Bibliografie tematiche / Cohesive bed

Letteratura scientifica selezionata sul tema "Cohesive bed"

Autore: Grafiati

Pubblicato: 22 giugno 2024

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Articoli di riviste sul tema "Cohesive bed":

Khazratov, A. N., O. Sh Bazarov, A. R. Jumayev, F. F. Bobomurodov e N. Z. Mamatov. "Influence of cohesion strength in cohesive soils onchannel bed erosion". E3S Web of Conferences 410 (2023): 05018. http://dx.doi.org/10.1051/e3sconf/202341005018.

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The results of experimental studies on the mechanical properties of cohesive soils associated with the use in the study of the erosion process are presented. The influence of the cohesion strength of cohesive soil on erosion is described. The relationship between the erosionflow velocities and cohesion strength has been obtained.

Gong, Mingze, Sivar Azadi, Adrien Gans, Philippe Gondret e Alban Sauret. "Erosion of a cohesive granular material by an impinging turbulent jet". EPJ Web of Conferences 249 (2021): 08011. http://dx.doi.org/10.1051/epjconf/202124908011.

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The erosion of a cohesive soil by an impinging turbulent jet is observed, for instance, during the landing of a spacecraft or involved in the so-called jet erosion test. To provide a quantitative understanding of this situation for cohesive soils, we perform experiments using a model cohesion controlled granular material that allows us to finely tune the cohesion between particles while keeping the other properties constant. We investigate the response of this cohesive granular bed when subjected to an impinging normal turbulent jet. We characterize experimentally the effects of the cohesion on the erosion threshold and the development of the crater. We demonstrate that the results can be rationalized by introducing a cohesive Shields number that accounts for the inter-particles cohesion force. The results of our experiments highlight the crucial role of cohesion in erosion processes.

Glasbergen, K., M. Stone, B. Krishnappan, J. Dixon e U. Silins. "The effect of coarse gravel on cohesive sediment entrapment in an annular flume". Proceedings of the International Association of Hydrological Sciences 367 (3 marzo 2015): 157–62. http://dx.doi.org/10.5194/piahs-367-157-2015.

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Abstract. While cohesive sediment generally represents a small fraction (<0.5%) of the total sediment mass stored in gravel-bed rivers, it can strongly influence physical and biogeochemical processes in the hyporheic zone and alter aquatic habitat. This research was conducted to examine mechanisms governing the interaction of cohesive sediments with gravel beds in the Elbow River, Alberta, Canada. A series of erosion and deposition experiments with and without a gravel bed were conducted in a 5-m diameter annular flume. The critical shear stress for deposition and erosion of cohesive sediment without gravel was 0.115 Pa and 0.212 Pa, respectively. In experiments with a gravel bed, cohesive sediment moved from the water column into the gravel bed via the coupling of surface and pore water flow. Once in the gravel bed, cohesive sediments were not mobilized under the maximum applied shear stresses (1.11 Pa) used in the experiment. The gravel bed had an entrapment coefficient (ratio between the entrapment flux and the settling flux) of 0.2. Accordingly, when flow conditions are sufficient to produce a shear stress that will mobilize the armour layer of the gravel bed (>16 Pa), cohesive materials trapped within the gravel bed will be entrained and transported into the Glenmore Reservoir, where sediment-associated nutrients may pose treatment challenges to the drinking water supply.

Borovkov, V. S., e M. A. Volynov. "RIVER BED EROSION IN COHESIVE SOILS". Vestnik MGSU, n. 4 (aprile 2013): 143–49. http://dx.doi.org/10.22227/1997-0935.2013.4.143-149.

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Safak, Ilgar. "Variability of Bed Drag on Cohesive Beds under Wave Action". Water 8, n. 4 (1 aprile 2016): 131. http://dx.doi.org/10.3390/w8040131.

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Geng, Tiesuo, Shuanghua Chen, Liuqun Zhao e Zhe Zhang. "Research on Bonding Performance of Anchorage Caisson Foundation with Different Contact Surfaces and Grouting Bed". Buildings 11, n. 8 (19 agosto 2021): 365. http://dx.doi.org/10.3390/buildings11080365.

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In view of the first domestic offshore suspension bridge with caisson foundation, this paper mainly studies the bonding properties between underwater pre-filled aggregate grouting bed and anchorage caisson foundation. Through the test, the cohesive force of adding ordinary concrete between the anchorage caisson foundation and the grouting bed, the cohesive force of adding paper base asphalt felt between the anchorage caisson foundation and the grouting bed, and the cohesive force of adding geotextile between the anchorage caisson foundation and the grouting bed are measured, respectively. When the contact surface is concrete and geotextile, the fracture form of the specimen was analyzed by numerical simulation, and the AE variation trend of the two specimens have been studied. The results of this article can provide references for other projects.

Berlamont, Jean E., e Hilde M. Torfs. "Modeling (partly) cohesive sediment transport in sewer systems". Water Science and Technology 33, n. 9 (1 aprile 1996): 171–78. http://dx.doi.org/10.2166/wst.1996.0204.

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Although the basic mechanisms of sediment transport in sewers are the same as in rivers, it is not necessarily appropriate to use the many models that have been developed for sediment transport in rivers also in sewers. Different reasons are: 1) sewer sediments are often mixtures of cohesive and non cohesive material, and the bed is often stratified; 2) due to consolidation of the (partly cohesive) bed material, the erosion resistance of the bed may vary with time; 3) the flow conditions in sewers are usually unsteady, which is not accounted for in the classical sediment transport models; 4) existing models have been derived from experiments in rectangular flumes: the results are not directly applicable to sewers with circular cross section where the distribution of bed shear stress may be completely different from a rectangular section; 5) the limited availability of erodible material and the varying supply of sediments add additional difficulty to the modelling of sediment transport in sewers.

Mosquera, R., V. Groposo e F. Pedocchi. "Acoustic measurements of a liquefied cohesive sediment bed under waves". Advances in Geosciences 39 (1 aprile 2014): 1–7. http://dx.doi.org/10.5194/adgeo-39-1-2014.

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Abstract. In this article the response of a cohesive sediment deposit under the action of water waves is studied with the help of laboratory experiments and an analytical model. Under the same regular wave condition three different bed responses were observed depending on the degree of consolidation of the deposit: no bed motion, bed motion of the upper layer after the action of the first waves, and massive bed motion after several waves. The kinematic of the upper 3 cm of the deposit were measured with an ultrasound acoustic profiler, while the pore-water pressure inside the bed was simultaneously measured using several pore pressure sensors. A poro-elastic model was developed to interpret the experimental observations. The model showed that the amplitude of the shear stress increased down into the bed. Then it is possible that the lower layers of the deposit experience plastic deformations, while the upper layers present just elastic deformations. Since plastic deformations in the lower layers are necessary for pore pressure build-up, the analytical model was used to interpret the experimental results and to state that liquefaction of a self consolidated cohesive sediment bed would only occur if the bed yield stress falls within the range defined by the amplitude of the shear stress inside the bed.

Wang, Rui, e Guoliang Yu. "Experimental study on incipient condition of fluidized bed sediment in oscillatory". E3S Web of Conferences 81 (2019): 01014. http://dx.doi.org/10.1051/e3sconf/20198101014.

