Cylindrical Solids Research Articles

Numerical analysis of transient MHD natural convection in a channel with four heat-generating cylindrical solids filled with in a non-Newtonian Fe3O4 ferrofluid

This article presents a numerical investigation and analysis of the cooling effectiveness of thermomagnetic transient natural convection in a long channel, equipped with four cylindrical heat-generating blocks. A non-Newtonian power-law ferrofluid was employed for the present investigation to achieve optimum cooling. The governing equations are the continuity equation, the momentum equation and the energy equation. The finite volume method was used to solve the resulting algebraic system. From an energy-saving point of view, this configuration can provide a good approximation for selecting effective physical and geometrical parameters to design a reliable thermal system. For this purpose, the study was carried out for various geometric and thermophysical parameters. Different values of thermal conductivity, power law index, Rayleigh number, Hartmann number and ferrofluid volume fraction, were considered. The results are illustrated in the form of streamlines, isotherms, average Nusselt and a spatio-temporal characterization of the mean ferrofluid velocity. From the results presented, we can conclude that the choice of non-Newtonian, pseudoplastic ferrofluid with a low thermal conductivity ratio subjected to a uniform magnetic field proves to be a crucial solution for efficient and stable cooling of heat-generating cylindrical blocks, which will have to be close to the cold walls of the channel.

Exceptional points in cylindrical elastic media with radiation loss

Exceptional points (EPs) are singular points on a parameter space at which some eigenvalues (scattering poles) and their corresponding eigenmodes coalesce. This study shows the existence of second- and third-order EPs in cylindrical elastic systems with radiation loss. We consider multilayered cylindrical solids under the plane-strain condition placed in a background elastic or acoustic medium. Elastic and acoustic waves propagating in the background media are subject to the radiation loss. We optimize the radii and the material constants of the multilayered solids, such that some scattering poles coalesce on the complex frequency plane. Some numerical experiments are performed to confirm that the coalescence originates from EPs. We expect that this study provides a new approach for enhancing mechanical sensors.

On critical value for surface tension-driven instability of a soft composite cylinder

Inspired by recent researches on the critical value for surface tension-driven instability of soft cylindrical solids characterized by infinite axial wavelength, the present work studies the existence of axially uniform non-zero solutions of the homogeneous problem of a composite cylinder with surface/interface tensions. The critical condition is examined for several cases of major interest based on linear elastic models with two different versions of surface/interface conditions. It is shown that the critical values for surface tension-driven instability of cylindrical solids reported in recent literature for several cases of major interest can be recovered by the present analysis of axially uniform axisymmetric solutions of a composite cylinder within the framework of generalized plane strain. In particular, the present analysis confirms that the critical values derived based on the two different versions of surface/interface conditions can be drastically different, and this discrepancy between different theoretical models deserves further investigation.

Temperature evolution on infinite/finite-length cylindrical solids subjected to reciprocating motion heat source

This work presents a physics-based predictive model for temperature rise in cylindrical solids heated by constant-strength, periodic-motion heat source. The heat source motion path, heat transfer boundary conditions and solid dimension are considered in the theoretical model. Analytical solutions to both the infinite or finite length cylinders are constructed with respect to convection and corresponding boundary conditions. Dimensionless controlling parameters are discussed to reveal temperature field evolution. The predicted results in the temperature rise agreed well with the measured data for a Z-direction feeding drive screw shaft system. The proposed model provides an efficient and accurate design tool for engineering calculation and process-parameter planning through inverse analysis.

Steady‐state estimation of thermal contact conductance between sliding disk and stationary cylinder with similar/dissimilar materials under the isothermally heated boundary condition

