Eccentric Cylinders Research Articles

Exploration of the dynamics of heated non-Newtonian Casson fluid within an annular region of eccentric cylinders subject to peristaltic motion

The flow of non-Newtonian fluids is widely observed in industry and biology, for example, enhanced oil recovery, chemical processes such as in distillation towers and fixed-bed reactors and in the applications of pumping fluids such as synthetic lubricants, colloidal fluids, liquid crystals, and biofluids (e.g., animal and human blood). Therefore, the present study delineates the heat transfer analysis of a Casson fluid within the annular region of eccentric cylinders subjected to peristaltic motion, considering the influence of thermal radiation. The outer cylinder remains rigid and moves at a constant speed, while the inner cylinder, featuring a sinusoidal wave along its wall, exhibits flexibility. The governing two-dimensional equations for the movement of the Casson fluid are reformulated under the assumption of the lubrication hypothesis. The perturbation scheme is used to find approximate results for velocity, temperature, and pressure gradient. A graphical representation is utilized to study the fluctuation of various flow fields with different imperative parameters. The results reveal that the liquid velocity declines as the Casson parameter increases, while the temperature decreases due to the amplified effect of thermal radiation. This study has applications in endoscopy, which is important for diagnosing problems in internal organs. Additionally, the variation of the pressure gradient helps maintain the flow rate, which is essential during the insertion of a catheter into an artery.

Kinetic theory analysis of microscale lubrication of a gas between eccentric circular cylinders with an arbitrary temperature difference

Kinetic theory analysis of microscale lubrication of a gas between eccentric circular cylinders with an arbitrary temperature difference

Analysis of the dynamic characteristics of an eccentric cylinder in axial flow

The simple pendulum model is a fundamental and widely studied concept in physics, its movement follows a tendency to stabilize towards the side with lower gravitational potential energy. Consequently, the simple pendulum structures have been extensive applications in petroleum, aerospace machinery, and others, particularly in gravity induction and actuator systems. The utilization of this model offers versatile solutions for complex engineering challenges. The research object of this study is an eccentric cylindrical stabilized platform. A nonlinear dynamic model of the eccentric cylindrical stable platform in axial flow with variable damping is established. Due to the complexity of the analytical solution of the simple pendulum motion, we adopt the method of numerical analysis to building the simulation and analysis model. Combined with the fluid calculation and dynamics simulation methods, the motion characteristics of the eccentric cylindrical model under steady and unsteady flow fields are analyzed by adjusting the rotational speed, inclination angle, and initial pendulum angle. The experimental platform is built to analyze the motion law of the eccentric cylinder under the action of axial flow, and the experimental results of the motion law of the eccentric cylindrical platform are consistent with the numerical calculation results.

Using electrical impedance spectroscopy to identify equivalent circuit models of lubricated contacts with complex geometry: In-situ application to mini traction machine

Electrical contact resistance or capacitance as measured between a lubricated contact has been used in tribometers, partially reflecting the lubrication condition. In contrast, the electrical impedance provides rich information of magnitude and phase, which can be interpreted using equivalent circuit models, enabling more comprehensive measurements, including the variation of lubricant film thickness and the asperity (metal-to-metal) contact area. An accurate circuit model of the lubricated contact is critical as needed for the electrical impedance analysis. However, existing circuit models are hand derived and suited to interfaces with simple geometry, such as parallel plates, concentric and eccentric cylinders. Circuit model identification of lubricated contacts with complex geometry is challenging. This work takes the ball-on-disc lubricated contact in a Mini Traction Machine (MTM) as an example, where screws on the ball, grooves on the disc, and contact close to the disc edge make the overall interface geometry complicated. The electrical impedance spectroscopy (EIS) is used to capture its frequency response, with a group of load, speed, and temperature varied and tested separately. The results enable an identification of equivalent circuit models by fitting parallel resistor-capacitor models, the dependence on the oil film thickness is further calibrated using a high-accuracy optical interferometry, which is operated under the same lubrication condition as in the MTM. Overall, the proposed method is applicable to general lubricated interfaces for the identification of equivalent circuit models, which in turn facilitates in-situ tribo-contacts with electric impedance measurement of oil film thickness – it does not need transparent materials as optical techniques do, or structural modifications for piezoelectric sensor mounting as ultrasound techniques do.

