Transverse Aspect Ratio Research Articles

Stress solution of transversely isotropic surrounding rock for shallow buried elliptic tunnels

This paper develops a method to obtain the stress solution of the transversely isotropic surrounding rock for shallow elliptical tunnels. Based on the stress solution of the transversely isotropic surrounding rock for deeply buried elliptical tunnels, the Schwarz alternating method is used to solve the stress of surrounding orthotropic rock with a shallow elliptical tunnel. A MATLAB program is developed to implement the derived theory, and the numerical simulation results are compared with those of existing solution and the finite element software ABAQUS, demonstrating the rationality and correctness of the present theory in this paper. Finally, the influences of factors such as rock and soil transverse isotropy, tunnel depth, and tunnel aspect ratio on the stress distribution around the tunnel are discussed.

On the effect of the transversal aspect ratio on the double‐glazed solar air heater performance

AbstractThe transversal aspect ratio of solar air heaters (SAHs) is a critical geometric parameter that influences the heat transfer from the absorber plate to the working fluid and, accordingly, the overall heat loss level. The present work addresses the effect of the aspect ratio on the performance of a solar air heating system and the behavior of heat transfer coefficients (HTCs) within it and along the flow channel. A mathematical model of energy‐balance equations was formulated to examine and analyze the double‐glazed solar air heater thermal behavior. The Eismann correlation, which is more accurate than Holland's correlation, was employed to determine the HTC between the two glass covers. The useful energy, Nusselt number (Nu), efficiency, overall loss, and HTCs as a function of the aspect ratio were evaluated across the collector length. On the basis of the findings, the higher the ratio, the better the efficiency of the SAH. Indeed, increasing the collector's cross‐sectional aspect ratio (r) up to 19 increases useful energy efficiency by more than 87%, Nu by 84%, thermohydraulic efficiency from 0.4 to 0.76, and overall heat loss by 1.15 W/(m2 K). Furthermore, reducing r from 19 to 2 will improve the collector power from 1.855 to 3.473 kW.

Dimensional and Physical Properties of Temperate Highland Rice Varieties

During the present investigation, eight commonly grown rice varieties of temperate highland regions of Kashmir were selected to study different quality attributes. The dimensional and physical properties of selected rice varieties differed significantly (p≤0.05). With regard to colour coordinates (L*, a*, b*, chroma and hue angle), all the varieties showed significant (p≤0.05) variation except b* value. Very high significant (P≤0.01) correlations were noticed amongst the different dimensional and physical attributes. Based on the nature and magnitude of character association recorded in the present study, the inference drawn was that dimensional properties like length, width, L/W ratio, thickness, equivalent diameter (De), geometric diameter (Dg), arithmetic diameter (Da), area of transverse surface (At), surface area (S) and aspect ratio (Ra); physical properties like 1000 grain weight, bulk density (BD), true density (TD), hardness and chalkiness should be used to formulate the selection indices for development of quality rice for temperate highland regions.

Improved SDOF and numerical approach to study the dynamic response of reinforced concrete columns subjected to close-in blast loading

In this study, the blast performance of steel reinforced concrete (RC) columns was experimentally and analytically investigated. The experiments consisted of 11 one-half-scale columns subjected to different levels of blast loading using TNT explosives. The experimental results show that when the scaled distance is relatively large, less damage occurs to steel RC columns with higher axial loads than to columns with smaller axial loads at the same blast level. As the scaled distance decreases, the axial load increases the level of damage to RC columns. In addition, the equivalent single-degree-of-freedom (SDOF) approach for determining the dynamic response of RC columns against combined axial and blast-induced transverse loads was improved. Nonlinear section and member analyses were incorporated into the suggested SDOF method by considering the effect of axial load and complex features of the material behavior, the high strain-rate effect and the column geometry. The SDOF model was validated by comparing the maximum displacements obtained from the SDOF analysis with experimental data from blast testing of RC columns. Parametric studies were also performed to investigate the effects of axial load, the longitudinal reinforcement ratio, transverse reinforcement ratio, aspect ratio and boundary conditions. In order to consider the local damage effect, the numerical study was undertaken to investigate the effects of transverse reinforcement spacing on the blast resistance of RC columns using LS-DYNA.

