Modeling design development in unpredictable environments

This paper presents a process simulation model representative for design development of a building system in an unpredictable environment. Unpredictability means that design criteria are prone to change as design development unfolds. The model was implemented with a discrete-event simulation engine based on event graphs. Events capture moments when tasks start or end, or changes that cancel future scheduled events and schedule new design iterations. Between conceptualization and concept development, we assume that managers can impose a time lag so as to minimize rework of concept development tasks due to upstream changes of design criteria. Simulation illustrates the effects of adopting different postponement strategies. The results show that postponing the start of concept development consistently reduces the average resources spent in concept development and increases process reliability, but it augments the average design duration. The judicious choice of a postponement lag can thus yield gains in terms of cost versus time.