Increasing Aspect Ratio Research Articles

Investigation of the aerodynamic characteristics of single-box girders with different aspect ratios

In this paper, the three dimensional LES method was used to generate a typical turbulent wind field. Three streamlined box girders with three different aspect ratios were adopted to investigate the effects of aspect ratios on the force coefficients and flow separation characteristics with different angles of attack. The results show that the aspect ratio has significant effects on the force coefficients of the streamlined box girder, and the larger the aspect ratio is, the larger the lift coefficient is. For the flow separation characteristics, as the aspect ratio increases, the spacing of wake vortex is shortened and the wake vortex dissipation rate is accelerated.

Decayless low-amplitude transverse oscillations in short coronal loops as manifestations of driven slow modes

ABSTRACT A recent theoretical study of slow magnetoacoustic oscillations in a curved magnetic slab shows that the principal slow mode causes both dominant longitudinal motions and radial (transverse) kink-like motions of a slab. This modification of wave properties occurs due to the violation of the symmetry of wave motions with respect to the waveguide axis and the slow to fast wave interaction in curved magnetic configurations. In this work, we carry out a comprehensive investigation of the principal slow mode depending on the model parameters. It is shown that the dominance of longitudinal motions in the principal slow mode decreases as both the internal plasma-β and slab aspect ratio increase. The results are used to explain the observed small amplitude decayless transverse oscillations in short coronal loops. In particular, these phenomena are interpreted as direct manifestation of slow mode oscillations in curved coronal loops excited at the footpoints by compressible oscillations of the underlying atmospheric layers. Numerical calculations have shown that the observed velocity range of V = 0.6–5 km s−1 corresponds to radial velocity amplitudes in the principal slow mode, provided that the plasma-β inside the short loops is in the range of βi= 0.3–0.5 and the loop aspect ratio 0.15 ≤ a/R ≤ 0.25. These parameters appear to be typical for low-lying small coronal loops extending from the transition region to the lower corona.

Piezoresistive Theory and Numerical Calculation for Carbon Nanotube Polymer Composite.

A three-dimensional theory has been established for the piezoresistivity of carbon nanotube (CNT) polymer composites. Based on the Mori-Tanaka method in meso-mechanics theory and considering quantum tunneling effect between CNTs, an approach to calculate equivalent electrical conductivity of composites was proposed. On this basis, a piezoresistive theory, which incorporates the effect of composites' geometric nonlinearity, was developed for CNT polymer composites. The theory is dependent only on some basic physical parameters of the materials. A finite element formula of the theory for the numerical calculation of piezoresistivity was presented from the analysis of both elastic and electric fields. Numerical simulations demonstrated that the results predicted by the theory were in good agreement with those of the experimental tests. Parameter sensitivity analysis revealed that when both the potential barrier height of the matrix and the initial average separation distance between CNTs increased, the piezoresistivity obviously increased. However, with the increase in aspect ratio and CNT conductivity, the piezoresistivity decreased gradually. A practical engineering application of this theory is also provided.

Influence of roll-bending deformation on microstructure and texture in an Al-Li alloy with different extrusion aspect ratio

The purpose of this investigation is to study the effect of roll bending deformation on the microstructure and texture in an Al-Li alloy with different extrusion aspect ratios. The results indicated that the substructure of most extruded fiber grains is not completely eliminated on the ND-ED section at position B with a low extrusion aspect ratio. However, the texture type of the ND-TD section changes from a single <114> texture to an adjacent <112> texture after roll-bending deformation, and the texture intensity decreases from 8.3 to 6.1. With the increase of the extrusion aspect ratio, the effect of roll-bending deformation on the microstructure began to be obvious, especially at position C. A large number of elongated recrystallized grains along the ED direction were transformed into approximately equiaxed grains on ND-ED section after the roll-bending deformation. There were also a small number of approximately equiaxed cell structures. The relative frequency of the low-angle grain boundary rose slightly from 42.1% to 46.7%. The single <313> texture moved to the adjacent <112> texture, and the texture strength increased from 4.8 to 6.3.

Bottom-Up Then Top-Down Synthesis of Gold Nanostructures Using Mesoporous Silica-Coated Gold Nanorods.

