TRANSIENT THERMOELASTIC CONTACT PROBLEM IN A LONG,CIRCULAR CYLINDER

This paper treats a transient thermoelastic contact problem in a long, circular cylinder to which a heated rigid band is bonded. The problem may be reduced to that of solving dual-integral equations. The radial, hoop, and axial stresses have singularities at the end of rigid band on the cylindrical surface. The coefficients which may determine the strength of singularities of stresses are introduced.     

COUPLED THERMOELASTIC ANALYSIS OF PERFECT ROLLING CONTACT: SOLUTION BEHAVIOR NEAR YIELD INITIATION

An insulated rigid cylinder of infinite length rolls without slip on a half-space at constant rolling speed. The equations of coupled thermoelasticity in the dynamic steady state hold. The analytical solution for the mixed boundary-value problem is extracted from robust asymptotic versions of exact integral transforms. The solution, in turn, gives contact zone size and location, and temperature change and von Mises yield function on the contact zone. The function exhibits a maximum at the contact zone center, which is above the location of its maximum in the half-space. For some insight into behavior near yield initiation, therefore, contact zone center yield is used to derive expressions for the corresponding contact zone size, compressive load on the cylinder, and zone temperature increase. Calculations for 4340 steel indicate that initiation is multi-axial and that mild temperature increases occur. In addition, the contact zone center, which corresponds to the contact point in the rigid–rigid limit, is found to have a small tangential speed. The rolling speed is allowed to take any value between zero and the thermoelastic Rayleigh speed. This range perhaps exceeds that required in applications, but allows a clearer view of variation with rolling speed.     

Inverse Problem of a Piezothermoelastic Cylinder Subject to Transient Heating

An inverse problem of a radially polarized piezoelectric hollow circular cylinder of crystal class 6 mm is investigated. It is assumed that a voltage induced by the action of a time-varying temperature applied to the inner surface of the cylinder is measured on the outer surface. The inverse problem entails a determination of the heating temperature from knowledge of the measured voltage. First, an exact solution to the problem is found by solving the equations of equilibrium and electrostatics for the cylinder subject to the prescribed boundary conditions. Then a least-squares residual method that incorporates Lagrange multipliers for satisfaction of the boundary equations is employed to derive an approximate analytic solution. Both formulations are utilized in order to calculate the unknown heating temperature, and the corresponding temperature, displacement and stress fields in a cylinder of cadmium selenide. Numerical results based upon the least-squares residual formulation are found to compare favorably with those obtained by the exact analysis.     

Thermal stress intensity factors for a cracked cylinder under transient thermal loading

Transient thermal stress intensity factors are calculated at the deepest and the surface points of an internal axial semi-elliptical surface crack in a thick-walled cylinder under thermal shock. The method of calculation is based on the weight function and an effective procedure of integrating of the weight integrals. Time-dependent thermal boundary conditions are assumed to act on the inner surface of the pressurized cylinder. Exact analytical solutions are derived for the weight function, and then integrated to compute transient thermal stress intensity factors. In the special case of a steady state problem and also the pressurized cylinder, the results show to be in accordance with those cited in the literature.     

CIRCUMFERENTIAL CRACK PROBLEM FOR AN FGM CYLINDER UNDER THERMAL STRESSES

The main objective of this study is to determine the stress intensity factors associated with a circumferential crack in a thin-walled cylinder subjected to quasi-static thermal loading. The cylinder is assumed to be a functionally graded material. In order to make the problem analytically tractable, the thin-walled cylinder is modeled as a layer on an elastic foundation whose thermal and mechanical properties are exponential functions of the thickness coordinate. Hence a plane strain crack problem is obtained. First temperature and thermal stress distributions for a crack-free layer are determined. Then using these solutions, the crack problem is reduced to a local perturbation problem where the only nonzero loads are the crack surface tractions. Both internal and edge cracks are considered. Stress intensity factors are computed as functions of crack geometry, material properties, and time.     

