Bed Shear Stress Coefficient Within the Surf Zone
Bed Shear Stress Coefficient Within the Surf Zone

Author: Carlos Severino Veitia Garcia

Publisher:

Published: 1977

Total Pages: 122

ISBN-13:

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An analytical formulation of the bed shear stress coefficient inside the surf zone is derived using the concept of radiation stress. A truncated Rayleigh p.d.f. is used to describe the wave field inside the surf zone and provides the input to calculate the variation of wave energy and longshore current as a function of wave height, water depth and distance to shore. The wave set-up is approximated using a sinusoidal wave solution. Field measurements of longshore current and waves within the surf zone are used to calculate the bed shear stress coefficient. Frequency distributions and statistics are calculated for the bed shear stress coefficient.

Nearshore Currents Over a Barred Beach
Nearshore Currents Over a Barred Beach

Author: Antonio Fernando Garcez Faria

Publisher:

Published: 1997

Total Pages: 182

ISBN-13:

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The objective of this dissertation is to develop numerical models and compare their predictions with data acquired during the DUCK94 experiment in order to improve our physical understanding of the hydrodynamic processes governing the vertical and cross shore distributions of both longshore and cross shore currents over a barred beach. The vertical structure of the mean longshore current is found to be well described by a logarithmic profile and a relationship between bed shear stress and bottom roughness, including the influence of ripples and mega-ripples, was also found. The vertical structure of the mean cross shore current (undertow) is modeled using an eddy viscosity closure scheme to solve for the turbulent shear stress and includes contributions from breaking wave rollers. These models of the vertical profiles of longshore and cross shore mean currents are combined to formulate a quasi three dimensional model to describe the cross shore distribution of the longshore current. This model includes turbulent mixing due to the cross shore advection of mean momentum of the longshore current by the mean cross shore current and contributions from wave rollers.

Longshore Sand Transport Distribution Across the Surf Zone Due to Random Waves
Longshore Sand Transport Distribution Across the Surf Zone Due to Random Waves

Author: Saad Mesbah M. Abdelrahman

Publisher:

Published: 1983

Total Pages: 180

ISBN-13:

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Water waves are one of the principal causes of shoreline changes. When waves break along the shore, they release their energy and momentum and give rise to a longshore current. The longshore current, along with the stirring action of the waves, is the primary mechanism for longshore sediment transport. The longshore sand transport rate is an essential factor determining erosion or accretion along a coast. If the longshore sand transport rate can be accurately estimated, a quantitative picture of shoreline evolution can be evaluated, including changes of the shoreline due to marine structures. In the present study, analytical and numerical models are developed based on a longshore current model for random waves and a sediment transport formulation by Thornton to predict the cross-shore sediment transport distribution and to compute the total volume of sand transport rate. The model is compared with the field data acquired from Leadbetter Beach, Santa Barbara, California.

Wind and Wave Forcing of Longshore Currents Across a Barred Beach
Wind and Wave Forcing of Longshore Currents Across a Barred Beach

Author: Dennis James Whitford

Publisher:

Published: 1988

Total Pages: 238

ISBN-13:

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Previous investigations of longshore currents have included simplifying assumptions and restriction (such as a planar beach, a steady and depth uniform flow, spatially-variant bed shear stress and turbulent momentum exchange, and the exclusion of surface wind stress. These assumptions are quantitatively investigated by calculating the relative importance of each term in the longshore momentum balance with an emphasis on the relative importance of wind forcing across the barred nearshore. Wind and wave forcing of longshore currents across a barred beach are examined using both a numerical model and field measurements. A local momentum balance was measured at various locations across the surf zone during the SUPERDUCK experiment held at the USACE CERC Field Research Facility, Duck, N.C. in October 1986. A moveable sled was instrumented with pressure, current, and wind sensors to measure the various terms in the longshore momentum equation. Stability-dependent atmospheric drag coefficients for the surf zone are determined from wind stress measurements acquired just beyond the surf zone and wind speed measurements acquired from an anemometer atop the 9 m sled mast. Breaking waves were visually identified and electronically marked on the data tapes. Keywords: Ocean currents; Air water interactions; Nearshore surf zone; Wind stress; Theses. (EDC).

Turbulence In Coastal And Civil Engineering
Turbulence In Coastal And Civil Engineering

Author: B Mutlu Sumer

Publisher: World Scientific

Published: 2020-03-23

Total Pages: 758

ISBN-13: 9813234326

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This book discusses the subject of turbulence encountered in coastal and civil engineering.The primary aim of the book is to describe turbulence processes including transition to turbulence; mean and fluctuating flows in channels/pipes, and in currents; wave boundary layers (including boundary layers under solitary waves); streaming processes in wave boundary layers; turbulence processes in breaking waves including breaking solitary waves; turbulence processes such as bursting process and their implications for sediment transport; flow resistance in steady and wave boundary layers; and turbulent diffusion and dispersion processes in the coastal and river environment, including sediment transport due to diffusion/dispersion.Both phenomenological and statistical theories are described in great detail. Turbulence modelling is also described, and several examples for modelling of turbulence in steady flow and wave boundary layers are presented.The book ends with a chapter containing hands-on exercises on a wide variety of turbulent flows including experimental study of turbulence in an open-channel flow, using Laser Doppler Anemometry; Statistical, correlation and spectral analysis of turbulent air jet flow; Turbulence modelling of wave boundary layer flows; and numerical modelling of dispersion in a turbulent boundary layer, a set of exercises used by the authors in their Masters classes over many years.Although the book is essentially intended for professionals and researchers in the area of Coastal and Civil Engineering, and as a text book for graduate/post graduate students, the contents of the book will, however, additionally provide sufficient background in the study of turbulent flows relevant to many other disciplines, such as Wind Engineering, Mechanical Engineering, and Environmental Engineering.

Nearshore Sediment Transport
Nearshore Sediment Transport

Author: R.J. Seymour

Publisher: Springer Science & Business Media

Published: 2013-11-11

Total Pages: 410

ISBN-13: 1489925317

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This book represents the efforts of over a hundred individuals who planned and executed the NSTS field experiments, analyzed the billions of data points, and distilled their findings and insights into the summaries found here. Because these experiments were of a scope that will seldom, if ever, be duplicated, and because the program brought together many of the foremost field experimentalists in this country, we all felt from the beginning that it was important to preserve the outcome. This was done in two ways. First, the raw data were made available to any interested investigator within 18 months of the completion of each experiment. Secondly, both the methodology of the experiments and the findings from them were codified in the form of a monograph. This book is that result. I have had the occasion recently (Sediments '87 Proceedings, Vol. 1, pp. 642-651) to assess the NSTS performance. I found that we made giant strides in our understanding of the surf zone hydrodynamics --far more than our fondest expectations at the beginning. We were able to do less than we had hoped about the response of the sediment, largely because of a limited ability to measure it at a point. As I reported in the Sediments '87 assessment, we established a new state of the art in measurement techniques and we demonstrated the effectiveness of large, multi-investigator, instrument-intensive experiments for studying nearshore processes.