Optimal pile design of dolphin structure considering axial compressive pressure-bending moment ratio under offshore load conditions

Abstract

This study proposes an optimal design of a dolphin structure under offshore load conditions such as berthing, mooring, wind, wave, and current loads. The design objective is to reduce the total weight of the pile structure by determining its diameter, thickness, and arraying direction with constraints of axial compressive pressure-bending moment ratio and total displacement. As design requirements, the stress has to be satisfied under the allowable compressive pressure-bending moment, and the total displacement of the steel piles should be less than 0.1 m on the upper deck. The structural analysis data are generated using Box–Behnken design based on the design of experiments. In the meta-model-based approximate optimization process, the pressure-bending moment ratio and total displacement are expressed using a backpropagation neural network, and the structural weight of the pile is approximated via a second-order polynomial-based response surface model. Compared with the initial design, the optimal solution of the total weight of the steel piles reduces by 27.37% under the satisfied constraint conditions. For the post-optimization study, the optimal sensitivity analysis with respect to the seabed level is conducted.