AbstractAn accurate understanding of the thermal contact conductance (TCC) is imperative for the enhancement of the performance and service life of metallic cylindrical joints. However, the evaluation of the TCC between conforming cylindrical solids is quite intricate, as it depends on the temperature, pressure, roughness, relative sliding speed, and thermophysical properties of solids. Instead of generating contacting surfaces stochastically, in this communication, an experimental setup in the lab‐scale consisting of a stationary cylinder and a sliding hot disk has been fabricated in which temporal evolutions of the temperature on both solids are recorded by thermocouples. Effects of the disk temperature and relative sliding speed on the steady‐state TCC have been investigated. There is a cylindrical interface between two conforming smooth solids of similar/dissimilar materials. As there is the differential expansion of cylindrical solids due to the temperature gradient, the diameter of sliding disks has been truncated to fix the radial gap (contact pressure). Inverse solution with the conjugate gradient method along with the adjoint problem has been applied to estimate the steady‐state TCC. One‐dimensional heat transfer analysis shows that frictional heating is negligible. The steady‐state TCC is almost constant longitudinally along the axis of the steel cylinder. Under identical initial and isothermally heated boundary conditions, the TCC between the aluminum disk and cylinder is higher than that between steel disk and cylinder. Also, the TCC has been increased with a rising slope when the working temperature is enhanced. However, the augmentation of the relative sliding speed engenders a decreasing slope in the TCC graph.

Исследование динамических эффектов при микромасштабном импульсном нагружении

Рассматривается осесимметричная задача облучения тепловым импульсом цилиндрического тела. Для описания нелинейного поведения материала используется модель Боднера-Партома, обобщенная на случай многофазового состава материала. Сущность обобщения заключается в использовании правила смесей для определения параметров модели, отвечающих за предел текучести и временное сопротивление. Рассмотренная модель позволяет более точно оценить остаточное напряженно-деформированное состояние, которое при дальнейшей эксплуатационной нагрузке цилиндрических деталей существенно влияет на временное сопротивление элементов конструкций. Задача решается численно методом пошагового неявного интегрирования по времени, итерационным методом и методом конечных элементов. На каждом временном шаге реализуется двойной итерационный процесс. Первый – внутренний – связан с интегрированием системы нелинейных уравнений течения, второй – внешний – с решением уравнений движения и теплопроводности. Расчеты проводятся для конечно-элементной сетки, сгущенной в области облучения, для более точного моделирования термомеханического поведения материала. Параметры сетки выбираются по критерию практической сходимости решений. На основе численного моделирования исследуется напряженно деформированное состояние неупругого материала при учете зависимости параметров модели от фазового состава материала. Основной результат: установлены качественные и количественные эффекты влияния фазового состава на неупругие характеристики; изменение растягивающих остаточных напряжений на сжимающие. Полученные результаты могут использоваться в инженерных расчетах на прочность элементов конструкций, а также параметров технологий поверхностного укрепления.

INFLUENCE OF IMPERFECT THERMAL CONTACT ON HEAT EXCHANGE IN THE SYSTEM OF MULTILAYER CYLINDRICAL BODIES

Introduction. Solving the problem of heat transfer in multilayer structures devoted a large number of works. The vast majority of them are limited to the case of perfect thermal contact between the layers. However, according to the authors, the problems of thermal conductivity in multilayer structures using into account the imperfect thermal contact are insufficiently studied. The number of such studies is quite limited. Also, known studies are usually limited to two layers. That is because the increase in the number of layers (given the choice of methods of practical implementation) leads to several computational difficulties. Therefore, the problem of constructing an effective analytical scheme for the study of heat transfer processes in multilayer structures in the presence of imperfect thermal contact between the layers remains an urgent task.Purpose. Application of the direct method to the study of heat transfer processes in the system "continuous cylinder inside a multilayer cylindrical shell" with imperfect thermal contact.Methods. An auxiliary problem set for the distribution of the temperature field in a multilayer solid cylindrical hollow body (a cylinder of the sufficiently small radius is "removed") taking into account the imperfect thermal contact between the individual layers. According to the already known scheme of the direct method solve this problem.Results. Boundary transition obtained the solution of the original problem. Boundary transition: the radius of the"removed" cylinder, with the centre at the origin, goes to zero. This approach established that the solution to the problemis limited in the whole structure. In this case, the solution obtained explicit formulas.Conclusions. Effective analytical scheme constructed for application of the direct method to the study of heattransfer processes in multilayer hard cylindrical solids taking into account the non-ideal thermal contact between thelayers. The number of layers, their size and arrangement are considered arbitrary.

