"Reliability-Based Design Optimization under Parametric Uncertainty"

Masoud Rais-Rohani, Professor of Aerospace Engineering and Engineering Mechanics, Center for Advanced Vehicular Systems, Mississippi State University

Uncertainties stem from insufficient knowledge or lack of adequate data about the system, fidelity of models and analysis methods, environmental factors and operating conditions combined with variability in the manufacturing process and material characteristics (e.g., microstructure). Although factors of safety have been used extensively for many decades to guard against the effects of uncertainties, they may fail to account for true failure probability since they are not derived from rational probabilistic analysis. In the case of parametric uncertainty, the theory of probability is well suited for mathematical modeling and propagation of uncertainty in the design optimization framework. Depending on the level of accuracy and efficiency sought, simulation, analytical, or hybrid methods may be used for the prediction of failure probability or corresponding structural reliability. The combination of probabilistic modeling and mathematical design optimization framework leads to what is known as reliability-based design optimization (RBDO).

In this seminar, an overview of RBDO methodology will be presented with description of alternative approaches for the modeling of probabilistic design constraints. Application problems will include crashworthiness optimization of automotive structures under different impact conditions and the use of strain-rate sensitive internal state variable-based constitutive models in RBDO of cast aluminum components. Due to the nonlinearity and complexity of the finite element simulations involved, low-cost surrogates (metamodels) are used for the prediction of responses of interest during the optimization process. In addition to the current efforts in the area of RBDO, future direction toward multilevel optimization of process-material-product systems under uncertainty will also be discussed.

Masoud Rais-Rohani received his Ph.D. with emphasis on structural and multidisciplinary design optimization from the department of aerospace and ocean engineering at Virginia Tech. He joined the aerospace engineering department at Mississippi State University in 1991 where he is currently serving as a professor and simulation-based design optimization task leader at the Center for Advanced Vehicular Systems. He has received a number of teaching and research awards at Mississippi State University. He is an Associate Fellow of AIAA and a past member of AIAA Multidisciplinary Design Optimization and Aircraft Design Technical Committees. He has been a principal or co-principal investigator on more than sixteen research grants and contracts sponsored mainly by NSF, NASA, DOD, and DOE. His research efforts have resulted in over sixty papers on such topics as stiffness tailoring of structures made of fiber-reinforced polymer composites; topology, shape, and sizing optimization of complex structures; design under uncertainty; probabilistic modeling and reliability-based design; and metamodeling methods. Application problems have included aircraft, automotive, civil, and marine structures.

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