Exact analysis for static response of cross ply laminated smart shells

Models and analytical solutions are formulated and developed for the static behavior of cross ply smart laminated shells with extension piezoelectric laminae. The models are based on a rigorous first order shell theory. The state space approach is used to find exact solutions for the static response of cross ply spherical, cylindrical and doubly curved shells with various boundary conditions. The smart shells possess two parallel edges simply supported and the remaining ones having any possible combination of boundary conditions: free, clamped or simply supported. Deflections of cross ply laminated shells incorporating piezoelectric layers are determined. Numerical results of six layer laminates are generated to investigate the shell static behavior. The exact solutions for deflections can be used as benchmarks for approximate solutions such as Rayleigh–Ritz and finite element methods.     

减摇鳍模糊免疫自适应PID控制器设计及仿真研究

针对船舶横摇的非线性模型，利用免疫反馈机理，设计了一种减摇鳍模糊免疫自适应PID控制器。控制器将模糊控制与PID控制相结合，采用Fuzzy推理，对非线性函数进行模糊逼近，用模糊免疫P调节器实时整定PID控制器的比例增益，采用常规模糊控制器在线调整免疫PID控制器的积分时间常数和微分时间常数。通过对船舶减摇鳍控制系统的仿真，可以看出采用模糊免疫自适应PID控制器其控制效果远优于常规PID控制器，使减摇鳍的减摇效果得到显著提高。     

基于形状记忆合金驱动的仿生鲫鱼尾鳍的设计和分析

 为了研制可主动运动控制的仿生机器尾鳍,以鲫鱼的尾鳍为研究对象,利用仿生学研究结果以及形状记忆合金材料的特点,设计形状记忆合金驱动的仿生鲫鱼尾鳍结构,实现尾鳍的主动运动控制.介绍了仿生尾鳍及其驱动器的机械结构和控制方法,详细分析了核心部件形状记忆合金鳍条的根部变形曲率和摆动幅度之间的关系.最后由实验给出了形状记忆合金鳍条厚度与最大输出力及摆动幅度之间的关系,同时给出加热电流占空比对鳍条最大摆幅和最高频率的影响规律.由实验结果可知：最大输出力随着SMA薄板的厚度增加而迅速增大,它们之间呈现非线性关系;鳍条厚度和摆动幅度之间呈线性反比关系,摆动幅度随着厚度的增加线性减小;随着驱动加热电流的增加,鳍条的响应频率显著加快;不同加热电流占空比下鳍条所能达到的最大摆幅显著不同．     

多孔式翅片传热与流阻特性分析

采用CFD数值模拟技术,研究了多孔式翅片传热与流阻特性,重点分析了不同孔口因素对多孔式翅片传热与流阻的影响.研究结果表明:随着孔隙率增加,多孔式翅片流阻增大,但其传热并未明显提升.同一孔隙率下,翅片传热与流阻随孔径减少而提升.开孔方式呈错列布置的流阻与传热性能高于孔口呈并行布置的情况.开孔结构对多孔式翅片传热性能影响较...     

Fracture analysis and improved design for a symmetrically bonded smart structure with linearly non-homogeneous magnetoelectroelastic properties

The mechanical model was established for the anti-plane interfacial fracture problem of a symmetrically bonded smart structure with linearly non-homogeneous magnetoelectroelastic properties. The system of Cauchy singular integral equations for the interfacial crack was derived by Fourier integral transform. The numerical solutions of the Cauchy singular integral equations were obtained by the Lobatto-Chebyshev collocation method put up by Erdogan and Gupta. The mechanical strain energy release rate and the total energy release rate were chosen as fracture parameters to discuss the effect of the non-homogeneity parameter on the extension force of the crack. A conclusion was drawn that, to reduce the weak-discontinuity of the interface in the magnetoelectroelastic structure would be beneficial to decrease the extension force of the interfacial crack. Based on this conclusion, a new improved design was suggested for the symmetrically bonded linearly non-homogeneous magnetoelectroelastic composite. The enhancement of the capability of the improved structure to resist interfacial fracture was validated by comparison between the improved and unimproved structures for their fracture responses.     

