Cylinder Radius Research Articles

Theoretical analysis and simulation of twist blockage and yarn tension in a dynamic twist-resistant device

In the ring spinning system, a dynamic twist-resistant device has been applied to improve yarn quality. In this paper, a mechanical model quantifies the relationship between twist blockage, yarn tension, and the parameters of the device and yarn when yarn passes through the dynamic twist-resistant device. During the modeling process, the force applied by the twist-resistant device was considered, and the twisting torque was precisely calculated by yarn tension rather than calculated by the assumption that yarn-twisting torque is linearly related to the yarn twist. Finally, twist blockage and yarn tension are given as a function of the normal force applied by the device, the radii of cylinders in the device, warp angle, deviation angle and radius of the yarn. The simulation results are presented and analyzed.

Unidirectional helical edge states for all-dielectric topological photonic crystals

The study of one-way edge states of electromagnetic wave based on quantum Hall effect in photonic crystals (PCs) has recently made a great progress. In particular, the pseudo-spin states in topological PCs made of dielectric materials can be realized by breaking pseudo-time-reversal symmetry. We perform a research on the influence of parameters, such as lattice constant, dielectric permittivity of cylinders, radius of the dielectric cylinder and scaling factor of PCs, on the photonic bandgaps of topological PCs. Based on the analysis results, we present a 2D topological PC configuration that supports robust unidirectional helical edge states along zigzag interface between the topologically trivial and nontrivial PCs. With the structure, an operating bandwidth as larger as of $$0.0173\;(2\pi c/a)$$, robust helical edge states with energy-condensed and great nonreciprocity can be achieved by exciting a circularly polarized source. Utilizing this kind of architecture, we construct Z-shaped channel to demonstrate the robustness of helical edge states transport in different cases. The research offers a valid way for realizing unidirectional edge states with robust transport in practicable quantum communication applications.

Calculation of the transformation plasticity strain in the shape memory cylinder

A connected thermomechanical boundary problem for an infinite shape memory alloy cylinder loaded by an axial force and subjected to heating or cooling from the surface is solved. The evolution of stress-strain state is calculated for a process of the transformation plasticity. The mechanical properties of a material point are given by a micromechanical model accounting for the deformations due to elasticity, thermal expansion and phase transformation. The obtained problem was solved numerically using the iterative procedure with a variable iterative parameter. The influence of the surface temperature rate and radius of cylinder on the transformation plasticity is investigated. It is shown, that the elongation due to the transformation plasticity effect decreases with the increasing temperature rate. The elongation also decreases with the increasing cylinder diameter. This phenomenon can be explained by an inhomogeneity of the temperature and stress fields causing different conditions for the phase transformation in different points of the body. Stress in the local region can overtop more than twice the mean value.

High-rated loading, deformation and fracture of thick-walled composite cylinders with an electric explosion of wires

The technique of experimental testing and estimation of failure strengths for composite thick-walled 2-component cylinder proposed. We estimated amplitude of the generated by the wire explosion pressure and portions of this pressure transmitted into the PMMA cylinder and the aluminium shell. Dependence between cylinder radius and radial pressure measured and recorded with developed by us piezo-probe. Failure stress for the PMMA cylinder as well as failure strass of the aluminium shell is also estimated.

Effect of thermal cycling on temperature changes and bond strength in different test specimens

Objectives To investigate temperature changes in various test specimens during thermal cycling and to evaluate difference in micro-tensile repair bond strength in specimens cut from the inner or the outer area of composite blocks after thermal cycling. Materials and methods Four rectangular composite blocks of various sizes were fabricated, and thermocouples placed in the centre of the specimens or halfway from the surface to the centre. Composite cylinders were made on ground flat extracted molars, as intended for micro-tensile and shear bond testing, with a thermocouple placed at the centre of the cylinder radius between composite and dentin. The specimens were thermal cycled between 5 °C and 55 °C with 20–60 s dwell times. The highest and lowest temperatures in the test specimens were recorded. Composite blocks were fabricated and stored in water for a week and then repaired with the same composite. After thermal cycling (5000×, 5 °C and 55 °C with a 20 s dwell time), test specimens were cut for micro-tensile testing. Results None of the specimens tested reached the cold and warm water bath temperatures after a 20 s dwell time. In the smallest composite block, the centre core temperature reached 5 °C and 55 °C after 40 s dwell time, but lacked 1 °C after 60 s in the largest block. None of the specimens involving teeth reached water temperatures. The micro-tensile repair strength was significantly different between the outer and the central cut rods (p < .05). Conclusions The most commonly used dwell times for thermal cycling are insufficient to create a homogeneous temperature change.

