Influence of Structural Elements on the Spatial Sediment Displacement around a Jacket-Type Offshore Foundation

Mario Welzel,Torsten Schlurmann,Arndt Hildebrandt,Alexander Schendel,Nils Goseberg

doi:10.3390/w12061651

Mario Welzel, Torsten Schlurmann + Show 3 more

Open Access

https://doi.org/10.3390/w12061651

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Abstract

This research advances the understanding of jacket-type platform induced local and global erosion and deposition processes for combined wave–current conditions. To this end, a laboratory study was carried out comparing the equilibrium scour depth for two structural designs that are differentiated in the geometrical distance of the structure’s lowest node to the seabed. Measurements of local scour depths over time have been conducted with echo sounding transducers. An empirical approach is proposed to predict the final scour depths as a function of the node distance to the seabed. Additionally, 3D laser scans have been performed to obtain the digital elevation model of the surrounding sediment bed. Novel methodologies were developed to describe and easily compare the relative volume change of the sediment bed per surface area due to structure–seabed interaction, enabling spatial analyses of highly complex erosion and deposition patterns. The seabed sediment mobility around the structure is found to be highly sensitive to a change in node distance. The decrease of the node distance results in a higher erosion depth of sediment underneath the structure of up to 26%, especially for current-dominated conditions, as well as an increased deposition of sediment downstream of the structure over a distance of up to 6.5 times the footprint length. The results of this study highlight the requirement to consider the interaction of the structure with the surrounding seabed within the design process of offshore structures, to mitigate potential impacts on the marine environment stemming from the extensive sediment displacement and increased sediment mobility.

Highlights

Wind energy is one of the most promising solutions for a sustainable renewable energy supply, not all regions can benefit from wind energy [1]
offshore wind farms (OWF) contribute to a reduction of the carbon footprint in global energy production, they have an impact on the marine environment, possibly leading to either habitat loss or habitat gain [6,7]
While final scour depths around the main piles of the present study are generally larger for a 0D distance, they are still on a comparable level with those obtained for a jacket structure with nodes and diagonal braces at a 1D distance [24]

Summary

Introduction

Wind energy is one of the most promising solutions for a sustainable renewable energy supply, not all regions can benefit from wind energy [1]. The offshore wind energy sector has grown significantly. Due to technological improvements such as optimized prediction methods for a more detailed load estimation or expected scour depth, offshore wind farms (OWF) are further expanded, even to greater water depths [4], to meet the rising energy demand and replace phased-out energy sources, such as coal and nuclear fuel. Understanding the influence of foundation structures on the marine environment is important for an economically optimized and sustainable design of foundation structures, as well as for an evaluation. OWFs contribute to a reduction of the carbon footprint in global energy production, they have an impact on the marine environment, possibly leading to either habitat loss or habitat gain [6,7].

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