Vertical Wall Research Articles

Sand-bentonite backfill amended with composite polymer exposed to organic acid: Hydraulic performance and microstructural properties

Soil-bentonite (SB) backfills in vertical cutoff walls are used extensively to contain contaminated groundwater. Previous studies show that the hydraulic conductivity of backfill can exceed the typically recommended maximum value (k = 1 × 10−9 m/s) if exposed to groundwater impacted by organic acids commonly released from uncontrolled landfills and municipal solid waste dumps. Polymer amended backfills exhibit excellent chemical compatibility to metal-laden groundwater. However, few studies to date have explored the effect of organic acid contaminated groundwater on hydraulic performance of polymer amended backfills. This study presents an experimental investigation on the hydraulic performance and microstructural properties of a composite polymer amended backfill used to contain flow of acetic acid-laden groundwater. A series of laboratory experiments were performed to evaluate free-swell indices of the composite polymer amended bentonites, liquid limits of the composite polymer amended and unamended bentonites, and slump heights and hydraulic conductivity (k) values of the amended backfills to acetic acid solutions with varying concentrations. The results were compared with those of the unamended bentonites and unamended backfills reported in a previous study. The results showed that the free-swell index and liquid limit of the amended bentonites were higher than those of the unamended bentonites. Permeation with acetic acid solutions with concentrations ranging from 40 mmol/L to 320 mmol/L conducted on the amended backfill only resulted in an increase in k of less than a factor of about 10 related to that based on permeation with tap water (1.68 × 10−10 -4.41 × 10−11 m/s to acetic acid solution versus 1.65 × 10−11 m/s to tap water). Mechanisms contributing to enhanced chemical compatibility of amended backfill were ascertained based on scanning electron microscopy, mercury intrusion porosimetry, and zeta potential analyses.

Assessment of Fiber Bragg Grating sensors for monitoring induced strains on the draft tube cone of hydraulic turbines

Abstract In hydraulic turbines, several flow instabilities can take place inside the draft tube cone during off-design and transient operating conditions such as the rotating vortex rope which can severely damage the structure if sustained in time. In the frame of the AFC4Hydro H2020 research project, an extensive measurement campaign has been carried out to monitor and predict this rotating vortex rope phenomenon in a reduced scale Kaplan turbine model at the Vattenfall Research and Development facility in Älvkarleby, Sweden. The hydraulic turbine model has been operated in propeller mode with a fixed blade angle corresponding to its best efficiency point. Several sensors have been placed along the test stand to monitor vibrations, strains and pressures. Concretely, the present paper assesses the performance of using Fiber Bragg Grating sensors to measure the strains induced on the draft tube cone walls with high-spatial resolution in three different zones of influence: the upper and lower flanges and the vertical cone wall between the runner outlet and the elbow. To do so, a total of 3 arrays embedding a total of 48 Fiber Bragg Grating sensors were glued inside three grooves previously machined on these particular areas of the draft tube cone. Analysing the frequency response of the different Fiber Bragg Grating sensors, the strain patterns induced by the rotating and plunging components of the rotating vortex rope have been precisely determined. Moreover, their impacts at the different part load conditions tested have also been quantified.

Design and Implementation of Water PH Level and Turbidity Monitoring System

Abstract: Building collapses have become a distressing and recurring issue in Nigeria, necessitating urgent action to mitigate their occurrence. This paper introduces an innovative approach to address this challenge by developing an Automated Structural Health Monitoring System (ASHMS) utilizing a mobile app. Focusing on major cities like Lagos and Abuja, the proposed system employs strategically placed sensors to gather data from various structural elements of buildings. The collected information, encompassing seismic activity, vibrations, bending moments, shear forces, and other key parameters, is wirelessly transmitted to the cloud where it can then be accessed and visualized using mobile app. The system offers real-time insights into the structural integrity of buildings and provides early warnings, thereby contributing significantly to reducing the risk of building collapses. Key findings show that when incorporated into an automated Structural Health Monitoring (SHM) system, the user's mobile app offers essential structural insights, capturing values such as a 0.5-unit vibration level, 20 units of shear force, 50 units of bending moment, and an 89-degree vertical wall angle. The app's userfriendly interface improves the effectiveness of monitoring and overseeing structural health, in line with the overarching objective of promoting safety in construction practices

