Shear Flow Research Articles

FLOW CURVES AND STRESS-STRAIN CURVES GENERATED BY A NONLINEAR MODEL FOR SHEAR FLOW OF THIXOTROPIC VISCOELASTIC MEDIA ACCOUNTING FOR STRUCTURE EVOLUTION

A systematic analytical study of the mathematical properties of the nonlinear shear flow model of thixotropic viscoelastic-plastic media is continued. It takes into account the mutual influence of а deformation process and structure evolution (the kinetics of the formation and destruction of intermolecular bonds and associates of macromolecules). The model is reduced to the system of two nonlinear differential equations for the dimensionless stress and the degree of structuredness (i.e. cross-links density and so on). Assuming six material parameters and an (increasing) material function governing the model are arbitrary, the phase portrait of the system is analytically studied in the vicinity of its single equilibrium point. Basic properties of flow curves and stress-strain curves with constant shear rate generated by the model are examined. Thus, the analysis of the model ability to describe the behavior of both liquid-like media and solid-like (thickening, hardening, solidifying) viscoelastic-plastic media has been started: the effects of strain-rate and strain hardening, relaxation, creep, recovery, etc. The stress-strain curves dependence on the shear deformation (monotonicity, convexity, instantaneous modulus, tangent modulus evolution), on the shear rate and initial structuredness and on the material parameters and function of the model (in particular, the parameters that control the effect of structuredness on viscosity and shear modulus and the influence stress on the rate of destruction of the structure) has been studied. It is proved that stress-strain curves can be both increasing and have sections of decrease, resembling a yield-drop, and damped oscillations; that all stress-strain curves have horizontal asymptotes (steady flow stress), monotonically dependent on shear rate, and the flow stress strictly increases with increasing shear rate; that their instantaneous shear modulus, on the contrary, depends on the initial structuredness, but does not depend on shear rate. Under certain restrictions on the material parameters, the model is also capable to provide a bilinear form of stress-strain curves, which is intrinsic for an ideal elastoplastic model, but with strain rate sensitivity. It has been established that the family of stress-strain curves does not have to be increasing function of initial structuredness or shear rate: in a certain range of shear rates, in which the equilibrium point is a “mature” focus and pronounced oscillations of stress-strain curves are observed, it is possible that stress-strain curves with different shear rates may interweave with each other. It is studied how structuredness changes in the process of deformation depending on shear rate, stress, material parameters and material function of the model. The initial structuredness affects only the initial arc of stress-strain curves, but does not affect their asymptotes and the steady value of the structuredness, which monotonically decreases with increasing shear rate. A variety of scenarios of structuredness behavior over time (in particular, the observed sharp collapse of the structuredness when critical stress values are reached) generates a number of unusual effects (unusual properties) in comparison with typical properties stress-strain curves of structurally stable materials.

A low-cost, open-source cylindrical Couette rheometer

Rheology describes the flow of fluids from food and plastics, to coatings, adhesives, and 3D printing inks, and is commonly denoted by viscosity alone as a simplification. While viscometers adequately probe Newtonian (constant) viscosity, most fluids have complex viscosity, requiring tests over multiple shear rates, and transient measurements. As a result, rheometers are typically large, expensive, and require additional infrastructure (e.g., gas lines), rendering them inaccessible for regular use by many individuals, small organizations, and educators. Here, we introduce a low-cost (under USD$200 bill of materials) Open Source Rheometer (OSR), constructed entirely from thermoplastic 3D printed components and off-the-shelf electromechanical components. A sample fluid rests in a cup while a micro stepping motor rotates a tool inside the cup, applying strain-controlled shear flow. A loadcell measures reaction torque exerted on the cup, and viscosity is calculated. To establish the measurement range, the viscosity of four Newtonian samples of 0.1–10 Pa.s were measured with the OSR and compared to benchmark values from a laboratory rheometer, showing under 23% error. Building on this, flow curves of three complex fluids – a microgel (hand sanitizer), foam (Gillette), and biopolymer solution (1% Xanthan Gum) – were measured with a similar error range. Stress relaxation, a transient test, was demonstrated on the biopolymer solution to extract the nonlinear damping function. We finally include detailed exposition of measurement windows, sources of error, and future design suggestions. The OSR cost is ∼1/25th that of commercially available devices with comparable minimum torque (200 µN.m), and provides a fully open-source platform for further innovation in customized rheometry.

