Bed Conditions Research Articles

Threshold of Motion Conditions Under Stokes Flow Regime and Comparison With Turbulent Flow Data

AbstractThe present study numerically investigates the effects of bed geometrical properties on particle entrainment driven by Stokes flow. We use different substrate arrangements to alter two important factors: The angle of repose, φ, and degree of exposure, e, of the test particle. The effectiveness of shear flow in mobilizing surface particles will change with e and φ, or collectively, η = e/tanφ, yielding a wide range of critical Shields parameter, θc, values. The use of η is better suited for describing local bed geometry as both e and φ values will change simultaneously during substrate rearranging processes. Furthermore, the range of θc values obtained in this study stems from the limitation of this parameter to relate the applied force variation to local flow and bed conditions. We therefore propose an effective shear ratio, α, to establish such connections between the global and local flow shear intensities. These results provide a unique perspective to examine typical θc data obtained from both Stokes and turbulence regimes. For the case of a single‐particle entrainment under given grain protrusion, Stokes flow‐based θc values are found to be 2 to 3 times larger than the counterpart turbulence data. For the case of channel bed mobility, however, the Shields curve suggests an order of magnitude difference in θc between the two regimes. In part, we attribute this significant θc variation to turbulent flow fluctuations in the first case and varied bed mobility levels in the second, given their distinct theoretical and empirical nature, respectively.

CFD-DEM modelling of sediment transport in sewer systems under steady and unsteady flow conditions.

Numerical and experimental investigations were undertaken to study sediment transport under steady flow conditions and under flush waves in sewer pipes. Experiments were carried out with sand and gravel of different size distributions under smooth and rough bed conditions. Moreover, different hydraulic boundary conditions were investigated for flush waves. The numerical part of this study was carried out in the computational fluid dynamics (CFD) software ANSYS Fluent, which is two-way coupled to the Discrete Element Method (DEM) software EDEM. The main focus of this study is to determine if the CFD-DEM coupled method could reasonably predict the behaviour of sediments in sewers and thus be used for studying various features of sediment transport that are not easy to determine in laboratory experiments or in-situ measurements. Furthermore, it is important to replace the traditional empirical approaches developed for fluvial conditions with new methodologies, which are able to consider the high number of variables involved in sediment transport in sewers. The numerical model was validated with laboratory experiments and used to study details of sediment transport processes in sewers.

Associations between Self-Reported Daily Affect Ratings and Sleep Duration during the First Two Weeks of Antidepressant Therapy

ABSTRACT Background: In the context of a randomized controlled trial evaluating the efficacy of augmenting fluoxetine treatment in young adults with major depressive disorder (MDD) using a modified repeated partial sleep deprivation protocol contrasting 2 weeks of restricted time in bed (i.e., 6 h TIB) to no time in bed restriction (i.e., 8 h TIB) the study examines whether sleep duration and the timing of repeated partial sleep deprivation predicts patient-reported affect ratings. Participants: Participants included 58 young adults with DSM-IV-diagnosed MDD. Methods: Daily ratings of affect and sleep were collected during the first 2 weeks of initiating fluoxetine treatment, yielding 630 person-days. Actigraphy monitoring was employed to assess compliance with time in bed condition. Results: Negative affect ratings and positivity ratios in the morning were more improved among participants assigned to the 6 h TIB condition compared to the 8 h TIB group. Participants whose bedtime was delayed by 2-h nightly demonstrated the most significant improvement in negative affect and positivity ratio during the first 2 weeks of fluoxetine therapy. Moreover, the trajectory of morning negative affect ratings in the first 2 weeks was predictive of remission after 4 weeks of fluoxetine therapy. Conclusions: These findings suggest that monitoring changes in daily affect may be a valuable marker of early treatment response in young adults with MDD.