Upper bound on angular momentum transport in Taylor-Couette flow.

We investigate the upper bound on angular momentum transport in Taylor-Couette flow theoretically and numerically by a one-dimensional background field method. The flow is bounded between a rotating inner cylinder of radius R_{i} and a fixed outer cylinder of radius R_{o}. A variational problem is formulated and solved by a pseudo-time-stepping method up to a Taylor number Ta=10^{9}. The angular momentum transport, characterized by a Nusselt number Nu, is bounded by Nu≤cTa^{1/2}, where the prefactor c depends on the radius ratio η=R_{i}/R_{o}. Three typical radius ratios are investigatedi.e., η=0.5,0.714,and0.909, and the corresponding prefactors c=0.0049,0.0075,and0.0086 are found to improve (lower) the rigorous upper bounds by Doering and Constantin [C. Doering and P. Constantin, Phys. Rev. Lett. 69, 1648 (1992)PRLTAO0031-900710.1103/PhysRevLett.69.1648] and Constantin [P. Constantin, SIAM Rev. 36, 73 (1994)SIREAD0036-144510.1137/1036004] by at least one order of magnitude. Furthermore, we show, via an inductive bifurcation analysis, that considering a three-dimensional background velocity field is unable to lower the bound.

Investigation of entropy generation in nanofluid’s axisymmetric stagnation flow over a cylinder with constant wall temperature and uniform surface suction-blowing

Dimensionless temperature, Nusselt number and entropy generation in stagnation flow of incompressible nanofluid over an infinite cylinder accompanying uniform suction and blow in steady state have been investigated in this study. Free stream has been steady as well with the initial stream rate of k¯. Dimensional analysis and similarity solution of Navier-stokes and energy equations have been presented. These equations are simplified implementing appropriate transformations introduced in this research. The similarity equations are solved where the cylinder’s wall is under constant Temperature. All these solutions are acceptable for Reynolds numbers Re=k¯a2/2υf of 0.1–1000, various dimensionless surface diffusion S=Uo/k¯a and specific volume fractions of nano particles where a is the cylinder radius and υf is the kinematic viscosity of the base-fluid. The results show that for all Reynolds numbers, diffusion depth of radial and axial components of velocity field and wall shear stress increases as a result of decline in nano particles volume fraction and growth in surface diffusion. Moreover, increase in nano particles volume fraction and surface suction raises heat transfer coefficient and Nusselt number. Also the largest amount of entropy generated is calculated.

Mixed convection in a trapezoidal enclosure filled with two layers of nanofluid and porous media with a rotating circular cylinder and a sinusoidal bottom wall

The laminar two-dimensional mixed convection in a trapezoidal enclosure with a rotating inner circular cylinder and a sinusoidal bottom wall is studied numerically. The fluid inside the enclosure is a CuO–water nanofluid layer in the top space of it, while the bottom space includes a CuO–water nanofluid saturated with a porous medium. Both the right and left sidewalls are assumed adiabatic, while the bottom and the top walls of the enclosure are maintained, respectively, at the hot and cold temperatures. The dimensionless governing equations are expressed for velocity and temperature formulation and modeled by using COMSOL code based on the Galerkin finite element method. Parametric studies on the effects of various significant parameters such as Rayleigh number, Darcy number, the inner cylinder radius, the porous layer thickness, the angular rotational velocity, the solid volume fraction and the number of undulations on the flow and thermal fields together with the heat transfer rate have been performed. The highest value of the stream function for (Ra = 103 and Ra = 105) is seen at (R = 0.2 and S = 0.2). The same thing is observed, when the bottom wall is considered wavy. For (Ra = 103 and N = 0) and (0.5 ≤ S ≤ 0.8), it can be seen that as the inner cylinder radius increases from (R = 0.1) to (R = 0.3), the stream function values increase continuously. It is found that the average Nusselt number increases as the Rayleigh and Darcy numbers, the solid volume fraction, inner cylinder radius and the angular rotational velocity of the cylinder increase, while it decreases as the porous layer thickness and the number of undulations increase. Comparisons with previously published numerical works are performed, and good agreements between the results are observed.

