Erosion Coefficient Research Articles

2D axisymmetrical numerical modelling of the erosion of a cohesive soil by a submerged turbulent impinging jet

This study focuses on 2D Computational Fluid Dynamics (CFD) numerical modelling of the erosion of a cohesive soil by a circular impinging turbulent jet. Initially, the model is validated in the case of a non erodible flat plate. Several turbulence models are compared to experimental results and to simplified formulas available in the literature. The results obtained show that the Reynolds Stress Model (RSM) is in good agreement with the semi-empirical results in the literature. Nonetheless, the RSM cannot be used with successive remeshings, due to its convergence issues. The shear stress at the wall is well-described by the k–ε model while the pressure is better-described by the k–ω model. The numerical model of erosion is based on adaptive remeshing of the water/soil interface to ensure the good precision of the mechanical values at the wall. The two erosion parameters are the critical shear stress and the erosion coefficient. The results obtained are compared with the semi-empirical model interpreting the Jet Erosion Test. The k–ε model underestimates the shear stress and does not allow simulation of the entire erosion process, whereas the results obtained with the k–ω model agree well with the semi-empirical model and experimental data. A study of the influence of erosion parameters on erosion kinetics and scouring depth shows that the shape and depth of scouring are influenced solely by the critical shear stress while the duration of scouring depends on both erosion parameters. Further research is nonetheless required to better understand the erosion mechanisms in the stagnation zone.

Laboratory soil piping and internal erosion experiments: evaluation of a soil piping model for low‐compacted soils

ABSTRACTMechanistic models have been proposed for soil piping and internal erosion on well‐compacted levees and dams, but limited research has evaluated these models in less compacted (more erodible) soils typical of hillslopes and streambanks. This study utilized a soil box (50 cm long, 50 cm wide and 20 cm tall) to conduct constant‐head, soil pipe and internal erosion experiments for two soils (clay loam from Dry Creek and sandy loam from Cow Creek streambanks) packed at uniform bulk densities. Initial gravimetric moisture contents prior to packing were 10, 12 and 14% for Dry Creek soil and 8, 12, and 14% for Cow Creek soil. A 1‐cm diameter rod was placed horizontally along the length of the soil bed during packing and carefully removed after packing to create a continuous soil pipe. A constant head was maintained at the inflow end. Flow rates and sediment concentrations were measured from the pipe outlet. Replicate submerged jet erosion tests (JETs) were conducted to derive erodibility parameters for repacked samples at the same moisture contents. Flow rates from the box experiments were used to calibrate the mechanistic model. The influence of the initial moisture content was apparent, with some pipes (8% moisture content) expanding so fast that limited data was collected. The mechanistic model was able to estimate equivalent flow rates to those observed in the experiments, but had difficulty matching observed sediment concentrations when the pipes rapidly expanded. The JETs predicted similar erodibility coefficients compared to the mechanistic model for the more erodible cases but not for the less erodible cases (14% moisture content). Improved models are needed that better define the changing soil pipe cross‐section during supply‐ and transport‐limited internal erosion, especially for piping through lower compacted (more erodible) soils as opposed to more well‐compacted soils resulting from constructing levees and dams. Copyright © 2013 John Wiley & Sons, Ltd.

Comparison of Computational Fluid Dynamic Simulations with Experimental Jet Erosion Tests Results

The jet erosion test (JET) is an experimental device increasingly used to quantify the resistance of soils to erosion. This resistance is characterized by two geotechnical parameters: the critical shear stress and the erosion coefficient. A previously published JET interpretation model provides an estimation of these erosion parameters. But the existing model is simplified and semiempirical and several assumed hypotheses can be discussed. The aim of this study is to determine the relevance of the JET interpretation model. Therefore, a numerical model was developed that is able to predict the erosion of a cohesive soil by a turbulent flow. The numerical model was first validated on a benchmark: erosion of an erodible pipe by a laminar flow. The numerical results were satisfactorily compared with the theoretical solution. Then, three JETs were modeled numerically with values of erosion parameters obtained experimentally. A parametric study was also conducted to validate the accuracy of the numerical results and a good agreement was observed. The erosion parameters found experimentally permit the numerical prediction of the evolution of the erosion pattern within good accuracy. This result contributes to the validation of the JET’s semiempirical model. The numerical model also gives a complete description of the flow, including vortices which can be observed in the cavity created by erosion. The entire erosion pattern evolution was given by the numerical results. This numerical model gives information that is not available otherwise.

