An efficient decoupled method for time-variant reliability-based design optimization

Time-variant reliability-based design optimization (tRBDO) can rationally consider the time-variant uncertainties in engineering structures and find the optimal design that can keep reliable throughout its whole life cycle. However, solving the tRBDO involves a nested double-loop procedure and requires excessive computational cost. In this paper, a novel decoupled method called sequential approximate time-variant reliability analysis and optimization (SATO) is proposed to improve the efficiency of tRBDO. First, a two-step method is proposed to transform the original tRBDO problem into an equivalent deterministic optimization problem according to the results of time-variant reliability analysis (TRA). Second, a novel approximate TRA (ATRA) method based the least-square method is proposed to reduce the computational cost of TRA. Finally, the proposed SATO method decouples the original double-loop procedure in tRBDO into a sequential process of ATRA and deterministic optimization. Test results of a complicated welded beam problem verify that the proposed method can achieve similar accuracy and much higher efficiency than the compared methods. A rocket inter-stage structure problem demonstrates the capability of the proposed method in practical engineering applications.