Non-uniform Shear Research Articles

On interfacial deformation and resistance characteristics over superhydrophobic surfaces: A numerical study

The air/water interface, known as the plastron, entrapped in submerged superhydrophobic surfaces (SHSs), plays a crucial role in underwater drag reduction. However, the plastron can be easily deformed or collapsed by turbulent flow, leading to decreased drag reduction or even an increase in drag. Most previous numerical studies have simplified these interfaces as idealized flat or curved rigid boundaries. To thoroughly investigate the interfacial behavior of SHSs, this study presents a numerical comparison between ideal and dynamic interfaces. The plastron undergoes regular oscillations after a brief adaptation period, transitioning between convex, nearly flat, and concave shapes. During the oscillatory decay, the dynamic properties of the interface modify the surface drag of the SHSs by both affecting the viscous drag and introducing pressure drag. The viscous drag is affected in two main ways. First, the momentum exchange across the dynamic interface is enhanced due to the roughness-like effect, leading to an increased viscous drag in groove region. Second, the trailing interfaces induce step flows and secondary flows downstream of the grooves, creating regions of nonuniform shear stresses. Consequently, the viscous drag of the downstream walls is slightly reduced. Overall, for convex and nearly flat interfaces, the drag increase within the groove region outweighs the drag reduction at the downstream walls, resulting in a total drag increase in 47.3% and 29.8%, respectively. Conversely, for concave interfaces, the drag increase within the groove region is smaller than the drag reduction at the downstream walls, leading to a 9.8% decrease in total drag.

Simplified site response analysis for regional seismic risk assessments

Seismic risk assessment on a regional scale requires an estimation of ground motion intensity and its spatial variation over large geographical areas. This task is particularly challenging in the presence of very soft soil deposits where significant amplification occurs at specific frequencies that are often referred to as local resonances. It is often not feasible to conduct a nonlinear site response analysis at thousands of sites of interest across a region such as an urban area due to the computational effort involved and the required detailed information on soil profiles at each site. Thus, in regional seismic risk analyses the hazard is typically represented by a field of response spectral ordinates estimated by ground motion models. This study proposes a simplified site response analysis procedure to improve the characterization of spectral ordinates to be used in regional seismic risk assessments. In the proposed procedure, reduced-order models are used to conduct site response analysis using very few parameters to transform response spectra at rock outcrop into response spectra at the surface of each of the sites. A particular emphasis is given to soft-soil sites characterized by low shear-wave velocities overlaid on rock or firm soils. A non-uniform continuous shear beam model with a parabolic variation of shear modulus along the depth and modal damping is used in combination with Random Vibration Theory. It is shown that the proposed approach provides better estimates than those of ground motion models or physics-based ground motion simulation models which often cannot capture the local resonances. Site-specific validation of the shear beam model and overall simplified site response analysis is performed at four soft-soil sites in San Francisco, California. Despite its simplicity, it is shown that the proposed procedure adequately captures the amplitudes and spectral shapes of the motions. It is also shown that in conjunction with ground motion models or physics-based models, the proposed simplified site response analysis procedure can be used to efficiently simulate the seismic hazard on a regional scale through an example of a regional seismic hazard analysis of 160 softer soil sites in Downtown San Francisco during the Loma Prieta earthquake.

Vibration Analysis of Perovskite Solar Cells Resting on Porous Nanocomposite Substrate in Thermal Environment

The free vibration analysis of a perovskite solar cell (PSC) within thermal environments is studied through a quasi-3D plate model. This model is designed to account for the stretching effects and non-uniform shear strains throughout the thickness. The PSC film is represented in the model as a thin laminated plate, comprising five distinct plies: ITO, PEDOT:PSS, perovskite, PCBM, and Au. A graphene platelets reinforced composite (GPLRC) substrate, made of Poly (methyl methacrylate), is assumed to be located under the noted five layers. The GPLRC substrate is conceptualized in the model as a porous foundation with finite depth. The foundation stiffnesses are determined using a modified Vlasov model, and the equivalent Young modulus of the foundation is evaluated using a modified Halpin–Tsai model, introducing the porosity coefficient. It is also considered that the material properties of GPLRC substrates exhibit temperature dependency. For the PSC with all edges simply supported, Navier solution method is applied to obtain the frequencies and associated mode numbers. Based on the results presented in this study, an increase in the porosity and thickness of the substrate can negatively impact the frequencies of the structure. However, natural frequencies experience almost no change if the temperature rises.