Gold nanostructures were synthesized by etching away gold from heat-treated mesoporous silica-coated gold nanorods (AuNR@mSiO2), providing an example of top-down modification of nanostructures made using bottom-up methodology. Twelve different types of nanostructures were made using this bottom-up-then-top-down synthesis (BUTTONS), of which the etching of the same starting nanomaterial of AuNR@mSiO2 was found to be controlled by how AuNR@mSiO2 were heat treated, the etchant concentration, and etching time. When the heat treatment occurred in smooth moving solutions in round-bottomed flasks, red-shifted longitudinal surface plasmon resonance (LSPR) was observed, on the order of 10-30 min, indicating increased aspect ratios of the gold nanostructures inside the mesoporous silica shells. When the heat treatment occurred in turbulent solutions in scintillation vials, a blue shift of the LSPR was obtained within a few minutes or less, resulting from reduced aspect ratios of the rods in the shells. The influence of the shape of the glassware, which may impact the flow patterns of the solution, on the heat treatment was investigated. One possible explanation is that the flow patterns affect the location of opened pores in the mesoporous shells, with the smooth flow of solution mainly removing CTAB surfactants from the pores along the cylindrical body of mSiO2, therefore increasing the aspect ratios after etching, and the turbulent solutions removing more surfactants from the pores of the two ends or tips of the silica shells, hence decreasing the aspect ratios after etching. These new stable gold nanostructures in silica shells, bare and without surfactant protection, may possess unique chemical properties and capabilities. Catalysis using heat-treated nanomaterials was studied as an example of potential applications of these nanostructures.

Stable orientations of small-scale floating cylinders

A coin always floats in stable equilibrium with its longitudinal axis normal to the air–liquid interface. In contrast, a long thin cylindrical pin floats with its longitudinal axis parallel to the air–liquid interface. In this context, we present a theoretical investigation of the stability of small-scale hydrophobic cylinders floating in vertical and horizontal orientations at various aspect ratios (length/diameter). The study is limited to cylinders denser than water floating at the air–water interface. Our analysis shows that, unlike large-scale vertically floating cylinders, the stability of vertically orientated small-scale cylinders increases with an increase in aspect ratio. A similar trend is observed in the stability of small-scale horizontal cylinders. We also explain the underlying mechanics that leads to a rise in the stability of floating cylinders with an increase in aspect ratio. Unlike large-scale floating cylinders with uniform density, we show that the effect of governing forces (weight, buoyancy and surface tension) in small-scale cylinders changes from a stabilising to a destabilising force with a change in the aspect ratio. For example, in the case of a vertically floating cylinder, the buoyancy force acts as a stabilising force at a small aspect ratio whereas, at large aspect ratios, the buoyancy force has a destabilising influence. Likewise, the body's weight has a destabilising influence at a small aspect ratio and stabilising effect at a large aspect ratio. The reason behind this transformation is that, above a particular aspect ratio, the centre of gravity of small-scale floating cylinders lies below the centre of buoyancy.

Assessing Seismic Behavior in RC Buildings with Varied Vertical Aspect Ratios: A Comparative Study

Limited space in cities due to urbanization and population growth has given rise to tall and distinctively designed buildings. This study focuses on how a building's vertical aspect ratio (height-to-width ratio) affects the seismic performance of residential concrete buildings. In earthquake-prone Nepal, seismic analysis is crucial for buildings in high-risk areas. We investigated the impact of vertical aspect ratio and the presence of masonry infills and soft stories in reinforced concrete frame buildings. Rectangular base models were analysed at 3, 5, and 7 stories. These models were categorized into bare frames, infill frames, and infill frames with soft stories at the ground level. Linear analysis, non-linear analysis, and design of the building have been performed as per the relevant Indian codes of practice. The effect of infills on dynamic characteristics, yield patterns and capacity has been studied with the help of Non-Linear Analysis. The result of the analysis indicates that the structures have lesser capacity and higher drift with the increase in vertical aspect ratio. It also has been observed that infills contribute to a large increase in the stiffness and strength of the structure, so the deformation capacity of the structure gets reduced.

