Influence of scour on soil-structure interaction of tripod supported offshore wind turbines

Offshore wind is expected to play a major role in sustaining the drive for renewable energy around the globe. Tripods are suitable support structures for offshore wind turbines in intermediate water depths (20 - 50m). While power production is stopped and the turbine is shut down during extreme sea states, it is essential that the integrity of the structure is not compromised by the incident waves. Existing literature seldom focuses on soil-structure-interaction, by assuming that the structure is fixed at the mudline. The present work makes use of a sequentially coupled scheme of aerodynamic-hydrodynamic analysis to investigate the influence of extreme sea states on the response of a tripod structure, supporting a 5-MW offshore wind turbine (OWT).

Sandy soil profiles are represented by means of discrete axial and lateral springs along the piles. The finite element method is used in the analysis. The lateral response characteristics of the OWT structure are found to be heavily influenced by the density classification of the sand. Scour susceptibility studies indicate the need for adequate protection at the pile-mudline interface, to combat the corresponding reduction in natural frequency and escalation of response.