Rheological Flow Research Articles

EHL Traction Coefficient Is Not a Property of the Liquid Alone

Abstract The slow progress in prediction of elastohydrodynamic film thickness and friction may be attributed to the mistaken notion that a traction curve is equivalent to a rheological flow curve. A similar concept is being standardized by Society of Automotive Engineers (SAE) for the traction coefficient of aerospace oils. Four standards teach that traction coefficient is an inherent physical property of an oil and that full film traction does not depend upon the roller material and that there can be traction measurements which do not depend on the test rig. These traction coefficients are to be employed in models for thermal management analyses without the need for measuring primary properties. Through example calculations, using primary properties of a turbine oil, it is shown here that elastohydrodynamic lubrication (EHL) friction is not a property of the liquid alone, and that it depends on at least two contact characteristics as well; namely, the aspect ratio and scale. Within the tribology literature, there is much evidence of the dependence of EHL friction on other contact parameters as well that are not characteristic of the fluid.

Modulating the Selective Enrichment and Depletion of Ions Using Electrorheological Fluids in Variable-Area Microchannels.

Electrorheological fluids are suspensions that are characterized by a strong functional dependence of their constitutive behavior on the local electric field. While such fluids are known to be promising in different applications of microfluidics including electrokinetic flows, their capabilities of controlling ion transport and preferential solute segregation in confined fluidic systems remain to be explored. In this work, we bring out the unique role of electrorheological fluids in orchestrating the selective enrichment and depletion of charged species in variable area microfluidic channels. Our reported phenomenon is fundamentally distinctive from other types of nonlinear electrokinetic effects previously reported, in a sense that here the dependence of the flow rheology on the electric field turns out to be the central mechanism toward orchestrating the observed nonlinear ion transport. Our results indicate exclusive features of the resulting ion concentration polarization, such as more pronounced ion concentration polarization, controlled largely by the influence of the variations in the channel cross section on the driving electrokinetic forces and the resistive viscous interactions. The underlying physical mechanism is captured aptly by a simple one-dimensional area-averaged model, and validated by full-scale three-dimensional simulations. Our illustrative case study for a converging-diverging microchannel with cross-sectionally uniform solute concentrations reveals that electrorheological effect with greater contrast between the deep and shallow region depths, greater solute concentration, and larger applied axial electric field, all acting in tandem, magnifies the solute enrichment and depletion in the respective segregation zones, bearing significant implications in analytical chemistry, bioanalysis, and beyond.

Rheology of Bingham viscoplastic flow triggered by a rotating and radially stretching disk

Purpose This study aims to investigate the flow and heat transfer characteristics of a Bingham viscoplastic fluid subjected to the combined effects of axial rotation and radial stretching of a circular disk. Building upon existing models for Bingham fluids on stationary walls, we extend the formulation to incorporate the effects of a linearly stretching disk using von Kármán similarity transformations. Design/methodology/approach The resulting system of nonlinear ordinary differential equations is solved to characterize the flow and thermal fields. Three dimensionless parameters govern the momentum layer: a swirling number capturing the balance between rotation and stretching, a Bingham number characterizing the fluid’s yield stress and a modified Reynolds number incorporating the disk stretching. The Prandtl number controls the thermal response. Findings For purely stretching flows, a two-dimensional flow structure emerges. However, the introduction of rotation induces three-dimensional flow behavior. Unlike previous studies suggesting that moderate Bingham numbers are sufficient for non-Newtonian effects on purely revolving disks, the findings indicate that significantly higher yield stresses are required to observe non-Newtonian characteristics under radial stretching conditions. This difference can be attributed to the enhancing influence of wall movement on the fluid dynamics. At high Bingham numbers, a two-layer flow structure develops, comprising an unyielded plug region above the disk and a yielded shear layer adjacent to the wall. The von Kármán viscous pump mechanism drives the Bingham flow within this regime. Originality/value Physical quantities such as drag force due to wall shear stress, torque resulting from tangential shear stress and Nusselt number are extracted from the quantitative data.

