Christopher Earl

Supporting change processes in design: Complexity, prediction and reliability

Change to existing products is fundamental to design processes. New products are often designed through change or modification to existing products. Specific parts or subsystems are changed to similar ones whilst others are directly reused. Design by modification applies particularly to safety critical products where the reuse of existing working parts and subsystems can reduce cost and risk. However change is rarely a matter of just reusing or modifying parts. Changing one part can propagate through the entire design leading to costly rework or jeopardising the integrity of the whole product. This paper characterises product change based on studies in the aerospace and automotive industry and introduces tools to aid designers in understanding the potential effects of change. Two ways of supporting designers are described: probabilistic prediction of the effects of change and visualisation of change propagation through product connectivities. Change propagation has uncertainties which are amplified by the choices designers make in practice as they implement change. Change prediction and visualisation is discussed with reference to complexity in three areas of product development: the structural backcloth of connectivities in the existing product (and its processes), the descriptions of the product used in design and the actions taken to carry out changes.

Product due date assignment for complex assemblies

A method is described to assign product due dates for multistage assemblies with uncertain manufacturing and assembly process times. Earliest start times of operations are specified by a predetermined production plan and processing time distributions for operations are truncated at minimum processing times. The method systematically decomposes the complex product structures of multistage assemblies into two-stage subsystems. Both exact and approximate distributions of completion time for two-stage assemblies are developed. The latter is applied recursively to multistage assemblies to yield an approximate distribution of product completion time. Product due dates are assigned to either minimise earliness and tardiness costs or to meet a service target. This method is applied to examples which use manufacturing and assembly data from a capital goods company. The results are verified by simulation.

A Typology of UK Engineer-to-Order Companies

A typology of four ideal types has been developed to classify the different forms of engineer-to-order (ETO) company. This framework is used to examine the impact of market changes on the configuration of production processes. Markets that were once stable are now dynamic and uncertain. The research found that ETO companies have responded to the environmental changes by adopting new configurations. Internal and external supply chains have been reorganised to gain competitive advantage. There has been a shift from vertical integration to the outsourcing of physical processes, as companies seek to reduce costs and lead-times whilst increasing external flexibility. The typology can be used first to map process configurations to environmental conditions, and second to identify the main drivers of configuration change.

Optimal empty vehicle repositioning and fleet-sizing for two-depot service systems

This paper considers the problem of determining optimal control policies for empty vehicle repositioning and fleet-sizing in a two-depot service system with uncertainties in loaded vehicle arrival at depots and repositioning times for empty vehicles in the fleet. The objective is to minimise the sum of the costs incurred by vehicle maintenance, empty vehicle repositioning and vehicle leasing. A novel integrated model is presented. The optimal empty repositioning policy for a particular fleet size is shown to be of the threshold control type. The explicit form of the cost function under such threshold controls is obtained. The optimal threshold values and fleet-size are then derived. Numerical examples are given to demonstrate the results.

An analysis of company structure and business processes in the capital goods industry in the UK

This work is based on a study of capital goods suppliers to the power generation and distribution, materials handling, and offshore industries. Business processes are project-based and interdependent. They include sales, marketing, tendering, engineering, manufacturing, procurement, assembly, and commissioning. A model is presented which groups these processes into three categories: nonphysical, physical, and support processes. Capital goods companies have dynamic and evolving structures, aggregating processes in ways which seek to exploit new and changing markets. The model provides a mechanism for describing and analyzing structures. The combination of structural, process, and operational perspectives offers a framework for the analysis of capital goods companies.

Shape exploration of designs in a style: Toward generation of product designs

Generative specifications have been used to systematically codify established styles in several design fields including architecture and product design. We examine how designers explore new designs in the early stages of product development as they manipulate and interpret shape representations. A model of exploration is proposed with four types of shape descriptions (contour, decomposition, structure, and design) and the results of the exploration are presented. Generative rules are used to provide consistent stylistic changes first within a given decomposition and second through changing the structure. Style expresses both the analytical order of explanation and the synthetic complexity of exploration. The model of exploration is consistent with observations of design practice. The application of generative design methods demonstrates a logical pattern for early stage design exploration. The model provides the basis for tools to assist designers in exploring families of designs in a style and for following new interpretations that move the exploration from one family to another.