Microrheometric study of damage and rupture of capsules in simple shear flow

Capsules, which are potentially active fluid droplets enclosed in a thin elastic membrane, experience large deformations when placed in suspension. The induced fluid–structure interaction stresses can potentially lead to rupture of the capsule membrane. While numerous experimental studies have focused on the rheological behaviour of capsules until rupture, there remains a gap in understanding the evolution of their mechanical properties and the underlying mechanisms of damage and breakup under flow. We here investigate the damage and rupture of bioartificial microcapsules made of ovalbumin reticulated with terephthaloyl chloride and placed in simple shear flow. We characterize damage by identifying how the surface shear modulus of the capsule membrane changes over time. Rupture is then characterized by comparing the number and size distribution of capsules before and after exposure to shear, while varying the shear rates and time during which capsules are sheared. Our findings reveal how the percentage of ruptured capsules increases with their size, exposure time to shear, and the ratio of viscous to elastic forces at rupture.

Lift force on a spherical droplet in a viscous linear shear flow

We study numerically the flow around a spherical droplet set fixed in a linear shear flow with moderate shear rates ( $Sr\leq 0.5$ , $Sr$ being the ratio between the velocity difference across the drop and the relative velocity) over a wide range of external Reynolds numbers ( $0.1<{{Re}}\leq 250$ , ${{Re}}$ based on the slip velocity and the viscosity of the external fluid) and drop-to-fluid viscosity ratios ( $0.01\leq \mu ^\ast \leq 100$ ). The flow structure, the vorticity field and their intrinsic connection with the lift force are analysed. Specifically, the results on lift force are compared with the low- ${{Re}}$ solution derived for droplets of arbitrary $\mu ^\ast$ , as well as prior data at finite ${{Re}}$ available in both the clean-bubble limit ( $\mu ^\ast \to 0$ ) and the solid-sphere limit ( $\mu ^\ast \to \infty$ ). Notably, at ${{Re}}=O(100)$ , the lift force exhibits a non-monotonic transition from $\mu ^\ast \to 0$ to $\mu ^\ast \to \infty$ , peaking at $\mu ^\ast \approx 1$ . This behaviour is related to an internal three-dimensional flow bifurcation also occurring under uniform-flow conditions, which makes the flow to evolve from axisymmetric to biplanar symmetric. This flow bifurcation occurs at low-but-finite $\mu ^\ast$ when the internal Reynolds number ( ${{Re}}^i$ , based on the viscosity of the internal fluid) exceeds approximately 300. In the presence of shear, the corresponding imperfect bifurcation enhances the extensional rate of the flow in the wake. Consequently, the streamwise vortices generated behind the droplet can be more intense compared with those behind a clean bubble. Given the close relation between the lift and these vortices, a droplet with ${{Re}}=O(100)$ and $\mu ^\ast \approx 1$ typically experiences a greater lift force than that in the inviscid limit.

Aerodynamic characteristic of limited micro-scale Taylor–Couette flow at hyper-rotate speed

To pursue improvements in the power-to-weight ratio, cost-effectiveness ratio, and reliability in the energy industry, rotating machinery has been developed with higher rotational speeds and smaller sizes, resulting in complex aerodynamic behavior of the rotational shearing flow between rotator and stator. This study reports experimental measurements of the aerodynamic characteristics of a limited micro-scale Taylor–Couette flow (TC flow) at hyper-rotational speeds for the first time. The maximum rotational speed and eccentricity ratio are 6.0 × 104 rpm and 0.8, respectively, and the minimum average clearance height is 100 μm. The static pressure of the shearing flow is measured using a high-response micro-manometer. A large eddy simulation has been employed to unveil flow fields of the gas film between the stator and the rotator. The results show that the micrometer-scale clearance height and end leakage due to limited length dominate the micro-scale Taylor–Couette flow. Decreasing the scale of the clearance height reduces the angular distance between the peak and bottom pressures compared to that observed in the TC flow with a large-scale clearance. Furthermore, ambient pressure cannot fully permeate into central section of the eccentric Taylor–Couette flow with a micrometer-scale clearance and end leakage, and the pressure upstream near the region the minimum size of clearance decreases along the axial end. Owing to the difference in the constraint degree at both ends along the axial direction, the peak value occurs near the region of Z/L = −0.32. The maximum pressure of the limited micro-scale Taylor–Couette flow increases with increasing rotational speed and eccentricity ratio, whereas it decreases with increasing clearance height. Within the scope of the parameters in this study, the maximum pressure is 0.025 MPa. Decreasing the size of gas film restrains the instability of the shearing flow, whereas increasing the rotational speed strengthens the turbulence. In this study, the shearing flow at the middle section (Z/L = 0) is in a nearly laminar state at δ < 0.012, whereas it is highly turbulent near the end of the clearance and in the ambient environment. The end leakage induces additional axial flow, which is conspicuous at a large eccentricity ratio. At hyper-rotational speeds, the micro-scale Taylor–Couette flow with end leakage exhibits distinctive patterns that have never been reported in classic Taylor–Couette flows with large clearances. This work of this study is significant because it can provide theoretical guidance and technical support for the design of actual dynamic pressure gas bearings and floating ring sealing flow.

