Wet Bed Research Articles

Rainfall-triggered mass movements on steep loess slopes and their entrainment and distribution

Mass movements are predominant geomorphic processes on steep hillslopes. However, the mechanisms governing the erosion and entrainment of mass movements remain poorly understood. In this study, experiments on natural loess slopes were conducted to induce a series of mass movements under simulated rainfalls in the Liudaogou Catchment on the Loess Plateau of China. A novel topography meter was used to observe random mass movements. A total of 499 mass movements in 42 rainfall events and an average of 11 mass movements for each rainfall event were observed. Three mass movement types were detected: landslides (67%) > mudflows (21%) > avalanches (12%). The volume of landslides dramatically increased through the entrainment of a wet gully bed material, and the volume of landslide mass was magnified by 29% on average through material entrainment. Based on the observed data, the probability of mass movement occurrences decreased with the increasing mass movement volume in a power-law relationship. The critical rainfall amount for mass movement failure was approximately 25.6 mm at a rainfall intensity of 50 mm h−1. These results can serve as guides to mitigate geological hazards and assess erosion processes on steep loess slopes of the Loess Plateau.

Experimental Study on Extreme Hydrodynamic Loading on Pipelines. Part 1: Flow Hydrodynamics

Over the past two decades, extreme flood events generated by tsunamis or hurricanes have caused massive damage to nearshore infrastructures and coastal communities. Utility pipelines are part of such infrastructure and need to be protected against potential extreme hydrodynamic loading. Therefore, to address the uncertainties and parameters involved in extreme hydrodynamic loading on pipelines, a comprehensive experimental program was performed using an experimental facility which is capable of generating significant hydraulic forcing, such as dam-break waves. The study presented herein examines the dam-break flow characteristics and influence of the presence of pipelines on flow conditions. To simulate conditions of coastal flooding under tsunami-induced inundation, experiments were performed on both dry and wet bed conditions to assess the influence of different impoundment depths and still water levels on the hydrodynamic features.

Phase field lattice Boltzmann model for air-water two phase flows

Two phase flows occur in different forms with liquid and gas in general, among which, the interaction of the flow of air and water is a common scenario. However, modeling the two phase flow still remains a challenge due to the large density ratio between them and different space-time scales involved in the flow regimes. In the present work, the lattice Boltzmann (LB) model capable of handling large density ratio (1000) and high Reynolds number (104) simultaneously is proposed. The present model consists of two sets of LB equations, one for the flow field in terms of normalized pressure-velocity formulation and the other for the solution of the conservative Allen-Cahn equation to capture the interface. The numerical tests such as stationary drop, bubble coalescence, and capillary wave decay have been performed, and the results exhibit excellent mass conservation property. The capability of the present model to handle complex scenarios has been tested through test cases, for example, rise of an air bubble, splash of a water droplet on a wet bed, and Rayleigh-Taylor instability. In all test cases, the simulation results agree well with the available reference data. Finally, as an application of the present model, the breaking of a deep water wave with high Reynolds number (104) is simulated. The plunging breaker with wave overturning and the generation of secondary jet and splashes are well described by the present LB model. The evolution of wave energy dissipation during and after breaking is in agreement with the reference data.

Two-Fluid-Model-Based Full Physics Simulations of Mixing in Noncohesive Wet Fluidized Beds

Mixing in a noncohesive wet fluidized bed was studied using the two-fluid model (TFM) and a zero-dimensional (0D) approach. The employed TFM was extended to simulate droplet deposition on the parti...

Comparison of measured dam-break flood waves in triangular and rectangular channels

Dam-break flows in both triangular and rectangular channels are investigated experimentally in the present study. Laboratory measurements are carried out in a prismatic and smooth flume with a horizontal and wet bed for two different reservoir heads and four tailwater levels. During the experiments, digital image processing is applied as a flow measurement technique. Both water surface profiles and stage hydrographs are obtained effectively by means of video images with eight adjacent cameras. The dam-break flows in triangular and rectangular channels show common features: jet formation in the downstream of the dam during the initial dam-break stage; similarity of the water surface profiles behind the dam for different depth ratios at a specific time; insignificant effects of the depth ratio on the negative wave front; and strong dependence of the shock wave front on the depth ratio. In a triangular channel, the negative wave front moves slower than that in a rectangular channel; and extra negative waves propagating towards upstream direction does not form for all depth ratios considered in this study while they have been observed in a rectangular channel for large values of α representing the ratio of initial tailwater depth and reservoir depth (i.e., α = 0.3 and 0.4). Meantime, these extra negative waves result in an undulation of the water surface profile in the reservoir and an apparent increase of water depth at the dam. The water depth at the dam section for different depth ratios is 60–70% of the initial reservoir head; and the shock wave front propagates slower as the depth ratio increases for the triangular channel. For water depth ratios α = 0.1 and 0.2, the shock wave front moves faster than that in a rectangular channel, and the contrary is true for α = 0.4. For α = 0.3, the propagation speed of the shock wave front approximates that in a rectangular channel. Present study contributes to the understanding of the effect of wet downstream conditions on dam-break flows in triangular channels and provides detailed experimental data for validating both the analytical and the numerical solutions.

