Assessing the effect of monopile dimensions on seismic response of offshore wind turbines

Abstract

This study investigates the impact of monopile dimensions on the seismic response of offshore wind turbines (OWTs), considering soil-water-structure interaction (SWSI). During earthquakes, OWTs may experience critical conditions, leading to operational shutdowns due to structural responses such as high acceleration, permanent rotation, and displacement. Key factors influencing seismic response include monopile diameter, driven length, and hybrid monopile designs, which are the main focus of this research. Eight physical models were constructed: one baseline model, two with modified monopile diameters, two with altered driven lengths, and three hybrid monopile models featuring shallow wheels of varying diameters. These models were tested under 1g conditions and on a shaking table with nine sinusoidal motions at three frequencies and three amplitudes, simulating saturated soil conditions. The pore water pressure generation, soil and superstructure acceleration, and displacement were monitored during each test. The results show that increasing the monopile's driven length reduces the superstructure's cumulative displacement and improves overall seismic performance. Moreover, increasing the monopile diameter or adding shallow wheels to create a hybrid monopile increases pore water pressure, which in turn results in greater cumulative displacement of the OWT.