A DEMATEL analysis of smart city determinants

Substantial population growth, increasing urbanization, overloaded infrastructure, more energy consumption, environmental impacts, and investment in technological developments are major challenges in city management and development. Municipalities seek to improve their citizens’ wellbeing and quality of life, but the need to find a balance between these complex factors makes decision-making processes more difficult. Experts must analyze the determinants of smart cities, which are urban centers intended to be socially involved, habitable, and economically and environmentally sustainable, and that rely strongly on technology and innovation. Based on multiple-criteria decision analysis (MCDA) principles, this study combines cognitive mapping techniques and the decision-making trial and evaluation laboratory (DEMATEL) method to develop a multicriteria model that can help managers analyze smart city determinants in a collaborative manner. The research included identifying these determinants and their respective cause-and-effect relationships using an expert panel’s experience and knowledge related to the subject under analysis. The results were validated by both the panel and the city councilor responsible for mobility and municipal projects within Évora City Council, Portugal, which has implemented smart city strategies. The latter specialist verified that the proposed evaluation system can be used as a tool to facilitate smart city collaborative decision-making processes. The study’s main advantages and limitations are also analyzed and discussed.     

螺旋槽锯齿翅片管在空调机冷凝器上的应用

螺旋槽锯齿翅片管是一种新型高效冷凝换热管。试验表明，在额定工况下，以R22为制冷剂，螺旋槽锯齿翅片管冷凝器与通常使用的低肋管冷凝器相比具有较高的冷凝换热性能，在换热面积减少30％的情况下，空调机的制冷量增加3．3％，能效比提高6．9％。     

Comparison of the static and dynamic fracture behaviour of an AE-460 structural steel

The ductile-to-brittle transition curves of a structural steel under low strain rate (static conditions) and impact (dynamic conditions) are compared in this work, and the influence of the geometry of the initial defect that promotes fracture (notch or crack) is evaluated. The toughness of the precracked specimens was characterised by the J-integral parameters obtained at the initiation of the stable crack growth, J_c, and when the unstable fracture takes place, J_u. The different methods used in dynamic tests in order to calculate the dynamic J-integral parameter, J_d, were evaluated. The use of cracked specimens, instead of notched ones, modifies the transition curve to higher temperatures and, finally, the transition temperature shift between static and dynamic test results is also quantified     

Geometrically nonlinear static and free vibration analysis of functionally graded piezoelectric plates

In this paper, nonlinear static and free vibration analysis of functionally graded piezoelectric plates has been carried out using finite element method under different sets of mechanical and electrical loadings. The plate with functionally graded piezoelectric material (FGPM) is assumed to be graded through the thickness by a simple power law distribution in terms of the volume fractions of the constituents. Only the geometrical nonlinearity has been taken into account and electric potential is assumed to be quadratic across the FGPM plate thickness. The governing equations are obtained using potential energy and Hamilton’s principle that includes elastic and piezoelectric effects. The finite element model is derived based on constitutive equation of piezoelectric material accounting for coupling between elasticity and electric effect using higher order plate elements. The present finite element is modeled with displacement components and electric potential as nodal degrees of freedom. Results are presented for two constituent FGPM plate under different mechanical boundary conditions. Numerical results for PZT-4/PZT-5H plate are given in dimensionless graphical forms. Effects of material composition and boundary conditions on nonlinear response are also studied. The numerical results obtained by the present model are in good agreement with the available solutions reported in the literature.     

Nonlinear static and dynamic buckling analysis of functionally graded shallow spherical shells including temperature effects

This paper presents an analytical approach to investigate the nonlinear static and dynamic unsymmetrical responses of functionally graded shallow spherical shells under external pressure incorporating the effects of temperature. Governing equations for thin FGM spherical shells are derived by using the classical shell theory taking into account von Karman–Donnell geometrical nonlinearity. Approximate solutions are assumed and Galerkin procedure is applied to determine explicit expressions of static critical buckling loads of the shells. For the dynamical response, motion equations are numerically solved by using Runge–Kutta method and the criterion suggested by Budiansky–Roth. A detailed analysis is carried out to show the effects of material and geometrical parameters, boundary conditions and temperature on the stability and dynamical characteristics of FGM shallow spherical shells.     

