Robust design of offshore jacket platform structure under random wave in dual response surface framework

Abstract

This paper presents robust design optimisation (RDO) of offshore jacket platforms under random wave force. It is well-established that the direct Monte Carlo Simulation (MCS) is the most accurate way to deal with RDO under uncertainty. However, such approach requires extensive computational time for real complex structures. In the present study, a new cumulative distribution function (CDF)-based RDO formulation is proposed in the framework of dual response surface method (RSM) with due consideration to record-to-record variation of random wave force. The proposed approach avoids direct MCS in RDO, thereby evading several repetitive nonlinear dynamic analyses inside the optimisation loop. As the conventional least-squares method-based RSM may be erroneous in response approximation, the adaptive moving least-squares method is adopted in the present study to construct the response surfaces. The RDO is posed as a two-criterion equivalent optimisation problem, where the expected value of objective function and its standard deviation are optimised, satisfying constraint feasibility criteria under uncertainty. Two illustrative examples are presented to demonstrate the effectiveness of the proposed RDO approach. The results show that the proposed approach yields more accurate and robust solutions than the conventional least-squares method-based RDO approach when compared with the most accurate direct MCS-based RDO results.