旋转圆环平面外振动的行波法研究

以高速球轴承保持架为应用对象,针对旋转薄壁圆环的平面外振动问题,开展弹性波传播的基本特性研究,分析平面外波动的色散方程、波数、截止频率、相速度以及位移耦合系数.基于行波动力学方法,根据波动正向传递的判据,将正负行波的波数进行分离.结合相位封闭原理和波传递矩阵,建立旋转圆环的频率特征方程.文中算例给出了旋转薄壁圆环平面外振动的固有频率,对其计算结果与文献结果作了比较,验证了计算方法的准确性.     

基于ANSYS的(P/FGM/P)悬臂矩形板的模态分析

基于有限元基本理论,用 ANSYS 软件对( P/FGM/P) 型的带压电层的功能梯度材料悬臂板的结构进行了模态分析,这里选用 SHELL99 单元类型. 给出( P/FGM/P) 型的带压电层 FGM 悬臂矩形板的振动模态图,得到固有频率,并且对前 8 阶模态做模态分析,讨论了其对结构的动力学行为的影响. 通过模态分析可以得知带压电层 FGM 悬臂矩形板的模态振型有横向振动,扭转振动,拉伸振动,横向振动以前两阶模态为主,分析结果对系统的结构设计与优化以及振动特性研究提供了有效的依据.     

带边角裂纹悬臂Mindlin 板的振动特性研究

本文基于Mindlin板理论,应用Ritz法研究带边角裂纹Mindlin板的振动特性,分析了不同裂纹参数如裂纹位置,裂纹长度,裂纹角度对悬臂Mindlin板的固有频率和模态的影响.利用Ritz法求解固有频率和模态函数,本文构造了一个特殊的模态函数,其模态函数由两部分构成,一部分是用梁函数组合法得到的无裂纹理想完整矩形板的振型,另一部分是利用裂纹尖端奇异性理论,构造描述裂纹附近位移和转角不连续的角函数.通过高精度的数值计算软件Maple得出结果,并与有限元软件ANSYS分析的结果进行对比,验证本文计算结果的准确性.     

薄壁圆柱壳的高阶模态振动特性研究

采用解析法研究了不同边界条件下薄壁圆柱壳的高阶模态振动特性.首先基于Love壳体理论,在简支-简支、固支-固支和固支-自由三种边界条件下,通过伽辽金法建立了动力学模型,对模态特性进行求解,得到了高阶固有频率和三维模态振型,并通过文献和有限元法进行了比较.算例结果表明,两端简支边界条件下采用解析法得到的固有频率误差值不超过2%,当周向波数较小时固有频率先减小后增加,在高阶时的固有频率逐渐升高,当轴向半波数增加时固有频率明显增大,通过解析法、文献和有限元法得到的三维模态振型相吻合.     

基于DMD方法的矩形断面涡振模态分析

为探究涡激振动下,矩形断面绕流场的模态演化规律及涡振发生机理,基于雷诺平均SST k-ω模型对宽高比为5∶1的矩形断面的涡激振动进行了二维数值模拟研究.通过CFD/CSD交错迭代求解,结合动网格技术实现了二维流固耦合计算,并与风洞试验结果进行对比分析,验证了数值计算的准确性.随后,对流场的瞬时状态进行可视化分析,以z方向涡量值为基本物理量,基于动力学模态分解(DMD)方法对其静态与涡振态流场模态进行了对比分析.结果表明：在涡振发展的不同阶段,主导流场的模态频率不同,主模态频率会由静态涡脱频率向结构固有频率转变,此主模态的转变表征了流固耦合的内在机制;与静态矩形相比,涡振态矩形由于运动诱导涡的存在,导致其前缘涡与尾缘涡的相位差减小,前缘涡与尾涡而合并时前缘涡占据主导,使得在尾缘脱落的Karman涡相关性减弱,形成了涡振锁频现象.     

轴向运动粘弹性夹层梁的横向振动

研究了小扰度下轴向匀速运动粘弹性夹层梁的振动模态和固有频率.基于Kelvin粘弹性本构方程,建立了轴向运动粘弹性夹层梁横向振动控制方程.分别采用Galerkin截断和复模态分析方法,研究两端简支的粘弹性夹层梁的固有频率和模态函数,讨论了轴向运动速度、夹心层与约束层厚度比、初始轴力等参数对夹层梁固有频率、临界速度及稳定性的影响.     