Bending and buckling of three-dimensional graphene foam plates

Abstract Bending and buckling behaviors of three-dimensional graphene foam (3D-GrF) plates are investigated in the framework of the two-variable refined plate theory (TRPT). The material properties of three-dimensional graphene foams vary continuously along thickness direction of the plate. The TRPT considers the effect of transverse shear strains that vary quadratically along the thickness of the plate. In addition, this theory does not need to consider the shear correction factor. By using Hamilton’s principle, the governing equations are obtained. Analytical solutions for the bending problem of 3D-GrF plates are derived via Navier’s method. Additionally, buckling problem of 3D-GrF plates with various boundary conditions are analyzed by employing the Galerkin method. Results obtained in this study are verified by comparing with the published ones. Finally, the influences of pore distribution, porosity coefficient, transverse distributed load, aspect ratio, length-to-thickness ratio, mode number and axial compression ratio on bending and buckling behaviors of 3D-GrF plates are discussed.

Piezoelectric property improvement of polyethylene ferroelectrets using postprocessing thermal‐pressure treatment

In this work, biaxially stretched polymer foams with well‐defined cellular structures were prepared from polyethylene via blown‐film extrusion and subjected to corona charging to produce a piezoelectric response. The charging parameters were first optimized in terms of charging voltage and needle distance, as well as the gas type and pressure to investigate their effect on the piezoelectric coefficient (d33). The results show that samples charged under nitrogen (N2) at 100 kPa had better d33 coefficient than those charged under ambient air or N2 at 20 kPa. Moreover, 2 different thermal pressure treatments were imposed to obtain an optimized eye‐like cellular structure with different cell aspect ratios (AR). The results showed that when the cells were elongated in both the longitudinal and transverse directions (higher AR), higher d33 coefficients were achieved. From all the samples produced, the best results were obtained for a longitudinal aspect ratio (AR‐L) of 7.1, a transversal aspect ratio (AR‐T) of 4.6, and a relative foam density of 0.52 leading to a d33 coefficient of 935 pC/N. This coefficient was further increased using reverse charging and multilayered films, reaching a maximum of 2550 pC/N. This value is much higher than typical ones reported so far for any polyethylene and polypropylene ferroelectrets. These results could increase the use of polyethylene in piezoelectric applications as these materials are very attractive for the large‐scale production of electret‐based sensors and transducers due to their low cost and easy processing.

Rivulet flow of generalized Newtonian fluids

Steady unidirectional gravity-driven flow of a uniform thin rivulet (i.e. a rivulet with small transverse aspect ratio) of a generalised Newtonian fluid down a vertical planar substrate is considered. The parametric solution for any generalised Newtonian fluid whose viscosity can be expressed as a function of the shear rate, and the explicit solution for any generalised Newtonian fluid whose viscosity can be expressed as a function of the extra stress are obtained. These general solutions are used to describe rivulet flow of Carreau and Ellis fluids, highlighting the similarities and differences between the behaviour of these two fluids. In addition, the general behaviour of rivulets of nearly Newtonian fluids and of rivulets with small or large prescribed flux, as well as the behaviour of rivulets of strongly shear-thinning Carreau and Ellis fluids, are also described. It is found that whereas the monotonic dependence of the viscosity of a Carreau fluid on its three non-dimensional parameters and of an Ellis fluid on two of its three non-dimensional parameters leads to the expected dependence of the behaviour of the rivulet on these parameters (namely that increasing the viscosity of the fluid leads to a larger rivulet), the non-monotonic dependence of the viscosity of an Ellis fluid on the non dimensional parameter that measures the degree of shear thinning leads to a more complicated dependence of the behaviour of the rivulet on this parameter. In particular, it is also found that when the maximum extra stress in the rivulet is sufficiently large a rivulet of an Ellis fluid in the strongly shear-thinning limit in which this parameter becomes large comprises two regions with different viscosities. In the general case of non-zero viscosity in the limit of large extra stress the two regions have different constant viscosities, whereas in the special case of zero viscosity in the limit of large extra stress one region has constant viscosity and the other has a non-constant power-law viscosity, leading to a plug-like velocity profile with large magnitude in the narrow central region of the rivulet.

