Seismic Fragility Assessment of a Novel Suction Bucket Foundation for Offshore Wind Turbine under Scour Condition

Duc-Vu Ngo,Dong-Hyawn Kim,Young-Jin Kim

doi:10.3390/en15020499

Abstract

This study proposed a new suction bucket (SB) foundation model for offshore wind turbines (OWT) suitable for a shallow muddy seabed, using more than three single buckets through kinetic derivation. The performance of new optimal foundation was evaluated by its horizontal displacement capacity and compared with a conventional SB composed of three buckets. Under external loads such as earthquakes, wind, and the combination of the both, the stability of this novel SB foundation was verified. The seismic fragility curve was also evaluated at some scour depths. These results were compared with the response of a tripod suction bucket (TSB) foundation, which was also designed for a shallow muddy seabed. The results indicated that scour significantly changed the dynamic response of this novel SB foundation but it had a better bearing capacity than the TSB foundation, despite its smaller size and weight. The fragility of TSB is always higher than the developed foundation in the same environmental condition. With reasonable volume and size, this novel SB foundation has great potential for future industrialization and commercialization.

Highlights

With the rapid development of offshore wind energy in Korea, a number of high capacity offshore wind turbines (OWT) are being installed, which moves towards offshore wind power generation with the goal of becoming one of the top three nations for offshore wind power generation in the world
The aim of this study is to propose an suction bucket (SB) foundation solution suitable for shallow seabed conditions to support 5.5 MW capacity OWTs
This study proposed a pentapod suction bucket (PSB) foundation as the feasible choice of foundation solution, suitable for locations with shallow muddy seabed conditions

Summary

Introduction

With the rapid development of offshore wind energy in Korea, a number of high capacity OWTs are being installed, which moves towards offshore wind power generation with the goal of becoming one of the top three nations for offshore wind power generation in the world. Mono-pile foundations are currently the most commonly used foundation solution for OWTs, but it is impossible or too expensive to implement at some sites where the seabed consists of a shallow sandy layer lying on a rock bed. Multi-pile foundation (Figure 1c) is the expansion of mono-pile foundation, but adapted to a greater water depth [3] This type of foundation is not suitable for muddy and shallow geological conditions, because three smaller and lighter piles should be penetrated up to 10–20 m into the seabed. This site is the shallow water area with the mean sea level of around 13.6 m. This SB, with the advantage of the fast and hassle-free installation, reduces the total installation cost by 30% [19]

Objectives

Methods

Findings

Conclusion