The Experts below are selected from a list of 189 Experts worldwide ranked by ideXlab platform
Andrew D Ashton - One of the best experts on this subject based on the ideXlab platform.
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Wave Angle control of delta evolution
Geophysical Research Letters, 2011Co-Authors: Andrew D Ashton, Liviu GiosanAbstract:[1] Wave-influenced deltas, with large-scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the Angles from which Waves approach a delta can have a first-order influence upon its plan-view morphologic evolution and sedimentary architecture. The directional spread of incoming Waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique Wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan-view form. This plan-form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self-organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand Waves—features observed on natural deltas. Somewhat surprisingly, Waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan-form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the Angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth.
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high Angle Wave instability and emergent shoreline shapes 2 Wave climate analysis and comparisons to nature
Journal of Geophysical Research, 2006Co-Authors: Andrew D Ashton, Brad A MurrayAbstract:[1] 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.
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high Angle Wave instability and emergent shoreline shapes 1 modeling of sand Waves flying spits and capes
Journal of Geophysical Research, 2006Co-Authors: Andrew D Ashton, Brad A MurrayAbstract:[1] Contrary to traditional findings, the deepwater Angle of Wave approach strongly affects plan view coastal evolution, giving rise to an antidiffusional “high Wave Angle” instability for sufficiently oblique deepwater Waves (with Angles between Wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport, ∼45°). A one-contour-line numerical model shows that a predominance of high-Angle Waves can cause a shoreline to self-organize into regular, quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers. The numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash, which is assumed to maintain a minimum barrier width. Systematic analysis shows that the Wave climate determines the form of coastal response. For nearly symmetric Wave climates (small net alongshore sediment transport), cuspate coasts develop that exhibit increasing relative cross-shore amplitude and pointier tips as the proportion of high-Angle Waves is increased. For asymmetrical Wave climates, shoreline features migrate in the downdrift direction, either as subtle alongshore sand Waves or as offshore-extending “flying spits,” depending on the proportion of high-Angle Waves. Numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude, a rate that is insensitive to the proportion of high-Angle Waves. The proportion of high-Angle Waves determines the offshore versus alongshore aspect ratio of self-organized shoreline undulations.
M Reza - One of the best experts on this subject based on the ideXlab platform.
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realistic Wave conditions and their influence on quantifying the tidal stream energy resource
Applied Energy, 2014Co-Authors: Matt J Lewis, Simon P Neill, M R Hashemi, M RezaAbstract:highlights � Waves are frequently aligned at an oblique Angle to the tidal current. � Wave Angle must be considered for realistic oceanographic conditions. � Waves have a significant impact on the tidal stream energy resource. � The net tidal resource is reduced by � 10% per metre Wave height increase. abstract When selecting suitable sites for tidal stream energy arrays a wide range of factors must be considered, from the magnitude of the tidal stream resource, to realistic oceanographic conditions. Previous compu- tational and laboratory-scale investigations into the impact of Waves upon tidal turbines (such as turbine blade loadings) and turbine arrays (such as array configuration) typically assume that Waves propagate ''inline'' to the tidal current (Waves following or Waves opposing the tidal current with a 20 tolerance limit). We investigated the Wave climate at typical tidal stream energy sites across the British Isles. The Wave climate was simulated at 18 sites using a 7-year (2005-2011) SWAN Wave model simulation of the northwest European shelf seas. The principal semi-diurnal lunar constituent (M2) was also esti- mated at these sites using the three-dimensional ROMS tidal model. A significant proportion of the Wave climate (between 49% and 93% of the time), including extreme Wave events (>10 m Wave heights), was found to be propagating in a direction which was ''oblique'' to the major axis of tidal flow (i.e. Waves which propagate at an Angle to the tidal current with a 20 tolerance limit) at all 18 selected sites. Fur- thermore, the average ''inline'' Wave climate was 2.25 m less in height and 2 s less in Wave period in com- parison to the oblique Wave climate. To understand the direct effect of Waves upon the tidal stream resource, the dynamically Wave-tide coupled COAWST modelling system was applied to an idealized headland case study, which represented the typical tide and Wave conditions expected at first generation tidal stream energy sites. Waves were found to alter the simulated tidal velocity profile, which, because tidal stream power is proportional to velocity cubed, reduced the theoretical resource by 10% for every metre increase in Wave height (R