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In this paper, the incipient condition of the fluidized bed sediment with different sizes and water contents were experimentally studied in an os- cillatory tunnel made of acrylic boards. One-hundred experimental runs were performed with sediment samples by varying the yield stress to determine the relationship between the critical condition of incipient motion and the rheolog- ical properties of the cohesive sediments. Experimental results showed that the yield stress of the bed sediment decreased as the fluidization level increased. When the yield stress is no longer changed, the bed sediment was considered completely fluidized. In oscillatory flow, the critical shear stress decreases with the increase of fluidization level. When the bed sediment reaches the full flu- idization state, the critical shear stress of the bed sediment at the bottom re- mained constant. For cohesive sediments, in the case that particle size and bulk density were known, the relationship between the yield stress and the critical shear stress was analyzed, and the incipient condition of the cohesive sediment under oscillatory flow action was determined.

Sherwood, Christopher R., Alfredo L. Aretxabaleta, Courtney K. Harris, J. Paul Rinehimer, Romaric Verney e Bénédicte Ferré. "Cohesive and mixed sediment in the Regional Ocean Modeling System (ROMS v3.6) implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST r1234)". Geoscientific Model Development 11, n. 5 (14 maggio 2018): 1849–71. http://dx.doi.org/10.5194/gmd-11-1849-2018.

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Abstract. We describe and demonstrate algorithms for treating cohesive and mixed sediment that have been added to the Regional Ocean Modeling System (ROMS version 3.6), as implemented in the Coupled Ocean–Atmosphere–Wave–Sediment Transport Modeling System (COAWST Subversion repository revision 1234). These include the following: floc dynamics (aggregation and disaggregation in the water column); changes in floc characteristics in the seabed; erosion and deposition of cohesive and mixed (combination of cohesive and non-cohesive) sediment; and biodiffusive mixing of bed sediment. These routines supplement existing non-cohesive sediment modules, thereby increasing our ability to model fine-grained and mixed-sediment environments. Additionally, we describe changes to the sediment bed layering scheme that improve the fidelity of the modeled stratigraphic record. Finally, we provide examples of these modules implemented in idealized test cases and a realistic application.

Più fonti

Tesi sul tema "Cohesive bed":

Shaker, Amjad Hamed. "An investigation of erosion and deposition of fine cohesive sediments". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242460.

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Letter, Joseph V. "Significance of probabilistic parameterization in cohesive sediment bed exchange". [Gainesville, Fla.] : University of Florida, 2009. http://purl.fcla.edu/fcla/etd/UFE0022613.

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Ockelford, Anne-Marie. "The impact of stress history on non cohesive sediment bed stability and bed structure". Thesis, University of Glasgow, 2011. http://theses.gla.ac.uk/2577/.

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Historically the inter-flood period has been disregarded from investigations as it was deemed that the stability of non cohesive beds could only be altered by above threshold flows capable of sediment transport. However, this is at odds with more recent ‘stress history’ data which provides unequivocal evidence that entrainment thresholds can be delayed to higher shear stresses after being subjected to longer periods of sub threshold flows. The magnitude of this effect appears related to the surface grain size distribution and relative grain size effects, whilst the specific mechanics associated to generating a more resistant bed under sub-threshold flows are merely speculated upon. The aim of the present thesis is therefore to provide a comprehensive and quantitative data set on stress history that specifically address comparative grade effects and provides a detailed mechanistic understanding of the processes responsible for generating a more resistant bed configuration under sub threshold flows. Using a range of grain size distributions, a series of flume based experiments assess two main aspects of the stress history process. Firstly the effects of grain size distribution on the relationship between stress history duration and entrainment threshold is quantified. This is split into two sets of experiments based on the duration of the applied sub threshold antecedent flow, prescribed as 50% of the critical shear stress ( ) of the median grain size (D50). The antecedent durations of first set of experiment ranged from 0 to 60 minutes, whilst the antecedent duration of the second set of experiments ranged from 0 to 960 minutes. To ascertain the effect of the antecedent period on critical entrainment threshold and transported bedload, each experiment is concluded with a stability test composed of incrementally increased flow discharges until critical threshold conditions were reached. Secondly, aspect of stress history investigated uses high resolution laser scanning to assess bed topography and particle repositioning in order to ascertain the granular mechanics underpinning the stability process. The bed is scanned before and after the application of the applied antecedent flow with changes to bed surface structure described using Digital Elevation Models (DEM’s), statistical analysis and 1D and 2D semi-variograms to analyse scaling behaviour. In all experiments, increasing the antecedent flow duration significantly increases river bed stability in that the critical shear stress increases by up to 25% where uniform beds are more responsive to antecedency than bimodal beds. Laser based analysis reveals that vertical settlement, localised changes to bed roughness, pockets of more pronounced development of hiding effects, and particle repositioning are all mechanisms by which the bed reorganises under an applied sub threshold flow. However, the different bed grain size distributions cause significant differences in the importance of each mechanism in determining the magnitude of stress history induced bed stability.

Ebisa, Fola Miressa. "Downstream hydraulic geometry of clay-dominated cohesive bed stream channels". Thesis, University of Ottawa (Canada), 2007. http://hdl.handle.net/10393/27838.

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Empirical downstream hydraulic geometry equations for clay-dominated cohesive bed (semi-alluvial) streams were derived using the data from five streams in eastern Ontario and four streams from other regions. The width exponent (0.57) is comparable to the exponents reported for previous studies; however, depth exponent (0.52) was greater for clay-dominated cohesive bed than for typical gravel-bed and sand-bed rivers. Furthermore, the recurrence intervals of bankfull discharges of those streams range from 1 to 2 years. To the author's knowledge, this is the first study which related bankfull hydraulic variables and discharges to derive downstream hydraulic geometry equations specifically for clay-dominated cohesive bed streams. Assessment of width:depth ratio depicted that large channels were deeper and narrower than comparable gravel-bed channels, but small channels were actually wider and shallower than typical gravel-bed rivers. This can likely be attributed to the resistance of stiff and consolidated cohesive-bed to erosive effects of more frequent flows.

Lintern, David Gwyn. "Influences of flocculation on bed properties for fine-grained cohesive sediment". Thesis, University of Oxford, 2003. http://ora.ox.ac.uk/objects/uuid:f26b7e9d-9de2-4ab0-8090-feef8c3bac9b.