Dynamic instability of spinning launch vehicles modeled as thin-walled composite beams

This paper presents the results of the dynamic stability analysis of a flexible spinning launch vehicle subjected to thrust modeled as a thin-walled composite beam with circular cross section. Due to the presence of gyroscopic forces, we mainly aimed to find divergence and/or flutter instabilities and establish the stability boundaries of the spinning beam. For this purpose, we implemented a circumferentially uniform stiffness (CUS) layup configuration to exhibit the coupled motion of bending–bending–shear. The solution of the eigenvalue problem is handled by the extended Galerkin method (EGM), and we computed the results addressing the effects of various parameters such as spin speed, axial load, ply angle, aspect ratio and transverse shear on the dynamic stability of the beam. Insights revealed by this study contribute to the design of advanced aerospace structures modeled as thin-walled composite beams reflecting the potential influence of transverse shear and aspect ratio on dynamic stability characteristics. A notable contribution is that we show that divergence/flutter instabilities can be delayed or even avoided using the directionality property of composite materials.

Lattice Boltzmann simulations of three-dimensional incompressible flows in a four-sided lid driven cavity

Numerical study on three-dimensional (3D), incompressible, four-sided lid (FSL) driven cavity flows has been conducted to show the effects of the transverse aspect ratio, K, on the flow field by using a multiple relaxation time lattice Boltzmann equation. The top wall is driven from left to right, the left wall is moved downward, whereas the right wall is driven upward, and the bottom wall is moved from right to left, all the four moving walls have the same speed and the others boundaries are fixed. Numerical computations are performed for several Reynolds numbers for laminar flows, up to 1000, with various transverse aspect ratios. The flow can reach a steady state and the flow pattern is symmetric with respect to the two cavity diagonals (i.e., the center of the cavity). At Reynolds number = 300, the flow structures of the 3D FSL cavity flow at steady state with various transverse aspect ratio, i.e., 3, 2, 1, 0.75, 0.5 and 0.25 only show the unstable symmetrical flow pattern. The stable asymmetrical flow pattern could be reproduced only by increasing the Reynolds number that is above a critical value which is dependent on the aspect ratio. It is found that an aspect ratio of more than 5 is needed to reproduce flow patterns, both symmetric and asymmetric flows, simulated by using 2D numerical models.

Effect of Transverse Aspect Ratio and Distinct Ventilation Techniques on Convective Heat Transfer from a Rectangular Enclosure: Experimental and Numerical Study

Our objective in this study was to investigate the convective heat transfer in a cavity with ventilation ports. The study has been divided into experimental and numerical sections and under the experimental study the enclosure considered with two exit ports at roof and one inlet opening with varying aspect ratio. Under the numerical study, the model validation is done at AR = 5, and then the study continued for one exit port each on the left side and right side. The enclosure is equipped with three discrete heat sources at the bottom wall and with an exhaust fan at the exit port. The ranges of parameters considered under experimental study as 1.25 ≤ AR ≤ 2.5, 3224 ≤ Re ≤ 6579, 8.5 × 106 ≤ Gr ≤ 1.03 × 108, and as a consequence Richardson number obtained in the range 0.21–9.58. Experimental results set out that the heat source surface Nusselt number decreases with an increase in aspect ratio however; at higher aspect ratio, the values of Nusselt number remain almost unchanged. The enclosure bulk fluid Nusselt number increases with an increase in aspect ratio. The study revealed that for a given aspect ratio with an increase in Re, the heat source Nu increases. The numerical study divulged that the ventilation port arrangement at the right side of enclosure exhibits the better thermal performance among all the three orientations considered and the results are supported with the streamline and temperature contours. The study of varying inlet port height disclosed that as the inlet port height is increased, the heater surface temperature drops and the enhanced heat transfer is achieved.

