Zhilin Sun

Method of Taylor Expansion Moment Incorporating Fractal Theories for Brownian Coagulation of Fine Particles

Abstract Fine particles aggregating into larger units or flocculation body is a random combination process. Increasing the size and density of flocculation body is the main approach to rapid particle removal or sedimentation in water. Aiming at the Brownian coagulation of fine particles, a new method of Taylor expansion moment construction of fractal flocs has been developed in this paper, incorporating the Taylor expansion approach based on the moment method and the fractal dimension of the floc structure originated from fractal theories. This method successfully overcomes the limit of previous moment methods that require pre-assumed particle size distribution. Results of the zero and second order moments of Brownian flocs from the proposed method are compared with those from the Laguerre method, integral moment method and finite element method. It is found that the higher accuracy and efficiency of computation have been achieved by the new method, compared to the previous ones. Effects of the fractal dimension on the zero and second order moments, geometric average volume and standard deviation are also analyzed using this method. The self-conservation characteristics of particle distribution is observed without presumption of initial distributions.

Large eddy simulation of sediment-laden turbulent flow in an open channel

Sediment transport in fully developed turbulent open channel flow has been investigated using large eddy simulation (LES) of the incompressible Navier–Stokes equations. The scalar transport equation of the sediments concentration, which is based on the continuous-phase approach, is adopted. The settling process is taken into account with a modified settling velocity appearing in the sediment concentration equation. A Smagorinsky model allowing for the interaction between the fluid flow and the suspended sediment is used to simulate the unresolved, subgrid scale terms. The LES results are compared with the experimental data, and good general agreement is achieved.

Hydraulic Features of Air-Water Mixture Flow on a Staircase with Rest Platforms

AbstractTo investigate hydraulic features of the flooding flow on a staircase with a rest platform, experiments were conducted on a 1:2-scale physical model of a staircase with a middle rest platform between two stair segments. The transition or skimming flow occurring on the first segment is similar to that on a stepped chute. However, a jet flow forms immediately downstream of the rest platform, followed by a redeveloping transition flow on the second segment. The measured profiles of air concentrations in those flow regions agree well with that in the skimming and transition flow known from stepped spillways. The amount of air entrained into the free-falling jet increases dramatically because of a higher air concentration in the approaching flow. Rapid rises of the air-water mixture depth and the flow velocity in part of the jet and the transition flow downstream were observed. These features could affect human maneuverability on a flooding staircase with rest platform(s) and make it more difficult for...

Effects of Sea Level Rise on Coastal Reclamation Projects in Jiaojiang Estuary, China

ABSTRACT Sun, Z.; Nie, H.; Huang, S.; Huang, S.; Huang, W.; Zhu, L., and Gao, Y., 2014. Effects of sea level rise on coastal reclamation projects in Jiaojiang estuary, China. In this paper, a series of numerical simulations are carried out to investigate the storm tide characteristics in Jiaojiang estuary and nearshore areas after the proposed cluster reclamation project (from 2011 to 2023) and in different amplitude of sea level rise (SLR) during TC9711 (tropical cyclone Winnie). Special attention is paid on the variations of tidal levels at different locations. Due to reclamation project, It can be found that the maximum tidal levels significantly increase along Niutou Necking-Shanjiaopu section, both banks inside estuary entrance, northern Toumen Harbor and in harbor basin. On the contrary, tidal levels along northern Toumen Harbor, Puba Harbor and southern bank outside entrance decrease clearly. Meanwhile, study on influence of SLR at Haimen Station indicates that impacts of SLR on tidal levels increase as SLR increment grows, appear as periodic variation with the same cycle of tide and bring about maximum variation of tidal levels of 0.382 m and −0.339 m for SLR at 0.6 m. Moreover, investigation of influence of SLR on maximum tidal levels reveals that the maximum tidal levels in domain generally decrease as SLR increases, but those will increase significantly for SLR of 0.03 m and 0.15 m along Sanjiangkou and Niutou Necking. The results are helpful to provide constructive references for disaster prevention and reduction in process of design, construction and completion of reclamation.

Numerical Study on Flow around Four Square-Arranged Cylinders at Low Reynolds Numbers

In this paper, numerical simulations of flow past four square-arranged cylinders are carried out at different spacing ratios ( ; is the center to center distance; is the cylinder diameter) and Reynolds numbers . The effects of spacing ratio and Reynolds number on the wake flow characteristics are investigated, such as the instantaneous vorticity contours, force coefficients, and vortex shedding frequencies. The results show that the flow characteristics behind the four-cylinder cases are significantly affected by the spacing ratios and Reynolds numbers. At the same spacing ratio, the transformation of flow pattern is advanced quickly with increasing of Reynolds numbers, the values of force coefficients are correspondingly fluctuated with large amplitude, and the vortex shedding frequency is increased significantly with .

Stability of jets in a shallow water layer

Purpose – The present work is devoted to the numerical study of the stability of shallow jet. The effects of important parameters on the stability behavior for large scale shallow jets are considered and investigated. Connections between the stability theory and observed features reported in the literature are emphasized. The paper aims to discuss these issues. Design/methodology/approach – A linear stability analysis of shallow jet incorporating the effects of bottom topography, bed friction and viscosity has been carried out by using the shallow water stability equation derived from the depth averaged shallow water equations in conjunction with both Chezy and Manning resistance formulae. Effects of the following main factors on the stability of shallow water jets are examined: Rossby number, bottom friction number, Reynolds number, topographic parameters, base velocity profile and resistance model. Special attention has been paid to the Coriolis effects on the jet stability by limiting the rotation numb...