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An understanding of the behaviour of newly deposited soil is important because of its direct applications in fields such as harbour siltation and storage of dredge slurries. In coastal regions the dominant mode for deposition of fine-grained cohesive material is through flocculation- the electrostatic aggregation of mud particles. The present study focuses on the measurement of both flocculation conditions and bed properties, towards the understanding of the influence of the former on the latter. A computerised laboratory setup, complete from sedimentation and flocculation to the long term consolidation allows each of these processes to be observed in instrumented perspex columns without the many variables present in an estuary. The bed deposition rates resemble those found in natural estuaries, and therefore this technique is a much improved method for examining natural processes than the method of slurry deposition, which is normally employed in soil mechanics. An image acquisition and analysis system has been designed specifically for this work. Image sequences are analysed in real time to give information about the dimensions and concentration of the particles, and the particle velocities. Floc sizes increase as the particle concentration increases in the column. Increasing the concentration further leads to an overall hindering of the sedimentation rate and breakup of the flocs. Images of beds formed through slow sedimentation clearly show aggregate features that are not present in slurry experiments. From low to medium sedimentation rates the bed height, normalised by the mass of sediment in the bed, increases. From medium to high rates of sedimentation, however, the normalised bed heights decrease. Overall slurry experiments have lower bed heights than slowly deposited experiments. Image analysis of the bed surface (top 0.5mm) has revealed that aggregates which are present immediately after deposition are broken down over tens of hours. The ISIS instrument has been modified to gather information about the resistance to erosion of the beds. A bed is more easily eroded after it has had a long period of consolidation. X-ray density measurements and imaging techniques are used to link the strength of the bed to biological factors. X-ray bulk density and pore pressure measurements allow calculations of void ratio, porosity, and effective stress. Bender element apparatus has been constructed to measure shear stiffness of the soil, and bed strength measurements are made using a shear vane. It is found that variations in the sedimentation conditions have significant effects on bed density and on void ratio. These effects continue to be visible in the consolidated bed, even after an order of magnitude increase in the total vertical bed stress (equivalent to the range of metres of overburden pressure). The variations in the bed structure can have profound effects on bed strength. Methods to compare floc measurements to bed measurements are complicated by the inherent variation in floc data. Possible techniques include the use of solids volume fraction, fractal dimension and intrinsic sediment properties. The usefulness of each of these is assessed. It is suggested that it is the frequency at which the bed is bombarded by flocs, and not the properties of the flocs themselves, that largely determines the bed properties.

Llull, Marroig Antoni Ignaci. "Ship propeller induced scour of non-cohesive sediment in low bed-clearance conditions". Doctoral thesis, Universitat Politècnica de Catalunya, 2022. http://hdl.handle.net/10803/673563.

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Ships maneuvering in low bed clearance conditions induce sediment scour due to the high speed jet generated by a rotating propeller. Sediment scour is known to cause instability to quay structures, damage to the bed protection and may create huge accretion areas reaching extremely low depths, preventing the free passage of large ships. This on-going problem is linked to the constant increase in commercial ship sizes and is widely recognized in current harbor management guidelines. This thesis presents in the first place the experimental work carried out to study the effects of two common propeller systems over the sediment bed: single and twin propellers. Next, the analysis of a case study is used to evaluate the impact of ship maneuvers over the seabed in a particular harbor basin. The first part of the thesis presents a set of experiments in propeller jet velocity and bed shear stresses. By measurements performed in a point-by-point grid, with a Pitot-static tube coupled to differential pressure sensors, the axial velocity distribution at the so-called efflux plane is characterized. After that, direct measurements of bed shear stress are performed at several speeds of rotation and two bed-clearance distances with a shear plate. Velocity and bed shear stress measurements are related by an empirical friction coefficient, which is dependent on the bed clearance. A new empirical model is presented to estimate the mean shear stress in case of unconfined ship propeller jets in low bed clearance conditions. The second part of this work shows the results of a new set of experiments in local scour due to confined twin propeller jets. The maximum scour depth is studied as a function of the bed clearance, the wall clearance and the efflux velocity of the jet. Aiming to reproduce more realistic maneuvers, scour due to forward and backward rotation of the propellers is analyzed, showing a different behavior compared to the traditional experiments with only forward rotation. The obtained results are compared to the existing formulae and later used to propose two different empirical models, one for each regime of rotation. A new non-dimensional parameter obtained from the Buckingham Pi analysis, proposed as Wall Froude number, is used to find a threshold triggering the scouring mechanism. The experimental results show that the distance to the vertical wall is the main contributor to the higher scour depths rather than the bed clearance. The last part of the thesis presents a case study that is used to relate the maneuvers of the ship with the scour observed in an inner basin of the port. The study ship characteristics are obtained from the port statistics. The morphological evolution of the seabed is analyzed through hydrographic surveys of the last decade, which allows characterizing the erosion pattern. Through AIS data, the maneuver of the study ship is analyzed and used as an input maneuver in a simulator. The maneuver is reproduced to obtain the behavior of the main engines and bow thrusters. The maneuvering pattern and the behavior of the engines are used to assess the most damaging maneuvering sections, which turns out to be the ship's lateral approach to the berth, during the arrival maneuver, and the early stages of the departure maneuver.
Els vaixells que maniobren en condicions de calat reduït poden provocar erosió local del llit de sediments a causa del raig d'aigua d'alta velocitat generat per les hèlix. L'erosió causa inestabilitat en les estructures dels molls, danys a la protecció del llit i pot crear grans àrees d'acreció, posant en risc la seguretat en la navegació. Aquest fenòmen està relacionat en gran mesura amb l'augment de les dimensions dels vaixells comercials en les darreres dècades i és àmpliament reconegut en les guies actuals de gestió portuària. Aquesta tesi presenta, en primer lloc, el treball experimental realitzat per estudiar els efectes erosius provocats per dos dels sistemes de propulsió més comuns: hèlix convencional i sistema de doble hèlix. A continuació, s'utilitza l'anàlisi d'un cas pràctic per avaluar l'impacte de les maniobres dels vaixells sobre el fons marí en una dàrsena portuària concreta. A la primera part de la tesi es presenten i s'analitzen en un conjunt de mesures experimentals de velocitat del flux d'aigua a la sortida de l'hèlix i de tensions de tall sobre un llit horitzontal. La distribució de velocitats axials es caracteritza a partir de mesures puntuals preses amb un sistema de tub de Pitot-estàtic acoblat a sensors de pressió diferencial. Posteriorment es realitzen mesures directes de les tensions de tall al llit amb una placa de tensions (shear plate) a tres velocitats de rotació de l'hèlix i dues distàncies verticals sobre el llit. Les mesures de la velocitat i la tensió de tall es relacionen amb un coeficient de fricció empíric que és dependent de la distància al llit. A la segona part d'aquest treball es presenta un nou conjunt d'experiments en erosió local per sistemes de doble hèlix confinats. La profunditat màxima d'erosió s'estudia en funció de la distància al sòl, la distància a la paret i la velocitat de sortida del raig d'aigua. Amb l'objectiu de reproduir maniobres de vaixells en entorns portuaris, s'analitza l'erosió generada pels sistemes de doble hèlix en règim combinat, és a dir, avant i invertit. Els resultats mostren diferències respecte els experiments tradicionals en què només es considera la rotació avant. Per estimar l'evolució temporal de la màxima profunditat d'erosió es proposen dos models empírics, un per a cada règim de rotació. De l'anàlisi de Pi de Buckingham s'obté un nou paràmetre adimensional que, proposat com a nombre de Froude del mur, permet establir un llindar d'erosió. Els resultats experimentals també mostren que la distància al mur vertical està més relacionada amb les majors profunditats d'erosió que amb la distancia al sòl. La darrera part de la tesi presenta un cas d'estudi en què les maniobres del vaixell es relacionen amb els canvis en la morfologia portuària observada al llarg del temps. El vaixell d'estudi s'obté a partir de les estadístiques d'ús de les dàrsenes portuàries. L'evolució morfològica del fons marí s'analitza mitjançant estudis hidrogràfics de la darrera dècada, que permet caracteritzar el patró d'erosió. A través de dades AIS, s'analitza la maniobra del vaixell d'estudi i s'utilitza com a model de maniobra en un simulador. La maniobra es reprodueix al simulador, d'on se n'extreu el comportament dels motors principals i de les hèlix de maniobra. El patró de maniobra i el comportament dels motors s'utilitzen per avaluar les seccions de maniobra més perjudicials, que resulten ser l'aproximació lateral del vaixell al moll d'atrac, durant la maniobra d'arribada, i les primeres etapes de la maniobra de sortida.
Enginyeria nàutica, marina i radioelectrònica naval

Mooneyham, Christian David. "Interaction of Clay Wash Load With Gravel Beds". Thesis, Virginia Tech, 2017. http://hdl.handle.net/10919/84547.

