Wall Effects Research Articles

Particle settling in a shear-thinning, viscoelastic fluid in the presence of wall effects

Abstract The settling of particles in fluids is a widespread phenomenon and commonly involves accounting for the effects of walls. Particle settling and wall effects are well understood for Newtonian fluids but the consequences of non-Newtonian fluid properties on particle settling are less well known. Here, we present the results from a set of experiments quantifying wall effects on particle settling within quiescent shear-thinning and viscoelastic (non-Newtonian) fluids for sphere-to-tube diameter ratios $$\lambda \le 0.3$$ λ ≤ 0.3 . We find that wall effects on particle settling are reduced in non-Newtonian fluids and settling velocities are poorly predicted by conventional wall-corrected Stokes’ equations. We show that deviations in settling velocity are due to both the shear-thinning and viscoelastic properties of the fluid. Supported by our experimental dataset, we are able to show that calculating the shear-rate based on the particle diameter length-scale corresponds to an apparent viscosity that appropriately accounts for shear-thinning effects. A further correction factor for viscoelastic behaviour based on $$\lambda$$ λ and the Weissenberg number, Wi, is applied, and shows good agreement with all experimentally measured velocities. Together, we provide a quantitative method to accurately predict the terminal settling velocity of particles in shear-thinning, viscoelastic fluids up to sphere-to-tube diameter ratios of 0.3.

Study on Ladle Baking Process with Oxygen-fuel Combustion

Oxygen-fuel combustion instead of air combustion for ladle baking has gradually become a new technology for ladle heating in the iron and steel industry. The optimization of oxygen-fuel burner structure is of great significance for the wide application of oxygen-fuel combustion technology in iron and steel enterprises. In this study, a three-dimensional model of 100 ton ladle was established by using the numerical simulation software FLUENT 21.0. The fluid flow, combustion and heat transfer in the process of ladle oxygen baking were studied. The ladle baking effects of four different gas pipeline diameters and four different gas nozzle spacing were compared. The results show that when the gas flow rate and oxygen flow rate are about 1:1, the roasting effect is the best. When the distance between fuel gas nozzle and oxygen nozzle is 150 mm~175 mm, the baking effect of ladle bottom and wall is better. When the diameter of gas pipe is 150 mm, the diameter of oxygen pipe is 60mm, and the distance between gas nozzle and oxygen nozzle is 150mm, the baking efficiency can reach 24.33%. The relevant research provides the basis for the application of oxygen-fuel combustion technology in 100t ladle.

Landslides induced by the 2023 Jishishan Ms6.2 earthquake (NW China): spatial distribution characteristics and implication for the seismogenic fault

This study provides a detailed interpretation of 2643 landslides triggered by the 2023 Ms6.0 Jishishan earthquake using remote sensing imagery and GIS analysis. The landslides’ spatial distribution, scale, and relationships with environmental factors were investigated. Findings show a concentration of landslides in the eastern hilly and plain areas, primarily under 1000 m2. Significant factors include elevations of 1700–2300 m, slope angle of 20–40°, southeast and south aspects, middle slope positions, Paleogene and Neogene strata, and proximity within 400 m of rivers, with NDVI values of 0.2–0.6 and PGA of 0.45–0.6 g. Our analysis indicates an NE-dipping thrust fault with a distinct “hanging wall effect”. These results contribute to the coseismic landslide database for Northwest China, advance the understanding of influencing factors, support seismogenic fault identification, and hold significance for improving risk assessment and emergency response capabilities.

A high-order immersed boundary method with ghost cells and flux reconstruction for inviscid flows

We propose a high-order immersed boundary (IB) method for simulating inviscid flows using the flux reconstruction (FR) method, which offers the advantages of a compact stencil, high-order near-wall accuracy, and the ability to handle thin geometries and sharp corners. We utilize the FR method on a Cartesian grid to achieve a compact stencil, which enhances accuracy without requiring surrounding cell information, laying the foundation for future adaptive mesh refinement. Compared to the symmetry wall condition treatment, we combine the curvature corrected symmetry technique with the FR-based IB method to achieve a high-order accuracy near the wall boundary and utilize a third-order polynomial distribution to impose the boundary conditions. We extend the multi-valued ghost-cell method to the present approach to handle thin geometries and sharp corners in the ghost-cell-based IB method. The proposed method can be easily extended to three-dimensional cases. The numerical framework is validated through several two-dimensional simulations of inviscid flows. The approach is first demonstrated for a superposition of an isentropic vortex and a background flow problem with a Mach number of 0.2, which examines the order of accuracy without wall effects in the grid convergence study. Then, inviscid flow around a cylinder and flow through a channel with a bump are tested and compared to body-fitted simulations. Finally, flows around a National Advisory Committee for Aeronautics 0012 airfoil with zero and non-zero angles of attack are demonstrated to show the robustness for the thin geometry calculation. In particular, third-order accuracy is maintained in the near-wall region.

