Cylinder Radius Research Articles

Band-Gap Tuning in Two-Dimensional Spatiotemporal Phononic Crystals

We investigate the effect of small spatiotemporal modulations in subwavelength-dimensioned phononic crystals with large band gaps, on the frequency spectrum for elastic waves polarized in the plane of periodicity. When the radius of cylinders periodically placed inside a matrix of highly-contrasting elastic properties is time-varying, we find that due to the appearance of frequency harmonics throughout the spectrum, the notion of a band gap is destroyed in general, although with the appropriate tuning of parameters, in particular the modulation frequency, it is possible that some band-gap region is retained, making such systems possible candidates for tunable bandpass filters or phononic isolators, accordingly, and for sensor applications.

Improving performance of mantle cloak for electrically large PEC cylinders by reducing higher-order scattering coefficients

Based on the scattering cancellation technique, an approach is proposed to improve the mantle cloak’s performance for electrically large cylinders. The procedure is based on the observation that the number of dominant scattering coefficients and corresponding magnitudes for a cylinder decreases when oriented obliquely to the incident wave. Thus, it is quite advantageous to design a mantle cloak under the oblique incidence than the normal incidence. The proposed method starts with determining the optimum angle of incidence at which if the object is oriented with respect to the incident wave, the maximum scattering reduction can be obtained with a mantle cloak explicitly designed for that orientation. The procedure is applied to cylinders of radii and , where is the design wavelength. The proposed approach’s advantages are highlighted by comparing it with the previously published literature. Additionally, the mantle cloak is realized using a periodic grid of metallic patches, and simulations in Ansys HFSS are performed to verify the design.

Damping of dark envelope soliton in a viscous bounded dusty plasma

The propagation of dust-acoustic waves in a dusty plasma bounded in finite symmetrical cylindrical geometry has been theoretically investigated. By using the reductive perturbation method, we obtain a quasi-nonlinear Schrodinger equation. It is shown that there is a dark envelope soliton under certain conditions, while its amplitude will decrease with the time. The dependence of both the dispersion relation and group velocity of envelope solitary waves on the radius of cylinder has been given. Moreover, we define the duration time of dark envelope solitons and give the theoretical ones. It is found that the duration time increases as the radius of cylinder increases, while it decreases as the viscosity coefficient of dusty plasmas increases.

Research on “Cylinder‐Four‐Beam” Microstructure Improvement of MEMS Bionic Vector Hydrophone

The existing MEMS bionic vector hydrophone has the problems of low‐sensitivity and narrow‐working band, and the sensitivity and working bandwidth cannot be improved simultaneously by changing the single microstructural parameter. In this paper, the MEMS bionic vector hydrophone microstructural parameters (length, width and height of cantilever, side length of the center block, height and radius of the rigid cylinder) have been optimized simultaneously to obtain a higher sensitivity at the almost same working bandwidth. Firstly, through the mechanical analysis of the microstructure, the objective function and feasible region are established to optimize the parameters of the microstructure, and a set of optimized parameters is obtained. Secondly, the optimized structure is verified by ANSYS simulation, and then, the optimized four‐beam structure is fabricated by the MEMS manufacturing technology. Finally, these two kinds of hydrophones (the previous one and the optimized one) are produced, and their performance tests are carried out. The testing results show that the performances of the optimized hydrophone have been greatly improved, exhibiting a receiving sensitivity of −181.2 dB@1 kHz (increasing by 6.5 dB, 0 dB reference 1 V/μ Pa), the frequency response ranging from 20 Hz to 1 kHz which is the same working bandwidth as before, and a good dipole directivity. The optimization researches in this paper provide a method and idea for the performance improvement of the following MEMS vector hydrophone.