Automated Structural Health Monitoring System for Mitigating Building Collapse in Nigeria: A Mobile App Approach

Abstract: Building collapses have become a distressing and recurring issue in Nigeria, necessitating urgent action to mitigate their occurrence. This paper introduces an innovative approach to address this challenge by developing an Automated Structural Health Monitoring System (ASHMS) utilizing a mobile app. Focusing on major cities like Lagos and Abuja, the proposed system employs strategically placed sensors to gather data from various structural elements of buildings. The collected information, encompassing seismic activity, vibrations, bending moments, shear forces, and other key parameters, is wirelessly transmitted to the cloud where it can then be accessed and visualized using mobile app. The system offers real-time insights into the structural integrity of buildings and provides early warnings, thereby contributing significantly to reducing the risk of building collapses. Key findings show that when incorporated into an automated Structural Health Monitoring (SHM) system, the user's mobile app offers essential structural insights, capturing values such as a 0.5-unit vibration level, 20 units of shear force, 50 units of bending moment, and an 89-degree vertical wall angle. The app's userfriendly interface improves the effectiveness of monitoring and overseeing structural health, in line with the overarching objective of promoting safety in construction practices.

Thermal analysis of hybrid nanoliquid contains iron-oxide (Fe3O4) and copper (Cu) nanoparticles in an enclosure

The major aim of this work is to analyze the thermophysical properties of hybrid nanoliquid inside a square lid driven enclosure under the effect of applied magnetic field and mixed convection. The Hybrid nanofluid is considered a suspension of Iron-oxide (Fe3O4) and Copper (Cu) nanoparticles into water. The cavity walls have varying properties such as top adiabatic wall is moving continuously while the lower wall is maintained at a high constant temperature, in addition, the vertical walls are kept at a low fixed temperature. The magnetic field is applied to the right vertical wall in a horizontal direction. Additionally, the effects of buoyancy forces caused by temperature gradients and shear forces caused by continuous lid motion are considered. The mathematical modelling of problem with all assumptions yields the nonlinear partial differential system. First this system is transferred into non-dimensional form and then transformed system is solved by using Galerkin finite element method (GFEM) along with Gaussian elimination method. Results for isotherms, streamlines and average Nusselt number are obtained versus Richardson number (0.1 ≤ Ri ≤ 15), Grashof number (10 ≤ Gr ≤ 10000), Hartmann number (0 ≤ Ha ≤ 100), volume fractions of solid nanoparticles (0.005 ≤ ϕ1 ≤ 0.02) and (0.005 ≤ ϕ2 ≤ 0.02). It is observed that the Richardson number and Grashof number have significant impacts on both flow velocity and temperature. In addition, concentration of hybrid nanoparticles improves the heat transfer performance. The obtained results may be crucial for thermal management in the cooling of electronics, heat exchangers, solar thermal collectors, industrial operations, medical equipment, HVAC systems, food processing, and renewable energy systems.

Experimental observations of the onset of unsteadiness for buoyant airflow along smooth and rough vertical isothermal walls

ABSTRACT The buoyant airflow along a vertical isothermal wall, under conditions close to transitional, is studied. The schlieren technique and miniature thermocouples are employed for qualitative (flow unsteadiness) and quantitative (heat transfer coefficient and local air temperature) observations. For the smooth surface, the phenomena are found to be sensitive to the enclosure configuration surrounding the plate. Roughening the heated surface with staggered rib segments of proper dimensions leads to increased heat transfer, ascribed to the onset of unsteadiness close to the segments’ edges, together with a better redistribution of the flow thanks to a favorable hydrodynamic interaction between fluid and protrusions.