The forces of tsunami waves on a vertical wall and on a structure of finite width

The hydrodynamic forces on coastal structures impacted by tsunami depend on the wave Froude number, the sizes and shapes of the structures and also on whether the structures stand in water or on dry land at the time of the impact. We conducted simulations using shallow-water hydraulic equations and then simulations using full Navier-Stokes equations to determine the wave impact on a vertical wall – i.e., a structure of infinite width – and a structure of finite width. In the case of steep waves on a wet bed, the wave-drag coefficient rose to a peak on impact and then settled to a wave-structure interaction equilibrium. In the case of smooth waves on dry land, the approach to the equilibrium was gradual. The numerical simulations determined the dependence of the wave-drag coefficients on the Froude number and the width-to-depth ratio for waves on wet beds and, separately, for waves on dry land. The simulations also reproduced the wave forces for the range of conditions observed in the laboratory.

Research on dam-break flow induced front wave impacting a vertical wall based on the CLSVOF and level set methods

The problem of a dam-break flow induced front wave impacting a vertical wall placed at the downstream end was numerically investigated by using the Level Set (LS) method and Coupled Level Set/Volume Of Fluid (CLSVOF) method. For the LS approach, the advection equation of the level set function to capture the interface is discretized by the fifth-order, weighted, essentially non-oscillatory (WENO5) scheme. For the CLSVOF approach, the Tangent of Hyperbola for Interface Capturing/Weighed Line Interface Calculation (THINC/WLIC) scheme is adopted to capture the interface and improve mass conservation. The interface normal vector in the WLIC reconstruction procedure can be estimated from the LS function instead of VOF function. The Navier–Stokes solver which uses an explicit Adams–Bashforth algorithm is performed on a staggered Eulerian grid. The numerical experiments are carried out in a rectangular flume with a smooth horizontal wet bed with four different tailwater levels. This study investigates the formation and propagation of the negative wave resulting from the reflection of flood waves against the downstream end wall. The numerical results are compared with laboratory experiment results studied in Ref (Kocaman and Ozmen-Cagatay, 2015). and a reasonable agreement is achieved. Numerical results show that the CLSVOF solutions are better than LS solutions in terms of mass conservation.

Enhanced coking resistance of a Ni cermet anode by a chromates protective layer

Abstract Ni-based anodes of SOFCs are susceptible to coking, which greatly limits practical application of direct methane-based fuels. An indirect internal reformer is an effective way to convert methane-based fuels into syngas before they reach anode. In this work, catalytic activity of a redox-stable perovskite La0.7Sr0.3Cr0.8Fe0.2O3-δ (LSCrFO) for methane conversion was evaluated. The catalyst was fabricated as an anodic protective layer to improve coking resistance of a Ni cermet anode. Using wet CH4 as a fuel, the LSCrFO-modified cell showed excellent power output and good coking resistance with peak power density of 1.59 W cm−2 at 800 °C. The cell demonstrated good durability lasting for at least 100 h. While the bare cell without the protective layer showed poor durability with the cell voltage fast dropped from 0.75 V to 0.4 V within 30 min. Under wet coal bed methane (CBM) operation, obvious performance degradation within 35 h (1.7 mV h−1) was observed due to the influence of heavy carbon compounds in CBM. The pre- and post-mortem microstructures and carbon analysis of the anode surface and catalyst surface were further conducted.

