Characteristics and Models of Iteration in Engineering Design

This paper examines the reasons for design iteration and describes models of design iteration. Iteration is the process of repeating tasks within a design project, and is common to all types of engineering design. Iteration is typically necessary for two reasons: an unexpected failure of a design or prototype to meet established criteria; and an expected response to information which was generated after the previous iteration was completed. Both types of iteration are typical of most engineering projects. This paper describes these two types of iteration, and presents two mathematical models which attempt to capture the effects of iteration on total development time. The models are the Probabilistic Sequential Iteration Model, which describes unexpected iteration, and the Work Transformation Model, which describes expected iteration. The two models correspond to the two reasons that iteration occurs in engineering design. They are useful in identifying some of the most important effects of iteration on development time, and can support important managerial decisions which affect successful completion of the design project in a timely manner.