Bed Surface Research Articles

Determination of Seismic Site Class and Potential Geologic Hazards using Multi-Channel Analysis of Surface Waves(MASW) at the Industrial City of Abu Dhabi, UAE

ABSTRACT Geophysical investigation activities were conducted at ICAD-II, Abu Dhabi, UAE using Multi-Channel Analysis of Surface Waves (MASW) to determine subsurface geology , material stiffness, potential weak zones down to ~35 m depth, and to propose the appropriate seismic site classification for a proper foundation design. A total of 20 MASW lines were carried out over a grid layout of 5 m spacing. Data acquisition, processing and inversion have been parameterised and selected to produce shear velocities that represent subsurface conditions. The estimated average shear-wavevelocity (Vs30 = 577.97 m/s) suggests that the investigated site can be classified as Class C (V.D. Soil & Soft Rock). The constructed geological model comprises sand, weak sandstone, weak mudstone, and hard mudstone. Analysing the shear wave velocities indicates the absence of apparent cavities/ hazardous zone . However, a relatively weak layer of sandstone/mudstone rocks intercalations was detected from ~7m to ~25m. Meanwhile, the uncorrelated part of 2D MASW data indicates potentially harder mudstone encountered at a depth starting from ~25 m to >35 m. Hence, the foundation layer may be placed on the upper surface of the sandstone bed (~7 m) depending on the height and load of the proposed building and following the construction standards and requirements of the structural engineer.

Processing of low-density waste in fluidized bed made out of lightweight expanded clay aggregate

The main aim of the study is to obtain a new, innovative method for the organization of combustion processes in fluidized bed reactors. A key aspect of the change in the organization of the fluidized bed combustion process is the creation of a fluidized bed made out of lightweight expanded clay aggregate (LECA). The new fluidized bed has a density of 0.5 g/cm3, therefore, allowing for thermal processing of low-density solid and liquid industrial wastes, as well as waste biomass. Polyolefins (polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, and polypropylene homopolymer) were selected as examples of low-density solid wastes. The use of an innovative fluidized bed for liquid waste degradation was studied on the example of glycerol combustion. Waste wood chips were chosen to represent low-density biomass. Thermal degradation of selected materials in the fluidized bed made out of LECA was carried out at a temperature range of 500–900 °C with an interval of 100 °C. Video analysis of the fluidized bed surface proved the sinking of waste materials into the bed and significant elimination of diffusion flames in the freeboard. Qualitative and quantitative flue gas analysis was carried out using the FTIR spectrometer. More than 95% conversion of the carbon contained in the polyolefins to CO2 was achieved already at 700 °C. At 500 °C, more than 30% of the polymeric carbon left the reactor as aromatic compounds. To avoid the emission of harmful aldehydes during the thermal processing of glycerol, the bed should be heated to at least 800 °C. Waste wood chips as an alternative fuel can be thermally incinerated in the fluidized bed made out of LECA. The disappearance of volatile organic compounds and CO emissions occurred at 700 °C and 800 °C.

Analytical and Machine Learning-based approaches to estimate the steady-state temperature limit on the surface of Cu powder beds when heated by a concentrated laser energy source

Surface temperature induced by concentrated energy sources, such as a laser beam used during a selective laser sintering process, has been measured, modeled, and estimated before by several authors. Estimating surface temperature by models including radiation heat transfer has commonly been pursued using elaborated numerical schemes such as finite differences, finite volumes, or finite element schemes, which could be costly to implement. A systematic study of the evolution of the surface temperature at a given fixed point in Cu powder beds exposed to the focused laser beam of a selective laser sintering system is presented here. Incorporation of radiation heat transfer effect into the classical 1-D surface heating-cooling heat transfer model allowed the development of an implicit predictive model for the surface temperature evolution during the heating and cooling of the specimen, which in turn and at its time limit, arrived at a closed-form analytical expression for the plateau temperature of a given superficial point when heated up by a focused laser beam. On the other hand, this latter asymptotic expression, as expected, corresponds to the surface temperature, which can be isolated directly from Stefan-Boltzmann's radiation law—making it possible to predict plateau temperatures (i.e., Stefan-Boltzmann temperature limit) of the Cu powder bed surface at different laser powers with an error of less than 2% compared to surface temperature measurements done using an infrared pyrometer. Concerning the prediction capacity of this expression, the developed technique could be applied not only to different material systems but could also be adapted to handle a moving laser in a given scan pattern, thus obtaining an analytical tool to model better the heat transfer phenomena of, for example, laser powder bed - sintering/melting processes. In parallel, three Machine Learning techniques were implemented, an artificial neural network, specifically the Multi-layer Perceptron, a Support Vector Regression, and Random Forests Regressor, to study the feasibility of these approaches in predicting the steady-state temperature as well, depending on the laser power and the measurement time. From the achieved results, both methodologies are considered suitable to model the temperature behavior of the analyzed specimens.