Near wake evolution of a tidal stream turbine due to asymmetric sheared turbulent inflow with different integral length scales

Tidal stream turbines deployed at highly energetic open water sites are subjected to sheared inflow in the rotor plane. The inflow shear is expected to cause asymmetric loading on the rotor blades and affect the downstream wake. In the current study, two different turbulent inflow conditions, static-high shear and dynamic shear, were generated via an active-grid turbulence generator. A 1:20 scaled three-bladed horizontal axis tidal turbine model was tested in those conditions. The results were compared to a quasi-laminar case with no imposed turbulence or shear. The results show that the high shear reduces the average performance, with a drop of up to 16% in the optimal power coefficient. Besides, the shear profiles increase torque fluctuations and induce significant differences in wake hydrodynamics between the high-speed (upper) and low-speed (lower) regions. The large integral length scales further enhance the load fluctuations perceived by the rotor but have a negligible effect on the mean wake field quantities. The wake recovery was found to be ∼2 to 4 times faster in the upper half region than in the lower region in the near wake. The lower half region featured a faster breakdown of tip vortex structure and a rapid drop of swirl number, a phenomenon conjectured to be a consequence of the strong turbulence intensities and Reynolds stresses in the lower half region. The sheared turbulent inflow also results in a very intensive energy redistribution process towards large-scale, low-frequency motions, which is important to the downstream turbines.

Development and Test of AFT-Fuselage BLI Propulsor Experiment

Aircraft boundary-layer ingestion (BLI) propulsion involves a deep mutual aerodynamic interaction between the embedded engines and the airframe. This paper presents wind-tunnel tests followed by numerical validation investigating the aerodynamic characteristics of a representative airframe model with tail-cone BLI propulsor. Starting from a reference fuselage and by means of several axisymmetric optimizations aimed at maximizing the ratio between the net force thrust power to BLI fan disk power, an optimized upswept fuselage geometry with a nonaxisymmetric aft nacelle are derived. The model is manufactured and tested in the Aircraft Research Association transonic wind-tunnel facility at Mach numbers from 0.20 to 0.80, measuring extensive flow data. A detailed computational fluid dynamics study is conducted to assess the ability of steady Reynolds-averaged Navier–Stokes solutions to replicate experimental data. Five grid resolutions for two topologies with three turbulence models are tested at low- and high-speed conditions. The computational fluid dynamics is generally able to reproduce with good accuracy the measured flowfield at the aerodynamic interface plane using a sufficient mesh resolution, with a higher sensitivity to the turbulence closures in areas affected by shear layers and flow separations.

Experimental analysis of the performance of screwed connections for steel-timber composite beams

The proposed research addresses the structural behavior of screwed connections in composite beams consisting of Cold-Formed Steel (CFS) profiles and timber boards. An experimental program consisting of 30 push-out tests involving six different models was conducted to evaluate the performance of different types of connection. The screw diameter and spacing were different in each model, and in one out of every five specimens of each model, the screws were installed with steel washers. Results indicate that the screws’ diameter influences the connection’s load-carrying capacity. Results also indicate that the spacing of screws influences the connection’s longitudinal shear flow: the larger the spacing between screws, the lower the longitudinal shear flow. Conversely, results from connections involving steel washers did not show any increase in load-carrying capacity or stiffness. The failure mode detected in the tested specimens resulted from the crushing of the Oriented Stranded Board (OSB) related to the rotation of the self-tapping screws. The typical failure mode, called "screw tilting", can be explained by analyzing the axial and transverse projections of the push-out force, where the latter causes crushing of the timber through contact pressure, and the former induces tension in the screw.

