Settlement and Consolidation Mechanism of Cohesive Sedimentation in Estuarine Environment

2011 ◽  
Vol 261-263 ◽  
pp. 1454-1458
Author(s):  
Shuai Jie Guo ◽  
Bao Tian Wang ◽  
Fu Hai Zhang ◽  
Liang Chen
Keyword(s):  
Volume Fraction ◽  
River Estuary ◽  
Column Experiment ◽  
Cohesive Sediment ◽  
Sediment Deposition ◽  
Whole Process ◽  
Sediment Consolidation ◽  
Consolidation Coefficient ◽  
Fraction Distribution ◽  
Theory Equation

Estuarine area is the intersection zone of river estuary, coastal and land-phase. Cohesive sediment deposition for mutation affects estuary channel transport and brings great challenges to dredging project. Consolidation indicators are closely related to sedimentation and dredging, and there are apparent errors in application of Terzaghi theory in cohesive sediment consolidation evaluation for large stain characteristics. Then it is necessary to modify some consolidation parameters to extend Terzaghi theory in cohesive sediment consolidation. Considering a whole process of sedimentation and consolidation, a unified equation can be established based on sediment deposition and consolidation theory. Equation parameters can be determined by the simulation test (settlement column experiment). According to the settlement curves and volume fraction distribution curves by simulation experiment, modified consolidation coefficient and the trends can be determined, and modified consolidation coefficient can apply in dredging and deposition project.

scholarly journals Drainage of soft cohesive sediment with and without <i>Phragmites australis</i> as an ecological engineer

2019 ◽  
Author(s):  
Rémon M. Saaltink ◽  
Maria Barciela-Rial ◽  
Thijs van Kessel ◽  
Stefan C. Dekker ◽  
Hugo J. de Boer ◽  
...  
Keyword(s):  
Phragmites Australis ◽  
Water Loss ◽  
Column Experiment ◽  
Predictive Modelling ◽  
Bare Soil ◽  
Cohesive Sediment ◽  
Ecological Engineer ◽  
Sediment Consolidation ◽  
Speed Up ◽  
Pore Pressure Gradient

Abstract. Conventional drainage techniques are often used to speed up consolidation of fine sediment. These techniques are relatively expensive, are invasive and often degrade the natural value of the ecosystem. This paper focusses on exploring an alternative approach that uses natural processes, rather than a technological solution, to speed up drainage of soft cohesive sediment. In a controlled column experiment, we studied how Phragmites australis can act as an ecological engineer that enhances drainage, thereby potentially promoting sediment consolidation. We measured the dynamics of pore water pressures at 10 cm depth intervals during a 129-day period in a column with and without plants, while the water level was fixed. Water loss via evaporation was measured using Mariotte bottles and the photosynthetic processes – including plant transpiration – were measured with a LICOR photosynthesis system. The results show that several processes initiated by P. australis interfere with the physical processes involved in sediment drainage and consolidation. Phragmites australis effectively altered the pore pressure gradient via water extraction, especially between 40 and 60 cm from the bottom of the column. In this zone, daily cycles in pore pressures were observed which could directly be linked to the diurnal cycle of stomatal gas exchange. On average, water loss via evaporation and transpiration of leaves of P. australis amounted to 3.9 mm day−1, whereas evaporation of bare soil amounted on average to 0.6 mm day−1. Moreover, the depth-averaged hydraulic conductivity increased on average by 40 % in presence of P. australis. The results presented in this study provide information needed for predictive modelling of plants as ecological engineers to speed up soil forming processes in the construction of wetlands with soft cohesive sediment.

Heat Transfer and Crystallization Modeling during Compression Molding of Thermoplastic Composite Parts

2015 ◽  
Vol 651-653 ◽  
pp. 1507-1512 ◽  
Author(s):  
Jalal Faraj ◽  
Baptiste Pignon ◽  
Jean Luc Bailleul ◽  
Nicolas Boyard ◽  
Didier Delaunay ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Physical Properties ◽  
Volume Fraction ◽  
Thermoplastic Composite ◽  
Large Temperature ◽  
Process Conditions ◽  
Thermoplastic Resin ◽  
Whole Process ◽  
Low Viscosity ◽  
Thermo Physical Properties

We present in this paper, the coupling of heat transfer to the crystallization of composite in a closed mold. The composite is based on thermoplastic resin (low viscosity PA 66) with glass fiber (50% volume fraction). In order to realize this coupling, an accurate characterizationof thermo physical properties in process conditions, especially in the molten and solid state is needed. In addition, theidentification of the parameters of crystallization kinetics is required. Therefore, we present the methods that were used to study the thermo physical properties as the thermal conductivity, heat capacity and the specific volume. Moreover, the kinetic of crystallization was estimated over a large temperature range by using Flash DSC and classical DSC. In order to validate the measurements, the whole process was modeled by finite elements. The model includes the resolution of the strong coupling between the heat transfer and crystallization. Finally, the experimental and numerical results were compared.