A combined method for modeling the triggering and propagation of debris flows

This study describes a combined method for rainfall-induced debris flow initiations (landslides) and propagations including a series of numerical analyses. In this study, the debris is assumed as a mixture of soils and water which is physically non-Newtonian fluid. The emphasis is placed on applying the effect of the combination of rainfall-induced landslides and debris flows to the numerical analysis. An analysis of rainfall-induced landslides is conducted to identify the thickness and location of the initial volume of debris flow. The movement of debris flow is subsequently simulated considering entrainments affected by the initial wetting condition (wetting front) estimated from the rainfall-infiltration analysis. The proposed method can simulate a sequential process from the initiation of the debris flows to the deposition based on the prediction of slope failure by rainfall, fluid dynamics based on Navier–Stokes equation, and the analysis of entrainments by considering the effect of the weight of debris and the wetting condition of soil beds. Based on the numerical results of this study, the proposed method could be applied to the analysis of regional-scale landslides and debris flows.

Exploring fire response to high wind speeds: fire rate of spread, energy release and flame residence time from fires burned in pine needle beds under winds up to 27 ms−1

The relationship between wildland fire spread rate and wind has been a topic of study for over a century, but few laboratory studies report measurements in controlled winds exceeding 5ms−1. In this study, measurements of fire rate of spread, flame residence time and energy release are reported for fires burning under controlled atmospheric conditions in shallow beds of pine needles subject to winds ranging from 0 to 27ms−1 (measured 5m above ground level). The data suggested that under constant flow conditions when winds are less than 10ms−1, fire rate of spread increases linearly at a rate of ~3% of the wind speed, which generally agrees with other laboratory-based models. When wind speed exceeds 10ms−1, the fire rate of spread response to wind remains linear but with a much stronger dependence, spreading at a rate of ~13% of the wind speed. Radiative and convective heating correlated directly to wind speed, with radiant heating increasing approximately three-fold as much as convective heating over the range of winds explored. The data suggested that residence time is inversely related to wind speed and appeared to approach a lower limit of ~20s as wind exceeded 15ms−1. Average flame residence time over the range of wind speeds was nominally 26s.

Bestimmung von Mineralstoffen in Blättern von 14 Apfelunterlagen aus der Abrissvermehrung

Very little is known about the mineral composition in the leaves of apple (Malus) rootstocks. Hence, in this study, variations in mineral composition were investigated among fourteen apple rootstocks (P.16, P.22, M.9, B.469, O.3, Mac.9, M.26, Pi.80, M.7, M.2, B.118, MM.11, M.25 and A.2) which have different growth vigor on a loamy soil in the stool bed conditions. Nitrogen (N) was determined by Kjeldahl method. Phosphorus (P) was analyzed using vanadate molybdate colorimetric method. Potassium (K), calcium (Ca), magnesium (Mg), manganese (Mn), iron (Fe), zinc (Zn) and copper (Cu) concentrations were determined using Inductively Coupled Plasma-Optical Emission Spectrometer (ICP-OES). The study results showed that the differences in mineral contents in leaves among apple rootstock genotypes were statistically significant. No problems were found in achieving adequate leaf N, P and Fe uptake of any rootstock. However, it was found to be lack of the K, Ca, Mg and Mn uptake in the majority of the rootstocks. Mac.9 rootstock, followed by B.469, showed high performance with in regard to the uptake of K, Ca and Mg. In general, the uptake of Fe, Ca and Mg of dwarf and semi-dwarf rootstocks were higher than those of vigorous rootstocks. Consequently, P.19, B.469, Mac.9 and M.26 rootstocks had adequate performances in the uptake of all macro and micro elements examined.

Double-averaged kinetic energy budgets in flows over mobile granular beds: insights from DNS data analysis

The equations for double-mean, form-induced and spatially averaged turbulent energy budgets are employed to analyse data from direct numerical simulations of turbulent open-channel flows over transitionally rough mobile beds with intermediate flow submergence. Two scenarios were considered related to (i) near-critical bed condition, and (ii) fully mobile bed condition. The bed was composed of a layer of mobile spherical particles moving on the top of one layer of fixed particles of the same size. Data analysis showed the leading energy exchanges between double-mean, form-induced, turbulent flow field contributions as well as particle motions. Above the fixed particles tops, the turbulent flow receives kinetic energy directly from the mean flow as well as from moving bed particles, which in turn also receive energy from the mean flow. For near-critical bed condition, particle aggregations enhanced mean-flow heterogeneity, strengthened turbulent stresses and their effects on the flow, while at increased bed-mobility, energy transport mechanisms became weaker and conversions induced by viscous stresses and pressure became stronger.

