On discrete supports and continued support of structures

There have been several papers dealing with elastic discrete supports of structures. And we are interested in what relation there is between elastic discrete supports and continued support and what difference would result in for dynamic properties of structures under the two kinds of support. Through the present analysis, it is pointed out that natural frequencies reflect a certain proportion of kinetic and potential energies in total energy of a system, and the frequencies can be guaranteed to be invariable in transforming between elastic discrete and continued supports by means of a proper energy equivalence. And the theoretical formulation of beams and numerical results of shells of revolution are presented in this paper.     

Piezoelectric wafer active sensor embedded ultrasonics in beams and plates

In this paper we present the results of a systematic theoretical and experimental investigation of the fundamental aspects of using piezoelectric wafe active sensors (PWASs) to achieve embedded ultrasonics in thin-gage beam and plate structures. This investigation opens the path for systematic application of PWASs forin situ health monitoring. After a comprehensive review of the literature, we present the principles of embedded PWASs and their interaction with the host structure. We give a brief review of the Lamb wave principles with emphasis on the understanding the particle motion wave speed/group velocity dispersion. Finite element modeling and experiments on thin-gage beam and plate specimens are presented and analyzed. The axial (S ₀) and flexural (A ₀) wave propagation patterns are simulated and experimentally measured. The group-velocity dispersion curves are validated. The use of the pulse-echo ultrasonic technique with embedded PWASs is illustrated using both finite element simulation and experiments. The importance of using high-frequency waves optimally tuned to the sensor-structure interaction is demonstrated. In conclusion, we discuss the extension of these results toin situ structural health monitoring using embedded ultrasonics.     

The reasonableness problem of theories of structures carrying concentrated masses, springs and supports in vibration problems

In vibration problems, some theories of structures carrying concentrated masses, springs and supports are reasonable, but others are unreasonable.The authors of the present paper would like to thank Professor Hal-Chang Hu for his valuable suggestions.     

Hollow golf club head modal characteristics: Determination and impact applications

The design of modern hollow golf club heads is a labor-intensive process involving extensive performance festing both by robotic and real golfers. This paper describes how, by correlating club head mechanical behavior with functional performance, it will become possible to use validated computational models to predict this performance as well as related contributions to the ill-defined concept of feel. Successful use of experimental modal analysis to validate a hollow golf club head finite element model is reported. Modal tests employing noncontacting, laser-based transducers facilitated identification of the natural frequencies and corresponding modeshapes for the three main surfaces of the club head. The experimental data suggest predominantly different modal characteristics for each surface, and this compares favorably with equivalent data obtained from the finite element model. The modal data are also used to identify surfaces responsible for particular frequency components present in the club head impact sound spectrum. The potential for detailed impact performance prediction using the finite element model is further demonstrated by comparison of computed and experimental club head acceleration measurements recorded during simulated and actual club-ball impacts.     

Graph theoretical duality perspective on conjugate structures and its applications

The paper shows that representing structures, beams and frames by mathematical models based on graph theory enables to provide new perspective on known conjugate structure theorems in mechanics. It is shown that the latter theorems can be derived from the graph theoretical duality principle applied upon the graph representations of the structures. The results reported indicate upon theoretical value of the approach, as the established mathematical foundation can be employed in a variety of mechanical disciplines.     

Optimal control of structures governed by variational and hemiva-riational inequalities and applications

The optimal control problem for broad classes of structures is studied, including those structures having as state relations variational equalities, variational inequalities and hemivariational inequalities. The optimal control problem consists in the minimization of a functional (performance index) having the state relation, enlarged by the control actions, as side condition. Certain new results are given of the optimal control of structures governed by variational and hemivariational inequalities.Some propositions are proved on the existence and the approximation of the solution of the static optimal control problem of structures having a variational inequality as state relation. Then a regularization procedure is proposed for the treatment of corresponding dynamic problem, as well as for the case of hemivariational inequalities. The theory is illustrated by applications concerning convex elastoplasticity and convex and nonconvex unilateral contact problems.     

Nanofluids: Stability, phase diagram, rheology and applications

There is no doubt about the potential technological significance of nanofluids. The promising application areas have been identified as effective heat transfer fluids, contrast agents in magnetic resonance imaging, magnetohyperthermia treatment, precursors to high performance nanocomposites and ordered nanostructures. However, commercial applications are rare, in part due to the limited understanding of the nanofluid fundamentals such as colloid stability, phase diagrams and rheology. This paper intends to provide a brief overview of the scientific disciplines that are important to nanofluids, and the interconnection among different disciplines in order to gain a perspective on the future development of this intriguing area.     

Elastic silicon-film-based nanoshells: Formation, properties, and applications

Controllable formation and properties of solid single-crystal micro-and nanoshells of various shapes (tubes and spirals, vertically positioned rings and cylinders, and bent and trough-shaped cantilevers) are briefly reviewed, and new results are given. The shells and complicated structures of prescribed size and shape are formed with the use of elastic energy of initial strained SiGe/Si films of nanometer thickness and methods of highly selective and directed detachment of the films from the silicon substrates. It is experimentally demonstrated that the diameters of the fabricated SiGe/Si nanotubes are several times smaller than the values predicted by the continuum elasticity theory. The properties of the shells made of semiconductor and hybrid (metal-semiconductor and metal-dielectric-semiconductor) films and their applications in micro-and nanoscale electrical engineering are discussed. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 47, No. 6, pp. 114–128, November–December, 2006.     