Capture method for digital twin of formation processes of sand bars

Hydraulic quantities governing the generation of bedforms (formed spontaneously on the bottoms of rivers) have been investigated through geomorphological methods, laboratory experiments, stability analyses, numerical analyses, and other research methods. Recently, numerical analysis has been conducted using fine spatial grids to accurately describe morphodynamics. However, numerical analysis cannot always describe the real phenomena, because it is based on assumptions. One effective way to verify physical assumptions is to compare numerical analysis with actual measurements of equivalent resolution. Measurement data with high resolution enable the construction of a duplicate of the measurement target on a computer called a “digital twin.” To construct a digital twin of the process of bedforms generation and development, geometries of the water surface and the bed surface must be simultaneously measured. We developed and verified a measurement method for the construction of a digital twin during the generation and development of bedforms. The measurement system uses two cameras and a line laser to simultaneously measure the water surface and bed surface. Accurate refraction correction at the water surface is possible by acquiring the shape of the water surface, allowing the bottom shape to be determined by geometric processing. The method provides sub-millimeter-accurate measurements of the water surface and bottom with a spatial resolution of 0.95 cm longitudinally and 0.038 cm transversely in a 12 m × 0.45 m flume and takes only 1 min per measurement. This method can provide measurement results that contribute to the understanding of the generation and development of bedforms.

Factors affecting the decorativeness of flower beds in a regular style on the example of the city of Izhevsk

The emotional state and quality of the citizens' rest depends on the quality of the decorative floral design. The purpose of this work is to evaluate the floral design of the central part of the city of Izhevsk, to determine the optimal planting area of annual ornamental crops per 1 m2 and the factors that influenced the quality and decorative effect of regular-style flower beds in the conditions of Izhevsk. The selected objects for research are located along one route: Victory Square, Kuzebai Gerd Square, Likhvintsev Boulevard, the square near the residence of the Head of the Udmurt Republic, the square near the Children's Cafe. The examination of flower beds was carried out according to the principle of the route method. For a qualitative assessment of flower beds, the following were taken into account: the surface of the flower bed, the habitus and decorative properties of plants, the presence of decay, the state of the soil, the planting rate, and the littering. To assess the decorative effect of flower beds in the floral design of Izhevsk, the Department of Plant Introduction and Acclimatization of the Udmurt Federal Research Center of the Ural Branch of the Russian Academy of Sciences (UdmFIC UrO RAS) developed a 4-point assessment taking into account the laws of composition. Flower beds located on the territory of the studied objects are decorated mainly with annual flower crops and occupy an area of 3464 m2 (99.5%), including 1570 m2 (45%) in regular style, 13 types of ornamental plants of single–season use belonging to 10 families participated in the landscaping of regular-style flower beds in 2019-2020. When studying flower beds in the central part of Izhevsk in 2019-2020, the dependence of the assessment of quality and decorative effect on the density of planting flower seedlings was revealed, with increasing density, the decorative effect of flower beds improves. Several reasons have been identified that have affected the deterioration of the decorative nature of flower beds: violation of the planting dates of flower crops, sparse plantings (16 pcs / 1 m2), low level of agronomic care of flower beds.

