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No description available.

An understanding of the clogging of fine sediments within gravel substrates is advanced through the use of dimensional analysis and macro-analysis of clogging experiments in hydraulic flumes. Dimensional analysis is used to suggest that the dimensionless clogging depth can be collapsed using the original and adjusted bed-to-grain ratios, substrate porosity, roughness Reynolds number, and Peclet number. Macro-analysis followed by statistical analysis of 146 experimental test results of fine sediment deposition in gravel substrates suggests that the dimensionless clogging depth can be collapsed using the substrate porosity and roughness Reynolds number reflecting the processes of gravity settling and turbulence induced fluid pumping between substrate particles. In addition, a clear cutoff of fine sediment unimpeded static percolation and sediment clogging is found using the adjusted bed-to-grain ratio. Thereafter, a physics-based approach is used to predict the clogging depth of fine sediment in gravel and in turn approve upon the preliminary findings in the empirical analysis. A momentum-impulse model that accounts for the critical impulse of a particle bridge is balanced with a fluid pulse resulting from turbulent pumping. The momentum-impulse model reduces the number of unknown parameters in the clogging problem and increases the model predictability as quantified using k-fold validation and model comparison with the empirical approach. A nomograph derived from applying the momentum-impulse model is provided herein, which will be useful for stream restoration practitioners interested in estimating embeddedness. Also, prediction of the clogging profile is shown using the clogging depth predicted with the momentum-impulse model.

A descriptive sediment movement model has been created for an area of the nearshore zone near Gibraltar Point, Lincolnshire on the basis of evidence from studies of sediments, sandbank and channel morphology, bedforms, tidal currents and sediment tracer experiments. The area is subject to linear tidal currents which have created a system of tidal current ridges, tidal channels and an ebb-tidal delta. Sediment movement associated with these sandbanks and channels was found to have a net northerly drift related to an ebb tidal residual in the Boston Deep, the largest channel in the area. Sediment circulation around the sandbank system was considered to be essentially closed with a large sediment storage element represented by the sandbanks. An area of the foreshore was identified as a possible location for movement of sediment from the nearshore zone to the foreshore zone. Six Woodhead seabed drifter experiments were conducted to assess the validity of the sediment movement model. The net northerly drift of the sediment within the sandbank system was confirmed and was found to extend as far north as Ingoldmells Point. Movement of sediment from the nearshore zone to the foreshore zone was confirmed at the location suggested in the sediment movement model and was also predicted at Ingoldmells Point. The time of stranding of seabed drifters was found to coincide with periods of winds blowing offshore and from the north-east and with, periods of increasing tidal current velocity as the lunar tidal cycle approaches spring tide conditions. Movement of sediment from the nearshore zone to the foreshore zone may also occur under these environmental conditions. A study of the historical development of the sandbanks suggested an overall decrease in the size of tidal current ridges since 1871 which may be related to a decrease in the amount of sediment available for the maintenance of the sandbanks. A ness south of the Skegness Middle sandbank was interpreted as a morphological expression of foreshore adjustment to the migration of sediment from the nearshore zone to the foreshore zone at this location.

Thesis (M.S. - Renewable Natural Resources)--University of Arizona, 1989. / Includes bibliographical references.

Thesis (Ph.D.)--University of Western Australia, 2007.

Thesis (Ph. D.)--Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1982. / Bibliography: p. 139-140.

Thesis (Ph.D.) - University of Queensland, 2006. / Includes bibliography.

Thesis (MScIng)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Marine anthropogenic noise is increasing, along with concern about its impact on the environment. Hence minimising noise within engineering design is important, including in applications such as ships, submarines and turbines. The desire to mitigate noise may also be related to reducing the detectability of certain types of marine craft. Noise reduction typically focuses on rotating machinery such as propellers, due to the high velocity of the blades. A common source of broadband noise in engineering scenarios is often termed inflow turbulence noise. Resulting from upstream turbulence impinging onto rotor blades, this source typically dominates the low to mid range of the frequency spectrum. This is due to the high turbulence intensity and large length scales present in the inflow turbulence, which exceed those generating competing noise sources. This thesis uses a library of numerical tools to simulate broadband inflow turbulence noise. Synthetic turbulence is generated numerically within the simulations. Turbulence is resolved on the grid by solving the filtered Navier-Stokes equations. Based on the assumption of incompressible flow, noise sources may be predicted without resolving acoustic waves on the grid. This decoupling of hydrodynamic and acoustic processes means that radiated noise may be estimated using an acoustic analogy. Validation of two inflow turbulence generators revealed the importance of obtaining the prescribed turbulence statistics, as well as minimising artificial pressure fluctuations. This is used to simulate homogeneous isotropic turbulence impinging onto a foil, allowing acoustic sources to be located. The far-field sound prediction is in good agreement with experimental measurement data for low frequencies. It is then shown that the effect of foil thickness on noise can successfully be predicted using the proposed methodology. Noise radiation from a tidal turbine is then estimated by fully resolving all turbine blades, both spatially and temporally, in the simulation. A good agreement is seen in comparison to an analytical model, demonstrating that the simulation captures the dominant flow features which affect the acoustic spectrum. These spectral ‘humps’ are a result of turbulence-rotor interaction, which is implicitly included. Full scale noise estimates made from the simulations are then used to inform environmental impact assessment; the turbine hydrodynamic noise is not expected to be an issue in this regard.