Ph.D. Dissertation Defense by Carolyn Conner Seepersad
Wednesday, September 8, 2004

(Dr. Farrokh Mistree, Chair)

"A Robust Topological Preliminary Design Exploration Method with Materials Design Applications"

Abstract

Problem: A paradigm shift is underway in which the classical materials selection approach in engineering design is being replaced by the design of material structure and processing paths on a hierarchy of length scales for specific multifunctional performance requirements. In this dissertation, the focus is on designing materials on mesoscopic length scales that are larger than microscopic features but smaller than the macroscopic characteristics of an overall part or system. The mesoscopic topology—or geometric arrangement of solid phases and voids within a material or product—is increasingly customizable with rapid prototyping and other manufacturing and materials processing techniques that facilitate tailoring topology with high levels of detail. Fully leveraging these capabilities requires not only computational simulation models but also a systematic, efficient design method for exploring, refining, and evaluating product and material topology and other design parameters for targeted multifunctional performance that is robust with respect to potential manufacturing, design, and operating variations.

Approach: In this dissertation, the Robust Topological Preliminary Design Exploration Method is presented for designing complex multi-scale products and materials together by topologically and parametrically tailoring them for multifunctional performance that is superior to that of standard designs and less sensitive to variations. This systems-based design approach is formulated by establishing and integrating principles and techniques for robust design, multiobjective decision support, topology design, and design space exploration along with approximate and detailed simulation models. As part of the approach, topology design techniques are established for multifunctional applications—such as ultralight, actively cooled structures with combined structural and thermal functionality—that are beyond the reach of conventional structural topology optimization approaches. The multifunctional topology design approach is augmented with robust design methods that facilitate (1) the search for design solutions that offer satisfactory performance despite variability from many sources, and (2) the distribution of analysis and synthesis activities among various collaborating designers with domain-specific models and expertise.

Applications and Future Work: Key aspects of the approach are demonstrated by designing linear cellular alloys—ordered metallic cellular materials with extended prismatic cells—for multifunctional applications. For a microprocessor application, structural heat exchangers are designed that increase rates of heat dissipation and structural load bearing capabilities relative to conventional heat sinks. Also, cellular materials are designed with structural properties that are robust to dimensional changes and topological imperfections such as missing cell walls. Finally, cellular combustor liners are designed to increase operating temperatures and efficiencies and reduce harmful emissions in next-generation turbine engines via active cooling and load bearing within topologically and parametrically customized cellular materials. Opportunities for broader investigation and application of systems-based design approaches in materials design and other fields are discussed.