Implications of Alternative Multilevel Design Methods for Design Process Management

Multilevel design problems are typically decomposed into a hierarchy of distributed and strongly coupled sub-problems, each solved by design teams with specialized knowledge and tools. There are two contrasting approaches to formulating and solving such collaborative design problems: (1) highly iterative exchanges of single design solutions, as in point-based optimization approaches, and (2) minimally iterative exchanges of multiple solutions, as in set-based approaches. In this paper, the effects of these alternative approaches on the overall lead time of a design process are explored. A discrete event simulation is developed to evaluate the lead times of highly iterative and minimally iterative multilevel design strategies and the sensitivity of those lead times to the level of noise in the design environment for a range of designer work loads. Designer work loads include not only the multilevel design task of interest, but also secondary design jobs that consume designer time. Noise is represented as variability in task processing times, arrival rates, and iteration levels. An example design process for an unmanned aerial vehicle is used to compare set-based and point-based design strategies. The results of the simulations indicate that the lead times of minimally iterative, set-based design processes are more robust to busy design environments than highly iterative, point-based alternatives. Accordingly, it may be advantageous to favor richer, but less frequent, exchanges of information in a multilevel design process, even if more effort is required to generate those sets of information.