Investigation on the deformation response of submarine pipelines subjected to impact loads by dropped objects

The response of pipelines to transverse impact loads by dropped objects is investigated experimentally and numerically. A series of experiments are carried out to examine the relevant effects, including the bed conditions (rigid or flexible seabed) and impact energy. A finite element numerical model is established to determine the dynamic response and it is validated against the experimental results, showing good consistency. An extensive parametric study is conducted, to examine the effects from various factors, including the velocity, weight and shape of dropped objects, pipeline wall thickness, concrete coating, internal pressure and free pipe span length. The effects of seabed flexibility, burial depth and soil properties on pipeline response are studied with a coupled Eulerian-Lagrangian method, able to simulate large deformation of the soil. Based on these analyses, the model applicability is validated and the research results give an insight to the effects of the various mechanisms on pipeline response, which provides a considerable reference for engineering design of submarine pipelines.

Solute mixing in a permeable non-rectangular channel

Understanding diffusion and solute transport, is regarded as a main activity in environmental management, sustainable development and sedimentation processes because of their role in diffusion of contaminants. The current paper presents an experimental study which was done in a parabolic channel with permeable and impermeable bed conditions in order to estimate the transverse mixing coefficient (TMC) and the maximum solute mixing length (SML) for different channel bed roughness coefficients and discharges. The cross section of the channel was 0.5 m wide and 0.3 m deep with a parabolic shape (i.e. similar to furrow irrigation). Three levels of bed roughness coefficient of 0.02, 0.04, and 0.06, and three discharges of 5, 10, and 15 L/s were considered. Bed infiltration channel was applied at a low level and medium level as well as a case without infiltration. In the current experiments, sodium chloride was used as a soluble tracer and was injected into the water at mid depth in the upstream cross section. The tracer concentration profile in the water and velocity profile were measured at eight cross sections in the channel. The results showed that the values of SML ranged between 20 and 46 m in impermeable and permeable beds channel beds respectively. The assessment of usual discharge values, infiltration, and roughness coefficient of a furrow (agricultural field) indicated that the SML of the furrows were less than 20 m. In the current research, the average dimensionless mixing coefficient was found to be 0.17 in the nonrectangular channel. Eventually, equations were developed to explain the TMC and SML in a permeable parabolic channel that could be beneficial in prediction of fertilizer transport in furrow irrigation.

Comparison of combusting pellets of agro and wood biomass in different fluidized bed conditions

The rise in pellet consumption has resulted in a wider variety of materials for pellet manufacture. Thus, pellet industry has started looking for alternative products in relation to wood biomass, such as wastes from agricultural activities, and related industries, along with the combination thereof, obtaining a broad range of these products. The results of the experiment showed significant differences between the analyzed biomass fuels burned under different operating conditions in a laboratory reactor with a model circulating bed. These differences are mainly associated with problematic phenomena during combustion, including sintering of ashes.

Parenteral re-exposure to an immunologically tolerated protein up to 6h after skin injuries improves wound healing in diabetic mice

