Details
| Original language | English |
|---|---|
| Article number | e2023JC020336 |
| Number of pages | 40 |
| Journal | Journal of Geophysical Research: Oceans |
| Volume | 129 |
| Issue number | 2 |
| Publication status | Published - 17 Feb 2024 |
Abstract
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.
Keywords
- bed roughness, bio-encrusted surfaces, near-bed turbulence, oyster reefs, ultra-rough oceanic surfaces, wave attenuation
ASJC Scopus subject areas
- Earth and Planetary Sciences(all)
- Oceanography
- Earth and Planetary Sciences(all)
- Geophysics
- Earth and Planetary Sciences(all)
- Geochemistry and Petrology
- Earth and Planetary Sciences(all)
- Space and Planetary Science
- Earth and Planetary Sciences(all)
- Earth and Planetary Sciences (miscellaneous)
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In: Journal of Geophysical Research: Oceans, Vol. 129, No. 2, e2023JC020336, 17.02.2024.
Research output: Contribution to journal › Article › Research › peer review
}
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 -