Shallow crustal imaging beneath NW Indian terrane from teleseismic P-wave coda using a Bayesian approach

Deciphering the crustal architecture of the Cretaceous Barmer-Sanchore Basin (BSB) and Neoproterozoic provinces in the NW Indian Shield presents significant challenges due to extensive sediment deposition and widespread felsic igneous rocks. To address such intricacies, we employ a transdimensional Bayesian joint inversion of teleseismic P-wave polarizations and receiver functions to resolve the detailed structure of the upper 10 km of the crust beneath 29 seismic stations deployed in the study area. The new data is analyzed separately within each of the three different backazimuthal groups to identify any strong variations in the shallow subsurface structure and derive a more robust, averaged model for every station site. The resulting 1-D models reveal heterogeneous sediment cover in BSB and Marwar Basin, with respective thicknesses ranging from ∼1.3–5.5 km and 1–1.5 km. Remarkably low shear-wave velocities (Vs < 1.0 km/s) of sediments with increased Vp/Vs (>2.3) are observed in BSB and adjacent areas, which are related to highly unconsolidated Quaternary-Tertiary deposits. The Marwar Basin is imaged to have 0.3–0.5 km of uncompacted sediments that overlie 0.5–1 km thick Marwar Supergroup sequence. The Erinpura Granites (EG) and Malani Igneous Province (MIP) are characterized by a variably thick sediment blanket, typically ranging within 1 km in thickness. The Vs of the sediments in these regions exceeds 2.4 km/s that possibly corresponds to Mesozoic and older sediments. The basement beneath EG exhibits Vs faster than 3.4 km/s, consistent with moderately metamorphosed granites. In MIP, the basement is characterized by non-uniform shear velocities, suggesting the influence of intrusions linked to magmatic episodes in NW India.

Irrigant dynamics of a back-to-back double side-vented needle in root canals with various tapers: a computational fluid dynamics study

Understanding the apical pressure and irrigant flow patterns in root canals is crucial for safe and effective irrigation. Therefore, this study aimed to assess the flow characteristics of irrigants in root canal models with varying tapers during final irrigation by employing various needle designs, including a back-to-back double-side-vented needle, through computational fluid dynamics. The root canal model was configured as a closed geometrical cone with a simulated apical zone (size 30) and features tapers of 4%, 6%, and 8%. Three needle types—open-ended needle (OEN), single side-vented needle (SSVN), and double side-vented needle (DSVN)—were investigated. The results indicated that for the 4% taper models, the open-ended needle generated the maximum apical pressure, followed by the double side-vented needle and the single side-vented needle. However, in the 6% and 8% tapering root canal models, the double-side-vented needle applied the lowest maximum apical pressure. Consequently, the DSVN can pose a risk for irrigant extrusion in minimally prepared canals due to heightened apical pressure. In wider canals, the DSVN exhibited lower apical pressure. The maximum irrigant replacement was observed with OEN compared to that of the closed-ended group for both flow rates. Additionally, compared with OENs, closed-ended needles exhibited nonuniform and lower shear wall stress.

Implementation and Validation of a Numerical Method for Concentrated Suspensions in Large Flows Based on the Particle Diffusion Equation

This work presents the development of an OpenFOAM solver aimed at correctly predicting dynamics of concentrated suspensions when subjected to non-uniform shear flows. The newly implemented solver is able to predict the behavior of a heterogeneous mixture whose characteristics depend on the solid particle local concentration. To simulate such behavior, the conservation equation expressing the time variation of the particle volume fraction has been implemented in OpenFOAM; this was achieved by modifying a pre-existing solver, pimpleFoam, which discretizes the Navier–Stokes system of equation through the PIMPLE algorithm. As a first step, the formulation of the momentum equation has been adapted to correctly solve cases with non-Newtonian fluids. Successively, the Krieger’s correlation has been used to model the viscosity variation in the domain to take in account heterogeneous particle distributions. Finally, the iterative cycle for the solution of the migration equation has been included within the time loop. The above-mentioned code has been successfully validated by comparing the numerical results with the measured data provided by experiments reported in literature.

