Generating flexibility in the design of engineering systems to enable better sustainability and lifecycle performance

Designing an engineering system that is both environmentally and economically sustainable is a challenging task. Designers need to cope with socio-technical uncertainties and design systems to provide high performance during long lifecycles. Flexibility in engineering design provides ways to address such challenges by making engineering systems changeable in the face of uncertainty. It is difficult, however, to identify suitable system elements for designing flexibility, especially when subjected to multiple sources of uncertainty and complex interdependency between socio-technical and systems elements. This paper considers embedding flexibility into the engineering design as a mechanism to ensure better sustainability and to improve economic performance in long-term lifecycles. The main contribution is a novel methodology to identify valuable opportunities to embed flexibility as a way to deal pro-actively with uncertainty in market and environment. The proposed methodology integrates Bayesian network into engineering system design to effectively model complex change propagation in the flexibility identification process. It helps structure concept generation activities by identifying candidate areas to embed flexibility in the system. It compares favorably to other concept generation methods (e.g., prompting, brainstorming) that require modeling and evaluation of a large number of concepts generated in order to identify the ones offering better performance. It differs from other flexibility enabler identification methods by considering indirect as well as direct dependencies, in addition to the probabilistic nature and risk resulting from possible changes. Another contribution is the demonstration application of the proposed methodology through the analysis of a waste-to-energy technology in Singapore based on anaerobic digestion. Results show that the expected net present value of the flexible design concepts provides more than 10 % improvement over a fixed benchmark design in terms of economic lifecycle performance. This design is conducive of better economic sustainability via additional power generation and better use of resources. Results also indicate that the flexible design can reduce downside risks and capitalize on upside opportunities significantly.