Natural convection boundary layer on a horizontal elliptical cylinder with constant heat flux and internal heat generation

In this paper the natural convection boundary layer on a horizontal elliptical cylinder with constant heat flux and temperature dependent internal heat generation is investigated. The mathematical problem is reduced to a pair of coupled partial differential equations for the temperature and the stream function, and the resulting nonlinear equations are solved numerically by cubic spline collocation method. Results for the local Nusselt number and the local skin-friction coefficient are presented as functions of eccentric angle for various values of heat generation parameters, Prandtl numbers and aspect ratios. An increase in the aspect ratio of the elliptical cylinder decreases the average surface temperature of the elliptical cylinder with blunt orientation, while it increases the average surface temperature of the elliptical cylinder with slender orientation. Moreover, an increase in the heat generation parameter for natural convection flow over a horizontal elliptic cylinder with constant heat flux leads to an increase in the average surface temperature of the elliptical cylinder.     

THREE-DIMENSIONAL TRANSIENT THERMAL STRESSES IN A FINITE CIRCULAR CYLINDER UNDER NONAXISYMMETRIC TEMPERATURE DISTRIBUTION

A general analysis is developed for the complete three-dimensional transient thermal-stress distribution in a finite circular cylinder subject to arbitrary heating of the lateral surface with arbitrary heat transfer into the surrounding medium. The problem is formulated in terms of the modified Boussinesq functions and the thermoelastic displacement potential, which seem convenient in form and have the advantage of being applicable to non-axisymmetric problems. The solution meets the tractionfree boundary conditions on both the lateral surface and the plane ends of the cylinder. Graphical illustrations are provided.     

Transient Thermoelastic Analysis of a Solid Cylinder Containing a Circumferential Crack Using the C–V Heat Conduction Model

This article presents the transient thermoelastic analysis in a long solid cylinder with a circumferential crack using the C–V heat conduction theory. The outer surface of the cylinder is subjected to a sudden temperature change. The Laplace transform technique is adopted to solve the one-dimensional hyperbolic heat conduction equation, and the axial thermal stress is obtained for the un-cracked cylinder in the Laplace domain. Then this axial thermal stress with a minus sign is applied to the crack surface to form a mixed boundary value problem in the cylindrical coordinate system. A singular integral equation is derived by applying the Fourier and Hankel transforms to solve the mode I crack problem. The transient thermal stress intensity factors are obtained by solving the singular integral equation numerically. The influences of thermal relaxation time, crack geometry, and Biot's number upon transient temperature distributions, axial stress fields, and stress intensity factors are analyzed.     

Experimental and numerical study of the natural convection from a heated horizontal cylinder

Natural convection heat transfer from a horizontal cylinder is studied experimentally and numerically. Experimental study had taken place in different environmental temperature in a conditioned room which can be maintained at a stable required value and inside a sufficiently designed test cabin. The environmental and cylinder surface temperatures varied between 10 °C–40 °C and 20 °C–60 °C respectively. In the experimental study, two cylinders having different diameters of 4.8 mm–9.45 mm are used and constant heat flux was applied. On the basis of the experimental data, a correlation for the average Nusselt number over the cylinder is proposed in the range of 7.4 10¹ < Ra < 3.4 10³. The proposed correlation is compared with the well known correlations on natural convection heat transfer from a horizontal cylinder in the specified range of Rayleigh number, and it is shown that the results are in satisfactory agreement. The problem is also investigated numerically. The experimental data and the numerical results fall in ± 20% band. The numerical results obtained in this study are also compared with the results of Merkin. The characteristics of trend lines are similar.     

Thermal fracture of cracked cylinders associated with nonclassical heat conduction: The effect of material property

The thermoelastic problem of a transversely isotropic hollow cylinder containing a circumferential crack is investigated in the present article based on the non-Fourier heat conduction theory. The temperature and stress fields are obtained by solving the coupled partial differential equations in the Laplace domain, and corresponding thermal axial stress with minus sign is then applied to the crack surface to form a mode I crack problem. Three different kinds of crack are considered, and the singular integral equation method is adopted to solve the fracture problem. Finally, with the definition of stress intensity factor, the effect of material properties, coupling parameter, and crack geometry on the hyperbolic thermal fracture responses of a transversely isotropic hollow cylinder excited by a thermal loading is visualized.     