캐비테이션 침식 추정 방법 개발 및 추진기에의 적용

In the present study, a practical method to predict cavitation erosion, which caused a critical damage on hydraulic machineries, was developed. Impact and critical velocities were defined to develop a practical method for the prediction of cavitation erosion. To develope the practical method, the computational fluid dynamics (CFD) was introduced. Cavitating flows with erosion in a converging-diverging nozzle and around a hydrofoil were simulated by developed and validated code. Based on the CFD results, the cavitation erosion coefficient was derived by a curve fitting method. The cavitation erosion coefficient was formulated as the function of the cavitation and Reynolds numbers. A cavitating flow in an axisymmetric nozzle followed by radial divergence was simulated to validate the developed practical method. For the application to a propeller, a cavitating flow around a propeller was simulated. Predicted damage extent showed similar with damaged full-scale propeller blade.

Measuring Soil Erodibility Using a Laboratory “Mini” JET

Abstract. Typically soil erodibility is quantified using an excess shear stress equation, dependent on two major soil parameters: the critical shear stress (I„ c ) and the erodibility coefficient (k d ). A submerged jet test (JET, Jet Erosion Test) is one method that has been developed and methodology of use established in the literature for measuring these parameters. In this study, a new miniature version of the JET device (“mini” JET), with the advantage of being easier to use in the field, was used to measure I„ c and k d for two soils (silty sand and clayey sand), and results were compared to the larger original laboratory JET. The objective of this research was to determine if the “mini” JET measured equivalent values for I„ c and k d compared to the original JET device. In-order to compare the performance and repeatability of both JET devices, tests were performed on paired samples prepared in the same way and tested at the same time. Samples of the soils tested were prepared at different water contents with a standard compaction effort of 600 kN-m/m 3 (ASTM). Some variability in measuring I„ c and k d was observed between paired samples due to variability in the soil texture of the soil samples and differences in soil moisture levels. The k d values measured by the two JET devices for both soils were not significantly different. The I„ c values measured by the “mini” JET were consistently lower than those measured by the original JET. This was hypothesized to be due to the structure of the soil sample due to the compaction method and the procedure utilized to determine I„ c . Adjustment of the equilibrium depth of the “mini” JET resulted in small differences in the estimated I„ c between both JET devices. Both JET devices also demonstrated consistent performance in measuring I„ c -k d relationships, which were compared with those observed in previous field research.

SAT0524 Automated Breast Volume Scanner (ABVS), a New Automated Ultrasonic Device, is Useful to Examine Joint Injury in Patients with Rheumatoid Arthritis

BackgroundAutomated Breast Volume Scanner (ABVS) is an ultrasonic device to be developed for the automated scanning for mammary glands. ABVS is able to scan mammary gland automatically in a short...

