Viscous Sediment Research Articles

Formal derivation and existence of global weak solutions of an energetically consistent viscous sedimentation model

The purpose of this paper is to derive a viscous sedimentation model from the Navier-Stokes system for incompressible flows with a free moving boundary. The derivation is based on the different properties of the fluids; thus, we perform a multiscale analysis in space and time, and a different asymptotic analysis to derive a system coupling two different models: the sediment transport equation for the lower layer and the shallow water model for the upper one. We finally prove the existence of global weak solutions in time for model containing some additional terms.

Ecological environmental flow estimation for rivers with complicated hydraulic conditions.

Estimating ecological environmental flow in tidal rivers is one of the major challenges for sustainable water resource management in estuaries and river basins. This paper presents an ecological environmental flow framework that was developed to accommodate highly dynamic medium tidal estuaries found along the Yellow Sea coast of China. The framework not only proposes a method of water quality-based ecological flow for tidal gate-controlled rivers but also proposes a method of water demand for scouring and silting to protect ports in coastal viscous sediment environments. The framework integrates the instream water requirements of water quality, sediment and basic ecological flow, and considers the temporal and spatial variation differences for the environmental flow requirements of tidal rivers. This study emphasizes the significance and necessity of continuous monitoring of ecological data in determining the environmental flow of tidal rivers. The output of this study could provide vital references for decision-making and management of the water resource allocation and ecological protection in tidal rivers.

Relative Energy Variation Characteristics Considering Interaction between Waves and Vegetation Structure

Although viscous sediment environments along the coast strongly attenuate waves, the attenuation dynamics and physical mechanism governing the attenuation process remain relatively unknown. Extremely complex interactions between muddy seabed have become increasingly important for wave evolution studies pertaining to coastal areas. The coastal protection function of mangroves was confirmed during the 2004 South Asian tsunami. Nevertheless, most research has been limited to macro-qualitative analyses, including those on variations in the transmission coefficient Kt and reflection coefficient Kr, and subsequent comparisons. However, determining the micro-physical characteristics is challenging, similar to coastal vegetation analyses with respect to mangrove vegetation characteristics. This study aims to quantify the attenuation difference in the wave energy owing to the coastal vegetation structure, under different layout conditions and combinations. Particle image velocimetry (PIV) technology is used to explore the variations in the velocity field and velocity distribution during the interaction process and calculate the wave-induced kinetic energy before and after setting up the vegetation structure. The research results emphasize that the resistance and frictional effects generated by vegetation are inversely proportional to the size of the stem, and the variation of kinetic energy determined from the velocity distribution and the thickness of the vegetation stem is mainly due to the larger frictional resistance of dense vegetation, relative to the fast flow velocity above the vegetation. Different vegetation heights slightly affect the short-period waves; however, the impact on energy reduction was smaller. For long-period waves, vegetation height significantly reduces wave kinetic energy.

Simulated and Experimental Study of Seabed Sediments Sampling Parameters Based on the VOF Method

Sediments in the seabed hold vital clues to the study of marine geology, microbial communities and history of ocean life, and the remote operated vehicle (ROV) mounted tubular sampling is an important way to obtain sediments. However, sampling in the seabed is a particularly difficult and complicated task due to the difficulty accessing deep water layers. The sampling is affected by the sampler’s structural parameters, operation parameters and the interaction between the sampling tube and sediments, which usually results in low volume and coring rate of sediments obtained. This paper simulated the soft viscous seabed sediments as non-Newtonian Herschel-Bulkley viscoplastic fluids and established a numerical model for the tubular sampling based on the volume of fluid (VOF) method. The influence rules of the sampling tube diameter, drainage area rate, penetration velocity, and sediments dynamic viscosity on coring rate and volume were studied. The results showed that coring volume was negatively correlated with all the parameters except the sampling tube diameter. Furthermore, coring rate decreased with increases in penetration velocity, drainage area rate, and sediments dynamic viscosity. The coring rate first increased and then decreased with increasing of the sampling tube diameter, and the peak value was also influenced by penetration velocity. Then, based on the numerical simulation results, an experimental sampling platform was set up and real-world sampling experiments were conducted. The simulation results tallied with the experimental results, with a maximum absolute error of only 4.6%, which verified that the numerical simulation model accurately reflected real-world sampling. The findings in this paper can provide a theoretical basis for facilitating the optimal design of the geometric structure of the seabed sediments samplers and the parameters in the sampling process.