Quantitative photothermal lock-in thermography imaging of curved surfaces of cylindrical solids

We extend the applications of photothermal radiometric diagnostics to continuously curved cylindrical surface solids using lock-in thermography (LIT) imaging, in which both the photothermally induced surface temperature and the angularly dependent infrared radiation emitted by the curved surface are not constant. Specifically, a theoretical photothermal model is established based on the Green Function method from which the thermal-wave field distribution at different azimuthal angles on the curved surface is obtained and characteristics of the thermal-wave field with different material and measurement parameters/schemes are discussed. A laser-infrared photothermal lock-in imaging system for solid cylindrical samples is established, and the thermal diffusivity of AISI 304 cylindrical steel samples is measured directly based on the LIT images combined with empirically obtained infrared radiation angular distributions over the curved surfaces. The experimental results are in excellent agreement with the theory, which provides a fast and non-destructive quantitative tool for thermophysical evaluation of curved surface solids.

Mathematical modelling of the process of internal technological stress fields development in cylindrical solids being layer-by-layer made of ageing viscoelastic materials

With the help of current approaches in mechanics of additively manufactured deformable solids, a non-classical mathematical model is developed to predict the stress-strain state of layers being gradually formed on a rotating substrate in an arbitrary number of continuous stages of ageing viscoelastic material application. On the basis of numerous calculations performed, the qualitative and quantitative features of the internal technological stresses distributions in the finished cylindrical product for different variants of its release from the mechanical loading and the kinematic bonds acting during the manufacturing process are analyzed in detail. Previously unknown mechanical effects are found. The appropriate recommendations of a practical nature are given.

Ultrasonic Scattered Field Distribution of One and Two Cylindrical Solids with Phased Array Technique

The scattered fields of plane waves in a solid from a cylinder or sphere are critical in determining its acoustic characteristics as well as in engineering applications. This paper investigates the scattered field distributions of different incident waves created by elastic cylinders embedded in an elastic isotropic medium. Scattered waves, including longitudinal and transverse waves both inside and outside the cylinder, are described with specific modalities under an incident plane wave. A model with a scatterer embedded in a structural steel matrix and filled with aluminum is developed for comparison with the theoretical solution. The frequency of the plane wave ranged from 235 kHz to 2348 kHz, which corresponds to scaling factors from 0.5 to 5. Scattered field distributions in matrix materials blocked by an elastic cylindrical solid have been obtained by simulation or calculated using existing parameters. The simulation results are in good agreement with the theoretical solution, which supports the correctness of the simulation analysis. Furthermore, ultrasonic phased arrays are used to study scattered fields by changing the characteristics of the incident wave. On this foundation, a partial preliminary study of the scattered field distribution of double cylinders in a solid has been carried out, and the scattered field distribution at a given distance has been found to exhibit particular behaviors at different moments. Further studies on directivities and scattered fields are expected to improve the quantification of scattered images in isotropic solid materials by the phased array technique.

Response to Dr Greenwood\u2019s Comments on \u201cExtending the Double-Hertz Model to Allow Modeling of an Adhesive Elliptical Contact\u201d

© 2018, The Author(s). An adhesive elliptical contact is normally found in microscale applications that involve cylindrical solids, crossing at an angle between 0° and 90°. Currently, only one model is available to describe the elliptical contact’s surface interaction: the approximate Johnson–Kendall–Roberts (JKR) model which is limited to soft materials. In this paper, a new adhesive elliptical model is developed for a wide range of adhesive contacts by extending the double-Hertz theory, where adhesion is modeled by the difference between two Hertzian pressure distributions. Both Hertzian pressures are assumed to have an equivalent shape of contact areas, the only difference being in size. Assuming that the annular adhesive region is obtained by the area difference between the two Hertzian contact areas, the pull-off force curves can be calculated. In the limiting case of an adhesive circular contact, the results are very close to results from the existing models. However, for an adhesive elliptical contact in the JKR domain, lower pull-off forces are predicted when compared to the JKR values. Unlike the developed model, the shape of the JKR contact area varies throughout contact. Results show, particularly for conditions close to the JKR domain, that it is important to take into account that the adhesive region is the result of the two Hertzian contact areas having a non-equivalent shape.

