Effects Of Different Aspect Ratios Research Articles

A hybrid simulator with novel bicone-wire grid antenna.

The simulator is an indispensable device for the study of high-altitude electromagnetic pulse (HEMP) effects. In order to improve the quality of the electric field waveforms of the HEMP simulator, we carried out simulation and experimental studies for the biconical-wire grid antenna. A new bicone-wire grid antenna HEMP simulator was designed by using skeletonized cones instead of solid cones, which can substantially improve the mobility of the simulator. The effects of different aspect ratios and different cone structures of the simulator on the waveform and distribution characteristics of the electric field were analyzed. The accuracy of the simulation results was verified by testing the bicone-wire grid antenna simulator with the new structure. The results obtained are as follows: First, the simulator can provide a HEMP environment compliant with the International Electrotechnical Commission (IEC) standard in an area of 5 × 6 × 2m3. Second, the simulator possesses optimal waveform quality and working space among simulators with different aspect ratios. Finally, the influence of using skeletonized cones instead of solid cones on the simulator's electric field waveforms is negligible, and the mobility of the new simulator is significantly improved compared to the original simulator.

Numerical investigation on the influence of geometrical parameters on the temperature distribution in marine hydrogen storage tanks during filling

This paper established a two-dimensional axisymmetric model with a marine high-pressure hydrogen storage tank as the research object. Using numerical simulation, the effects of different aspect ratios, inlet diameters, and inlet pipe lengths on the temperature rise of the hydrogen storage tank during the filling process were studied. As the L/D ratio of the hydrogen storage tank increases, the momentum of the hydrogen gas reaching the bottom of the tank gradually decreases, making it easier to form localized high-temperature regions. For a hydrogen storage tank with an L/D of 6.0, the difference between the maximum and average temperature at the end of filling was 155.85 K. In contrast, the temperature difference of the tank with an L/D of 3.6 was only 32.81 K. In addition, the inlet pipe delivers the hydrogen deep into the tank and reduces the obstructing effect of the existing hydrogen in the tank on the newly filled hydrogen. For smaller L/D hydrogen storage tanks, the inlet pipe may backfire and create a high-temperature zone at the shoulder of the tank. In contrast, for larger L/D hydrogen storage tanks, a suitable length of inlet pipe can deliver the hydrogen deep into the tank. This will enhance the gas flow inside the tank, facilitating heat exchange and avoiding the formation of localized high-temperature areas at the bottom of the tank. However, excessively long inlet pipes can also lead to high-temperature areas on the shoulders. At a specific charge mass flow rate, the lower the inlet diameter, the higher the hydrogen flow rate. The larger flow rate helped promote uniform hydrogen mixing in the tank and made it challenging to form localized high-temperature regions.

Investigating the coupled effect of different aspect ratios and leeward protrusion lengths on vortex-induced vibration (VIV)-galloping energy harvesting: Modelling and experimental validation

Flow-induced vibration energy harvesting is one of the promising approaches for realizing self-powered wireless sensor networks. Incorporation of metasurfaces or surface protrusions on the bluff bodies is an emerging way of enhancing energy harvesting performance. This paper experimentally and numerically investigates the coupled effect of implementing different aspect ratios and leeward protrusion lengths on the performance of vortex-induced vibration (VIV)-galloping energy harvesters. A total of sixteen protruded bluff bodies with four different aspect ratios and four protrusion lengths are proposed for comparative studies. A comprehensive mathematical model is established based on the extended Hamilton’s principle and Tamura’s aerodynamic force model. Both the wind tunnel experiments and numerical simulations manifest a different development trend for the bluff bodies with aspect ratios greater or lower than the unity. For most of the bluff bodies, increasing the protrusion length can lead to an increase in both the VIV-galloping cut-in speed and output power at higher wind speeds. Wind tunnel computational fluid dynamics (CFD) simulations are also performed to investigate the underlying aerodynamic reasons for the observed phenomena. Based on the classic Den Hartog’s criterion and Hu’s findings, it can be found that there is a consistency among the wind tunnel CFD simulation results and the experimental and numerical findings. Furthermore, the wind speed ratio of quasi-steady galloping to Kármán-vortex resonance is selected as an index to evaluate the interaction extent of VIV and galloping oscillations. It is revealed that strongly conjoint VIV-galloping oscillations can be more easily observed when the ratio approaches unity, while no interaction can be detected when the ratio is higher than a value between 11.91 to 23.27 in this study. Further, impedance matching tests and forward wind sweep experiments show that the maximum output power measured among all the studied cases is 0.992 mW, which occurs at the test speed of 5.1 m/s and an optimal load resistance of 200 kΩ, for the bluff body with an aspect ratio of 3:2 and a leeward protrusion length of 10 mm. This outperforms the optimal case of our previous study by 31.04%. Moreover, using the optimization theory, this bluff body is proved to be the global optimal solution of this study, which can well balance the cut-in speed and output power for the applications in the natural gentle breeze.

