Author(s): Zihao Tang; Bruce Melville; Asaad Shamseldin; Naresh Singhal; Dawei Guan
Linked Author(s): Naresh Singhal, Asaad Yahia Shamseldin, Bruce W. Melville
Keywords: Scour countermeasures; Monopile foundations; Offshore wind turbines; Collar protection; Threshold elevation
Abstract: The offshore wind energy industry is now thriving due to the increasing demand for renewable and green energy. The latest report from the Wind Europe Association stated that 70% of Europe’s newly constructed offshore wind turbines use monopile foundations. Local scour around monopile foundations is one of the most crucial factors for the substructure’s stability. Previous studies show that about 33% of the cost of windfarms relates to the design and construction of foundations. Thus, research into improving the performance of local scour countermeasures is essential for structural safety and cost control, contributing to the future development and prosperity of the offshore windfarm industry. Scour protection is a common approach to mitigate local scouring of soil around monopile foundations at offshore windfarms. The present study is focused on the use of collars as a local scour countermeasure at monopile foundations. According to the collar installation height, a new definition of collar threshold elevation for no scour is given. Using this concept, scour patterns with collar protection are categorised into three types, each with unique scour topography. They are collars placed below the threshold elevation, collars placed above the bed level, and collars placed between these two elevations. The threshold elevation varies with different test conditions, and is mainly influenced by collar width and flow intensity. It is emphasised that the threshold elevation can be set at the bed level. Results for the local scour and scour topography are presented, as well as a comprehensive equation for prediction of the equilibrium scour depth with collar protection. An equation for determining the threshold elevation is also proposed.
Year: 2023