Dynamic Displacements of Offshore Wind Turbine Monopile Foundations Including the Effects of Soil-Structure Interactions

Abstract

The classical method of designing offshore monopile foundations consists of using static wave force theory. With this method, the largest wave to be expected in the locale is selected as the design wave. By applying relevant wave theory, wave force coefficients to the selected wave, forces and moments on the monopile foundation can be calculated assuming static equilibrium. While the approach may seem logical, it may not address resonance. Resonance may actually occur when a smaller wave whose fundamental period of vibration converges near the natural period of vibration of the monopile structure. This phenomenon may amplify defections and stresses causing significant dam-age. Using the elastic properties of the monopile structure and its dynamic response to wave forces a new method is presented for calculating stresses and displacements of a monopile foundation. Furthermore, soil-structure interactions of monopile foundations are investigated. Different approaches such as the p-y method or the Winkler model have been used to design monopile foundations subjected to lateral static and dynamic loading. However, a new design approach that considers other significant interaction mechanisms between the pile and the soil is discussed.