IntroductionOral tolerance is an immunological phenomenon defined by specific inhibition of immune responses to proteins contacted by the oral route. However, parenteral re-exposure to orally-tolerated proteins has systemic effects that reduce inflammation to unrelated agents injected soon afterward. Chronic skin wounds are major complications for diabetic patients, which may be related with pro-inflammatory conditions in the wound bed, as well as with impaired angiogenesis. We used a mouse-model of streptozotocin-induced diabetes to test whether injection of a regular dietary protein (zein) concomitantly with skin lesions reduces wound bed inflammation and improves wound healing in diabetic mice. MethodsC57BL/6 mice fed a standard chow containing zein (corn protein) were turned diabetic by streptozotocin injection. Two full skin thickness excisional wounds were created on the dorsum of anaesthetized mice. Experimental groups received one i.p. injection of 10 μg zein in adjuvant, 10 min before or 6 h after wounding and were sacrificed 7 and 40 days thereafter. Skin samples were processed and examined macroscopically and microscopically. ResultsIntraperitoneal injection of zein either before or after skin injuries, reduced the number of leukocytes (CD45+ cells) and of myofibroblasts, increased the number of alternatively activated (M2) macrophages, increased the expression transforming-growth factor (TGF)-β3 and rescued angiogenesis in the wound bed of diabetic mice. Zein treatment reduced the scar area and improved the organization of collagen fibers in the neodermis. ConclusionParenteral re-exposure to a protein previously contacted by the oral route concomitantly with or 6 h after skin injuries reduces wound inflammation and improves wound healing in diabetic mice.

Elsterian ice‐sheet retreat in the southern North Sea: antecedent controls on large‐scale glaciotectonics and subglacial bed conditions

High‐resolution shallow sub‐bottom seismic survey data obtained for the Dudgeon windfarm site located 50 km offshore of the north Norfolk coast in the southern North Sea have revealed that the chalk bedrock in this area is overlain by sediments deposited during the Elsterian and Weichselian glacial periods. A buried N–S‐trending subglacial drainage channel (tunnel valley) filled with Swarte Bank Formation (MIS 12) sediments indicates that the maximum extent of the Elsterian ice‐sheet margin occurred further to the south. Detailed cross‐sections constructed from the seismic data reveal the presence of buried thrust‐block moraine system composed of deformed (folded and thrusted) Swarte Bank Formation sediments, lying beneath a younger sequence of sediments dominated by the glacigenic Bolders Bank Formation (MIS 2). The geometry of the folds and sense of offset on the thrusts, coupled with the morphology of the ridge‐like landforms within this buried moraine system, are consistent with deformation having occurred in response to ice‐push from the N/NE. The chalk bedrock that underlies the glaciotectonized sequence is thought to have provided an antecedent control on the location and preservation of this moraine system. A three‐phase model is proposed to explain the evolution of this thrust‐moraine complex that formed at the oscillating ice margin during the overall active retreat of the Elsterian ice sheet.

Temporal changes of the fish community in a seagrass bed after disappearance of vegetation caused by disturbance of the sea bottom and sediment deposition

AbstractTo investigate the response of the fish community structure to a natural disturbance in their habitat, fish abundance, biomass and species composition were analysed in relation to temporal variability of environmental conditions in a seagrass Zostera marina bed. A total of 3024 fishes belonging to 46 taxa (22 families) were collected by quantitative sampling for 10 years from 2007 to 2016 in the Seto Inland Sea, south-western Japan. Seagrass shoot density decreased to less than 1/20 of its original density after disappearance of vegetation caused by heavy rain in the autumn of 2011 and the area did not recover for the next five years. In order to analyse temporal changes of fish community, the fishes were divided into three groups depending on their habitats or lifestyles: pelagic or migratory species (PM), sand or mud bottom-associated species (SM) and seagrass (Z. marina) – or substrate (rocky bottom including macrophytes) – associated species (ZS). Multiple regression analysis showed seagrass shoot density had the most significant effect on biomass of ZS among the three groups, with higher fish biomass under higher seagrass shoot density. Fish community composition changed after the disappearance of the seagrass vegetation coverage with an increase in abundance of SM during the five years of the post-disturbance period. Seagrass vegetation was concluded to affect temporal change of fish community structure through a stronger influence on fish species that are more dependent on seagrass beds as habitat.

