Optimum Structure Design of a Multilayer Piezo-Composite Disk for Control of Thermal Stress

This article deals with a control problem of a thermal stress in a composite circular disk consisting of a transversely isotropic structural layer onto which multiple piezoelectric layers with concentrically arranged electrodes are perfectly bonded. When a prescribed heating temperature distribution acts on the structural layer surface, the optimum structure design of the composite disk is performed so that the maximum thermal stress in the structural layer is minimized subject to constraints on stresses in the piezoelectric layers. A hybrid optimization technique combining the particle swarm optimization with the simplex method is employed for solving the optimum design problem. To resolve the difficulty in solving the problem with many optimization variables, three improvements are added to the hybrid optimization technique and an efficient design method is introduced. For a composite disk constructed of a CFRP layer and cadmium selenide layers, the layer thicknesses, the electrode dimensions, and the voltages applied to the electrodes are determined and the numerical results are presented in tabular and graphical forms. Finally, it is shown from the optimum design results that the highest suppression ratio of the maximum thermal stress reaches 40.8% in the case of a five-layer composite disk and is considered to be almost saturated.     

COMPUTATION OF TRANSIENT THERMAL STRESSES IN ELASTIC-PLASTIC TUBES: EFFECT OF COUPLING AND TEMPERATURE-DEPENDENT PHYSICAL PROPERTIES

The objective of this study is to obtain the transient solution of the thermoelastic-plastic deformation of internal heat-generating tubes by considering the thermomechanical coupling effect and the temperature-dependent physical properties of the material. The previously developed steady-state model describing the elastic-plastic behavior of the tubes is modified to obtain the transient solution. The propagation of the elastic-plastic interface for a given heat load is obtained; and the corresponding stress, displacement, and plastic strain components are computed. The effect of the coupling is investigated using three different engineering materials, namely, steel, aluminum, and magnesium; and it has been found to be negligible. On the other hand, the temperature dependence of the mechanical and thermal properties affects the computed profiles significantly.     

Control of Thermally Induced Vibration in a Composite Beam with Damping Effect

ABSTRACT

This article deals with control of thermally induced vibration in a composite beam with damping effect. The beam consists of a central thermoelastic structural layer and two outer piezothermoelastic layers. The thermoelastic vibration in the beam is suppressed by the superposition of electroelastic vibration. The electroelastic vibration is repeatedly excited through application of electric potential differences across the piezoelectric layers. The initiation and termination times of the applied electric pulses are determined by a method similar to the optimization procedure developed previously by the authors. The amplitudes of the applied electric pulses are determined using a control method based on speed feedback. Numerical results for an aluminum/PZT ceramic beam are illustrated graphically.     

Theoretical Stress Analysis of Rotating Hyperbolic Disk without Singularities Subjected to Thermal Load

A theoretical method for the evaluation of elastic stresses and strains in rotating hyperbolic disks without singularity, also subjected to thermal load, is introduced. The differential equation governing the radial displacement field of the hyperbolic disk without singularity has been deduced from the governing equation of non-linearly variable thickness disks given by the power of a linear function of the radius. A general temperature distribution along the radius expressed by a polynomial relation is considered. To overcome convergence problems of the solution, with hypergeometric functions, analytic continuations of these series have been introduced that allow the extension the theoretical thermoelastic analysis to all cases of technical interest. Then, for the first time the authors are aware, closed-form solutions of the governing equation of hyperbolic disks without singularity are presented.     

燃气轮机涡轮盘温度及应力场计算分析

用通用有限元计算程序ANSYS对某燃气轮机透平第一级涡轮盘的轴对称原模型温度和应力场进行稳态计算。计算中考虑了材料的非线性,惯性力和温度边界条件。分析了温度和应力场,根据计算结果对结构进行了修改,对修改前后的数据作了对比,提出了改进设计建议。本计算结果为涡轮盘疲劳寿命预测提供了依据。     

Body Force Analogy for Transient Thermal Stresses

A body-force analogy for transient thermal stresses in linear elastic solids is presented. The analogy is derived in the framework of the stress equations of motion and the corresponding stress-based characterization of initial boundary-value problems of elasticity. The latter framework was introduced by Professor Jozef Ignaczak, to whom the present contribution is dedicated. Starting from Ignaczak's stress-based formulation, we subsequently derive a body-force analogy by studying conditions, under which a certain time-dependent volume integral, being positive in case of non-vanishing stresses, and vanishing otherwise, becomes zero. These conditions lead us to the formulation of a boundary-value problem, which must be satisfied by the auxiliary body-forces, surface tractions and kinematic boundary conditions, in order that the stresses in the auxiliary isothermal problem and in the thermal stress problem do coincide. As a numerical example, Finite Element Computations for a beam-type structure are presented.     