Influence of Carbon Content on Toughening in Ultrafine Elongated Grain Structure Steels

(0.2–0.6)%C-2%Si-1%Cr-1%Mo steels were quenched and tempered at 773 K and deformed by multi-pass caliber rolling (i.e. warm tempforming) with a rolling reduction of 78%, in order to obtain ultrafine elongated grain (UFEG) structures. The tensile and Charpy impact properties of the warm tempformed (TF) steels were investigated to determine the influence of the carbon content on toughening in the UFEG structures. The TF samples consisted of UFEG structures with strong <110>//rolling direction (RD) fiber textures. The transverse grain size and aspect ratio in the UFEG structure tended to reduce as the carbon content increased, whilst the carbide particle size became slightly larger. The increase in the carbon content resulted in an increase in the yield strength from 1.68 to 1.95 GPa at room temperature; however, it was accompanied by a loss of tensile ductility. In contrast to quenched and tempered samples exhibiting ductile-to-brittle transitions, the TF samples exhibited inverse temperature dependences of the impact toughness. This was due to delaminations, where cracks were observed to branch in the longitudinal direction (//RD) of the impact test bars. The upper-shelf energy of the TF sample was enhanced as the carbon content decreased, and higher absorbed energy was also achieved as delamination occurred at lower temperatures. The delamination was found to be controlled not only by the transverse grain size, the grain shape, and the <110>//RD fiber texture but also by carbide particle distribution in the UFEG structure.

Experimental study of the effect of noncondensables on buoyancy-thermocapillary convection in a volatile low-viscosity silicone oil

The convective flow in a layer of volatile silicone oil with a kinematic viscosity of 0.65 cSt confined to a sealed cavity with a transverse aspect ratio of 3.2 was visualized using particle pathlines and quantified by particle-image velocimetry at dynamic Bond numbers estimated to be of order unity and laboratory Marangoni numbers as great as 3600. The effect of noncondensables (i.e., air) was studied by comparing convection in the liquid layer below a vapor space at pressures ranging from 4.8 kPa to 101 kPa, corresponding to air molar fractions ranging from 14% to 96%, respectively, and silicone-oil vapor, under otherwise identical conditions. The results for convection at 101 kPa are in qualitative agreement with previous studies, and clarify the time-dependent flow observed at high Marangoni numbers. The results show that decreasing the relative air concentration increases the critical Marangoni numbers for transition between different flow states, even though the air concentration does not appear to affect the speeds near the interface. Linear stability analysis shows that transitions are suppressed due to the latent heat generated or absorbed at the interface due to the enhancement of phase change. Furthermore, the experimental results suggest that air, even at relative concentrations as small as 14%, or partial pressures of O(102 Pa), has a significant effect on the vapor flow, and that the fluid in the vapor space should be modeled as a binary mixture in many cases of practical interest.

Size effects on the magnetoelectric response on PVDF/Vitrovac 4040 laminate composites

Tri-layered and bi-layered magnetoelectric (ME) flexible composite structures of varying geometries and sizes consisting on magnetostrictive Vitrovac and piezoelectric poly(vinylidene fluoride) (PVDF) layers were fabricated by direct bonding. From the ME measurements it was determined that tri-layered composites structures (magnetostrictive–piezoelectric–magnetostrictive type), show a higher ME response (75 V cm−1 Oe−1) than the bi-layer structure (66 V cm−1 Oe−1). The ME voltage coefficient decreased with increasing longitudinal size aspect ratio between PVDF and Vitrovac layers (from 1.1 to 4.3), being observed a maximum ME voltage coefficient of 66 V cm−1 Oe−1. It was also observed that the composite with the lowest transversal aspect ratio between PVDF and Vitrovac layers resulted in better ME performance than the structures with higher transversal size aspect ratios. It was further determined an intimate relation between the AreaPVDF/AreaVitrovac ratio and the ME response of the composites. When such ratio values approach 1, the ME response is the largest. In addition the ME output value and magnetic field response were controlled by changing the number of Vitrovac layers, which allows the development of magnetic sensors and energy harvesting devices.