Inverse problem on the identification of temperature and thermal stresses in an FGM hollow cylinder by the surface displacements

A problem on the identification of time-dependent temperature on one of the limiting surfaces of a radially inhomogeneous hollow cylinder is formulated and solved under the temperature and radial displacement given on the other limiting surface. The analysis of temperature and thermal stress distribution in the cylinder is performed. The solution has been constructed by the reduction to an inverse thermoelasticity problem. By making use of the finite difference method, a stable solution algorithm is suggested for the analysis of inverse problem. The solution technique is verified numerically by making use of the solution to a relevant direct problem. It is shown that the proposed technique can be e?ciently used for the identification of a heat flux or unknown parameters (the surrounding temperature or the heat-exchange coe?cient) in the third-kind boundary conditions.     

Steady mixed convection in a differentially heated square enclosure with an active rotating circular cylinder

Mixed convection in a square enclosure with a rotating cylinder centered within it is numerically studied. Depending on the rotation of the cylinder, the natural and forced convection effects can be combined or opposite. However, due to the complex flow structure assumed by the flow, in some conditions the combined effects do not lead to the maximum overall heat transfer crossing the enclosure. The rotating cylinder participates on both the conductive and convective heat transfer processes, and exchanges heat with the fluid naturally, without imposition of a thermal condition at its surface. It is explored the influence of the cylinder through its radius, rotating velocity, thermal conductivity and thermal capacity on the resulting mixed convection problem. Thermal field is visualized using the isotherms, the flow structure is visualized through the streamlines, and the heat transfer process is visualized through the heatlines. For the first time, these visualization tools are applied to a moving solid. The overall thermal performance of the enclosure is analyzed through the overall Nusselt number. For a better understanding of the participation of the cylinder on the heat transfer process, the local heat exchanged between the cylinder surface and the fluid is also analyzed. Results clearly show how the rotating cylinder affects the thermal performance of the enclosure, and how the thermophysical properties of the cylinder are important on the overall heat transfer process across the enclosure.     

Inverse Transient Heat Conduction Problems of a Multilayered Functionally Graded Cylinder

Inverse transient heat conduction problems of a multilayered functionally graded (FG) cylinder are presented. The approach is based on measurement of temperature on the outer surface of the cylinder to estimate the heat flux and convection heat transfer coefficient on its inner surface. The non-Fourier heat transfer equation is employed to accurately formulate the problem. The conjugate gradient method (CGM) is used for the optimization procedure and the incremental differential quadrature method (DQM) is applied to solve the direct, sensitivity, and adjoint problems. The accuracy of the presented approach is examined by simulating the exact and noisy data through different examples. Good accuracy of the obtained results validates the presented approach.     

柴油机气缸盖振动信号特征提取方法的研究

研究了基于短时AR分析、小波多分辨率分析和小波包分析的故障特征提取和识别方法,分析了柴油机气缸盖振动信号特征提取方法。得出了两条重要结论:基于短时AR分析的柴油机气缸盖振动信号整循环特征提取方法特别适合于短序列数据的分析;利用小波多分辨率分析和小波包分析以及Kllback-Leibler信息量最小,对柴油机表面振动信号进行分解与分析,确定各故障状态的特征频带,进而可用频带的时间序列的时序模型作为特征矢量,实现对柴油机运行状态故障的诊断。     

Experimental and numerical study of the natural convection from a heated horizontal cylinder wrapped with a layer of textile material