Thick-shell finite element analysis of reinforced concrete flat plates with non-uniform connection stresses

This paper presents the application of a thick-shell nonlinear finite element analysis procedure to estimate the punching shear resisting performance of reinforced concrete slab-column connections under variable connection shear stress conditions. In the analyses performed, varied connection shear stress conditions stem from slabs being supported by columns with different cross-section aspect ratios, being subjected to different distributions of gravity loading, being constructed with different planar reinforcement ratios in orthogonal directions, as well as the application of unbalanced bending moments. Forty-eight isolated slab-column connection specimens presented in the literature were modelled and analyzed using a thick-shell finite analysis procedure. All numerical results were developed using a predefined set of material models and analysis parameters, a consistent meshing procedure, and are shown to provide meaningful agreement with experimental data without the need for case-specific model calibration or the adoption of specialised failure criteria. The results show that thick-shell modelling methods can be suitable for estimating the punching shear response of slabs subjected to non-uniform shear stress development in connection regions, and can provide similar levels of precision to that obtained for the analysis of idealised slab-column connections typically used for design procedure and model development.

Cross-streamline migration and near-wall depletion of elastic fibers in micro-channel flows.

The complex dynamics of elastic fibers in viscous fluids are central to many biological and industrial systems. Fluid-structure interactions underlying these dynamics govern the shape and transport of flexible fibers, and understanding these interactions can help tune flow properties in applications such as microfluidic separation, printing and clogging. In this work, we use slender-body theory to study micromechanical dynamics that arise from the coupling between the elastic backbone of a fiber and the local straining flow that contributes to filament flipping and cross-streamline migration. The resulting transverse drift is unbiased in either direction in simple shear flow. However, a non-uniform shear rate results in bias towards regions of high shear, which we connect to the shape transitions during flips. We discover a depletion layer that forms near the boundaries of pressure-driven channel flow due to the competition between such a cross-streamline drift and steric exclusion from the walls. Finally, we develop scaling laws for the curvature of filaments during flip events, demonstrating the origin of the drift bias in non-uniform flows, and confirm this behavior from our simulations. Put together, these results shed light on the role of a local and dominant coupling between elasticity and viscous resistance in dictating long-term dynamics and transport of elastic fibers in confined flows.

Experimental investigation of rotational behavior of pseudo-ductile adhesive angle joints exhibiting variable strain rate

Pseudo-ductile behavior in composite structural frames can be achieved by enabling their beam-column joints to exhibit nonlinear structural response due to progressive damage, by using pseudo-ductile adhesives. This study investigates the static behavior of a novel pseudo-ductile bonded-bolted angle joint with a bolt at the geometric centroid of the joint. A pseudo-ductile elastomer adhesive is used which is notably sensitive to the strain rate. The bolt ensures structural integrity and produces pure torsional moments in the adhesive planes. This configuration induces nonuniform strain rates in the adhesive layers in the radial direction, i.e., from the center outwards. The experimental results reveal that under the nonuniform shear strain distribution, the initial stiffness, yield rotation, and maximum torsion exhibit an increasing trend with strain rate, while maximum rotation decreases. An analytical model was developed using stress-strain relations obtained from single-lap joints with uniform stress distribution to predict the angle joint responses. The analytical model overestimates the initial joint stiffness due to the nonuniform stress distribution but shows good agreement for strength and post-yield behavior. Lastly, the angle joint exhibits the lowest ductility ratios compared to linear lap joints, showing that the pseudo-ductile adhesive capacity may not be fully utilized in the angle configuration.