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This study focuses on the interaction of wash load particles with gravel bed rivers. The effects of excess fine sediment loading to streams on general water quality, contaminant transport, and benthic organism mortality has been well examined. A fundamental assumption in fluvial geomorphology and river engineering is that wash load particles ($d<63mu m$) do not deposit to stream beds, but are instead transported downstream until they deposit in reservoirs or estuaries. The goal of this study is to determine if wash load sized particles can deposit to gravel beds, where within the bed substrate deposition occurs, under what hydraulic conditions it occurs, and how the composition of the bed affects the spatial and temporal deposition pattern. Further, this study attempts to quantify the mass flux of wash load to the bed based on a simple mass conservation model using the aforementioned conditions as model parameters. This was accomplished through a series of experiments in which a mixture of pure kaolinite clay was allowed to deposit at constant shear over an acrylic, gravel, or sand-gravel mixture. Discharge was then increased to determine the effects of increased bed shear stress on deposited material and further wash load interaction with the bed. Results indicate that wash load will deposit to acrylic, gravel, and sand-gravel beds during conditions where no bedload movement is occurring. Bed composition is the primary factor controlling the mass flux of wash load from the water column to the bed. Deposition on acrylic beds forms clay ripples which translate downstream, while deposition in porous beds occurs primarily within the bed substrate. Shear stress also affects mass flux and the magnitude of its effects are related to the bed composition. Discharge increases below the threshold of bedload movement only cause large scale entrainment of deposited particles over non-porous beds. Periods of higher discharge over porous beds result in continued deposition within the bed substrates. This research enhances not only our knowledge of sediment processes within fluvial systems, but also allows for the quantification of the wash load portion of those processes given minimal initial condition information. The model developed here may be used within larger hydrologic models when examining contaminant spills or mass loading of stream networks with wash load to estimate the mass deposition to the bed. Instances where wash load is contaminated the mass of contaminated sediment retained by the bed is of great importance to local communities given a reliance of residents on that water source for water, livelihood, and recreation.
Master of Science

Harsanto, Puji. "Erosion Characteristics of Cohesive Sediment Bed and Bank, and Their Effects on River Morphology". 京都大学 (Kyoto University), 2012. http://hdl.handle.net/2433/160989.

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Thompson, Charlotte E. L. "The role of the solid-transmitted bed shear stress of mobile granular material on cohesive bed erosion by unidirectional flow". Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.398824.

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Rangel, Roberto Carlos. "Evolution of a non-cohesive granular bed subject to a succession of erosive turbidity currents". Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/36712.

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Abstract (sommario):

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2006.
Includes bibliographical references (leaf 18).
An experiment was performed to study the evolution of a non-cohesive granular bed subject to a succession of erosive turbidity currents to evaluate the applicability of a proposed interface model that prescribes a relationship between the bed shear stress and the local bed elevation and local bed slope. This study considered only the relationship between the local bed elevation and the shear stress by using non-cohesive plastic particles as bed sediment that was laid down in a subaqueous straight channel. The elevation of the plastic bed was measured before and after it was subjected to two erosive salt water turbidity currents using a high resolution displacement laser mapping system. These changes in elevation of the sediment bed are compared to determine whether a correlation exists between local bed elevation and bed erosion. The results from this experiment display a weak correlation between the erosion of the plastic bed and the initial local bed elevation when the initial elevation height is small relative to the thickness of the turbidity currents.
(cont.) However, a strong correlation exists when the initial elevation height is approximately 2% to 6% of the turbidity current thickness. The strength of this correlation also depends upon the window size of the analysis which is shown to be associated with the downstream variability in bed roughness.
by Roberto Carlos Rangel.
S.B.

Più fonti

Libri sul tema "Cohesive bed":

Thompson, Charlotte. The effect of the presence of cockle shells on the erosion of a cohesive sediment bed. Southampton: University of Southampton, School of Ocean and Earth Science, 1997.

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Saw, L. C. An investigation of the relationship between the properties of a settled cohesive bed and the eroded flocs. Manchester: UMIST, 1997.

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Ritzen, J. M. M. On "good" politicians and "bad" policies: Social cohesion, institutions, and growth. Washington, DC: World Bank, World Bank, Office of the Vice President, Development Policy, and Development Research Group, Macroeconomics and Growth, 2000.

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Liu, Xianggang. He cheng jun dui zhan dou zhuang bei bao zhang fen dui xing dong. 8^a ed. Beijing: Jun shi ke xue chu ban she, 2009.

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Heath, Anthony F., Elisabeth Garratt, Ridhi Kashyap, Yaojun Li e Lindsay Richards. The Challenge of Social Corrosion. Oxford University Press, 2018. http://dx.doi.org/10.1093/oso/9780198805489.003.0008.

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Has increasing inequality and ethnic diversity served to corrode social cohesion in Britain? The evidence discussed in this chapter suggests that in many respects, such as levels of national pride, social trust, and civic engagement, Britain has not in fact changed all that much since the 1950s and 1960s. Nor is Britain all that out of line with peer countries. However, there are long-standing problems of social division, low trust, and disconnection from politics, albeit sometimes taking new forms. In some respects, then, Britain is not all that cohesive. Moreover, there are some new emerging challenges such as declining election turnout, especially among young people, and declining sense of British identity in Ireland and Scotland. However, these emerging challenges cannot be blamed on inequality and diversity. Instead, the explanations, and the solutions, are more likely to be specific and political.

Ornston, Darius. Good Governance Gone Bad. Cornell University Press, 2018. http://dx.doi.org/10.7591/cornell/9781501726101.001.0001.

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The small, open economies of Nordic Europe are hailed as paragons of good governance, adapting flexibly to rapid, technological change and shifting patterns of economic competition. But they have also made strikingly poor policy choices and suffered devastating economic crises, as evidenced by the Finnish and Swedish banking crises of the early 1990s, Finnish dependence on Nokia, and Iceland's financial meltdown. Good Governance Gone Bad argues that the reasons for these two, seemingly contradictory phenomena is one and the same. The dense, cohesive relationships that enable these countries to adapt to economic crises with radical reform and restructuring render them vulnerable to policy overshooting and overinvestment. After examining the rise and decline of heavy industry in postwar Sweden, the emergence and disruption of the Finnish ICT industry, and Iceland's impressive but short-lived reign as a financial powerhouse, this book tests the argument against ten similar and contrasting cases in Europe and North America. In doing so, it demonstrates how small and large states alike can learn from the Nordic experience.

Woolcock, Michael, William Easterly e Jo Ritzen. On Good Politicians and Bad Policies: Social Cohesion, Institutions, and Growth. The World Bank, 2000. http://dx.doi.org/10.1596/1813-9450-2448.

