Shape Of Sediment Particles Research Articles

Modeling on effective thermal conductivity of hydrate-bearing sediments considering the shape of sediment particle

The estimation of effective thermal conductivity (ETC) of hydrate-bearing sediment is of great importance for the exploitation of natural gas hydrate. At present, existing ETC models have been lack of consideration of the influences of sediment particle shape and stacking patterns. Thus, in this work, new models considering the shape (octahedral, plate-shaped, spindle-shaped and elongated) of sediment particles and stacking patterns were established and verified by a series of existed laboratory data. The verification results indicate that the octahedral model, plate-shape model and the average values of the four models have high accuracy in predicting ETC of hydrate-bearing sediments. The ETC of hydrate-bearing sediment under water-saturated state were calculated by the models in this work. The average ETC predicted by four models decreased from 2.87 W⋅m-1⋅K-1 to 1.47 W⋅m-1⋅K-1 with porosity increasing from 0.22 to 0.47 and decreased from 1.61 W⋅m-1⋅K-1 to 1.58 W⋅m-1⋅K-1 with hydrate saturation increasing from 0 to 1. Finally, the effects of porosity, hydrate saturation and intrinsic thermal conductivity of sediment particles on the ETC were discussed and analyzed. This modeling work could contribute to the understanding and prediction of the ETC of hydrate-bearing sediment with different shapes of sediment particles in the complex porous system.

Predicting reservoir volume reduction using artificial neural network

One of the modern methods for predicting the behavior of natural phenomena is using artificial neural network (ANN) model that predicts new data through applying experimental data and finding out the rules behind the data. Area-reduction experimental model is a method for distributing sediments in the reservoirs. The main goal of the present study is to evaluate the feasibility and utilization of ANNs in predicting reservoir volume reduction under low data conditions. The present paper focuses on applying the ANN model with a multi-layer perceptron (MLP) in MATLAB software. Prediction of the volume reduction of ANN model is done by using a 10-year period of data (2003–2013) at Baroon dam reservoir in Maku, Iran as a case study. Furthermore, for modeling the distribution of sediments in dam reservoir, area-reduction experimental model is used for a 30-year period (2009–2037). The analysis of data shows that a volume of 1.67 million cubic meters per second (MCM) on annual average is reduced from the total volume of Baroon dam due to the inflow discharge of sediment loads. Also, it is observed that the reservoir of the dam will be inoperable after 30 years because sediments will reach the minimum level of operation in the dam reservoir. It would be concluded that using experimental models such as area-reduction method for modeling sediment distribution in dam reservoirs is a complicated and costly process. Also, having other datasets such as sediment particle shape and density for modeling and generalization is not considered in the area-reduction method, while application of ANN can predict sediment distribution in dam reservoirs and also reservoir volume reduction properly and precisely.

Numerical investigation on the incipient motion of non-spherical sediment particles in bedload regime of open channel flows

Theoretical analysis and nowadays advanced numerical simulations for bedload particle transport widely share a popular assumption: All sediments are spherical and can be simplified as spheres, which apparently differs from reality. In order to explore the shape effects of sediment particles on their transport and to find out the possible consequence originated from the spherical assumption, a particle resolved computational model is established by combining the large eddy simulation for fluid and the discrete element method for the solid particles using an immersed boundary (IB) technique. Using this model, simulations are conducted for spherical and non-spherical bedload particles in both laminar and turbulent open channel flows. Simulation results show that shape of sediment particles has direct influence on the incipient motion in both laminar and turbulent flows. In laminar flows, the widely adopted spherical particles tend to exhibit over 5 times higher traveling speed compared with the non-spherical particles, and over 4 times longer time lag during incipient motion. In turbulent flows, the disk-shaped non-spherical particle yields up to 60% higher travel speed, 50% larger saltation height and 126% longer saltation length compared with spherical particles. The travel modes of non-spherical sediment particles during incipient motion are also analyzed.

