Experimental study on three dimensional movements of particles Ⅰ Effects of particle diameter on velocity and concentration distributions

Based on the three Dimensional Particle Tracking Velocimetry （3D PTV） system, the characteristics of motion of particles with four different diameters were investigated under the steady flow conditions The longitudinal average velocity profiles of these particles were in accordance with Log-law, while the vertical and transverse velocities remained very low with minimal fluctuation. The time-average velocity of particles in the bed load layer was 8.50u., close to Bagnold＇s assumptionUn -60. The vertical concentration distribution of particles in the suspension region agreed with the Rouse equation. When the diameter of particles was relatively large, there existed an evident concentration gradient in the bed load layer.     

Using a Lagrangian model to estimate source regions of particles in sediment traps

A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED(Dynamique des Flux Atmosphériques en Méditerranée) station by tracking particles backwards from March 1 to August 31, 2001. The analysis suggests that source regions depend on the flow fields, the settling speed of the particles, and the deployment depths of the traps. Monthly variation is observed in the distribution patterns of source regions, which is caused by the currents. The source regions are located around the traps and up to hundreds of kilometers away. As the settling speed increases with the particle diameters, the distance to the source regions decreases. The vertical flux can be approximately estimated in 1D for the particles with diameters larger than 500 μm. Furthermore, traps moored at various depths at the DYFAMED can collect particles that originated from different regions in the Ligurian Sea.     

The settling of resuspended lake sediment related to physicochemical properties of particles of different sizes: Implication for environmental remediation

Sediment resuspension is an important way for shallow lake internal pollution to interact with the overlying water column,and the pollution risks are reasonably related to the retention of resuspended sediment particles in overlying water.In the current study,the settling of resuspended sediment particles was comprehensively investigated under different disturbances using five urban lake sediments.The results show that the particle size distributions of resuspended sediment from different lakes exhibited similar variations during settling with disturbance,although varied settling times were observed under static conditions.During settling with and without disturbance,sediment particle sizes were mainly within 8-63μm at the initial stage,and were<8μm in the later stages of settling.Based on these settling characteristics,the sediment particle size was divided into sand(>63μm),silt(8-63μm),and very fine silt and clay(<8μm)fractions.Kinetic analysis suggested that sediment settling for different particle sizes could be well described by the first-and second-order kinetic equations,especially when settling was disturbed(r²=0.727-0.999).The retention of resuspended sediment could be enhanced as particle sizes decreased and disturbance intensities increased.Furthermore,a water elutriation method was successfully optimized,with separation efficiencies of 56.1%-83%,to separate sediment particles into the defined three particle size fractions.The chemical compositions of sediment were found to change with different particle sizes.Typically,calcium tended to form large-size sediment,while the total contents of aluminum,iron,magnesium,and manganese showed significantly negative correlations with sediment particle sizes(p<0.01)and tended to distribute in small-size particles(e.g.,<8μm).Overall,the sediment particle size related settling dynamics and physicochemical properties suggested the necessity on determining the pollution of resuspended sediment at different particle sizes for restoration of shallow lakes.     

On the numerical analysis of bed-load transport of saltating grains

The focus of this paper is on the analysis of the influence of particles’ velocity distribution and their concentration on the sediment transport rate in bed-load from the Lagrangian perspective.Such aims are addressed by use of the relevant Lagrangian model of spherical saltating particles in which turbulence plays a significant role.The Monte Carlo approach is employed in the simulations to obtain the velocity and concentration of the saltating particles.Numerical simulations using two saltating particle models:(1) with;and(2) without particle-particle collisions are carried out.Based on the numerical results,we address the hypothesis that instead of averaged characteristics,the distributions of particles’ velocity and sediment concentration should be taken into account in the calculation of sediment transport rate.Moreover,our results also show that the interaction between particles during their collisions is the key for better understanding of the physics of sediment transport.All results are compared with well-known experimental formulae i.e.Meyer-Peter and Muller and Fernandez Luque and van Beek.     