Dam-Break Flows: Comparison between Flow-3D, MIKE 3 FM, and Analytical Solutions with Experimental Data

The objective of this study was to evaluate the applicability of a flow model with different numbers of spatial dimensions in a hydraulic features solution, with parameters such a free surface profile, water depth variations, and averaged velocity evolution in a dam-break under dry and wet bed conditions with different tailwater depths. Two similar three-dimensional (3D) hydrodynamic models (Flow-3D and MIKE 3 FM) were studied in a dam-break simulation by performing a comparison with published experimental data and the one-dimensional (1D) analytical solution. The results indicate that the Flow-3D model better captures the free surface profile of wavefronts for dry and wet beds than other methods. The MIKE 3 FM model also replicated the free surface profiles well, but it underestimated them during the initial stage under wet-bed conditions. However, it provided a better approach to the measurements over time. Measured and simulated water depth variations and velocity variations demonstrate that both of the 3D models predict the dam-break flow with a reasonable estimation and a root mean square error (RMSE) lower than 0.04, while the MIKE 3 FM had a small memory footprint and the computational time of this model was 24 times faster than that of the Flow-3D. Therefore, the MIKE 3 FM model is recommended for computations involving real-life dam-break problems in large domains, leaving the Flow-3D model for fine calculations in which knowledge of the 3D flow structure is required. The 1D analytical solution was only effective for the dam-break wave propagations along the initially dry bed, and its applicability was fairly limited.

Experimental study on mixing behaviors of wet particles in a bubbling fluidized bed

Mixing behavior of binary particles with different densities in a wet fluidized bed has been experimentally investigated in this work. Some important hydrodynamic characteristics during mixing, such as the minimum fluidization velocity, flow pattern, and flotsam particle distribution are measured. The differences between dry and wet particles are systematically compared. It is found that the minimum fluidization velocity Umf of wet particles is higher than that of dry particles due to the liquid bridge force between particles. Umf reaches its maximum when the liquid saturation S = 0.1, and then decreases, and does not change much when the liquid saturation in the region of S = 0.2–0.3. Liquid addition can bring two opposite effects on the mixing of a binary mixture of particles with different densities. First, the intensity of bubbling in the wet fluidized bed is lower than that in the dry fluidized bed at the same operation gas velocity Uf, which will weaken the mixing. Secondly, the liquid bridge forces between particles can restrain the density segregation, which is beneficial for mixing. A simple method is developed based on the analysis of forces on flotsam particles to evaluate the effect of liquid bridge force on mixing. A segregation index Se, defined as Se = Flift/Fresis, where Flift contains the drag force Fd and buoyancy force Fb, and Fresis contains the gravitation force Fg and liquid bridge force Flb, is used to indicate the segregation potential. The calculated results show that Se > 1 in the dry fluidized bed and Se < 1 in the wet fluidized bed, and dry particles are more inclined to segregate than wet particles.

Rheology and microstructure of unsaturated wet granular materials: Experiments and simulations

When dealing with unsaturated wet granular materials, a fundamental question is: What is the effect of capillary cohesion on the bulk flow and yield behavior? We investigate the dense-flow rheology of unsaturated granular materials through experiments and discrete element simulations of homogeneous, simple annular shear flows of frictional, cohesive, spherical particles. Dense shear flows of dry, cohesionless granular materials exhibit three regimes: Quasistatic, inertial, and intermediate [B. Andreotti et al., Contemp. Phys. 55, 151–152 (2013)]. Herewith, we show that the quasistatic and the intermediate regimes persist for unsaturated materials and that the rheology is essentially described by two dimensionless numbers: The reduced pressure P* comparing the cohesive to confining forces and the inertial number I, for a wide range of liquid content. This is consistent with recent numerical simulations [S. Khamseh et al., Phys. Rev. E 92, 022201 (2015)]. Finally, we measure the effective friction coefficient and the solid fraction variation throughout the wet bed. From this, we show that, in the quasistatic regime, the Mohr–Coulomb yield criterion is a good approximation for large enough P*. The experimental results agree quantitatively with the numerical simulation ones, provided the intergranular friction coefficient μ is set to its physical value identified from dry material rheology [M. Badetti et al., Eur. Phys. J. E 41, 68 (2018)]. To directly and quantitatively determine what happens inside the sheared granular bed, x-ray tomography measurements are carried out in a custom-made setup that enables imaging of a wet granular material after different shear histories. For the explored range of liquid content, samples remain homogeneous but exhibit some complex microscopic morphologies far from simple capillary bridges. From the x-ray microtomographic images, we can clearly distinguish liquid capillary bridges and liquid clusters by their morphologies. We see that the total number of capillary bridges decreases when one increases the liquid content and interestingly increases, at the expense of other morphologies, when we increase the shear strain. This explains the concordance between the experimental and numerical measurements since the numerical model is restricted to the pendular state, for which the liquid phase is completely discontinuous and no coalescence occurs between liquid bridges.

INFLUENCE OF SURFACE HEATING TEMPERATURE ON EXTERNAL HEAT-EXCHANGE IN WET VIBRO-FLUIDIZED BED

Experimental data are given on the influence of the temperature of the heating surface, placed to a wet vibro-fluidized bed of non-porous particles, and higher that the saturation temperatures on the external heat-transfer coefficient at conductive supply of the heat.