Quantifying the role of paleoclimate and Andean Plateau uplift on river incision

River incision over geologic timescales can be a valuable indicator of regional surface uplift. However, extracting the timing of surface uplift relative to the onset of incision is complicated by changes in precipitation commensurate with topographic development. Evidence of large‐scale river incision on the flanks of the Andean plateau has been cited in support of a rapid and recent surface uplift event. Recent climate modeling studies demonstrate large magnitudes of regional climate change associated with surface uplift of the Andes, which may have influenced river incision processes. Here we present an analysis of mid‐Miocene (16 Ma) to present river incision of the southwest Peruvian Ocoña River. A Monte Carlo approach with ~1.6 × 105 different simulations is used to explore the range of surface uplift and paleoclimate histories that are compatible with the modern river profile and geological constraints on the incision timing and magnitude. A range of channel properties, including the erodibility coefficient and erosion threshold, are considered. Results indicate that deep canyon incision on the plateau flanks may not be as diagnostic of rapid surface uplift as previously thought. More specifically, the evolution of the Ocoña River is consistent with local plateau elevations of 1–3 km at 16 Ma and either a steady or punctuated uplift of 1.5–3.5 km since then. The range of acceptable uplift histories is sensitive to the long‐term magnitude and temporal evolution of precipitation. Similar paleoprecipitation changes are expected to have modified river profile evolution elsewhere in the Andes.

Mechanism of mining-induced slope movement for gullies overlaying shallow coal seams

This paper provides an improved understanding of the movement mechanisms of both bed-rock gully and sandy soil gully when underground mining occurs underneath, followed by systematic analysis of the contributing factors such as mining advance direction, gully slope angle, gully erosion coefficient and mining height. This paper presents the results from monitoring, theoretical analyses and up to date modeling based on the geological features in the gully affected area, and the implications of these results to the success of roof support trial. It was observed that when mining occurred towards the gully, sliding of slope block along the fracture surface occurred, which resulted in unstable roof condition; when mining progressed away from the gully, polygon blocks developed in the gully slope and rotated in reversed direction forming hinged structure; within the bed-rock slope, the hinged structure was unstable due to shear failure of the polygon block; however, within the sandy soil slope, the structure was relatively stable due to the gradual rotating and subsiding of the polygon block. The increase of the value of slope angle and mining height lead to a faster and more intensive fracture development within the gully slope, which had a pronounced effect on gully slope stability and underground pressure. Various remediation approaches are hence proposed in this paper including introducing more powerful support and reasonable mining height, setting up working face along or away from gullies, using room and pillar, strip mining and backfill instead of longwall mining.

Experimental Evidence of Erosion of Critical Load in Interactive Buckling

AbstractThe paper starts with a selective review of some basic contributions related to local-overall buckling mode interactions in thin-walled steel members. Then, the results of an intensive experimental study carried out at the Politehnica University of Timisoara with the purpose of evaluating the erosion of a theoretical bifurcation load in the distortional-flexural buckling interaction range in pallet rack uprights are presented. Two different sizes of cross sections, with and without perforations, have been studied. To evaluate and quantify the erosion, the erosion of the critical bifurcation load approach is applied. This approach enables one to use the European buckling curves in the Ayrton-Perry format, expressing the imperfection factor (α) in terms of the erosion coefficient (ψ). It allows estimation of the member’s ultimate capacity, taking into account the interaction of sectional (local or distortional) and member (flexural, torsional, or flexural-torsional) instability modes. Test results a...

Erosion of tungsten and its brazed joints with bronze irradiated by pulsed deuterium plasma flows

This work presents results on erosion of mono- and polycrystalline tungsten and its brazed joints with bronze substrates under irradiation by high-temperature pulsed (τp∼20μs) deuterium plasma flows, with a power density q=19–66GW/m2 and pulses numbering from 2 to 10, simulating the expected plasma disruptions and ELMs in fusion reactors. The surface erosion and heat resistance of tungsten and brazed joints were investigated by scanning electron microscopy, and erosion coefficients were determined by target mass loss.It is found that for both types of tungsten the surface starts to significantly crack even under relatively weak irradiation regimes (q=19GW/m2, N=2), at which point surface melting is not observed. Local melting becomes visible with an increase of q up to 25GW/m2. In addition, there is formation of blisters with a typical size of 1–2μm on the surface of monocrystalline samples and craters up to 2μm in diameter on polycrystalline samples. In addition, craters ∼10–30μm in diameter are formed on defects similar to those observed under unipolar arcs. At that point, the erosion coefficients change to within ranges of 0.2–0.7×10−5kg/Jm2.It is found that at q=50GW/m2, the brazed joints of monocrystalline tungsten with bronze of Cu-0.6% Cr-0.08% Zr have the highest heat resistance.

