scholarly journals SHEETFLOW SEDIMENT TRANSPORT UNDER SKEWED - ASYMMETRIC WAVES AND CURRENTS

2012 ◽  
Vol 1 (33) ◽  
pp. 50 ◽  
Author(s):  
Le Phuong Dong ◽  
Shinji Sato
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Fine Sand ◽  
Sand Transport ◽  
Phase Lag ◽  
Half Cycle ◽  
Experimental Conditions ◽  
Wide Range ◽  
Waves And Currents ◽  
Asymmetric Flows

Prototype scale laboratory experiments have been conducted to investigate the sheetflow sediment transport of uniform sands under different skewed-asymmetric oscillatory flows. Experimental results reveal that in most of the case with fine sand, the “cancelling effect”, which balances the on-/off-shore net transport under pure asymmetric/skewed flows and results a moderate net transport, was developed for combined skewed-asymmetric flow. However, under some certain conditions (T > 5s) with coarse sands, the onshore sediment transport was enhanced by 50% under combined skewed-asymmetric flows. Sand transport mechanism under oscillatory sheetflow conditions is also studied by comparing the maximum bed shear stress and the phase lag parameter at each half cycle. A comparison of measurements including the new experimental data with a number of practical sand transport formulations shows that the Dong et al. (2013) formulation performs the best in predicting the measured net transport rates over a wide range of experimental conditions

scholarly journals NEW PRACTICAL MODEL FOR SAND TRANSPORT INDUCED BY NON-BREAKING WAVES AND CURRENTS

2011 ◽  
Vol 1 (32) ◽  
pp. 10
Author(s):  
Dominic Alexander Van der A ◽  
Jan S Ribberink ◽  
Jebbe J Van der Werf ◽  
Tom O'Donoghue
Keyword(s):  
Fine Sand ◽  
Breaking Waves ◽  
Sand Transport ◽  
Phase Lag ◽  
Flow Conditions ◽  
Large Wave ◽  
Lag Effects ◽  
Flow Acceleration ◽  
Wide Range ◽  
Waves And Currents

Many existing practical sand transport formulae for the coastal marine environment are restricted to limited ranges of hydrodynamic and sediment conditions. This paper presents a new practical formula for net sand transport induced by non-breaking waves and currents, and currents alone. The formula is based on the semi-unsteady, half wave-cycle concept, with bed shear stress as the main forcing parameter. Unsteady phase-lag effects between velocities and concentrations are accounted for, which are especially important for rippled bed and fine sand sheet-flow conditions. Recently recognized effects on the net transport related to flow acceleration skewness and progressive surface waves are also included. The formula is calibrated against a large dataset of net transport rate measurements from oscillatory flow tunnels and a large wave flume covering a wide range of flow and sand conditions. Good agreement is obtained between observations and predictions, and its validity is shown for bedload dominated steady flow conditions.

scholarly journals SHEETFLOW SEDIMENT TRANSPORT UNDER ASYMMETRIC WAVES AND STRONG CURRENTS

2011 ◽  
Vol 1 (32) ◽  
pp. 17
Author(s):  
Le Phuong Dong ◽  
Shinji Sato
Keyword(s):  
Image Analysis ◽  
Sediment Transport ◽  
Layer Thickness ◽  
Experimental Conditions ◽  
Oscillatory Flows ◽  
Image Analysis Technique ◽  
Analysis Technique ◽  
Wide Range ◽  
Nearshore Waves ◽  
Wave Shapes

Experiments have been conducted to investigate the sheetflow sediment transport of uniform sand under asymmetric oscillatory flows in combination with relatively strong opposite currents. Two kinds of nearshore waves were performed, namely, velocity asymmetric waves and acceleration asymmetric waves. Image analysis technique is utilized to study major influences of wave shapes and current through observing the instantaneous sheetflow layer thickness. Maximum sheetflow layer thickness was formulated and incorporated to an enhanced Watanabe and Sato’s formulation. The new conceptual model is examined its validity for a wide range of experimental conditions

scholarly journals O Controle da Deriva Litorânea no Desenvolvimento do Campo de Dunas e da Antepraia no Litoral Médio do Rio Grande do Sul

2006 ◽  
Vol 33 (2) ◽  
pp. 35 ◽  
Author(s):  
ELÍRIO TOLDO JR ◽  
LUIZ ALMEIDA ◽  
LUCIANO ABSALONSEN ◽  
NELSON GRUBER
Keyword(s):  
Sediment Transport ◽  
Surf Zone ◽  
Rio Grande ◽  
Fine Sand ◽  
Sediment Flux ◽  
Sand Transport ◽  
Rio Grande Do Sul ◽  
Coastal Jet ◽  
Longshore Transport ◽  
Alongshore Sediment Transport

