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.