Thermally conductive process and mechanism of TATB‐based polymer‐bonded explosives filled with graphene: Effects of interfacial thermal resistance and morphology/content of graphene

AbstractThe thermal conductivity of energy‐containing materials has a significant impact on their environmental suitability during manufacturing, transportation, and storage. In order to effectively regulate the thermal conductivity of polymer‐bonded explosives (PBXs), this study investigates the effects of different aspect ratios of graphene binder and interfacial thermal resistance on the thermal conductivity of TATB‐based PBXs using the finite element method. A model was constructed using Abaqus software to establish the constitutive relationship between graphene with varying aspect ratios and the thermal conductivity of PBXs. The results indicate that the effect of different graphene aspect ratios on the overall thermal conductivity of PBXs is small when the graphene content is lower than 3%. However, the thermal conductivity of PBXs increases nonlinearly with the increase in graphene aspect ratio when the graphene content is higher than 8%. Furthermore, the interfacial thermal resistance reduces the thermal conductivity of the PBX system by approximately 0.16 W/(m K), and its effect on the thermal conductivity of the system is relatively stable and does not change significantly with increasing graphene content and aspect ratio.Highlights Thermally conductive behavior of graphene‐filled PBX is revealed by simulation. The effects of content and aspect ratio of graphene are systematically investigated. The effect of interface thermal resistance is considered in the simulation.

Effect of different aspect ratios of rectangular hole on magnetic shielding property for cylindrical shield

In this paper, the influence of rectangular holes with different aspect ratios in a cylinder on shielding properties is investigated using the finite element method. The two indicators used to assess the shielding properties of the cylinder are its internal residual magnetic field and its outer-surface magnetic field map. The internal residual magnetic field (B) of a cylinder as a function of the aspect ratio of a rectangular hole and its area is simulated, and the conclusions are as follows: with increasing length of the hole, the value of B increases first and then decreases. A cylindrical shield with square holes (the hole aspect ratio is equal to 1) delivers the worst shielding performance. A cylinder with a smaller hole area has better shielding properties, resulting from a less flux leakage from the environmental magnetic field. The anisotropy of the shielding properties is evaluated, and the magnetic shielding in the radial direction is better than that in the axial direction. This research provides a theoretical guide for the application and optimization of magnetic shields.

Crosslinked poly (vinyl alcohol) composite reinforced with tunicate, wood, and hybrid cellulose nanocrystals: Comparative physicochemical, thermal, and mechanical properties

The development of sustainable and biodegradable composites has gained increasing attention in recent years. Effective interaction and adhesion between polymers and fillers are crucial. In this study, the effect of different aspect ratios of cellulose nanocrystals (CNCs) and their hybrid within a crosslinked poly (vinyl alcohol) (PVA) nanocomposite has been investigated to develop biodegradable materials. The physicochemical, thermal, and mechanical properties of the specimens have been studied. SEM images indicate that the addition of CNC reduced the porosity of the films. The XPS results confirmed the significant formation of covalent bonds for all composites except those reinforced with wood-CNC, which showed a lower amount of crosslinking and CC formation. EDS maps reveals that the dispersity of the CNCs could be different depending on the aspect ratio of the CNCs. Results from the solubility in water (SW) tests indicated that the use of hybrid-CNC in a crosslinked system decreased the SW significantly. The crosslinking and addition of CNC to the PVA composite led to improved mechanical properties. Elongation at break (EB) decreased significantly for the crosslinked hybrid-CNC nanocomposite. Overall, the results of this study indicate that the aspect ratio of CNCs as fillers in nanocomposites may contribute to their physicochemical, mechanical, and thermal properties for the development of biodegradable materials.