EHD Effects in Lubricated Journal Bearing

This paper presents a numerical analysis of the influence of deformation of infinite parallel cylindrical solids in partial journal bearing on the oil film characteristics. The stationary elastohydrodynamic EHD problems for three design models of bearings are considered: (1) The bearing in which the basic contribution to the elastic displacement of the surface brings the thin elastic liner; (2) The elastic cylinder and the elastic bushing which is modeled by the elastic space with a cylindrical cut; (3) The elastic cylinder and the elastic bushing in the presence of the thin elastic liner with a small module of elasticity. It is shown that when the minimum film thickness is fixed and deformations of the elastic solids increase, then the load capacity increases, reaches a maximum, and then decreases. The deformation of solids can raise load capacity many times over. When the deformation of solids increases from zero, the pressure distribution changes from the distribution of pressure in the case of rigid bodies to the distribution of pressure which takes place with the dry contact of elastic bodies.

Extending the Double-Hertz Model to Allow Modeling of an Adhesive Elliptical Contact

An adhesive elliptical contact is normally found in microscale applications that involve cylindrical solids, crossing at an angle between 0° and 90°. Currently, only one model is available to describe the elliptical contact’s surface interaction: the approximate Johnson–Kendall–Roberts (JKR) model which is limited to soft materials. In this paper, a new adhesive elliptical model is developed for a wide range of adhesive contacts by extending the double-Hertz theory, where adhesion is modeled by the difference between two Hertzian pressure distributions. Both Hertzian pressures are assumed to have an equivalent shape of contact areas, the only difference being in size. Assuming that the annular adhesive region is obtained by the area difference between the two Hertzian contact areas, the pull-off force curves can be calculated. In the limiting case of an adhesive circular contact, the results are very close to results from the existing models. However, for an adhesive elliptical contact in the JKR domain, lower pull-off forces are predicted when compared to the JKR values. Unlike the developed model, the shape of the JKR contact area varies throughout contact. Results show, particularly for conditions close to the JKR domain, that it is important to take into account that the adhesive region is the result of the two Hertzian contact areas having a non-equivalent shape.

Nonlinear mechanics of surface growth for cylindrical and spherical elastic bodies

In this paper we formulate the initial-boundary value problems of accreting cylindrical and spherical nonlinear elastic solids in a geometric framework. It is assumed that the body grows as a result of addition of new (stress-free or pre-stressed) material on part of its boundary. We construct Riemannian material manifolds for a growing body with metrics explicitly depending on the history of applied external loads and deformation during accretion and the growth velocity. We numerically solve the governing equilibrium equations in the case of neo-Hookean solids and compare the accretion and residual stresses with those calculated using the linear mechanics of surface growth.

Experimental investigation of convective heat exchange in chamber furnaces at heat treatment of cylindrical solids

In this paper, the process of convective heat exchange between the cooling air and the cylindrical solid is experimentally studied in a chamber furnace at double-sided cross-flow around the solid, and the corresponding criterial equation is obtained.

Cylindrical Rayleigh surface waves on a layer-coated cylinder measured by PVDF transducer and defocusing measurement method

This paper develops a measurement method for accurately determining dispersion curves of Rayleigh-type surface waves propagating on layer-coated elastic cylinders. It utilizes PVDF acoustic transducers and a defocusing measurement system. To deal with the cylindrically curved surface, a new cross-correlation waveform processing approach is proposed and verified. Cylindrical Rayleigh wave velocities of layered cylindrical solid samples have been successfully measured over a frequency range from 3 to 20MHz. The measured dispersion curves are in good agreement with their theoretical counterparts. It demonstrates the potential application for non-destructive evaluation of coating layers deposited on cylindrical solids.

Physical characterization of meso-erythritol as a crystalline bulking agent for freeze-dried formulations.