Elastic limit load prediction and equivalent cylinder proposal for circular concave shells subjected to axial compression

The paper aims to propose an equivalent cylinder radius approach for circular cross-section concave shells under axial compression. Several buckling relations are introduced to predict critical stresses and to limit loads considering the extensive range of geometrical parameters. A detailed parametric study is conducted to reveal the influence of concavity on critical stress using geometrically nonlinear analysis (GNA). The amount of reduction in limit load of a concave shell, as a reference to an ideal case, is expressed as a function meridional curvature. An asymmetry factor is described to evaluate the change of critical stresses for longitudinally asymmetric concave shells. A similarity approach is given for the concave shells. A statistical procedure is utilized to examine the accuracy of the equations and relatively satisfactory results are achieved.

Analysis of Laminar Convective Heat Transfer Over Structured Non-Wetting Surfaces

Structured non-wetting surfaces provide alternating no-slip and partial slip boundary conditions to the fluid flow which, in turn, affects the convective heat transfer performance over the surfaces. In this paper, an analytical model is developed for the interfacial Nusselt number, the overall Nusselt number and a thermal hydraulic performance factor for fluid flow in a cylinder patterned with structured non-wetting surfaces, for the two cases of uniform wall heat flux and uniform wall temperature. In addition, by considering the stability of the Cassie state of wettability and its transition to the Wenzel state for flow over superhydrophobic surfaces, the present model overcomes certain limitations of the previously reported studies in the literature. Based on the analytical formulations and the stability constraints, the present paper provides optimum design maps for tailoring structured non-wetting surfaces for maximizing convective heat transfer and the combined thermal-hydraulic performance in applications. Use of the design maps on example cases is also discussed. It is shown that the use of structured non-wetting surfaces is most effective for low Reynolds numbers and/or small cylinder radius.

Numerical investigation of the effect of temperature variation on heat transfer rate in a square cavity filled water-Al2O3 nanofluid with a hot circular cylinder in the center of the cavity

In this paper, the natural convection flow in a square cavity filled with nanofluid water-[Formula: see text] with a hot circular cylinder in the center of the cavity is numerically analyzed. All the walls are in lower temperatures than the circular cylinder. The Navier–Stokes and energy equations in the primitive variable form are discretized and solved by the finite element method (FEM). The effect of the volume fraction, the radius of the circular cylinder, the temperature and Rayleigh number is considered on the average Nusselt number. For the calculation of the viscosity coefficient and thermal conductivity coefficient of water-[Formula: see text] nanofluid, an experimental model is used which is the function of the volume fraction, temperature and nanoparticles diameter. This model is compared to the Brinkman model for viscosity and Maxwell model for thermal conductivity which are only the functions of volume fraction and are used by many researchers. The results show the experimental model leads to different results in comparison with the Brinkman model and Maxwell model, and indicate that the rate of the heat transfer can increase or decrease with the increase in volume fraction and temperature.

Cylindrical 3D printed configurable ultrasonic lens for subwavelength focusing enhancement

In this study, we report the characteristics of acoustic jets obtained through a mesoscale (radius less than 5 wavelengths) ABS cylinder made with a 3D printer. We have analyzed the influence of cylinder size on the characteristic parameters of an acoustic jet, such as maximum acoustic intensity at focus, Full Width at Half Maximum and length of Acoustic Jet. FWHM below 0.5 wavelength in AJ was experimentally obtained. It has been observed that there are two operating regimes depending on the cylinder radius: the resonant and the non-resonant. In the resonant regime, the excitation of Whispering Gallery Modes results in optimal parameter values of the acoustic jet. However, as it is a resonant regime, any minimal variation in cylinder size, working frequency or refractive index would make resonance disappear. In non-resonant mode, a phononic crystal has been embedded inside the cylinder and the characteristic parameters of the acoustic jet have been studied. These have been observed to improve. Finally, we have shown that curved acoustic jets can be obtained with the ABS cylinder with a phononic crystal embedded inside.