Effect of Obstacle Shape on Natural Convection in Partially Open Square Enclosure

The present study reports a real-time experimental analysis of natural convection of air using a noninvasive technique (Mach-Zehnder interferometry). The experiments are conducted in a partially open square cavity with a centrally placed adiabatic obstacle and a heat source positioned at the center of the bottom horizontal wall. The left vertical wall has a partial opening occupying 50% of the wall height. The effect of obstacle shapes (square, circular, and triangular) and Rayleigh number on natural convection is evaluated. The interferograms obtained from the experiments give temperature field in the cavity. Air velocity at the opening is measured using an air velocity transducer. The experimental results are compared with numerical findings obtained using ANSYS Fluent 2020. The fringe density in the cavity enhances with increase in Rayleigh number. The temperature gradient, average Nusselt number, and average exit velocity of the flowing fluid are higher for triangular obstacle, whereas minimum for square obstacle. For Rayleigh numbers in the range of 107 to 108, an average increment in Nusselt number and average exit velocity is up to 15% and 16%, respectively. The maximum temperature in the enclosure is higher for square obstacle, whereas it is lower for triangular obstacle.

Numerical Simulation of the Solute Migration Regulated by Vertical Cutoff Wall based on FEFLOW

Cutoff wall has been widely used in desalination of coastal aquifers in many coastal regions and remediation of industrial waste water pollution. In recent years, the excessive exploitation of resources in the coastal brine distribution area leads to the salinization of deep soil. At the same time, the mine water pollution caused by improper discharge of industrial waste water into the abandoned mining area is a new form of pollution in Shandong, China. However, due to the complex geological conditions of abandoned mining areas, loose collapse of overlying strata in roadway and gob layer, it is difficult to prevent and control groundwater pollution in deep gob layer. It is a major difficulty in practical engineering to evaluate the cutoff interception performance of vertical cutoff wall on the pollution of gob layer in such mining areas and optimize cutoff interception measures. In this paper, a typical polluted abandoned mining area in Shandong, China is taken as an example, and COD is used as the main simulation factor for numerical simulation. The numerical simulation results show that in the process of groundwater pollution control, the cutoff wall with appropriate thickness and hydraulic conductivity can effectively block the diffusion of solute. The horizontal transport of solute can be significantly weakened when the thickness of the cutoff wall is 90 cm and the hydraulic conductivity is 1.0×10-4 m/d. Compared with increasing the thickness, reducing the hydraulic conductivity of the cutoff wall is more effective in controlling the migration of solute in the site. When the hydraulic conductivity is reduced by an order of magnitude, the diffusion range of solute is reduced by 19.74% compared to before. Therefore, priority should be given to reducing the hydraulic conductivity of the cutoff wall in order to optimize its influence on pollutant migration.

Thermo-convection driven Sodium Alginate-based Darcy–Forchheimer EMHD Williamson hybrid nanofluid flow with varying thermal distribution

A computational investigation is furnished to explore the responses of a Darcy–Forchheimer EMHD Williamson flow of a Sodium Alginate [Formula: see text]-based Ag-Al2O3 hybrid nanofluid passing over a vertically exponentially stretching cylinder emerged through a porous region. The prime focus of this research is to encompass the inclusion of nonlinear variations in heat distribution, Newtonian boundary heating (NBH) effects, and the influence of thermo-convection alongside suction effects. Key parameters, including thermal buoyancy, Darcy porous medium effects, heat source/sink effects, Biot number, variable thermal index, and thermal convection factor, are comprehensively analyzed as these combining factors can play a crucial role in optimizing the efficacy of several systems such as heat exchanger, material processing and geothermal system that involve the concept of thermo-transportation mechanism. The physical flow dynamics are modeled, employing suitable similarity transformations, and subsequently translated into a dimensionless form. The ensuing collection of modified nonlinear ordinary differential equations is solved by employing the Bvp4c solver bundled into the MATLAB program. Several parameters are scrutinized through graphical presentations to elucidate their impacts on the velocity curve, temperature curve, skin friction coefficient, and Nusselt index. It is worth mentioning that the heat distribution profile significantly escalated for the rising values of several factors such as electric field parameter, varying thermal index, Biot number and shape factor, but the reverse is the pattern with suction and thermo-convection effect. Also, the thermal transportation rate at the proximity of the vertical cylindrical wall appears to exhibit an increment of about an average of 47% in SA-based Williamson hybrid nanofluid compared to Williamson fluid for thermo-convective effect, NBH, and thermal buoyancy. Furthermore, the proximate shear stress rate appears to be amplified by approximately 39% in Williamson hybrid nanofluid when contrasted with Williamson fluid for electric field parameter and thermo-convection effect alongside the raised Darcy–Forchheimer factor.