The viscous-brittle transition in flowing crystal-bearing volcanic dome lavas

The ascent and advance of volcanic dome lava is non-linear and viscoelastic. There exists a mismatch between current theoretical approaches to dome lava rheology, which are based on rheological laws for viscous suspensions, and empirical experimental approaches to convolved viscous-brittle deformation, which show mixed evidence for simultaneous lava flow and fracturing. The missing requirement is a unified framework for understanding the transition between micro-mechanical flow mechanisms that are dominantly viscous, and those that include micro-cracking in multiphase suspensions such as magmas. Here, we use high-temperature compression rheology with sample-scale acoustic emission analysis to constrain the conditions under which crystal-rich volcanic dome lava can flow by mixed viscous and brittle fracturing processes at small scales, leading to ‘crackling’ acoustic signals, even at moderate shear stresses extant in nature. Using multi-directional permeability measurements on large 60 mm diameter quenched samples of natural magmas, we show that this micro-cracking flow mechanism leads to permeability anisotropy, localizing outgassing into pathways that are off-axis relative to the direction of flow. Finally, we use a scaling approach and a database of published observations from real eruptions to upscale our findings, and show that bulk, apparently ductile flow of low-porosity dome magma is likely to involve a local mixed-mode of micro-cracking and viscous flow during the shallowest portions of ascent and during emplacement on the Earth's surface. The micro-cracking involved in lava advance divorces real crystal-bearing lava emplacement from most current rheology models based on a purely viscous micro-mechanism and shows that a revised solution for the rheology of mixed brittle-viscous flow is required. By re-examining published numerical models for dome emplacement, we demonstrate that the viscous-brittle transition can be intercepted in spatially heterogeneous zones within the dome core.

Impact of calcination temperature, organic additive percentages, and testing temperature on the rheological behaviour of dried sewage sludge

Abstract The main objective of the present work is to evaluate the influence of calcination pretreatment (600–1,000°C), organic additive incorporation (4% methocel, 4% amijel, and 8% starch), and testing temperature (20–60°C) on the rheological flow behaviour of dried sewage sludge and sewage sludge ashes. Besides, the dependency of sludge systems rheology on total solid content (4–15%) and methocel percentage (3–6%) was also evaluated. Furthermore, characterization techniques such as thermal gravimetric analysis-differential scanning calorimetry, X-ray fluorescence, X-ray diffraction, Brunauer–Emmett–Teller, and scanning electron microscopy were employed to investigate, respectively, the thermal decomposition, the chemical composition, the structural variations, the specific surface area, the surface morphology, and microstructure of sludges. The analysis of rheological characteristics according to best-fitting rheological models such as Herschel–Bulkley, Ostwald–de Waele, Cross, and Carreau models revealed that the yield stress (τ 0) and infinite apparent viscosity (η ∞) increase with an increase in TS or methocel percentage and decrease with increasing calcination or testing temperature. The strong impact of testing temperature concerning the reduction of the viscosity involves high activation energy (E a). This last criterion was used to compare the inter-particle strength of sludge systems.

Pipeline Transport Performance of Paste Backfill Slurry in Long-Distance Underground Backfilling: A Review

This paper reviews recent advancements in the pipeline transport performance of paste backfill slurry in long-distance underground backfilling operations, with a primary focus on applications in metal mines. Key aspects, including flow performance, energy consumption during transport, and operational stability, are discussed in detail. Slurry concentration and rheological properties, including viscosity, yield stress, and flow behavior, as well as particle size distribution, are examined for their effects on transport efficiency. The relationship between these characteristics and pipeline resistance is also examined. Factors like pipeline orientation, configuration, diameter, length, elbow design, and elevation gradients are explored, demonstrating that careful design can optimize flow performance, reduce energy consumption, and minimize the risk of blockages and bursts. Additionally, the roles of commonly used additives, such as water reducers, foaming agents, antifreeze agents, and thickeners, are discussed in terms of their impact on slurry flowability, stability, and resistance losses. Optimal slurry regulation, strategic pipeline design, and effective additive utilization improve flow efficiency, extend service life, and reduce maintenance costs, thereby ensuring reliable backfill operations. Future research should focus on innovative pipeline designs, such as improving material selection and configuration to optimize flow stability and reduce energy consumption. Advanced additives, including thickeners and water reducers, could further enhance slurry flowability, reduce pipeline resistance, and improve system reliability.