Modeling Recrystallization for 3D Multi-Pass Forming Processes

2007 ◽  
Vol 558-559 ◽  
pp. 1201-1206 ◽  
Author(s):  
Mihaela Teodorescu ◽  
Patrice Lasne ◽  
Roland E. Logé
Keyword(s):  
Numerical Simulation ◽  
Grain Size ◽  
Present Model ◽  
Static Recrystallization ◽  
Volume Fraction ◽  
The Other ◽  
Finite Element Code ◽  
3D Numerical Simulation ◽  
Fraction Distribution ◽  
Simulation Results

The present work concerns the simulation of metallurgical evolutions in 3D multi-pass forming processes. In this context, the analyzed problem is twofold. One point refers to the management of the microstructure evolution during each pass or each inter-pass period and the other point concerns the management of the multi-pass aspects (different grain categories, data structure). In this framework, a model is developed and deals with both aspects. The model considers the microstructure as a composite made of a given (discretized) number of phases which have their own specific properties. The grain size distribution and the recrystallized volume fraction distribution of the different phases evolve continuously during a pass or inter-pass period. With this approach it is possible to deal with the heterogeneity of the microstructure and its evolution in multi-pass conditions. Both dynamic and static recrystallization phenomena are taken into account, with typical Avrami-type equations. The present model is implemented in the Finite Element code FORGE2005®. 3D numerical simulation results for a multi-pass process are presented.

scholarly journals Functional trait responses to sediment deposition reduce macrofauna-mediated ecosystem functioning in an estuarine mudflat

2018 ◽  
Vol 15 (9) ◽  
pp. 2587-2599 ◽  
Author(s):  
Sebastiaan Mestdagh ◽  
Leila Bagaço ◽  
Ulrike Braeckman ◽  
Tom Ysebaert ◽  
Bart De Smet ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Ecosystem Functioning ◽  
River Estuary ◽  
Functional Trait ◽  
Sediment Deposition ◽  
Sediment Chemistry ◽  
Sediment Layer ◽  
Sediment Reworking ◽  
Macrobenthic Communities ◽  
The Impact

Abstract. Human activities, among which dredging and land use change in river basins, are altering estuarine ecosystems. These activities may result in changes in sedimentary processes, affecting biodiversity of sediment macrofauna. As macrofauna controls sediment chemistry and fluxes of energy and matter between water column and sediment, changes in the structure of macrobenthic communities could affect the functioning of an entire ecosystem. We assessed the impact of sediment deposition on intertidal macrobenthic communities and on rates of an important ecosystem function, i.e. sediment community oxygen consumption (SCOC). An experiment was performed with undisturbed sediment samples from the Scheldt river estuary (SW Netherlands). The samples were subjected to four sedimentation regimes: one control and three with a deposited sediment layer of 1, 2 or 5 cm. Oxygen consumption was measured during incubation at ambient temperature. Luminophores applied at the surface, and a seawater–bromide mixture, served as tracers for bioturbation and bio-irrigation, respectively. After incubation, the macrofauna was extracted, identified, and counted and then classified into functional groups based on motility and sediment reworking capacity. Total macrofaunal densities dropped already under the thinnest deposits. The most affected fauna were surficial and low-motility animals, occurring at high densities in the control. Their mortality resulted in a drop in SCOC, which decreased steadily with increasing deposit thickness, while bio-irrigation and bioturbation activity showed increases in the lower sediment deposition regimes but decreases in the more extreme treatments. The initial increased activity likely counteracted the effects of the drop in low-motility, surficial fauna densities, resulting in a steady rather than sudden fall in oxygen consumption. We conclude that the functional identity in terms of motility and sediment reworking can be crucial in our understanding of the regulation of ecosystem functioning and the impact of habitat alterations such as sediment deposition.

Simulation to Investigate the Reasons for the Sediment Deposition in the Upper Reach of the Deepwater Navigation Channel in the Changjiang River Estuary

2012 ◽  
Vol 610-613 ◽  
pp. 1237-1241
Author(s):  
Jie Gu ◽  
Wei Chen ◽  
Xin Qin ◽  
Dan Qing Ma ◽  
Xiao Li Wang ◽  
...  
Keyword(s):  
River Estuary ◽  
Sediment Deposition ◽  
Changjiang River ◽  
Changjiang River Estuary ◽  
The Changjiang River ◽  
The North ◽  
Velocity Magnitude ◽  
Navigation Channel ◽  
The Changjiang River Estuary ◽  
Set Up

At present, the upper reach of the Deepwater Navigation Channel is silted heavily, which brings negative influences on navigation. A two-dimensional numerical model is set up to simulate the hydrodynamics of the Changjiang River Estuary with Delft3D-FLOW in this paper. This model has been validated with the observed tidal level, flow velocity magnitude and direction, and the computed results agree well with the observed data, which also shows the model can well simulate the hydrodynamics of the Changjiang River Estuary caused by the Deepwater Navigation Channel Project. Based on the analysis of computed results, especially the velocity along the South Passage and North Passage, the flood and ebb flow in the Hengsha Passage, and the flow spilt ratio of South Passage and North Passage, it presents that one fundamental reason for the sediment deposition in the upper reach of the Deepwater Navigation Channel is that the velocity along the North Passage is far less than that along South Passage, above all, the velocity in North Passage upstream of the Hengsha Passage is even smaller; another reason is that the flood and ebb flow of Hengsha Passage are large, which weakens the water exchange between the North Passage and South Channel.

