含空腔的两端固定壁板的发散失稳研究

本文针对含有空腔的两端固定壁板模型的发散失稳进行了研究，基于势流理论、薄翼理论、Galerkin法等理论方法，建立了一种简化的失稳模态求解方式，计算了不同边界条件(简支-简支、简支-固支、固支-固支)下空腔壁板的失稳边界，并对流体黏性、湍流度、空腔壁面对失稳边界的影响进行了分析。结果表明，低雷诺数(Re)下流体黏性较大，对壁板产生较强增稳作用，当Re>>2 000时可以合理忽略黏性作用；湍流度对系统失稳边界有较强影响；该种空腔壁板工况下，空腔体壁面对失稳流速影响微弱。     

陶瓷/金属非保守FGM斜板的颤振分析

研究了陶瓷/金属非保守功能梯度材料（FGM）斜板的颤振问题。以薄板理论为基础,假定材料的等效物性参数为沿厚度方向体积分数的幂律变化,在斜坐标系下建立了非保守FGM斜板的运动微分方程。运用微分求积法,对四边固支边界条件下陶瓷/金属非保守FGM斜板的量纲一复频率进行了数值计算,分析了FGM斜板的梯度指标、夹角和长宽比的变化对非保守FGM斜板稳定性的影响。结果表明,非保守FGM斜板的临界颤振荷载随梯度指标和夹角的增大而减小,随长宽比的增大而增大。     

轴向运动热弹耦合楔形梁的振动特性

以工程中的基本构件楔形梁作为研究对象,分析梁在温度场和弹性场耦合条件下的振动特性。采用D'Alembert原理建立两端固支热弹耦合运动梁的运动微分方程,依据微分求积法得到其特征方程,并对两端固支耦合热弹运动梁的复频率进行了数值计算。得到不同的梁高比下,两端固支轴向运动热弹耦合梁的复频率和速度与频率的变化关系。楔形梁的第一阶模态发散失稳的临界速度随着梁高比的减小而减小,单一模态颤振的临界速度也呈现同样的变化趋势。     

动静压气体径向轴承的静态性能转速效应

通过仿真与试验对纯动压、纯静压、动静压气体径向轴承的静态性能进行了对比分析,得到了轴颈转速、偏心率、气膜的动压效应和静压效应对轴承静态承载力和静态刚度的影响规律。随着转子转速或轴承偏心率的增大,动静压轴承的径向承载力逐渐增大;当转子转速较小时,气膜的静压效应起主导作用,静态刚度随动静压轴承偏心率增大而减小;当转子转速较大时,气膜的动压效应起主导作用,静态刚度随动静压轴承偏心率的增大而增大。     

复合材料板分层损伤识别的曲率模态差法

以单侧固支的分层损伤复合材料层合板为研究对象,利用有限元分析软件ABAQUS得到层合板结构振型位移分析数据,针对分层损伤进行了曲率模态分析。分析结果表明,在层板内一个区域存在分层损伤的情况下,其振型与频率的变化非常小,难以用于判断损伤位置,但分层损伤区域的曲率模态差值变化显著,采用曲率模态差法可以对层合板结构分层损伤位置进行准确判定。     

不同转速下动压气体轴承静动力学特性分析

建立了动压气体轴承非线性气膜力模型,基于DyRoBes-Beperf软件分析了不同转速下动压气体轴承静、动力学特性,如偏心率、最小气膜厚度、最大气膜压力、摩擦功耗、临界轴颈质量、刚度系数、阻尼系数等。结果表明:动压气体轴承主刚度随转速增加呈先减小后增大,同静压气体轴承相似;偏心率对最大气膜压力影响显著;当工作转速低于临界转速时,转速对最大气膜压力影响较大,当工作转速高于临界转速时,转速对最大气膜压力影响不大。     

通过声辐射模态计算矩形薄板的模态辐射效率

模态辐射效率是评价振动结构声辐射能力的一项重要指标。结构振动引起的声辐射问题是声学中一个长期的研究课题。评价振动结构的声辐射能力的一项重要指标就是模态辐射效率。通过声辐射模态理论,推导了任意边界条件下矩形薄板模态辐射效率的计算方法,通过计算方法可以直接得到模态辐射效率的数值解,而不需要进行数值积分。最后,以四边简支、四边固定、对边简支和对边固定、三边固定和一边自由矩形板为例,进行数值计算和分析。通过与前人的计算结果比较,验证了方法的有效性。     

盘形制动系统颤振临界速度的计算及分析

建立干摩擦的单自由度盘形制动系统动力学模型,基于微分包含理论建立其数学模型,采用数值方法计算系统发生颤振运动的临界速度,并讨论阻尼比、动摩擦因数以及最大静摩擦因数与动摩擦因数之差对临界速度的影响。结果表明:系统发生颤振的临界速度随着阻尼比的增大而减小;随动摩擦因数的增大而增大;在动摩擦因数确定的情况下,随最大静摩擦因数与动摩擦因数之差增大而增大,但最终趋于恒定,在阻尼比ζ=0.001情况下最大静摩擦因数为动摩擦因数1.115倍左右时临界速度不再发生变化。     