Jump effect of an eccentric cylinder rolling on an inclined plane

This work addresses the intriguing phenomenon of the jump effect exhibited by an eccentric cylinder rolling on an inclined plane. Our main objective is to determine the region of the parameter space where the cylinder can undergo a jump after pure rolling motion. In previous works, it was assumed that slipping always precedes a jump, leading to the belief that slip is necessary. In contrast, our study challenges this prevailing notion by demonstrating the existence of situations where a jump can occur after pure rolling motion. We present a detailed theoretical description of the jump effect, investigating the dependence of the jump behavior on the initial conditions, the forces involved, and the parameter values. Through rigorous analysis, we determine the restricted region in the parameter space that allows for jumps to occur without slipping. Our findings contribute to the ongoing debate surrounding the jump effect in eccentric cylinder dynamics.

Saffman–Taylor instability in eccentric cylinders at gaseous cavitation

A flow of silicon fluid in the gap between eccentric cylinders was studied experimentally. The condition of gaseous cavitation inception during the rotation of internal cylinder was considered. It was shown that at reduction of the gap between cylinders Saffman–Taylor instability appeared on surface of the internal cylinder and then gaseous cavitation was observed. Possibility of one uniform gas formation appearance under this type of instability was demonstrated.

Generalized Reynolds equation for microscale lubrication between eccentric circular cylinders based on kinetic theory

A microscale lubrication flow of a gas between eccentric circular cylinders is studied on the basis of kinetic theory. The dimensionless curvature, defined by the mean clearance divided by the radius of the inner cylinder, is small, and the rotation speed of the inner cylinder is also small. The Knudsen number, defined by the mean free path divided by the mean clearance, is arbitrary. The Boltzmann equation is studied analytically using the slowly varying approximation following the method proposed in the author's previous study (Doi,Phys. Rev. Fluids, vol. 7, 2022, 034201). A macroscopic lubrication equation, which is a microscale generalization of the Reynolds lubrication equation, is derived. To assess this, a direct numerical analysis of the Boltzmann equation in a bipolar coordinate system is conducted using the Bhatnagar–Gross–Krook–Welander kinetic equation. It is demonstrated that the solution of the derived lubrication equation approximates that of the Boltzmann equation over a wide range of the eccentricity and the whole range of the Knudsen number. It is also demonstrated that another lubrication equation derived by a formal application of the slowly varying approximation produces a non-negligible error of the order of the square root of the dimensionless curvature for large Knudsen numbers.

Higher-order elastic topological insulators with reconfigurable route and tunable corner states

In recent years, topological insulators (TIs) have been introduced in classical wave systems as a new type of quantum material, opening up new ways and approaches for manipulating the propagation of acoustic/elastic waves. The excellent topological protection characteristics of the edge states and corner states in TIs have the potential to significantly impact various scientific and technological advancements, which has attracted widespread attention from the academic community. However, in the case of the majority of elastic TIs, the application is significantly restricted by the fixed interface path and corner state frequency once the structural materials are prepared. To overcome this limitation, this paper presents an elastic TI with reconfigurable topological paths. By manipulating the rotation angle of each unit cell's eccentric cylinder, it becomes feasible to achieve interface paths of any desired shape. Numerical simulation and experimental results indicate that elastic waves exclusively propagate along topological interface paths of different configurations, demonstrating excellent robustness to defects. Furthermore, by incorporating magnetorheological elastomers into the structure, it becomes possible to generate higher-order corner states by adjusting the width of the connected narrow bands. For a structure composed of nontrivial unit cells, it is possible to generate edge states as well as two distinct types of corner states. Elastic waves exhibit strong confinement to edges or corner points and have topological protection properties. By harnessing the magnetorheological effect, it becomes possible to overcome the limitations of traditional higher-order topological insulators, where the corner state frequency is fixed. This approach allows for active manipulation of the working frequency by applying different magnetic fields. Consequently, this research provides valuable insights and serves as a reference for designing intelligent elastic waveguide devices and energy harvesting devices.