Soret and Dufour effects in two-phase boundary layer flow of non-Newtonian and Newtonian fluids with uniform shear strength ratio

BackgroundThis study numerically investigates heat and mass transfer in two-phase boundary layer shear flows, focusing on a non-Newtonian Casson fluid interacting with an adjacent Newtonian fluid under the influence of thermal radiation. By incorporating both Soret and Dufour effects, we examine how temperature gradients influence mass flux and how concentration differences affect energy flux. These coupled effects are essential for applications involving simultaneous heat and mass transport, such as chemical reactors, separation processes, and thermal management systems. MethodsThe analysis explores boundary layer convergence with varying shear intensities, utilizing the MATLAB solver “bvp4c” with appropriate similarity transformations for computational accuracy. The resulting numerical data are presented in graphical form to illustrate the impact of key parameters on flow characteristics. Additionally, variations in the Sherwood number, Nusselt number, and interfacial shear stress are depicted for each fluid across different parameter values. To evaluate the accuracy of our numerical method, we conducted a comparative analysis with the results reported by Weidman and Wang [4] and Wang [2]. This comparison demonstrated an excellent match, confirming the reliability of our approach, as shown in Table 1 and Fig. 2. Significant findingsThe results demonstrate that the fluid temperature increases with the Dufour number, while the concentration rises with the Soret number. Higher Casson parameter values lead to a reduction in interfacial shear stress in both fluids. Furthermore, the Nusselt and Sherwood numbers increase with an enhanced radiation parameter, highlighting the influence of thermal radiation on heat and mass transfer. These insights offer a valuable understanding of flow behavior in systems with coupled thermal and concentration gradients.

Extreme summer drought increased soil detachment capacity of biocrusts in subtropical China

Biological soil crusts (Biocrusts) are considered to have significant effects on soil detachment processes. Increasing extreme droughts are expected to affect the structure and functioning of biocrust ecosystems. However, understanding how biocrust ecosystems will respond to drought requires further investigation in the subtropical region. This study conducted continuously monitoring of understory biocrusts in subtropical China from May to November 2022, analyzed the monthly variation of near-surface characteristics of biocrusts and performed scouring experiments with six flow shear stresses (7.61–21.08 Pa) to assess the monthly variation of soil detachment capacity (Dc) of biocrusts. Finally, we elucidated the complex effects of summer drought (August-September) on Dc of biocrusts. Results showed that summer drought led to significant reductions in biocrust coverage (BC) and biocrust thickness (BT) (P<0.05), as well as notable declines in soil stability (including soil cohesion and Mean weight diameter) and soil nutrient content (including soil organic matter, total Nitrogen, total Phosphorus) (P<0.05), except for a non-significant increase in bulk density (P>0.05). Furthermore, Dc of biocrusts significantly increased by 172.2 % during the summer drought compared to the previous months (P<0.05). These changes of biocrusts are mainly affected by moisture stress more than heat stress. Partial least squares path modeling (PLS-PM) revealed that reduced rain and lower soil moisture increased Dc mainly by diminishing the BC and BT, followed by reducing soil cohesion and soil aggregate stability. The results provide empirical evidence for the cumulatively detrimental effects of future climate on biocrusts and contribute to more comprehensive understanding of biocrusts multifunctionality.