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Holtug, Nils. The Politics of Social Cohesion. Oxford University Press, 2021. http://dx.doi.org/10.1093/oso/9780198797043.001.0001.

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In contemporary liberal democracies, it is difficult to find a policy issue as divisive as immigration. A common worry is that immigration poses a threat to social cohesion, and so to the social unity that underpins cooperation, stable democratic institutions, and a robust welfare state. At the heart of this worry is the suggestion that social cohesion requires a shared identity at the societal level. The Politics of Social Cohesion considers in greater detail the impact of immigration on social cohesion and egalitarian redistribution. First, it critically scrutinizes an influential argument, according to which immigration leads to ethnic diversity, which again tends to undermine trust and solidarity and so the social basis for redistribution. According to this argument, immigration should be severely restricted. Second, it considers the suggestion that, in response to worries about immigration, states should promote a shared identity to foster social cohesion in the citizenry. It is argued that the effects of immigration on social cohesion do not need to compromise social justice and that core principles of liberty and equality not only form the normative basis for just policies of immigration and integration, as a matter of empirical fact, they are also the values that, if shared, are most likely to produce the social cohesion among community members providing the social basis for implementing justice. This argument draws heavily on both normative political philosophy and empirical social science. The normative framework defended is cosmopolitan, liberal egalitarian, and to some extent multicultural.

Whitman, John, e Yohei Ono. Diachronic interpretations of word order parameter cohesion. Oxford University Press, 2017. http://dx.doi.org/10.1093/oso/9780198747840.003.0004.

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This chapter uses statistical tools to investigate the interrelationship between typological features in the World Atlas of Language Structures Online (Dryer and Haspelmath 2013) in the WALS 201 language sample, with the objective of determining how crosscategorial word order generalizations might emerge as the result of syntactic change. Multiple Correspondence Analysis and a variety of cluster analyses show that word order features tend to group along the familiar lines of the Head Parameter. But there is an important caveat to this, previously noticed by Albu (2006): word order features in NP (e.g. [Order of noun and determiner], [Order of noun and adjective]) group separately from word order features in VP and PP, with the exception of [Order of noun and genitive]. We provide a diachronic explanation for this fact: nouns and their arguments may be reanalysed as PPs, or in the case of reanalysed nominalizations, clauses.

McCarty, Megan, e Steven Karau. Social Inhibition. A cura di Stephen G. Harkins, Kipling D. Williams e Jerry Burger. Oxford University Press, 2016. http://dx.doi.org/10.1093/oxfordhb/9780199859870.013.9.

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Social inhibition is the tendency for behaviors that are exhibited when one is alone to be minimized in the presence of others. Despite the long tradition of research investigating the effects of social presence on behavior, research on social inhibition does not constitute a cohesive literature. This chapter integrates social inhibition research from different traditions, focusing on helping behaviors, emotional expression, and behaviors that elicit social disapproval. We discuss moderators and processes that explain when and why social inhibition occurs: arousal, ambiguity, pluralistic ignorance, diffusion of responsibility, feelings of capability, evaluation apprehension, and confusion of responsibility. Key distinctions between social inhibition and related concepts are presented, helping to establish social inhibition as a central social influence concept. We conclude with an analysis of why social inhibition research has not formed a cohesive literature, and we hope that our review of social inhibition facilitates the integration of future research on the topic.

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Capitoli di libri sul tema "Cohesive bed":

Hayter, Earl J. "Estuarial Sediment Bed Model". In Estuarine Cohesive Sediment Dynamics, 326–59. New York, NY: Springer New York, 1986. http://dx.doi.org/10.1007/978-1-4612-4936-8_16.

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Hayter, Earl J. "Estuarial Sediment Bed Model". In Estuarine Cohesive Sediment Dynamics, 326–59. New York Inc.: Springer-Verlag, 2013. http://dx.doi.org/10.1029/ln014p0326.

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Sills, Gilliane C., e Don McG Elder. "The Transition from Sediment Suspension to Settling Bed". In Estuarine Cohesive Sediment Dynamics, 192–205. New York, NY: Springer New York, 1986. http://dx.doi.org/10.1007/978-1-4612-4936-8_10.

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Sills, Gilliane C., e Don McG Elder. "The Transition from Sediment Suspension to Settling Bed". In Estuarine Cohesive Sediment Dynamics, 192–205. New York Inc.: Springer-Verlag, 2013. http://dx.doi.org/10.1029/ln014p0192.

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Kusuda, Tetsuya, Ryoichi Watanabe, Tohru Futawatari e Hiroyuki Yamanishi. "Fluid mud movement on an inclined bed". In Nearshore and Estuarine Cohesive Sediment Transport, 281–94. Washington, D. C.: American Geophysical Union, 1993. http://dx.doi.org/10.1029/ce042p0281.

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Xu, Jishang, Jinjing Pu e Guangxue Li. "Field Observations of Seabed Scours around a Submarine Pipeline on Cohesive Bed". In Advances in Intelligent and Soft Computing, 23–33. Berlin, Heidelberg: Springer Berlin Heidelberg, 2012. http://dx.doi.org/10.1007/978-3-642-27957-7_4.

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Villaret, C., e B. Latteux. "Long-Term Simulation of Cohesive Sediment Bed Erosion and Deposition by Tidal Currents". In Computer Modelling of Seas and Coastal Regions, 363–78. Dordrecht: Springer Netherlands, 1992. http://dx.doi.org/10.1007/978-94-011-2878-0_27.

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Partheniades, Emmanuel. "Effect of Bed Shear Stresses on the Deposition and Strength of Deposited Cohesive Muds". In Frontiers in Sedimentary Geology, 175–83. New York, NY: Springer New York, 1991. http://dx.doi.org/10.1007/978-1-4612-4428-8_18.

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Zhou, Heng, Sheng-li Wu, Ming-yin Kou, Shun Yao, Bing-jie Wen, Kai Gu e Feng Chang. "DEM Simulation of Dispersion of Cohesive Particles by Spontaneous Inter-particle Percolation in a 3D Random Packed Bed". In The Minerals, Metals & Materials Series, 225–35. Cham: Springer International Publishing, 2018. http://dx.doi.org/10.1007/978-3-319-72131-6_20.

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Ikeda, Sanford. "Social Networks and Action Space in Cities". In A City Cannot Be a Work of Art, 131–77. Singapore: Springer Nature Singapore, 2023. http://dx.doi.org/10.1007/978-981-99-5362-2_5.

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AbstractThis chapter builds on Jacobs’s insights into social networks as a cohesive force in cities. It introduces social-network concepts into market-process economics, links it to Jacobsian economics, and grounds them both on a common social theory. In doing so, it further develops the concepts of Jacobs Density and action space.

Atti di convegni sul tema "Cohesive bed":

Teixeira, Senhorinha F. C., Maria Amélia Araújo e José C. Teixeira. "Flow Structure Over a Simulated Bed for Costal Cohesive Sediment Erosion Studies". In ASME 2013 Fluids Engineering Division Summer Meeting. ASME, 2013. http://dx.doi.org/10.1115/fedsm2013-16243.

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Houwing, Erik-Jan, e Leo C. van Rijn. "In-Situ Determination of the Critical Bed-Shear Stress for Erosion of Cohesive Sediments". In 24th International Conference on Coastal Engineering. New York, NY: American Society of Civil Engineers, 1995. http://dx.doi.org/10.1061/9780784400890.150.