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realistic Wave conditions and their influence on quantifying the tidal stream energy resource
Applied Energy, 2014Co-Authors: Matt J Lewis, Simon P Neill, M R Hashemi, M RezaAbstract:When selecting suitable sites for tidal stream energy arrays a wide range of factors must be considered, from the magnitude of the tidal stream resource, to realistic oceanographic conditions. Previous computational and laboratory-scale investigations into the impact of Waves upon tidal turbines (such as turbine blade loadings) and turbine arrays (such as array configuration) typically assume that Waves propagate “inline” to the tidal current (Waves following or Waves opposing the tidal current with a 20° tolerance limit). We investigated the Wave climate at typical tidal stream energy sites across the British Isles. The Wave climate was simulated at 18 sites using a 7-year (2005–2011) SWAN Wave model simulation of the northwest European shelf seas. The principal semi-diurnal lunar constituent (M2) was also estimated at these sites using the three-dimensional ROMS tidal model. A significant proportion of the Wave climate (between 49% and 93% of the time), including extreme Wave events (>10m Wave heights), was found to be propagating in a direction which was “oblique” to the major axis of tidal flow (i.e. Waves which propagate at an Angle to the tidal current with a 20° tolerance limit) at all 18 selected sites. Furthermore, the average “inline” Wave climate was 2.25m less in height and 2s less in Wave period in comparison to the oblique Wave climate. To understand the direct effect of Waves upon the tidal stream resource, the dynamically Wave-tide coupled COAWST modelling system was applied to an idealized headland case study, which represented the typical tide and Wave conditions expected at first generation tidal stream energy sites. Waves were found to alter the simulated tidal velocity profile, which, because tidal stream power is proportional to velocity cubed, reduced the theoretical resource by 10% for every metre increase in Wave height (R2 94% with 22 degrees of freedom) – depending upon Wave period and direction. Our research indicates that Wave Angle should be considered when quantifying the impact of Waves upon tidal turbines, such as computational fluid dynamic (CFD) studies, or laboratory-scale experiments of wake characteristics and turbine fatigue loading. Further, dynamically coupled tide-Wave models may be necessary for a thorough resource assessment, since the complex Wave-tide interaction affected the tidal resource; however, in situ observations of tidal velocity profiles during a range of Wave events will be essential in validating such modelling approaches in the future.
Brad A Murray - One of the best experts on this subject based on the ideXlab platform.
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high Angle Wave instability and emergent shoreline shapes 2 Wave climate analysis and comparisons to nature
Journal of Geophysical Research, 2006Co-Authors: Andrew D Ashton, Brad A MurrayAbstract:[1] 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.
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high Angle Wave instability and emergent shoreline shapes 1 modeling of sand Waves flying spits and capes
Journal of Geophysical Research, 2006Co-Authors: Andrew D Ashton, Brad A MurrayAbstract:[1] Contrary to traditional findings, the deepwater Angle of Wave approach strongly affects plan view coastal evolution, giving rise to an antidiffusional “high Wave Angle” instability for sufficiently oblique deepwater Waves (with Angles between Wave crests and the shoreline trend larger than the value that maximizes alongshore sediment transport, ∼45°). A one-contour-line numerical model shows that a predominance of high-Angle Waves can cause a shoreline to self-organize into regular, quasiperiodic shapes similar to those found along many natural coasts at scales ranging from kilometers to hundreds of kilometers. The numerical model has been updated from a previous version to include a formulation for the widening of an overly thin barrier by the process of barrier overwash, which is assumed to maintain a minimum barrier width. Systematic analysis shows that the Wave climate determines the form of coastal response. For nearly symmetric Wave climates (small net alongshore sediment transport), cuspate coasts develop that exhibit increasing relative cross-shore amplitude and pointier tips as the proportion of high-Angle Waves is increased. For asymmetrical Wave climates, shoreline features migrate in the downdrift direction, either as subtle alongshore sand Waves or as offshore-extending “flying spits,” depending on the proportion of high-Angle Waves. Numerical analyses further show that the rate that the alongshore scale of model features increases through merging follows a diffusional temporal scale over several orders of magnitude, a rate that is insensitive to the proportion of high-Angle Waves. The proportion of high-Angle Waves determines the offshore versus alongshore aspect ratio of self-organized shoreline undulations.
Matt J Lewis - One of the best experts on this subject based on the ideXlab platform.