A comparative analysis of interface erosion tests

Interface erosion is one of the main phenomena in dams, dikes and their foundations which may increase their failure risk. In laboratories, the jet erosion test (JET) and the hole erosion test (HET) are commonly used for the evaluation of the sensibility of interface erosion of fine soils. The results are interpreted by two distinct methods that are valid for one test only. A new energy analysis of the tests is developed, relating the total eroded mass to the dissipated fluid energy, and a new erosion resistance index is proposed. Seven naturally occurring fine-grained soils, covering a large range of erodibility, are compacted with the Proctor protocol, and they are tested with the two devices. It was shown that by using the commonly used methods, the values of the erosion coefficient are systematically higher with the JET than with the HET and the HET critical shear stress is about fifty times higher than the JET critical shear stress. Thus, the relative soil classifications yielded by the two erodimeters are not exactly the same. Based on energy analysis, values of erosion resistance index are roughly the same for each tested soil with the two apparatuses and a single classification of soil erodibility is obtained.

Experimental and physicomathematical simulation of the effect of an incident flow of atomic oxygen on highly filled polymer composites

The effect of the flow of atomic oxygen (AO) on highly filled composites of a high-impact polystyrene (HIPS) and a superfine silicon-organic filler is investigated. Erosion coefficients after the treatment with AO are calculated, and the postirradiation relief of the composites is studied by the method of scanning electron microscopy (SEM). A physicomathematical simulation of erosion processes is performed on the basis of the obtained data.

Numerical Modelling of Electro-Discharge Machining Process Using Moving Mesh Feature

This paper is concerned with numerical modelling of Electro Discharge Machining (EDM) process using moving mesh feature. Coefficient of erosion was defined and found to be constant using analytical equations. This was validated by conducting experiments on electro discharge machining. Then, the machining process was modelled in software using the coefficient of erosion. When the same conditions were applied in the real time machining, the results obtained were in good agreement with that of the software results. The application of software modelling was demonstrated to determine the process efficiency of drilling process. The process efficiency helps to find out if there is any scope for improvement in process and therefore enhanced productivity. Also, machining time which is one of the critical factors in micro-EDM process was predicted using software. This greatly saves time and resources and also, the difficulty in manufacture of micro sized electrodes for research is greatly reduced. A comparison study was performed with the use of conventional and concentric electrode for drilling concentric micro size holes. It was concluded that reduced machining time and perfect concentricity was observed when conventional electrodes were replaced by concentric electrodes. Yet another study was performed to justify the reduction in machining time due to usage of conductivity enhancement rings in the direction of passage of current to enhance current flow by avoiding air gap insulation. Thus, software modelling helps to perform research by predicting machining time without the need of real time experimentation.

New procedures to estimate soil erodibility properties from a hole erosion test record

The estimation of representative values of the properties quantifying soil erodibility (critical shear stress and coefficient of soil erosion) is of great difficulty. The difficulty lies in the complexity of the phenomenon in question in addition to the uncertainty of the used experimentation (hole erosion test). In this paper, the procedure used to estimate these properties is presented, and two new procedures are proposed. The proposed procedures are more accurate for the quantification as well as to detect the initiation of the internal erosion. It is found that the erodibility properties depend on the hydraulic charge and that for one soil sample, it is possible to find more than one pair of solutions (critical shear stress, coefficient of soil erosion) which explains the non-observation of significant relationship between these two properties and other soil properties.