机翼颤振模型的结构动力学设计

介绍了围绕某型飞机机翼颤振模型的结构动力学设计所开展的研究工作，内容包括设计目标与设计参数的确定、设计模型与设计变量的选取、设计方法与优化方法、主体结构与边界条件设计等。试验结果表明，设计出的颤振模型满足预定的振动特性要求。     

一种嵌入式远程测控平台的设计和实现

嵌入式可以很好地满足现代科技发展对测控技术提出的新的要求，本文概述了一个嵌入式远程测控平台的硬件的构建和软件开发过程，并给出了一个应用实例。     

五腔串联压电泵的设计制作与试验

为提高压电泵的输出能力,提出一种多腔串联压电泵,并从理论和试验两方面进行了研究.理论分析表明,在其他条件确定时,多腔串联压电泵的输出压力与泵腔数量n成正比,输出流量与姨%n成正比.设计制作了金属阀五腔串联压电泵,并以水为工作介质测试了工作腔数量不同时的输出特性.结果表明,压电泵工作腔数量不同时,存在不同的最佳工作频率使其输出压力或流量最大,且压力最佳频率及流量最佳频率均随工作泵腔数量的增加而增加,但增加幅度不同;在最佳频率时,五腔串联泵输出压力及流量均与工作腔数量成正比.在电压为150 V、工作频率为最佳频率时,5腔工作时的最大压力和流量分别为100 kPa和246.54 mL/min,分别为单腔工作时的6.7倍和4.2倍.     

压电陶瓷驱动三自由度精密定位系统的弹性动力学与输入调理特性研究

对压电陶瓷驱动三自由度精密定位系统的动力学性能进行了研究。首先建立了系统的弹性动力学模型，采用变截面框架单元描述柔性铰链，给出了其单元刚度矩阵和质量矩阵。通过实验获得了系统的低阶模态参数，并和分析结果进行了比较，验证了所建动力学分析模型的正确性。提出了基于动力学特性分析的驱动输入调理概念。分别采用正弦曲线和五次多项式作为调理函数对系统驱动的动态性能进行了研究。研究结果表明：对驱动输入进行必要的调理是十分必要的，所采用的两种调理方法均有效改善了系统的驱动特性，但由于采用五次多项式作为调理函数完全避免了驱动开始和结束时的加速度冲击，因而可获得更好的驱动效果。     

压电驱动合成喷的设计及分析

介绍了合成喷的基本原理,并分析了压电驱动合成喷设计的基本思路和关键点。对喷的两个重要部件：压电驱动器和腔体的尺寸设计作了分析和说明。讨论了合成喷的电输入参数,选择并实验研究了驱动器的相关特性。分析认为：压电驱动合成喷的尺寸设计应使Rc/Rm,h,m和腔体体积V较小,而电输入则应选择为较高电压,频率为驱动器谐频的方法输入。     

Experimental investigation of a cooled thick fin in dry and humid air flows

The results of a study are reported in which a cooled, thick vertical fin was tested in a closed loop tunnel with and without condensation from the air flowing over it. In particular, the temperature distributions for the dry and wet fin cases, together with the condensate film thickness in the wet fin case, were investigated. From a flow visualization investigation, it was found that the boundary layer separates at the leading edge, resulting in a higher air heat transfer coefficient. The wet fin test results also indicated that the mode of condensation was dependent on fin surface characteristics and that the wet fin performance was governed by the air flow parameter. Within the laminar air flow range, the condensate film flowed downward under the action of gravity. However, at higher air velocities, both gravity and shear forces affected the condensate flow, a variation in the condensate film in the direction of air flow being noticed.     