Heating and evaporation of a mono-component spheroidal droplet with non-uniform surface temperature

A new mathematical model for spheroidal droplet heating and evaporation is proposed. This model takes into account the effect of liquid finite thermal conductivity and is based on the previously obtained analytical solution for the vapour mass fraction at the droplet surface and a new correlation for the convective heat transfer coefficient incorporated into the numerical code. The heat transfer equation in the liquid phase is solved numerically using the finite-element heat transfer module of COMSOL Multiphysics. It is shown that the lifetime of spheroidal (prolate and oblate) droplets is shorter than that of spherical droplets of the same volume. The difference in the lifetimes of spheroidal and spherical droplets, predicted by the new model, is shown to increase with increasing aspect ratios for prolate droplets and decreasing aspect ratios for oblate droplets. As in the case of stationary spherical droplets, the d2-law is shown to be valid for spheroidal droplets after the completion of the heat-up period. The predictions of this model agree with experimental observations. The duration of the heat-up period is shown to decrease with increasing aspect ratios for prolate droplets and decreasing aspect ratios for oblate droplets. The maximal surface temperatures are predicted near the regions where the surface curvature is maximal. The aspect ratios are shown to be weak functions of time, in agreement with experimental observations.

Experimental Investigation of Electrochemical Capacitive Responses versus Pore Geometries through Artificial Nanotubes.

Electrochemical supercapacitors have attracted significant attention due to their large capacity, high-power output, and long cycle life. However, despite extensive studies and advancements in developing highly porous electrode materials, little quantitative research on the impact of pore geometry on electrochemical responses has been conducted. This paper presents the first quantitative investigation of the relationship between electrochemical capacitive responses and pore geometries at the nanoscale. To achieve this, we constructed a uniform cylindrical pore array with controllable pore diameter and depth by using anodized aluminum oxide (AAO) to serve as a template and atomic layer deposition (ALD) technology for TiN conductive layer decoration. Our findings reveal that, at the nanoscale, increasing the specific surface area through pore diameter and depth does not proportionally increase the capacitive response, even at low scan rates. Meanwhile, we observe a critical pore parameter (170/5000 nm, diameter/depth), where the specific capacitance density and characteristic frequency dramatically decrease with a further increase in the pore aspect ratio. These results indicate that blindly pursuing the absolute specific surface area of the electrode material is not advisable. Instead, optimal pore geometry should be designed based on the desired operational conditions, and this work may serve as valuable guidance.

Numerical investigation on atomization characteristics of sustainable aviation biofuel

It is critical to investigate the atomization features of sustainable aviation biofuel (SAF) to reduce carbon emissions. Fluent software was used to quantitatively simulate the atomization of the fuel. The control variable method was utilized to compare SAF to Chinese aviation fuel RP-3. The volume of fluid model (VOF) and the discrete phase model (DPM) were used to explore the variation law of SAF atomization characteristics in a two-way centrifugal nozzle with a pressure drop of 2–8 MPa and various nozzle configurations. The experimental results suggest that the model is effective. The results demonstrate that when pressure increases, the average diameter of SAF’s Sauter mean diameter reduces from 80 to 23 µm and the spray penetration distance increases from 0.32 to 0.6 m, allowing for more stable fuel combustion. Meanwhile, as the nozzle outlet aspect ratio increases, such as increasing the nozzle diameter from 2.0 to 2.6 mm, the atomization cone angle varies from 60° to 110° and gradually declines, although the average diameter of Sauter only varies minimally within a limited range of 30–40 µm. All of these findings indicate that SAF has good atomization properties and the potential to be used as an aviation fuel.

Initiation and evolution of butterflies in roller bearings due to rolling contact fatigue

This investigation entails analysis of 520 butterfly formations (BFs) and non-metallic inclusions without BFs in two RCF-tested roller bearings to elucidate the influence of inclusion characteristics and stress level they are subject to, on the initiation and growth of BFs. The results show duplex inclusions, though least frequent in the bearing steels, exhibit the highest butterfly formation rate comparing with pure sulphide/oxide inclusions. It is also found that larger inclusions and those with smaller aspect ratios are more prone to butterfly formation; BF wing length decreases with the increase of inclusion aspect ratio; BF orientation is significantly influenced by inclusion size and stress level; stress magnitude appears to either impede or facilitate BF wing growth depending on BF orientation.

