Seismic Design of Offshore Wind Turbines: Good, Bad and Unknowns

Subhamoy Bhattacharya,Muhammed Aleem,Athul Prabhakaran,Harsh K Mistry,Ganga Prakhya,Suryakanta Biswal,Domenico Lombardi,Sadra Amani

doi:10.3390/en14123496

Abstract

Large scale offshore wind farms are relatively new infrastructures and are being deployed in regions prone to earthquakes. Offshore wind farms comprise of both offshore wind turbines (OWTs) and balance of plants (BOP) facilities, such as inter-array and export cables, grid connection etc. An OWT structure can be either grounded systems (rigidly anchored to the seabed) or floating systems (with tension legs or catenary cables). OWTs are dynamically-sensitive structures made of a long slender tower with a top-heavy mass, known as Nacelle, to which a heavy rotating mass (hub and blades) is attached. These structures, apart from the variable environmental wind and wave loads, may also be subjected to earthquake related hazards in seismic zones. The earthquake hazards that can affect offshore wind farm are fault displacement, seismic shaking, subsurface liquefaction, submarine landslides, tsunami effects and a combination thereof. Procedures for seismic designing OWTs are not explicitly mentioned in current codes of practice. The aim of the paper is to discuss the seismic related challenges in the analysis and design of offshore wind farms and wind turbine structures. Different types of grounded and floating systems are considered to evaluate the seismic related effects. However, emphasis is provided on Tension Leg Platform (TLP) type floating wind turbine. Future research needs are also identified.

Highlights

As offshore wind is one of the most advanced technologies for producing carbon-neutral energy, offshore wind farms will be deployed in different regions, including those prone to earthquakes; there is limited track-record of long-term performance of offshore wind turbines (OWTs) under seismic effects
Offshore wind turbines are currently designed for a lifespan up to 30 years [17]
The design return period corresponds to a 10% probability of exceedance in 50 years [17], where the assumed lifespan of a typical structure is taken as 50 years

Summary

Introduction

The decade will see engineering efforts to achieve net-zero, a climate-neutral continent (the ambition of EU) and develop climate-smart cities. One way to achieve net-zero is carbonizing the energy/power sources and working towards an entirely clean energy system. As offshore wind is one of the most advanced technologies for producing carbon-neutral energy, offshore wind farms will be deployed in different regions, including those prone to earthquakes; there is limited track-record of long-term performance of offshore wind turbines (OWTs) under seismic effects.

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