二维圆环结构中弹性波传播的谱单元分析

为研究弹性波在结构中的波场特征,推导建立一种任意四边形二维谱单元,将其应用于二维圆环结构中的波传播行为模拟.以矩形平板结构中弹性导波传播分析为例,通过与传统有限元分析结果对比,验证所建立谱单元的有效性.有裂纹和无裂纹二维圆环结构谱单元模拟结果表明:弹性波在圆环结构中传播会发生频散;圆环结构表面的裂纹对瑞利波的传播影响最大;根据其反射波包位置可以确定损伤位置.     

复模态分析超临界轴向运动梁横向非线性振动

近似解析研究了简支边界条件下超临界轴向运动梁横向非线性自由振动的固有频率和模态函数.采用复模态方法处理控制方程,一个积分偏微分方程.将Galerkin截断思想用于近似处理线性化方程,一个含空间依赖系数的常微分方程.给出了不同截断项数对固有频率的影响.基于8项截断,讨论了系统参数对模态函数的影响.     

基于自适应控制的硅微振动陀螺仪驱动电路研究

硅微振动陀螺仪驱动模态的稳定性对其性能及可靠性有着重要作用.自激驱动能够使单个驱动模态稳定谐振在固有频率上,但对于双驱动模态,由于微机械加工误差的影响,固有频率存在偏差,很难实现频率匹配.研究了基于自适应控制的硅微振动陀螺仪的驱动电路设计,通过固定频率信号驱动和自适应调谐实现双驱动模态的一致性.理论仿真和实验结果表明该设计切实可行.     

运动车辆梁模型的横向振动频率及模态

将运动车辆的车身模型化为Eder-Bernoulli梁,车轮模型化为梁两端边界处的弹性不等的弹簧,形成半车模型.通过复模态分析法研究平滑路面上移动车体的横向振动特性,给出车体横向振动的频率方程以及模态的表达式,通过数值方法求解系统固有频率以及模态函数.并通过数值算例研究车辆运行速度、车体刚度、轮胎弹性系数对车体横向振动...     

海水中VLF传播特性分析

本文以电磁波反射定律与折射定律为基础,建立了电磁波在两种介质分界面处的传播模型,研究了甚低频电磁波在导电媒质中的传播特性,推导了甚低频波在海面及海水中传播的电场表达式,分析了导电媒质对不同频率的电磁波所产生的影响,分析结果表明,甚低频电磁波在海水中的穿透深度较大,能够满足水下通信要求。     

8字型环形腔内光强的分布特性

基于光线传播2×2传输矩阵理论,建立了光波在四频差动激光陀螺一般性环形腔内高斯光束特征参数和电场矢量方程,在此基础上探讨了8字型空腔和石英腔内光波的传输机理,包括分别以环形腔内束腰位置和一般位置作为起始点,高斯光束传播一周,光强最大值、光斑半径大小和光强空间分布的变化规律。结果表明：以束腰位置0-1处作为起始位置,光波沿石英腔内传输一周,再次回到0-1横截面上可以获得整个环形腔内最大光强7．9837×10-6,最小光斑半径0．3539mm,因而此处是激活介质最佳的安装位置。     

Predicting plasma properties using power‐controllable fluorescent lamps under electromagnetic wave radiation

This research proposed an experimental method to predict plasma properties in fluorescent lamps with the aid of electromagnetic (EM) wave propagation. A set of power‐controllable fluorescent lamps are placed between two antennas as a layered plasma medium. The electron density of plasma was adjusted through luminance control of the fluorescent lamps, and the transmission of the EM wave through the area occupied by plasma was achieved. The EM wave reflection and transmission through the plasma area were experimentally measured. By using the time‐domain experimental method, and with aid of the Fourier transformation, EM wave changes in the phase and variance in the intensity are tested. The plasma collision frequency and electron density are then mathematically derived based on the EM wave scattering model theory in unmagnetized plasma. This research provides an experimental approach to predict the plasma properties and diagnose the interaction between EM waves and plasma. The proposed experimental method can be implemented with other types of antennas and extended to a wide range of circumstances, such as monitoring the discharge changes in other plasma sources.     