Quantification of particle shape by an automated image analysis system: a case study in natural sediment samples from extreme climates

Sediment particle shape and microtexture are key parameters utilized for characterizing sediment transport and weathering (both physical and chemical) processes, which in turn are governed by environmental conditions such as climate. Assessing particle shape often involves either qualitative descriptors or time-consuming measurements of shape parameters by a human operator. This study employs a state-of-the-art, quantitative shape analysis instrument known as the “Morphologi G3” from Malvern Instruments, an automated microscope system capable of determining quantitative shape parameters via static image analysis of > 1000 particles in less than two hours. This instrument captures 2D projected images of particles and provides information on grain size measurements such as circle-equivalent diameter, length, width, perimeter, and area, as well as shape parameters such as circularity and convexity. As a case study, we conducted analyses on mud- and sand-sized particles collected from fluvial/alluvial systems of end-member climates to assess variations in sediment particle morphology potentially related to climate and/or transport distance and processes. Sediment samples were collected from fluvial systems in four contrasting climates: hot-arid (southeastern California, USA), hot-humid (eastern Puerto Rico), glacial-arid (proglacial stream of the Dry Valleys, Antarctica), and glacial-humid (Austerdalen proglacial stream, Norway). Results provide quantitative constraints on shape differences that relate to climate and transport, even for very fine-grained sand and mud size fractions. Comparison of the circularity of sediment particles from the four end-member climates indicates that the very fine sand fractions reflect differential physical abrasion and transport processes, whereas the morphology of the mud fraction seemingly imprints chemical weathering processes. We conclude that this new technique has great potential to further document impacts of climate on particle shape with applications to both modern and deep-time depositional systems.

Quantitative, SEM-based shape analysis of sediment particles in the Yellow River

The shape of a sediment particle can reveal part of the particle׳s transportation history and is a significant variable in sediment transport mechanics. Measuring sediment shapes is a difficult and time-consuming task. A whole sample sediment particle shape quantitative analysis method (WSQAM) was applied in this research for sediment statistical analysis. The shape parameter was found using sphericity and roundness descriptors: three samples were collected from the middle reach of the Yellow River at different depths. Scanning electron microscopy (SEM) was used to obtain sediment particles images. The sphericity and roundness descriptors were represented by the particle aspect ratio (AR) and the Fourier shape coefficient (FSC). The Fourier series approximation matched the particle outlines. From the statistical results of the whole sediment particle sample, as counted by WSQAM based on digital image processing, fine sediment particles with smooth surfaces accounted for approximately 80% of all of the observed sediment particles. For the majority of sediment particles, AR was greater than 0.3 and FSC was less than 0.1. When AR was greater than 0.5, FSC exponentially decayed with AR. When AR was less than 0.5, the two parameters, AR and FSC, should be combined to describe the sediment particle shape. The combined use of these two parameters can provide a reference for future sediment-related calculations. The sediment particle shape analysis model, programmed in Fortran, was rapid and flexible. It proved efficient to use WSQAM for sediment statistical analysis, and the results were found to be accurate.

On the Sediment Dynamics in a Tidally Energetic Channel: The Inner Sound, Northern Scotland

Sediment banks within a fast-flowing tidal channel, the Inner Sound in the Pentland Firth, were mapped using multi-frequency side-scan sonar. This novel technique provides a new tool for seabed sediment and benthic habitat mapping. The sonar data are supplemented by sediment grab and ROV videos. The combined data provide detailed maps of persistent sand and shell banks present in the Sound despite the high energy environment. Acoustic Doppler Current Profiler (ADCP) data and numerical model predictions were used to understand the hydrodynamics of the system. By combining the hydrodynamics and sediment distribution data, we explain the sediment dynamics in the area. Sediment particle shape and density, coupled with persistent features of the hydrodynamics, are the key factors in the distribution of sediment within the channel. Implications for tidal energy development planned for the Sound are discussed.

3D shape and morphology characterization of sediment particles

In this work, we developed a method to decipher the shape message imprinted in single sediment particles, a method that would reflect the detail information of surface morphology. It uses 2D mathematical descriptions to restore and characterize 3D shape and surface morphology of sediment particles in terms of the “mathematical sediment”, so as to better understand 3D geometric characteristics reflected by single sediment particles. To prevent the simplification of morphology description and overcome the deficiencies of lower-dimensional characteristics, we proposed a concept of “mathematical sediment” in this paper. The mathematical sediment uses image analysis of scanning electron microscope photographs and complex Fourier shape analysis to describe the planar projection shape of sediment particles and further restore the 3D morphology of sediment particles through a certain combination ways. The shapes of sediment particles are controlled using Fourier coefficients to generate a variety of mathematical sediments with various shapes, which allow the realization of the description and analysis of the 3D morphology of sediment particles. The fractal theory is further used to verify the rationality of mathematical sediment. Compared with the traditional method, the mathematical sediment overcomes the lack of particle system and smooth sphere systems and can reproduce 3D irregular surfaces for the morphology analysis. The rationality verification showed that the complex surface morphology of mathematical sediment is basically similar to the surface morphology of natural sediment. The mathematical sediment can reflect the true surface characteristics of sediment particles. The characteristics of shape properties and surface morphology it conveys are consistent with the natural sediment and can be used as a research basis for the further study both in fresh water and marine.