An all-silicon microfabricated gas chromatographic column with a high aspect ratio

Increasing the aspect ratio of the microchannels of microfabricated gas chromatographic columns (μGCCs) can allow analytes to quickly reach equilibrium between the stationary phase and mobile phase, which helps improve their separation performance. In this paper, an all-silicon microfabricated gas chromatographic column (AS-μGCC) with a high aspect ratio was proposed and fabricated using deep reactive-ion etching (DRIE) and silicon direct bonding. Two AS-μGCCs with the lengths of 2 m and the aspect ratios of 6.6 (100 µm-width × 660 µm-depth) and 25 (30 µm-width × 750 µm-depth) were successfully fabricated. The effects of different aspect ratios on the column efficiency of AS-μGCCs were studied. A separation experiment showed that the column efficiency of the AS-μGCC with an aspect ratio of 25 (AS-μGCC-25) was 12 times higher than that of the AS-μGCC with an aspect ratio of 6.6 (AS-μGCC-6.6). The column efficiency of the AS-μGCC-25 was 1961 plates/m, and a heavy hydrocarbon mixture (C8–C20) could be separated using AS-μGCC-25 within 4.5 min

Vortex shedding, flow separation, and drag coefficient in the flow past an ellipsoid of different aspect ratios at moderate Reynolds number

Incompressible viscous flow past an ellipsoid of different aspect ratios (ARs, the ratio of the vertical to the horizontal axis of the ellipsoid, is ranged from 0.5 to 2) at a Reynolds number of 300 is investigated numerically by a finite volume method with adaptive mesh refinement, and the effects of different aspect ratios on vortex shedding, flow separation, and drag coefficient are analyzed in detail. The accuracy of the present results is ascertained by comparing the present drag coefficient and Strouhal number with other literature studies. The results show that the Strouhal frequency of vortex shedding decreases and the magnitude of vortex shedding becomes weaker with an increase in the aspect ratio. In particular, a secondary frequency will occur within a certain interval of 0.8 ≤ AR ≤ 1.2. The vortex shedding appears as a hairpin vortex at AR ∈ [0.5, 1.6], whereas it becomes a double-line vortex at AR ≥ 1.8. Both the upper flow separation angle and the length of the separation bubble increase with an increase in the aspect ratio. The flow separation is symmetrical about the (x, z)-plane only at 0.5 ≤ AR ≤ 0.7 and AR ≥ 1.8. Furthermore, the total drag coefficient and the pressure drag coefficient both increase gradually with an increase in the aspect ratio. Due to the trend of the contact area between the fluid and the surface of the ellipsoid, the friction drag coefficient decreases first (AR ≤ 1) and then increases (AR ≥1). The pressure drag coefficient reinforces the contribution to the total drag coefficient, and the contribution of the pressure drag coefficient grows with an increase in the aspect ratio.

Chitosan Based Aerogels with Low Shrinkage by Chemical Cross-Linking and Supramolecular Interaction.

Chitosan (CTS) aerogel is a new type of functional material that could be possibly applied in the thermal insulation field, especially in energy-saving buildings. However, the inhibition method for the very big shrinkage of CTS aerogels from the final gel to the aerogel is challenging, causing great difficulty in achieving a near-net shape of CTS aerogels. Here, this study explored a facile strategy for restraining CTS-based aerogels’ inherent shrinkage depending on the chemical crosslinking and the interpenetrated supramolecular interaction by introducing nanofibrillar cellulose (NFC) and polyvinyl alcohol (PVA) chains. The effects of different aspect ratios of NFC on the CTS-based aerogels were systematically analyzed. The results showed that the optimal aspect ratio for NFC introduction was 37.5 from the comprehensive property perspective. CTS/PVA/NFC hybrid aerogels with the aspect ratio of 37.5 for NFC gained a superior thermal conductivity of 0.0224 W/m·K at ambient atmosphere (the cold surface temperature was only 33.46 °C, despite contacting the hot surface of 80.46 °C), a low density of 0.09 g/cm3, and a relatively high compressive stress of 0.51 MPa at 10% strain.

