Monopiles are widely used for offshore wind turbines. In the harsh environmental conditions, monopiles sustain long term horizontal cyclic loads from wind and wave loads, which result in cumulative deformation. It is important to assess the additional deformation of monopiles, as it may lead to the malfunction of a wind turbine. Finite element (FE) analysis using a cyclic stiffness model explains the phenomena. The cyclic model of sand’s secant stiffness is obtained by constructing loading and unloading stress-strain curves of sand, with R-O loading curve and modified Masing rule, together with the results of cyclic triaxial tests. By comparing with the results of a published centrifuge test of a laterally loaded monopile in sand, the rationality of the cyclic stiffness model is verified. A parametric analysis considering different embedment length of the pile is also undertaken. It is believed that the FE analysis with evolution model of sand’s secant stiffness can simulate the development of the accumulated rotation of a horizontal cyclic loaded monopile, which provides theoretical support for the design of the cyclic response of wind turbines.
Chenrong Zhang, Feng Yu, Zhiqi Zhu and Maosong Huang
Keywords: monopile, long term, lateral cyclic loading, cyclic stiffness model, finite element method, deformation accumulation
Publisher: DFI