Creeping flow of a sphere nearby a cylinder

We present a three-dimensional solution of a sphere nearby an infinite cylinder at low Reynolds number. We utilize the Lamb’s general solution based on spherical harmonics and develop a framework based on cylindrical harmonics to solve the flow field around the sphere and outside the cylinder, respectively. The solution is solved semi-analytically by considering geometrical parameters, including sphere radius, sphere velocity, separation distance and cylinder radius. The drag force coefficients of the sphere which are dependent on the distance between the cylinder surface and the sphere, as well as the velocity contours in the vicinity of the sphere, are analyzed. We also provide an analytical formula to calculate the drag force. The analytical formula has good quantitative agreement with the semi-analytical solution when the radius of the cylinder is smaller than the sphere. Such analysis can give insights into the details of the complex interaction between the sphere and cylinder.

A Combinatorial Approach for Constructing Lattice Structures

Abstract Lattice structures exhibit unique properties including a large surface area and a highly distributed load-path. This makes them very effective in engineering applications where weight reduction, thermal dissipation, and energy absorption are critical. Furthermore, with the advent of additive manufacturing (AM), lattice structures are now easier to fabricate. However, due to inherent surface complexity, their geometric construction can pose significant challenges. A classic strategy for constructing lattice structures exploits analytic surface–surface intersection; this, however, lacks robustness and scalability. An alternate strategy is voxel mesh-based isosurface extraction. While this is robust and scalable, the surface quality is mesh-dependent, and the triangulation will require significant postdecimation. A third strategy relies on explicit geometric stitching where tessellated open cylinders are stitched together through a series of geometric operations. This was demonstrated to be efficient and scalable, requiring no postprocessing. However, it was limited to lattice structures with uniform beam radii. Furthermore, existing algorithms rely on explicit convex-hull construction which is known to be numerically unstable. In this paper, a combinatorial stitching strategy is proposed where tessellated open cylinders of arbitrary radii are stitched together using topological operations. The convex hull construction is handled through a simple and robust projection method, avoiding expensive exact-arithmetic calculations and improving the computational efficiency. This is demonstrated through several examples involving millions of triangles. On a typical eight-core desktop, the proposed algorithm can construct approximately up to a million cylinders per second.

Plasma-Dielectric Traveling Wave Antenna

The paper investigates the efficiency of transformation of traveling wave into radiation in longitudinally inhomogeneous plasma cylinder. The plasma is limited by a dielectric shell of finite thickness. The investigation involves the use of the method of spectral field expansion in terms of a set of functions including the surface and spatial waves of plasma cylinder with dielectric shell. A system of integro-differential equations for expansion coefficients has been obtained. These coefficients determine the amplitudes of transmitted, reflected, and scattered waves and also radiation patterns (RP). The system of equations is solved for the case of strong longitudinal variation of plasma density. The relationships of the transformation coefficients of surface wave energy as a function of the plasma density gradient, electrical length of section of plasma inhomogeneity, the electric radius of plasma cylinder, dielectric permittivity, and the thickness of dielectric were calculated. The fraction of surface wave energy that is transformed into radiation at acute angles can amount to 35%. The resultant narrow-beam RPs have only one lobe. The radiation maximum fits into an angle of several degrees with respect to the direction of surface wave propagation. With an increase of plasma density gradient, the lobe width is reduced, while its position shifts to 0°. The impact of dielectric properties on radiation characteristics has been also investigated.

Aeroacoustic noise calculation of noncompact bodies with time-domain scattered green’s function

In view of the scattering effect induced by non-compact bodies, and the growing time cost of the noise calculation with high-order methods, tailored green function methods gradually become effective means to study acoustic noise of noncompact bodies. With the help of free-space green function and convective wave equation, time-domain integral method is presented to calculate scattered green function under arbitrary boundary condition. In order to verify the present method, the cylinder noise under solid wall condition is firstly calculated with stationary point source. The scattered green functions are in good agreement with Gloerfelt’s analytical solution and Takaishi’s frequency method. The pressure distribution demonstrates that the pressure appears as circle shape at low frequency but petal-like pattern at high frequency. Furthermore, point sources in parabolic moving form is chosen to study the influence of scattering effect to far field noise. Numerical results illustrate that the scattering effect is closely related to cylinder radius and the location of sound sources, large body size and sound sources adjacent closely to body surface could lead to serious scattered noise. Besides, time-domain method overcomes the limit that noise calculations have to be performed in relative coordinate system, and it can calculate scattered noise accurately and instantaneous.