Modeling of transient bending wave in an infinite plate and its coupling to arbitrary shaped piezoelements

Estimating the location and energy of impacts is of primary importance for assessing the condition of structures. Particularly, such estimation can be easily obtained from the energy flow in the structures, which is usually derived from the Poynting vector. In order to measure the Poynting vector in a thin plate using piezoelements bonded on the plate, an analytical formulation of the impulse response in thin infinite plates is presented. The knowledge of the impulse response of any linear time invariant (LTI) system is precious information for the determination of its behavior under arbitrary inputs. When dealing with propagation, and especially mechanical wave propagation, a common approach consists in using numerical methods that are often time-consuming, especially for multi-coupled systems. This paper proposes a new approach for modeling the impulse response of an infinite plate with surface-bonded piezoelectric elements. The proposed analytical formulation allows bypassing numerical analysis drawbacks, in particular instabilities occurring at high frequencies, case-dependent systems and computational requirements, while giving the response for any time and space domain values using a simple convolution. The proposed model relies on flexural wave decomposition over the spatial frequency domain and corresponds to a time generalization of the angular spectrum theory, thus introducing flexural wave propagation as a time-varying spatial filter. Once the impulse is know in the spatial frequency domain, the inverse Fourier transform is applied and leads to the impulse response in the physical domain. From this model, an analytical expression of the impulse voltage response of the piezoelectric transducers and the Poynting vector can be derived quite easily. The predicted impulse response is then compared to FEM simulation results and experimental measurements in order to assess the model.     

Both transversal negative permeability and backward‐wave propagation in X‐Band waveguide with double‐side SRR metamaterials

In this article X‐band rectangular waveguides partially filled with the double‐side single ring resonator (DSRR) array are investigated for miniaturization, stop‐band, and multi‐band filters applications. Several rectangular waveguides loaded with the DSRR array in 2–10 GHz frequency band have been studied and optimized. We observe both the transversal negative permeability presented above the cutoff frequency and the backward‐wave located below the cutoff frequency with the DSRR array in X‐band waveguide. Both simulation and measurement results of DSRR array are with good agreement. The DSRR array provides better performance of the transversal negative permeability and the backward‐wave than the split‐ring resonator array. The physical explanation of backward‐wave is presented. The power loss distributions are clearly presented for the negative permeability attenuation and the backward‐wave propagation. © 2016 Wiley Periodicals, Inc. Int J RF and Microwave CAE 26:240–246, 2016.     

多视SAR图像交叉谱虚部反演海浪信息

提出利用多视处理子视图交叉谱虚部反演海浪信息的方法。子视图中心频率差分别为400Hz,600Hz和800Hz。所用四幅SAR图像均由JERS-1不同时间采集的。地点为东京附近海域,并有对应的测量所得海浪信息,包括波向、波高和周期。反演结果表明,中心频率差为400Hz的处理方法所得结果精度最高,对应的波向和周期信息都与实测数据相差无几。     

Vibration modelling of complex waveguide structures

In this paper, a general wave propagation approach for the vibration analysis of three-dimensional waveguide structures is presented. The analysis is based on a ray tracing method that considers wave propagation and scattering in the formulation, including the effects of decaying near-field wave components. The waveguide dispersion characteristics of straight and curved beams, which govern the propagation and decay of waves as they travel through the different components, are taken into account for different wave types (flexural, torsional, and axial). Separate elements are coupled using reflection and transmission coefficients, and these are derived for a general connection between several non-planar elements. A matrix formulation is used that offers an automatic and concise method for tackling free and forced vibrations problems of complex ring-beam structural systems. The general methodology is demonstrated on simple applications, and the predictions made using the proposed approach are shown to be in excellent agreement with a conventional finite element analysis, with the advantage of reduced computational costs.     

FEM modeling of SAW organic vapor sensors

A finite element method (FEM) simulation approach of surface acoustic wave (SAW) organic vapor sensors was investigated. The effects of the polymer coating on the propagation characteristics of the SAW were studied by FEM modeling in the absence and presence of vapor. The sensitivities for each vapor-coating combination can be obtained from the simulation frequency shift in different vapor concentration. Comparisons of the simulation sensitivities of SAW vapor sensors with the experimental values reported by Edward T. Zellers and co-workers confirm the general validity of the approach. The approach is expected to select polymer, which offers the best sensitivity for particular vapor.