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Yu, Hui, Wenkai Wang e Yuchuan Wang. "Experimental research on suction beneath pile foundation being pulled out from cohesive soil bed". In 21st International Scientific Conference Engineering for Rural Development. Latvia University of Life Sciences and Technologies, Faculty of Engineering, 2022. http://dx.doi.org/10.22616/erdev.2022.21.tf010.

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Roy, Samit, Priyank Upadhyaya, Mohammad H. Haque e Hongbing Lu. "A Multi-Scale Viscoelastic Cohesive Layer Model for Predicting Delamination in HTPMC". In ASME 2014 International Mechanical Engineering Congress and Exposition. American Society of Mechanical Engineers, 2014. http://dx.doi.org/10.1115/imece2014-36397.

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In this paper, a novel numerical-experimental methodology is outlined to predict delamination in pristine as well as isothermally aged (in air) polymer matrix composites. A rate-dependent viscoelastic cohesive layer model was implemented in an in-house test-bed finite element analysis (FEA) code to simulate the delamination initiation and propagation in unidirectional polymer composites before and after aging. This unified model is fully rate-dependent and does not require a pre-assigned traction-separation law. The actual shape of traction separation law depends on: (a) the strain rate via the viscoelastic constitutive relationship, (b) the degree of thermo-oxidative aging via the changes in the experimentally measured creep compliance due to oxidation, and (c) the evolution of the internal state variable defining the state of damage. To determine the model parameters, double cantilever beam (DCB) experiments were conducted on both pristine and isothermally aged IM-7/bismaleimide (BMI) composite specimens. The J-Integral approach was adapted to extract cohesive stresses near the crack tip. A principal-stretch dependent internal damage state variable defines the damage in the cohesive layer. Within the cohesive layer, pristine and cohesive stresses were compared to estimate the damage parameters. Once the damage parameters had been characterized, the test-bed FEA code employed a micromechanics based viscoelastic cohesive layer model to simulate interlaminar delamination. From a numerical stability standpoint, the viscous regularization effect of the viscoelastic constitutive equations in the cohesive layer helps mitigate numerical instabilities caused by elastic energy released due to crack growth, thereby enabling the FEA model to simulate the load-deflection response of the composite structure well beyond peak load. The present cohesive-layer based FEA model was able to accurately predict not only the macro level load-displacement curve, but also the micro level crack growth history in IM-7/BMI laminate before and after thermal aging, using only three parameters.

Hossfeld, Roderick J., David A. Craig e Roger A. Barnum. "What You Need to Know to Reliably Handle Waste Coal". In 17th International Conference on Fluidized Bed Combustion. ASMEDC, 2003. http://dx.doi.org/10.1115/fbc2003-155.

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Many power producers have been designing for, or switching to waste coal. A major consideration when dealing with waste coal is the design of the fuel handling system. Since waste coal is typically finer and more cohesive and therefore harder to handle in silos, bunkers, chutes and feeders, design of the handling system for reliable, non-stagnant flow is essential. This paper describes a systematic approach to designing and retrofitting handling systems to avoid bulk solids flow problems. Potential trouble areas such as coal hoppers, silos, bunkers, and transfer chutes are discussed. Mass flow and funnel flow patterns that develop in silos and bunkers are presented. Funnel flow results in large stagnant regions, which are a major problem for coals that combust easily and are prone to problems such as arching and ratholing. Mass flow patterns, which eliminate the stagnant coal regions, are also explained. Coal properties and bunker designs that result in mass flow and funnel flow are described. Transfer chute design techniques to avoid pluggages, reduce dusting, and minimize chute wear are discussed. The Panther Creek Energy facility in Nesquehoning, Pennsylvania is used as an example where solids flow handling methodologies were used to solve handling problems with anthracite culm. The modifications presented were required for reliable, stagnant-free coal flow, which prevented belt slippage and high belt loading on gravimetric feeders.

Xu, Bao H., Richard A. Williams e Ai-Bing Yu. "Simulation of Flow of Cohesive Powder in a Gas-Fluidised Bed by a Combined Continuum and Discrete Model". In Third International Conference on Discrete Element Methods. Reston, VA: American Society of Civil Engineers, 2002. http://dx.doi.org/10.1061/40647(259)34.

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Mawatari, Yoshihide, Yasmasa Hamada, Masato Yamamura e Hiroyuki Kage. "Effect of Mechanical Vibrating Condition on Flow Patterns of Fine Cohesive Powders in A Gas-solid Fluidized Bed". In 5th Asian Particle Technology Symposium. Singapore: Research Publishing Services, 2012. http://dx.doi.org/10.3850/978-981-07-2518-1_188.

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Wilkens, Yannik, Ebrahim Ghavampour e Tim Lantzsch. "Influence Of Particle Size Variations And Nanoparticle Coating On Flow Behavior Of 316L Stainless Steel Powder And Mechanical Properties In Powder-based Additive Manufacturing". In Euro Powder Metallurgy 2023 Congress & Exhibition. EPMA, 2023. http://dx.doi.org/10.59499/ep235761175.

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In powder-bed-based additive manufacturing (AM) processes, the flowability of the powder is decisive for the quality of the manufactured part. Since fine particle fractions worsen the flowability, in the laser powder bed fusion (LPBF) process the lower limit of the powder fraction is usually 15 µm. Nanoparticle coatings can reduce the cohesive forces between particles. It has been investigated how the fumed silica (SiO2) nanoparticle coating affect the initial flow behavior of standard gas-atomized (15-45 µm) 316L powder and powders with modified particle size distribution (0-45 µm, 15-63 µm, 0-63 µm). It was demonstrated that flowability and bulk density increased as a result of the coating. Relative density and mechanical properties of the LPBF specimen showed similar results compared to the un-coated powder with increased tensile strength. The economic potential of coated powder for AM was demonstrated by the successful LPBF processing of fractions 15-45 µm and 0-63 µm.

Thoman, Robert W., e Sue L. Niezgoda. "Estimating the Erodibility of Ephemeral, Cohesive Streams that Receive Coal Bed Natural Gas Product Water in the Powder River Basin of Wyoming". In World Environmental and Water Resources Congress 2007. Reston, VA: American Society of Civil Engineers, 2007. http://dx.doi.org/10.1061/40927(243)383.

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Miedema, Sape A. "Constructing the Shields Curve: Part C — Cohesion by Silt, Hjulstrom, Sundborg". In ASME 2013 32nd International Conference on Ocean, Offshore and Arctic Engineering. American Society of Mechanical Engineers, 2013. http://dx.doi.org/10.1115/omae2013-10524.

