Sediment Motion beneath Surges and Bores

Positive surges and bores can induce significant bed-load transport in estuaries and river channels. Based upon physical modelling, the present study investigated the sediment motion beneath bores on a relatively long gravel bed. The freesurface measurements at a series of locations showed that the bore shape varied during its upstream propagation. An ultrahigh speed camera captured the details of gravel motion at 1200 fps. Frame-by-frame analysis of slow-motion video movies demonstrated three basic modes of pebble motion: rotation, rolling and saltation. More complicated pebble motion was a combination of 2 or 3 basic modes. The synchronous measurements of near-bottom velocity and bed-load material trajectories highlighted the importance of the adverse longitudinal pressure gradient and transient flow recirculation on the inception of particle motion. Long durations of gravel motion also indicated that the weak negative flow under secondary waves played some role in maintaining the upstream transient sediment transport

Sediment Motion beneath Surges and Bores

Positive surges and bores can induce significant bed-load transport in estuaries and river channels. Based upon physical modelling, the present study investigated the sediment motion beneath bores on a relatively long gravel bed. The freesurface measurements at a series of locations showed that the bore shape varied during its upstream propagation. An ultrahigh speed camera captured the details of gravel motion at 1200 fps. Frame-by-frame analysis of slow-motion video movies demonstrated three basic modes of pebble motion: rotation, rolling and saltation. More complicated pebble motion was a combination of 2 or 3 basic modes. The synchronous measurements of near-bottom velocity and bed-load material trajectories highlighted the importance of the adverse longitudinal pressure gradient and transient flow recirculation on the inception of particle motion. Long durations of gravel motion also indicated that the weak negative flow under secondary waves played some role in maintaining the upstream transient sediment transport

Closing the Implementation Gap: Bringing Clean Air to the Region

This report identifies 25 clean air measures that can positively impact human health, crop yields, climate change and socio-economic development, as well as contribute to achieving the Sustainable Development Goals. Implementing these measures could help 1 billion people breathe cleaner air by 2030 and reduce global warming by a third of a degree Celsius by 2050

Physical Modeling of Vanishing Bores in Open-Channel Flows

When an undular bore is propagating upstream against a subcritical flow in a flat channel, its leading front may weaken and vanish. The present study physically investigated the whole decaying process of vanishing bores in a relatively large facility. The invert was made of mobile or fixed natural river gravels. Detailed sampling of water surface elevations and velocities was performed in combination with high-resolution photo and video recordings. Despite some increased turbulence characteristics linked to the bore front arrival, no sediment motion was observed underneath the vanishing bores. The quantitative results provide a unique benchmark data set for further study of the later-stage bore propagations.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Backwater in a long channel

The purpose of this practical is to demonstrate the effect of open channel control features on gradually-varied flows, and to quantify friction and backwater effects that occur differently in "steep" and "mild"-sloped waterways carrying steady flows. The practical procedure includes observations, modelling, prediction (numerical modelling) and evaluation

Effect of magnetic field on the physical properties of water

In this study, the effect of magnetic field (MF) on the partial physical properties of water are reported, tap water (TW) and 4 types of magnetized water (MW) were measured in the same condition. It was found that the properties of TW were changed following the MF treatment, shown as the increase of evaporation amount, the decrease of specific heat and boiling point after magnetization, the changes depend on the magnetization effect. In addition, magnetic field strength (MFS) has a marked influence on the magnetization effect, the optimal magnetizing condition was determined as the MFS of 300 mT. The findings of this study offered a facile approach to improve cooling and power generation efficiency in industrial. Keywords: Magnetic field, Water, Specific heat, Evaporation, Boiling poin

A simple early warning method for large internal solitary waves in the northern South China Sea

Internal solitary waves (ISWs) are ubiquitous phenomena in many coastal oceans, especially the northern South China Sea (SCS). They can pose a serious threat to the deep-water drilling platforms and other ocean engineering structures. In this paper, we describe a simple and economical early warning method by estimating ISW propagation speeds using the measurements by a single acoustic Doppler current profiler (ADCP). This method is based on the Korteweg-de Vries (KdV) equation. As an example, a set of observational data collected by mooring buoys at the Liwan block (19-20 degrees N,115-116 degrees E) of the northern SCS are used to calculate the propagation speeds and directions of measured ISWs. The accuracy of estimated ISW propagation speeds is also tested by tracking the signals of ISWs using two ADCP moorings and it is found that the prediction deviation is less than 10%. The force and torque exerted by an ISW on a semisubmersible drilling platform are also estimated according to Morison's equation and other empirical formulas, which can provide a reference for safety controls on offshore platforms. (C)\ 2016 Elsevier Ltd. All rights reserved