FORCED AND FREE VIBRATIONS OF RECTANGULAR SANDWICH PLATES WITH PARAMETRIC STIFFNESS MODULATION

An active control of the resonant vibrations of a rectangular sandwich plate performed by the parametric stiffness modulation is analyzed. The controlled vibrations are those of the dominantly flexural type excited by the transverse force acting at the first resonant frequency of dominantly flexural vibrations. The stiffness modulation is performed at a comparatively high frequency identified by the resonance of a mode of the dominantly shear type. The method of direct partition of motions is used that predicts an existence of the modal interaction between these two modes of vibrations due to the parametric stiffness modulation. It is shown that such a parametric control can provide a significant shift of the first eigenfrequency of a controlled plate (the one subjected to the stiffness modulation) from its nominal value for an uncontrolled plate. Heavy fluid loading conditions are accounted for as well as the energy dissipation in the material of a plate. It is demonstrated that although heavy fluid loading reduces resonant frequencies of forced vibrations, the suggested mechanism of control remains valid in these cases. Dynamics of an elementary two-degree-of-freedom model mechanical system is considered to illustrate the mechanism of modal interaction, which is involved in the suggested way of an active control of vibrations of sandwich plates.     

NON-LINEAR TRANSVERSE VIBRATIONS OF A SIMPLY SUPPORTED BEAM CARRYING CONCENTRATED MASSES

An Euler-Bernoulli beam carrying concentrated masses is considered to be a beam-mass system. The beam is simply supported at both ends. The non-linear equations of motion are derived including stretching due to immovable end conditions. The stretching introduces cubic non-linearities into the equations. Forcing and damping terms are also included. Exact solutions for the natural frequencies are given for the linear problem. For the non-linear problem, an approximate solution using a perturbation method is searched. Non-linear terms of the perturbation series appear as corrections to the linear problem. Amplitude and phase modulation equations are obtained. Non-linear free and forced vibrations are investigated in detail. The effect of the positions, magnitudes and number of the masses are investigated.     

FREE VIBRATION ANALYSIS OF NON-UNIFORM BEAMS WITH AN ARBITRARY NUMBER OF CRACKS AND CONCENTRATED MASSES

An exact approach for free vibration analysis of a non-uniform beam with an arbitrary number of cracks and concentrated masses is proposed. A model of massless rotational spring is adopted to describe the local flexibility induced by cracks in the beam. Using the fundamental solutions and recurrence formulas developed in this paper, the mode shape function of vibration of a non-uniform beam with an arbitrary number of cracks and concentrated masses can be easily determined. The main advantage of the proposed method is that the eigenvalue equation of a non-uniform beam with any kind of two end supports, any finite number of cracks and concentrated masses can be conveniently determined from a second order determinant. As a consequence, the decrease in the determinant order as compared with previously developed procedures leads to significant savings in the computational effort and cost associated with dynamic analysis of non-uniform beams with cracks. Numerical examples are given to illustrate the proposed method and to study the effect of cracks on the natural frequencies and mode shapes of cracked beams.     

VIBRATION AND STABILITY OF ANNULAR PLATES IN NON-LINEAR CREEP CONDITIONS

This paper presents a study on the influence of the physical non-linearity of material in creep conditions on vibration and stability of non-uniform annular plates subjected to a follower force radially distributed at the outer edge. The stability analysis requires first the calculation of a membrane stress distribution and then the application of the kinetic stability criterion, making use of small superposed vibrations. The differential equations of the membrane and vibration states have been integrated by means of the transfer matrix method which allowed the determination of the relationships between the real and imaginary parts of the complex frequency and compressive force (characteristic curves). The results have been presented in numerous figures.     