Zones of erosion and accretion were delimited by comparing a DGPS shoreline mapping in 1997 and the beach line reproduced from the army chart collection of 1975. The results show extensive shore retreat along of Rio Grande do Sul central coast, while accretion was observed in Mostardas and Dunas Altas beach. Mathematical estimative of the regional longshore transport potential along the Rio Grande do Sul coast, a 630-km long holocenic fine sand barrier, resulted in a large net northward annual sand volume. Additionally, the estimated potential of sediment transport based on the CERC formula predicts a substantial variation of the energy flux into the surf zone, due to little changes in shoreline alignments and in the potential alongshore sediment transport. The reduction in the sediment flux due to changes in the shoreline alignment produce a jam in the longshore transport, meaning that part of the sediment arriving from the upstream stretch may be deposited or diverted offshore by coastal jet. Based on that, it is possible that changes in the net longshore sand transport are responsible for the increase in the shoreface width from less than 1 km to more than 3 km in Mostardas beach and Dunas Altas beach. Interesting to note that wider dune fields are associated to those beaches where shoreface is also wider. In this way, the volume of longshore sand transport and the sediment jam provide by changes on shoreline alignment in Mostardas and Dunas Altas beaches are important for both coastal dune fields and shoreface width.

The effects of artificial pebble concentrations on eolion sand transport on a beach

1997 ◽  
Vol 34 (11) ◽  
pp. 1499-1508 ◽  
Author(s):  
Robin G. D. Davidson-Arnott ◽  
Davina C. White ◽  
Jeff Ollerhead
Keyword(s):  
Sediment Transport ◽  
Laboratory Experiments ◽  
Three Dimensional ◽  
Effective Area ◽  
Sand Transport ◽  
Data Sets ◽  
Ceramic Tiles ◽  
Sand Beach ◽  
Random Array ◽  
Protected Surface

A field experiment to measure the effects of differing concentrations of pebbles on rate of eoliao sediment transport was carried out on a sand beach on the Northumberland Strait, New Brunswick. Square ceramic tiles (0.15 m × 0.15 m) were used to replicate pebbles. These were deployed in a stratified random array in a rectangular plot 5 m wide and 2 m deep at five different concentrations (surface covers of 19, 24, 29, 34, and 44%) and both singly (two dimensional) and stacked three high (three dimensional). An adjacent plot of similar size was left bare and served as a control. Sediment transport was measured with pairs of vertical traps deployed downwind from each plot and wind speed with three-cup anemometers. Nine data sets totalling 45 runs of 10 min duration each were collected over a total of 4 days. Sediment transport over the tiled plot was normalized against transport over the bare plot. The results show an increase in sediment transport compared with the bare surface for the lowest coverage, followed by a continuous decrease in transport with increasing coverage up to the maximum coverage employed. The rate of decrease was greatest for runs that utilized a three-dimensional form, reflecting an increase in the effective area protected. The results confirm laboratory experiments, which suggest that erosion and transport are initially enhanced by acceleration of flow around pebbles and more efficient transport over the hard surface, but that this is counteracted at higher coverage densities by the increasing area of protected surface.

Strongly Coupled Redox-Linked Conformational Switching at the Active Site of the Non-Heme Iron-Dependent Dioxygenase, TauD

2019 ◽  
Author(s):  
Christopher John ◽  
Greg M. Swain ◽  
Robert P. Hausinger ◽  
Denis A. Proshlyakov
Keyword(s):  
Active Site ◽  
Structural Model ◽  
Heme Iron ◽  
Chemical Transformations ◽  
Experimental Conditions ◽  
Strongly Coupled ◽  
Non Heme Iron ◽  
Reversible Redox ◽  
Wide Range ◽  
Complex Structural

2-Oxoglutarate (2OG)-dependent dioxygenases catalyze C-H activation while performing a wide range of chemical transformations. In contrast to their heme analogues, non-heme iron centers afford greater structural flexibility with important implications for their diverse catalytic mechanisms. We characterize an <i>in situ</i> structural model of the putative transient ferric intermediate of 2OG:taurine dioxygenase (TauD) by using a combination of spectroelectrochemical and semi-empirical computational methods, demonstrating that the Fe (III/II) transition involves a substantial, fully reversible, redox-linked conformational change at the active site. This rearrangement alters the apparent redox potential of the active site between -127 mV for reduction of the ferric state and 171 mV for oxidation of the ferrous state of the 2OG-Fe-TauD complex. Structural perturbations exhibit limited sensitivity to mediator concentrations and potential pulse duration. Similar changes were observed in the Fe-TauD and taurine-2OG-Fe-TauD complexes, thus attributing the reorganization to the protein moiety rather than the cosubstrates. Redox difference infrared spectra indicate a reorganization of the protein backbone in addition to the involvement of carboxylate and histidine ligands. Quantitative modeling of the transient redox response using two alternative reaction schemes across a variety of experimental conditions strongly supports the proposal for intrinsic protein reorganization as the origin of the experimental observations.

scholarly journals Low-Energy Electron Damage to Condensed-Phase DNA and Its Constituents

2021 ◽  
Vol 22 (15) ◽  
pp. 7879
Author(s):  
Yingxia Gao ◽  
Yi Zheng ◽  
Léon Sanche
Keyword(s):  
Condensed Phase ◽  
Genetic Material ◽  
High Energy ◽  
Dna Lesions ◽  
Low Energy ◽  
Experimental Investigations ◽  
Experimental Conditions ◽  
Strand Breaks ◽  
Sequence Of Events ◽  
Wide Range