To spill or not: Short-time pouring dynamics of a toppled liquid bottle

A typical culinary setting involves liquid condiments with different constitutive behaviors stored in jars, bottles, pitchers, or spouts. In the dynamic kitchen environment, handling these condiments might require pouring, drizzling, squeezing, or tapping, demonstrating the interplay of the container geometry, the fluid properties, and the culinary expertise. There is, of course, the occasional accidental toppling. We investigate the combined effects of surface properties, fluid properties, and confinement dimensions on the short-time spilling or pouring dynamics of a toppled cuvette. While attesting to the fact that smaller cuvettes (which can be termed as capillaries as well) do not spontaneously spill, larger cuvettes exhibit spilling dynamics that are dependent on the surface property, fluid viscosity, and flow rheology. For Newtonian liquids, it is observed that the spilling dynamics are determined largely by the coupling of viscous and gravity forces with surface properties, inducing non-intuitive behavior at higher conduit dimensions. The inclusion of rheology for non-Newtonian liquids in the soup makes the spilling dynamics not only an interplay surface and fluid properties but also a function of meniscus retraction demarcating a “splatter” of three regimes “not spilling,” “on the verge of spilling,” and “spontaneous spilling.” We not only delineate the interactions leading to meniscus motion but also provide a mapping on whether or not a container would spill if it is momentarily toppled and then immediately returned to upright position. This study aids in understanding the fascinating physics of fluid pouring dynamics and could lead to new kitchen, biomedical, and industrial technologies.

Enhanced physicochemical and antifungal properties of starch bionanocomposites reinforced with nanocellulose and functionalized with AgNPs derived from cocoa bean shell.

This study explored the synergistic combination of silver nanoparticles (AgNPs), eucalyptus-derived nanofibrillated cellulose (NFC) and cassava starch to develop bionanocomposites with advanced properties suitable for sustainable and antifungal packaging applications. The influence of AgNPs synthesized through a green method using cocoa bean shell combined with varying concentrations of NFC were investigated. Morphological (scanning electron microscopy and atomic force microscopy), optical (L*, C*, °hue, and opacity), chemical (Fourier transform infrared spectroscopy), mechanical (puncture force, tensile strength, and Young's modulus), rheological (flow curve and frequency sweeps, strain, and stress), barrier, and hydrophilicity properties (water vapor permeability, solubility, wettability, and contact angle), as well as the antifungal effect against pathogens (Botrytis cinerea, Penicillium expansum, Colletotrichum musae, and Fusarium semitectum), were analyzed. The morphological analysis indicated excellent interaction between the bionanocomposites constituents. The maximum NFC addition increased the tensile strength of the bionanocomposites by approximately 283.93 % (14.85 MPa) while Young's modulus also showed a significant increase of 303.03 % (417.14 MPa), indicating increased stiffness. Water vapor permeability of the materials decreased by approximately 47.89 %. The materials exhibited hydrophilic properties while maintaining low wettability. Furthermore, the bionanocomposites demonstrated pseudoplastic (Ȳ = 0.59) behavior and an inhibitory effect against fungal pathogens. In conclusion, these innovative materials have the potential to transform packaging technology by serving as sustainable alternatives to petroleum-derived polymers while simultaneously adding value to agro-industrial waste.