Studies on Solids Flow in a Cold Model of a Dual Fluidized Bed Reactor for Chemical Looping Combustion of Solid Fuels

Abstract The results of investigations on solids flow in a cold model of the dual fluidized bed reactor designed for chemical looping combustion of solid fuels (DFB-CLC-SF) are presented in this paper. The constructed unit consists of two interconnected reactors. The first one, so-called fuel reactor (FR), is operated under bubbling fluidized bed (BFB) conditions, whereas the second one, so-called air reactor (AR), is structurally divided into two sections. The bottom part of AR works under BFB while the upper part, i.e., the riser, is operated in the fast fluidized bed (FFB) regime. In these studies, the air was used for fluidization process in all parts of the DFB-CLC-SF reactor. The glass beads with similar parameters to oxygen carriers (OCs) used in the CLC process were utilized as an inventory. The fluidization conditions are controlled by using the sets of pressure sensors installed around the circulation loop. The experimental data acquired in the tests are further employed to the analysis of solids behavior in a cold model of the DFB-CLC-SF reactor. The main goal of these studies was to establish the conditions for smooth fluidization, which concurrently provide the required residence time of solids in both reactors that is one of the most crucial factors in the CLC process. It was found that the fluidizing gas velocity in reactors has a significant impact on solids behavior and the investigated parameters. However, what is the most important, it was confirmed that the operation condition of the DFB-CLC-SF reactor can be adjusted to meet the requirements resulting from the properties of OCs.

Oil shale reactor: process analysis and design by CFD

The oil shale pyrolysis process using a moving bed reactor was investigated with a three-dimensional mathematical model considering turbulent and multiphase flow in a porous moving bed, under non-isothermal and reactive conditions. Mass, heat and momentum balances involving chemical reactions of interest were formulated following a Eulerian approach to represent the process behavior. In the present approach, the shale bed was modeled as a porous medium and the advection due to its movement was implemented. Process analysis via CFD enabled the location of the drying, heating, reacting and cooling zones to be identified in the pilot-scale reactor. Moreover, it was possible to analyze in detail the conversion of organic matter to products, according to the reaction mechanism. The effects of heat and mass transfer inside the reactor were assessed through parametric sensitivity analysis, considering five parameters and five response values. The results were analyzed using the response surface method, which established the influence of each variable. The best values obtained for the thermal-energy consumption and the mechanical-energy consumption were 126.16 and 12.39kJ/kg, respectively. Considering the best operational conditions, scaling-up effects were also evaluated to shed light on the technical viability as well to carry out the design and analysis of the process.

Multi-phase-flow modeling of underwater landslides on an inclined plane and consequently generated waves

An underwater landslide is a complex multiphase flow phenomenon with potential to cause large waves and destruction. Particle size is an important parameter that affects flow behaviors of multiphase flows. This numerical study examines underwater granular landslides on an inclined plane and their resultant waves with the purpose of exploring how the particle size affects landslide kinematics and wave amplitudes. A rheology-based multi-phase flow model is employed, newly incorporating the Navier-slip condition. Smooth and rough beds that reflect ideal and practical conditions, respectively, are simulated. Five types of particle are used; they are very fine sand, medium sand, coarse sand, granules, and pebbles. The granular masses are initially in the loose-packing condition. Our numerical results demonstrate that a smooth bed results in the faster landslides and the larger impulsive waves than a rough bed. The effects of particle size differ between the two bed conditions. For the rough bed, the relationship between the landslide speed and the particle size is negative, and so is the relationship between the wave amplitude and the particle size. For the smooth bed, the two relationships become concave and non-monotonic.

Chlorination of Alumina Obtained from Nepheline Concentrate Processing and Comparative Assessment of the Complete Aluminum Production Cycle