The Effect of Vibrating Inner Cylinder on Natural Convective Heat Transfer in Concentric and Eccentric Horizontal Cylindrical Annuli

In this study, natural heat convection caused by centric and vertically eccentric long horizontal cylinders under the influence of vibration is experimentally investigated. The internal wall of the annulus is heated and kept at a constant heat flux, while the outside wall is cooled and maintained at a constant temperature. The vibration frequency impacts the annular convection heat transfer process and the effects of the Rayleigh number, heat flow, and eccentricity. This work employed a moderate, laminar-ranging Rayleigh number from (5×104 to 6.48×106), while the eccentricity range is varied from (-0.667, 0, and+0.667). The investigation is carried out at five different frequencies (0, 2, 5, 10, 15, and 20 Hz); therefore, it was decided to compare the case under the same circumstances in both the absence and presence of vibration. The present results' verification worked exceptionally well in concordance with previous studies. When heat fluxes are considered, the study demonstrates that the temperature difference along the gap (radial difference) between the two cylinders significantly decreases for negative as opposed to positive eccentricities for each Rayleigh number. For different eccentricities, it was discovered that the temperature difference decreased as the Rayleigh number increased. Along with these reductions, the temperature difference was promoted as the vibration frequency increased, which is significant at (20 Hz) within the range considered for controlling parameters. It was also observed that the decrease in temperature difference is higher for the negative eccentric position than for the centric and positive positions. At vertical positive eccentricity at a low Rayleigh number, the gain in vibrational average Nusselt number caused by applying vibration had a minimum value of 22.50601475%, While at the higher value of the Rayleigh number, the maximum increase in negative vertical eccentricity was 86.66933125%. However, the gain in the average Nusselt number depends on the position of the heated inner cylinder, the Rayleigh number, and the vibrational frequency.

Vortex-induced rotational vibration of an eccentric circular cylinder at low Reynolds number of 100

Vortex-induced rotational vibration of an eccentric circular cylinder at low Reynolds number of 100

High-Efficiency Second-Harmonic Generation Using Quasi-Bound State in LiNbO3 Metasurface

We numerically demonstrated a high-efficiency second-harmonic generation (SHG) using quasi-bound state in the continuum (quasi–BIC) in thin film LiNbO3 (TFLN) metasurface. The TFLN possessed exceptionally high second-order nonlinear coefficients, contributing to the enhanced SHG performance. An eccentric cylinder unit cell was presented to achieve high Q–factor resonances associated with the asymmetric parameter introduced. Simulations showed that the high efficiency of the second-harmonic conversion was obtained by using the high Q–factor of the asymmetric dielectric cylinder metasurface, and it achieved a high SHG efficiency of 6.5% at pump intensities as low as 1 MW/cm2 at a normal incident. Furthermore, the simulation results indicated that breaking the symmetry through oblique incidence was more effective in achieving a higher Q–factor compared to altering the structural parameters. Specifically, under 1° oblique incidences, the conversion efficiency could reach 1.2% at an incident power of 1 kW/cm². We have proposed a method to achieve a high conversion efficiency of second-harmonic generation in low-refractive-index materials. Our work not only offers theoretical support but also provides valuable insights for the advancement of efficient nonlinear frequency doubling technology, optical communication, and sensing applications.

Effect of heat transfer on peristaltic flow of Newtonian fluid through eccentric cylinders

Heat transfer effect on peristaltic Newtonian flow in an annular region of eccentric cylinders is considered. An approximate solution for temperature and velocity is obtained using perturbation technique. For constant flow rate, the variation of pressure gradient and velocity with respect to several non-dimensional parameters is studied using graphical representation. It is seen in these graphs that velocity, pressure gradient and temperature enhance with raise in eccentricity and amplitude ratio. Heat diffuses with faster rate with depletion in area of cross section eccentric annulus through parameter inner cylinder radius. Also, velocity rises with increase in heat transfer parameters such as Grashof number and heat transfer co-efficient. Thus velocity of peristaltic flow in eccentric annulus enhances rapidly in presence of heat transfer compared to absence of heat transfer. A study of peristaltic flow in concentric annulus in presence of heat transfer is obtained analytically and compared with present study at eccentricity equal to zero, to validate the approximate solution. It is seen that flow rate increases more in case of eccentric annulus compared to concentric in presence of heat transfer. Present study has application in endoscope, which is important to diagnose problems in internal organs. Also, the variation of pressure gradient helps to maintain flow rate which is essential during insertion of catheter into artery.

