The dynamic response and perturbation of magnetic field vector of orthotropic cylinders under various shock loads

In this paper, an analytical method is introduced to solve the problem for the dynamic stress-focusing and centred-effect of perturbation of the magnetic field vector in orthotropic cylinders under thermal and mechanical shock loads. Analytical expressions for the dynamic stresses and the perturbation of the magnetic field vector are obtained by means of finite Hankel transforms and Laplace transforms. The response histories of dynamic stresses and the perturbation of the field vector are also obtained. In practical examples, the dynamic focusing effect on both magnetoelastic stress and perturbation of the axial magnetic field vector in an orthotropic cylinder subjected to various shock loads is presented and discussed.     

Theoretical and finite-element modeling of autofrettage process in strain-hardening thick-walled cylinders

The optimum autofrettage pressure and the optimum radius of the elastic–plastic boundary of strain-hardening cylinders in plane strain and plane stress have been studied theoretically and by finite-element modeling. Equivalent von-Mises stress is used as yield criterion. Comparison of the results of the two methods shows good agreement. Although there is no explicit expression for the optimum autofrettage pressure in plane stress, the equation for plane strain can be used with good accuracy. It has also been observed that the optimum autofrettage pressure is not a constant value but depends on working pressure.     

Magnetothermoelastic transient response of multilayered conical shells

This paper considers problems of the three-dimensional axisymmetric quasi-static coupled magnetothermoelasticity for the laminated circular conical shells subjected to magnetic and temperature fields. The temperature and pressure relation are assumed for the inner boundary. The formulation begins with the basic equations of magnetothermoelasticity in curvilinear circular conical coordinates. Laplace transform and finite difference methods are used to analyze problems. The solution is obtained by using the matrix similarity transformation and inverse Laplace transform. We obtain solutions for the temperature and thermal deformation distributions in a transient and steady state. Moreover, the computational procedures established in this thesis, can solve the generalized magnetothermoelasticity problem for multilayered conical shells with nonhomogeneous materials.     

Effect of stochastic thermal input on elastic and thermal properties of an infinitely long annular cylinder

Random elastic and thermal properties for an infinitely long solid conducting circular cylinder are investigated under the effect of random thermal input. The problem is considered in the context of a generalized thermoelasticity theory with one relaxation time. The lateral surface of the solid is traction free and subjected to known stochastic temperature, driven by an additive Gaussian white noise. Laplace transform technique is used to obtain the solution in the transformed domain. Statistically, we derive and analyze the mean and variance for temperature, displacement and stress. Numerical inversion of the transformed solution is carried out, represented graphically and discussed.     

4105柴油机曲轴系自由模态及受迫振动分析

使用模态综合法,在Adams中建立刚柔混合的4105柴油机多体动力学模型,对曲轴系进行自由模态和受迫振动研究,通过受迫振动活塞侧向加速度和曲轴位移、位移速度等分析,探讨了曲轴运行状态下的扭振响应特性.结果表明,4105柴油机曲轴自由模态振型主要以弯曲变形为主,在2079 r·min-1、1882 r·min-1两个转速会产生共振,共振时刻4个气缸活塞侧向加速度同时达到峰值,而曲轴的位移、位移速度、应变能也同时达到峰值.     

自由活塞式内燃发电机振动特性

对自由活塞式内燃发电机建立了数学模型,理论上阐述了自由活塞的运动特性并对应制作了该系统的固有频率特性脉谱图;利用Matlab/Simulink建立了该系统仿真模型,分析讨论了自由活塞的实际运动规律,并与上述理论解进行了对比、分析.研究结果表明,自由活塞式内燃发电机的活塞运动不同于传统旋转内燃机,它可视为变阻尼、变刚度的单自由度受迫振动,振动频率与外部周期性燃烧激励相关联;此外,由于该系统的等效刚度系数以及阻尼系数均为正数,它对周期性激励表现出的响应最终稳定收敛进而保障内燃机稳定运行.该结果有利于进一步掌握自由活塞式内燃发电机的运动特性,并为实际样机设计提供了理论依据.     

Vibration of Thermally Post-Buckled Orthotropic Circular Plates

Axisymmetric vibrations of a statically buckled polar orthotropic circular plate due to uniform temperature rise have been studied numerically. Effects of geometric nonlinearities have been incorporated into the problem formulation. The problem is challenging because the buckled configuration is unknown a priori. By assuming that the amplitude of plate's vibration and the additional strains induced in it are infinitesimal, and its response harmonic, the non-linear partial differential equations are reduced to two sets of coupled ordinary differential equations; one for the thermal post-buckling, and the other for linear vibrations of the plate superimposed upon the post-buckled configuration. The plate's boundary is taken to be either clamped or simply supported but restrained from moving in the radial direction. The two sets of coupled boundary value problems are solved numerically by a shooting method. The dependence of the first three frequencies upon the temperature rise, for both pre-buckled and post-buckled plates, have been computed, and characteristic curves of the frequency versus temperature rise for different values of material anisotropy parameters are plotted. It is found that the three lowest frequencies of the pre-buckled plate decrease with an increase in the temperature, but those of a buckled plate increase monotonically with the temperature rise. The fundamental frequency of the deformed plate approaches zero at the onset of buckling.     