Water–sediment separation efficiency prediction of gill-piece separation device

Abstract As the key piece of equipment of a micro-irrigation system, the filter can prevent clogging of the emitter and ensure normal operation of the micro-irrigation system. A gill-piece separation device is used for the removal of viscous sediment, which helps to reduce the sediment concentration and decrease the burden on the filter. In this study, using the water–sediment separation efficiency as an evaluation index, a uniform orthogonal experiment was conducted to study the flow rate, sediment concentration, and gill-piece spacing using a physical model. Based on the experimental results of the physical model, multiple linear regression and projection pursuit regression were used for analysis. The results showed that the order of the factors affecting the water–sediment separation efficiency was as follows: flow rate at muddy water inlet > gill-piece spacing > sediment concentration. The correlation coefficients of the water–sediment separation efficiency models established using multiple linear regression and projection pursuit regression were 0.93 and 0.98, respectively. Both models could predict the water–sediment separation efficiency and determine the optimal working conditions of the gill-piece separation device.

On the Existence of Global Weak Solutions to 1D Sediment Transport Model

This paper is devoted to the study of the existence of weak solution in time with a periodic domain of sediment transport model. We consider a one-dimensional viscous sediment transport model which combines a viscous Shallow-Water system with a transport equation that describes the bottom evolution. The model studied does not take into account all the regularizing terms used by Roamba Brahima, Zongo Yacouba and Jean de Dieu Zabsonré (2017) and we use a better transport equation than that used by Zabsonré (2012).

Grain-Size Composition of Bottom Sediments of the Simmy River in the Bolon Nature Reserve

The composition of bottom sediments in the Simmy River (the Amur River tributary, the Bolon Nature Reserve, Khabarovsk krai, Russia) was studied using laser diffractometry, sedimentation analysis, and electron microscopy. It was found that the grain-size composition of sediments from the area treated was mainly constituted by small-size grains and characterized by the accumulation of fine sand which conformed to lacustrine–alluvial genesis of the territory. The sediments in the near-mouth area were mainly formed by particulate alluvium with prevailing silty fraction. The definitive effect on the composition of sediments is exerted by hydrological conditions of Lake Bolon receiving the riverine waters: the variations in the lake water level conform to those in the Amur River. It was shown that the coagulation and precipitation of suspended solids at low content of organic matter (below 1%) resulted in the appearance of volume-aggregated dense and viscous sediments. A higher content of organic matter (>6% in the Kirpu tributary of the Simmy River) caused the “nodal” differentiation of volume-aggregated spatial structures to form porous microaggregates.

Laboratory study on response of underwater cohesive sediment to columnar vibration source

Abstract This paper investigates the responses of cohesive sediment to mechanical vibration by experimental observation, containing: (1) the dynamic soil pressure, dynamic pore water pressure and dynamic acceleration to the vibration source; (2) the soil pressure distribution in the near field centered in an artificial columnar vibration source. Under the mechanical vibration with a frequency of 200 Hz and an amplitude of 1.15 mm, the dynamic soil pressure, dynamic pore water pressure and dynamic acceleration of underwater viscous sediment were measured in the sediment of four different depositing conditions. Results of the dynamic soil pressure, dynamic pore water pressure and dynamic acceleration of underwater viscous sediment in the near field responding to artificial vibration source are exhibited and discussed. It is found that, excited by the sinusoidal vibrator, the soil pressure presents a response of statistical sinusoidal fluctuation with the same frequency to the vibration source. In the sediment of lower initial yield stresses, the soil pressure distribution distinctly tends to firstly increase and then decrease with distance. The amplitude of the soil pressure is attenuated exponentially with distance.

Dimensions and conformations of macromolecules of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride in solutions in a wide interval of ionic strength

Fractions of the copolymer of N-methyl-N-vinylacetamide and N-methyl-N-vinylamine hydrochloride containing 15.7 ± 0.5% of charged units are obtained by radical polymerization, fractionation, and hydrolysis. Viscous flow, velocity sedimentation, and translational diffusion of their dilute solutions are studied in 0.2 M NaCl. Viscosimetric studies are also carried out in a wide range of ionic forces: from the minimum (~10–6 mol/L) to the maximum (6 mol/L). The hydrodynamic volumes and equilibrium rigidity of the copolymer under study are compared with the data obtained earlier for an uncharged homopolymer and a copolymer with a higher linear charge density (~44% of charged units) in solutions with different ionic strength. The correspondence of the values obtained to the theories of Odijk, Skolnik, and Fixman (OSF) as well as Dobrynin is discussed.

