TY - JOUR

T1 - Understanding the Role of Sharp Edges in the Propagation of Surface Gravity Waves

AU - Hitzegrad, Jan

AU - Köster, Sebastian

AU - Windt, Christian

AU - Goseberg, Nils

N1 - Funding Information: The project “BIVA‐WATT” on which this work is based was funded by the Ministry of Education and Research of Germany (BMBF) under the funding code 03KIS127. We acknowledge the support by the Open Access Publication Funds of Technische Universität Braunschweig.

PY - 2024/2/17

Y1 - 2024/2/17

N2 - Ultra-rough oceanic surfaces, such as oyster reefs, are characterized by densely-packed, sharp-edged roughness elements that induce high frictional resistance on the ambient flows. To effectively employ, for example, oyster reefs as a nature-based solution in coastal protection, a detailed understanding of the frictional wave energy dissipation processes is necessary. This work reports on an experimental study in which six surrogates of very to ultra-rough oceanic bed surfaces were subjected to regular waves. The influences of different sharpness' of roughness elements (bluntly-shaped, sharp-edged, and a combination thereof) and relative spacing between elements compared to the near-bed horizontal excursion amplitude, λ/ab, on the wave attenuation have been investigated. Turbulence is 2–27 times larger for sharp-edged surfaces and 1 to 18 times larger for mix surfaces than those of bluntly-shaped surfaces. Maximum bed shear stresses, hydraulic roughness lengths, and wave friction factors are likewise significantly larger for sharp-edged compared to bluntly-shaped surfaces. These observations indicate that the sharp edges are crucial for frictional energy dissipation. Comparing the maximum bed shear stresses determined from wave height reductions to those determined from velocity measurements indicates that in addition to turbulent kinetic energy (TKE), periodic form-induced stresses significantly contribute to the overall bed shear stresses. This study provides new insight into the frictional dissipation processes of oscillating flows encountering ultra-rough surfaces.

AB - Ultra-rough oceanic surfaces, such as oyster reefs, are characterized by densely-packed, sharp-edged roughness elements that induce high frictional resistance on the ambient flows. To effectively employ, for example, oyster reefs as a nature-based solution in coastal protection, a detailed understanding of the frictional wave energy dissipation processes is necessary. This work reports on an experimental study in which six surrogates of very to ultra-rough oceanic bed surfaces were subjected to regular waves. The influences of different sharpness' of roughness elements (bluntly-shaped, sharp-edged, and a combination thereof) and relative spacing between elements compared to the near-bed horizontal excursion amplitude, λ/ab, on the wave attenuation have been investigated. Turbulence is 2–27 times larger for sharp-edged surfaces and 1 to 18 times larger for mix surfaces than those of bluntly-shaped surfaces. Maximum bed shear stresses, hydraulic roughness lengths, and wave friction factors are likewise significantly larger for sharp-edged compared to bluntly-shaped surfaces. These observations indicate that the sharp edges are crucial for frictional energy dissipation. Comparing the maximum bed shear stresses determined from wave height reductions to those determined from velocity measurements indicates that in addition to turbulent kinetic energy (TKE), periodic form-induced stresses significantly contribute to the overall bed shear stresses. This study provides new insight into the frictional dissipation processes of oscillating flows encountering ultra-rough surfaces.

KW - bed roughness

KW - bio-encrusted surfaces

KW - near-bed turbulence

KW - oyster reefs

KW - ultra-rough oceanic surfaces

KW - wave attenuation

UR - http://www.scopus.com/inward/record.url?scp=85185697120&partnerID=8YFLogxK

U2 - 10.1029/2023JC020336

DO - 10.1029/2023JC020336

M3 - Article

AN - SCOPUS:85185697120

VL - 129

JO - Journal of Geophysical Research: Oceans

JF - Journal of Geophysical Research: Oceans

SN - 2169-9275

IS - 2

M1 - e2023JC020336

ER -