LINEAR ACTIVE STRUCTURES AND MODES （ Ⅱ ） — DISCRETE SYSTEMS AND BEAMS

The basic concepts about the active structures and some attributes of the modes were presented in paper “Liner Active Structures and Modes ( Ⅰ ) “. The characteristics of the active discrete systems and active beams were discussed, especially, the stability of the active structures and the orthogonality of the eigenvectors. The notes about modes were portrayed by a model of a seven-storeyed building with sensors and actuators. The concept of the adjoint active structure was extended from the discrete systems to the beams that were the representations of the continuous structures. Two types of beams with different placements of the measuring and actuating systems were discussed in detail. One is the beam with the discrete sensors and actuators, and the other is the beam with distributed sensor and actuator function. The orthogonality conditions were derived with the modal shapes of the active beam and its adjoint active beam. An example shows that the variation of eigenvalues with feedback amplitude for the homo-configuration and non-homo-configuration active structures.     

Dispersion characteristics of wave propagation in layered piezoelectric structures: Exact and simplified models

This article presents a study of the dispersion characteristics of wave propagation in layered piezoelectric structures under plane strain and open-loop conditions. The exact dispersion relation is first determined based on an electro-elastodynamic analysis. The dispersion equation is complicated and can be solved only by numerical methods. Since the piezoelectric layer is very thin and can be modeled as an electro-elastic film, a simplified model of the piezoelectric layer reduces this complex problem to a non-trivial solution of a series of quadratic equations of wave numbers. The model is simple, yet captures the main phenomena of wave propagation. This model determines the dispersion curves of PZT4-Aluminum layered structures and identifies the two lowest modes of waves: the generalized longitudinal mode and the generalized Rayleigh mode. The model is validated by comparing with exact solutions, indicating that the results are accurate when the thickness of the layer is smaller or comparable to the typical wavelength. The effect of the piezoelectricity is examined, showing a significant influence on the generalized longitudinal wave but a very limited effect on the generalized Rayleigh wave. Typical examples are provided to illustrate the wave modes and the effects of layer thickness in the simplified model and the effects of the material combinations.     

LINEAR ACTIVE STRUCTURES AND MODES （ Ⅰ ） — BASIC CONCEPTS AND PROPERTIES

Some basic concepts about the active structures were firstly explained, and the main subjects to study in the field of active structure dynamics were synthesized. For the linear active structures, the annotations on the modes were done in detail. The physical meanings of the right and left eigenvectors were explained. The right eigenvectors are the modal shapes and the modal responses of an active structure depend on the left ones. The adjoint structure of an active structure was defined and the reciprocity theorem was interpreted. For two active structures, which are adjoint to each other and with the reciprocal gain-matrices, the right and left eigenvector are reciprocal The relationship between an active structure and the corresponding passive structure is expressed with the transfer functions, which is employed to resolve the estimation problems.     

Dynamic characteristics and load-sharing performance of concentric face gear split-torque transmission systems with time-varying mesh stiffness,flexible supports and deformable shafts

Meccanica - The concentric face gear split-torque transmission system is a new gear mechanism which integrates the advantages of face gears, split-torque transmissions and concentric transmissions....     

结构主动开闭环多重调谐质量阻尼器（AMTMD）新控制策略

提出了一种新控制策略——主动开闭环多重调谐质量阻尼器(AMTMD)。AMTMD控制系统频率呈线性分布。AMTMD中的MTMD保持相同的刚度和阻尼系数但质量变化。基于TMD的工作原理定义了AMTMD的主动控制力构成即保持相同的位移和速度反馈增益系数但变化结构和地震加速度反馈增益系数。基于结构的广义振型模型，导出了设置AMTMD时结构的动力放大系数(DMF)，于是优化准则可定义为：Min．Min．Max．DMF．通过最优搜寻，研究了反映AMTMD有效性和鲁棒性的参数。这些参数包括：频率间隔、平均阻尼比、调谐频率比、总数、质量比和标准化加速度反馈增益系数。为了比较，多重调谐质量阻尼器(MTMD)和主动开闭环调谐质量阻尼器(ATMD)也被考虑。     

Preface: theory,methods, and applications of mesoscopic modeling

正With increasing attention to complex fluids and soft matter,we have witnessed a fastgrowing research in mesoscopic modeling and simulation in the past decades.The development of mesoscopic methods offers many potential opportunities as well as challenges in modeling of complex materials for diverse applications.Despite significant progress in the past decade,mesoscopic methods are still under development.New formulation in the models,novel theo-     

非节点连接有限元及其在加筋结构中的应用

针对现有加筋结构有限元模型的不足,提出了自由度层次的非节点连接方法.加筋单元的各节点可位于一个或多个其它单元内部,内节点的自由度无需全部与母单元的位移场一致;通过在节点坐标系下对内节点设置独立自由度,可模拟加筋构件与基体材料之间的粘结滑移、无粘结和体外布置等位移不连续性.节点为内节点的单元的刚度矩阵和荷载向量利用虚功原理变换到对应于其广义自由度向量的形式,按照广义自由度的位置向结构整体刚度矩阵和荷载向量组装,以此实现单元问非节点位置的连接.利用开发的有限元软件计算了多个算例,验证了非节点连接方法用于加筋结构有限元建模的正确性和便利性.