Sediment Transport on a Sand Bed With Dunes: Deformation and Translation Fluxes

AbstractAs dunes move along the riverbed, they change in size, shape, and arrangement. This involves sediment fluxes on top of the net downstream motion of the dune field, but how much dune dynamics affect total sediment flux remains unclear. In this study, we obtain high‐resolution and high‐frequency digital elevation models of migrating submerged dunes in the laboratory. We use the measurements to identify three‐dimensional dune sediment fluxes and characterize dune interaction processes. We show how variations in dune migration lead to flux variations. Varying bed and water surface slopes and time‐varying sizes and shapes of dunes are imprinted in the observed flux variations, with a corresponding time lag. Feedback between bed morphology and water surface slope causes (some) dunes with high crests to lengthen into long dunes (of about twice the mean dune length), until a breakup of this dune into shorter dunes occurs, typically facilitated by merging of superposed bedforms until the primary dune splits. A large number of short dunes have high overall transport rates. Dune interaction causes patterns in the dune deformation flux. Dune splitting, defect creation and defect repulsion cause a peak in the deformation flux, whilst merging triggers a temporal increase of the total flux. Estimating the fluxes with spatially varying dune migration, and contributing fluxes to either deformation or translation processes continues to be a challenge, even for the detailed data set we have presented. Our analysis suggests that sediment transport variability over dune‐covered riverbeds is best described by considering the topography of multiple dunes.

Device-related pressure ulcers: SECURE prevention. Second edition.

Device-related pressure ulcers: SECURE prevention. Second edition.

Bedload transport: beyond intractability.

Scrutiny of multifarious field and laboratory data amassed over nine decades reveals four distinct bedload transport regimes and demonstrates the search for a universal formula is a fallacious pursuit. In only one regime, in which the supply of transportable material is unconstrained, does the transport rate in some rivers approximate the expected proportional relationship with dimensionless specific stream power (ω∗). At the other extreme, transport occurs at or near the threshold of particle motion, and the availability of sediment is regulated by the characteristics of the bed surface. In each regime, there is an underlying variation of transport rates at a given discharge, that is neither obscured by long measurement times nor standardized methodologies, and to properly differentiate them, the bedload size must be known. We show a data-driven relationship based on measurements made over several years, across the entire flow range, that requires no a priori specification of the association between the transport rate and ω∗, can reveal nonlinear trends that may otherwise be masked by omni-present temporal and spatial variability. The demise of the search for a universal formula will be accelerated by the development of idiomatic relations that embrace the specificity of rivers in each transport regime.

Infrared temperature measurements and DEM simulations of heat transfer in a bladed mixer

AbstractAn understanding of heat transfer in a bladed mixer is important for drying of pharmaceutical drug crystals. This study presents thermal imaging experiments of the particle bed surface in a bladed mixer to investigate how the impeller speed influences the rate and the uniformity of heat transfer. Next, the process is simulated using the discrete element method. The bed thermal properties are lumped into an effective thermal conductivity, that is calibrated for one impeller speed. The experiments and the simulations show the same trends and generally agree well for all agitated beds. However, to obtain good agreement of the rate of heat transfer between the simulations and experiments in a static bed, we need to adopt a higher thermal conductivity than for the agitated beds. Finally, we discuss the implications of these results for the design of operating protocols.

A new mixing equation for bed material composition in bed form dominant conditions

Vertical mixing beneath the bed surface and its effect on sediment composition has long been underestimated. This paper proposes a mixing equation to illustrate the temporal and spatial variations of bed material composition for bed form dominant rivers. A continuous mass conservation equation for elevation-specific nonuniform bed material composition is initially presented. A vertical mixing equation is finally derived as a diffusion-type partial differential equation with a source term characterized by a vertical diffusion coefficient and the geometric dimensions of bed forms. Coupled with boundary conditions, this equation is further developed in a vertical mixing model at the scale of bed forms, in which the variations of bed material composition are clearly illustrated. The equation accounts for vertical exchange fluxes driven by bed form migration and their effect on bed material composition, which helps elucidate the mixing mechanism. In application to riverbed degradation, the proposed equation is capable to describe armoring development in consideration of the interior mixing, which provides more satisfying predictions for bed surface materials. The new mixing equation helps gain insight into predicting the variations of bed material composition during morphological changes.