Experimental study on the morphology of turbulent diffusion flames with different aspect ratios under slope conditions

In this paper, the morphology of turbulent diffusion flames with varying aspect ratios under slope conditions was investigated. A simulated fire source using propane gas with an area of 80 cm2 was utilized. The influences of slope angle and aspect ratio of the fire source on the flame tilt angle (between the plume centerline and the slope), flame length, and flame height were systematically studied. The aspect ratio of the fire source (L/W) was changed from 1 to 8, and the slope angle was changed from 0° to 40°. Results indicate that the presence of a slope causes asymmetrical air entrainment on both sides of the fire plume, causing a pressure difference that leads to a decrease in the flame tilt angle as the slope angle increases. Additionally, the flame length increases monotonically with the slope angle due to the enhanced component of thermal buoyancy along the slope. Under the same slope condition, the flame tilt angle and flame height (perpendicular to the slope) decrease as the aspect ratio increases. This phenomenon is attributed to the increased entrainment restriction effect of the slope on the fire plume. New models for calculating flame tilt angle, flame length, and flame height, which consider the slope angle and aspect ratio of the fire source were established by using the equivalent perimeter of plume entrainment. To further verify the reliability of the newly established models, reference data with wide heat release rate (6.15 kW–231 kW), different slope inclination angle (0°–80°), pool size (equivalent diameter: 9 cm–44.1 cm), and different fuels (propane, ethylene) were used to against with the predicted values of our correlations. It is found that the maximum error of all correlations is within 15–20%, their universality and accuracy are further verified.

Extensive analysis of PCM-based heat sink with different fin arrangements under varying load conditions and variable aspect ratio

The present study compares a modified variable height fin heat sink with the conventional constant height fin heat sink. The two heat sinks are filled with an equal volume of PCM (n-eicosane) and a fin volume fraction of 8 %. The experiments are performed for constant loads and also different power surge conditions. The pulsed heat loads are applied for two scenarios: 1. Constant load 4 W - power surge and constant load 4 W - power surge - 1800 s no-load condition, and 2. Power surge (50 s, 100 s, and 150 s) - no-load conditions of 1800 s. During experiments, the proposed variable height fin heat sinks possess better thermal performance for all load scenarios. Further, a 3D computational model is developed using ANSYS Fluent 19 to assess not only the effect of fin arrangement for different aspect ratios but also the impact of fin shape. The enclosure aspect ratio employed for the given study ranges from 0.3 to 0.8 for both the heat sinks. Regarding the fin structure in a heat sink, four types of fin shapes are adopted: square, circular, diamond, and triangular. The contour images of temperature and the liquid fraction are shown for the charging process. For the discharging process, the time required for the heat sinks to completely solidify the PCM is discussed. From the outcomes, variable height fin heat sinks provide enhanced melting/solidification for all the aspect ratios and fin shapes considered. As the aspect ratio increases, the time difference between the heat sink for the completion of the discharging cycle is reduced. Moreover, the triangular shaped fin shows a higher enhancement percentage of 2.29 % and 1.43 % during melting and 6.25 % and 12.5 % during solidification for both the heat sinks, respectively.

Capture and transport of rod-shaped cargo via programmable active particles

We study the influence of the cargo shape on the capture and transport process of colloidal rods via swarms of active particles using Brownian dynamics simulations. Starting at random initial conditions, active particles that interact via the Lennard-Jones potential and possess a tuneable speed are utilised to capture passive rods inside a hexagonal cage of individually addressable units. By adjusting the velocity of the individual active particles, the rod can then be transported. To guarantee a successful capture process (with a strong localisation), we find that specific geometric and energetic constraints have to be met; i.e., the length of the rod must approximately be in the vicinity of an odd multiple of the lattice constant of the hexagonal cage, and the Lennard-Jones interaction strength must be in the range of 3.0 , k_B T to 6.0 , k_B T. If the cargo aspect ratio gets too large, the subsequent transport of successfully captured rods can fail. For systems where transport is possible, an increase in the cargo aspect ratio decreases the achievable transport velocity. Our work shows that the particle shape must be considered while designing interaction rules to accomplish specific tasks via groups of controllable units.