Thermoelastic transient response of multilayered conical shells subjected to vapor field

The problems of the three-dimensional axisymmetric quasi-static coupled thermoelastic for the laminated circular conical shells subjected to vapor field. The water vapor temperature and pressure relation assumed for the inner boundary. The water vapor temperature and pressure data were obtained from a thermodynamic steam table. The formulation begins with the basic equations of thermoelasticity in curvilinear circular conical coordinates. Laplace transform and finite difference methods are used to analyze problems. The solution is obtained by using the matrix similarity transformation and inverse Laplace transform. We obtain solutions for the temperature and thermal deformation distributions in a transient and steady state. Moreover, the computational procedures established in this thesis, can solve the generalized thermoelasticity problem for multilayered conical shells with nonhomogeneous materials.     

Motion characteristic of a free piston linear engine

A mathematical model of a free piston linear engine is established. The motion characteristics as well as the natural frequency map of the free piston are established. Then, its motion characteristics are successfully explained from the oscillation point. The full simulation model is built up in Matlab/Simulink for a better understanding of its motion features. The results show that the free piston system is a forced vibration system with variable damping coefficient and stiffness. Its steady-state response of periodical excitation is convergent which means that the system is stable under the periodical combustion. Furthermore, it has some unique features which are different from those of traditional Internal Combustion (IC) engines.     

The effect of fractional thermoelasticity on two-dimensional problems in spherical regions under axisymmetric distributions

Abstract

Two-dimensional axisymmetric problems are considered within the context of the fractional order thermoelasticity theory. The general solution is obtained in the Laplace transform domain by using a direct approach without the use of potential functions. The resulting formulation is used to solve two problems of a solid sphere and of an infinite space with a spherical cavity. The surface in each case is taken to be traction free and subjected to a given axisymmetric temperature distribution. The inversion of the Laplace transforms is carried out using the inversion formula of the transform together with Fourier expansion techniques. Numerical methods are used to accelerate the convergence of the resulting series to obtain the temperature, displacement, and stress distributions in the physical domain. Numerical results are represented graphically and discussed. Some comparisons are shown in figures to estimate the effect of the fractional order parameter on all studied fields.     

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.     

Transient response analysis of a spherical shell embedded in an infinite thermoelastic medium based on a memory-dependent generalized thermoelasticity

In the context of a memory-dependent generalized thermoelasticity, the thermal-induced transient response in an infinite elastic body containing a spherical shell is investigated. A thermal shock is applied on the inner surface of the spherical shell. The infinite body and the spherical shell are assumed to be isotropic but two dissimilar materials. By using an analytical technique based on the Laplace transform along with its numerical inversion, the governing equations of the problem are solved and the non-dimensional physical quantities in the two materials, i.e., temperature, displacement and stress, are obtained and illustrated graphically respectively. In simulation, the accuracy of memory-dependent derivative (MDD) is verified by degrading the present model into L-S model to compare the results obtained from the cases with interfacial thermal resistance and without interfacial thermal resistance. In addition, the effects of the different kernel functions as well as the ratios of the two materials, including the ratios of the density, the thermal-conductivity and the time-delay, on the distributions of the considered variables are obtained and demonstrated graphically respectively.     

Simulation study of electrical dynamic characteristics of lithium-ion battery

The electrical dynamic characteristics of a lithium-ion battery have been simulated by an equivalent circuit, which is derived from the measured impedance. The transient voltage response to the various kinds of applied current waves such as single pulse, single rectangular, triangle, and sawtooth waves is experimentally examined and calculated by using the numerical Laplace transform with the equivalent circuit. The experimental and calculated results are compared and discussed, focusing on the range of current where the linear relationship is valid. Changing the time range, the state of charge (SOC) and the battery temperature as parameters, their influence on the linear range of the applied current has been investigated.     

A nonlinear Hermitian transfinite element method for transient behavior analysis of hollow functionally graded cylinders with temperature-dependent materials under thermo-mechanical loads

In the present paper, an algorithm for nonlinear transient behavior analysis of thick functionally graded cylindrical vessels or pipes with temperature-dependent material properties under thermo-mechanical loads is presented. In contrast to researches presented so far, a Hermitian transfinite element method is proposed to improve the accuracy and to prevent artificial interference or cohesion formation at the mutual boundaries of the elements. Time variations of the temperatures, displacements, and stresses are obtained through a numerical Laplace inversion. Another novelty of the present research is using the transfinite element method to solve nonlinear problems. A sensitivity analysis includes investigating effects of the volume fraction index, dimensions, and temperature-dependency of the material properties is performed. Results confirm the efficiency of the present algorithm and reveal the significant effects of the temperature-dependency of the material properties and the elastic wave reflections and interferences on the responses. In comparison to other techniques, the present technique may be used to obtain relatively accurate and stable results in a less computational time.     

