TY - JOUR

T1 - Role and Impact of Hydrograph Shape on Tidal Current-Induced Scour in Physical-Modelling Environments

AU - Schendel, Alexander

AU - Welzel, Mario

AU - Hildebrandt, Arndt

AU - Schlurmann, Torsten

AU - Hsu, Tai-Wen

N1 - Funding Information: The authors gratefully acknowledge the support of the German Federal Ministry for Economic Affairs and Energy within the funded project "Giga-Wind Life" (BMWI: 0325575A). The publication of this article was funded by the Open Access Fund of the Leibniz Universität Hannover. Furthermore, the authors thank Y. Hashemi, C. Schierl and M. Sultygov for their support in conducting the laboratory experiments and the Federal Maritime and Hydrographic Agency of Germany (BSH) for providing tidal field data from the FINO 1 platform within the RAVE (research at alpha ventus) initiative. A. Schendel was also supported by the Centre of Excellence of Ocean Engineering at the National Taiwan Ocean University in Keelung, Taiwan. Funding Information: Acknowledgments: Furthermore, the authors thank Y. Hashemi, C. Schierl and M. Sultygov for their support in conducting the laboratory experiments and the Federal Maritime and Hydrographic Agency of Germany (BSH) for providing tidal field data from the FINO 1 platform within the RAVE (research at alpha ventus) initiative. A. Schendel was also supported by the Centre of Excellence of Ocean Engineering at the National Taiwan Ocean University in Keelung, Taiwan.

PY - 2019/12

Y1 - 2019/12

N2 - For physical model tests, the time-varying characteristics of tidal currents are often simplified by a hydrograph following a shape of a unidirectional current or by resolving the tidal velocity signal into discrete steps of constant flow velocity. The influence of this generalization of the hydrograph's shape on the scouring process in tidal currents has not yet been investigated systematically, further increasing the uncertainty in the prediction of scour depth and rate. Therefore, hydraulic model tests were carried out to investigate and quantify the influence of the hydrograph shape on the scouring processes under tidal currents. Several different hydrographs including those with continuously changing velocities, constant unidirectional currents, square-tide velocities and stepped velocity time series were analyzed. Results show that the scouring process in tidal currents is characterized by concurrent sediment backfilling and displacement which can only be reproduced by hydrographs that incorporate a varying flow direction. However, if only a correct representation of final scour depths is of interest, similar scour depths as in tidal currents might be achieved by a constant, unidirectional current, provided that a suitable flow velocity is selected. The effective flow work approach was found capable to identify such suitable hydraulic loads with reasonable practical accuracy.

AB - For physical model tests, the time-varying characteristics of tidal currents are often simplified by a hydrograph following a shape of a unidirectional current or by resolving the tidal velocity signal into discrete steps of constant flow velocity. The influence of this generalization of the hydrograph's shape on the scouring process in tidal currents has not yet been investigated systematically, further increasing the uncertainty in the prediction of scour depth and rate. Therefore, hydraulic model tests were carried out to investigate and quantify the influence of the hydrograph shape on the scouring processes under tidal currents. Several different hydrographs including those with continuously changing velocities, constant unidirectional currents, square-tide velocities and stepped velocity time series were analyzed. Results show that the scouring process in tidal currents is characterized by concurrent sediment backfilling and displacement which can only be reproduced by hydrographs that incorporate a varying flow direction. However, if only a correct representation of final scour depths is of interest, similar scour depths as in tidal currents might be achieved by a constant, unidirectional current, provided that a suitable flow velocity is selected. The effective flow work approach was found capable to identify such suitable hydraulic loads with reasonable practical accuracy.

KW - Hydrograph

KW - Laboratory tests

KW - Scour

KW - Sediment transport

KW - Temporal scour development

KW - Tidal currents

KW - Unsteady flow

KW - Flow velocity

KW - Hydraulic models

KW - Ocean currents

KW - Structural geology

KW - Velocity

KW - Hydraulic model test

KW - Hydrographs

KW - Laboratory test

KW - Physical model test

KW - Practical accuracy

KW - Time-varying characteristics

KW - flow velocity

KW - hydrograph

KW - hydrological modeling

KW - laboratory method

KW - scour

KW - sediment transport

KW - tidal current

KW - unsteady flow

UR - http://www.scopus.com/inward/record.url?scp=85079675220&partnerID=8YFLogxK

U2 - 10.3390/w11122636

DO - 10.3390/w11122636

M3 - Article

VL - 11

JO - Water (Switzerland)

JF - Water (Switzerland)

SN - 2073-4441

IS - 12

M1 - 2636

ER -