Reliability-based design optimization of laterally loaded monopile foundations for offshore wind turbines

The aim of reliability-based design optimization in this study is to minimize the production, installation and failure cost of a monopile foundation with respect to reliability constraint. Design cost is expressed as a function of deterministic design variables (i.e., monopile diameter, wall thickness and embedded length) and uncertain parameters (i.e., lateral load, undrained shear strength). The reliability constraint is defined by limiting the probability of exceeding the ultimate limit state with respect to uncertain parameters to \(P_F^{lim}=10^{-4}\). Optimization is conducted by coupling the Simulated Annealing stochastic optimization with the Subset Simulation reliability algorithm. This study adapts the Simulated Annealing algorithm to search for minimum under reliability constraint by modifying the acceptance probability. Probabilistic response of the monopile foundation is obtained by coupling the deterministic p-y beam spring finite element model with random load and random field model of undrained shear strength variability.