Symbiont-induced intraspecific phenotypic variation enhances plastic trapping and ingestion in biogenic habitats

Plastic contamination has major effects on biodiversity, enhancing the consequences of other forms of global anthropogenic disturbance such as climate change and habitat fragmentation. Despite this and the recognised importance of intraspecific diversity, we still know relatively little about how plastic pollution affects diversity below the species level. Here, we assessed the effects of intraspecific variation in a habitat forming species (the Mediterranean mussel Mytilus galloprovincialis) on the trapping and ingestion of microplastics. We focused on symbiont-induced phenotypic variation in mussel beds. Using fractal analysis, we measured an increase in the complexity of mussel bed surfaces by ca. 15% caused by phototropic shell-degrading endoliths. By simulating high tide flow conditions and incoming waves, we found that symbionts significantly increased microplastic accumulation in mussel beds. This likely reflects deceleration of near-bed flow velocities, creation of turbulence in the bottom boundary layer and consequently increased particle retention. This effect was not constant at high tide, with no effect of infestation on retention at the base of the mussel bed under mid and high flow conditions and reduced microplastic trapping on the surface of mussel shells. Nevertheless, under natural conditions, the ingestion and trapping of microplastic were higher by the mussels comprising beds with symbionts than those in beds without symbionts. Given the dependency of many species on mussel biogenic habitats, there is an increased risk of plastics moving up the food chain in mussel beds infested by symbiotic endoliths. Our results highlight how the effects of within-species phenotypic diversity may influence the consequences of rising levels of plastic pollution.

A Numerical Research on the Relationship between Aeolian Sand Ripples and the Sand Flux

Theoretically, the sand flux will not change after the wind-driven sand particle transport reaches the saturated state. However, it has been found in many wind-tunnel experiments that the sand flux will gradually decrease with time in long-term particle transport duration and will eventually reach a new stable state. In this work, we used numerical simulations to study the source of this kind of decrease and found it is caused by the sand ripple on the bed surface. The ripple index showed a strong correlation to the sand flux, and it decreased during the initial stage of the ripple formation. With a simplified theoretical model, we found the linear relationship between the Shields number and the particle transport load holds. However, the slope of this relationship and the dynamic threshold of particle entrainment decreased with the ripple index. As the sand flux scales linearly with the particle transport load, we finally derived an expression that describes how the sand flux on the ripple bedform varies with the wind strength. From this expression, we found the sand flux increases with ripple index, and it was easier to be influenced by the ripple bed form in small wind strength.

Coarsening Dynamics of 2D Subaqueous Dunes

AbstractFluid flow over an initially flat granular bed leads to the formation of a surface‐wave instability. The sediment bed profile coarsens and increases in amplitude and wavelength as disturbances develop from ripples into dunes. We perform experiments and numerical simulations to quantify both the temporal evolution of bed properties and the relationship between the initial growth rate and the friction velocity u∗. Experimentally, we study underwater bedforms originating from a thin horizontal particle layer in a narrow and counter‐rotating annular flume. We investigate the role of flow speed, flow depth and initial bed thickness on dune evolution. Bedforms evolve from small, irregular disturbances on the bed surface to rapidly growing connected terraces (2D equivalent of transverse dunes) before splitting into discrete dunes. Throughout much of this process, growth is controlled by dune collisions which are observed to result in either coalescence or ejection (mass exchange). We quantify the coarsening process by tracking the temporal evolution of the bed amplitude and wavelength. Additionally, we perform Large Eddy Simulations (LES) of the fluid flow inside the flume to relate the experimental conditions to u∗. By combining the experimental observations with the LES results, we find that the initial dune growth rate scales approximately as . These results can motivate models of finite‐amplitude dune growth from thin sediment layers that are important in both natural and industrial settings.

Effects of discharge on the velocity distribution and riverbed evolution in a meandering channel