Making the diamond vortex phase masks for the METIS instrument

Direct observation of exoplanets and proto-planetary disks with the METIS instrument at the Extremely Large Telescope will provide new insights into the processes of planet formation and exoplanet atmospheres. This will be possible thanks to a powerful vector vortex coronagraph that can suppress the starlight to reveal faint signals around it. Here we present the process of making the phase masks at the heart of the coronagraph. These annular groove phase masks consist of deep sub-wavelength gratings in diamond that are etched using inductively coupled oxygen plasma with a strong bias. The METIS instrument requires a wider bandwidth than such components have previously been demonstrated for, leading to a grating design with higher aspect ratio and more vertical walls. To achieve this, the etch mask used for diamond etching was changed from aluminium to silicon and the plasma power was increased. We also improved on our method for reducing the grating depth of finished components to fine-tune them. Together with improved optical testing, this allowed us to produce the best vortex phase masks so far demonstrated for the astronomical N-band.

Free convection and entropy generation inside porous cavities with irregular vertical walls nonuniformly heated from below

In the current study, numerical analyses of heat transfer through free convection and entropy generation characteristics inside three distinct enclosures filled with porous media have been analyzed. The study involves exploring three cavity configurations that differ in the shape of their vertical irregular walls: wavy, convex and concave. The cavities were subjected to sinusoidal heat from below, with the left vertical walls being maintained at a constant cold temperature and the other walls are adiabatic. The governing equations were solved using the finite-element method. The parameters considered are the Darcy and Rayleigh numbers, paying attention to the implication of irregular shapes of the sidewalls. At high Rayleigh numbers, the Darcy number becomes more significant in influencing the Nusselt number and a more noticeable effect is observed with a higher Darcy number. Entropy generation due to heat transfer irreversibility is the dominant contributor of irreversibility at the lowest value of Darcy number while for higher values of Darcy and Rayleigh numbers entropy generation due to fluid friction becomes dominant. Moreover, when Rayleigh reaches 106, the irreversibility due to fluid friction is more significant in the case of the cavity with undulations on the sidewalls as compared to the two other cases. In contrast, the entropy generation associated with heat transfer is significant in the case of a cavity with a convex wall compared to the other two cases.

Cavefish dorsoventral axis angle during wall swimming: laterality asymmetry

The Astyanax fish exhibits two morphs: an eyed, pigmented surface morph and an eyeless, depigmented cave morph. Previous studies have shown that blind morphs swim nearly parallel to the wall and can sense detailed information about objects by gliding alongside them and sensing changes in the flow field around their body using their lateral line sensory system. Hence, cavefish can build hydrodynamic images of their surroundings. Field observations showed that one of their presumptive prey, mysid shrimp, is predominately found not on the floor, but crawling on the walls. In our study, the angle of the body axis with respect to a vertical wall was measured while fish swam in a tank. Results show that when swimming by a wall, cavefish incline the vertical axis of their body away from the wall. But most significantly, this angle is different when the right side or the left side of their body is oriented towards the wall. Intriguingly, cavefish have a leftward-biased dorso-cranial bend, where the convex side of the head is towards their right side. Other studies have shown behavioral “handedness”. When exhibiting Vibration Attraction Behavior (VAB), cavefish in the field show laterality on the preponderant side they circle to explore a vibrating stimulus. Likewise in larval prey capture (LPC) behavior, larvae strike towards prey preferentially located on one side. Our results support that cavefish also express behavioral lateralization during passive swimming by walls and/or when searching for food that is perched on the walls, such as mysid shrimp.

