Numerical simulation of gravity current descending a slope into a linearly stratified environment.

yesThe accurate prediction of the dilution and motion of the produced denser water (e.g. discharge of concentrated brine generated during solution mining and desalination) is of importance for environmental protection. Boundary conditions and ambient stratification can significantly affect the dilution and motion of gravity currents. In this study, a multiphase model is applied to simulate the gravity current descending a slope into a linearly stratified ambient. The k- turbulence model is used to better simulate the near bed motion. The mathematical model, initial and boundary conditions and the details of the numerical scheme are described. The time-dependent evolution of the gravity current, the flow thickness and the velocity and density field are simulated for a range of flow parameters. Simulations show that the Kelvin–Helmholtz billows are generated at the top of trailing fluid by the interfacial velocity shear. The K-H type instability becomes weaker with the slope distance from the source due to the decrease of the interfacial velocity shear along slope. The ambient stratification restricts and decreases the current head velocity as it descends slope, which differs from the situation in homogenous ambient while the head velocity remains an approximately steady state. Motion of the descending flow into the stratified ambient has two stages: initial acceleration and deceleration at later stage based on the balance of inertial, buoyancy and friction forces. When the descending current approaches the initial neutral position at later stage, it separates from the slope and spreads horizontally into environment. The simulated results, such as vertical velocity and density profiles and front positions, agree well with the measurements, indicating that the mathematical model can be successfully applied to simulate the effect of the boundary condition and ambient stratification on the dilution and propagation of gravity currents.UK EPSR

Correlation between flood frequency and geomorphologic complexity of river network -A case study of Hangzhou China

yesUrban flooding is a combined product of the climate and watershed geomorphology. River system is one of the vital components of watershed geomorphology. The geomorphic characteristics of rivers have important effect on the formation of flooding. However, there have been few attempts so far to investigate the relationship between flooding frequency, the probability of flooding, and the geomorphological complexity of river system. Such relationship is essential in order to predict likely responses of flooding frequency to the large-scale changes in the complexity of the river networks induced by accelerating urbanization around river. In this study we investigate the correlation between geomorphological characteristics of river system and the probability of flooding. Hangzhou city in China, which has suffered severe flooding, is chosen as a case study to evaluate this correlation and to investigate the impact of changes of drainage networks morphology on the local flooding. The fractal dimension, which is used to quantitatively assess geomorphological complexity of river network, is calculated by using box-counting method based on fractal geometry for eight sub river networks in Hangzhou. A model based on the correlation of flooding frequency and fractal dimension is established. The model is applied to investigate the effect of the rapid urbanization induced changes of river geomorphology on the local flood frequency in two typical regions in Hangzhou. The results show that the flood frequency/events increases with the decrease of fractal dimension of the river network, indicating that the geomorphologic complexity of river network has an important effect on flooding. This research has great referential value for future flood quantitative investigation and provides new method for urban flood control and river system protection.Key Scientific and Technical Project of Water Conservancy of Zhejiang Province (Grant No: RB1401

Modelling of sediment transport and bed deformation in rivers with continuous bends

Peer reviewedPostprin

Numerical simulation of the spreading of aerated and nonaerated turbulent water jet in a tank with finite water depth

YesNumerical simulations are carried out to investigate the spreading of two-dimensional plane turbulent aerated and nonaerated jets in a tank filled with finite water depth. A multiphase model is applied to simulate the problem under investigation. The governing equations, their numerical scheme and the boundary conditions are presented. Aerated and non-aerated turbulent jets are simulated for a range of the jet velocity and width at exit, the initial air content at exit and the water depth in tank. The simulated results show that a self-similar Gaussian velocity distribution exists from the distance downstream being larger than five jet slot width for both the aerated and nonaerated jets. Good agreement between the simulated velocity profiles and available laboratory experiments is obtained. The simulated slope of the jet velocity decay along the jet centreline is in good agreement with the experimental measurements. The effect of air content on pressure distribution and the maximum impinging hydrodynamic pressure at the tank bottom is discussed.the Open Funding from the State Key Laboratory of Hydraulics and Mountain River Engineering, Sichuan University (SKHL1302