Deriving Parameters of a Fundamental Detachment Model for Cohesive Soils from Flume and Jet Erosion Tests

Abstract. The erosion rate of cohesive soils is commonly quantified using the excess shear stress model, which is dependent on two major soil parameters: the critical shear stress (I„ c ) and the erodibility coefficient (k d ). A submerged jet test (jet erosion test, or JET) is one method that has been developed for measuring these parameters. The disadvantage of using the excess shear stress model is that parameters I„ c and k d change according to erosion conditions, such as soil structure, soil orientation, type of clay, presence of roots, and seepage forces. A more mechanistically based detachment model, called the Wilson model, is proposed in this article for modeling the erosion rate of soils using hydraulic analysis of a JET. The general framework of the Wilson model is based on two soil parameters (b 0 and b 1 ). The objectives of this study were to: (1) develop methods of analysis of the JET to determine parameters b 0 and b 1 for the Wilson model in a similar fashion to the previous methodology developed for open-channel flow, and (2) compare the excess stress model parameter (k d ) and the Wilson model parameters (b 0 and b 1 ) determined from the flume tests and JETs for two cohesive soils. Flume tests, treated as the standard test method, and original and “mini” JETs were conducted on two soils to independently measure the excess shear stress model parameter (k d ) and the Wilson model parameters (b 0 and b 1 ). Soil samples of two cohesive soils (silty sand and clayey sand soils) were packed in a soil box for the flume tests and the JETs at water contents ranging from 8.7% to 18.1%. No statistically significant differences were observed for the excess shear stress model parameter (k d ) and for the Wilson model parameters (b 0 and b 1 ) when determined from the flume tests and JET devices, except for b 1 with the original JET. The Wilson model is advantageous in being a more mechanistic, fundamentally based erosion equation as compared to the excess shear stress model. The Wilson model can be used in place of the excess shear stress model with parameters that can be estimated using existing JET techniques.

Investigating the Effect of Lignosulfonate on Erosion Rate of the Embankments Constructed with Clayey Sand

Internal erosion is known as the most important cause of dam failure after overtopping. It is important to improve the erosion resistance of the erodible soil by selecting an effective technique along with the reasonable costs. To prevent internal erosion of embankment dams the use of chemical stabilizers that reduce the soil erodibility potential is highly recommended. In the present study, a lignin-based chemical, known as lignosulfonate, is used to improve the erodibility of clayey sand specimen. The clayey sand was tested in various hydraulic heads in terms of internal erosion in its natural state as well as when it is mixed with the different percentages of lignosulfonate. The results show that erodibility of collected clayey sand is very high and is dramatically reduced by adding lignosulfonate. Adding 3% of lignosulfonate to clayey sand can reduce the coefficient of soil erosion from 0.01020 to 0.000017. It is also found that the qualitative erodibility of stabilized soil with 3% lignosulfonate is altered from the group of extremely rapid to the group of moderately slow.

Sediment Transport Model for a Surface Irrigation System

Controlling irrigation-induced soil erosion is one of the important issues of irrigation management and surface water impairment. Irrigation models are useful in managing the irrigation and the associated ill effects on agricultural environment. In this paper, a physically based surface irrigation model was developed to predict sediment transport in irrigated furrows by integrating an irrigation hydraulic model with a quasi-steady state sediment transport model to predict sediment load in furrow irrigation. The irrigation hydraulic model simulates flow in a furrow irrigation system using the analytically solved zero-inertial overland flow equations and 1D-Green-Ampt, 2D-Fok, and Kostiakov-Lewis infiltration equations. Performance of the sediment transport model was evaluated for bare and cropped furrow fields. The results indicated that the sediment transport model can predict the initial sediment rate adequately, but the simulated sediment rate was less accurate for the later part of the irrigation event. Sensitivity analysis of the parameters of the sediment module showed that the soil erodibility coefficient was the most influential parameter for determining sediment load in furrow irrigation. The developed modeling tool can be used as a water management tool for mitigating sediment loss from the surface irrigated fields.