Numerical Modeling of Fluid Flow and Thermal Behavior of Different Nanofluids on a Rotating Disk

The thermal and velocity profiles of various nanofluid systems on a rotating disk are simulated. Finite difference method, the orthogonal collocation method, and the differential quadrature method (DQM) of numerical approaches are used to solve the governing equations and are compared to determine the faster and more accurate solution procedure. Five nanoparticles Al, Al₂O₃, Cu, CuO, and TiO₂ solved in three base fluids water, ethylene glycol, and engine oil are considered to be used on the disk at different volume fractions. A new general algorithm is presented for solving equations of a rotating‐disk problem quickly and accurately and it is found that the DQM method is the best approach for this numerical simulation. Heat transfer performance of a rotating disk would be much better enhanced with water based Al nanofluid. A wide range of results for different base–fluid combinations with nanoparticles is presented with untransformed 3D results and effects of the variation of different parameters provides comprehensive insight and prevents inaccurate deductions.     

Adaptive control of maximum thermal stress in a smart piezocomposite disk

In this paper, an adaptive control problem of the maximum thermal stress in a smart composite disk is analyzed. The disk consists of a transversely isotropic structural layer onto which piezoelectric sensor and actuator layers are bonded. It is considered that an unknown heating temperature distribution acts on the structural layer and a thermally induced voltage distribution is measured on the sensor layer. The unknown heating temperature distribution is inferred from the knowledge of the measured voltage distribution. Applied voltages to electrodes arranged on every actuator layer are determined by optimization so that the maximum thermal stress in the structural layer is minimized and stress constraints imposed on the piezoelectric layers are satisfied. Finally, the suppression ratio of the maximum thermal stress is discussed based on numerical results.     

Thermal Stress Intensity Factors for a Normal Crack in a Piezoelectric Material Strip

This paper investigates the electromechanical fracture behavior of a normal crack in a piezoelectric material strip subjected to a uniform heat flow far away from the crack region. The crack faces are supposed to be insulated thermally and electrically. By using the Fourier transform, the thermal and electromechanical problems are reduced to singular integral equations, respectively, which are solved numerically. Both the cases of an internal crack and an edge crack are studied. Numerical calculations are carried out, and detailed results are presented to illustrate the influence of the crack location and length on the temperature distribution and the stress intensity factors.     

Mechanical and thermal stresses in a functionally graded rotating disk with variable thickness due to radially symmetry loads

Rotating disks have many applications in the aerospace industry such as gas turbines and gears. These disks normally work under thermo mechanical loads. Minimizing the weight of such components can help reduce the overall payload in aerospace industry. For this purpose, a rotating functionally graded (FG) disk with variable thickness under a steady temperature field is considered in this paper. Thermo elastic solutions and the weight of the disk are related to the material grading index and the geometry of the disk. It is found that a disk with parabolic or hyperbolic convergent thickness profile has smaller stresses and displacements compared to a uniform thickness disk. Maximum radial stress due to centrifugal load in the solid disk with parabolic thickness profile may not be at the center unlike uniform thickness disk. Functionally graded disk with variable thickness has smaller stresses due to thermal load compared to those with uniform thickness. It is seen that for a given value of grading index, the FG disk having concave thickness profile is the lightest in weight whereas the FG disk with uniform thickness profile is the heaviest. Also for any given thickness profile, the weight of the FG disk lies in between the weights of the all-metal and the all-ceramic disks.     

Numerical Analysis of Transient Stress Field of a Functionally Graded Nickel-Zirconia Profile under Thermal Loading

One-dimensional analysis of the thermomechanical response of a 3-layered nickel-functionally graded material-zirconia composite configuration under thermal loading, is the aim of this contribution. A Finite Element code is developed for the analysis. The thickness of the lower layer (nickel) is considered to be “infinite,” when compared to the thickness of the first two layers. The influence of the thickness of the functionally graded layer on the thermomechanical response of the composite material is analysed. Several distributions of the properties inside the functionally graded layer are also examined.     

Analytical Solution of Classic Coupled Thermoelasticity Problem in a Rotating Disk

A fully analytical solution of the classic coupled thermoelasticity problem in a rotating disk subjected to thermal and mechanical shock loads is presented. Axisymmetric thermal and mechanical boundary conditions are considered in general forms of arbitrary heat transfer and traction, respectively, at the inner and outer radii of the disk. To solve the governing system of equations, an analytical procedure based on the Fourier-Bessel transform is employed. Closed form formulations are presented for temperature and displacement fields. The results of the present formulations are in good agreement with the numerical results available in the literature. The radial distribution and time history of temperature, displacement and stresses are shown and discussed. The propagation of elastic waves and their reflection from the boundary of the disk are clearly shown. In addition, effects of coupling parameter and angular velocity on temperature, displacement and stress fields are investigated.     