Vibrations of Nonlocal Polymer-GPL Plates at Nanoscale: Application of a Quasi-3D Plate Model

An analysis is performed in this research to obtain the natural frequencies of a graphene-platelet-reinforced composite plate at nanoscale. To this end, the nonlocal elasticity theory is applied. A composite laminated plate is considered where each layer is reinforced with GPLs. The amount of GPLs may be different between the layers, which results in functionally graded media. To establish the governing equations of the plate, a quasi-3D plate model is used, which takes the non-uniform shear strains as well as normal strain through the thickness into account. With the aid of the Hamilton principle, the governing equations of the plate are established. For the case of a plate that is simply supported all around, natural frequencies are obtained using the well-known Navier solution method. The results of this study are compared with the available data in the open literature, and, after that, novel numerical results are provided to explore the effects of different parameters. It is depicted that, with the introduction of GPLs in the matrix of the composite media, the natural frequencies of the plate enhance. Also, a proper graded pattern in GPL-reinforced composite plates, i.e., an FG-X pattern, results in the maximum frequencies of the plate. In addition, the introduced quasi-3D plate theory is accurate in the estimation of the natural frequencies of thick nanocomposite plates at nanoscale.

Dense bidisperse suspensions under non-homogeneous shear

We study the rheological behaviour of bidisperse suspensions in three dimensions under a non-uniform shear flow, made by the superimposition of a linear shear and a sinusoidal disturbance. Our results show that (i) only a streamwise disturbance in the shear-plane alters the suspension dynamics by substantially reducing the relative viscosity, (ii) with the amplitude of the disturbance determining a threshold value for the effect to kick-in and its wavenumber controlling the amount of reduction and which of the two phases is affected. We show that, (iii) the rheological changes are caused by the effective separation of the two phases, with the large or small particles layering in separate regions. We provide a physical explanation of the phase separation process and of the conditions necessary to trigger it. We test the results in the whole flow curve, and we show that the mechanism remains substantially unaltered, with the only difference being the nature of the interactions between particles modified by the phase separation.

A novel thermomechanical model for predicting interfacial stresses in flexible hybrid laminate

Triggered by the growing needs for photoelectric conversion and optical interconnections, flexible optoelectronics have recently attracted a surge of interest. Flexible hybrid laminates are promising components of these devices owing to their high performance and flexibility. However, the thermomechanical mismatch of heterostructures usually induces interfacial stresses and resultant failures, particularly for multilayer structures with soft polymeric substrates. The interfacial stresses in flexible laminates remain a challenging matter to be understood distinctly. Herein, the interfacial stresses are investigated via a representative case composed of hard and soft hybrid laminate under nonuniform temperature. By introducing nonuniform shear strain in the thickness direction of bond layer, and nonuniform temperature changes of multilayer simultaneously, a novel analytical model is developed to describe the interfacial stresses with considering adjusted interfacial compliances for the bond layer with varying thicknesses. Our analytical expressions are suitable for different interfacial compliances and a trilinear approximation is verified by the finite element method (FEM) for the adhesive layers with different thicknesses, and comparative analyses were carried out with the existing literatures. The characteristics of the shear stresses are quantitatively illustrated under different temperature variations, elastic moduli and geometrical dimensions. Based on above the vital influencing factors, the mitigating strategies for shear stress are proposed to decrease the interfacial damage. By optimizing key parametric designs, the model and analysis of interfacial stresses could be useful for characterizing the interfacial thermal stress of rigid-flexible films, and enhancing the mechanical stability of heterogeneous multilayers.

The Shear Stress-Regulated Expression of Glypican-4 in Endothelial Dysfunction In Vitro and Its Clinical Significance in Atherosclerosis.

Retention of circulating lipoproteins by their interaction with extracellular matrix molecules has been suggested as an underlying mechanism for atherosclerosis. We investigated the role of glypican-4 (GPC4), a heparan sulfate (HS) proteoglycan, in the development of endothelial dysfunction and plaque progression; Expression of GPC4 and HS was investigated in human umbilical vein/artery endothelial cells (HUVECs/HUAECs) using flow cytometry, qPCR, and immunofluorescent staining. Leukocyte adhesion was determined in HUVECs in bifurcation chamber slides under dynamic flow. The association between the degree of inflammation and GPC4, HS, and syndecan-4 expressions was analyzed in human carotid plaques; GPC4 was expressed in HUVECs/HUAECs. In HUVECs, GPC4 protein expression was higher in laminar than in non-uniform shear stress regions after a 1-day or 10-day flow (p < 0.01 each). The HS expression was higher under laminar flow after a 1 day (p < 0.001). Monocytic THP-1 cell adhesion to HUVECs was facilitated by GPC4 knock-down (p < 0.001) without affecting adhesion molecule expression. GPC4 and HS expression was lower in more-inflamed than in less-inflamed plaque shoulders (p < 0.05, each), especially in vulnerable plaque sections; Reduced expression of GPC4 was associated with atherogenic conditions, suggesting the involvement of GPC4 in both early and advanced stages of atherosclerosis.