Creation of Short Microwave Ablation Zones: In Vivo Characterization of Single and Paired Modified Triaxial Antennas

PurposeTo characterize modified triaxial microwave antennas configured to produce short ablation zones. Materials and MethodsFifty single-antenna and 27 paired-antenna hepatic ablations were performed in domestic swine (N = 11) with 17-gauge gas-cooled modified triaxial antennas powered at 65 W from a 2.45-GHz generator. Single-antenna ablations were performed at 2 (n = 16), 5 (n = 21), and 10 (n = 13) minutes. Paired-antenna ablations were performed at 1-cm and 2-cm spacing for 5 (n = 7 and n = 8, respectively) and 10 minutes (n = 7 and n = 5, respectively). Mean transverse width, length, and aspect ratio of sectioned ablation zones were measured and compared. ResultsFor single antennas, mean ablation zone lengths were 2.9 cm ± 0.45, 3.5 cm ± 0.55, and 4.2 cm ± 0.40 at 2, 5, and 10 minutes, respectively. Mean widths were 1.8 cm ± 0.3, 2.0 cm ± 0.32, and 2.5 cm ± 0.25 at 2, 5, and 10 minutes, respectively. For paired antennas, mean length at 5 minutes with 1-cm and 2-cm spacing and 10 minutes with 1-cm and 2-cm spacing was 4.2 cm ± 0.9, 4.9 cm ± 1.0, 4.8 cm ± 0.5, and 4.8 cm ± 1.3, respectively. Mean width was 3.1 cm ± 1.0, 4.4 cm ± 0.7, 3.8 cm ± 0.4, and 4.5 cm ± 0.7, respectively. Paired-antenna ablations were more spherical (aspect ratios, 0.72–0.79 for 5–10 min) than single-antenna ablations (aspect ratios, 0.57–0.59). For paired-antenna ablations, 1-cm spacing appeared optimal, with improved circularity and decreased clefting compared with 2-cm spacing (circularity, 0.85 at 1 cm, 0.78 at 2 cm). ConclusionsModified triaxial antennas can generate relatively short, spherical ablation zones. Paired-antenna ablations were rounder and larger in transverse dimension than single antenna ablations, with 1-cm spacing optimal for confluence of the ablation zone.

超微細繊維状結晶粒組織鋼の強靭化に及ぼす炭素量の影響

(0.2-0.6)%C-2%Si-1%Cr-1%Mo steels were quenched and tempered at 773 K and then deformed by multi-pass caliber rolling (i.e.,warm tempforming) with a rolling reduction of 78% to obtain ultrafine elongated grain (UFEG) structures. Tensile and Charpy impact properties of the warm tempformed (TF) steels were investigated to make it clear the influence of the carbon content on toughening in the UFEG structures. The TF samples consisted of UFEG structures with a strong <110>//RD fiber deformation texture. Transverse grain size and aspect ratio in the UFEG structure tended to reduce with increasing the carbon content while carbide particle size slightly became larger. The increase in carbon content resulted in an increase in yield strength from 1.68 to 1.95 GPa at room temperature, while it was accompanied by a loss of tensile ductility. In contrast to quenched and tempered samples exhibiting ductile-to-brittle transitions, the TF samples exhibited inverse temperature dependences of the impact toughness due to the delaminations, where the cracks branched in the longitudinal direction (//RD) of the impact test bars. The upper-self energy of the TF sample was enhanced as the carbon content decreased, and the higher absorbed energy was also obtained through occurrence of the delamination at lower temperature. The delamination was found to be controlled not only by the transverse grain size, the grain shape, the <110>//RD fiber deformation texture but also by the carbide particle distribution in the UFEG structure.

Effective dipole-dipole interactions in multilayered dipolar Bose-Einstein condensates

We propose a two-dimensional model for a multilayer stack of dipolar Bose-Einstein condensates formed by a strong optical lattice. We derive effective intra- and interlayer dipole-dipole interaction potentials and provide simple analytical approximations for a given number of lattice sites at arbitrary polarization. We find that the interlayer dipole-dipole interaction changes the transverse aspect ratio of the ground state in the central layers depending on its polarization and the number of lattice sites. The changing aspect ratio should be observable in time of flight images. Furthermore, we show that the interlayer dipole-dipole interaction reduces the excitation energy of local perturbations, affecting the development of a roton minimum.

