CHAPTER 7
RELIABILITY-BASED DESIGN OPTIMIZATION USING DETERMINISTIC
OPTIMIZATION AND MULTI-FIDELITY TECHNIQUE
Introduction
The probabilistic sufficiency factor (PSF) developed in Chapter six is integrated to
reliability-based design optimization (RBDO) framework in this chapter. The classical
RBDO is performed in coupled double loop fashion, where the inner loop performs
reliability analysis and the outer loop performs design optimization. RBDO using double
loop framework requires many reliability analyses and is computationally expensive.
Wu et al. (1998, 2001) developed a safety-factor based approach for performing
RBDO in a decoupled single loop fashion, where the reliability constraints are converted
to equivalent deterministic constraints by using the concept of safety factor. The
similarity between Wu's approach and the probabilistic sufficiency factor approach
indicates that it may be worthwhile to study the use of probabilistic sufficiency factor
converting RBDO to sequential deterministic optimization.
For many problems the required probability of failure is very low, so that good
estimates require a very large MCS sample. In addition, the design response surface
(DRS) must be extremely accurate in order to estimate well a very low probability of
failure. Thus we may require an expensive MCS at a large number of design points in
order to construct the DRS. A multi-fidelity technique using probabilistic sufficiency
factor for RBDO is investigated to alleviate the computational cost. The two approaches
of reducing computational cost of RBDO for low probability of failure are compared.