions describe how experienced designers approach design tasks (Ahmed, 2003). The eight strategies, are known as C-QuARK and are formulated as generic questions. The experienced designers were observed to formulate questions during their design activity, which were used to progress the design. These are questions that the designers asked themselves. The eight design strategies are now presented together with the associated generic questions. Consider issues: experienced designers were more aware of relevant issues, and decided which were the most important. An example of generic question is: Which are the most important issues? Aware of reason: experienced designers tended to be aware of the reasons behind the use of, for example, a particular component or manufacturing process in a particular design. An example of generic question is: What is the reason why this component or manufacturing process was used? Refer to past designs: experienced designers often referred to past designs from the following sources: memory, drawings, reports and colleagues. An example of generic question is: Which designs are similar to the current design problem? Question is it worth pursuing: experienced designers frequently asked themselves how much they could expect to achieve if they continued a particular approach i.e. if they implemented a decision. An example of generic question is: How much can I expect to achieve if I continue this approach? Question data: experienced designers regularly questioned the data they obtained including values given for tolerances, standards, stress models, etc. An example of generic question is: How accurate is this value? Keep options open: the experienced designers would often reject an option if it limited later options in the design process. An example of generic question is: What should be considered further down the design process (task y and z)?
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Aware of trade-offs: experienced designers were clearly aware of the relationships between issues. When considering an issue they knew the effect this issue had on other issues and were aware that many decisions were based on compromises. An example of generic question is: What other issues does this effect? Aware of limitations: experienced designers were evidently aware of the limitations of the current design task. An example of generic question is: What should the current task expect to achieve?
F
1 IB
F
F
2 3
PB
IB
1
Past project
2
2 3
PB
Past project
Current project
IB(X)
PB(X)
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V. RESULTS The transcripts used for this research were already annotated with the strategic questions asked by the designers. Given that the transcripts account for approximately two hours of design work as part of tasks that lasted several weeks, the design activity did not generally cover all of the three activities represented in the model in Figure 2. The analysis of the transcripts allowed the identification of fragments of the design discourse that were converted into reasoning questions. This process allowed the design activities undertaken by the designers, i.e. generation, analysis or evaluation, to be clearly identified and associated with the strategies. The designers employed multiple strategies in each of the three activities. More analysis is required to establish with confidence which strategies are used during which activity. Important observations can be made as to the frequency with which the strategies are used, the role of the strategies in the design activities and their relation to reasoning questions: • The timing and type of strategic questions as well as their associated answers have a key role in the formation, development and refinement of reasoning questions. • Obtaining a satisfactory reasoning question to generate, analyze and evaluate a solution is strongly dependent on the use of precedents, i.e. information from past design experience. Refer to past designs, Aware of Reason and Consider issues are strategies that were observed to be used in combination. The experienced designers were observed to follow these combinations very frequently. • The retrieval of past project information triggers designers to ask reasoning questions associated to that design. Refer to past designs seems to be a critical strategy as it allows to retrieve past project designs to understand how to progress a current project design. The second and third observation suggest extending the model presented in Figure 2 as shown in Figure 4. The three basic processes in the model are linked through dashed lines to three identical models. If the main model is associated with the current project, the smaller models are associated with past projects. These models, therefore, show that designers, while undertaking the processes to shape the current project design, tend to refer to past project designs.
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NODES F: Form IB: Intended Behaviour PB: Predicted Behaviour X: Any additional driver in the design process
F
1
2
ARCS IB
3 Past project
PB
: Trasfromation : Comparison 1: Generation 2: Analysis 3: Evaluation
Figure 4. Extended model of design
A. An example of approaching the design activity asking questions The design of a variable area nozzle for a new supersonic engine is now considered. The design concept consists of a nozzle with clam-shell buckets that are attached through appropriate mechanisms to two hinges at the side of the engine. After a first design of the engine was completed, the design team was asked to redesign the engine to account for a new requirement. The customer wished to have a more powerful engine, i.e. needed more performance to fly higher. This means that the engine required to have more thrust. Hence, the design team changed the engine design to match the new requirement. The nozzle was therefore redesigned to suit the new design of the main engine. This design task was observed eight weeks (out of a total of twelve weeks) after the designer began work upon the project. The particular designer was observed for around 90 minutes, hence this is only an episode of the overall design task. The observation was followed-up with an interview to clarify the observation and to gain a better understanding of the context of the observed task. The designer involved had over 32 years of relevant experience in the aerospace industry. During the design process the designer formed the questions reported in Table 1. The table describes the phase of the design activity, the type of question (both reasoning questions (R) and strategic questions (S)), the design progression with extracts from the transcript, and the progression of the drawing. A period can be observed from N1 until N4 where the designer understands the problem of designing a variable area nozzle through the use of strategic questions. At N5, the first description of the problem is stated Where do I have to pick the hinge point to provide the right change in area?