A THEORETICAL APPROXIMATION FOR LAMINAR FLOW BETWEEN ECCENTRIC CYLINDERS

Taylor-Couette flow between two concentric cylinders has received much attention due to its use in various applications, including biomedical devices, micro electro-mechanical systems, polymer pumping and electric motor cooling. Due to the complex interaction of the viscosity and the involved geometry within the confined space, different flow regimes are dominant under different conditions, affecting the fluid dynamics and heat transfer. In analyzing the mentioned flow, besides the experimental and computational studies, analytical models have been developed with varying levels of complication. In the present study, using the homotopy of both the flow and the domain geometry between the concentric and eccentric cylinders, a practical formula for flow between eccentric cylinders is developed. In doing so, an appropriate transformation function for the geometry is developed and embedded into the velocity equation for the concentric cylinders. The resultant equation is tested against flow simulation results. A validity margin analysis is performed based on the variation of the mass flow rate between the cylinders. It is seen that the proposed model for eccentric cylinders is applicable for all gap distances, unlike the previous models that are restricted to narrow gaps. Finally, a separate formula to quantify the error in the estimates of the present method is also derived, which involves the ratio of the cylinders and the eccentricity.

Experimental Study of Cavitation Development and Secondary Circulation Flow between Two Eccentric Cylinders

The flow of a hydrophobic fluid in the gap between eccentric cylinders has been experimentally studied. The experimental setup was designed and built for this study. Experimental setup consists of two eccentric cylinders with the ability to rotate and a camera, a microscope, and a pressure sensor. The conditions for gaseous cavitation occurrence during the rotation of the outer cylinder was considered in this study. The discreteness of gaseous cavitation occurrence in the form of individual bubbles is shown. When cavitation bubbles merge, the charge is redistributed at the gas–liquid interface, and bubble luminescence is observed. It has been shown that near the surface of the inner cylinder, in the area of flow expansion and compression, reverse flows occur.

Mode characteristics of a graphene-coated cylindrical dielectric waveguide with a nested eccentric hollow elliptical cylinder

A cylindrical dielectric nanowire waveguide embedded with an eccentric hollow elliptical cylinder is designed. The mode characteristics of the first three modes supported by the waveguide are studied by the multipole method and verified by the finite element method. Results show that the waveguide has the best transmission performance when the symmetric center of the hollow elliptical cylinder is located on the y axis of the cylindrical dielectric nanowire. The influence of the working wavelength, the Fermi energy, and the dielectric constant of region II on the transmission performance of the waveguide is great, while the influence of the semi-long axis, the semi-short axis of the elliptic cylinder, the radius of the cylinder, and the minimum distance between two rods on the transmission performance of the waveguide is less. Compared with the other waveguide structures, the waveguide introduced in this paper has a better overall transmission performance. This kind of waveguide can provide a theoretical basis for the design, fabrication, and application of graphene-coated nested nanowire waveguides.

Dynamics of chiral liquid crystals between cylinders using Landau-de Gennes theory

ABSTRACT This study employs the Landau-de Gennes theory to investigate the behaviour of chiral liquid crystals (CLCs) between concentric and eccentric cylinders under different flow conditions. This theory was implemented in dynamic finite element simulations to solve the evolution of the microstructure of CLCs and couple it with linear momentum balance equation (modified Navier–Stokes equation) to capture the structure of CLCs. The study focused on the microstructure formation of CLCs and their performance as lubricants under various chirality strengths (θ), Deborah numbers (De), and eccentricity of eccentric cylinders. The hexagonal structure of the CLCs was found between cylinders at low De (0.001), where the chiral term predominates. Moreover, the number of hexagonal structures between cylinders was shown to be significantly correlated to the chiral strength. We showed that increasin De resulted in vanishing hexagonal pattern of CLCs and the De value at which the hexagonal pattern vanishes depends on the chiral strength. We also observed that a higher eccentricity ratio significantly increased the pressure force per length on the inner cylinders and caused more non-uniformity in the structure. Based on the findings, we concluded that the performance of CLCs as lubricants is greater at higher θ and eccentricity and lower De.