Flow patterns in a steady lid-driven rectangular cavity with an embedded circular cylinder

A detailed investigation of the flow in a steady lid-driven cavity of depth to width ratio 1:2 containing a circular cylinder is provided. Three different Reynolds numbers (based on the lid velocity and cavity depth) of 100, 500 and 1000 as well as four different cylinder radii to cavity depth ratios (0.1, 0.2, 0.3 and 0.4) located at three different positions along the horizontal centerline of the cavity, are considered. It appears that these flows can be classified into seven different flow patterns. These flow patterns are given for different cylinder radii and positions as well as Reynolds numbers. There is a tendency that for a given cylinder radius, there are more transitions between different flow patterns for a small radius than for a large radius while for a given Reynolds number, the number of transitions is larger for high Reynolds numbers than for low Reynolds numbers. Overall, a larger number of flow patterns tend to emerge as the Reynolds number increases for small radii. The largest variety of flow patterns occur for the left-sided cylinder due to the interaction with the large anti-clockwise circulation flow formed at the bottom left corner.

Laminar–Turbulent Intermittency in Annular Couette–Poiseuille Flow: Whether a Puff Splits or Not

Direct numerical simulations were carried out with an emphasis on the intermittency and localized turbulence structure occurring within the subcritical transitional regime of a concentric annular Couette–Poiseuille flow. In the annular system, the ratio of the inner to outer cylinder radius is an important geometrical parameter affecting the large-scale nature of the intermittency. We chose a low radius ratio of 0.1 and imposed a constant pressure gradient providing practically zero shear on the inner cylinder such that the base flow was approximated to that of a circular pipe flow. Localized turbulent puffs, that is, axial uni-directional intermittencies similar to those observed in the transitional circular pipe flow, were observed in the annular Couette–Poiseuille flow. Puff splitting events were clearly observed rather far from the global critical Reynolds number, near which given puffs survived without a splitting event throughout the observation period, which was as long as outer time units. The characterization as a directed-percolation universal class was also discussed.

Non-normal-Mode Onset of Convection in a Vertical Porous Cylinder

This is the first study reporting a full three-dimensional (3D) non-normal-mode onset of convection in a porous medium. In this paper, the onset of thermal convection in a vertical porous cylinder is investigated theoretically. In particular, the contribution includes the following novelties. The homogeneous cylinder has a circular cross section. The eigenvalue problem is non-separable in space because of a constant heat flux condition at the upper boundary. In addition, a partly conducting cylinder wall is represented by a Robin parameter a. All boundaries are impermeable. The eigenvalue problem is solved numerically in the COMSOL Multiphysics environment. The critical Rayleigh number for the lowest onset modes is reported as a function of the ratio of the cylinder radius and its height. The only mode number, m, represents azimuthal dependency. The axisymmetric mode $$m=0$$ corresponds to the preferred mode of convection for a small-cylinder radii. The numerical onset criterion is validated with the well-known analytical limit case, $$a \rightarrow \infty$$ . Finally, we performed a visual comparison of the thermo-mechanical eigenfunctions against an established problem, where the only difference is the thermal condition at the upper boundary. The present 3D analysis is a step toward a full adequate modeling of experimental reality for convection onset, beyond the standard constraints of mathematical convenience.

Particle-in-cell simulation of ion-acoustic solitary waves in a bounded plasma* *Project supported by the National Natural Science Foundation of China (Grant Nos. 11965019 and 11847142).

We study some nonlinear waves in a viscous plasma which is confined in a finite cylinder. By averaging the physical quantities on the radial direction in some cases, we reduce this system to a simple one-dimensional model. It seems that the effects of the bounded geometry (the radius of the cylinder in this case) can be included in the damping coefficient. We notice that the amplitudes of both Korteweg–de Vries (KdV) solitary waves and dark envelope solitary waves decrease exponentially as time increases from the particle-in-cell (PIC) simulation. The dependence of damping coefficient on the cylinder radius and the viscosity coefficient is also obtained numerically and analytically. Both are in good agreement. By using a definition, we give a condition whether a solitary wave exists in a bounded plasma. Moreover, some of potential applications in laboratory experiments are suggested.