The purpose of this study was to identify and characterize new crystalline bulking agents applicable to freeze-dried pharmaceuticals. Thermal analysis of heat-melt sugar and sugar alcohol solids as well as their frozen aqueous solutions showed high crystallization propensity of meso-erythritol and D-mannitol. Experimental freeze-drying of the aqueous meso-erythritol solutions after their cooling by two different methods (shelf-ramp cooling and immersion of vials into liquid nitrogen) resulted in cylindrical crystalline solids that varied in appearance and microscopic structure. Powder X-ray diffraction and thermal analysis indicated different crystallization processes of meso-erythritol depending on the extent of cooling. Cooling of the frozen meso-erythritol solutions at temperatures lower than their Tg' (glass transition temperature of maximally freeze-concentrated phase, -59.7°C) induced a greater number of nuclei in the highly concentrated solute phase. Growth of multiple meso-erythritol anhydride crystals at around -40°C explains the powder-like fine surface texture of the solids dried after their immersion in liquid nitrogen. Contrarily, shelf-ramp cooling of the frozen solution down to -40°C induced an extensive growth of the solute crystal from a small number of nuclei, leading to scale-like patterns in the dried solids. An early transition of the freezing step into primary drying induced collapse of the non-crystalline region in the cakes. Appropriate process control should enable the use of meso-erythritol as an alternative crystalline bulking agent in freeze-dried formulations.

Shear adhesion strength of aligned electrospun nanofibers.

Inspiration from nature such as insects' foot hairs motivates scientists to fabricate nanoscale cylindrical solids that allow tens of millions of contact points per unit area with material substrates. In this paper, we present a simple yet robust method for fabricating directionally sensitive shear adhesive laminates. By using aligned electrospun nylon-6, we create dry adhesives, as a succession of our previous work on measuring adhesion energies between two single free-standing electrospun polymer fibers in cross-cylinder geometry, randomly oriented membranes and substrate, and peel forces between aligned fibers and substrate. The synthetic aligned cylindrical solids in this study are electrically insulating and show a maximal Mode II shear adhesion strength of 27 N/cm(2) on a glass slide. This measured value, for the purpose of comparison, is 270% of that reported from gecko feet. The Mode II shear adhesion strength, based on a commonly known "dead-weight" test, is 97-fold greater than the Mode I (normal) adhesion strength of the same. The data indicate a strong shear binding on and easy normal lifting off. Anisotropic adhesion (Mode II/Mode I) is pronounced. The size and surface boundary effects, crystallinity, and bending stiffness of fibers are used to understand these electrospun nanofibers, which vastly differ from otherwise known adhesive technologies. The anisotropic strength distribution is attributed to a decreasing fiber diameter and an optimized laminate thickness, which, in turn, influences the bending stiffness and solid-state "wettability" of points of contact between nanofibers and surface asperities.

Comparative Study of Thermal-Wave Fields in Bi-layered Semi-cylindrical and Fully Cylindrical Solids

A theoretical model for characterizing two-layered semi-cylindrical solid samples illuminated with a modulated incident beam on a curved surface using the Green function method is developed. The analytical expression for the thermal-wave (TW) field in such a semi-cylindrical sample is presented. Based on the model, characteristics of the TW field are simulated with different parameters, and comparisons with the whole cylinder model are conducted. It is found that TW properties of semi- and full cylinders show significant differences, especially in the low frequency range. Preliminary experimental validation is also presented with semi-cylindrical samples. The model provides a theoretical basis to quantitatively characterize semi-cylindrical samples using the TW method in a noncontact and nondestructive way.

A method to estimate anisotropic diffusion coefficients for cylindrical solids: Application to the drying of carrot

In this study, a method to estimate water diffusivity in axial, radial and angular directions during drying of anisotropic cylindrical solids is proposed. The method is based on the analytical solution for non-steady state mass transfer equation in products shaped as longitudinal sections of finite anisotropic cylinders. A sequential approach is applied where radial and axial diffusion coefficients are first estimated from drying curves of whole cylinders with increasing height, while angular diffusivity is obtained thereafter from drying experiments carried out with longitudinal sections of fixed-height cylinders varying cut angle. Developed theory was applied to the analysis of two sets of convective drying data of carrot obtained at 80°C with an air velocity of 2m/s. The first experiment set was conducted with carrot cylinders of 2.2cm diameter and heights of 1, 2,…,10cm, while cylinders in the second set were longitudinally cut as halves, quarters, sixths and eighths with a constant height of 10cm. Under such experimental conditions, identified water diffusivities were in the range of 0.53–2.93×10−9m2/s. Differences in water diffusivity for studied mass transfer directions were significant (p<0.05), with SEM images revealing structural differences between longitudinal and transversal product cuts, thus further supporting numerical results. Present findings suggest that, depending on product, anisotropic diffusion should be included in drying modeling in order to obtain an accurate process description.