Stress and strain-inertia gradient elasticity in free vibration analysis of single walled carbon nanotubes with first order shear deformation shell theory

A gradient-enriched shell formulation is introduced in the present study based on the first order shear deformation shell model and the stress gradient and strain-inertia gradient elasticity theories are used for dynamic analysis of single walled carbon nanotubes. It provides extensions of the first order shear deformation shell formulation with additional higher-order spatial derivatives of strains and stresses. The higher-order terms are introduced in the formulation by using the Laplacian of the corresponding lower-order terms. The proposed shell formulation includes two length scale size parameters related to the strain gradients and inertia gradients. The effects of the transverse shear, aspect ratio, circumferential and half-axial wave numbers and length scale parameters on different vibration modes of the single-walled carbon nanotubes are elucidated. The results are also compared with those obtained from a classical shell theory with Sanders–Koiter strain-displacement relationships.

A three–dimensional study of the onset of convection in a horizontal, rectangular porous channel heated from below

The onset of convection is studied in a rectangular channel filled with a fluid saturated porous medium, bounded above and below by impermeable isothermal walls at unequal temperatures and laterally by partially conducting walls. A three–dimensional linear stability analysis is carried out under the assumption of an infinite longitudinal channel length. Then, this assumption is relaxed in order to determine the threshold length for the three–dimensional convection to be the preferred mode at onset. Sensible parameters influencing the conditions for the instability are the aspect ratio of the transverse cross–section and the Biot number associated with the sidewall heat transfer to the external environment. The neutral stability is investigated by expressing the Darcy–Rayleigh number as a function of the longitudinal wave number, for assigned values of the transverse aspect ratio and of the Biot number.

Sidewall and thermal boundary condition effects on the evolution of longitudinal rolls in Rayleigh-Bénard-Poiseuille convection

Experimental and numerical studies of steady longitudinal convection rolls that develop in a Poiseuille air flow in a rectangular channel heated from below and cooled from the top are conducted in the range 3500 ≤ Ra ≤ 6000 and 20 ≤ Re ≤ 200. The effect of the lateral vertical walls on the onset and development of the convection cells is investigated by changing the transverse aspect ratio of the channel from 4.7 to 18.4. The influence of the entrance temperature and adiabatic or conductive thermal boundary conditions at the side and top walls of the channel is also investigated. The scenario of the roll formation is described in details. It results in a symmetric pattern in the form of steady longitudinal rolls with an even number of rolls that depends not only on the aspect ratio but possibly on the inlet temperature of the flow. It is shown that the fully developed pattern is determined by the two rolls nearby each vertical side wall that are triggered just at the entrance of the channel due to the presence of velocity boundary layers adjacent to the walls. It is also shown that the heat conduction in the top horizontal wall of the experimental channel must be taken into account in the numerical simulations so that the experimental wavenumber can be properly depicted.

Aspect ratio effects on three-dimensional incompressible flow in a two-sided non-facing lid-driven parallelepiped cavity

A numerical study of the three-dimensional fluid flow has been carried out to determine the effects of the transverse aspect ratio, A y , on the flow structure in two-sided non-facing lid-driven cavities. The flow is complex, unstable and can undergo bifurcation. The numerical method is based on the finite volume method and multigrid acceleration. Computations have been investigated for several Reynolds numbers and various aspect ratio values. At a fixed Reynolds number, Re = 500 , the three-dimensional flow characteristics are analyzed considering four transverse aspect ratios, A y = 1 , 0.75 , 0.5 and 0.25. It is observed that the transition to the unsteady regime follows the classical scheme of a Hopf bifurcation. An analysis of the flow evolution shows that, at A y = 0.75 , the flow bifurcates to a periodic regime at ( Re = 600 ) with a frequency f = 0.093 less than the predicted value in the cubical cavity. A correlation is established when A y = 0.5 and gives the critical Reynolds number value. At A y = 0.25 , the periodic regime occurs at high Re value beyond 3500, after which the flow becomes chaotic. It is shown that, when increasing A y over the unit, the flow in the cavity exhibits a complex behavior. The kinetic energy transmission from the driven walls to the cavity center is reduced at low A y values.