SEISMIC ANALYSIS OF AN OFFSHORE WIND TURBINE ON THE MONOPOLE FOUNDATION USING THE TWO-STEP METHOD

Abstract

This study employs a two-step method to examine the seismic response of offshore wind turbine (OWT) systems supported by monopile foundations. In the first step, the soil-monopile interaction (SMI) is simulated using the professional software program OpenSeesPL. In the second step, the OWT structure is simulated employing the lumped-parameter method (LMP). The response of the OWT structure is then analyzed using the results from the first step with a single degree of freedom (DOF). An OWT with a capacity of 5 MW is studied numerically. Three different soil profiles are analyzed, and the effects of ignoring soil-structure interaction (SSI) using fixed-base models are investigated. In comparison to the fixed-base model, the SMI increases the peak acceleration values of monopile tops: the ratios for dense sand, stiff clay, and multiple strata are 3.68, 2.62, and 2.58, respectively. Peak absolute displacements in the SSI model at the top of the tower are 10-20 times higher than those in a fixed-base model, and the SMI significantly contributes to absolute displacements.