Mechanism of shear-enhanced rotating-disk microfiltration for separation of microbe/protein bio-suspension

Shear-enhanced dynamic filtration is a promising approach for separating fermented biological products. In this study, we aimed to investigate the separation of bovine serum albumin (BSA) and polymethyl methacrylate (PMMA) particles in a binary suspension using rotating-disk microfiltration. Type-R and Type-RB rotating-disk configurations were designed and compared using experimental data and simulated results. The effects of operating conditions, including rotational speed and filtration pressure, on filtration flux, resistance, and protein rejection, were analyzed. Because the filter membrane rejected all the PMMA particles, the primary source of filtration resistance in the PMMA/BSA suspension was the fouling cake. Although BSA rejection increased with higher filtration pressure, it decreased as the rotational speed increased. Computational fluid dynamics simulations were used to model the flow velocity and shear stress distributions within the rotating-disk dynamic microfiltration system. The results showed that Type-RB achieved a 55 % increase in flux compared to Type-R, owing to a significant reduction in cake resistance by approximately 46 %. A proportional relationship between the mean cake mass and the ratio of qs/τw under varying operating conditions was established using a force balance model. These findings suggest that elevated shear stress significantly enhances filtration performance, with Type-RB demonstrating superior effectiveness for bio-suspension separation.

On the origin of circular rolls in rotor-stator flow

Rotor-stator flows are known to exhibit instabilities in the form of circular and spiral rolls. While the spirals are known to emanate from a supercritical Hopf bifurcation, the origin of the circular rolls is still unclear. In the present work we suggest a quantitative scenario for the circular rolls as a response of the system to external forcing. We consider two types of axisymmetric forcing: bulk forcing (based on the resolvent analysis) and boundary forcing using direct numerical simulation. Using the singular value decomposition of the resolvent operator the optimal response is shown to take the form of circular rolls. The linear gain curve shows strong amplification at non-zero frequencies following a pseudo-resonance mechanism. The optimal energy gain is found to scale exponentially with the Reynolds number $Re$ (for $Re$ based on the rotation rate and interdisc spacing $H$ ). The results for both types of forcing are compared with former experimental works and previous numerical studies. Our findings suggest that the circular rolls observed experimentally are the effect of the high forcing gain together with the roll-like form of the leading response of the linearised operator. For high enough Reynolds number it is possible to delineate between linear and nonlinear responses. For sufficiently strong forcing amplitudes, the nonlinear response is consistent with the self-sustained states found recently for the unforced problem. The onset of such non-trivial dynamics is shown to correspond in state space to a deterministic leaky attractor, as in other subcritical wall-bounded shear flows.

Geometrically nonlinear analysis of composite beams based on global–local superposition

A composite beam finite element is designed to capture through-thickness effects, specifically normal stress and strain and transverse shear, in the context of geometrically nonlinear analyses. The starting point for the formulation is a similar element already proposed for linear analyzes based on a global–local superposition approach, where local functions are defined in each layer of the laminate, and global functions are defined along the thickness. The consistency of the kinematic hypotheses is guaranteed by imposing the continuity equations of displacements through the thickness, the force balance equations along the thickness, directly or indirectly, by imposing the continuity of transverse stresses, and by applying the boundary conditions on the lower and upper surfaces of the elements. In the context of nonlinear analyzes, the imposition of continuity of displacements is straightforward. However, the continuity of the transverse stresses needs to be carefully imposed, as the relevant stresses are the second order Piola-Kirchhoff stresses and the strains are the Green-Lagrange strains, consistent with the total Lagrangian approach used. The constitutive equations are written in incremental form and a detailed analysis is conducted to ensure that the stresses and strains involved are physically consistent across the different reference frames employed. In order to assess the accuracy of the numerical model implemented, a unique semi-analytical technique is developed to obtain the response of asymmetrical laminated beams under compression.

Correlation times of velocity and kinetic helicity fluctuations in non-helical hydrodynamic turbulence

Non-helical turbulence within a linear shear flow has demonstrated efficient amplification of large-scale magnetic fields in numerical simulations, but its precise mechanism remains elusive. The incoherent $\alpha$ mechanism proposes that a zero-mean fluctuating transport coefficient $\alpha$ (linked to kinetic helicity) in the shear flow is a candidate driver. Previous renovating-flow models have proposed that the correlation time of helicity fluctuations must be sufficiently extended to overcome turbulent magnetic diffusivity, yet only empirical validation of this concept has been obtained. In this study, we conduct direct numerical simulations of weakly compressible non-helical hydrodynamic turbulence. We scrutinize the correlation times of velocity and kinetic helicity fluctuations in distinct flow configurations, including rotation, shearing and Keplerian flows, as well as the shearing burgulence counterpart. Our findings indicate that rotation contributes to a prolonged correlation time of helicity compared with velocity, particularly notable in auto-correlations of both volume-averaged quantities and individual Fourier modes due to the formation of large-scale vortices. In contrast, moderate shear strength does not exhibit significant scale separation, with shear flows elongating vortices in the shear direction. Shearing burgulence, characterized by shorter helicity correlation times, appears less conducive to hosting the incoherent $\alpha$ effect. Notably, at modest shear rates, only Keplerian flows exhibit sufficiently coherent helicity fluctuations, in contrast to shearing flows. However, the relative strength of helicity fluctuations compared with turbulent diffusivity is significantly lower, raising doubts about the viability of the incoherent $\alpha$ effect as a potential dynamo driver in the subsonic flows examined in this study.