Statistical Analysis on Depth Distribution Model of Earthquake Hypocenters

In order to improve reliability of probabilistic seismic hazard analysis, shallow earthquake (depth <70 km) data, recorded with orientation precision grades 1 and 2 by modern instrument and containing depth information after 1970, are selected as statistical samples, meanwhile, North China seismic region, Central China seismic region, South China seismic region, Xinjiang seismic region and Qinghai-Xizang Plateau seismic region are chosen as statistical units to study the depth distribution characteristics of shallow earthquakes. Considering the differences of depth distribution characteristics of earthquakes with different magnitudes, the following magnitude intervals are adopted to analyze earthquakes with different magnitude scales, respectively: M S=2.0～2.9, M S=3.0～3.9, M S=4.0～4.9, M S=5.0～5.9 and M S=6.0～6.9. The results show that hypocenter depths are normally distributed by and large around the mean depth of the corresponding seismic region. The probabilistic distribution curves of earthquake depth in West China are wider than those in East China. The probabilistic distribution deviation, σ, of West China is greater than those of East China, that is, earthquakes in West China have a wider range in terms of depth. There is also a tendency that the absolute value of mean hypocenter depth increases with the magnitude by and large.     

Measurements of coupled fluid and sediment motion over mobile sand dunes in a laboratory flume

The relationship between turbulent fluid motions and sediment particle motions over mobile sand dunes was investigated by using a laser Doppler velocimeter and an acoustic backscatter system in laboratory experiments performed at the USDA-ARS-National Sedimentation Laboratory. Profiles of acoustic backscatter from particles and at-a-point turbulence data were collected while translating both measurement devices downstream at the speed of mobile dune bedforms. The resulting data set was used to examine the frequency （recurrence frequency） at which the fluctuating backscatter and fluid velocity signals exceeded magnitude thresholds based on the standard deviation （σ） of the local velocity and the magnitude the acoustic signal resulting from backscatter from suspended particles. The slope of the downstream and vertical velocity recurrence frequencies generally indicated a gradually increasing recurrence time with increasing elevation. The recurrence frequency for acoustic backscatter data was not strongly variable with elevation. The closest correspondence between the recurrence frequencies of sediment backscatter and vertical velocities at the 1σ magnitude threshold was in a region defined by X/L〈0.4 and y〈6 cm. The downstream velocity was most closely related to backscatter in a small region at 0.4〈X/L〈0.8 and less than 3-4 cm from the bed.     

Magnitude and distance distribution of strong aftershocks in Sichuan-Yunnan region

Using the earthquake sequences data with MS≥6.5 since 1966 in Sichuan-Yunnan region, we research the charac-teristic of the magnitude difference distribution between main shocks and their strong aftershocks; and then study the spatial distribution characteristic of the strong aftershocks away from their main shocks. The result shows that the magnitude difference distribution obeys intercepted exponential distribution, while the spatial distribution of strong aftershocks obeys normal distribution and the dominated distribution area of strong shocks is 10~39 km away from main shock. Finally the probability density function of the magnitude difference distribution and the spatial distribution of strong aftershocks is deduced.     

Experimental Study of the Subsidence Characteristics of Clayey Loess

Presented in this paper are the results of experimental study and analysis of the subsidence characteristics obtained from soil samples with different contents of clay particles though laboratory dynamic triaxial test, Laser particle size analysis, chemical analysis and electronic microscope scanning. By comparison of the obtained data, the following conclusions are drawn out:(1)The stability of the loess varies with different content of clay; (2) The relation between the dynamic shear strength and the clay particles is not monotonous, but parabolic; (3) In the same consolidation ratio, the clayey loess is the weakest subsidence-resistant when the clay particle content is between 16%～17%.     