On reactive thin liquid films falling down a vertical cylinder

Chemical reactions in thin liquid films falling down vertical cylinders are widely present in various industrial settings, such as in combustion chambers of internal combustion engines. However, the effect of chemical reactions, especially the non-isothermal reactions, on the dynamics of thin films remains poorly understood. Therefore, in this paper, we systematically study the dynamics of a thin liquid film flowing down vertical cylinders in the presence of an exothermic or endothermic chemical reaction. A reduced model based on the assumption that the film thickness is much smaller than the cylinder radius is firstly derived. We then examine the effect of chemical reactions on the linear stability of the evolution equation as well as its nonlinear behaviors, including the profile and propagation speed of steady traveling waves. We find that the size and propagation speed of sliding beads on the cylinder are suppressed for an exothermic chemical reaction and promoted for an endothermic chemical reaction, respectively. In the end, we perform direct numerical simulations of the full nonlinear evolution equation, which are consistent with the predications from linear stability analysis and nonlinear traveling wave solutions. Our results provide new insight into the influence of chemical reactions on the dynamics of thin films falling down the cylindrical substrate.

Peering at the outflow mechanisms in the transitional pulsar PSR J1023+0038: simultaneous VLT, XMM-Newton, and Swift high-time resolution observations

We report on a simultaneous near-infrared, optical, and X-ray campaign performed in 2017 with the XMM-Newton and Swift satellites and the HAWK-I instrument mounted on the Very Large Telescope (VLT) on the transitional millisecond pulsar PSR J1023+0038. Near-infrared observations were performed in fast-photometric mode (0.5 s exposure time) in order to detect any fast variation of the flux and correlate this with the optical and X-ray light curves. The optical light curve shows the typical sinusoidal modulation at the system orbital period (4.75 h). No significant flaring or flickering is found in the optical, nor any signs of transitions between active and passive states. On the contrary, the near-infrared light curve displays a bimodal behaviour, showing strong flares in the first part of the curve, and an almost flat trend in the rest. The X-ray light curves instead show a few low-high mode transitions, but no flaring activity is detected. Interestingly, one of the low-high mode transitions occurs at the same time as the emission of an infrared flare. This can be interpreted in terms of the emission of an outflow or a jet: the infrared flare could be due to the evolving spectrum of the jet, which possesses a break frequency that moves from higher (near-infrared) to lower (radio) frequencies after the launching, which has to occur at the low-high mode transition. We also present the cross-correlation function between the optical and near-infrared curves. The near.infrared curve is bimodal, therefore we divided it into two parts (flaring and quiet). While the cross-correlation function of the quiet part is found to be flat, the function that refers to the flaring part shows a narrow peak at ∼10 s, which indicates a delay of the near-infrared emission with respect to the optical. This lag can be interpreted as reprocessing of the optical emission at the light cylinder radius with a stream of matter spiraling around the system due to a phase of radio ejection. This strongly supports a different origin of the infrared flares that are observed for PSR J1023+0038 with respect to the optical and X-ray flaring activity that has been reported in other works on the same source.

Numerical investigation on heat transfer characteristics of Taylor Couette flows operating with CO2

An accurate prediction of heat transfer characteristics is essential for the design of bearings in supercritical CO2 power cycles, where the flow at the rotating surface is characterised as Taylor Couette flows. However, the high pressure CO2 leads to Taylor numbers exceeding the applicable range of existing empirical correlations, challenging the suitability. Few studies are found to consider this issue. In this paper, the heat transfer characteristics and windage losses of Taylor Couette flows are investigated. Two representative pressures of 1.4 MPa and 7.8 MPa are studied. It is demonstrated that the heat transfer performance is significantly enhanced at high operation pressures, in particular for the operation temperature towards the critical regime, while a reasonable windage loss is maintained. This is attributed to the increased Taylor number and abrupt changes of thermophysical properties near the critical regime. In addition, empirical correlations underpredict the heat transfer performance, particularly for high operation pressures. The difference is up to three times. The effect of annual gap, cylinder radius and axial length are further compared. This work provides the insight into heat transfer characteristics of Taylor Couette flows operating with CO2. The outcome can be used to the design of CO2 bearings.

Numerical simulations of heat transfer around a circular cylinder immersed in a shear-thinning fluid obeying Cross model

Mathematical analysis for fluid flow and heat transfer outside a stretchable hollow cylinder placed in a generalized Newtonian fluid is the focus of present research. Constitutive equations due to Cross model are employed for problem formulation. Unlike power-law model, Cross model is valid for vanishingly low and infinitely high strain rates. Numerical calculations are worked out by two different procedures namely the shooting method and the MATLAB built-in function bvp4c. Solutions are elucidated for a specific range of power-law index n (0≤n≤1) that depicts the shear-thinning character of the fluid. The obtained solution also contains a curvature parameter M, which is inversely proportional to the cylinder radius. A notable outcome of this study is that increasing power-law index n substantially assists the axially directed flow which is accompanied by a reduction in resisting wall shear. However, heat transfer rate from the cylindrical surface is drastically lowered when n is enhanced. A few noteworthy deviations of present model from that of the flat surface are deliberated. Furthermore, numerical solutions corresponding to the flat surface case (M=0) agree very well with the available literature.