Abstract—Extended tests of alumina fluid chlorination are performed. The implementation of the chlorine technology is possible when using alumina, which has a high reactivity with chlorine. The improved nepheline technology for obtaining such an oxide is proposed: non-desilicated aluminate liquors undergo carbonization followed by separation of aluminum hydroxide with sodium hydroaluminosilicate and its calcination at 600–800°C. The proposed upgrade, compared to the existing method, is less energy intensive. Two-stage desilication is eliminated, and more favorable conditions are created for the low-temperature digestion of sintered material, reducing the secondary losses of alumina and alkali. The technological parameters of charge chlorination, both powdered and pelleted, are worked out on a scaled-up installation in fluidized bed conditions. The operational and capital cost of a complete aluminum production cycle based on the chlorine technology are evaluated in comparison with the conventional alumina production according to the Bayer process and subsequent electrolysis of cryolite-alumina melts. The comparative cost analysis has shown the advantages of the chlorine technology at the stage of aluminum chloride electrolysis (up to 30%) and the presence of additional costs at the stage of obtaining the intermediate product for chlorination. The chlorine method of aluminum production in modern conditions has the prospects of development not as a mass technology, but as an effective process for obtaining high-purity aluminum (HPA) in small workshops.

Effect of bed material density on the performance of steam gasification of biomass in bubbling fluidized beds

Steam gasification of lignocellulosic biomass in a bubbling fluidized bed reactor was analyzed by means of the composition of the producer gas, including tars, and temperature distribution in the reactor. The catalytic and sorbent effect of sepiolite particles was studied by comparison of the tars generated with those produced in a bed of olivine, widely used in biomass gasification applications. Sepiolite has a lower particle density, which influences the forces acting on fuel and char particles and leads to a more homogeneous distribution of them in the dense bed during the gasification process. Fluidized beds of sepiolite particles contribute to increase the heating value of the producer gas and its hydrogen content compared to gasification under the same operating conditions in olivine beds. Furthermore, the tar yield is around 25% lower when gasifying in sepiolite beds, reducing the requirement of secondary methods for tars removal. Long-term gasification tests were also conducted in a sepiolite bed to evaluate the mitigation of the sorbent/catalytic effect of sepiolite with time.

The velocity patterns in rigid and mobile channels with vegetation patches

Studying the hydraulic characteristics in an open channel with vegetation is very important for controlling environment pollution and for restoring river ecology. In this paper, the authors investigate the influence of bed form and vegetation patch density on the spatial velocity pattern. Rigid fiberglass circular cylinders were used to simulate vegetation and a 3D acoustic Doppler velocimeter (ADV) was used to measure the local flow velocities. Two types of bed forms and a series of vegetation patch densities were considered. The experimental results show that the bed form significantly influences the vertical distribution of streamwise velocity. Besides, the value of velocity is susceptible to the bed form while the lateral distribution shape of streamwise velocity as well as the lateral and longitudinal distribution shape of depth-averaged velocity is less affected. When all test conditions but bed condition remains same, as a result of water energy consumption by sediment movement, the velocity value under mobile bed case is smaller than that under rigid bed case. The vegetation patch density has obvious effect on the flow velocity. The distribution shape of flow velocity and velocity values at different locations show different trends with the increase of vegetation patch density. The upstream adjustment length has nothing to do with vegetation patch density and the steady wake length is susceptible to vegetation patch density.

Evaluation of the parameters affecting the roughness coefficient of sewer pipes with rigid and loose boundary conditions via kernel based approaches

One of the important issues in water transport and sewer systems is determining the flow resistance and roughness coefficient. An accurate estimation of the roughness coefficient is a substantial issue in the design and operation of hydraulic structures such as sewer pipes, the calculation of water depth and flow velocity, and the accurate characterization of energy losses. The current study, applies two kernel based approaches [Support Vector Machine (SVM) and Gaussian Process Regression (GPR)] to develop roughness coefficient models for sewer pipes. In the modeling process, two types of sewer bed conditions were considered: loose bed and rigid bed. In order to develop the models, different input combinations were considered under three scenarios (Scenario 1: based on hydraulic characteristics, Scenarios 2 and 3: based on hydraulic and sediment characteristics with and without considering sediment concentration as input). The results proved the capability of the kernel based approaches in prediction of the roughness coefficient and it was found that for prediction of this parameter in sewer pipes Scenario 3 performed better than Scenarios 1 and 2. Also, the sensitivity analysis results showed that Dgr (Dimensionless particle number) for a rigid bed and wb/y (ratio of deposited bed width, wb, to flow depth, y) for a loose bed had the most significant impact on the modeling process.