Abstract

This research aimed at investigating tripod and three-legged offshore wind turbine substructures. A comparison between the two substructures based on their weight as well as the installation method of piles, i.e. pre-piling and post-piling, was carried out. The in-place (Ultimate Limit State), Dynamic, natural frequency check and fatigue (Fatigue Limit State) analyses were conducted considering aerodynamic and hydrodynamic loads imposed on substructures in 50m water depth. An optimisation process was carried out in order to reduce the mass of substructures. The results revealed that the three-legged substructure is more cost effective with 25% lesser structure mass. However, the construction of the three-legged structure usually takes more time due to increased number of members and subsequently welding joints. The results, furthermore, showed that the pre-piling method reduces the time and cost of offshore installation, and reduces the weight of piles by 50%.

Highlights

  • Due to oil shortage and climate change, scientists are currently putting more emphasis on alternative energy sources, wind energy which plays an effective role to produce green energy

  • Ample of projects were deployed in shallow water under 30m water depth and further research is required to make offshore wind turbines (OWT) more cost-effective for deeper water depths

  • The study considered 0-30m as shallow water that is suitable for monopoles and gravity foundation, 30-60m as transitional water, which is suitable for tripods, jackets and truss-type towers and greater than 60m as deep water, which may require floating structures

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Summary

Introduction

Due to oil shortage and climate change, scientists are currently putting more emphasis on alternative energy sources, wind energy which plays an effective role to produce green energy. Different types of wind turbine substructures can be selected based on water depth, dynamic loads, seabed soil properties and the cost/availability of transportation vessel and lifting crane. Ashish and Panneer Selvam [7] recommended the use of fixed offshore wind turbine substructures in deep water where winds are more powerful Reliable substructures such as jacket and gravity base can withstand the meta-ocean loads as well as dynamic loads from the wind turbine compared to floating structures. This study aimed at investigating the structural behaviour/response of three-legged and tripod substructures of offshore wind turbines considering all imposed loads during the lifetime in a transition water depth, e.g., 50m water depth in the Persian Gulf. A comparison between the two substructures based on the weight of substructures as well as the installation method of piles was carried out

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