Probabilistic seismic hazard analysis in Nepal

The seismic ground motion hazard for Nepal has been estimated using a probabilistic approach. A catalogue of earthquakes has been compiled for Nepal and the surrounding region （latitude 26% N and 31.7% N and longitude 79° E and 90° E） from 1255 to 2011. The distribution of catalogued earthquakes, together with available geological and tectonic information were used to delineate twenty-three seismic source seismic source information and probabilistic earthquake hazard prediction relationship, peak ground accelerations （PGAs） have zones in Nepal and the surrounding region. By using the parameters in conjunction with a selected ground motion been calculated at bedrock level with 63%, 10%, and 2% probability of exceedance in 50 years. The estimated PGA values are in the range of 0.07-0.16 g, 0.21 0.62 g, and 0.38-1.1 g for 63%, 10%, and 2% probability of exceedance in 50 years, respectively. The resulting ground motion maps show different characteristics of PGA distribution, i.e., high hazard in the far-western and eastern sections, and low hazard in southern Nepal. The quantified PGA values at bedrock level provide information for microzonation studies in different parts of the country.     

Some Analyses on Effects of Site Classification on Ground Motion Characteristics in the Chi-Chi, Taiwan Earthquake

According to the epicenter distance and the site classification, the 404 groups of earthquake recordings of the main shock of the Chi-Chi, Taiwan China earthquake in 1999 are catalogued. Based on these data, we analyze the statistical features of duration, PGA, envelopes and the response spectra ratio of the horizontal and vertical components of the acceleration recordings. The results of these analyses show that the effect of site classification on the acceleration of various components is obvious; furthermore, fault direction also has certain effects on the characteristics of the horizontal components of ground motion. The detailed research results are as follows： （ 1 ） the duration of the horizontal components of acceleration records increases with the softening of the site; （2） the direction of fault slip has some effects on PGA＇s attenuation features; （3） the average envelopes of acceleration records at different distances and site dames are basically single peak functions of time and the envelopes of horizontal and vertical components of ground motion are obviously different; （4） with the same epicenter distance, EW/NS response spectrum ratios tend to approximate 1.0 as the site becomes softer and the period shorter. V/H response spectrum ratios in short periods （〈 0. 1s） increase with the softening of site, however, V/H ratios within the long-period range （ 〉 characteristic period） decrease with the softening of the site, and the decrease of V/EW ratio speeds up relatively.     

Variation of Seismic Frequency in the Yunnan Region After the Indonesia Earthquake With Ms8.7

The seismic frequency increased significantly in the Yunnan region after the Indonesia earthquake with M_S8.7 on December 26, 2004. This was estimated by analyzing the seismic frequency ratio between the influenced and normal times, the spatial distribution characteristics of the increased seismic frequency, the temporal-spatial distribution and types of seismic swarms. Seismic frequency increased at 71.3% of the statistical sites in the Yunnan area. The maximal increase ratio is 18.2.     

Characteristics of energy dissipation in hyperconcentrated flows

An equilibrium equation for the turbulence energy in of solid-liquid two-phase flow theory. The equation sediment-laden flows was derived on the basis was simplified for two-dimensional, uniform, steady and fully developed turbulent hyperconcentrated flows. An energy efficiency coefficient of suspended-load motion was obtained from the turbulence energy equation, which is defined as the ratio of the sediment suspension energy to the turbulence energy of the sediment-laden flows. Laboratory experiments were conducted to investigate the characteristics of energy dissipation in hyperconcentrated flows. A total of 115 experimental runs were carried out, comprising 70 runs with natural sediments and 45 runs with cinder powder. Effects of sediment concentration on sediment suspension energy and flow resistance were analyzed and the relation between the energy efficiency coefficient of suspended-load motion and sediment concentration was established on the basis of experimental data. Furthermore, the characteristics of energy dissipation in hyperconcentrated flows were identified and described. It was found that the high sediment concentration does not increase the energy dissipation; on the contrary, it decreases flow resistance.     