Coupled Effects of Time and Temperature on the Rheological and Pipe Flow Properties of Cemented Paste Backfill

As mineral resources at shallow depths become increasingly depleted, the development of these resources is progressively shifting to greater depths. This transition presents challenges for the pipeline transport of cement paste backfill (CPB), particularly in terms of long-distance transport and elevated temperatures. To investigate this phenomenon, we conducted rheological tests, developed a resistance model that accounts for both time and temperature, and performed numerical simulations. The results show that the rheological parameters of CPB exhibit a gradual decline as the flow progresses. Specifically, at 20 °C, the plastic viscosity of CPB decreases by 1.6 Pa·s, and the yield stress decreases by 48.15 Pa; at 30 °C, the plastic viscosity decreases by 1.3 Pa·s, and the yield stress decreases by 18.69 Pa; at 40 °C, the plastic viscosity decreases by 0.84 Pa·s, and the yield stress decreases by 12.55 Pa; and at 50 °C, the plastic viscosity decreases by 0.58 Pa·s, with the yield stress decreasing by 12.53 Pa. Furthermore, the influence of shear time on the rheological properties of CPB diminishes as temperature increases within the range of 20 °C to 50 °C. These results offer significant insights for optimizing the pipeline transport of CPB in mining operations. These findings provide valuable guidance for pipeline transport of CPB in mining operations.

Entropy generation and sensitivity analysis for a squeezed flow of a Williamson hybrid nanofluid under the supervision of microcantilever sensor

The primary objective of this study is to investigate the thermal and fluidic behavior of a Williamson hybrid nanofluid, which is an integration of nanoparticles with Williamson fluid. Williamson hybrid nanofluid is composed of a non-Newtonian fluid (Ethylene glycol) with nanoparticles (Molybdenum disulfide, Zirconium dioxide and Graphene oxide). The impact of various combinations of nanoparticles with the base fluid has been examined and it has been determined that Molybdenum disulfide + Graphene oxide / Ethylene glycol is an effective combination of efficient and enhanced heat transfer. A microcantilever sensor was positioned amidst the plates to monitor the rheological behavior and flow characteristics. This study has potential applications in microscale heat transfer devices and also in an advanced thermal management system. The governing equations incorporating the Williamson fluid model as well as the effects concentration of nanoparticles, magnetohydrodynamics (MHD), permeability, thermal radiation and viscous dissipation are derived. Further, a comprehensive numerical analysis of the squeezed flow of Williamson hybrid nanofluid over a microcantilever sensor has been performed and solved using MATLAB solver. The graphical and tabulated illustrations are used to depict the influence of different control factors on flow phenomena. Elevation in the Weissenberg number and the permeable velocity parameter shoots up the temperature profile. As the values of permeable velocity parameter and squeezed flow index rise, the velocity profile decelerates. On the other hand, the velocity profile uplifts when there is an escalation in the magnetic number. The magnitude of the Nusselt number gets amplified for the increasing values of squeezed flow index. Moreover, the importance of fluid friction and heat transfer is analysed elaborately.

A numerical investigation on rheological turbulent flow through a 90° mixing elbow

Mixing elbows are widely used in various industrial processes to mix two different Newtonian or non-Newtonian fluids under turbulent flow conditions. This study numerically investigates the fluid flow and mixing characteristics in 90-degree elbows with different bend curvatures (curvature ratios of 3, 6, and 9) and Reynolds numbers ranging from 1 × 104 to 5 × 105 for both fluid types. The Reynolds-Averaged Navier–Stokes equations are solved using the turbulent k-epsilon model in ANSYS Fluent. Results show that the bend curvature creates an adverse pressure gradient that drives secondary flows, which become more pronounced with higher Reynolds numbers and lower curvature ratios. Higher Reynolds numbers improve mixing quality, as indicated by velocity and temperature variations quantified using standard deviations. For Reynolds numbers in the range of 104, velocity fluctuations initially increase, but at higher values (~ 105), they decrease, even by up to 64% as the Reynolds number rises from 1 × 105 to 5 × 105. Similarly, increasing the curvature ratio enhances mixing efficiency, with a 32% reduction in velocity fluctuations when the curvature ratio increases from 6 to 9. Furthermore, shear-thinning fluids (n=0.6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n = 0.6$$\\end{document}) exhibit superior mixing performance, with a standard deviation of velocity fluctuations at the outlet of 0.32, compared to 0.54 for shear-thickening fluids (n=1.4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$n = 1.4$$\\end{document}). In terms of temperature fluctuations also, a similar trend is observed. These findings are valuable for optimizing mixing and fluid transport in industries such as chemical processing and food production, where effective mixing of complex fluids is critical. This study provides insights for improving the design of mixing systems that handle fluids with various rheological characteristics.