Energy evolution characteristics of engineered cementitious composites (ECC) under tensile and compressive loading

To more truly reflect the failure law of engineered cementitious composites (ECC), this research investigates the multiple cracking and failure process of ECC from the perspective of energy and reveals the energy evolution characteristics of this process. The mechanical properties and energy evolution characteristics of ECC under different water-binder ratios were studied by uniaxial compression test. The effects of water-binder ratios, fiber volume fractions, and fiber aspect ratio on the tensile properties, energy evolution characteristics, and fracture energy of ECC were systematically investigated. It was found that the increase in the water-binder ratios decreases the compressive strength and elastic strain energy release rate, but increases the dissipated energy. The increase of fiber volume fraction and fiber aspect ratio can effectively improve the tensile properties, elastic strain energy, dissipated energy, and fracture energy. The abrupt change in the elastic energy consumption ratio can be used as a criterion for ECC failure.

The strength of a constrained lithium layer

A constrained compression test is developed to replicate the mechanical state of a lithium filament within a solid state battery. Lithium microspheres are compressed between parallel quartz plates into a pancake shape of thickness on the order of 15 µm. Full adhesion with no slip exists between the lithium and platens, and the attendant mechanical constraint implies that the average pressure on the pancake-shaped specimens increases with increasing aspect ratio of radius to height. In addition to mechanical constraint, a thickness-dependant size effect is observed whereby the apparent flow strength of the lithium increases from 0.7 MPa in the bulk to 2.0 MPa at a thickness of 15 µm. The lithium deforms in a power-law creeping manner at room temperature, and to simplify interpretation of the results, the relative velocity of the loading platens is adjusted to ensure that the true compressive strain rate is held fixed at 10−3 s−1. Additional measurements of lithium flow strength are obtained by subjecting the pancake-shaped specimens to simple shear. The size effect under shear loading is comparable to that in constrained compression. The observed size effect for lithium is consistent with that reported in the literature for lithium in indentation tests and in single pillar compression tests. Finally, the size effect of lithium in the power law creep regime is compared with that for rate-independent plasticity (for copper).

Experimental analysis and optimization of abrasive waterjet deep hole drilling process parameters for SS AISI 316L

Recent breakthroughs in component downsizing and miniaturization emphasise the requirement for deep-hole drilling with an increased aspect ratio, especially in the automobile sector for fuel injectors and the medical sector for manufacturing bone screws or surgical equipment. In this research, deep hole drilling on stainless steel AISI 316L has been conducted using an Abrasive Waterjet Machine (AWJM), and the influence of drilling variables on the material removal rate, roundness deviation of drilled holes have been evaluated to assess the machining and hole characteristics. In addition, machining parameters' statistical relevance has been investigated using a multi-parametric analysis of variance. Quadratic mathematical models for material removal rate and roundness deviation have been established by correlating drilling parameters. The Grey Wolf Optimization (GWO) algorithm has been applied in this research to identify the optimal combination of deep hole drilling parameters for maximizing material removal rate and minimizing the roundness deviation. The results have been compared with Derivative-free optimization, Whale optimization, and Harmony search algorithms. The comparison revealed that the GWO algorithm performed better than other algorithms. In addition, a validation test has been carried out to confirm the accuracy of the results produced by the GWO. The images obtained from the scanning electron microscope showed that the surfaces of the deep holes are smooth. Additionally, the ploughing action was shown to be the principal mechanism responsible for removing the material.

Charge-driven liquid-crystalline behavior of ligand-functionalized nanorods in apolar solvent.