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realistic Wave conditions and their influence on quantifying the tidal stream energy resource
Applied Energy, 2014Co-Authors: Matt J Lewis, Simon P Neill, M R Hashemi, M RezaAbstract:highlights � Waves are frequently aligned at an oblique Angle to the tidal current. � Wave Angle must be considered for realistic oceanographic conditions. � Waves have a significant impact on the tidal stream energy resource. � The net tidal resource is reduced by � 10% per metre Wave height increase. abstract When selecting suitable sites for tidal stream energy arrays a wide range of factors must be considered, from the magnitude of the tidal stream resource, to realistic oceanographic conditions. Previous compu- tational and laboratory-scale investigations into the impact of Waves upon tidal turbines (such as turbine blade loadings) and turbine arrays (such as array configuration) typically assume that Waves propagate ''inline'' to the tidal current (Waves following or Waves opposing the tidal current with a 20 tolerance limit). We investigated the Wave climate at typical tidal stream energy sites across the British Isles. The Wave climate was simulated at 18 sites using a 7-year (2005-2011) SWAN Wave model simulation of the northwest European shelf seas. The principal semi-diurnal lunar constituent (M2) was also esti- mated at these sites using the three-dimensional ROMS tidal model. A significant proportion of the Wave climate (between 49% and 93% of the time), including extreme Wave events (>10 m Wave heights), was found to be propagating in a direction which was ''oblique'' to the major axis of tidal flow (i.e. Waves which propagate at an Angle to the tidal current with a 20 tolerance limit) at all 18 selected sites. Fur- thermore, the average ''inline'' Wave climate was 2.25 m less in height and 2 s less in Wave period in com- parison to the oblique Wave climate. To understand the direct effect of Waves upon the tidal stream resource, the dynamically Wave-tide coupled COAWST modelling system was applied to an idealized headland case study, which represented the typical tide and Wave conditions expected at first generation tidal stream energy sites. Waves were found to alter the simulated tidal velocity profile, which, because tidal stream power is proportional to velocity cubed, reduced the theoretical resource by 10% for every metre increase in Wave height (R
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realistic Wave conditions and their influence on quantifying the tidal stream energy resource
Applied Energy, 2014Co-Authors: Matt J Lewis, Simon P Neill, M R Hashemi, M RezaAbstract:When selecting suitable sites for tidal stream energy arrays a wide range of factors must be considered, from the magnitude of the tidal stream resource, to realistic oceanographic conditions. Previous computational and laboratory-scale investigations into the impact of Waves upon tidal turbines (such as turbine blade loadings) and turbine arrays (such as array configuration) typically assume that Waves propagate “inline” to the tidal current (Waves following or Waves opposing the tidal current with a 20° tolerance limit). We investigated the Wave climate at typical tidal stream energy sites across the British Isles. The Wave climate was simulated at 18 sites using a 7-year (2005–2011) SWAN Wave model simulation of the northwest European shelf seas. The principal semi-diurnal lunar constituent (M2) was also estimated at these sites using the three-dimensional ROMS tidal model. A significant proportion of the Wave climate (between 49% and 93% of the time), including extreme Wave events (>10m Wave heights), was found to be propagating in a direction which was “oblique” to the major axis of tidal flow (i.e. Waves which propagate at an Angle to the tidal current with a 20° tolerance limit) at all 18 selected sites. Furthermore, the average “inline” Wave climate was 2.25m less in height and 2s less in Wave period in comparison to the oblique Wave climate. To understand the direct effect of Waves upon the tidal stream resource, the dynamically Wave-tide coupled COAWST modelling system was applied to an idealized headland case study, which represented the typical tide and Wave conditions expected at first generation tidal stream energy sites. Waves were found to alter the simulated tidal velocity profile, which, because tidal stream power is proportional to velocity cubed, reduced the theoretical resource by 10% for every metre increase in Wave height (R2 94% with 22 degrees of freedom) – depending upon Wave period and direction. Our research indicates that Wave Angle should be considered when quantifying the impact of Waves upon tidal turbines, such as computational fluid dynamic (CFD) studies, or laboratory-scale experiments of wake characteristics and turbine fatigue loading. Further, dynamically coupled tide-Wave models may be necessary for a thorough resource assessment, since the complex Wave-tide interaction affected the tidal resource; however, in situ observations of tidal velocity profiles during a range of Wave events will be essential in validating such modelling approaches in the future.
A X Gray - One of the best experts on this subject based on the ideXlab platform.
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momentum resolved electronic structure at a buried interface from soft x ray standing Wave Angle resolved photoemission
EPL, 2013Co-Authors: A X Gray, J Minar, L Plucinski, Mark Huijben, Aaron Bostwick, Eli Rotenberg, Seehun Yang, J BraunAbstract:Angle-resolved photoemission spectroscopy (ARPES) is a powerful technique for the study of electronic structure, but it lacks a direct ability to study buried interfaces between two materials. We address this limitation by combining ARPES with soft X-ray standing-Wave (SW) excitation (SWARPES), in which the SW profile is scanned through the depth of the sample. We have studied the buried interface in a prototypical magnetic tunnel junction La0.7Sr0.3MnO3/SrTiO3. Depth-and momentum-resolved maps of Mn 3d eg and t2g states from the central, bulk-like and interface-like regions of La0.7Sr0.3MnO3 exhibit distinctly different behavior consistent with a change in the Mn bonding at the interface. We compare the experimental results to state-of-the-art density-functional and one-step photoemission theory, with encouraging agreement that suggests wide future applications of this technique.