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Type of question Aware of reason (S)
Actual question
Design progression
1
Phase of model Generate
How does a supersonic nozzle function?
2
Generate
Consider issues (S)
3
Generate
4
Generate
Aware of trade-offs (S) Aware of reason (S)
What issues do I have to consider in the design of the nozzle? What issue does thrust affect? How does the change in area work?
This flow comes along inside the duct. In supersonic flow, you have got to expand the flow to control it. So what you really need is to expand it out. You want a certain nozzle size to work at different conditions. For altitude, you need a large nozzle, and for take-off you need a small nozzle. Another reason you need to vary the nozzle area is to work efficiently at different conditions like take-off, supersonic cruise, climb, and they all require different nozzle areas. So we need to make a nozzle that changes in area More thrust; change in area; position of the hinge; correct airflow; smooth outside profile; engine length, performance points for flight cycle
5
Generate
Reasoning question (R)
6
Generate
7
Generate
8
Generate
9
Generate
Consider issues (S) Aware of reason (S) Refer to past design (S) Aware of reason (S)
10
Generate
11
Generate
12
Generate
13
Generate
14
No.
Where do I have to pick the hinge point to provide the right change in area? What other issue do I have to consider? How does thrust reversal work? Which designs are similar? How does the change in area work on the Concorde?
Reasoning question (R) Reasoning question (R) Consider issues (S) Aware of reason (S)
Where do I have to consider the nozzle to start? What should the core and bypass duct areas be? What other issues are important? What is the reason why there is a bleed flow?
Generate
Aware of reason (S)
Why is bleed flow an issue?
15
Generate
16
Generate
17
Generate
18
Generate
Aware of trade offs (S) Aware of trade-offs (R) Reasoning question (R) Reasoning question (R)
19
Analyze
Reasoning question (R)
What other issue does the bleed flow affect? What other issue does the boat-tail angle affect? What should the core and bypass duct areas be? Where do I have to pick the hinge point to provide the right area change and to account for the correct airflow (core plus bleed) but still keeping the external boat-tail angle value? How does the nozzle close with a hinge point in here?
20
Evaluate
Reasoning question (R)
Does this manner of closing meet the requirement?
Drawing progression
Engine cross section and therefore nozzle size. The more thrust the bigger the nozzle We have got 2 static sections on each side, and 2 buckets hinge from these static sections. Like an ice cream cone in a cylinder, we have to take a slice of section and also have to put a hydraulic ram (open question)
I want the nozzle to act as a thrust reverser when slowing down The engine revs up again when landing to deflecting the flow forward so as to slow down Concorde There are two half doors coming on the side, when there is any need they go to closed positions, and they allow the change in area. This is the back of the engine. The air comes in here, flows into there and it helps to fill up the nozzle. This is N8 nozzle. This is the N9 nozzle and this is when they are closed. When the doors are closed they deflect the air which follows the direction, so the aircraft … That is what they look like and that is the principle. They look cleaner aerodynamically. The doors have got a hinge point here and hydraulic jacks there Point is identified
Point drawn
Areas are calculated
Areas drawn
Bleed flow; boat-tail angle We have got bleed flow to cool pieces. Inside there is bleed flow passing round the outside of the engine, which is used to cool all the equipment inside the engine. The reason for the bleed flow is also in order to make the engine intake better. It is preferred to swallow a larger amount of air and then bleed it off We have got to allow space in the final nozzle to make this flow go through. So what I will need to do at those conditions is to not only let pass the air from the air from the core but also have to accommodate lacking bleed flow Geometry and configuration of the rear nozzle Drag. If the boat-tail angle is more than a certain amount, the drag increases and that’s the penalty on thrust Area are recalculated Picked a position
Areas redrawn Hinge-point drawn
The clam-shells close together and the area decreases Yes it can provide a variable area to meet the different operating conditions
Table 1. An example of approaching design activity through question asking
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This is then followed by a period from N6 until N9 where strategic questions are used to understand further the problem. At N10 and N11, the geometry of the duct is defined by identifying the start of the nozzle and calculating its areas. From N12 to N16 another period of strategic questions can be seen that allows the development of new understanding on how to design the nozzle. At N17, the designer resizes the areas to account for a new issue. At N18, the problem is restated in a more precise format Where do I have to pick the hinge point to provide the right area change and to account for the correct airflow (core plus bleed) but still keeping the external boat-tail angle value? This generation question states the problem including functional requirements and constraints, and