In-plane cyclic performance of confined partially grouted masonry walls with joint and vertical reinforcement

This article presents the experimental results and analysis of five full-scale walls subjected to in-plane reversed cyclic displacements. All walls were constructed with reinforcement in both vertical and horizontal directions and, with a reinforced concrete frame in the perimeter of the wall as confinement. This research focuses on the effect of different aspect ratios of the walls on shear response. Force versus displacement diagrams and failure modes allowed the assessment of the seismic performance based on the stiffness degradation, ductility, drift capacity, and dissipated energy. An influence on the stiffness degradation derived from the aspect ratio was found. Ductility and equivalent viscous damping seem not to be affected by aspect ratio variations. The shear capacity is overestimated when the contribution of RC columns is explicitly considered. Using an equivalent masonry element instead of the reinforced concrete column gives a more conservative and realistic approach to the shear capacity.

A Quasi 3D Modified Strain Gradient Formulation for Static Bending of Functionally Graded Micro beams Resting on Winkler-Pasternak Elastic Foundation

This paper presents the bending analysis of simply supported functionally graded (FG) size dependent beams based on modified strain gradient theory. The shear and normal deformations are considered in displacement field according to hyperbolic shear deformation theory. Governing equations and corresponding boundary conditions for FG micro beam are derived utilizing principle of minimum total potential energy. Mori–Tanaka homogenization scheme and the classical rule of mixture are used for prediction of material properties through the thickness. Effects of Winkler-Pasternak elastic foundation parameters are studied for different side to thickness ratios. Effects of different aspect ratios, elastic foundation parameters, power law gradient indexes and different loading conditions are investigated. The efficiency and accuracy of present model is demonstrated by comparing to the existing results in especial cases.

Effect of aspect ratio on frequency and power generation of a free-piston linear generator

The thermal efficiency (40–50%) of free-piston linear generator (FPLG) engines is widely known to be higher than the conventional reciprocating engine (CRE) (30–40%). Future technology to optimise FPLG engine combustion necessitates the identification of a stroke to bore ratio (Aspect Ratio, AR). This paper presents a report on the effects of different aspect ratios (1, 1.5, and 2) on the FPLG operating frequency and power output. The development of an experimental test rig was through the utilisation of the FPLG principle of a dual-piston (bounce and combustion chamber) air-driven system. The mechanical function of the FPLG is converted into electric power through the linear generator. The piston velocity, power output (Prms), operating frequency, as well as system energy density and conversion efficiency are discussed in the paper. The FPLG operation using long-stroke (AR2) shows obvious advantages in the peak velocity and Prms; however, the operating frequency is higher in the short stroke, although the in-cylinder pressure, compression ratio, and piston velocity are slightly lower. The calculated energy density indicates the medium stroke (AR1.5) is the optimum in the operating frequency and Prms for overall FPLG operation; besides, it works perfectly in a lean condition. The shortest stroke has better combustion efficiency (38.5%) at the stoichiometric condition; however, this percentage significantly increased in a lean condition (ER = 0.4) for AR1.5 and AR2 to 55.67% and 62.39%, respectively, with an increment of 49.3% and 46.6%. The system conversion efficiency decreases with the increase of the aspect ratio.

Dynamic stress concentration of an elliptical cavity in a semi-elliptical hill under SH-waves

The method of wave-function expansion in elliptical coordinates, elliptical cosine half-range expansion and Mathieu function were applied to obtain an exact analytical solution of the dynamic stress concentration factor (DSCF) around an elliptical cavity in a shallow, semi-elliptical hill. An infinite system of simultaneous linear equations for solving this problem was established by substituting the wave expression obtained by the Mathieu function including the standing wave expression of elliptical lining given herein into the boundary condition obtained by the region-matching method. The finite equations system with unknown coefficients obtained by truncation were solved numerically, and the results in the case of an ellipse degenerating into a circle were compared with previous results to verify the accuracy of the method. The effects of different aspect ratios, incident wave angles and aperture ratios on the dynamic stress concentration around the elliptical cavity were described. Some numerical results, when the elliptical hill was changed into a circular one, were analyzed and compared in detail. In engineering, this model can be regarded as a semi-cylindrical hill with an elliptical cylindrical unlined tunnel under the action of SH waves, and the results are significant in aseismic design.