On the beam properties of radio pulsars with interpulse emission

ABSTRACT In the canonical picture of pulsars, radio emission arises from a narrow cone centred on the star’s magnetic axis but many basic details remain unclear. We use high-quality polarization data taken with the Parkes radio telescope to constrain the geometry and emission heights of pulsars showing interpulse emission, and include the possibility that emission heights in the main and interpulse may be different. We show that emission heights are low in the centre of the beam, typically less than 3 per cent of the light cylinder radius. The emission beams are underfilled in longitude, with an average profile width only 60 per cent of the maximal beamwidth and there is a strong preference for the visible emission to be located on the trailing part of the beam. We show substantial evidence that the emission heights are larger at the beam edges than in the beam centre. There is some indication that a fan-like emission beam explains the data better than conal structures. Finally, there is a strong correlation between handedness of circular polarization in the main and interpulse profiles, which implies that the hand of circular polarization is determined by the hemisphere of the visible emission.

DSmT-Based Ultrasonic Detection Model for Estimating Indoor Environment Contour

As for uncertainties of ranging and direction angle in the ultrasonic sensor measurement, an ultrasonic distance measurement model is first proposed for representing these uncertainties through analyzing the working principle of the ultrasonic sensor, which can be adopted to detect the contour of wall plan and cylinder. Moreover, the Dezert–Smarandache Theory (DSmT) method is employed to fuse the uncertainty data measured by using the ultrasonic sensor. Next, extended Hough transform (EHT) and least-squares method (LSM) are combined to identify the environmental contour. Then, the measurement uncertainty of the ultrasonic sensor is analyzed for setting the threshold Th used for distinguishing line and cylinder, and the detection range of the cylinder radius is estimated. Finally, we build an indoor environment and design the ultrasonic sensor hardware system to detect the indoor environment for experimental verification. The indoor environment contour obtained in the experimental results is consistent with the real environment, which illustrates the feasibility and effectiveness of the proposed method. The proposed method has certain reference value for research of simultaneous localization and mapping (SLAM) of the mobile robot.

Noise calculation of noncompact bodies with impedance boundary in limited enclosed space

The present paper mainly investigates noise propagation in limited enclosed space with non-compact bodies. In view of the scattering effect induced by solid boundaries, tailored green’s function methods are used to study the noise propagation. Frequency-domain integral equation is presented to calculate scattered noise under impedance boundary condition in enclosed space. At first, the scattered noise of circular cylinder with solid boundary condition is calculated to verify the validity of the present algorithm. Secondly, the impedance boundary condition is executed on the cylinder wall. Furthermore, the impedance boundary conditions are carried out on the boundaries of enclosed space. Numerical results demonstrate that the total noise drastically reduces in some areas with impedance boundary, but increases in other areas. The phenomenon is related with the cylinder radius, the location of sound sources and the scattering effect. In practical engineering problems, the impedance boundary should be applied locally according to the configuration.

Analytical investigation of rotationally symmetrical oscillating flows of viscoelastic fluids

This paper deals with the analytical investigation of rotationally symmetrical oscillating Couette flows of a viscoelastic Oldroyd-B fluid, taking the inertial force into account. The fluid is enclosed between two coaxial cylinders. One or both cylinders oscillate rotatingly. The periodic responses of the velocity distribution and the stress field are analytically obtained and graphically presented. The decaying transient motion of the fluid in respect of an arbitrary initial velocity field and the stationary cylinders is also acquired. The corresponding natural oscillations of the fluid system are also analyzed. The inertial, viscous and elastic effects on the flow behavior are extensively discussed with reference to the dimensionless parameters – Reynolds number, Deborah number, the ratio of the relaxation time to the retardation time and the ratio of the two cylinder radii. It is shown that with increasing inertial effect (increasing Reynolds number), and increasing fluid elasticity (increasing Deborah number) the fluid responds to the cylinder oscillation with an increasing phase shift, which increases further with the distance to the exciting cylinder, up to a phase shift of several periods. The resonance response of the flow system can be clearly identified in terms of various parameters and the corresponding eigenmodes are demonstrated.