Investigating the magnetic field effects on thermomechanical stress behavior of thick-walled cylinder with inner FGM layer

In this article, an analytical solution is presented to evaluate the stress field in axisymmetric double-walled cylinder made of functionally graded materials (FGMs) and homogeneous layers subjected to pressure, temperature gradient, and magnetic field loadings. Closed form expressions for radial and circumferential stresses as well as the normalized effective stresses are extracted through solving the governing differential equations. It is concluded that both magnetic field and grading indices of FGM have significant effects on the stress distribution in the cylinder, while the proper parameters setting will result into considerable reduction in the stress quantities.     

A boundary layer analysis of heat transfer by free convection from permeable horizontal cylinders of elliptic cross-section in porous media using a thermal non-equilibrium model

This work uses a thermal non-equilibrium model to study the free convection boundary layer flow driven by temperature gradients near a permeable horizontal cylinder of elliptic cross-section with constant wall temperature in a fluid-saturated porous medium. A coordinate transformation is used to obtain the nonsimilar boundary layer equations. The transformed boundary layer equations are then solved by the cubic spline collocation method. Results for the local Nusselt numbers are presented as functions of the porosity scaled thermal conductivity ratio, the heat transfer coefficient between solid and fluid phases, the transpiration parameter, and the aspect ratio when the major axis of the elliptical cylinder is vertical (slender orientation) and horizontal (blunt orientation). An increase in the porosity scaled thermal conductivity ratio or the heat transfer coefficient between the solid and fluid phases increases the heat transfer rates. Moreover, the use of suction (positive transpiration parameter) tends to increase the heat transfer rates between the porous medium and the surface.     

基于振动和缸压信号的柴油机敲缸故障识别

针对某型船用柴油机的敲缸故障,提出一种基于振动和缸压信号的联合分析诊断方法。结合上止点传感器的脉冲信号,将振动和缸压时域信号根据柴油机曲轴转角位置转换为曲轴转角域信号。根据在曲轴转角域出现敲缸特征信号时对应的振动加速度判断柴油机敲缸激励源频率范围,在此基础上通过带通滤波降噪提高敲缸特征信号的信噪比。基于四冲程柴油机工作周期与曲轴转角的关系对振动和缸压曲轴转角域信号提取故障特征。经柴油机多工况数据验证,本方法对识别柴油机敲缸故障简便、有效、准确性高。     

Solution of the Graetz-Brinkman problem with the Laplace transform Galerkin method

The present study concentrates on the effects of viscous dissipation in laminar forced convection. A power law fluid rheology model is applied and the effect of heat conduction in the axial direction is considered negligible. The physical properties are considered constant. Assuming fully developed velocity profile, the development of the temperature profile and its asymptotic behavior are investigated. For the solution of the problem the Laplace transform Galerkin technique is used. The method allows for the most general boundary conditions. A detailed comparison with previously published results provides a verification of the numerical technique. An important feature of the approach is that derivatives and integrals with respect to the axial location can be obtained through the operational rules of the Laplace transformation and hence no numerical derivation or integration is needed. As an application of the numerical model, we focus on the natural cooling regime, when the viscous dissipation of energy is counter-balanced by keeping the wall temperature at the ambient value. We derive a correlation for the asymptotic behavior of the Nusselt number in the natural cooling regime. This correlation reproduces the known value for the Newtonian case and provides a convenient means to normalize the Nusselt number for a wide range of flow behavior indices.     

Transient response of a hygrothermoelastic cylinder based on fractional diffusion wave theory

A coupled fractional hygrothermoelasticity theory is formulated within the framework of fractional calculus. Both the classical Fourier’s and Fick’s laws are generalized to anomalous diffusion which is characterized by the time- fractional diffusion-wave equation. Based on the fractional hygrothermoelasticity theory, the transient response of an infinitely long cylinder subjected to hygrothermal loadings at the surface is analyzed. The finite Hankel integral transform method and decoupled technique are used to derive closed-form expressions for temperature, moisture, displacement, and hygrothermal stresses in the solid. The coupling effect of temperature and moisture on elastic fields is discussed. Numerical results of transient response of hygrothermoelastic fields are presented graphically for the cases of subdiffusion, normal diffusion, and superdiffusion, respectively.     

Analysis of thermoelastic response in functionally graded hollow sphere without load

In this article, a model concerning free vibrations of spherically symmetric, thermoelastic, isotropic, and functionally graded sphere has been developed and analyzed in the context of linear theory of generalized thermoelasticity with one relaxation time. Laplace transform has been used to solve the problem which yields natural frequencies of free vibrations without performing inversion of the transform. The analytical results for coupled, uncoupled, and homogeneous spheres have been deduced as special cases of the general case. Natural frequencies of first 10 modes of vibrations have been obtained for different values of grading index of cobalt material regarding coupled thermoelastic, generalized thermoelastic, and elastic functionally graded spheres. The frequency shift and thermoelastic damping for Fourier and non-Fourier processes of heat propagation, temperature change, radial, and hoop stresses have been presented graphically. It has been analyzed here that grading index parameter helps in detecting the strength of signals in such material devices and the thermal relaxation time contributes in improving the quality of signals. The analysis also leads to the fact that grading index parameter is useful from design point of view and it can be tailored to specific applications for controlling the stress.