To discuss the effects of discharge on the velocity distribution and riverbed evolution in a meandering river, a generalized meandering channel model was designed, and the instantaneous velocities and water levels in thirteen cross-sections and the digital elevations of the bed surfaces were measured. The results show that for the same discharge, the transverse water surface gradients are large at the downstream positions adjacent to the apex sections and small near the middle positions of the crossover areas. With increasing discharge, the transverse water surface gradients in the curved segments increase, the transverse underflows strengthen, and the transverse surface flows exhibit no obvious changes. If the curvature of a meandering channel is large and there are a large number of sediment particles whose incipient velocities are smaller than the transverse underflow velocities near the apex sections, then the regions between the apex-sectional convex sides and the outlets of the adjacent downstream crossover areas are prone to sediment deposition, and the frequency distributions of the bed surface elevations are positively skewed. For the same cross-section, the cross-sectional average velocity increases with increasing discharge. For the same discharge, the cross-sectional average velocities are large near the middle positions of the crossover areas and small near the apex sections. The thalweg swings randomly along the channel, but its overall trend is approximately the same as that of the flow dynamic axis. In a cross-section, the positions with large turbulent kinetic energy are located in the mainstream area, and the average turbulent kinetic energy increases with increasing discharge.

Effects of fluvial instability on the bed morphology in vegetated channels

Flume experiments are conducted to investigate the effect of streambed instability in channels with randomly-distributed vegetation, varying vegetation density and flow conditions, in the absence of upstream sediment supply. The bed morphology is captured with the photogrammetry technique and a Laser Scanner, and its changes with the vegetation and flow conditions are investigated. The results demonstrate that the presence of vegetation contributes in promoting the stability of the streambed and the formation of multiple bars. In runs with low vegetation density, the trajectory of sediment transport is predominantly in the longitudinal direction. However, a slight lateral dispersion of sediments is observed in the run with low flow discharge. By increasing the vegetation density, the bed structures become shorter, with a lower wavelength, than before, but with a similar trend. The analysis of the energy spectra and the high-order generalized structure functions of bed elevation fluctuations demonstrates that the bed surfaces are monofractals and can be described by a single exponent. However, the runs affected also by a lateral dispersion of sediments during the sediment transport phase are characterized by multifractality, which implies that a complex bed morphology at small spatial lags occurs at the end of these runs. The study of the two-dimensional (2D) second-order structure functions demonstrates that the bed is characterized by an anisotropic behavior, with flow-aligned bed structures that reflect the way in which the bed was formed.Article HighlightsVegetation contributes in promoting the stability of the streambedMultiple bars are formed in vegetated channels with different wavelengths, depending on the flow and the vegetation density conditionsBed surfaces in the presence of vegetation are monofractals, except those in which lateral sediment transport occurs

A Method for Measuring Hydrodynamic Force Coefficients Applied to an Articulated Concrete Mattress

A physical model testing method to determine the hydrodynamic force coefficients of an object is proposed and applied to an articulated concrete mattress placed on a flat surface under steady current condition. The test setup, which comprises of a pulley system that is able to pull the concrete mattress in either direction relative to the flow (e.g., with the flow direction or against the flow direction) and one load cell to measure the force required to pull the mattress, is simple and straightforward. Writing the equations of load balance for two different pulling directions allows the force coefficients to be deduced. The novelty and advantages of the method are that it completely removes the difficulties associated with measuring forces on individual concrete blocks and isolating the mattresses from contacting the solid surface, which were common in conventional test methods for measuring hydrodynamic forces on structures founded on a solid surface. A series of flume tests have been conducted to demonstrate the validity of the proposed method. It is expected that the proposed testing method is applicable to a wide range of structures, bed surfaces and flow conditions.

Elutriation and agglomerate size distribution in a silica nanoparticle vibro-fluidized bed

Fluidization of nanoparticle agglomerates is a promising technique to process nanoparticles. However, possible elutriation of small agglomerates may cause significant loss of bed material. To obtain the elutriation behavior under stable operation, in this study the elutriation fraction of silica nanoparticle agglomerates is measured in a vibro-fluidized bed, which is operated for several hours. Among conditions with different fluidizing gas velocities, Ug, and vibration strength, Λ, the lowest elutriation fraction measured is around 5% after 7-hour fluidization. The elutriation fraction increases significantly with Ug, while varies slightly with Λ. To help elucidating the elutriation behavior, the agglomerates at three different locations (bed surface, splash zone, and bed outlet) are sampled and their size distributions are determined. The elutriation rate constant is found to be much smaller than the literature results for ordinary particles, and the reasons are discussed in detail. Finally, an empirical correlation considering size distribution is proposed to fit the elutriation rate constant for the conditions in this study.