Experimental and numerical study of the rheological characteristics and flow law of water-based drilling fluids in high-temperature and high-pressure wellbores

Experimental and numerical study of the rheological characteristics and flow law of water-based drilling fluids in high-temperature and high-pressure wellbores

From flow to furnace: Low viscosity of three-phase lavas measured at Kīlauea 2018 eruption conditions

Abstract Melt composition, temperature, and crystallinity are often seen as the three most important characteristics driving lava rheology, which controls eruptive behavior. Traditional methods of measuring the viscosity of crystallizing basalts often yield different mineral characteristics to natural samples and are typically bubble-free. To quantify the viscosity of basalts inclusive of bubble and crystal cargo, we developed a new technique to measure high-temperature three-phase isothermal lava viscosity and applied it to samples from the 2018 eruption of Kīlauea. This new experimental technique begins at subliquidus temperatures, preserving original phenocrysts. A short experimental duration allows for the retention of most of the original bubble population (19%–31% vs. 36% in the original lava) and accurate replication of crystal textures from field samples, as documented in quenched postexperiment samples. The observed rheological behavior in these experiments, conducted at syneruptive temperatures (1150–1105 °C) and strain rates (0.4–18 s–1), should therefore be representative of the lava flows. We measured average viscosities of 116 Pa·s at 1150 °C to 167 Pa·s at 1115 °C (i.e., only 10%–25% higher than calculated liquid viscosities at those temperatures) and a maximum of 1800 Pa·s at 1105 °C. These results are much lower than viscosity measured in traditional bubble-free experiments, which plateaued at ~14,000 Pa·s at 1115 °C. Our results suggest the effect of bubbles in three-phase magmas may be greater than predicted by models based on two-phase bubbly liquids, and this effect must be included in realistic lava flow rheology models. The method proposed here supplies a framework for providing the necessary experimental constraints.

Sub-lacustrine debrite system: Facies architecture and sediment distribution pattern

The deep-water systems in different types of sedimentary basins exhibit significant variability. Current knowledge of deep-water deposition is mainly derived from deep-marine turbidite systems. However, the characteristics and differences of sub-lacustrine gravity flow deposition systems have been a research focus in the fields of sedimentology and petroleum geology. This study investigates the facies architecture, depositional processes, and sediment distribution patterns of a sub-lacustrine debrite system in the Eocene Dongying Rift of the Bohai Bay Basin, China, through the analysis of integrated core data, 3-D seismic data, and well-log data. Nine facies have been identified within the debrite system, representing various depositional processes such as sandy debris flow, muddy debris flow, turbidity currents, sandy slide, sandy slide/slump, and mud flow. Our research indicates that the sub-lacustrine system is primarily influenced by debris flow rather than turbidity currents, as supported by facies quantification, interpretation, and flow rheology analysis. Additionally, we have identified five basic facies building blocks in debrite systems, including slide masses, slump masses, debrite channels, debrite lobes, and turbidite sheets. We have also elucidated and proposed detailed sedimentary processes, flow transport, and transformation within the sub-lacustrine system through analysis of flow origins, facies sequences, and distribution characteristics. Our findings highlight the evolutionary progression from delta-front collapse to sandy slide/slump, sandy debris flow, and finally muddy debris flow. The efficient generation of turbidity currents from parental landslides on sand-prone slopes is deemed unlikely due to rift-basin morphology and transport distances. The formation of the five basic facies building blocks is closely linked to depositional processes and dominant flow types. Consequently, we present a deep-water depositional model for sub-lacustrine debrite systems, focusing on flow dynamics, sediment distribution patterns, and basin morphology within deep lacustrine rifts. This model offers valuable insights into the variability of deep-water deposition in diverse basin settings and aids in predicting lithologic reservoirs during deep-water hydrocarbon exploration.