Measurement and analysis of residual stress of multilayer carbon fiber laminate based on incremental drilling method

In the automotive and aerospace industries, carbon fiber is widely used in structures such as chassis and wings due to its lightweight and excellent mechanical properties, and the residual stresses are crucial for product design. In this paper, six kinds of carbon fiber laminates with different layup directions are investigated by using the integral method, and the calibration coefficient matrix is numerically solved by using ABAQUS finite element software, and the effects of laminate direction and incremental step on the three-direction residual stresses are experimentally analyzed. The residual stresses in different oriented layers were predicted by classical lamination theory (CLT), and the longitudinal, transverse and in-plane shear stresses were compared by combining incremental drilling experiments with calibration factors. The results showed that the ply with [45/90/−45/0/45/90/−45/0] laminate had the best performance,the difference between theoretical and experimental values for σx was 0.421MPa. The maximum τxy measurement was 1.7103MPa, with a maximum percentage error of 25.3%. The maximum difference for σy was 0.7306MPa. These findings indicate that the method is more accurate in predicting the residual stresses in the first four layers of composite material. This provides important theoretical and experimental support for the optimal design of composites.

Single-cell electro-mechanical shear flow deformability cytometry

The complex structural and molecular features of a cell lead to a set of specific dielectric and mechanical properties which can serve as intrinsic phenotypic markers that enable different cell populations to be characterised and distinguished. We have developed a microfluidic technique that exploits non-contact shear flow deformability cytometry to simultaneously characterise both the electrical and mechanical properties of single cells at high speed. Cells flow along a microchannel and are deformed (elongated) to different degrees by the shear force created by a viscoelastic fluid and channel wall. The electrical impedance of each cell is measured using sets of integrated microelectrodes along two orthogonal axes to determine the shape change and thus the electrical deformability, together with cell dielectric properties. The system performance was evaluated by measuring the electro-mechanical properties of cells treated in different ways, including osmotic shock, glutaraldehyde cross-linking and cytoskeletal disruption with Cytochalasin D and Latrunculin B. To confirm the accuracy of the system images of deformed cells were also captured using a camera. Correlation between the optical deformability and the electrical deformability is excellent. This novel cytometer has a throughput of ~100 cells s—1 is simple, does not use sheath flow or require high speed optical imaging.

Investigation of Sutterby fluid flow through elliptic multi-stenosed artery: analytical solutions of blood flow problem

PurposeThe presence and progression of stenosis disturb the normal circulation of blood through an artery and cause serious consequences. The proposed investigation is aimed to assess non-Newtonian characteristics of blood in an elliptical artery having stenosis. The blood is taken as Sutterby fluid flowing via a multi-stenosed elliptical cross-section artery.Design/methodology/approachThe analytical solution of a mathematical model representing the considered problem is extracted in a non-dimensional form by utilizing the perturbation technique under the mild stenosis assumptions.FindingsThe graphical nature of these results is examined and discussed comprehensively for different physical parameters. The height and shape of stenosis are noted to have prominent effects on flow velocity. The wall shear stress and flow velocity attained high values in the stenotic portion of the artery. The non-uniform stenosis is observed to create higher resistance to the flow than the uniform stenosis. Further, a high disorder is noticed in the constricted region of the artery by streamlines analysis.Research limitations/implicationsThe manuscript completely comprehends the blood’s non-Newtonian flow in the arteries of elliptical shape having multiple stenoses. The present study is about the properties of non-Newtonian blood flow through an elliptical artery with many stenoses. The Sutterby fluid model is used to describe the blood’s non-Newtonian nature. By utilizing presumptions of mild stenosis, the mathematical model’s non-linearity is decreased, and the perturbation method is applied to generate the resulting equations.Practical implicationsThe presence of stenosis can significantly impact the circulation of blood flow. When an artery becomes narrowed, it can create a constriction or obstruction in the flow path of blood, which can lead to several important fluid dynamics phenomena, i.e. increased velocity, shear stress, pressure drop, etc. The presence of stenosis can cause various damages and complications in the affected blood arteries and surrounding tissues, resulting in heart attacks or diseases like atherosclerosis.Originality/valueThe work presented in the manuscript was not published earlier in any form.