Ergodicity of turbulence measurements upon complex terrain in Loess Plateau

To display the distribution characteristics of turbulence eddy under condition of complex terrain in Loess Plateau,and to enhance the precision of turbulence measurements,the research of turbulence ergodicity is considered to be the prior section of the experiment.With the statistics of single-site turbulence measurements obtained in Baimiao Tableland,Ping Liang,Gan Su,analysis result shows that not only the turbulence with scale less than 10 min,which can easily satisfy the ergodicity,the tableland terrain can also be a major cause of the coherent structure of periodic,large-scale turbulence;compared to which for the turbulence above the flat underlying surface,the distribution of 10–40 min,large-scale turbulence in the tableland region tends to be more steady and,thus,can also satisfy the ergodicity easily.Under the condition of extremely unstable stratification,the wind is comparatively low in speed and features distinctly large-scale,periodical fluctuation,and with the trend of smooth increase in temperature,large-scale wind turbulence and temperature turbulence both tend to satisfy ergodicity.In comparison,under the condition of extremely stable stratification,the aperiodicity of large-scale wind turbulence and temperature turbulence caused by intermittency is comparatively strong,and the turbulence cannot satisfy ergodicity easily.     

Effect of self-weight consolidation on a hydro-sedimentological model for the Río de la Plata estuary

The effect of the consolidation process on the morphodynamics and fine sediment dynamics of the Río de la Plata estuary is explored through a circulation-wave-sediment transport model. The consolidation model is calibrated based on settling column experimental data. Different simulations are done in order to initialize the mud layer distribution and to investigate the impact of different erosion parameter assumptions on the modeled sediment dynamics. Finally a two-year simulation is done with and without the consolidation process and realistic hydrodynamic forcings. Considering the consolidation process, the model correctly reproduces measured vertical density profiles in the Montevideo Bay access channel. The simulated suspended sediment dynamics behavior in Montevideo Bay with the consolidation process provides a more realistic deposition pattern in regard to the dredging activities.     

The effects of vertical viscosity coefficients with different distribution characteristics on classical Ekman spiral structure

The classical Ekman theory tells us that the ocean surface current turns to the right(left) side of wind direction with 45° in the north(south) hemisphere,but the observation and research results show that the surface current deflexion angle is smaller than 45° in the Arctic and high latitude areas while larger than 45° in the low latitude areas.In order to explain these phenomena,a series of idealized numerical experiments are designed to investigate the influence of vertical viscosity coefficients with different vertical distribution characteristics on the classical and steady Ekman spiral structure.Results show that when the vertical viscosity coefficient decreases with water depth,the surface current deflexion angle is larger than 45°,whereas the angle is smaller than 45° when the vertical viscosity coefficient increases with water depth.So the different observed surface current deflexion angles in low latitude sea areas and the Arctic regions should be attributed to the different vertical distribution characteristics of vertical viscosity coefficients in the upper ocean.The flatness of the Ekman spiral is not equal to one and does not show regular behaviors for the numerical experiments with different distribution of vertical viscosity.However,the magnitudes and directions of volume transport of Ekman spirals are almost the same as the results of classical Ekman theory,i.e.,vertical viscosity coefficient distributions have no effect on the magnitudes and directions of volume transport.     

The Relationship Between Strong Earthquake Activity of Ms≥ 7.0 on the Chinese Mainland and the West Kunlun-A＇nye^maqe^n Secondary Arcuate Tectonic Zone

The active and quiet phenomenon of moderate strong earthquakes one year before the earthquakes with Ms ≥ 7.0, the spatial distribution characteristics of the solid tide modulating and triggering earthquakes and the strong earthquake mechanisms on the Chinese continent have been studied. The secondary arcuate tectonic zone composed of the west Kunlun-A‘nye^maqe^n faults is believed to be a very important boundary to characterize strong earthquake activity of Ms ≥ 7.0 on the Chinese continent, that is, a boundary between the seismically active region and the quiet region of moderately strong earthquakes one year before earthquakes with Ms ≥ 7.0, and a boundary of the spatial distributions between the solid tidemodulating strong earthquakes ( Ms ≥ 7.0) and the non-modulating ones. It might be related with the characteristics of spatial distribution of focal mechanism solutions of strong earthquakes on the Chinese Continent.     

