Stochastic Dynamic Analysis of an Offshore Wind Turbine Considering Soil-Structure Interaction

Abstract

This work investigates the dynamic response of a 5 MW offshore wind turbine with monopile foundation subjected to wind and wave actions. The study includes the dynamic interaction between the monopile and the underlying soil subjected to wind and wave loading. The presence of softer soil strata can influence the dynamic response of the structure. The offshore wind turbine tower has been modelled as multi degree of freedom (MDOF) structure. The model comprises of a rotor blade system, a nacelle and a flexible tower where the mass of the rotor, blade and nacelle has been lumped at the top of the tower for simplicity. In this work a lumped mass model for the dynamic analysis of a monopile-type support structure for offshore wind turbine has been presented using the finite element software ANSYS 14. Simulations are performed for the MDOF turbine subjected to stochastic wind and wave loading using the Kaimal spectrum and the Pierson-Markowitz spectrum correlating wind and wave forces, respectively. The soil-structure interaction effect is taken into consideration by including rotational as well as lateral spring constants. The results are visualized in frequency domain for both wind and wave spectral forcing in the form of power spectral density functions which gives an insight on how the response of the structure depends not only on the external forces but also on the soil structure interaction effect. The structure shows significant increase in response when the soil-structure interaction effect is taken into account.