Spontaneous flows and quantum analogies in heterogeneous active nematic films

Incorporating the inherent heterogeneity of living systems into models of active nematics is essential to provide a more realistic description of biological processes such as bacterial growth, cell dynamics and tissue development. Spontaneous flow of a confined active nematic is a fundamental feature of these systems, in which the role of heterogeneity has not yet been considered. We therefore determine the form of spontaneous flow transition for an active nematic film with heterogeneous activity, identifying a correspondence between the unstable director modes and solutions to Schrödinger’s equation. We consider both activity gradients and steps between regions of distinct activity, finding that such variations can change the signature properties of the flow. The threshold activity required for the transition can be raised or lowered, the fluid flux can be reduced or reversed and interfaces in activity induce shear flows. In a biological context fluid flux influences the spread of nutrients while shear flows affect the behaviour of rheotactic microswimmers and can cause the deformation of biofilms. All the effects we identify are found to be strongly dependent on not simply the types of activity present in the film but also on how they are distributed.

Research on Influence Mechanism of Nozzle Structure on Properties of Thick Carbon Steel Plate by Laser Cutting

Aiming at problems such as slow cutting speed, poor cutting quality and inability to cut thick plates effectively with traditional single-layer nozzle structure, it is proposed to add an outer ring core to form a double-layer nozzle structure on the basis of the single-layer nozzle structure to improve its cutting performance. The three-dimensional entity of single- and double-layer nozzle is established, and the simulation model of auxiliary gas flow field is established by using N-S equation and SST k-ω turbulence model assisted by laser cutting in this paper. The simulation results show that under the same cutting parameters, the auxiliary gas flow rate, oxygen concentration, mass flow rate, shear force and dynamic pressure of the double-layer nozzle structure are higher than those of the single-layer nozzle structure. In addition, compared with the single-layer nozzle structure, the double-layer nozzle structure can effectively improve the attenuation of oxygen concentration in the direction of sheet thickness. Two nozzle structures were used to laser cutting carbon steel plates with a thickness of 20 mm in the experiment, and the experimental parameters of cutting speed were 1.2–1.6 m/min. The comparison results show that the cutting speed and cutting section quality of the double-layer nozzle are better than those of the single-layer nozzle, and the results of simulation analysis are consistent with the cutting test results.

Free vibration and stability analyses of functionally graded plates resting on elastic foundations based on 2D and quasi-3D shear deformation theories using the finite strip method

This paper explores the elastic buckling and free vibration behavior of thick functionally graded material (FGM) plates placed on elastic foundations, using two-dimensional (2D) and quasi-three-dimensional (quasi-3D) shear deformation theories. The material properties of the FGM plates are assumed to vary continuously through the thickness based on a power-law distribution. By minimizing the total potential energy and solving the associated eigenvalue problem, the classical finite strip method is applied to determine the critical buckling loads and natural frequencies of the FGM plates. A key novelty of this work lies in the development of a quasi-3D shear deformation theory, which incorporates thickness stretching effects, providing a more accurate distribution of transverse shear strains across the plate thickness. Additionally, the FSM is utilized to efficiently discretize the in-plane geometry, offering a computationally cost-effective solution for analyzing free vibration and mechanical buckling characteristics. The elastic foundation is modeled using Winkler and two-parameter Pasternak models. The complexity of the governing equations is reduced by decomposing the transverse displacement into bending, shear, and thickness stretching components. Numerical results for FGM plates with various boundary conditions are validated by comparing them with analytical solutions from existing literature. Additionally, the effects of parameters such as plate thickness-to-length ratio, length-to-width ratio, boundary conditions, and the power-law index are analyzed and discussed.