Recent developments on multiscale simulations for rheology and complex flow of polymers

AbstractThis review summarized the multiscale simulation (MSS) methods for polymeric liquids. Since polymeric liquids have multiscale characteristics of monomeric, mesoscopic, and macroscopic flow scales, MSSs that relate different hierarchical levels are adequate to reproduce flow properties accurately. Our review includes pioneering studies to the most advanced MSS studies on rheology predictions and flow simulations of polymeric liquids. We discuss two major types of MSS methods: the bottom-up and model-embedded MSS methods. The former method mainly connects all-atom molecular dynamics models and mesoscopic models to predict rheological properties. In contrast, the latter method, where a microscopic or mesoscopic model is embedded in a macroscopic computational domain, is designed to predict macroscopic flow properties. Finally, we also discuss MSS methods using machine learning techniques. Graphical abstract

Slot coating of time-dependent structured materials: Effects of thixotropy on the flow dynamics and operating limits

Some of the most common liquid-like formulations rooted in the coating industry consist of rheologically complex structured materials such as inks, paints, and slurries. Yet, the impact of time-dependent structuring effects due to thixotropy on thin film coating applications remains elusive and still unclear. Here, we present a computational study of the effects of thixotropy on slot coating of time-dependent structured materials. By coupling a recent fluidity-based constitutive model for thixotropic materials with a well-established finite element/elliptic mesh generation method for free surface flows, we assess the role of thixotropy by comparing the predictions from the thixotropic model with those from a simple Generalized Newtonian Fluid model that uses the same flow curve for the material steady-state equilibrium viscosity. We find that thixotropy can indeed have a major impact on slot coating applications, potentially bringing strong implications not only to the flow dynamics but also to the operating limits of the process. In conclusion, the results and discussions we present in this study underscore the importance of accounting for thixotropy to genuinely model and fundamentally understand the behavior of time-dependent structured materials with complex rheology in processing flows like those ubiquitous across the broad fields of coating science and engineering.

Numerical simulation of open channel basaltic lava flow through topographical bends

In this study, we utilised computational fluid dynamics to investigate the behaviour of open-channel basaltic lava flows navigating bends on shield volcanoes. Our focus was on understanding the relationship between flow velocity, rheology, and bend geometry. Employing a simple Force Balance Model (FBM), which considers the equilibrium between hydrostatic pressure and centrifugal force, we accurately approximated the changes in the height of the lava’s free surface through various bend geometries. Our analysis includes examining the influence of channel depth, width, and bend radius on the flow, revealing that variations in these parameters significantly affect the flow’s vertical displacement. Additionally, the bend sector angle emerged as a critical factor, indicating a minimum angle necessary for the flow to fully develop before exiting the bend.Further, we assessed the applicability of the Shallow Water Equations (SWE) for modelling the inertial displacement of the lava flow in bends, finding a good fit. The study extended to comparing the FBM’s predictions of the tilt angle of the flow’s free surface with the SWE results, showing notable agreement under specific conditions, particularly at a bend angle of 90 degrees. The impact of fluid density was also considered, revealing that density is a contributing factor to the development of the wetted line in the bend, a factor that is not captured by the simple FBM model. Finally, we explored different rheologies akin to natural lava flows, such as viscoplastic flow, and determined that factors like yield stress, consistency index, and power law index have a small impact on the flow behaviour in a steady-state condition within a bend.

Towards a framework for predicting immunotherapy outcome: a hybrid multiscale mathematical model of immune response to vascular tumor growth.