矩形薄板通透开裂缝对固有频率和模态的影响分析

针对四边固支矩形板薄受到通透开裂影响,引起模态中固有频率和模态振型变化的问题,对两种开裂位置中不同开裂长度进行了研究。首先,应用ANSYS软件建立有限元模型;然后,对开裂裂缝平行于薄板短边且位于板中心(对称开裂)和不位于板中心(不对称开裂)的各25种裂缝长度进行了仿真计算,获得了薄板的固有频率和模态振型。分析结果表明,裂缝的长度和位置影响矩形薄板的固有频率和振型;开裂的缝长和开裂中心位于节线上或者附近是产生模态交叉的两个重要因素,可为板结构开裂的检测提供依据。     

双弹性体再生颤振的稳定性研究

通过理论分析与试验观测相结合的方法,对机床加工系统的加工稳定性进行了研究.从维持颤振需要足够的能量补充以及加工系统质量分布特点的角度,得出了颤振最有可能发生在工件或刀具系统上的推论.在此前提下,将现在常用的再生颤振模型拓展为拥有两个弹性环节的模型.分析和试验结果表明:当这两个弹性环节的动柔度相差较大时,具有较大动柔度的环节为颤振的主动体,颤振将发生在该环节的固有频率附近,该环节即为系统薄弱环节;当两个弹性环节的动柔度相差较小时,颤振主动体则取决于具体的加工条件.试验测试的结果较为直观地反映了颤振主动体在切深连续增加情况下的转换过程和结果.     

Use of internally resonant energy transfer from the symmetrical to anti-symmetrical modes of a curved beam isolator for enhancing the isolation performance and reducing the source mass translation vibration: Theory and experiment

This study aims to use the internally resonant energy transfer from the symmetrical to anti-symmetrical modes of a simply supported curved beam isolator to enhance the isolation performance and reduce the source mass vibration. The model is setup and based on the differential equation of the Euler-Bernoulli beam. The dynamic modal displacements and forces are then obtained from the model using a numerical integration method. The numerical and experimental results indicate that when the ratio of the resonant frequencies of the first bending symmetric and anti-symmetric modes is close to 2 and the excitation frequency is equal to the resonant frequency of the first symmetric mode, the contribution of the first anti-symmetric mode is significant, even though the curved beam and excitation are symmetrical. The net modal force induced by the first anti-symmetric mode acting on the ground is much smaller than that of the first symmetric mode because the two reaction forces at the beam ends induced by the first anti-symmetric mode are equal but opposite. Further, the source mass translational vibration is significantly reduced because it is placed on the node of the anti-symmetric mode.     

Passive suppression of nonlinear panel flutter using piezoelectric materials with resonant circuit

In this study, a passive suppression scheme for nonlinear flutter problem of composite panel, which is believed to be more reliable than the active control methods in practical operations, is proposed. This scheme utilizes a piezoelectric inductor-resistor series shunt circuit. The finite element equations of motion for an electromechanically coupled system is derived by applying the Hamilton’s principle. The aerodynamic theory adopted for the present study is based on the quasi-steady piston theory, and von-Karrnan nonlinear strain-displacement relation is also applied. The passive suppression results for nonlinear panel flutter are obtained in the time domain using the Newmark-β method. To achieve the best damping effect, optimal share and location of the piezoceramic (PZT) patches are determined by using genetic algorithms. The effects of passive suppression are investigated by employing in turn one shunt circuit and two independent shunt circuits. Feasibility studies show that two independent inductor-resistor shunt circuits suppresses flutter more effectively than a single shunt circuit. The results clearly demonstrate that the passive damping scheme that uses piezoelectric shunt circuit can effectively attenuate the flutter.     

Dynamic response of composite panels under thermo-mechanical loading

In this communication, large amplitude flexural vibration behavior of composite curved and doubly curved panels has been studied using the finite element method. Here nonlinear governing equations of motion has been derived based on first order shear deformation theory with von Karman's kinematics, and these governing equations are solved by employing second-order time integration scheme proposed by Bathe. The efficacy of the method for the nonlinear static and dynamic response of curved panels is validated with the published results. Thereafter, the nonlinear dynamic response of cylindrical and spherical panels under thermal shock loading with and without radial pressure is investigated; the parametric study is also being carried out. This study will be valuable for the scientific community.