FREE VIBRATIONS OF SIMPLY SUPPORTED AND MULTILAYERED MAGNETO-ELECTRO-ELASTIC PLATES

Analytical solutions are derived for free vibrations of three-dimensional, linear anisotropic, magneto-electro-elastic, and multilayered rectangular plates under simply supported edge conditions. For any homogeneous layer, we construct the general solution in terms of a simple formalism that resembles the Stroh formalism, from which any physical quantities can be solved for given boundary conditions. In particular, the dispersion equation that characterizes the relationship between the natural frequency and wavenumber can be obtained in a simple form. For multilayered plates, we derive the dispersion relation in terms of the propagator matrices. The present solution includes all previous solutions, such as piezoelectric, piezomagnetic, and purely elastic solutions as special cases, and can serve as benchmarks to various thick plate theories and numerical methods used for the modelling of layered composite structures. Typical natural frequencies and mode shapes are presented for sandwich piezoelectric/piezomagnetic plates. It is shown clearly that some of the modes are purely elastic while others are fully coupled with piezoelectric/piezomagnetic quantities, with the latter depending strongly upon the material property and stacking sequence. These frequency and mode shape features could be of particular interest to the analysis and design of various “smart” sensors/actuators constructed from magneto-electro-elastic composite laminates.     

DSC ANALYSIS OF RECTANGULAR PLATES WITH NON-UNIFORM BOUNDARY CONDITIONS

This paper introduces the discrete singular convolution (DSC) for the vibration analysis of rectangular plates with non-uniform and combined boundary conditions. A systematic scheme is proposed for the treatment of boundary conditions required in the proposed approach. The validity of the DSC approach for plate vibration is tested by using a large number of numerical examples that have a combination of simply supported, clamped and transversely supported (with non-uniform elastic rotational restraint) edges. The present results are in excellent agreement with those in the literature.     

三合板的一般弹性理论

一.引言 本文所指之三合板是一种轻质板材,在航空工业上近年来有广泛的应用。板由三层材料构成:外层为二硬薄钣(金属薄钣),夹心为较轻软之材料(如泡状醋酸赛璐珞、软木、或蜂巢状金属材料)。前者称为表钣,后者称为夹心,表钣与夹心胶合成一综合板。三合板之形变与应力之计算在十多年来曾引起力学家与工     

城市垃圾与煤混烧的灰渣中重金属的特性分析

在0.15MWt循环流化床燃烧试验台上进行了城市垃圾与煤混烧试验,对焚烧后的灰渣中重金属的特性进行了研究。研究结果显示,重金属在焚烧产物中通常以不同的化合物形态存在,改变垃圾与煤混烧时的燃烧工况条件,可以改变重金属的化合物形态,从而改变重金属在灰渣中的分布;灰渣中重金属的浸出毒性低于危险废物浸出毒性鉴别标准中的限定值。     

叶片的周向弯曲与弦向弯曲及其数值分析

六十年代提出的静叶片的倾斜或弯曲方法是以透平轴的平行线为转动轴将叶片转动（构成倾斜叶片）或沿叶高弯曲（构成弯曲叶片）。本文提出将转动轴在Ｓ１平面旋转到弦向，然后倾斜或弯曲叶片，称这种叶片为弦向倾斜或弯曲叶片。应用欧拉方程和高精度ＴＶＤ格式对不同弯曲方法的叶片的数值分析表明弦向弯曲叶片控制径向二次流的能力大于周向弯曲叶片。     

重离子束在等离子体靶中的能量损失

借助于线性Vlasov方程,我们研究了重离子束在等离子体靶中的有效电荷数和电子阻止本领。在高速情况下,分别得到了它们的解析表示式。以~(40)Ga,~(74)Ge,~(84)Kr,~(110)pd,~(208)pb及~(238)U等重离子束在氢等离子体中的能量损失为例,将我们的理论结果与Hoffmann等人的实验结果进行了比较。     