Studying tumor immune microenvironment (TIME) is pivotal to understand the mechanism and predict the outcome of cancer immunotherapy. Systems biology mathematical models can consider and control various factors of TIME and therefore explore the anti-tumor immune response meticulously. However, the role of tumor vasculature in the recruitment of T cells and the mechanism of T cell migration through TIME have not been studied comprehensively. In this work, we developed a hybrid discrete-continuum multi-scale model to study TIME. The mathematical model includes angiogenesis and T cell recruitment via tumor vasculature. Moreover, solid tumor growth, vascular growth and remodeling, interstitial fluid flow, hemodynamics, and blood rheology are all considered in the model. In addition, different aspects of T cells, including their migration, proliferation, subtype conversion, and interaction with tumor cells are thoroughly included. The model reproduces spatiotemporal distribution of tumor infiltrating T cells that mimics histopathological patterns. Furthermore, TIME model robustly recapitulates different phases of tumor immunoediting. We also examined a number of biomarkers to predict the outcome of immune checkpoint blockade (ICB) treatment. The results demonstrated that although tumor mutational burden (TMB) may predict non-responders to ICB, a combination of different biomarkers is essential to predict the majority of the responders. Based on our results, the ICB response rate varies significantly from 28 to 89% depending on the values of different parameters, even in the cases with high TMB.

Nonlinear viscoelasticity of filamentous fungal biofilms of Neurospora discreta

The picture of bacterial biofilms as a colloidal gel composed of rigid bacterial cells protected by extracellular crosslinked polymer matrix has been pivotal in understanding their ability to adapt their microstructure and viscoelasticity to environmental assaults. This work explores if an analogous perspective exists in fungal biofilms with long filamentous cells. To this end, we consider biofilms of the fungus Neurospora discreta formed on the air-liquid interface, which has shown an ability to remove excess nitrogen and phosphorous from wastewater effectively. We investigated the changes to the viscoelasticity and the microstructure of these biofilms when the biofilms uptake varying concentrations of nitrogen and phosphorous, using large amplitude oscillatory shear flow rheology (LAOS) and field-emission scanning electron microscopy (FESEM), respectively. A distinctive peak in the loss modulus (G″) at 30–50 % shear strain is observed, indicating the transition from an elastic to plastic deformation state. Though a peak in G″ has been observed in several soft materials, including bacterial biofilms, it has eluded interpretation in terms of quantifiable microstructural features. The central finding of this work is that the intensity of the G″ peak, signifying resistance to large deformations, correlates directly with the protein and polysaccharide concentrations per unit biomass in the extracellular matrix and inversely with the shear-induced changes in filament orientation in the hyphal network. These correlations have implications for the rational design of fungal biofilms with tuneable mechanical properties.

Lateral Shear Stress Calculation Model Based on Flow Velocity Field Distribution from Experimental Debris Flows

Debris flows continuously erode the channel downward and sideways during formation and development, which changes channel topography, enlarges debris flow extent, and increases the potential for downstream damage. Previous studies have focused on debris flow channel bed erosion, with relatively little research on lateral erosion, which greatly limits understanding of flow generation mechanisms and compromises calibration of engineering parameters for prevention and control. Sidewall resistance and sidewall shear stress are key to the study of lateral erosion, and the distribution of the flow field directly reflects sidewall resistance characteristics. Therefore, this study has focused on three aspects: flow field distribution, sidewall resistance, and sidewall shear stress. First, the flow velocity distribution and sidewall resistance were characterized using laboratory debris flow experiments, then a debris flow velocity distribution model was established, and a method for calculating sidewall resistance was developed based on models of flow velocity distribution and rheology. A calculation method for the sidewall shear stress of debris flow was then developed using the quantitative relationship between sidewall shear stress and sidewall resistance. Finally, the experiment was validated and supplemented through numerical simulations, enhancing the reliability and scientific validity of the research results. The study provides a theoretical basis for the calculation of the lateral erosion rate of debris flows.