Influence of rough surfaces on airfoil aerodynamics and the ground effect on near-wall flow

Agricultural aircraft play a pivotal role in crop dusting and aerial applications of fertilizers, pesticides, and herbicides, where their close proximity to crop surfaces during operations has significant implications. These interactions affect not only crop safety and treatment efficacy but also environmental impact and operational optimization. This study investigates the aerodynamic interactions between an airfoil and a rough surface, representing crops, focusing on the dual effects of airfoil proximity on surface flow dynamics and the influence of the rough wall on airfoil aerodynamics. A computational framework employing overset (Chimera) mesh for a movable airfoil is developed and rigorously validated against experimental data. Using this validated model, we examine the aerodynamic consequences of proximity, revealing that the rough wall substantially modifies the flow field around the airfoil, altering lift and drag characteristics. Conversely, the airfoil's motion significantly influences wall shear stress and surface flow patterns on the rough wall. These findings provide new insights into the coupled dynamics of airfoil aerodynamics and wall effects, offering a basis for optimizing agricultural aircraft operations while mitigating environmental and crop impacts.

Prediction method for lateral displacements of geosynthetic-reinforced soil walls with segmental block facings

Predicting the performance of geosynthetic-reinforced soil walls with segmental block facings in service is a challenging task due to their complex interaction mechanisms. This paper proposes a semi-analytical method to estimate the performance of such walls by considering a prescribed reduction factor. Rough back of the wall and unreinforced zone effects can be taken into account. It also incorporates an empirical formula to consider reinforcement stiffness to accurately characterize the nonlinear interaction between geosynthetics and soil. Seven full-scale tests and three robust numerical simulations were employed to evaluate the proposed method. The results demonstrate satisfactory estimations of lateral displacement and reinforcement force location with a rational reduction factor. Additionally, the physical significance of the reduction factor is identified, and a method for its determination based on data analysis is proposed. This method eliminates the need for sophisticated numerical analyses to determine lateral displacements. Further investigation is required to explore the correlation between the reduction factor and various design parameters, aiming to establish a more generalized formula for predicting the performance of GRS segmental walls.

Numerical simulations of bubble condensation under a wall effect in a subcooled liquid flow

Numerical simulations of bubble condensation under a wall effect in a subcooled liquid flow

The Use of Different Cell Wall Degrading Enzymes for Pectin Extraction from Carrot Pomace, in Comparison to and in Combination with an Acid Extraction

The effect of different cell wall degrading enzymes, cellulase (C) and hemicellulase (HC), during the enzyme-assisted extraction (EAE) of pectin from carrot pomace was investigated. The EAE with C and a heat treatment resulted in a pectin yield, purity, and molecular structure comparable to an acid extraction (AE), except for a slightly lower molar mass and a slightly higher degree of methylesterification. The addition of HC had a negligible influence on the pectin yield and structure and mainly resulted in more hemicellulose co-extraction. Overall, the AE still resulted in the highest pectin yield, but, despite the much milder extraction conditions, the optimal EAE process resulted in 80% of the pectin yield of the AE. Additionally, this study investigated an EAE with C in combination with an AE, and both combination treatments, i.e., EAE as pretreatment or as an additional treatment, resulted in a significant increase in the pectin yield (up to 72%), while minor structural differences were observed in the extracted pectin. Overall, it can be concluded that the EAE process can be used as a more environmentally friendly alternative for the AE or that EAE can be used in combination with an AE to improve the efficiency of the extraction process.