Concentrated colloidal suspensions of nanorods often exhibit liquid-crystalline (LC) behavior. The transition to a nematic LC phase, with long-range orientational order of the particles, is usually well-captured by Onsager's theory for hard rods, at least qualitatively. The theory shows how the volume fraction at the transition decreases with increasing aspect ratio of the rods. It also explains that the long-range electrostatic repulsive interaction occurring between rods stabilized by their surface charge can significantly increase their effective diameter, resulting in a decrease in the volume fraction at the transition, as compared to sterically stabilized rods. Here, we report on a system of ligand-stabilized LaPO4 nanorods, of aspect ratio ≈11, dispersed in apolar medium exhibiting the counter-intuitive observation that the onset of nematic self-assembly occurs at an extremely low volume fraction of ≈0.25%, which is lower than observed (≈3%) with the same particles when charged-stabilized in polar solvent. Furthermore, the nanorod volume fraction at the transition increases with increasing concentration of ligands, in a similar way as in polar media where increasing the ionic strength leads to surface charge screening. This peculiar system was investigated by dynamic light scattering, Fourier-transform infrared spectroscopy, zetametry, electron microscopy, polarized light microscopy, photoluminescence measurements, and X-ray scattering. Based on these experimental data, we formulate several tentative scenarios that might explain this unexpected phase behavior. However, at this stage, its full understanding remains a pending theoretical challenge. Nevertheless, this study shows that dispersing anisotropic nanoparticles in an apolar solvent may sometimes lead to spontaneous ordering events that defy our intuitive ideas about colloidal systems.

Exploring the impacts of spatial morphology of underground shopping mall atriums on natural lighting performance

ABSTRACT The natural lighting environment in the atrium space of an underground shopping street directly determines the spatial quality of the building. It has a significant impact on the quality of the indoor light environment, people’s mental experience, and the energy consumption of the building. Based on field research, this study combined Radiance and Rhino 7 software to construct realistic scene simulation models of the different shapes for each atrium’s underground shopping street. Daylight factor (DF) and useful daylight illuminance (UDI) were utilized as the evaluation metrics for assessing the natural lighting efficacy of the atriums. Simulation data were further processed and quantitatively analyzed with line charts and quadratic curve fitting methods. The results demonstrate that the DF of an atrium space in underground shopping streets declines rapidly as the height/width ratio (H/W) increases, followed by a gradual weakening trend. Meanwhile, as the aspect ratio (L/W) increases, the peak value of the DF gradually increases. The UDI of the atrium space in an underground shopping street will usually rise first and then fall as the height/width ratio (H/W) increases. Meanwhile, as the aspect ratio (L/W) increases, the UDI peak value gradually decreases. The experiment confirms that DF and UDI atrium space can be effectively improved by adjusting different combinations of the height/width ratio (H/W), aspect ratio (L/W), and lighting glass inclination angle. By doing so, this research provides architects with a theoretical foundation for the spatial morphology design of an atrium.

Buckling analysis of sandwich plates reinforced with various loading of multi-walled carbon nanotubes

The current investigation aims to examine the buckling behavior of sandwich structures reinforced with faces containing varying weight percentages (wt.%) of multi-walled carbon nanotubes (MWCNT), through the combined employment of experimental and numerical analysis techniques. In particular, the numerical analysis is executed through the implementation of the generalized differential quadrature method (GDQM). The study first determines the mechanical properties of the pure and reinforced samples via experimental tests. The buckling equations of the sandwich plate are then derived using the Frostig approach and a high-order shear deformation theory (SDT) for the flexible core. The continuity conditions between the faces and the core are considered to obtain the structural equations of the system, and Lagrange coefficients are introduced to enhance the accuracy of the governing equations. Subsequently, the study investigates the impact of various parameters, such as core thickness, aspect ratio, different boundary conditions (BC), and the addition of MWCNT nanoparticles on the critical buckling load of the system, utilizing the mechanical properties obtained for the composite faces. The present investigation reveals that the incorporation of MWCNT into the composite matrix brings about notable enhancements in the mechanical characteristics of sandwich structures. Specifically, the elastic modulus and ultimate strength of the faces are found to increase following the addition of MWCNT. Additionally, the critical buckling load of the sandwich plates is observed to rise with an increase in aspect ratio and length-to-thickness ratio, while a decrease in axial load yields similar results. The clamped boundary condition has higher critical buckling loads than the simply supported boundary condition. The addition of MWCNT nanoparticles decreases the dimensionless critical buckling force as the b/a ratio increases. Finally, the reported results of the current investigation present noteworthy findings about the advancement and improvement of sandwich composite structures to meet various application requirements.