Concept Design Trade-Offs Considering Performance Margins

DS 85-1: Proceedings of NordDesign 2016, Volume 1, Trondheim, Norway, 10th - 12th August 2016

Year: 2016
Editor: Boks, Casper; Sigurjonsson, Johannes; Steinert, Martin; Vis, Carlijn; Wulvik, Andreas
Author: Tan, James; Otto, Kevin; Wood, Kristin
Series: NordDESIGN
Institution: 1: Aalto University, Finland; 2: Singapore University of Technology and Design, Singapore
Section: Methodology: Special Applications
Page(s): 421-429
ISBN: 978-1-904670-80-3


Multi-disciplinary optimization (MDO) methods have become mature as commercial and open-source toolboxes and applications. Typically, engineers formulate concept design problems as multiple system-level responses to allow simultaneous optimization along a Pareto trade-off frontier. Often these tools make use of trade-off graphs depicting each design concept as a point in a scatter plot, to observe the frontier versus dominated solutions. However, often lost in this work is the real design engineering consideration of the equipment compeonents that compose the system. In particular, there are the operational performance limits of the equipment components usually expressed as safety margins. In an MDO formulation, these margins are often modelled with fixed constraint limits. Given the optimization, the MDO search typically drives these constraints active in the considered Pareto optimal solutions. That is, MDO methods typically drive a designer toward aggressive risky concepts on equipment margins. Our research question is can margin constraints be made objective functions and effectively traded-off against system level requirements, and whether that will enable more robust design concepts. Our method and approach is to reformulate the MDO problem to allow trade-off between the component performance limits and the system level engineering requirements. This will facilitate feasible design configurations that are not only high performing at a system level, but also more robust. We develop here an MDO problem formulation allowing design performance requirements to be traded off against component performance limits. We show that improved designs can be generated when trading off performance limits slightly but greatly increasing the constraint safety margins. We do this by considering a family of Pareto frontiers at several levels of constraint margin limits. This highlights the relative sensitivity of component limits with performance levels, by adjusting either the performance requirements or engineering margins.

Keywords: Optimization, safety margins, trade-offs, robust design

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