11 / 9 / 2000 1 Input - Output Flow Analysis : Flow Metrics

Reid Bailey Department of Mechanical & Aerospace Engineering University of Dayton Dayton, OH 45469-0210 Bert Bras and Janet K. Allen Systems Realization Laboratory G. W. Woodruff School of Mechanical Engineering Georgia Institute of Technology Atlanta, Georgia 30332-0405, USA * corresponding author Abstract Continuing with the themes of the first part of this paper, this second part is focused on further expounding the capabilities of input-output techniques as applied to material flows in industrial systems. Material flows are the primary focus due to their role in directly linking natural and industrial systems and thereby being fundamental components of environmental issues in industrial economies. The specific topic in this paper concerns several material flow metrics used to characterize systems behavior that are derived from the ecological interpretation of input-output techniques; most notable are several measure of material cycling and a measure of the number of processes visited by material while in a system. These metrics are shown to be useful in analyzing the state of material flow systems. Furthermore, the metrics are shown to be a central link in connecting input-output flow analysis to synthesis. Through connecting the flow metrics to both environmental objectives and controllable aspects of flow models, changes to existing flow systems are synthesized to generate improved system behavior. To bring this two-part paper to a close, several limitations of input-output flow analysis are introduced with the goal being to stimulate further interest and research.