Effective viscoelastic behavior of polymer composites with regular periodic microstructures

Polymer matrix exhibit linear viscoelasticity during processing of composites. The viscoelastic homogenization problem in the time-domain play a vital role in the virtual process simulations. In this paper, full-field simulations using finite element (FE) are carried out for different regular periodic microstructures of unidirectional (UD) fiber reinforced polymer (FRP) (i.e., short, and long fiber) composite and particulate composites. The incremental variational based mean-field homogenization (MFH) as proposed by Lahellec and Suquet (Lahellec and Suquet, 2007a) is used here for comparing with the full-field solutions. Two different elastic bounds-based homogenization methods are coupled with this scheme. Implementation is validated with benchmark problems of particulate composites. These are then compared with the solutions of different particulate microstructures (face centered cubic (FCC), body centered cubic (BCC) and simple cubic (SC)). Mean-field response is closer to FCC arrangement. Additionally, FCC and BCC arrangement indicated nearly the same response with different local field statistics. Relaxation in the effective modulus of UD FRP composites obtained from the MFH compared well with the full-field solution as a function of direction and time for hexagonal arrangement of long fiber and staggered arrangement of ellipsoidal short fibers. The effect of different aspect ratio, volume fraction and contrast in properties on the macroscopic response is additionally investigated. Glass and carbon fiber with an isotropic approximation is used for studying the effect of contrast. Double inclusion MFH scheme coupled with the incremental variational approach indicated better comparisons with the full-field solution of UD FRP composites.

Translational and rotational velocities in shear-driven jamming of ellipsoidal particles.

We study shear-driven jamming of ellipsoidal particles at zero temperature with a focus on the microscopic dynamics. We find that a change from spherical particles to ellipsoids with aspect ratio α=1.02 gives dramatic changes of the microscopic dynamics with much lower translational velocities and a new role for the rotations. Whereas the velocity difference at contacts-and thereby the dissipation-in collections of spheres is dominated by the translational velocities and reduced by the rotations, the same quantity is in collections of ellipsoids instead totally dominated by the rotational velocities. By also examining the effect of different aspect ratios we find that the examined quantities show either a peak or a change in slope at α≈1.2, which thus gives evidence for a crossover between different regions of low and high aspect ratio.

An analytical solution of Reynolds equation for evaluating the characteristics of surface textured bearing

PurposeCurrently, there is a lack of fast and highly accurate on analytical solution of Reynolds equation for evaluating the characteristics of surface textured bearing. This paper aims to develop such an analytical solution of Reynolds equation for an effective analysis of the characteristics of surface textured bearings.Design/methodology/approachBy using the separation of variables method and mean eigenvalue method, the analytical solution is constructed. The CFD simulations and experimental results are used to validate the correctness of the analytical solution.FindingsThe analytical solution can accurately evaluate the characteristics of textured bearings. It is found that the larger the eccentricity ratio and aspect ratio, the greater the oil film force. It also found that the smaller the eccentricity ratio, the larger the Sommerfeld number S. When eccentricity ratio e = 0.65, the attitude angles of different oil boundaries are same. The effect of different aspect ratios on dynamic stiffness and damping coefficient generally follows a same trend. It is numerically shown that the critical speed of rotor-bearing is 3500 rpm.Originality/valueThe analytical solution provides a simple yet effective way to study the characteristics of surface textured bearings.

