Numerical study on accumulated deformation of laterally loaded monopiles used by offshore wind turbine.

The design of an offshore monopile is generally governed by its accumulated response to lateral cyclic load, e.g., loads induced by winds and waves. In order to investigate the characteristic of this accumulated response, a user subroutine of degradation stiffness model (DSM) is developed and incorporated into a commercial finite difference program. Based on this program, the effect of load character, pile embedded length, and load eccentricity on the displacement development of monopile is quantified, and the applicability and reliability of the two most used models, power function model, and logarithmic function model, for the prediction of accumulated pile displacement are evaluated. Based on the numerical results, a design model which accounts for the influence of number of loading cycles, load amplitudes, and pile embedded length on the accumulated pile displacement is proposed. The proposed design model is validated against measurements from the field test on scaled monopile driven in dense sand deposit, which proves the validity of the recommended design in this paper. [ABSTRACT FROM AUTHOR]