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The ‘standard’ Shields curve is intended for determining an erosion criterion for non-cohesive particles. Non-cohesive in this respect means that the particles are subject to drag and lift forces and subject to turbulent instantaneous velocities. The particles are not subject to inter-particle attraction or repulsion forces such as van der Waals forces and electro-chemical forces. The bed also is not subject to shear strength or yield stress. A cohesive sediment however is subject to these phenomena, resulting in higher critical shear stresses and higher Shields values. The cohesive effect can result from the presence of a silt (quartz) fraction or the presence of a clay fraction in the sediment. Here only the presence of a silt fraction will be considered. The silt particles in general are small enough to be subject to van der Waals forces. These attraction forces are strong enough to act like glue between the larger sand particles. In order to determine these attraction forces a Virtual Attraction Particle Diameter (VAPD) is introduced. The VAPD is the diameter of a virtual silt particle that can explain for the attraction forces in combination with the d50 of the sand. The VAPD will be in the range of the d1-d5. The van der Waals forces (if strong enough) increase the critical shear stress and thus the Shields parameter with a factor, which is inversely proportional with the d50 and inversely proportional with the VAPD (the diameter of the smallest fraction of the silt particles) to the third power. The relation often found in literature for this factor, inversely proportional with the d50 to the second power, can be explained by the fact that there is often a relation between the d50 and the VAPD. The smaller the d50, the smaller the VAPD. This however can lead to inverse proportionalities with different powers between the first power and the third power, depending on the coincidental choice of the diameter of the silt fraction. The model developed also shows that there does not exist a single Shields curve for sands with a cohesive silt fraction, but for a given set of the sediment density, the maximum sediment density (minimum porosity) and the VAPD, a Shields curve can be constructed. Using a density of 1.95 ton/m3, a minimum porosity of 0.32 (a rather uniform PSD) and a VAPD of 3 μm, the Brownlie equation can be approximated very closely. If the silt does not contain particles with a diameter smaller than 10 μm, there is hardly any cohesive effect. If the silt however contains a fraction of particles with a diameter around 1 μm, the cohesive effect is huge and already influences sand particles with a diameter of 1 mm. The model developed has been verified and validated with experiments from literature and gives a very good match, both quantitatively and qualitatively. The model developed also gives a good explanation of the famous Hjulström and Sundborg diagrams and gives these diagrams a more fundamental basis.

Rapporti di organizzazioni sul tema "Cohesive bed":

Bradford, Joe, Itzhak Shainberg e Lloyd Norton. Effect of Soil Properties and Water Quality on Concentrated Flow Erosion (Rills, Ephermal Gullies and Pipes). United States Department of Agriculture, novembre 1996. http://dx.doi.org/10.32747/1996.7613040.bard.

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Concentrated flow erosion in rills, pipes, ephermal gullies, and gullies is a major contributor of downstream sedimentation. When rill or gullies form in a landscape, a 3- to 5-fold increase in soil loss commonly occurs. The balance between the erosive power of the flow and the erosion resistance of the bed material determines the rate of concentrated flow erosion. The resistance of the bed material to detachment depends primarily on the magnitude of the interparticle forces or cohesion holding the particles and aggregates together. The effect of soil properties on bed material resistance and concentrated flow erosion was evaluated both in the laboratory and field. Both rill erodibility and critical hydraulic shear were greater when measured in 9.0 m long rills under field conditions compared with laboratory mini-flumes. A greater hydraulic shear was required to initiate erosion in the field compared to the mini-flume because of the greater aggregate and clod size and stability. Once erosion was initiated, however, the rate of erosion as a function of hydraulic shear was greater under field conditions because of the greater potential for slaking upon wetting and the greater soil surface area exposed to hydraulic shear. Erosion tests under controlled laboratory conditions with the mini-flume allowed individual soil variables to be studied. Attempts to relate rill erosion to a group soil properties had limited success. When individual soil properties were isolated and studied separately or grouped separately, some trends were identified. For example, the effect of organic carbon on rill erodibility was high in kaolinitic soils, low in smectitic soils, and intermediate in the soils dominated by illite. Slow prewetting and aging increased the cohesion forces between soil particles and decreased rill erodibility. Quick prewetting increased aggregate slaking and increased erodibility. The magnitude of the effect of aging depended upon soil type. The effect of clay mineralogy was evaluated on sand/clay mixtures with montmorillonite (M), Illite (I), and kaolinite (K) clays. Montmorillonite/sand mixtures were much less erodible than either illite or kaolonite sand mixtures. Na-I and Na-K sand mixtures were more erodible than Ca-I and Ca-K due to increased strength from ionic bonding and suppression of repulsive charges by Ca. Na-M was less erodiblethan Ca-M due to increased surface resulting from the accessibility of internal surfaces due to Na saturation. Erodibility decreased when salt concentration was high enough to cause flocculation. This occurred between 0.001 mole L-1 and 0.01 mole L-1. Measuring rill erodibility in mini-flumes enables the measurement of cohesive forces between particles and enhances our ability to learn more about cohesive forces resisting soil detachment under concentrated water flow.

Hendry, J. A., J. K. Dix, C. E. L. Thompson, R. J. S. Whitehouse e J. M. Harris. Scour evolution around a vibrating monopile in cohesive beds. Natural Resources Canada/ESS/Scientific and Technical Publishing Services, 2017. http://dx.doi.org/10.4095/305857.

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Mateo-Berganza Díaz, María Mercedes, Marco Ferroni e J. Mark Payne. Social Cohesion and Development in Latin America and the Caribbean: Analysis, Action, and Coordination. Inter-American Development Bank, gennaio 2006. http://dx.doi.org/10.18235/0008994.

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The present document seeks to set forth the IDB's commitment to the objectives contained in the Declaration of Guadalajara and the parallel Memorandum of Understanding, a commitment that has taken shape in Bank programs and lending, as well as in a growing number of coordination efforts and analytical contributions. Despite progress thus far made, a long road lies ahead if more cohesive societies are to be achieved. Challenges in the operational arena include moving from good design to good execution, the need to improve and expand evaluation, and the building and further consolidation of country institutional capacity. We hope that this document, with its proposal on how to define and measure social cohesion and its discussion of Bank activity and the situation in Latin America and the Caribbean, will help to ensure that such opportunities result in concrete achievements for the region.

Shmulevich, Itzhak, Shrini Upadhyaya, Dror Rubinstein, Zvika Asaf e Jeffrey P. Mitchell. Developing Simulation Tool for the Prediction of Cohesive Behavior Agricultural Materials Using Discrete Element Modeling. United States Department of Agriculture, ottobre 2011. http://dx.doi.org/10.32747/2011.7697108.bard.