Heat transfer by oil natural convection in an annular space under combined effects of carbon nanotubes and electric field

In this study, the combined impact of carbon nanotube volume fractions and the electric field on the enhancement of dielectric oil heat transfer is investigated. The geometry studied is an annular layer filled with the dielectric oil and bounded by two eccentric or concentric cylinders. A temperature gradient and an electrical potential difference are applied between the two cylindrical walls. The goal is to analyse the flow behaviour and the heat transfer improvement using a double enhancement technique by combining an active (electric field) and passive (nanoparticles) approach. An in-house numerical simulation code using the finite volume method was developed to solve the set of coupled equations describing the conservation laws of the electro-thermo-hydrodynamic flow associated with the oil. A parametric study, outlining the influence of different relevant variables has been performed. The parameters investigated are the thermal Rayleigh number (2000 ≤ T ≤ 100 000), the electrical Rayleigh number (100 ≤ T ≤ 600), the radius ratio (0.1 ≤ Γ ≤ 0.9), the eccentricity (0 % ≤ e ≤ 90%), the nanotubes volume fraction (0 % ≤ Φ ≤ 0.5%)and the injection level (1 ≤ C ≤ 10) respectively. The effect of these variables on the heat transfer intensification is examined in detail. According to the adopted configuration, heat transfer intensifications between 3% and 77% have been recorded essentially when an electric field was applied. Also, the addition of a 0.5% volume fraction of carbon nanotubes provides a heat transfer improvement of around 27%. Furthermore, for a first time a multiparameter correlation has been developed. This correlation can be useful to better understand the impact of various physical parameters on the heat transfer in annular spaces and also to predict exact values of the Nusselt number.

Computational optimum design of natural convection in a concentric and eccentric annular cylinder using nanofluids

Free convection of various nanofluids inside concentric and eccentric annular cavity with internal heat flux, fully filled with porous media is studied numerically and its heat transfer rate and pressure drop are examined. The impact of inner cylinder inclination angles (βecc = 45°, 135°, 225°, and 270°) and nanofluids (Al2O3/water, CuO/water and SiO2/water) for different heat flux (1000, 2000, 3000, and 4000 w/m2) on the heat transfer rate are evaluated. Initially, a validation process has been implemented to ensure that the predicted results obtained from this model are accurate. Results indicate that Al2O3 Nanofluid provides a better enhancement in the heat transfer rate when compared to SiO2 and Cu Nanofluids. Furthermore, the heat transfer coefficient increased with the inclination angle of βecc = 225°, and maximum heat transfer occurred at a heat flux of 4000 W/m2, which was roughly 6% greater than the concentric annular cylinder. The findings also indicated that while increasing the eccentricity has a minor impact on the heat transfer rate for convection-dominated flows (high heat flux), on the other hand, it has a significant impact on the heat transfer rate for conduction-dominated flows (low heat flux).

Perturbation Solution for Anisotropic Circular Waveguides Loaded With Eccentric Rods

A perturbation method is developed for the analysis of anisotropic circular waveguides partially filled with eccentric cylinders. The method allows to compute axial wavenumbers and field patterns for hybrid modes supported in waveguides with small eccentricities via a perturbation series. The proposed method is validated against analytical results and numerical results based on the finite-element method (FEM) and the finite-integration technique (FIT) in different configurations. The results show that the presented approach can solve, for example, the longitudinal wavenumbers of anisotropic waveguides with an eccentricity of 23% with a relative error less than 1.78% at a much lower computational cost when compared to numerical techniques.

Eccentric High-Force Soft Pneumatic Bending Actuator for Finger-Type Soft Grippers

Abstract Soft pneumatic actuators (SPAs) play an important role in leading the development of soft robotics. However, due to the inherent characteristics of soft materials, the low driving force limits the application of SPAs. This study presents a high-force soft pneumatic bending actuator (SPBA) that consists of a spring, an eccentric silicone cylinder, and a limiting fiber. Based on the Neo-Hookean model, a theoretical model is established to predict the relationship between the bending angle and the pressure of SPBA. Furthermore, we characterize the performance of SPBA in terms of the bending capability, tip force, as well as response time. The results demonstrate the effectiveness of the theoretical model, as well as the high tip force (10.2 N) and fast response capability of SPBA. Finally, SPBAs are used to construct a three-finger soft gripper. The load capacity of the gripper is proofed, which indicates that the gripping force of the gripper increases with the pressure of the fingers and the diameter of the object. The gripping test of the gripper is performed. The result shows that the gripper with the pinching mode can grip objects of various sizes and shapes in the air and underwater, and the gripper with enveloping mode can grip objects with weight up to 1.25 kg.