Abstract
The present article presents results of a laboratory study on the assessment of erosion patterns around a hydrodynamic transparent offshore foundation exposed to combined waves and currents. The model tests were conducted under irregular, long-crested waves in a scale of 1:30 in a wave-current basin. A terrestrial 3D laser scanner was used to acquire data of the sediment surface around the foundation structure. Tests have been conducted systematically varying from wave- to current-dominated conditions. Different volume analyzing methods are introduced, which can be related for any offshore or coastal structure to disclose physical processes in complex erosion patterns. Empirical formulations are proposed for the quantification of spatially eroded sediment volumes and scour depths in the near-field and vicinity of the structure. Findings from the present study agree well with in-situ data stemming from the field. Contrasting spatial erosion development between experimental and in-situ data determines a stable maximum of erosion intensity at a distance of 1.25 A, 1.25 times the structure’s footprint A, as well as a global scour extent of 2.1–2.7 A within the present study and about 2.7–2.8 A from the field. By this means, a structure-induced environmental footprint as a measure for erosion of sediment affecting marine habitat is quantified.
Highlights
To meet the rising demand for renewable energy, the expansion of offshore wind energy converters (OWECs) in coastal waters is progressing steadily
It is reasonable to assume from current understanding of scouring and scour extent, that the near bed flow acceleration around a jacket structure is focused along the individual piles
To visualize the impact of the structure on the spatial erosion and deposition of sediment, Figure 4 presents an exemplary photo of the model setup and the final scour pattern after test 4
Summary
To meet the rising demand for renewable energy, the expansion of offshore wind energy converters (OWECs) in coastal waters is progressing steadily. Only a limited understanding of environmental impacts and the impairment of the structure’s stability over its lifetime due to scouring processes around complex foundation structures exist. This is why for some structures that are affected by scouring, e.g., gravity-based foundations (GBF), the installation of a scour protection system became mandatory. The protection of those structures against the degradation due to scour is often designed following a conservative, and inefficient approach that is based on monopiles. This evident mismatch may lead to Energies 2019, 12, 3089; doi:10.3390/en12163089 www.mdpi.com/journal/energies
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