Evaluating the Performance of a Combined Vertical Wall–Horizontal Roof Solar Chimney for the Natural Ventilation of Buildings

The natural ventilation of buildings can be achieved effectively with solar chimneys, which are classified into wall, roof, and combined wall–roof configurations. Among the combined systems investigated in the literature, vertical wall–horizontal roof solar chimneys have not been evaluated thoroughly. This study investigates the performance of a combined vertical wall–horizontal roof solar chimney numerically. A two-dimensional Computational Fluid Dynamics (CFD) model is employed to examine the flow and thermal characteristics under various influencing factors relating to the chimney’s geometry, the flow resistance caused by the bend connecting the vertical and horizontal portions, the reverse flow at the outlet, and the location of the heat source. Compared to a vertical wall chimney at the same cavity height, the combined system always had a lower flow rate but had a higher thermal efficiency at some length-to-total-height ratios. Heating the upper walls induced higher flow rates but lower thermal efficiency. Particularly, the effect of the bend on the flow rate was more important than that of the reverse flow at the outlet. These results imply that a combined chimney is preferred over a vertical one for heating applications, wherein the combined chimney should have transparent upper walls.

Mathematical modeling of water-nano encapsulated phase change material in an enclosure subject to various wave heating

The unsteady buoyancy-driven flow in a square enclosure created by a hot vertical wall is the main focus of the mathematical modeling. The hot left wall undergoes variations following triangle, sine, or square-wave heating. Meanwhile, the right wall remains at a constant cold temperature. The hybrid nanofluid in the enclosure comprises water and nano-encapsulated phase change material (NEPCM). The momentum and energy equations were solved numerically using finite element method. It is found that square-wave heating is responsible for producing the most extensive melting region, while triangle-wave heating produces a relatively modest melting region compared to the broader expansion observed with sine-wave heating. Triangle-wave heating resonates at F = 30 π for ϕ = 0.05 , while sine-wave heating resonates at F = 25 π for ϕ = 0.05 , and square-wave heating resonates at F = 50 π for ϕ = 0.05 . At these resonant frequencies, using 4% NEPCM concentration achieves maximum enhancements of 55%, 44%, and 395% for triangle, sine, and square-wave heating, respectively.

Entropy generation analysis of MHD nanofluid in a corrugated vertical walls enclosure with a rectangular baffle using the Brinkmann-Forchheimer model

Entropy generation analysis of MHD nanofluid in a corrugated vertical walls enclosure with a rectangular baffle using the Brinkmann-Forchheimer model

К вопросу транформации формы провальной воронки при взаимодействии перекрестно-балочного фундамента и наклонного с карстовой полостью

The article presents the changes in the shape of karst sinkholes obtained in the course of modeling experiments during the joint operation of a cross-beam foundation bounded by a rigid vertical wall and an inclined base with a karst cavity. The regularities of transformation of the failure prism depending on the base inclination angle have been determined. The influence of the main variable factors was evaluated: the diameter of the karst cavity, the distance from the foundation footing to the center of the cavity, the distance from the center of the cavity to the retaining structure and the base inclination angle. Based on the results of model experiments, the values of the angle of deviation of the sinkhole formation from the vertical were obtained.

On the structure dynamic response induced by the dam-break surge impact using multivariate copulas

In this study, the dam-break induced surge impact pressure data on a vertical wall are used to investigate the corresponding structure dynamic response. Both the hydrodynamic and structure parameters are confirmed to be crucial in assessing the structure dynamic responses. The surge peak pressure pk, the pressure rise time Tr, the surge impact duration Td, and the structure natural period Tn are considered to establish the statistical model. The present study determines the dependencies among these parameters which describe the structure dynamic response due to the complexity of dam breaking. Accordingly, two multivariate copulas, i.e., the Gaussian copula and the Vine copula, are used to simulate the statistical properties of the maximum dynamic amplification factor ψm, allowing a better understanding of the dependencies and correlations among different parameters. The tail dependence of variable pairs (pk, Tr) and (pk, ψm) are not significant, while the variable pairs (Tr, ψm) and (Td/Tn, ψm) show lower and upper tail dependence. With respect to the experiment data, simulation using the Gaussian copula shows good results regarding variable pairs of symmetric dependence structures, whereas the Vine copula is more suitable for variable pairs of asymmetric dependence structures.