Utilizing prior information in the estimation of volume fraction distribution

2005 ◽  
Vol 63 (12) ◽  
pp. 1719-1740 ◽  
Author(s):  
Lasse M. Heikkinen ◽  
Robert M. West ◽  
Marko Vauhkonen
Keyword(s):  
Prior Information ◽  
Volume Fraction ◽  
Fraction Distribution

scholarly journals Gas Distribution Law for the Fully Mechanized Top-Coal Caving Face in a Gassy Extra-Thick Coal Seam

2018 ◽  
Vol 2018 ◽  
pp. 1-8
Author(s):  
Wenlin Wang ◽  
Fangtian Wang ◽  
Bin Zhao ◽  
Gang Li
Keyword(s):  
Longwall Mining ◽  
Volume Fraction ◽  
Vertical Direction ◽  
Thick Coal Seam ◽  
Working Face ◽  
Coal Wall ◽  
The Face ◽  
Fraction Distribution ◽  
Gas Volume Fraction ◽  
Gas Volume

Mine gas overflow is a serious threat to the safe and efficient longwall mining of gassy coal seams. Based on the field mining conditions and gas extraction of the fully mechanized top-coal caving face of a gassy coal mine, the space volume fraction distribution and emission (extraction rate) of gas in the face were tested by an arrangement of measuring points in the stereo grid. The isograms of gas volume fraction distribution for each measurement section and air direction in the face are drawn. The research shows that each measurement section gas volume fraction distribution is presented for an asymmetric concave curve along the vertical direction of the coal wall in the air-inlet side and the air-return side of the face; on the working face air-return side, the determination of gas volume fraction distribution of the section appears as falling straight line along the vertical direction of the coal wall. Before the first weighting, the absolute quantity of gas emission in the working face increased with the advancing of the working face, reached the maximum at the time of the first weighting, and then remained stable.

scholarly journals Effect of Gate Selection on the Non-Cohesive Sedimentation in Irrigation Schemes

Water ◽  
2020 ◽  
Vol 12 (10) ◽  
pp. 2765
Author(s):  
Shaimaa Theol ◽  
Bert Jagers ◽  
Jigyasha Rai Yangkhurung ◽  
F.X. Suryadi ◽  
Charlotte de Fraiture
Keyword(s):  
Cohesive Sediment ◽  
Sediment Deposition ◽  
Hydraulic Parameters ◽  
Crop Water ◽  
Gate Operation ◽  
Control Structures ◽  
Sediment Removal ◽  
1D Model ◽  
The Impact ◽  
Selection Of

In order to cover the crop water requirements, flow control structures such as gates and weirs are used to transfer the desired amount of water from the canals to the field canals. This paper examines the impact of gate operation and the selection of gates on the deposition of non-cohesive sediment. The Delft3D model is used to simulate the effects of different scenarios regarding gate operation and the location of the gate that is opened. The model results showed that the gate selection affects not only hydraulic parameters but also morphological parameters. It was found that opening the gates closer to the offtake resulted in less sediment deposition at the entrance of the branch canal when compared to opening the gates further away. Gate selection can be used as a tool in sediment management. By alternating the opening of different gates sediments that are already deposited after opening one gate can be eroded when another gate is operated, thus minimizing the additional cost of sediment removal. The use of Delft3D proved beneficial as the selection of different gates leads to asymmetric sediment deposition patterns which would be missed when using a 1D model.

The Correlation of Drop-Size Distributions in Fuel Nozzle Sprays—Part I: The Drop-Size/Volume-Fraction Distribution

1977 ◽  
Vol 99 (3) ◽  
pp. 309-314 ◽  
Author(s):  
H. C. Simmons
Keyword(s):  
Drop Size ◽  
Volume Fraction ◽  
Operating Conditions ◽  
Different Types ◽  
Median Diameter ◽  
Fraction Distribution ◽  
Fuel Nozzle ◽  
Drop Size Distributions ◽  
Mass Median ◽  
Mass Median Diameter

The paper presents data on the drop-size/volume-fraction distributions of sprays observed with a large number of gas-turbine fuel nozzles of different types including both pressure and air-atomizers, using a range of fuel viscosities, at a variety of operating conditions. The data were obtained by both optical and wax-droplet methods. It is shown that a universal nondimensional correlation can be established for all the fuel nozzles when the drop-size is normalized to the mass median diameter. The correlation enables prediction of the drop-size/volume-fraction distribution for a spray given only the mass median or Sauter mean diameter.

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