Experimental study on forces exerted on buildings with openings due to extreme hydrodynamic events

Previous studies and field surveys showed that specific structural designs can decrease the load on free-standing buildings along the coast, providing safer vertical shelters. This experimental study investigated the effect of openings in buildings (windows, doors and foyers) on horizontal forces and tilting moments induced by both dry bed surges and wet bed bores. Four configurations with seven porosity values ranging from 0% (impervious) to 84% (highly permeable) were systematically tested. Due to the presence of openings, the flow through the building reduced the upstream water depths. The porosity resulting from the presence of openings was shown to produce a linear reduction of the maximum horizontal force, when compared to the corresponding impervious building. The configuration with an impervious back showed results similar to those measured for the fully impervious buildings. The occurrence of the maximum tilting moment was shown to coincide with the maximum horizontal force and an estimation of the cantilever arm was therefore possible. The latter was constant for all configurations, independent of the geometry of the openings. Finally, two equations to predict the maximum horizontal force and the tilting moment were proposed, taking into account the effect of building openings within the resistance coefficient. These showed good agreement with experimental data and previous studies. These findings provide engineers with practical information for the design of safer vertical shelters in tsunami-prone areas.

Experimental Study of Tsunami-Like Waves Generated with a Vertical Release Technique on Dry and Wet Beds

Tsunamis, impulse waves, and dam failures are disasters that challenge humanity, often leading to massive casualties and extreme economic losses. The highly unsteady flow conditions generated by such events are often in the form of turbulent bores. The purpose of this study was to investigate and validate a new generation system for bores propagating over dry and wet bed conditions. There are multiple techniques to generate such waves experimentally, and the study focused on the generation of tsunami-like inundation conditions through the vertical release of a water volume. A detailed methodology to characterize the generated waves hydraulically, in terms of their wave heights and flow velocities, is presented, and good agreement with the classical dam-break case for both dry bed surges and wet bed bores was demonstrated. Because of the importance of estimating the impact forces induced by such waves, particular attention was given to the wavefront celerity and the velocity profiles measured behind the wavefront; these were found in agreement with Prandtl's power law for open channel flows, and in-depth measurements allowed for the definition of an expression to estimate flow deceleration behind the wavefront. Along with considerations of the Froude number and momentum, this paper provides relevant information to assist engineers in designing safer infrastructures in areas prone to such extreme loading.

Growth Parameter and Yield Attributes of Rice ( Oryza Sativa ) as Influenced by Different Combination of Nitrogen Sources

The study was carried out in agronomy farm of Paklihawa Campus, IAAS, Rupandehi, Nepal. The objective of the study was to determine the response of rice as influenced by different combination of organic and inorganic nitrogen sources. The study consists of three nitrogen sources i.e. urea, farmyard manure and blue green algae at various levels comprising seven treatments in randomized complete block design with three replications. Rice seedling were raised in wet nursery bed and transplanted in experimental plots. Growth parameters, yield attributing traits and grain yield of rice were recorded. Result indicates that treatment combination of 75% of recommended dose of nitrogen (90 kg ha-1), farmyard manure (5 tons ha-1) and blue green algae (9 kg ha-1) contributes to higher plant height (96.13 cm), effective tiller per square meter (345.6), filled grain per panicle (180.9), grain yield (4.787 tons ha-1), and straw yield (9.07 ton ha-1) (p < 0.05). Also, there was a positive correlation between the grain yield and effective tillers per square meter (R2=0.254), grain yield and number of filled grains per panicle (R2=0.315). Hence, 75% of recommended dose of nitrogen (90 kg ha-1), farmyard manure (5 tons ha-1) and blue green algae (9 kg ha-1) were found to improve plant characteristics thus improving rice yield.

Experimental study on the hydrodynamic impact of tsunami-like waves against impervious free-standing buildings

ABSTRACTTsunamis, landslide-generated waves, and dam failures are rare, but highly destructive phenomena, associated with extreme loading on infrastructure. Recent events showed that specific measures must be taken to guarantee safety of both people and the built environment. This experimental study investigates the forces and moments exerted on free-standing buildings that are induced by both surges and bores. The hydrodynamic impact was characterized by high splash, subsequently followed by a quasi-steady flow around the structure. For dry bed surges, the time history of the horizontal force was proportional to the momentum flux per unit width. For wet bed bores, an attenuation of the peak force due to the presence of an aerated front was observed and the introduction of a reduction coefficient was necessary to achieve a realistic force estimation. Additional force analysis in terms of peak time, wave height at maximum force and impulse also pointed out some key differences between forces exerted by dry bed surges and wet bed bores. The occurrence of the maximum tilting moment on the building coincided with the maximum horizontal force and an evaluation of the cantilever arm was possible. These findings provide engineers with practical information for the design of safer coastal structures.

