205 research outputs found
Erosion of a granular bed driven by laminar fluid flow
Motivated by examples of erosive incision of channels in sand, we investigate
the motion of individual grains in a granular bed driven by a laminar fluid to
give us new insights into the relationship between hydrodynamic stress and
surface granular flow. A closed cell of rectangular cross-section is partially
filled with glass beads and a constant fluid flux flows through the cell.
The refractive indices of the fluid and the glass beads are matched and the
cell is illuminated with a laser sheet, allowing us to image individual beads.
The bed erodes to a rest height which depends on . The Shields
threshold criterion assumes that the non-dimensional ratio of the
viscous stress on the bed to the hydrostatic pressure difference across a grain
is sufficient to predict the granular flux. Furthermore, the Shields criterion
states that the granular flux is non-zero only for . We find
that the Shields criterion describes the observed relationship when the bed height is offset by approximately half a grain diameter.
Introducing this offset in the estimation of yields a collapse of the
measured Einstein number to a power-law function of
with exponent . The dynamics of the bed height relaxation are
well described by the power law relationship between the granular flux and the
bed stress.Comment: 12 pages, 5 figure
Practical sand transport formula for non-breaking waves and currents
Open Access funded by Engineering and Physical Sciences Research Council Under a Creative Commons license Acknowledgements This work is part of the SANTOSS project (‘SANd Transport in OScillatory flows in the Sheet-flow regime’) funded by the UK's EPSRC (GR/T28089/01) and STW in The Netherlands (TCB.6586). JW acknowledges Deltares strategic research funding under project number 1202359.09. Richard Soulsby is gratefully acknowledged for valuable discussions and feedback on the formula during the SANTOSS project.Peer reviewedPostprin
Effects of wave shape on sheet flow sediment transport
Author Posting. © American Geophysical Union, 2004. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 109 (2004): C05025, doi:10.1029/2003JC002075.A two-phase model is implemented to study the effects of wave shape on the transport of coarse-grained sediment in the sheet flow regime. The model is based on balance equations for the average mass, momentum, and fluctuation energy for both the fluid and sediment phases. Model simulations indicate that the responses of the sheet flow, such as the velocity profiles, the instantaneous bed shear stress, the sediment flux, and the total amount of the mobilized sediment, cannot be fully parameterized by quasi-steady free-stream velocity and may be correlated with the magnitude of local horizontal pressure gradient (or free-stream acceleration). A net sediment flux in the direction of wave advance is obtained for both skewed and saw-tooth wave shapes typical of shoaled and breaking waves. The model further suggests that at critical values of the horizontal pressure gradient, there is a failure event within the bed that mobilizes more sediment into the mobile sheet and enhances the sediment flux. Preliminary attempts to parameterize the total bed shear stress and the total sediment flux appear promising.We gratefully acknowledge the financial
supports of the National Ocean Partnership Program and the Department
of Civil and Environmental Engineering, University of Delaware
Contrasting geomorphological storm response from two adjacent shorefaces.
Shorefaces play a critical role in cross-shore sediment transport between the beach and inner shelf, particularly during storm conditions. A comparison and examination of storm-driven sedimentary changes on two adjacent shorefaces in Northern Ireland, located only 5 km apart, revealed significantly different geomorphological responses. The steeper shoreface at West Strand responded with extensive sediment deposition across almost the entire shoreface, in contrast with the more dissipative and quasi- linear shoreface at Portstewart, which mostly showed nearshore bar changes. Results from the two sites, which have similar wave/wind characteristics and seabed sediments, suggest that: (i) cross-shore morphology, (ii) immediately previous (antecedent) shoreface morphodynamic behaviour and (iii) the presence, or lack of, offshore sand appear to be the primary controls on storm- driven sedimentary changes attributed to the high-energy event
High-angle wave instability and emergent shoreline shapes : 2. Wave climate analysis and comparisons to nature
Author Posting. © American Geophysical Union, 2006. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 111 (2006): F04012, doi:10.1029/2005JF000423.Recent research has revealed that the plan view evolution of a coast due to gradients in alongshore sediment transport is highly dependant upon the angles at which waves approach the shore, giving rise to an instability in shoreline shape that can generate different types of naturally occurring coastal landforms, including capes, flying spits, and alongshore sand waves. This instability merely requires that alongshore sediment flux is maximized for a given deepwater wave angle, a maximum that occurs between 35° and 50° for several common alongshore sediment transport formulae. Here we introduce metrics that sum over records of wave data to quantify the long-term stability of wave climates and to investigate how wave climates change along a coast. For Long Point, a flying spit on the north shore of Lake Erie, Canada, wave climate metrics suggest that unstable waves have shaped the spit and, furthermore, that smaller-scale alongshore sand waves occur along the spit at the same locations where the wave climate becomes unstable. A shoreline aligned along the trend of the Carolina Capes, United States, would be dominated by high-angle waves; numerical simulations driven by a comparable wave climate develop a similarly shaped cuspate coast. Local wave climates along these simulated capes and the Carolina Capes show similar trends: Shoreline reorientation and shadowing from neighboring capes causes most of the coast to experience locally stable wave climates despite regional instability.This research was funded by the Andrew
W. Mellon Foundation and NSF grants DEB-05-07987 and EAR-04-44792
Observations of bedforms on a dissipative macrotidal beach
NERC NE/H004262/1 and NE/H02543X/1 DRIB
Sport and social media research: A review
The emergence of social media has profoundly impacted the delivery and consumption of sport. In the current review we analysed the existing body of knowledge of social media in the field of sport management from a service-dominant logic perspective, with an emphasis on relationship marketing. We reviewed 70 journal articles published in English-language sport management journals, which investigated new media technologies facilitating interactivity and co-creation that allow for the development and sharing of user-generated content among and between brands and individuals (i.e., social media). Three categories of social media research were identified: strategic, operational, and user-focussed. The findings of the review demonstrate that social media research in sport management aligns with service-dominant logic and illustrates the role of social media in cultivating relationships among and between brands and individuals. Interaction and engagement play a crucial role in cultivating these relationships. Discussion of each category, opportunities for future research as well as suggestions for theoretical approaches, research design and context are advanced
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