轰击阴极的重粒子能量分布

采用蒙特卡罗模拟对氮辉光放电等离子体中轰击极阴的重粒子（N2^ ,N^ ,Nf及N2f）能量分布随放电参数的变化规律进行了研究。结果表明：阴极臂前诸粒子的能量分布取决于粒子被加速的能量和碰撞频率,能量较低的快原子Nf的密度比高能粒子N^ 的密度最近两个量级。在活性氮粒子（N^ ,Nf）产率最高的放电条件下,适当降低放电气压,提高阴极位降和气体温度,有利于两种活性氮粒子（N^ ,Nf）达到阴极。     

不同负冲角工况下透平叶栅二次流的数值模拟及分析

本文应用TVD格式和Baldwin－Lomax代数紊流模型求解三维NS方程，对一个透平直列叶栅流场在两个不同的负冲角工况下进行了数值模拟，给出了叶栅马蹄涡及其分离鞍点、通道涡、角涡等二次流涡系的结构及其产生发展过程，并对不同工况下的涡系结构及冲角的影响作了详细的分析和比较．本文结果有助于对叶栅二次流涡系结构的产生发展机制的深入了解，同时表明所用数值求解技术有较高的精度和分辨率。     

FREE VIBRATIONS OF MULTILAYERED PLATES BASED ON A MIXED VARIATIONAL APPROACH IN CONJUNCTION WITH GLOBAL PIECEWISE-SMOOTH FUNCTIONS

This paper presents a two-dimensional model for the analysis of freely vibrating laminated plates. The governing differential equations, associated boundary conditions and constitutive equations are derived from Reissner's mixed variational theorem. Both the governing differential equations and the related boundary conditions are presented in terms of resultant stresses and displacements. The model is able to provide the results for the corresponding three-dimensional theory. Such a performance is guaranteed from an appropriate expansion of relevant kinetic and stress quantities through the thickness of the multilayered plate. The expansion is realized by using a novel selection of global piecewise-smooth functions (GPSFs). The number of GPSFs can be arbitrarily increased to achieve a two-dimensional plate theory which is, at least, as accurate as that of a full layerwise theory. It is also shown that GPSFs permit to deal a multilayered plate as if it was virtually made of a single layer. Indeed, the theory need not explicitly introduce continuity conditions for both displacements and relevant stresses. The performance of the present two-dimensional model in conjunction with the global piecewise-smooth functions is tested and discussed by comparing its resulting eigen-parameters, for a class of simply supported plates, with those of other two-dimensional models and with those existing of the exact three-dimensional theory.     

高能重离子碰撞实验中的软物理研究现状

高能重离子碰撞实验中的软物理研究能够帮助我们清楚认识系统的集体演化过程,并且有助于理解碰撞产生的热密系统的性质.本文介绍了高能重离子碰撞实验中软物理的研究现状及其新近取得的实验成果,包括七部分内容:1)高能重离子碰撞简介;2)碰撞几何方面的研究现状;3)粒子产生方面的研究现状;4)关联与起伏方面的研究现状;5)集体膨胀方面的研究现状;6)强子化方面的研究现状,7)LHC/ALICE实验上的软物理预期.最后,本文对高能重离子碰撞实验中的软物理研究现状进行总结.     

单模光纤连接损耗研究

本文从单模光纤高斯模场解析分析法入手,推出了单模光纤归一化频率与高斯模场直径的解析表达式,此后,导出了单模光纤连接中同时存在横向偏移,轴线倾斜,端面间隙,以及光纤直径不匹配时的连接损耗更加完整而普通的计算公式,从而为单模光纤连接器及单模光纤熔接机对准系统的设计提供了依据。     

样条混合元法解板壳问题

应用三次B样条插值函数与二类变量广义变分原理建立一种样条混合元法来求解板壳结构的弯曲问题。应用样条函数来构造壳体的二类场函数:一类为位移场函数,另一类为广义力场函数,由二类变量广义变分原理导出样条混合元法的系统方程组。给出若干数值算例,其计算结果与其它方法作了比较。