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Author : Carlos Manuel da Costa Ventura Soares
Release : 1995
Genre : Ocean circulation
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Book Synopsis Vertical Profiles of Longshore Currents by : Carlos Manuel da Costa Ventura Soares
Download or read book Vertical Profiles of Longshore Currents written by Carlos Manuel da Costa Ventura Soares. This book was released on 1995. Available in PDF, EPUB and Kindle. Book excerpt:
Author : Carlos Manuel da Soares Costa Ventura
Release : 1995
Genre :
Kind : eBook
Book Rating : /5 ( reviews)
Book Synopsis Vertical Profiles of Longshore Currents by : Carlos Manuel da Soares Costa Ventura
Download or read book Vertical Profiles of Longshore Currents written by Carlos Manuel da Soares Costa Ventura. This book was released on 1995. Available in PDF, EPUB and Kindle. Book excerpt: The vertical structure of the mean longshore current is examined on three strong current days during the DUCK94 experiment and it is found well described by a logarithmic profile (mean correlation coefficient for all 22 profiles, 0.98). This hypothesis works better in the trough where turbulent bottom boundary layer processes are predominant than over the bar, where breaking wave induced turbulence generated at the surface modifies the profile. A relationship between near bottom vertical velocity profiles and bottom roughness was found. The bed shear stress coefficient varied by an order of magnitude across the surf zone (0.001-0.05). For the three days considered, it is concluded that the bed shear stress coefficient increased with increasing bottom roughness, and therefore is an important parameter to characterize the bottom boundary layer. The influence of the wind is parameterized by an exponential approximation that works well in 50% of the analyzed profiles. This parameterization assumes that the residual Data Normal distribution of data is only due to the wind and does not consider the alongshore component of mass transport velocity, which is assumed small. These results should be treated carefully since there were obtained for only three days over a barred beach with strong longshore currents and cannot be generalized without further studies.
Author : John Casey Church
Release : 1993
Genre : Littoral drift
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Book Synopsis Topics in Longshore Currents by : John Casey Church
Download or read book Topics in Longshore Currents written by John Casey Church. This book was released on 1993. Available in PDF, EPUB and Kindle. Book excerpt: The momentum equation governing mean longshore currents on straight beaches is a balance of forcing from the momentum transfer of the oscillatory wave motion, turbulent momentum transfer (mixing), and bottom stress. Of these, the wave's contribution is well understood, but the remaining two are not, principally due to the complicated hydrodynamics of the surf-zone. Addressing the bottom stress term, a longshore current model is developed which includes a modification of the bottom stress due to the effects of breaking-wave induced turbulence. A one-dimensional turbulent kinetic energy equation is used to model this breaking-wave induced turbulence, producing a spatially varying bottom friction coefficient. The modeled longshore current cross-shore profiles show improved agreement with field observations. In a second bottom stress study, vertical profiles of mean longshore currents are examined using field data obtained with vertically stacked electromagnetic current meters with the goal of measuring the bottom stress and its associated drag coefficient. The profiles are observed to become vertically uniform whenever the ratio of wave height to depth exceeds 0.3, indicating that nearly all of the waves passing a given location are breaking. Finally, horizontal turbulent momentum transfer (mixing) is examined for the case of shear instabilities of the longshore current.
Author : Antonio Fernando Garcez Faria
Release : 1997
Genre : Science
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Book Synopsis Nearshore Currents Over a Barred Beach by : Antonio Fernando Garcez Faria
Download or read book Nearshore Currents Over a Barred Beach written by Antonio Fernando Garcez Faria. This book was released on 1997. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Author : Antonio Fernando Garcez Faria
Release : 1995
Genre : Ocean circulation
Kind : eBook
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Book Synopsis A Simple Quasi-three Dimensional Model of Longshore Currents Over Arbitrary Profile by : Antonio Fernando Garcez Faria
Download or read book A Simple Quasi-three Dimensional Model of Longshore Currents Over Arbitrary Profile written by Antonio Fernando Garcez Faria. This book was released on 1995. Available in PDF, EPUB and Kindle. Book excerpt: The long shore current maximum observed in the trough of a barred beach during the nearshore dynamics experiment DELILAH at Duck, North Carolina, is not predicted by present theory. The simplest longshore curren models balance cross-shore changes in the alongshore wave momentum (radiation stress) with the alongshore bottom shear stress. Waves break over the bar, reform in the trough and again break on the foreshore resulting in changes in the radiation stress, which predicts two jets, one over the bar and the other at the foreshore, which does not agree with the observed current maximum in the trough. The advection of the momentum of the longshore current by mean cross-shore currents as a source of momentum mixing is investigated. The longshore current is strongest toward the surface and decreasing to zero at the bottom. The cross-shore mean current has an onshore transport in the wave crest/trough region and an offshore transport beneath (undertow). The net interaction can induce significant lateral mixing of the alongshore momentum of the mean currents, which is shown using a simplified three- dimension model of nearshore currents to explain much of the differences with observations.