<i>In Situ</i> Soil Pipeflow Experiments on Contrasting Streambank Soils

Abstract. Soil piping has been attributed as a potential mechanism of instability of embankments and streambanks. Limited field work has been conducted on quantifying and modeling pipeflow and internal erosion processes in the field with either natural or artificially created soil pipes. This research utilized an innovative constant-head trench system to conduct constant-head soil pipe experiments in two contrasting streambanks: Dry Creek in northern Mississippi and Cow Creek in northern Oklahoma. Experiments included open pipes, in which the soil pipe was directly connected to the constant-head trench and open at the streambank face, and clogged pipes, which involved plugging the outlet of the soil pipe using soil excavated adjacent to the pipe. A tensiometer network was used to measure soil water pressures surrounding open and clogged pipe outlets on the streambank face. When pipeflow occurred, flow and sediment samples were collected using flow collection pans to quantify sediment concentrations. Flow and sediment data were used with an existing turbulent pipeflow and internal erosion model to estimate erodibility and critical shear stress properties of the soils, which were subsequently compared to similar properties derived from jet erosion tests. Clogged soil pipes resulted in pore water pressure increases in the soil adjacent to the pipe, which generally remained below saturation during these experimental periods, except at locations close to the plug. Depending on the density of the plugged soil material, the clogged soil pipes either burst, resulting in turbulent pipeflow, or were manually punctured to establish pipeflow. Calibrated critical shear stress from the turbulent pipeflow and internal erosion model matched that observed from jet erosion tests for the less erodible soils on the Dry Creek streambank, where sediment concentrations were consistently below 2 g L -1 even with fairly large hydraulic gradients on the pipe (0.3 m m -1 ). Calibrated erodibility coefficients were much smaller than those measured with jet erosion tests. For the more erodible streambank soils of Cow Creek, sediment concentrations approached 40 g L -1 . There is a need for improved pipeflow modeling that accounts for rapidly changing pipe geometries, partially filled soil pipes, and pipeflow/soil matrix interactions.

The effects of floodplain soil heterogeneity on meander planform shape

Past analytical studies of meander planform development have mostly focused on the complexity of the governing equations, i.e., hydrodynamics, and less so on the stream bank resistance to erosion, whose spatial heterogeneity is difficult to describe deterministically. This motivated the use of a Monte Carlo approach to examine the effects of floodplain soils and their distribution on planform development, with the goal of including bank erosion properties in the analysis. Simulated bank erosion rates are controlled by the resistance to hydraulic erosion of the bank soils using an excess shear stress approach. The spatial distribution of critical shear stress across the floodplain is delineated on a rectangular, equidistant grid with varying degrees of variability. The corresponding erodibility coefficient is computed using a field‐derived empirical relation. For a randomly disturbed distribution, in which the mean resistance to erosion exponentially increases away from the valley centerline, two relevant parameters are identified: the standard deviation of the critical shear stress distribution, which controls skewness and variability of the channel centerline, and the cross‐valley increase in soil resistance, which constrains lateral migration and also affects bend skewness. For a purely random distribution, migrated centerlines exhibit larger variability for increasing spatial scales of floodplain soil heterogeneity. For equal stochastic variability of the corresponding governing parameters, relating meander migration to hydraulic erosion of the bank soils produces more variability and shape complexity than the “classic” bank migration approach of Ikeda et al. (1981), which relates migration rate to excess velocity at the outer bank. Finally, the proposed stochastic approach provides a foundation for estimating a suitable spatial density of measurements to characterize the physical properties of floodplain soils and vegetation.

Improving the Durability of Concrete for Mechane Engineering

In order to improve the durability of concrete for mechane engineering, the experimental investigation of the preparation process condition of concrete have been reported.The effect of mix proportion design and chemical admixture on the strength of concrete are studied, the anti-permeability and anti-erosion by acid are analyzed. The results indicated that the addition of 1% water-reducing admixture and 3% organic Si waterproof (the precent of admixture and cement in mass) are useful to improve the mechanics property and durability of the concrete, the compressive strength after dipped in water 48 h enhance 100% , the permaebility grade enhance from P4 to P10, the erosion coefficient K decrease from 6.1% to 2.2% and the erosion degree R decrease from 57.5% to 32.8%, respectively, compare with that without dopant the water-reducing admixture. The results gained in this study are helpful for improving the the durability of the concrete and enlarge application the mechane engineering in rural areas.