Evaluation of predictive models of aneurysm focal growth and bleb development using machine learning techniques

BackgroundThe presence of blebs increases the rupture risk of intracranial aneurysms (IAs).ObjectiveTo evaluate whether cross-sectional bleb formation models can identify aneurysms with focalized enlargement in longitudinal series.MethodsHemodynamic, geometric, and anatomical...

The Involvement of Cx43 in JNK1/2-Mediated Endothelial Mechanotransduction and Human Plaque Progression.

Atherosclerotic lesions preferentially develop at bifurcations, characterized by non-uniform shear stress (SS). The aim of this study was to investigate SS-induced endothelial activation, focusing on stress-regulated mitogen-activated protein kinases (MAPK) and downstream signaling, and its relation to gap junction proteins, Connexins (Cxs). Human umbilical vein endothelial cells were exposed to flow ("mechanical stimulation") and stimulated with TNF-α ("inflammatory stimulation"). Phosphorylated levels of MAPKs (c-Jun N-terminal kinase (JNK1/2), extracellular signal-regulated kinase (ERK), and p38 kinase (p38K)) were quantified by flow cytometry, showing the activation of JNK1/2 and ERK. THP-1 cell adhesion under non-uniform SS was suppressed by the inhibition of JNK1/2, not of ERK. Immunofluorescence staining and quantitative real-time PCR demonstrated an induction of c-Jun and c-Fos and of Cx43 in endothelial cells by non-uniform SS, and the latter was abolished by JNK1/2 inhibition. Furthermore, plaque inflammation was analyzed in human carotid plaques (n = 40) using immunohistochemistry and quanti-gene RNA-assays, revealing elevated Cx43+ cell counts in vulnerable compared to stable plaques. Cx43+ cell burden in the plaque shoulder correlated with intraplaque neovascularization and lipid core size, while an inverse correlation was observed with fibrous cap thickness. Our results constitute the first report that JNK1/2 mediates Cx43 mechanoinduction in endothelial cells by atheroprone shear stress and that Cx43 is expressed in human carotid plaques. The correlation of Cx43+ cell counts with markers of plaque vulnerability implies its contribution to plaque progression.

Local gyrokinetic simulations of tokamaks with non-uniform magnetic shear

In this work, we modify the standard flux tube simulation domain to include arbitrary ion gyroradius-scale variation in the radial profile of the safety factor. To determine how to appropriately include such a modification, we add a strong ion gyroradius-scale source (inspired by electron cyclotron current drive) to the Fokker–Planck equation, then perform a multi-scale analysis that distinguishes the fast electrons driven by the source from the slow bulk thermal electrons. This allows us to systematically derive the needed changes to the gyrokinetic model. We find new terms that adjust the ion and electron parallel streaming to be along the modified field lines. These terms have been successfully implemented in a gyrokinetic code (while retaining the typical Fourier representation), which enables flux tube studies of non-monotonic safety factor profiles and the associated profile shearing. As an illustrative example, we investigate tokamaks with positive versus negative triangularity plasma shaping and find that the importance of profile shearing is not significantly affected by the change in shape.

Development of Novel Low-Cost Sustainable Abrasive Flow Finishing Media From Ground Tire Rubber and Its Performance Evaluation