Numerical study of the effect of barrier wall on liquid hydrogen leakage and dispersion

Numerical study of the effect of barrier wall on liquid hydrogen leakage and dispersion

Experimental study of optimized graphene sheet layout with simulated annealing algorithm on cooling effect of the photovoltaic wall

Experimental study of optimized graphene sheet layout with simulated annealing algorithm on cooling effect of the photovoltaic wall

Turbulent flow pattern and flow resistance characteristics of cross flow over square-arranged tube bundles with different pitch to diameter ratios

Helical tube bundles are used in steam generators and intermediate heat exchangers of high temperature gas-cooled reactors due to their compactness and good thermal expansion adaptation performance. However, the characteristics of cross flow over inline tube bundles are sensitive to pitch to diameter ratios (S/D) and Reynolds numbers (Re), and the influence of S/D and Re variation on the flow patterns (especially wake patterns) and pressure drop coefficients (ξ) remains unclear. In the current investigation, the flow characteristics of tube bundles with S/D = 1.58 and 1.88 with various Re are investigated with the aid of wind tunnel experiments and large eddy simulations (LES). For the tube bundle with S/D = 1.88, the results of LES with periodical geometry align well with wind tunnel experiments, successfully predicting the decreasing recirculation region size as Re increases. In contrast, for the tube bundle with S/D = 1.58, the recirculation region size remains almost constant with varying Re, filling the space between two adjacent tubes even when Re = 36 000. However, the LES with periodical geometry only successfully predicts flow phenomena up to Re = 25 285. The wakes become oblique when Re = 36 000, which differs from experiments. Based on the force balance on the recirculation region, the pressure drop coefficient (ξ) of the cross flow over tube bundles is related to the size of the recirculation region. For the tube bundle with S/D = 1.88, the recirculation region size decreases as Re increases when Re ≥ 18 000, resulting in a larger flow cross section area in the main flow region. The increasing main flow cross section area leads to an increased pressure coefficient along the separation streamlines. Since the Reynolds normal and shear stresses cancel each other out, the increasing pressure coefficients along the recirculation region boundary lead to the increasing surface pressure coefficients in the rear side of the tube and ultimately lead to the ξ decrease from 0.26 to 0.24 when Re increases from 18 000 to 44 571. Conversely, when Re ≤ 10 285, the recirculation area fills the space between two adjacent tubes, so the ξ barely change with Re. For tube bundle with S/D = 1.58, the recirculation area fills the space between tubes even when Re ≥ 18 000, leading to almost the unchanged ξ (≈0.27) with Re. The higher ξ at Re = 10 285 is related to the bounding wall effects on the near wall tubes.

Study of the N2 vibrational relaxation behaviors via the CO rovibrational thermometry.

This paper performed a comprehensive study of the thermal nonequilibrium effects of CO/Ar mixtures with various degrees of N2 additions and probed the N2 relaxation behaviors via the CO rovibrational thermometry. The rovibrational temperature time histories of shock-heated CO/N2/Ar mixtures were measured via a laser-absorption technique, and the corresponding vibrational relaxation data were summarized at 1890-3490K. The measured results were compared with predictions from the Schwartz-Slawsky-Herzfeld (SSH) formula and the state-to-state (StS) approach (treating CO and N2 as pseudo-species). The vibrational state-specific inelastic rate coefficients for N2-N2 collisions were supplemented using the mixed quantum-classical calculations. The StS predictions, informed by experimentally measured pressures, showed good agreement with experimental data. Additionally, the impact of coupling between flow dynamics and StS kinetics behind reflected shock waves was evaluated using two different one-dimensional approaches, which provide limiting bounds (accounting for unsteady flow and end wall effects) in post-reflected shock flow conditions. Moreover, the vibrational relaxation data of the N2-N2 system were modified via sensitivity analysis to improve the performance of the SSH formula. Further analysis highlighted that the vibration-vibration-translation path provides an efficient way for vibrational energy transfer between CO and N2, resulting in almost the same vibrational temperature time histories for CO and N2. Therefore, the N2 relaxation behaviors can be characterized by the CO rovibrational thermometry, considering N2 is infrared inactive. Finally, the heat sink effects and the reflected-shock-bifurcation phenomena were highlighted.

Assessment of Seismic Vulnerability for a Hospital Building Using Field Data and Various Numerical Analyses Considering Bidirectional Ground Motion Effects