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The underlying similarity between soils, grains, fertilizers, concentrated animal feed, pellets, and mixtures is that they are all granular materials used in agriculture. Modeling such materials is a complex process due to the spatial variability of such media, the origin of the material (natural or biological), the nonlinearity of these materials, the contact phenomenon and flow that occur at the interface zone and between these granular materials, as well as the dynamic effect of the interaction process. The lack of a tool for studying such materials has limited the understanding of the phenomena relevant to them, which in turn has led to energy loss and poor quality products. The objective of this study was to develop a reliable prediction simulation tool for cohesive agricultural particle materials using Discrete Element Modeling (DEM). The specific objectives of this study were (1) to develop and verify a 3D cohesionless agricultural soil-tillage tool interaction model that enables the prediction of displacement and flow in the soil media, as well as forces acting on various tillage tools, using the discrete element method; (2) to develop a micro model for the DEM formulation by creating a cohesive contact model based on liquid bridge forces for various agriculture materials; (3) to extend the model to include both plastic and cohesive behavior of various materials, such as grain and soil structures (e.g., compaction level), textures (e.g., clay, loam, several grains), and moisture contents; (4) to develop a method to obtain the parameters for the cohesion contact model to represent specific materials. A DEM model was developed that can represent both plastic and cohesive behavior of soil. Soil cohesive behavior was achieved by considering tensile force between elements. The developed DEM model well represented the effect of wedge shape on soil behavior and reaction force. Laboratory test results showed that wedge penetration resistance in highly compacted soil was two times greater than that in low compacted soil, whereas DEM simulation with parameters obtained from the test of low compacted soil could not simply be extended to that of high compacted soil. The modified model took into account soil failure strength that could be changed with soil compaction. A three dimensional representation composed of normal displacement, shear failure strength and tensile failure strength was proposed to design mechanical properties between elements. The model based on the liquid bridge theory. An inter particle tension force measurement tool was developed and calibrated A comprehensive study of the parameters of the contact model for the DEM taking into account the cohesive/water-bridge was performed on various agricultural grains using this measurement tool. The modified DEM model was compared and validated against the test results. With the newly developed model and procedure for determination of DEM parameters, we could reproduce the high compacted soil behavior and reaction forces both qualitatively and quantitatively for the soil conditions and wedge shapes used in this study. Moreover, the effect of wedge shape on soil behavior and reaction force was well represented with the same parameters. During the research we made use of the commercial PFC3D to analyze soil tillage implements. An investigation was made of three different head drillers. A comparison of three commonly used soil tillage systems was completed, such as moldboard plow, disc plow and chisel plow. It can be concluded that the soil condition after plowing by the specific implement can be predicted by the DEM model. The chisel plow is the most economic tool for increasing soil porosity. The moldboard is the best tool for soil manipulation. It can be concluded that the discrete element simulation can be used as a reliable engineering tool for soil-implement interaction quantitatively and qualitatively.

Perkey, David, e Danielle Tarpley. Using geophysical and erosion properties to identify potential beneficial use applications for Atlantic Intracoastal Waterway sediments. Engineer Research and Development Center (U.S.), luglio 2022. http://dx.doi.org/10.21079/11681/44825.

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In an effort to identify alternative and beneficial use placement strategies for dredged sediments from the Atlantic Intracoastal Waterway (AIWW), the US Army Corps of Engineers, Savannah District (SAS), and the US Army Engineer Research and Development Center (ERDC) performed a series of physical property tests of 34 core borings from the SAS AIWW. Physical property testing found that 14 of the borings were non-cohesive sandy materials that may be suitable for potential beach renourishment or berm construction. The remaining 20 borings had mud contents sufficient enough to result in cohesive behavior. A subset of six of these materials from across the geographic region were further evaluated to characterize their erosion behavior. Following a self-weight consolidation period of 30 days, erosion testing showed that the tested cohesive sediments had critical shear stress values that ranged from 1.7 Pa to 2.9 Pa, suggesting that these sediments would likely be resistant to erosion in most wetland environments after placement. Additionally, the cohesive sediments were found to produce gravel-sized mud clasts. These clasts could account for 20% or more of the eroded mass and significantly reduce the amount of silts and clays incorporated in suspended plumes during and immediately following placement.

Perkey, David W., Danielle R. N. Tarpley e Renée M. Styles. Using Geophysical and Erosion Properties to Identify Potential Beneficial Use Applications for Atlantic Intracoastal Waterway Sediments. U.S. Army Engineer Research and Development Center, luglio 2022. http://dx.doi.org/10.21079/11681/44906.

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Mateo-Berganza Díaz, María Mercedes, Marco Ferroni e J. Mark Payne. La cohesión social en América Latina y el Caribe: Análisis, acción y coordinación. Inter-American Development Bank, maggio 2006. http://dx.doi.org/10.18235/0010209.

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Este documento tiene como objetivo hacer avanzar la discusión generada alrededor del tema de cohesión social así como informar sobre las acciones emprendidas por el Banco Interamericano de Desarrollo (BID) desde que tuviese lugar la Cumbre de Guadalajara en mayo de 2004, que reunió a 58 Jefes de Estado y de Gobierno de países de América Latina y el Caribe (ALC) y de la Unión Europea (UE). El documento pretende igualmente orientar las reflexiones en el marco del esfuerzo conjunto que la Comisión Europea (CE) y el BID han emprendido con el propósito de intercambiar experiencias y aunar acciones en la cooperación al desarrollo y el aumento de la cohesión social en ALC.

Perez-Rivera, Anthony, Jonathan Trovillion, Peter Stynoski e Jeffrey Ryan. Simulated barge impacts on fiber-reinforced polymers (FRP) composite sandwich panels : dynamic finite element analysis (FEA) to develop force time histories to be used on experimental testing. Engineer Research and Development Center (U.S.), gennaio 2024. http://dx.doi.org/10.21079/11681/48080.

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The purpose of this study is to evaluate the dynamic response of fiber-reinforced polymer (FRP) composite sandwich panels subjected to typical barge impact masses and velocities to develop force time histories that can be used in controlled experimental testing. Dynamic analyses were performed on FRP composite sandwich panels using the finite element method software Abaqus/Explicit. The “traction-separation” law in the Abaqus software is used to define the cohesive surface interaction properties to evaluate the damage between FRP composite laminate layers as well as the core separation within the sandwich panels. Numerical models were developed to better under-stand the damage caused by barge impacts and the effects of impacts on the dynamic response of composite structures. Force, displacement, and velocity time histories were obtained with finite element modeling for several mass and velocity cases to develop experimental testing procedures for these types of structures.

Edstrom, Jerker, Ayesha Khan, Alan Greig e Chloe Skinner. Grasping Patriarchal Backlash: A Brief for Smarter Countermoves. Institute of Development Studies, gennaio 2023. http://dx.doi.org/10.19088/backlash.2023.002.

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Nearly three decades ago the UN World Conference on Women at Beijing appeared to be uniting the international community around the most progressive platform for women’s rights in history. Instead of steady advancement, we have seen uneven progress, backsliding, co-option, and a recent rising tide of patriarchal backlash. The global phenomenon of ‘backlash’ is characterised by resurgent misogyny, homo/transphobia, and attacks on sexual and reproductive rights. It is articulated through new forms of patriarchal politics associated with racialised hyper-nationalist agendas, traditionalism, authoritarianism, and alterations to civic space that have become all too familiar both in the global North and South. A wide range of actors and articulations are involved and influenced by underlying drivers and dynamics. A clearer view of the patriarchal nature of current backlash is a prerequisite for building a cohesive movement to counter it, strategically engaging researchers, activists, policymakers and donors in development.

Clifford, Robert, e Doug Cahn. Health, Safety and Environmental Issues in Haiti. Inter-American Development Bank, dicembre 2013. http://dx.doi.org/10.18235/0006979.

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This paper is intended to serve as a resource on the current status of Health, Safety and Environmental (HSE) issues in the apparel industry in Haiti. Section II of this document provides a brief description of the content of the workshops which have been conducted in Haiti and the target audiences. The possible future utilization of the training information and materials in shorter training modules is discussed. Section III is intended to be a resource for IDB staff and other stakeholders with interests in the apparel industry, whether globally or specifically in Haiti. The HSE issues which comprise the core of this section have provided the focus of the training workshops. The recommendations and proposed action plans on these issues are offered to enhance HSE performance in the Haitian factories and to further collaborative efforts with Better Work in Haiti and in other developing countries. Section IV serves a cohesive role by providing some conclusions and final thoughts on the issues which have been addressed in the paper.