Abstract The present experimental endeavor aims to develop and study the characteristics of a novel ground tire rubber media (GTRM) through rheological, thermal, and mechanical characterizations. Thermogravimetric analysis reveals the presence of natural and styrene butadiene rubber in ground tire rubber (GTR) and confirms the thermal stability of developed GTRM under the working temperature of the abrasive flow finishing (AFF) process. Investigation reveals that incorporating GTR into media improves AFF performance up to 50 phr, after which it degrades due to poor self-deforming characteristics and abrasive holding capacity at higher GTR fractions. It has also been observed that the percentage of oil and the size of the GTR particles are significant media parameters that govern the GTRM property and thus influence its performance. GTRM with bigger GTR produces deep abrasive cut marks and nonuniform shearing. A comprehensive study reveals that GTRM containing 50 phr GTR (80 mesh), 10% oil, and 60% SiC (220 mesh) results in the highest percentage improvement in surface roughness (% ΔRa) of 44% on flat geometry. The same media, but with coarser SiC (80 mesh), was also used to polish a micro-grooved workpiece. Results show 64% improvement in Ra for the top surface and 58% for the bottom, respectively. Both surfaces still contain a few pits and unevenness; however, the surfaces and top edge of the groove became smooth after AFF.

Giant overreflection of magnetohydrodynamic waves from inhomogeneous plasmas with nonuniform shear flows

We theoretically study mode conversion and resonant overreflection of magnetohydrodynamic waves in an inhomogeneous plane-stratified plasma in the presence of a nonuniform shear flow using precise numerical calculations of the reflection and transmission coefficients and the field distributions based on the invariant imbedding method. Cases where the flow velocity and the external magnetic field are directed perpendicularly to the inhomogeneity direction and both the flow velocity and the plasma density vary arbitrarily along it are considered. When there is a shear flow, the wave frequency is modulated locally by the Doppler shift, and resonant amplification and overreflection occur where the modulated frequency is negative and its absolute value matches the local Alfvén or slow frequency. For many different types of the density and flow velocity profiles, we find that, especially when the parameters are such that the incident waves are totally reflected, there arises a giant overreflection where the reflectance is much larger than 10 in a fairly broad range of the incident angles, the frequency, and the plasma β, and its maximum attains values larger than 105. In a finite β plasma, both incident fast and slow magnetosonic waves are found to cause strong overreflection and there appear multiple positions exhibiting both Alfvén and slow resonances inside the plasma. We explain the mechanism of overreflection in terms of the formation of inhomogeneous and open cavities close to the resonances and the strong enhancement of the wave energy due to the occurrence of semi-bound states there. We discuss the observational consequences in magnetized terrestrial and solar plasmas.

Effects of initial compression/tension, foundation damping and pasternak medium on the dynamics of shear and normal deformable GPLRC beams under moving load

An attempt is made in this research to investigation the free vibration and dynamic response of an arbitrary thick composite beam which is reinforced with graphene platelets (GPLs). Distribution of GPLs in the layers may be different which leads to a functionally graded media. To this end a shear and normal deformable beam is adopted. The developed beam model has four unknowns and takes the non-uniform shear strains and also thickness stretching into account. Also the effects of compressive or tensile force, a two parameter Pasternak elastic foundation and also foundation damping are taken into account for both free and forced vibration responses. The governing equations of the beam are established using the Hamilton principle. By applying the Navier solution method suitable for simply supported edges, results of the present studies are provided. It should be noted that for forced vibration problem, Newmark time marching method is applied. For dynamic response the case of moving load is assumed. Results of this study are first compared with the available data in the open literature especially with those developed by 3D elasticity to show the accuracy of the developed formulation. After that novel results are given to discuss the effects of different parameters. It is highlighted that weight fraction and distribution pattern of GPLs are two important factors on the dynamic response of the structure.

Axisymmetric Free Vibration Analysis of Functionally Graded Sandwich Annular Plates: A Quasi-3D Shear and Normal Deformable Model

This paper concentrates on axisymmetric free vibration of functionally graded (FG) sandwich annular plates obtained using a quasi-3D plate theory. Motion equations and corresponding boundary conditions are established via the mentioned plate theory which takes into consideration the non-uniform shear strains across the thickness and also stretching trough the thickness. Generalized differential quadrature method (GDQM) is applied to discrete the annular sandwich plate governing equations. The results of this study are applicable for optional thick plates since the adopted theory considers the shear and normal strains across the thickness direction. Outcoming results are verified on the basis of information accessible in the open literature. To investigate the influences of power law index of functionally graded materials (FGMs) and dimensions of the sandwich annular plate layers, parametric studies are presented. It was well demonstrated that the applied theory precisely predicts the natural frequencies of FG annular sandwich plates with arbitrary thickness.