Hydrodynamic boundary layer at a rising air bubble and entrapment of fine solids: Gravity effects on particle–bubble interactions

ABSTRACTA model study of the dynamic interactions of fine non-neutrally buoyant solids with background boundary layer (BL) flow on rising bubbles is developed. The aim is to clarify the specific role of the gravity effects. The approach is based on the acquisition of asymptotic equations about the disturbed flow field in the particle vicinity and accounts for both viscous deformation and sedimentation effects. It is established that two particle density regions are of major interest. In Region I the coupling of hydrodynamic and gravity effects results in granulometric separation of the solids. In Region II the role of particle sedimentation dominates over the purely hydrodynamic interactions. As a result, the lighter the particles are, and the smaller their sizes are, the more important is the granulometric effect inside the BL. For high-density fines and larger bubbles, the gravity effects couple with the BL flow. The particle capture results in significant amplification of the collision chances. The obtained results are expected to refine the approach to recovery of fine species from ground materials in conventional flotation and should be taken into account in the assessment of the overall capture efficiency for fine particles in microflotation and separation processes.

Particle organization after viscous sedimentation in tilted containers

A series of sedimentation experiments and numerical simulations have been conducted to understand the factors that control the final angle of a static sediment layer formed by quasi-monodisperse particles settling in an inclined container. The set of experiments includes several combinations of fluid viscosity, container angle, and solids concentration. A comparison between the experiments and a set of two-dimensional numerical simulations shows that the physical mechanism responsible for the energy dissipation in the system is the collision between the particles. The results provide new insights into the mechanism that sets the morphology of the sediment layer formed by the settling of quasi-monodisperse particles onto the bottom of an inclined container. Tracking the interface between the suspension solids and the clear fluid zone reveals that the final angle adopted by the sediment layer shows strong dependencies on the initial particle concentration and the container inclination, but not the fluid viscosity. It is concluded that (1) the hindrance function plays an important role on the sediment bed angle, (2) the relation between the friction effect and the slope may be explained as a quasi-linear function of the projected velocity along the container bottom, and (3) prior to the end of settling there is a significant interparticle interaction through the fluid affecting to the final bed organization. We can express the sediment bed slope as a function of two dimensionless numbers, a version of the inertial number and the particle concentration. The present experiments confirm some previous results on the role of the interstitial fluid on low Stokes number flows of particulate matter.

Ecological desert environment suffers from industrial wastewater pollution in northwestern China

There is an increasing number of high-energy and waterconsumption industries locating in arid regions of China. In recent years a number of pollution incidents have occurred in these desert areas, damaging the desert ecosystem, in some cases irreparably. Using the Tengger Desert and Mu Us Desert as two cases in point, the serious situation of uninhibited discharge of industrial wastewater in desert regions is discussed. How can governments effectively environmentally protect fragile desert environments and at the same time sustainably develop these areas? The authors point out the vulnerability of the ecosystem in desert areas and the prerequisites to its protection that involve the immediate strengthening of supervision, reporting and enforcement of waste disposal from manufacturing and chemical industries. China is one of the countries that suffers from the most serious desertification in the world, with 2.622 million km land area having become desert, over 27 % of the national territorial area (Ministry of Land and Resources of the People’s Republic of China 2011). The local ecosystem in areas of desertification is fragile, mainly due to the low biodiversity, poor ability of self-regulation and simple community structure (Ma et al. 1998). More and more manufacturing and chemical plants were built and caused problems of groundwater overexploitation and excessive wastewater discharge, which led to the formation of a number of large sewage pools. In some incidents, the wastewater seeped into groundwater through a sand layer and led to the deterioration of groundwater quality and the death of plants. Currently, to control the wastewater discharge into deserts and restore their local ecosystems, there is an urgent need for the government to improve the regulations and their enforcement. In September 2014, The Beijing News (2014a, c) reported that several large wastewater pools had been detected in the hinterland of the Tengger Desert and Mu Us Desert. Tengger Desert is located between the Mount Helan and the Mount Yabulai in northwest China and the Mu Us Desert is located in the south part of the Ordos region in Inner Mongolia and adjacent with Shaanxi and Ningxia. These pools were factory-waste evaporation ponds that were improperly planned for the local chemical industry use (Caixin Online 2014a). All of the pools of wastewater, each of which is as large as a football field, are full of black chemical wastewater and give off a terrible smell. The wastewater accumulated in the pools and was left to evaporate. Thereafter, the viscous sediments at the bottom were dug out and buried directly in the desert without any treatment, which recontaminated the surrounding environment (The Beijing News 2014a). The pollution is not only making the ecosystem of the desert oasis breakdown, but also having a strong negative impact on the water security. According to some local herdsmen, many livestock have been moved away from this region because of the serious grassland deterioration and environmental pollution. The cases of chemical wastewater drainage and groundwater pollution in the Tengger Desert were reported in March 2014, but drew little attention from the local governments. To maintain the local fiscal revenue, the governments hid the truth of these events from the public using the excuse of insufficient supervision and became the shelters of the & Ming Dou dou_ming@163.com