Implementation of Curved Shape Grammars

Research into shape grammar implementation has been largely concerned with rectilinear shapes and there has been limited research into implementation on shapes composed of curves. This reflects developments of the shape grammar formalism which has been defined largely according to straight lines, planes, and associated volumes. In this paper, implementation of shape grammars on curved shapes is examined using algorithms for shape operations on shapes composed of parametric curves. These algorithms have been implemented in a shape grammar interpreter for shapes composed of quadratic Bézier curves, which is illustrated via application of a shape grammar that generates Celtic knotwork patterns. Implementing shape grammars on shapes composed of Bézier curves highlights difficulties that arise when the shape grammar formalism is applied to curved shapes, and the paper concludes with a discussion that explores these difficulties and indicates potential implications for the shape grammar formalism.

Witnesses to Design: A Phenomenology of Comparative Design

This research is concerned with describing the experience of being a designer and doing design. Many case studies have described individual experiences, both of designers reflecting on their own work, and academic studies of expert design work as performed in a professional context. Such studies are an important component of design research, and provide an essential foundation and sounding board for design theory. Traditionally, this research has concentrated on practice in a particular industry or company, generalizing to an industry sector or designing at large, from a relatively small number of cases. We depart from the common practice by comparing the experience of designers across a very wide range of domains, reported outside of its normal professional context, and in comparison to other design contexts. We report on a series of research workshops, each including several professional designers, initiated with the specific objective of making a comparison across design disciplines. At each workshop, designers presented case study illustrations of their practice for discussion with designers from other disciplines. This paper describes the motivation, methodology, and results of this project. We also propose a novel theoretical basis for our comparative approach, and the implications that this might have for other design research. The nature of our research and findings naturally is quite different from research that focuses on specific design activities. Previous comparative research more often has aimed to establish general criteria for defining concepts and theories, relating core concepts in research and theory-making to designing and designs1 Our aim is not to produce generic findings applying to all cases of design in all circumstances, but rather to develop a rich understanding of recurring behaviors across different domains, even though these might not apply to every process. As a result, comparative design is complementary to research on specific design practice, as well as research that aims to describe design in generic terms.

Graph theory and Q-analysis

Structures of graph theory are compared with those of Q-analysis and there are many similarities. The graph and simplicial complex defined by a relation are equivalent in terms of the information they represent, so that the choice between graph theory and Q-analysis depends on which gives the most natural and complete description of a system. The higher dimensional graphs are shown to be simplicial families or complexes. Although network theory is very successful in those physical science applications for which it was developed, it is argued that Q-analysis gives a better description of human network systems as patterns of traffic on a backcloth of simplicial complexes. The q-nearness graph represents the q-nearness of pairs of simplices for a given q-value. It is concluded that known results from graph theory could be applied to the q-nearness graph to assist in the investigation of q-connectivity, to introduce the notion of connection defined by graph cuts, and to assist in computation. The application of the q-nearness graph to q-transmission and shomotopy is investigated.

The construction of curved shapes

Application of a shape grammar involves the repetitive task of matching and replacing subshapes of a design under transformation, and as such is well suited for computer implementation. As a result, ever since the conception of the shape grammar formalism, efforts have been made to develop computer programs that automate shape grammar applications. Much of this effort has been directed towards the problem of subshape detection, which involves recognising subshapes embedded in a design. Solutions to this problem have been presented for shapes composed of rectilinear geometric elements, such as straight lines, and algorithms based on these solutions have been implemented in a variety of shape grammar interpreters. However, there has been less research concerning the solution of the subshape detection problem for shapes composed of nonrectilinear geometric elements, such as curve segments. In this paper a method of intrinsic matching is presented, which enables comparison of the embedding properties of parametric curves. This method has been employed in order to develop shape algorithms which can be implemented in shape grammar interpreters for shapes composed of parametric curve segments, arranged in two-dimensional or three-dimensional space.