Numerical modelling of ammonia-coal co-firing in a pilot-scale fluidized bed reactor: Influence of ammonia addition for emissions control

The co-firing of coal and NH3 is a sustainable solution allowing the retrofitting of coal power facilities without major modifications while contributing to global decarbonization goals. However, the use of NH3 for power generation still presents some research gaps. This study delivers a 2D Eulerian-Lagrangian numerical model describing the co-firing of coal-NH3 in a pilot-scale fluidized bed reactor. The numerical model is validated against experimental data on coal combustion to assess the accuracy of the model·NH3 co-firing ratio is varied between 0 and 80% (by mass) and the effect on the combustion process is broadly investigated to determine the impact on heat release, and carbon, NO, and NH3 emissions. The effect of NH3 injection position into the reactor and air staging on NO formation is studied. Also, the impact of NH3 on the reactor temperature distribution and radiative flux is evaluated. Results indicate that NH3 co-firing delivers CO2 emissions decrease of up to 26% compared to pure coal firing. For a co-firing fraction of 10% NH3, NO emissions level was identical to that of coal firing alone, yet between 20 and 80% ratio NO emissions gradually decreased by up to 40%. The NH3 injection location had a substantial effect on NO emissions, with injection points further downstream the bed surface leading to increased NO concentrations. Air staging also proved to have a dominant effect on NO formation, with a 50% reduction of NO emissions obtained for a 20% air staging alone. Lower gas temperatures and decreased radiative flux were predicted as the NH3 ratio increased. Given the similar heat transfer rates measured between 10 and 20%, a 20% NH3 operation would be possible without a detrimental effect on temperature and radiative flux.

Experimental Study of the Dynamic Characteristics of a New Antidrainage Subgrade Structure for High-Speed Railways in Diatomaceous Earth Areas.

The experience needed to carry out engineering and construction in diatomaceous earth areas is currently lacking. This project studies the new Hang Shaotai high-speed railway passing through a diatomaceous earth area in Shengzhou, Zhejiang Province, and analyzes the hydrological and mechanical properties of diatomaceous earth on the basis of a field survey and laboratory. Moreover, a new antidrainage subgrade structure was proposed to address the rainy local environment, and field excitation tests were performed to verify the antidrainage performance and stability of the new subgrade structure. Finally, the dynamic characteristics and deformation of the diatomaceous earth roadbed were examined. The hydrophysical properties of diatomaceous earth in the area are extremely poor, and the disintegration resistance index ranges from 3.1% to 9.0%. The antidrainage subgrade structure has good water resistance and stability under dynamic loading while submerged in water. After 700,000 loading cycles, the dynamic stress and vibration acceleration of the surface of the subgrade bed stabilized at approximately 6.37 kPa and 0.94 m/s2, respectively. When the number of excitations reached 2 million, the settlement of the diatomaceous earth foundation was 0.08 mm, and there was basically negligible postwork settlement of the diatomaceous earth foundation. These results provide new insights for engineering construction in diatomaceous earth areas.

Investigation of the Impact of Pinus Silvestris Pine Needles Bed Parameters on the Spread of Ground Fire in Still Air

ABSTRACT Systematic experiments and complementing numerical simulations have been reported for the first time to understand the spread of a ground fire over pine needle bed of the Siberian boreal forests (Pinus silvestris) in still air. Using equipment and instrumentations specifically developed for the purpose, careful experiments have been conducted to reveal the effects of the bed width, fuel moisture content, fuel load, and the packing ratio on flame spread rate, temperature distributions in both gas and condensed phases. Temperatures are measured using fine thermocouples fixed at various locations from the bed surface. The surface temperature of the bed during flame propagation has been measured using a micro-thermocouple inserted in a single pine needle in the bed as well as using an infrared (IR) camera. Further, for the first time, the total and radiant heat fluxes from the flame to the bed surface have been measured using compact cooled sensors placed inside the needle bed, over which the flame propagates. In order to understand more about the flow field and flame spread process, a 3D numerical model based on the Fire Dynamics Simulator (FDS) has been used to simulate few of the experiments. The processes governing pine needle pyrolysis, char oxidation, gas phase combustion and radiation have been modeled using simplified approaches reported in literature. The model is capable of predicting experimentally measured flame propagation velocities for most of the cases quite well.