Thermal Stresses in Type III Thermo-Elastic Plates

ABSTRACT

We consider the linear theory of homogeneous and isotropic thermoelastic solids for the types II and III theories. First, we present the basic equations which characterize the bending of thin thermoelastic plates. Then, we establish a uniqueness result with no definiteness assumption on constitutive coefficients. Existence of solutions is proved under the assumption that the internal energy density is positive definite; the asymptotic behavior is then analyzed. Finally, we study the spatial behavior of solutions.     

热力除氧系统的计算机控制

介绍了某炼油厂除氧系统计算机控制系统的结构组成、控制功能和特点,设计了耦合系统的模糊控制叙述了压力和水位的控制方案和控制软件,该系统投入运行以来,效果良好。     

Thermal Stress Analysis for Octagonal Quasicrystals

The complex variable method for solving the two-dimensional thermal stress problem of octagonal quasicrystals is stated. The closed-form solutions for octagonal quasicrystals containing an elliptical hole subjected to a remote uniform heat flow are obtained. When the hole degenerates into a crack, the explicit solutions for the stress intensity factors and energy release rate are presented.     

Transient Temperature and Thermal Stress Distributions in a Hollow Disk Subjected to a Moving Uniform Heat Source

This study presents numerical analyses of transient temperature and thermally induced stress distributions in a stationary hollow steel disk partially heated by a moving uniform heat source from its outer surface under stagnant ambient conditions. The moving heat source applied on a certain angular segment of the processed surface rotates with a constant angular speed (ω). The peak levels of the temperature gradients and the thermal stress ratios at the heated segments do not rise very much after 2–3 cycles. When the value of ω is increased, the maximum effective thermal stress ratio can be decreased in a considerable amount.     

Dynamic Behavior of Thermal Stress in a Functionally Graded Material Thin Film Subjected to Thermal Shock

In the present article, a one-dimensional dynamic thermoelastic problem in a functionally graded material (FGM) thin film subjected to a thermal shock loading is analyzed. An exact analytical solution is obtained by employing techniques of the space-variable transformation and Laplace transform, in the case where variations in material properties of the FGM thin film are expressed as exponential functions of the space-variable. Numerical calculations for time histories of thermal stresses have been carried out. Obtained numerical results reveal that the thermal stress oscillation is unsteady when the mechanical impedance depends on the space-variable, whereas it is monotonic and periodic when the impedance is independent of the space-variable. The factor which causes the different behavior of the thermal stress oscillations is also investigated based on the analytical and numerical results.     

Integrated Photoelasticity for Axisymmetric Thermal Stress Measurement Using the Stress Function

By investigating axisymmetric stress fields with integrated photoelasticity, the stress components σ_z and σ_rz can be determined directly from the experimental data. Stress components σ_r and σ_θ are usually determined using the equilibrium and compatibility equations. In this article it is shown that the stress function for an axisymmetric thermoelastic stress field can be determined on the basis of experimental data, obtained with integrated photoelasticity. Knowledge of the stress function permits one to calculate all the stress components as well as the temperature field in the test object.     

发动机电磁气门驱动过渡过程的闭环控制

以一个发动机电磁气门驱动(EVA)装置为对象,采用试验方法研究EVA过渡过程。根据EVA的过渡过程工作特点,把过渡过程分为远程、近程两段分别予以控制。远程采用PI控制,控制目标是在远程结束时励磁线圈达到某一电流;近程则采用跟踪位移理想曲线的方法,使落座速度降低。通过试验确定了远程阶段的目标电流和PI控制参数、近程阶段的理想位移曲线和控制点数目,使单次上下行过渡过程落座速度分别达到了0．22m/s和0．10 m/s,实现了EVA连续动作且可使EVA动作适应转速变化。     

内燃机排气歧管热应力分析

采用流固耦合方法计算了内燃机排气歧管的热应力。首先,计算了排气歧管的瞬态内流场和稳态外流场,得到了排气歧管内外壁面的对流换热系数和环境温度,再用有限元的方法计算了排气歧管的温度场和热应力。计算结果表明,排气歧管裂纹产生处就是热应力最大处,根据计算结果提出了改进建议,经试验验证改进措施是有效的。