     

Parametric combination resonance instability characteristics of laminated composite curved panels with circular cutout subjected to non-uniform loading with damping

The dynamic instability of laminated composite doubly curved panels with centrally located circular cutout, subjected to non-uniform compressive in-plane harmonic edge loading is investigated. The present work deals with the problem of the occurrence of combination resonances in contrast to simple resonances in parametrically excited antisymmetric angle-ply and symmetric cross-ply laminated composite doubly curved panels with central circular cutout. The method of multiple scales is used to obtain analytical expressions for the simple and combination resonance instability regions. It is shown that other cases of the combination resonance can be of major importance and yield a significantly enlarged instability region in comparison to the principal instability region. The effects of non-uniform edge loading, centrally located circular cutout, damping, number of layers, orthotropy, the static load factor and the width-to-thickness ratio on dynamic instability behavior of simply supported laminated composite doubly curved panels are studied. The results show that under localized edge loading, combination resonance instability zones are as important as simple resonance instability zones. The effects of damping show that there is a finite critical value of the dynamic load factor for each instability region below which doubly curved panels cannot become dynamically unstable. A central circular cutout has the destabilizing effect on the dynamic stability behavior of laminated composite doubly curved panels subjected to non-uniform edge loading. This example of simultaneous excitation of two modes, each oscillating steadily as its own natural frequency, may be of considerable interest in vibration testing of actual structures.     

壁板结构热屈曲后模态特性试验

高速飞行器在服役期间面临着严酷的气动加热效应,热载荷会引起材料性能变化,会在结构内部产生热应力、热变形及热屈曲,从而改变结构的有效刚度,影响其动力学特性。针对铝合金壁板结构开展热屈曲后模态特性的试验,采用石英灯辐射加热方法模拟气动加热,利用热应变与温度的关系,获得了壁板结构热屈曲临近温度,进而选取屈曲前、屈曲后一系列温度状态开展热模态试验。试验结果表明,模态频率随加热温度的增加先降低,在临近屈曲温度附近达到最低值,热屈曲后随着温度增加又逐渐增加。由于不同阶模态对热载荷的敏感程度不一样,第3阶和第4阶模态在加热过程中发生交换,而模态阻尼随着加热温度的增加呈现增加的趋势。     

动力流体传输曲管振动特性有限元分析

针对悬臂的动力流体传输曲管,建立了它的振动方程和有限元分析模型。并通过对AN-SYS软件的二次开发,自定义了单元,以求解带有陀螺矩阵的曲管振动方程;同时考察了输液曲管的稳定性,求出了输液曲管发生颤振失稳时的临界流速。实例计算结果表明自定义的单元是正确的,具有很高的计算精度。用该自定义单元分析输液曲管的振动特性具有一定的实际意义。     

Widening the sound absorption bandwidths of flexible micro-perforated curved absorbers using structural and acoustic resonances

In this paper, the sound absorptions of flexible curved micro-perforated panels that are backed by an air cavity are studied in detail. A theoretical model that is based on the classical plate equation coupled with an acoustic wave equation is developed for the prediction of sound absorption. This model considers both symmetrical and antisymmetrical structural acoustic responses. Using the electro-acoustic analogy approach, another model is developed that only considers single structural and acoustic modes. It is proposed to make use of panel and cavity resonances to widen the absorption bandwidth of a single/double perforated absorber. The absorption of a flexible micro-perforated panel can be further enhanced by adjusting its curvature to bring the resonant frequencies closer together. The effects of various parameters such as boundary condition, incidence angle, and curvature on the absorption are studied. Predicted results for the single and double layer absorbers show good agreement with measurements.     

Vibration and dynamic stability of pipes conveying fluid on elastic foundations

The paper deals with the vibration and dynamic stability of cantilevered pipes conveying fluid on elastic foundations. The relationship between the eigenvalue branches and corresponding unstable modes associated with the flutter of the pipe is thoroughly investigated. Governing equations of motion are derived from the extended Hamilton’s principle, and a numerical scheme using finite element methods is applied to obtain the discretized equations. The critical flow velocity and stability maps of the pipe are obtained for various elastic foundation para-meters, mass ratios of the pipe, and structural damping coefficients. Especially critical mass ratios, at which the transference of the eigenvalue branches related to flutter takes place, are precisely determined. Finally, the flutter configuration of the pipe at the critical flow velocities is drawn graphically at every twelfth period to define the order of the quasi-mode of flutter configuration.     

LP compressor blade vibration characteristics at starting conditions of a 100 MW heavy-duty gas turbine

In this paper are presented the blade vibration characteristics at the starting conditions of the low pressure multistage axial compressor of heavy-duty 100 MW gas turbine. Vibration data have been collected through strain gauges during aerodynamic tests of the model compressor. The influences of operating modes at the starting conditions are investigated upon the compressor blade vibrations. The exciting mechanisms and features of blade vibrations are investigated at the surge, rotating stall, and buffeting flutter. The influences of operating modes upon blade dynamic stresses are investigated for the first and second stages. It is shown that a high dynamic stress peak of 120 MPa can occur in the first stage blades due to resonances with stall cell excitations or with inlet strut wake excitations at the stalled conditions.     

基于特征映射的超临界机翼整体壁板板坯快速建模技术研究

将整体壁板分解为特征的集合,并进一步将特征分解为特征的位置、方向、几何尺寸、布尔运算等信息的集合。采用曲面优化展开映射实现了特征映射,通过特征的分解、映射与重构解决了超临界机翼整体壁板板坯快速建模的问题。喷丸成形实验表明,采用特征映射法计算完成的板坯成形后尺寸达到了设计要求的精度。