Study on hydraulic conductivity of dredged sediment-attapulgite vertical cutoff walls under confining pressure

Landfills require effective containment systems to prevent the leakage of leachate into the underground environment. Cutoff walls are commonly employed for this purpose, with options including rigid and flexible designs. In areas where structural strength is not a primary concern, flexible cutoff walls offer lower permeability and environmental benefits due to their lack of cement content, thereby reducing CO2 emissions. This study investigates the use of dredged sediment and attapulgite as materials for flexible cutoff walls. Through analyses of bound water content, free water content, hydraulic conductivity, and scanning electron microscopy, we explore the impact of confining pressures on cutoff wall permeability.Our findings reveal that the consolidation induced by confining pressure does not significantly alter the bound water content within the cutoff wall. Instead, changes in water content are predominantly attributed to variations in free water content. Under identical confining pressures, we observe a positive correlation between permeability and hydraulic gradient, with permeability increasing as the hydraulic gradient rises, and anti-permeability decreasing accordingly. Additionally, when holding the hydraulic gradient constant, increasing confining pressure leads to a continuous decrease in permeability. Microscopic analyses highlight that high confining pressure not only compresses pore diameter but also alters pore morphology, thereby influencing permeability.This study contributes to the understanding of cutoff wall behavior under different conditions. Our results demonstrate that increasing confining pressure during soil consolidation effectively reduces cutoff wall permeability to meet design standards. However, the influence of high leachate head on permeability should also be considered. These findings provide a more environmentally friendly and lower permeability option for landfill sites, which is significant for the design and enhancement of containment systems in landfill sites.

Enhanced Efficiency of MHD-Driven Double-Diffusive Natural Convection in Ternary Hybrid Nanofluid-Filled Quadrantal Enclosure: A Numerical Study

The study investigates the performance of fluid flow, thermal, and mass transport within a cavity, highlighting its application in various engineering sectors like nuclear reactors and solar collectors. Currently, the focus is on enhancing heat and mass transfer through the use of ternary hybrid nanofluid. Motivated by this, our research delves into the efficiency of double-diffusive natural convective (DDNC) flow, heat, and mass transfer of a ternary hybrid nanosuspension (a mixture of Cu-CuO-Al2O3 in water) in a quadrantal enclosure. The enclosure’s lower wall is set to high temperatures and concentrations (Th and Ch), while the vertical wall is kept at lower levels (Tc and Cc). The curved wall is thermally insulated, with no temperature or concentration gradients. We utilize the finite element method, a distinguished numerical approach, to solve the dimensionless partial differential equations governing the system. Our analysis examines the effects of nanoparticle volume fraction, Rayleigh number, Hartmann number, and Lewis number on flow and thermal patterns, assessed through Nusselt and Sherwood numbers using streamlines, isotherms, isoconcentration, and other appropriate representations. The results show that ternary hybrid nanofluid outperforms both nanofluid and hybrid nanofluid, exhibiting a more substantial enhancement in heat transfer efficiency with increasing volume concentration of nanoparticles.

Two-Fluid and Discrete Element Modeling of a Parallel Plate Fluidized Bed Heat Exchanger for Concentrating Solar Power

Abstract A novel high-temperature particle solar receiver is developed using a light trapping planar cavity configuration. As particles fall through the cavity, the concentrated solar radiation warms the boundaries of the receiver and in turn heats the particles. Particles flow through the system, forming a fluidized bed at the lower section, leaving the system from the bottom at a constant flowrate. Air is introduced to the system as the fluidizing medium to improve particle heat transfer and mixing. A laboratory scale cavity receiver is built by collaborators at the Colorado School of Mines and their data are used for model validation. In this experimental setup, near IR quartz lamp is used to provide flux to the vertical wall of the heat exchanger. The system is modeled using the discrete element method and a continuum two-fluid method. The computational model matches the experimental system size and the particle size distribution is assumed monodisperse. A new continuum conduction model that accounts for the effects of solid concentration is implemented, and the heat flux boundary condition matches the experimental setup. Radiative heat transfer is estimated using a widely used correlation during the post-processing step to determine an overall heat transfer coefficient. The model is validated against testing data and achieves less than 30% discrepancy and a heat transfer coefficient greater than 1000 W/m2 K.