Computational and experimental study of effects of sediment shape on erosion of hydraulic turbines

Hard particles as Quartz and Feldspar are present in large amount in most of the rivers across the Himalayan basins. In run-off-river hydro power plants these particles find way to turbine and cause its components to erode. Loss of turbine material due to the erosion and subsequent change in flow pattern induce several operational and maintenance problems in the power plants. Reduction in overall efficiency, vibrations and reduced life of turbine components are the major effects of sediment erosion of hydraulic turbines. Sediment erosion of hydraulic turbines is a complex phenomenon and depends upon several factors. One of the most influencing parameter is the characteristics of sediment particles. Quantity of sediment particles, which are harder than the turbine material, is one of the bases to indicate erosion potential of a particular site. Research findings have indicated that shape and size of the hard particles together with velocity of impact play a major role to decide the mode and rate of erosion in turbine components. It is not a common practice in Himalayan basins to conduct a detail study of sediment characteristics as a part of feasibility study for hydropower projects. Lack of scientifically verified procedures and guidelines to conduct the sediment analysis to estimate its erosion potential is one of the reasons to overlook this important part of feasibility study. Present study has been conducted by implementing computational tools to characterize the sediment particles with respect to their shape and size. Experimental studies have also been done to analyze the effects of different combinations of shape and size of hard particles on turbine material. Efforts have also been given to develop standard procedures to conduct similar study to compare erosion potential between different hydropower sites. Digital image processing software and sieve analyzer have been utilized to extract shape and size of sediment particles from the erosion sensitive power plants. The experimental studies of impact of different shapes and sizes of sediment particles on hydraulic turbine material have been conducted on two different test rigs method at Kathmandu University, High velocity test rig method and Rotating Disc apparatus (RDA) at Kathmandu University. Twenty one different sediment shape samples and four different sand size range were studied to correlate the effects of sediment shape and size with the erosion of turbine material. It was observed that the shape of sediment particles have considerable effect on erosion of turbine material. In general Irregular shapes have more erosion potential than regular shapes. It was also observed that the particles with the irregular shape of smaller size induce higher erosion rates than that of the larger size with the same shape. These findings will help to select the proper site of a power plant in erosion prone basins and would also help to design suitable settling basins to trap sediment particles having higher erosion potentials.

Sediment characteristics at river confluences: a case study of the Mula-Kas confluence, Maharashtra, India

River bed and floodplain sediments are a direct reflection of river channel processes. This paper examines sediment transfer processes at river junctions, using as a case study the River Kas, a tributary of the River Mula, Godavari basin, Maharashtra, India. The study uses four cross-sections, two from upstream tributaries, one in the main confluence zone, and one downstream. Sediment samples are collected from each cross-section and adjacent banks. To understand the tributary impact on the main channel, variations in sand, silt and clay percentages and variations in the shape of sediment particles were recorded. Data suggest that the percentage of silt and clay increased away from the active channel towards banks along a cross-section, except for the mid-channel bar and the downstream segment of the confluence. The `a axis' and `c axis' lengths of particles increased for the samples on the confluence compared to upstream and downstream samples. Sediment characteristics between tributary and the main stream reflect both downstream distance from sediment source and the characteristics of the respective transport processes. The distribution of fine material at the tributary mouth suggests that there have been instances in the past where the mainstream flow has dominated the confluence and has led to slack water deposits on the tributary mouth. Construction of a weir for local flow regulation also affects the pattern and character of sediments. In this large, seasonal river, confluence sedimentology is a joint product of flow variation, confluence morphology and the additional effects of human activity. The study thus provides insights into confluence dynamics and characteristics which may not be revealed in the more intensively researched temperate confluences of smaller scale.