Challenges in Design of Foundations for Offshore Wind Turbines

Abstract

Designing foundations for offshore wind turbines (OWTs) are challenging as these are dynamically sensitive structures in the sense that natural frequencies of these structures are very close to the forcing frequencies of the wind, wave and 1P (rotor frequency) and 2P/3P (blade shadowing frequency) loading. Typically for the widely used soft-stiff design (target frequency of the overall wind turbine is between 1P and 2P/3P), the ratio of forcing frequency to natural frequency is very close to 1 and as a result is prone to dynamic amplification of responses such as deflection/rotation which may enhance the fatigue damage, thereby reducing the intended design life. Therefore, a designer apart from accurately predicting the natural frequency of the structure, must also ensure that the overall natural frequency because of dynamic-soil-structure-interaction does not shift towards the forcing frequencies making the value of ff /fn even closer to 1. Therefore, foundations are one of critical components of OWTs not only because of the overall stability of the structure but also because of financial viability of the project. The article highlights technical challenges associated with foundation design for offshore wind farm.