For the assessment of seismic effects on RC buildings, the real structural condition has to be modelled as accurately as possible. Medical facilities and hospitals have to resist seismic actions and remain operational after seismic events. For this reason, a detailed seismic vulnerability assessment of a hospital building located in Orihuela, Spain, is presented in this paper using a combination of field monitoring data and numerical analysis. Ambient noise measurements from field monitoring using Raspberry Shake-based sensors are used to capture dynamic characteristics that describe the building behaviour. Data from these sensors were used to update and refine the finite element model of the structure for a detailed analysis of the building’s seismic performance. The different analytical procedures included both elastic and inelastic modelling, as well as static and dynamic assessments, to provide an exhaustive evaluation of the building’s behaviour under seismic loads. In the numerical model, the effect of masonry infill walls is considered, taking into account detailed material properties and structural configurations. Furthermore, the study carefully selects ground motion records representing two limit states—Damage Limitation (DL) and Severe Damage (SD)—to conduct an extensive seismic analysis. In each limit state applied to the structure, there are 14 bidirectional ground motions with components alternately directed along the two principal directions of the building. This analysis evaluated the structural response, focusing on torsional effects, inter-storey drift ratios, and the seismic performance of individual components. The results were compared to other analysis types, considering both overall and localised behaviour, to determine the reliability of different approaches. The findings support the idea that field monitoring data should be combined with advanced modelling techniques to achieve a more accurate evaluation of the building’s seismic vulnerability, considering bidirectional effects.

Assessing and monitoring with ultrasonic pulse velocity testing the critical effects of hygrothermal actions on the infill masonry walls of the envelope of buildings with reinforced concrete structure

The external envelope of buildings with reinforced concrete structures (RCS buildings) is usually subjected to various external environmental actions. Among these external environmental actions, hygrothermal actions are particularly relevant, mainly related to external temperature and humidity variations. These variations could negatively influence the hygrothermal behavior of that envelope and lead to problems related to an increased risk of material degradation of the external face of unreinforced masonry (URM) infill walls of the building envelope URM infill. In the survey of the degradation of these URM infill walls and of concrete elements, nondestructive evaluation (NDE), such as ultrasonic pulse velocity testing (UPV testing), had been used before. The main objective of the study is to assess the potential use of UPV testing in the evaluation of the influence of moisture content in the behavior of URM infill walls, and the methodology of the study consists, firstly, concerning the hygrothermal actions, which RCS buildings are subjected, which are here described summarily. An assessment is made of the most usual types of degradation of URM infill walls of the envelope of RCS buildings, mainly due to moisture and thermal effects in URM infill walls. UPV testing in the survey of the degradation of the external face of URM infill walls of the building envelope, essentially due to hygrothermal actions, is analyzed, based on an example of the use of UPV testing in a building façade. Subsequently, the potential use of UPV testing in evaluating the influence of moisture content in the behavior of URM infill wall is made, particularly with the use of UPV testing in a compression test of a masonry specimen with variable moisture content during the test. Their results are presented, followed by a discussion of these results, and finally by the conclusions of the study.

Numerical Simulation on Self-Propulsion Characteristics of Bionic Flexible Foil Considering Ground Wall Effect.

In order to figure out the wall effect on the propulsive property of an auto-propelled foil, the commercial open-source code ANSYS Fluent was employed to numerically evaluate the fluid dynamics of flexible foil under various wall distances. A virtual model of NACA0015 foil undergoing travelling wavy motion was adopted, and the research object included 2D and 3D models. To capture the foil's moving boundary, the dynamic grid technique coupled with the overlapping grid was utilized to realize the foil's positive deformation and passive forward motion. The ground wall effect on fluid dynamics (thrust force, lift force and propulsive efficiency) and the flow structures of travelling wavy foil were analyzed. The numerical results show that the existence of the ground wall is beneficial for the propulsive property of foil. Specifically, the existence of the wall can improve the forward speed and efficiency of foil, with a maximum increase of 13% in moving velocity and a 10.5% increase in propulsive efficiency. The conclusions acquired in the current study are of great significance for the design of bionic UUV.

Numerical studies on the effects of infill walls for progressive collapse resistance of RC building

Numerical studies on the effects of infill walls for progressive collapse resistance of RC building

Experimental study on the effect of energy absorption and wave attenuation of sand wall in ground motion under explosion

Abstract Sand walls have a good energy absorption and wave attenuation effect on explosion shock waves, which can also have an impact on the seismic waves generated by the evolution of shock waves. In order to study the effect of sand wall in energy absorption on the results of explosive ground motion, four repeated explosion experiments were conducted by using different sand wall configurations. A ground motion measurement system was designed to measure the velocity at different distances from the explosion center. The measurement and analysis results showed that under the action of the sand wall, the peak velocity and the total energy based on vibration velocity both significantly decreased, fully demonstrating the energy absorption and wave attenuation effect of the sand wall. The sand wall also has an impact on the cube root similarity rate, resulting in the distribution of ground motion parameters no longer strictly following this law, but the sand wall has no significant impact on the frequency distribution. Under different sand wall configurations, the circle shaped sand wall has a better energy absorption and wave attenuation effect, while the circle shaped sand wall with nested circle shaped ends can enhance the energy absorption and wave attenuation effect by 21%.