The aspect ratio of gold nanorods as a cytotoxicity factor on Raphidocelis subcaptata

Gold nanorods (AuNRs) are promising nanoscale materials for several technological and biomedical applications. The physicochemical properties of AuNRs, including size, shape and surface features, are crucial factors affecting their cytotoxicity. In this study, we investigated the effects of different aspect ratios of AuNRs (1.90, 2.35, 3.25 and 3.50) at concentrations of 2 and 10 μg mL−1 on their cytotoxicity and cellular uptake in green algae Raphidocelis subcaptata. The experiment was performed in oligotrophic freshwater medium in a growth chamber with constant agitation of 80 rpm under controlled conditions (120 μEm−2s−1 illumination; 12:12h light dark cycle and constant temperature of 22 ± 2 °C). The algal growth was monitored daily for 96 h via electronic absorbance scanning at 600–750 nm. Oxidative stress, cell viability and autofluorescence were evaluated using a flow cytometer. Oxidative stress quantified by loading cultures with the fluorescent dye 2′, 7′-dichlorofluorescein diacetate. To assess algal cell viability, propidium iodide was selected as the fluorescent probe. Our results indicated that the aspect ratio of AuNRs mediates their biological effects in green algae R. subcaptata. A positive correlation between oxidative stress and increase of aspect ratio was found at concentration of 10 μg mL−1. Higher cytotoxicity and mortality were observed for algae incubated with higher aspect ratios AuNRs (3.50). These findings may be useful to understand the impact of the AuNRs in aquatic environments, contributing to ecosystem management and nanomaterials regulation.

Prediction of hydrodynamic instability in the curved ducts by means of semi-analytical and ANN approaches

Curved ducts with non-circular cross-sectional geometry have significant applications in different industries. Hydrodynamic stability in these curved ducts is an interesting issue in field of fluid mechanics. In the present study, the linear hydrodynamics stability of fluid flow in the curved rectangular duct is semi-analytically investigated. Then, the hydrodynamic stability in these ducts is estimated via using artificial neural networks (ANNs). To this accomplishment, critical Dean number (Dn c ) is estimated under various aspect ratios and curvature ratios. Based on the semi-analytical results, the Dn c is increased by curvature ratio enhancement. In addition, irregular variation on trend of Dn c is found by an enhancement in the aspect ratio. Moreover, maxima of mean square error and minima of correlation coefficient for intended ANN are obtained 0.00144 and 0.98621, respectively. Finally, predictive equation is suggested to estimate of Dn c using weights and bias of designed ANN. • Hydrodynamics instability in curved rectangular duct is studied by using semi-analytical and ANNs approaches. • Effects of different aspect ratios and curvature ratios on hydrodynamics instability are evaluated. • An equation to predict of critical Dean number in curved ducts by using ANNs is proposed.

Formation Mechanism of Residual Stresses in Micro-Injection Molding of PMMA: A Molecular Dynamics Simulation.

Injection molding is an economical and effective method for manufacturing polymer parts with nanostructures and residual stress in the parts is an important factor affecting the quality of molding. In this paper, taking the injection molding of polymethyl methacrylate (PMMA) polymer in a nano-cavity with an aspect ratio of 2.0 as an example, the formation mechanism of residual stresses in the injection molding process was studied, using a molecular dynamics simulation. The changes in dynamic stress in the process were compared and analyzed, and the morphological and structural evolution of molecular chains in the process of flow were observed and explained. The effects of different aspect ratios of nano-cavities on the stress distribution and deformation in the nanostructures were studied. The potential energy, radius of gyration and elastic recovery percentage of the polymer was calculated. The results showed that the essence of stress formation was that the molecular chains compressed and entangled under the flow pressure and the restriction of the cavity wall. In addition, the orientation of molecular chains changed from isotropic to anisotropic, resulting in the stress concentration. At the same time, with the increase in aspect ratio, the overall stress and deformation of the nanostructures after demolding also increased.

Influence of Aspect Ratio on the Performance Characteristics of Plain Journal Bearing Lubricating With Non-Newtonian Lubricant

This article presents the static performance characteristics of a plain journal bearing with non-Newtonian lubricant (power law) at different aspect ratio. Finite difference approach is employed to solve the modified Reynold equation. Hydrodynamic regime is assumed to be isothermal. The fluid film pressure is established using modified Reynold equation and Reynold boundary condition through iteratively. Thus the obtain pressure is used to find-out the performance characteristics for instance load carrying capacity, attitude angle, friction force and side leakage. Three aspect ratios are assumed 0.5, 1 and 1.5 for the present study. The effect of different aspect ratios on performance characteristics at different power law index (0.9, 1 and 1.1) has been presented.