Ionospheric perturbations before Pu’er earthquake observed on DEMETER

A destructive shock with magnitude of 6.3 occurred on 2 June 2007 at 21h34min56s UT in Pu’er region (23.0°N, 101.1°E), Yunnan Province, China. The data from DEMETER satellite during the period from 23 May to 2 June, i.e., ten days before the earthquake and one day just on the day of earthquake occurrence, were analyzed. Among the 284 orbits of DEMETER during the period, 29 orbits with the trace passing through the region within 1 888 km from the epicenter were selected to be studied. Seven anomalous events were found on the dataset of the seven orbits among the 29 ones. There existed synchronous perturbations on the variations of the spectrogram of the electric field and the variations of the density and temperature of the ions and electron, in contrast with the variations of its surround- ing area. And five events appeared in the space within 1 888 km from the epicenter while the other two were out of the studied area. Electrostatic turbulences were also recorded with the synchronous perturbations with that in the electron density and ions density in plasma in the region near the epicenter in the five events, which seems to sug- gest that there be some physical relation between these events and the preparation processes of Pu’er earthquake.     

A holistic computational model for prediction of clay suspension structure

The formation of clay suspensions involves complex interactions among clay particles subjected to the geochemical environment during the sedimentation process. The structural characteristics have a major influence on the physical and mechanical behavior of the suspension. A modeling framework involving a Discrete Element Method (DEM) model with customized particle mechanical interactions is proposed in this paper for the holistic prediction of the physical structure of clay suspensions. The particle interaction force model is based on the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory that accounts for electrostatic repulsion, van der Waals attraction, contact repulsion, etc. Kaolinite is used as the model clay to demonstrate the model performance. The surface charge density of kaolinite is obtained through Atomic Force Microscope (AFM) force measurement and is implemented in the particle interaction force model in the subsequent simulations. Influencing factors, such as centrifugal acceleration, ionic concentration, platy structure of particles, and particle size, on the formation of kaolinite suspensions are studied with the numerical model and compare favorably well with the experimental data. This work lays down a unique framework consisting of computational modeling and microscale characterization of clay particles to holistically predict the characteristics of clay suspensions, which paves the basis to model and predict their bulk physical and mechanical behavior.     

Mineral composition and particle size distribution of river sediment and loess in the middle and lower Yellow River

Hyperconcentrated flows often occur in the middle and lower Yellow River(MLYR)and its tributaries,within which the main sediment source originates from the Loess Plateau of China due to serious water erosion.Little is known about the properties of river sediment that is transported by hyperconcentrated flows,particularly with respect to the mineral composition and size distribution.Samples of sediment and loess were collected in the northern,middle,and southern Loess Plateau and the mainstream and tributaries of the MLYR.A total of 18 loess samples and 24 river sediment samples were analyzed to determine their sediment size distribution and mineral composition.The bottom loess samples reflected the original sedimentary features of the Loess Plateau,and the median particle size reduced,and the clay content increased from the north to the south of the study region.The surface loess has been weathered under the action of wind and rainfall,and the clay particle content in the surface loess samples was higher than that in the undisturbed bottom loess.Erosion of the surface soil due to rainfall and surface runoff means that fine particles(mostly clay)have been washed away.The median diameter of surface loess particles was a little larger than that of the bottom loess particles where water erosion dominates.The particle size became coarser with increasing distance from the estuary in the MLYR,which reflects depositional sorting in the river channel.Significant logarithmic relations were found between the median diameter of the sediment particles and the i)non-clay mineral content and ii)clay mineral content.Thus,clay and non-clay mineral compositions can be conveniently estimated from the particle size distribution.     

Effect of sediment particles on the velocity profile of sediment-water mixtures in open-channel flow

The presence of sediment particles in open-channel flow has an important effect on turbulence; thus, an empirical, turbulent eddy viscosity formula was established for application in the limit for low concentrations. The current study establishes a theoretical relation for the mixture viscosity based on the two-phase mixture model. The percentage contribution of the three mechanisms of mixture viscosity,namely, fluid turbulence(FT), particle turbulence(PT), and inter-particle collisions(IPCs), w...