is accompanied by the first step to define the position of the hinge point. Finally at N19 and N20, this decision is analyzed and evaluated. The example shows an episode of design activity primarily focusing upon the generation phase. The strategic questions (N1-N4) are used before the first statement of the problem to understand it. Finding an answer to the first generative question (N5) is not possible because the problem is not clear yet. Then series of strategic and generative reasoning questions (N6-N11 and N12-N17) are used to understand further the problem and generate design definitions for dependent aspects of the design. Finally, finding an answer to the last generative reasoning question (N18) allows making the move from intended behavior to form. The use of the strategic questions before the first problem statement is formed (and then reformed), links to Cross’s notion of framing, where the questions are used to frame and then reframe the problem (Cross, 2003). This may form the basis of an understanding of how task clarification takes place at lower levels of design activity. The example also shows evidence of the designer building questions based upon previous information as observed by Baya (Baya, 1996). At the end of the episode the design is not completed. However, the design is beginning to be defined and the decision has to be analyzed and evaluated. This example transcript shows evidence of a four of the eight strategic questions and only a limited number of reasoning questions. The other transcripts examined show evidence of the other types of questions. If this design episode was to continue, keep options open and is it worth pursuing (strategic questions) would be expected to be considered in the analysis and evaluation of various steps of the design definition. The example shows the progress from intended behavior to form, and the steps to move from the initial proposition to the final proposition. The use of past designs (in this case from memory), shows how the strategic questions are also applied in the past context, e.g. N8 and N9 in Table 1. B. Discussion and Implications Questions and answers appear to be a powerful instrument to analyze the design activity. They allow the breaking down of the development of the design activity into very fine elements and thus its analysis at a micro level. The descriptions of design activity obtained through the use of reasoning and
strategic questions are richer than those obtained through the use of one type of question only. This indicated that the two groups of questions are complementary. Previous research to classify design questions did not provide a set of questions to describe design activity in such a way. Strategic questions alone have already been used to guide designers when designing. However, through the linkages of strategic questions to different phases of design problem solving activity and to reasoning questions, a more complete set of questions has been developed that could be used to train designers. The understanding of the questions proposed in this paper and the observations from literature begins to connect different explanations of how designers carry out the design activity. Building upon this understanding can lead to the development of tools to both acquire information, and to assist in the design process. A deeper understanding of design activity, together with concrete examples, can provide a basis for design education as well as an understanding of designers thinking. VI. LIMITATIONS AND FURTHER WORK The results of this research were derived from data focusing on variant aerospace engineering design of complex products. Further research is planned to extend this to include more types of design work and to include diagnostic activity. The reasoning and strategic questions were identified from studies that focused upon individual design activity and hence do not consider team work. A deeper analysis of the protocols is expected to identify which strategies are used at the various stages of the model. In addition, the use of past knowledge will be examined further. VII. CONCLUSIONS An investigation of design activity based on question asking has been conducted through protocol analysis of design tasks. Two types of questions formed the basis of this research: 1) reasoning questions, and 2) strategic questions. Reasoning questions where found to be very useful to describe problem solving in design. However, it was not clear how these questions emerged during design activity. Strategic questions were developed independently from a model of problem solving in design. The investigation of these two types of questions led to very detailed descriptions of design activity. Strategic questions are used to formulate, develop and refine reasoning questions. It seems that strategic questions allow designers to collect important information to generate, analyze and evaluate design solutions. Overall, the combination of the different types of question has lead to the development of a deeper understanding of design activity. The evidence from the transcripts shows that the questions are a natural part of the progression of a design task. ACKNOWLEDGEMENTS The authors acknowledge the support for this research from the Engineering and Physical Sciences Research Council (EPSRC) and Rolls-Royce Aerospace plc. The authors
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