The complex physical and chemical reactions between the large number of low-energy (0–30 eV) electrons (LEEs) released by high energy radiation interacting with genetic material can lead to the formation of various DNA lesions such as crosslinks, single strand breaks, base modifications, and cleavage, as well as double strand breaks and other cluster damages. When crosslinks and cluster damages cannot be repaired by the cell, they can cause genetic loss of information, mutations, apoptosis, and promote genomic instability. Through the efforts of many research groups in the past two decades, the study of the interaction between LEEs and DNA under different experimental conditions has unveiled some of the main mechanisms responsible for these damages. In the present review, we focus on experimental investigations in the condensed phase that range from fundamental DNA constituents to oligonucleotides, synthetic duplex DNA, and bacterial (i.e., plasmid) DNA. These targets were irradiated either with LEEs from a monoenergetic-electron or photoelectron source, as sub-monolayer, monolayer, or multilayer films and within clusters or water solutions. Each type of experiment is briefly described, and the observed DNA damages are reported, along with the proposed mechanisms. Defining the role of LEEs within the sequence of events leading to radiobiological lesions contributes to our understanding of the action of radiation on living organisms, over a wide range of initial radiation energies. Applications of the interaction of LEEs with DNA to radiotherapy are briefly summarized.

scholarly journals Review of the Upright Balance Assessment Based on the Force Plate

2021 ◽  
Vol 18 (5) ◽  
pp. 2696
Author(s):  
Baoliang Chen ◽  
Peng Liu ◽  
Feiyun Xiao ◽  
Zhengshi Liu ◽  
Yong Wang
Keyword(s):  
Postural Balance ◽  
Force Plate ◽  
Assessment Method ◽  
Balance Assessment ◽  
Experimental Conditions ◽  
Methodological Research ◽  
Assessment Tests ◽  
Wide Range ◽  
Foot Posture ◽  
Plate System

Quantitative assessment is crucial for the evaluation of human postural balance. The force plate system is the key quantitative balance assessment method. The purpose of this study is to review the important concepts in balance assessment and analyze the experimental conditions, parameter variables, and application scope based on force plate technology. As there is a wide range of balance assessment tests and a variety of commercial force plate systems to choose from, there is room for further improvement of the test details and evaluation variables of the balance assessment. The recommendations presented in this article are the foundation and key part of the postural balance assessment; these recommendations focus on the type of force plate, the subject’s foot posture, and the choice of assessment variables, which further enriches the content of posturography. In order to promote a more reasonable balance assessment method based on force plates, further methodological research and a stronger consensus are still needed.

2D and 3D CFD Investigations of Seabed Shear Stresses Around Subsea Pipelines

2013 ◽  
Author(s):  
Wenwen Shen ◽  
Terry Griffiths ◽  
Mengmeng Xu ◽  
Jeremy Leggoe
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Interaction Model ◽  
Suspended Sediment Transport ◽  
Shear Stresses ◽  
Parametric Function ◽  
Ample Evidence ◽  
North West ◽  
Wide Range ◽  
Subsea Pipelines

For well over a decade it has been widely recognised that existing models and tools for subsea pipeline stability design fail to account for the fact that seabed soils tend to become mobile well before the onset of pipeline instability. Despite ample evidence obtained from both laboratory and field observations that sediment mobility has a key role to play in understanding pipeline/soil interaction, no models have been presented previously which account for the tripartite interaction between the fluid and the pipe, the fluid and the soil, and the pipe and the soil. There are numerous well developed and widely used theories available to model pipe-fluid and pipe-soil interactions. A challenge lies in the way to develop a satisfactory fluid-soil interaction algorithm that has the potential for broad implementation under both ambient and extreme sea conditions due to the complexity of flow in the vicinity of a seabed pipeline or cable. A widely used relationship by Shields [1] links the bedload and suspended sediment transport to the seabed shear stresses. This paper presents details of computational fluid dynamics (CFD) research which has been undertaken to investigate the variation of seabed shear stresses around subsea pipelines as a parametric function of pipeline spanning/embedment, trench configuration and wave/current properties using the commercial RANS-based software ANSYS Fluent. The modelling work has been undertaken for a wide range of seabed geometries, including cases in 3D to evaluate the effects of finite span length, span depth and flow attack angle on shear stresses. These seabed shear stresses have been analysed and used as the basis for predicting sediment transport within the Pipe-Soil-Fluid (PSF) Interaction Model [2] in determining the suspended sediment concentration and the advection velocity in the vicinity of pipelines. The model has significant potential to be of use to operators who struggle with conventional stabilisation techniques for the pipelines, such as those which cross Australia’s North West Shelf, where shallow water depths, highly variable calcareous soils and extreme metocean conditions driven by frequent tropical cyclones result in the requirement for expensive and logistically challenging secondary stabilisation measures.

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