Study of total variation diminishing (TVD) slope limiters in dam-break flow simulation

A two-dimensional (2D) dam-break flow numerical model was developed based on the finite-volume total variation diminishing (TVD) and monotone upstream-centered scheme for conservation laws (MUSCL)-Hancock scheme, which has second-order accuracy in both time and space. A Harten-Lax-van Leer-contact (HLLC) approximate Riemann solver was used to evaluate fluxes. The TVD MUSCL-Hancock numerical scheme utilizes slope limiters, such as the minmod, double minmod, superbee, van Albada, and van Leer limiters, to prevent spurious oscillations and maintain monotonicity near discontinuities. A comparative study of the impact of various slope limiters on the accuracy of the numerical flow model was conducted with several dam-break examples including wet and dry bed cases. The numerical results of the superbee and double minmod limiters agree better with the theoretical solution and have higher accuracy than other limiters in one-dimensional (1D) space. The ratio of the downstream water depth to the upstream water depth was used to select the proper slope limiter. For the 2D numerical model, the superbee limiter should not be used, owing to significant numerical dispersion.

An Implicit Scheme for Shallow Water Flow with Wet Dry Interface

A finite difference implicit scheme is presented in this paper for solution of the shallow water equations in one dimensional (1D) form. The present model has many advantages like, handling of discontinuous and complex bed topography, satisfying C-property (preservation of motionless water surface over a wet or dry bed) and capability of handling large value of temporal step etc. Another very important feature of the present model is that, no special treatment of the source vector of the governing equations is required here to deal with very less water depth. To investigate the performance of the present model in diverse situations, it is used to replicate four different problems of known analytical solution, and the model is found to be quite capable for varied situations.

Bedwetting, Doctors, and the Problematization of Youth in Britain and America, c.1800–1980

This article argues that bedwetting evolved from being seen, in the nineteenth century, as a bad behavioral habit into a deeply problematic twentieth-century condition linked to deeper, psychological problems. Approaches to bedwetting moved away from techniques of habit adjustment and physical interventions towards a deeper assessment of personality and mind. The case study of bedwetting reveals much about how early-twentieth-century medical communities re-defined certain types of bodily behavior but also shaped them around contemporary socio-cultural concerns about matters such as deviance and youth. For medical professionals, wasn’t so much the wet bed itself but the broader implications raised about childhood abnormality; a failure to control night-time impulses to relieve his or her bladder signified a child turning into something monstrous; into an individual whose sadistic actions threatened the safety of those around him. Even when seemingly beyond the control of a sleeping child, bedwetting was now presented as a somewhat animalistic, impulsive practice that crossed the threshold of acceptable modern, civilized behavior. The end result was a way of thinking about the inner body that risked casting the owners of leaky bladders as potential deviants or sexual perverts. To achieve its aims, the article examines two similar, but in some ways contrasting, geographical contexts, Britain and America, to also shed light on how particular socio-cultural contexts shaped ideas about bedwetting.

Experimental study of gas pressure drop in rotating packed bed with rotational‐stationary packing

AbstractRotating packed bed (RPB) with rotational‐stationary packing is a novel instrument that could greatly enhance mass transfer compared with the conventional packed columns. The structure of rotational‐stationary packing makes the gas repeatedly enter the packing to increase the end effect. Meanwhile, owing to the resistance of the packing to the gas, the gas pressure drop of rotating packed bed with rotational‐stationary packing becomes the necessary factor that can evaluate the equipment. The gas pressure drop of the dry bed and wet bed were determined at various operating variables, including the rotational speed, the gas flow rate, and the liquid flow rate. In this work, the gas pressure drop was classified on the basis of the gas flow path and the corresponding theoretical formulas were provided. The pressure drop of the dry bed increased with increasing rotational speed and gas flow rate was observed, and the liquid flow rate had little influence on the pressure drop of the wet bed. Finally, the experimental values were fitted to the theoretical formula and the relationship between total pressure drop and rotational speed, gas flow rate in a RPB with rotational‐stationary packing was presented. The theoretical calculated values agreed well with the experimental data with a deviation within 6 %. These will provide the gas pressure drop theoretical calculation formula for a kind of RPB with rotational‐stationary packing.