Effect of infill walls on the seismic performance of a severely damaged substandard RC building during the February 6, 2023, Kahramanmaras earthquake sequence

On February 6, 2023, two catastrophic earthquakes with moment magnitudes of Mw 7.7 and Mw 7.6 struck southern cities of Türkiye, occurring only nine hours apart. Spectral accelerations obtained from some of the recorded ground motions exceeded the design spectrum specified in the Turkish Building Earthquake Code (TBEC 2018) for the maximum credible earthquake level. This has prompted a review of seismic design practices within the framework of TBEC 2018. To address this concern, this study evaluates the performance of a reinforced concrete (RC) building with a ribbed slab that sustained heavy damage, according to official damage assessments, after the February 6th earthquake sequence. Numerical models were developed both with and without infill walls to assess their influence on the building’s response. Time history analysis and static pushover methods were used for its seismic performance assessment. Time history analyses were conducted under ground motions recorded at three different stations in close proximity to the investigated building. The inclusion of infill walls in the numerical model significantly influences the seismic performance analysis results. Peak floor accelerations of the building are determined to be higher at infilled model compared to the bare frame. The distribution of damaged columns in the actual building aligns well with the analysis results of the numerical model that includes infill walls. Notably, the numerical analysis using the ground motion record of the closest station to the building most accurately represents the actual damage distribution observed after the earthquakes. Finally, while the inclusion of infill walls in the model increases the lateral stiffness of the structure, it was also observed that displacement-dependent results obtained in the nonlinear time history analysis, such as relative story drifts, could increase depending on the selected ground motion record. This highlights the complex interaction between the infill walls, modal properties of the building, and the dynamic characteristics of the earthquake record.

Effects of probiotic and yeast extract supplement on liver functionality index and metabolic parameters in transition period of dairy cattle

This research sought to evaluate the potential effects of probiotics and yeast cell wall (YCW) supplements on the liver functionality index (LFI) and metabolic parameters of dairy cattle throughout the transitional period. A cohort of forty dry cows was randomly divided into four groups, namely the probiotic group (Pr) receiving a basal diet combined with a blend of Bacillus subtilis, Bacillus lechiniformis, Streptococcus Thermophilis, and Enterococcus faecium; the YCW group receiving a basal diet enriched with Saccharomyces cerevisiae; the probiotic and yeast cell wall extract group (P & Y) receiving a basal diet supplemented with a mixture of probiotic and yeast cell wall extract; and the control group adhering to the basal diet. The intervention was initiated 21 days before calving and persisted until 28 days post-calving, except for the control group. The study entailed the collection of blood samples at four sampling times, encompassing 21 days preceding calving, seven days before calving, seven days post-calving, and four weeks post-calving. Multiple biochemical parameters were assessed, including urea, blood urea nitrogen (BUN), Gamma-glutamyl transferase (GGT), total bilirubin (TB), albumin, total protein (TP), globulin, glucose, triglyceride, cholesterol, and liver functionality index. The results showed that the Pr group exhibited reduced average levels of GGT and glucose compared to the control group (P < 0.05). Similarly, the P & Y group demonstrated lower average BUN, TB, and cholesterol levels than the control (P < 0.05). Notably, the LFI exhibited a discernible trend towards elevation in the Pr group compared to the control group (P = 0.007) and the P & Y group (P = 0.007). In essence, supplementation of YCW and probiotics is associated with advantageous effects on metabolic parameters and liver function.

A maneuverable underwater vehicle for near-seabed observation

Underwater robots can collect comprehensive information on species and habitats when conducting seabed operations, enhancing localized insights and expanding underwater ecological understanding. One approach uses autonomous underwater vehicles, but proximity operations may disturb sediments and compromise observation quality. Another approach uses wheeled or legged benthic robots, but unavoidable contact limits their application in delicate ecosystems like coral reefs. To address these challenges, we propose a maneuverable underwater vehicle for near-seabed observations. This vehicle moves with minimal turbulence and shows strong resistance to external disturbances, enabling high-quality seabed observation as close as 20 cm. It rapidly detects intense disturbances like turbulence and wall effects, allowing real-time path planning to prevent bottoming. Multiple tests in various marine environments, including sandy areas, coral reefs, and sheer rock, show low sediment disturbance and improved adaptability to rugged underwater terrain.