Investigation on scour scale of piggyback pipeline under wave conditions

YesLaboratory experiments are presented to investigate the effect of different piggyback pipeline configurations on the morphology of local scour under wave conditions. Scour depth and width around the pipelines under regular and irregular waves are measured and analyzed for a range of pipeline and wave conditions; such as the spacing between two pipes (G), gap between the main pipe and seabed (e), pipe diameter (D), wave height (H) and period (T). Experimental results reveal that both the scour depth and width around piggyback pipeline is much larger than those around single pipe under the same wave conditions. Scour depth increases with the increase of the Keulegan-Carpenter (KC) number and decreases with increase of G and e. When e exceeds 0.5D, scour depth tends to approach 0.When spacing G is greater than 0.4D, the destabilization from small pipe to large one is greatly reduced, resulting in scour depth around piggyback pipeline being close to that around single pipe. Similar to scour depth, scour width broadens with the increase of KC number increasing and decreases with the increase of G. Experiments also show that the effect of e on scour depth is greater than that of G under the same test conditions, while their impact on scour width is opposite. Furthermore, scour width under irregular waves is extended slightly compared with regular wave for otherwise the identical conditions.National Natural Science Foundation (No. 51279189)

An investigation of key factors that influence employee motivation: A comparative study between male and female employees in Chinese Internet industry

Recently, as the concept of sustainable development has been advocated, gender equality as an important issue of sustainable development has also been widely discussed. Thus, the underrepresentation of women in the Chinese Internet industry has again aroused concern. Meanwhile, the demand for high-quality talents is increasing due to the rapid development of the industry. In this context, this study aims to explore the factors that influence employee motivation in the Chinese Internet industry and to compare some differences between men and women in influencing factors to provide some insights to address the current challenges of gender equality and talent management in the Chinese Internet industry. The researcher collected data by using the questionnaire survey in the Chinese Internet industry, and received 246 valid responses. Finally, the data were processed through statistical analysis. It was found that recognition, job autonomy, and task significance have a positive and significant effect on the motivation of employees in the Chinese Internet industry. Among them, recognition, job autonomy and task significance are the key factors that influence female employees’ motivation, while recognition and task significance are the key factors that influence male employees’ motivation. What is noteworthy is that recognition is the factor that has the greatest influence on their motivation, regardless of whether they are male or female. However, in terms of the degree of influence, the influence degree of recognition on male motivation is slightly greater than that of recognition on female motivation. There is no significant difference in the influence degree of task significance on male and female motivation

An investigation of key factors that influence employee motivation: A comparative study between male and female employees in Chinese Internet industry

Recently, as the concept of sustainable development has been advocated, gender equality as an important issue of sustainable development has also been widely discussed. Thus, the underrepresentation of women in the Chinese Internet industry has again aroused concern. Meanwhile, the demand for high-quality talents is increasing due to the rapid development of the industry. In this context, this study aims to explore the factors that influence employee motivation in the Chinese Internet industry and to compare some differences between men and women in influencing factors to provide some insights to address the current challenges of gender equality and talent management in the Chinese Internet industry. The researcher collected data by using the questionnaire survey in the Chinese Internet industry, and received 246 valid responses. Finally, the data were processed through statistical analysis. It was found that recognition, job autonomy, and task significance have a positive and significant effect on the motivation of employees in the Chinese Internet industry. Among them, recognition, job autonomy and task significance are the key factors that influence female employees’ motivation, while recognition and task significance are the key factors that influence male employees’ motivation. What is noteworthy is that recognition is the factor that has the greatest influence on their motivation, regardless of whether they are male or female. However, in terms of the degree of influence, the influence degree of recognition on male motivation is slightly greater than that of recognition on female motivation. There is no significant difference in the influence degree of task significance on male and female motivation

Free surface air entrainment and single-bubble movement in supercritical open-channel flow

YesThere has been little study on the microscopic bubble entrainment and diffusion process on the high-speed self-aerated flows although the problem under investigation is theoretically important and has important engineering application. This study presents an experimental investigation on visual processes of free surface air entrainment and single bubble diffusion in supercritical open channel flows. The typical surface deformation, single air bubble rising and penetration are recorded using a high-speed camera system. Results show that for a single bubble formation process, surface entrapment development and bubble entrainment through a deformation evolution underneath the free surface are the two main features. The shape variation of local surface deformation with time follows an identical power law for different bubble size generations. The entrained bubble size depends on both size scale and shape of entrapped free surface. As the single bubble moves downstream, its longitudinal velocity is approximately the same as that of water flow surrounded it, while its vertical velocity for rising and penetration increases with the increase of the water flow velocity. An empirical-linear relationship for the bubble rising and penetration velocity with water flow velocity is obtained. This study demonstrates that the microscopic bubble movement can improve the self-aeration prediction in the open channel flow and advance the knowledge of our understanding of the macroscopic and microscopic air–water properties in hydraulic engineering.National Natural Science Foundation of China (Grant number 51609162), Sichuan Science and Technology Program (Grant number 2019JDTD0007) and the Open funding of the State Key Laboratory of Hydraulics and Mountain River Engineering of Sichuan University (Project No: Skhl1809)