ANALYSIS OF ICE-INDUCTED STRUCTURE VIBRATION OF OFFSHORE WIND TURBINES BASED ON DEM-FEM COUPLED METHOD

The ice load is one of the most important factors that cannot be ignored for offshore wind turbines (OWTs) in cold regions. The ice-induced vibrations (IIVs) can bring serious fatigue and damage to the OWTs structure. In this paper, a coupling method of the discrete element method (DEM) and the finite element method (FEM) is adopted to establish the IIVs model of monopile-type OWTs. The breakage and failure process of level ice are simulated with the spherical DEM with bonding-breaking effect, and the finite element model of monopile-type OWTs is constructed by the beam element and triangular plate shell element. The DEM-FEM coupled method is adopted to simulate the interaction progress between monopile-type OWTs and level ice under different ice velocity and ice thickness conditions. The accuracy of ice load calculated by the DEM-FEM coupled method is verified by comparing with the empirical formula of IEC (International Electrotechnical Commission) and ISO (the International Organization for Standardization). By comparing the displacements and the acceleration of the top of the wind turbine tower and the top of the foundation, the dynamic response characteristic of the OWTs is qualitatively analyzed. The reason for the difference of dynamic characteristics in different parts of OWTs is structural model characteristic of OWTs：the lower part is a large stiffness pile foundation and the upper part is a high flexibility tower, which makes its dynamic characteristic show the characteristics of the main and subordinate structure. The characteristics of “Main-Subordinate structure” make the tower (subordinate) and pile foundation (main) show different response behaviors under complex ice load, and the vibration period and acceleration power spectrum density (PSD) of different parts of OWTs are different. This study can provide a useful reference for the OWTs anti-ice design and the fatigue analysis of OWTs in cold regions.