Depth-integrated equation for hydro-acoustic waves with bottom damping

AbstractWe present a depth-integrated equation for the mechanics of generation, propagation and dissipation of low-frequency hydro-acoustic waves due to sudden bottom displacement in a weakly compressible ocean overlying a weakly compressible viscous sediment layer. The model is validated against a full 3D computational model. Physical properties of these waves are studied and compared with those for waves over a rigid sea bed, revealing changes in the frequency spectrum and modal peaks. The resulting model equation can be used for numerical prediction in large-scale domains, overcoming the computational difficulties of 3D models while taking into account the role of bottom dissipation on hydro-acoustic wave generation and propagation.

Discussion of Muddy Surface Settling of Xiaolangdi Reservoir

Sediment settling velocity is an important parameter in particle suspension and indispensable link of hyperconcentrated flow as well as basic theory support for efficient sediment transport of Xiaolangdi Reservoir. This paper has adopted current sediment sample in Xiaolangdi Reservoir to take still water settling experiment, observed carefully silt sediment distribution during different settling duration under various initial concentrations, analyzed common settling velocity calculation method, and adopted settling duration curve method as calculation method to obtain a constant settling velocity of free settling section. Typical settling velocity that is obtained from experiments makes supplement and fitness to settling velocity formula of the existing groups of sediment sample, amends the formula coefficient, further explore the settling characteristics and settling velocity of fine particle mixed viscous sediment with water concentration change, and meanwhile this paper researched settling distance impact on settling velocity, existing sediment group settling transition to mesh settling critical transition silt concentration of Xiaolangdi Reservoir.

Turbulent and viscous sediment transport – a numerical study

Abstract. Sediment transport is studied as a function of the grain to fluid density ratio using two phase numerical simulations based on a discrete element method (DEM) for particles coupled to a continuum Reynolds averaged description of hydrodynamics. At a density ratio close to unity (typically under water), sediment transport occurs in a thin layer at the surface of the static bed, and is called bed load. Steady, or "saturated" transport is reached when the fluid borne shear stress at the interface between the mobile grains and the static grains is reduced to its threshold value. The number of grains transported per unit surface therefore scales as the excess shear stress. However, the fluid velocity in the transport layer remains almost undisturbed so that the mean grain velocity scales with the shear velocity u*. At large density ratio (typically in air), the vertical velocities are large enough to make the transport layer wide and dilute. Sediment transport is then called saltation. In this case, particles are able to eject others when they collide with the granular bed. The number of grains transported per unit surface is selected by the balance between erosion and deposition and saturation is reached when one grain is statistically replaced by exactly one grain after a collision, which has the consequence that the mean grain velocity remains independent of u*. The influence of the density ratio is systematically studied to reveal the transition between these two transport regimes. Finally, for the subaqueous case, the grain Reynolds number is lowered to investigate the change from turbulent and viscous transport.