CFD analysis of employing a novel ecofriendly nanofluid in a miniature pin fin heat sink for cooling of electronic components: Effect of different configurations

This research aims to study the thermal and hydraulic attributes as well as energy efficiency of a new ecofriendly nanofluid including functionalized graphene nanoplatelets in a mini heat sink with three different pin fins. The circular, triangular and drop-shaped pin fins are investigated and compared with each other. The effects of nanoparticle fraction and flow velocity on the thermal resistance, temperature uniformity, convective heat transfer coefficient, maximum surface temperature, average surface temperature, pressure loss and pumping power are assessed. Increasing the concentration or velocity reduces the temperature on the heated wall, and also improves the temperature distribution uniformity. At both constant velocity and invariant pumping power, the heat sink fitted with the circular pin fins leads to the best performance while that equipped with the triangular pin fins results in the worst efficiency. In addition, the Figure of Merit (FoM) is greater than 1 for all conditions, which proves that the nanoparticle suspension possesses a greater merit to be employed as the coolant in the heat sinks compared to the base fluid.     

两种不同组合形式的环形网耗能性能的对比分析

通过对单个R0CCO圆环的静力试验和理论分析,推导了圆环等效半径的计算方法。建立了两种组合形式环形网的计算模型：第一种组合形式（模型1）中1个R0CCO圆环与4个R0CCO圆环相连接;第二种组合形式（模型2）中1个R0CCO圆环与6个R0CCO圆环相连接,采用数值分析方法对模型1、2的静动力耗能性能进行了研究。结果表明：①当采用相同的ROCCO圆环组成模型1、2时,模型2中单个ROCCO圆环的耗能能力高于模型1;②当采用相等的材料组成模型1、2时,在相同动能的落石冲击作用下,模型2的变形距离低于模型1,且模型1受到的落石冲击荷载开始时低于模型2,随着落石直径的增大,逐渐高于模型2;③模型1、模型2在落石冲击作用下的极限耗能能力随着落石直径的增大而逐渐增大,且模型1的极限耗能能力开始时高于模型2,当落石直径达到一定程度后,模型2的耗能能力逐渐高于模型1。因此,当实际工程中需要考虑防护系统变形距离时,选择第二种组合形式的环形网可以节约工程造价,而当需要考虑系统极限耗能能力时,可以根据落石特征选择经济合理的环形网结构形式。     

Two-dimensional stress analysis of functionally graded solids using the MLPG method with radial basis functions

The meshless local Petrov–Galerkin (MLPG) method is used for analysing two-dimensional (2D) static and dynamic deformations of functionally graded materials (FGMs) with material response modelled as either linear elastic or as linear viscoelastic. The multiquadric radial basis function (RBF) is employed to approximate the trial solution. Results are computed with two different choices of test functions, namely a fourth-order spline weight function, and a Heaviside step function, each having a compact support. No background mesh is used to numerically evaluate integrals appearing in the weak formulation of the problem, thus the method is truly meshless. A benefit of using RBFs is that they possess the Kronecker delta property; thus it is easy to satisfy essential boundary conditions. For five problems, the computed results are found to match well with those either from their analytical solutions or numerical solutions of other researchers who employed different algorithms. For a dynamic problem, the Laplace-transform technique is utilised. The numerical examples illustrate that displacements and stress distributions in a structure made of an FGM differ considerably from those at the corresponding points in the same structure made of a homogeneous material. Thus, the inhomogeneity in material properties can be exploited to optimise stress distribution, minimise deflection and reduce the maximum stress.     

Finite element piezothermoelasticity analysis and the active control of FGM plates with integrated piezoelectric sensors and actuators

 An efficient finite element model is presented for the static and dynamic piezothermoelastic analysis and control of FGM plates under temperature gradient environments using integrated piezoelectric sensor/actuator layers. The properties of an FGM plate are functionally graded in the thickness direction according to a volume fraction power law distribution. A constant displacement-cum-velocity feedback control algorithm that couples the direct and inverse piezoelectric effects is applied to provide active feedback control of the integrated FGM plate in a closed loop system. Numerical results for the static and dynamic control are presented for the FGM plate, which consists of zirconia and aluminum. The effects of the constituent volume fractions and the influence of feedback control gain on the static and dynamic responses of the FGM plates are examined. Received: 13 March 2002 / Accepted: 5 March 2003 The work described in this paper was supported by a grant awarded by the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. CityU 1024/01E).