Natural convection heat transfer enhancement from a horizontal cylinder with a textile coating is studied experimentally and numerically. The coating layer may be used for two purposes. According to the thickness of the coating it may be used as an insulating material or for surface augmentation. In the experimental study, two cylinders having different diameters of 4.8 mm and 9.45 mm are used. The bare cylinders having a radius smaller than a certain critical size were wrapped with a textile material. Wrapped cylinder diameters were increased to 9 and 12.8 mm respectively after coating and constant heat flux was applied to all bare and wrapped cylinders. Experimental study was carried out at different ambient temperatures in a conditioned room which can be maintained at a stable required value and inside a sufficiently designed test cabin. The ambient and cylinder surface temperatures (T_∞ and T_w) varied between 10 °C – 40 °C and 20 °C – 60 °C respectively. Heat transfer rates from bare and wrapped horizontal cylinders were compared and heat transfer enhancement was observed. On the basis of the experimental data average Nusselt numbers were calculated and compared with the well known correlations on natural convection heat transfer from a horizontal cylinder in the specified range of Rayleigh number, and it is seen that the results are in good agreement. The problem is also investigated numerically. Experimental and the numerical results fall in ± 30% band.     

Estimation of heat flux on the surface of an initially hot cylinder cooled by a laminar confined impinging jet

In this study, an inverse algorithm based on the conjugate gradient method and the discrepancy principle is applied to estimate the unknown space-and time-dependent heat flux at the surface of an initially hot cylinder cooled by a laminar confined slot impinging jet from the knowledge of temperature measurements taken on the cylinder’s surface. It is assumed that no prior information is available on the functional form of the unknown heat flux; hence the procedure is classified as the function estimation in inverse calculation. The temperature data obtained from the direct problem are used to simulate the temperature measurements, and the effect of the errors in these measurements upon the precision of the estimated results is also considered. The results show that an excellent estimation on the space-and time-dependent heat flux can be obtained even the distributions of thermal properties inside the cylinder is unknown.     

Interaction between surface mass transfer and transverse curvature in natural convection boundary layersBзaимoдeиcтвиe мeздy пepeNocoм мaccы Na пoвepчNocти и пoпepeчNoи кpивизNoи в ecтecтвeNNoкoNвeктивNыч пoгpaNичNыч cлoяч

The heat transfer characteristics for natural convection about an isothermal vertical cylinder with surface mass transfer (blowing or suction) have been determined by analysis. The problem was formulated by applying the local nonsimilarity method, and solutions were obtained by a numerical scheme which employs integrated forms of the governing differential equations. Numerical solutions were carried out for a wide range of values of parameters which respectively characterize the transverse curvature of the cylinder and the magnitude and sign of the surface mass transfer. The Prandtl number was varied between 0.01 and 10. It was found that the local Nusselt numbers for a vertical cylinder are less sensitive to surface mass transfer than are those for a vertical plate. The sensitivity of both the cylinder and the plate Nusselt numbers to the mass transfer is diminished at low Prandtl numbers and increased at high Prandtl numbers.     

Fluent关于刚性植被尾流区两种数值模拟方法对比

为探究Fluent中更加有效的刚性植被尾流区模拟方法.基于已有试验数据,对比Fluent在模拟刚性植被时两种模拟方法(细圆柱群模型和多孔介质模型)的差异。结果表明,二维刚性植被尾流区模拟中,在待模型稳定时间可忽略不计的情况下综合前处理、模拟情况对比,多孔介质模型更加高效便捷、模拟效果更好。     

CONJUGATE NATURAL CONVECTION FROM A HORIZONTAL CIRCULAR CYLINDER

ABSTRACT

Steady, laminar natural convection flow from a horizontal circular cylinder with a heated core region has been theoretically analyzed by taking account of the thermal conduction of the core region. The problem is conjugate, and the main focus of the study is to examine the effect of conduction in the core region on the natural convection flow from the cylinder. The governing equations were solved numerically using a finite difference technique. The effects of various parameters are presented in graphical form. Approximate solutions for the average boundary temperature at the surface of the cylinder and for the average Nusselt number are also found. In the parametric range investigated, both the theoretical and numerical results predict nearly the same values for the average boundary temperature at the surface of the cylinder and the same values for the average Nusselt number, showing the validity of the present analysis.