Modelling sediment resuspension in industrial tanks using SPH

The present paper uses the weakly compressible smoothed particle hydrodynamics (SPH) to model numerically the sediment suspension and the shear layer induced by rapid flows resulting in scouring of the sediment with two yield criteria based on the Mohr-Coulomb and Drucker-Prager formulations. To the best of the authors’ knowledge this is the first time that the two yield criteria have been rigorously assessed in SPH where they are both expressed in terms of Coulomb-type parameters. The sediment is treated as a pseudo-Newtonian fluid where two different conditions distinguish between the state of the sediment – either still or suspended- according to the yield criteria. A variable viscosity is used to depict accurately the suspension layer. The models have been implemented using the DualSPHysics code, an SPH solver capable of dealing with high deformations and free surface flows. Three validation cases have been used to assess the validity of the yield criteria. The still sediment/water case was used to investigate the stability of the interface and the interaction with the boundaries that produced acceptable results for both criteria. The global relative error in the still case was used to assess the yield behaviour of the solid phase with both models performing satisfactorily. It was shown that the Mohr-Coulomb criterion was more conservative in particle movement. The second validation case was the tangential flow between two co-rotating co-axial cylinders using an analytical solution to confirm the rheological behaviour of the viscous sediment. With this case it was shown that the variable viscosity of the Drucker-Prager is lower than the Mohr-Coulomb model making the sediment less viscous. Finally, the erosional dam break was used to visualize the scour induced by the fluid. Following on from the results of the previous test cases in terms of variable viscosity and interface interaction the scour predicted with the Drucker-Prager model was larger and closer to the experimental results with a larger and deeper shear layer capturing the dune and scour. The Mohr-Coulomb yield criterion appears to underpredict the scouring process in addition to a small lag in the toe front of the solid phase that may be accounted to the smaller shear layer of the sediment. A sensitivity analysis on the Coulomb parameters and a convergence study must be performed in order to assess any deviations from the results discussed herein.

PTV and PIV study of the motion of viscous drops in yield stress material

We report a study of the slow viscous sedimentation of viscous Newtonian drops in a viscoplastic domain comprised of low concentration Carbopol aqueous solution. The study applies visualization methods. Direct photography is used to track the drop settling speed. In steady sedimentation PTV (Particle Tracking Velocimetry) is applied to determine the boundary of the yield stress region around the drop, while PIV (Particle Image Velocimetry) techniques are employed for the quantitative description of the flow field within this region. In infinite domains, the study addresses undisturbed sedimentation of slow and fast moving single drops and a tracking of the coalescence process of a train of two drops. Maps of the flow structure and intensity within the yielded regions around the drops in these cases are provided. When the sedimentation occurs in the vicinity of an adjacent vertical glass wall the drop settling speed may be either enhanced or retarded depending on the proximity to the wall. It is shown that the motion is retarded when the yielded region boundary remain intact but is deformed toward the drop on the wall side. Whenever the yielded region achieves complete contact with the wall the drop speed is augmented and an apparent slip is evident at the wall.

Formation of Polymeric Toroidal-Spiral Particles

Compared to spherical matrices, particles with well-defined internal structure provide large surface to volume ratio and predictable release kinetics for the encapsulated payloads. We describe self-assembly of polymeric particles, whereby competitive kinetics of viscous sedimentation, diffusion, and cross-linking yield a controllable toroidal-spiral (T-S) structure. Precursor polymeric droplets are splashed through the surface of a less dense, miscible solution, after which viscous forces entrain the surrounding bulk solution into the sedimenting polymer drop to form T-S channels. The intricate structure forms because low interfacial tension between the two miscible solutions is dominated by viscous forces. The biocompatible polymer, poly(ethylene glycol) diacrylate (PEG-DA), is used to demonstrate the solidification of the T-S shapes at various configurational stages by UV-triggered cross-linking. The dimensions of the channels are controlled by Weber number during impact on the surface, and Reynolds number and viscosity ratio during subsequent sedimentation. We anticipate applications of the T-S particle in drug delivery, wherein diffusion through these T-S channels and the polymer matrix would offer parallel release pathways for molecules of different sizes. Polyphosphate, as a model macromolecule, is entrained in T-S particles during their formation. The in vitro release kinetics of polyphosphate from the T-S particles with various channel length and width is reported. In addition, self-assembly of T-S particles occurs in a single step under benign conditions for delicate macromolecules, and appears conducive to scaleup.

Testing a mathematical model of the electrodischarge effect on viscous sediments

This work describes the results of testing a mathematical model of the electrodischarge effect on viscous sediments. It is shown that the model can be used to describe the processes that occur in the discharge circuit and the spark channel during the discharge and the hydrodynamic processes in the well and perforated apertures under conditions of the electrodischarge demudding method.

AN ENERGETICALLY CONSISTENT VISCOUS SEDIMENTATION MODEL

In this paper we consider a two-dimensional viscous sedimentation model which is a viscous Shallow–Water system coupled with a diffusive equation that describes the evolution of the bottom. For this model, we prove the stability of weak solutions for periodic domains and give some numerical experiments. We also discuss around various discharge quantity choices.