Co-simulations of a semi-passive oscillating foil turbine using a hydraulic system

Turbines based on oscillating foils possess obvious advantages in shallow waters. In this study, a hydraulic system was designed for the semi-passive oscillating foil, which is more suitable for practical applications than the traditional spring-damper system. Co-simulations using software Fluent® and AMESim™ were carried out to examine the performance of the hydraulic system. Based on the results of the spring-damper system, three typical cases were analyzed for each variable to study the effects of kinematic and mechanical parameters. The results demonstrated that the oscillating foil based on the hydraulic system could achieve a regular heaving response. However, a significant feature of the developed system is that the foil stops briefly at the endpoint of the heaving motion. The kinematic parameter had a significant effect on both the hydrodynamic characteristics and the heaving response. Maximum energy is harvested at reduced frequency f ∗ = 0.10, while the maximum efficiency occurred at f ∗ = 0.125. The mechanical parameters, including the spring, cylinder radius, and rotary load, affected the hydrodynamic characteristics slightly. However, the parameters of the cylinder and the rotary load had a significant impact on the heaving response and the power output performance. The results also indicated that the unstable heaving response should be avoided, as it would decrease the energy harvesting efficiency.

Simulations of a Sloshing Circular Cylinder Inside an Enclosure Filled with Nanofluids

This study applied an incompressible version of the smoothed particle hydrodynamics (SPH) method for simulating a sloshing circular cylinder during natural convection flow over a T-shaped fin in an enclosure occupied by nanofluid. The center area of the enclosure is saturated with a heterogeneous porous medium. Variations in the thermal conditions of the embedded circular cylinder and T-shaped fin were considered. Vertical sloshing of the circular cylinder under a resonance sway excitation was carried out for different values of amplitudes and frequencies. The embedded circular cylinder and T-shaped fin inside the enclosure are maintained at a high temperature . The side walls of the enclosure are maintained at a low temperature , and the horizontal walls are adiabatic. The ranges of key physical parameters are T-shaped fin length (), circular cylinder radius (), Rayleigh number (), Darcy parameter (), solid volume fraction (), wave amplitude (), and resonance frequency (). The simulations revealed that an increment on T-shaped fin length augments the temperature distributions and flow velocity in the enclosure. The circular cylinder radius rises the temperature distributions in the enclosure. At a lower Darcy parameter, the horizontal heterogeneous porous medium in the center area of the enclosure is impeding the nanofluid flow. The hot circular cylinder gives the highest values of the fluid velocity and temperature distributions inside the enclosure.

Numerical Investigation of the nanofluid mixed convection on two layers enclosure with rotating cylinder: High Darcy Number Effects

The present study, numerically investigated of mixed convection in a square enclosure with two layers, with Al2O3–water nanofluid (upper layer) and nano-porous medium (lower layer) with an adiabatic rotating circular cylinder at the center of the enclosure. The top and bottom walls are assumed adiabatic, while the left sidewall is heated, and the right sidewall kept cooled. Numerically, COMSOL code based on the Galerkin finite element method used for solved the dimensionless governing equations. The non-dimensional parameters that used in this study are: Rayleigh number (Ra) ranged from 103 up to 106, Darcy number (Da) equal to 10−3, the angular rotational velocity (Ω) ranged (0 and 6000), the solid volume fraction (ɸ=0.06), and the inner circular cylinder radius as (R = 0.2). The results showed that when Rayleigh numbers increase, a noticeable increase in the flow intensity and the steep temperature gradient, while the values increase when the cylinder rotates. The value of the local Nusselt number was high in the upper half of the cavity. The effect of the cylinder rotates is greater on the value of the local Nusselt number when using the low Rayleigh Numbers.

Airflow of the Two-Port Velopharyngeal Closure: Study Using Computational Fluid Dynamics.

Posterior pharyngeal flap palatoplasty is used to restore the function of velopharyngeal (VP) closure, after which 2 ports remain between the nasal and oral cavity. The authors hypothesized that the airflow dynamics of the upper airway is different in PPF patients compared to health subjects, who only has 1 movable port. Twenty adults who have multislice spiral computed tomography scan were included in this study. Two cylinders (radius, 2.00 mm; height, 4.5 mm) were used to recapitulate the 2-port VP structure after PPF palatoplasty. The areas of ports were modified by changing the radius of 2 cylinders. Real-time computational fluid dynamics simulation was used to capture the airflow velocity and pressures through the 2 ports. The airflow velocity and pressure of upper airway were recorded as the total areas of 2 VP ports increased. The total orifice areas of the 2-port VP closure for 4 VP conditions, including adequate closure, adequate/borderline closure, borderline/inadequate closure, and inadequate closure, were demonstrated. Significant differences between the 2-port VP function for demonstrating PPF reconstruction and the 1-port VP function were found. Airflow dynamics is dependent on the VP structure. The 2-port airflow model for mimicking VP closure after PPF palatoplasty demonstrated airflow characteristics that were significantly different from the 1-port model in normal VP closure.

Leapfrogging criteria for a line vortex pair external to a circular cylinder

The interaction of two line vortices of differing strengths in the presence of a circular cylinder is considered. Explicit criteria are derived, a function of vortex strengths (including strengths of opposite signs) and the cylinder radius, which separate different behaviors of the system. If the initial position of the vortices satisfies these criteria, they will undergo a periodic leapfrogging motion as they rotate around the cylinder; otherwise, the vortices still interact weakly with one another except without leapfrogging. This is in contrast to the planar wall case where if no periodic leapfrogging occurs, the vortices move apart and do not interact with each other. Numerical results for initial vortex positions which do and do not satisfy these criteria are presented to demonstrate the different motions available, as well as the robustness of the criteria.

Influence of Graphene Coating of the Elements in a Two-Dimensional Parabolic Mirror Consisting of Parallel Cylinders on Radio Wave Focusing

We model the diffraction of a plane TE-polarized electromagnetic wave by a parabolic structure consisting of N parallel circular cylinders, where N ∼ 50. The problem of diffraction of a plane wave by a cylinder with arbitrary coordinates of its center is solved. The coupling of individual structural elements is not allowed for in the performed calculations. The field behavior in the vicinity of the focus of the considered parabolic antenna is studied for cylinders made of a dielectric, a dielectric with a graphene monolayer, and perfectly conducting cylinders. It is found that a layer of graphene can lead to an almost twofold increase in the maximum amplitude of the field in the focus, which makes the focusing properties of the dielectric antenna rather close to those of an antenna consisting of perfectly conducting cylinders. It is shown that the field amplitude in the focus oscillates strongly as the frequency increases, and the focus itself moves slightly off the center of the reflector system. The size of the focal spot is studied as a function of the incident-field frequency, cylinder radii, and the distance between the individual reflectors. It is shown that the field in the vicinity of the considered structure has certain features, such as slow and fast oscillations of the field amplitude, which occur as the frequency of the incident wave varies.

Double maxima of angular momentum transport in small gap Taylor–Couette turbulence

Abstract

The compaction zone parameters’ determination when grinding the cement clinker particles

The article discusses the process of grinding cement clinker in a ball mill. A technique for determining the deformations parameters that the crushed particle receives when it interacts with the grinding body, is proposed. The relation for determining the maximum linear size of deformation during the grinding body’s interaction with the cement clinker particle is obtained. The expression for determining the grinding body contact area with the cement clinker particle is proposed. It is shown how the compaction zone is formed during the interaction of the grinding body with the crushed particle. The sealing zone has a cylindrical shape with the cylinder radius. It is shown that under the action of the introduced fracture energy by the grinding body, the material in the compaction zone starts expanding in the direction perpendicular to the impact force. This allows to determine the number of particles into which the cement clinker particle breaks up when hit by a grinding body.