移动装备的振动和声学特性分析

为了解决客车车身振动导致乘员室产生低频噪声的问题,在对车身骨架结构、车室腔体进行模态特性分析和对车身结构进行频响分析的基础上,运用边界元法对车室进行声场分析和车身板块贡献度分析,进而找出车内噪声声压峰值处所对应的振动频率及该峰值下的“噪声源”板块,提出对车身结构的修改建议.     

用有限元法分析铁路客车车内空间的声学特性

降低铁路客车车内噪声,提高乘坐舒适度已经成为铁路客车车辆设计者越来越重视的问题。针对某型铁路客车应用有限元法在较低的频率范围内对客车车内的声学特性进行了研究分析,得出了客车车内流体自身的模态和流体与车体耦合后车内流体的模态,并在给定激励下计算了客车车厢内部的声场。     

大型客车车身的阻尼减振降噪技术研究

本文基于边界元法对车室进行声场分析和车身板块贡献度分析,进而找出车内噪声声压峰值处所对应的振动频率及该峰值下的“噪声源”板块,围绕车身减振降噪这一目标和车身设计轻量化的要求,基于响应面法建立阻尼复合结构的声辐射特性、模态频率和损耗因子与结构参数关系的数值模型,并对相应约束条件下的最佳阻尼复合结构参数匹配进行优化设计,综合研究内容对车身结构阻尼处理后取得了较好减振降噪效果。     

基于车身模态和板块贡献分析的阻尼优化降噪方法研究

车身结构上的阻尼材料优化布置对车内振动和噪声控制有重要的意义。以某实车的白车身为研究对象,基于有限元法和边界元法对车内声腔进行声场分析和车身板块进行声学贡献量分析,找出车内场点噪声声压峰值频率及对应的贡献量较大的板块。进而基于白车身模态振型分析,对车身部件上的局部约束阻尼的敷设位置进行优化配置。分析了阻尼优化布置前后分别在悬置、前悬架和后悬架等不同位置处激励下的车内噪声,确认了降噪优化方案的有效性,并在实车上进行了验证。结果表明,对车身相关板块进行局部阻尼处理后,降低车内噪声2 d B(A),证明了该方法的有效性。     

基于有限元法的车身振动与噪声特性研究

针对某客车车型,介绍车身结构振动与噪声特性研究的有限元法,即模态分析和频率响应分析方法的具体实施过程。采用MSC-Nastran 2010软件,选用壳单元类型,按前后各一个吊耳的实际结构定义边界条件。模态分析的结果提示车身结构前10阶固有频率应避开发动机经常工作的频率,并可以判断有无局部模态产生及其发生的位置,确定位置后应予以刚度优化,以避免影响其车身NVH特性。通过有限元法的频率响应分析可获得在任何一个稳态激励下车身结构任意一点的位移、速度、加速度响应,判断是否存在局部共振现象,能够较早地预测结构动态设计不足的问题,以改善车身结构NVH特性。     

开关磁阻电动机振动特性的有限元分析

本文建立了开关滋阻电动机(SR电机)振动特性的二维和三维有限元模型，利用有限单元法计算了SR，电机的振动模态和固有频率，对各种模型计算结果进行了对比分析，研究了SR电机定子结构对其振动模态和固有频率的影响，并与模态实验的结果进行了比较。     

轮胎振动特性实验研究

利用振动实验模态分析的方法,建立了自由悬置状态下轮胎的振动特性模态测试与分析系统,通过轮胎径向激振测试信号的数据处理与分析,提取了各阶的频率及其径向模态振型,分析了轮胎的模态参数随充气压力变化的规律,为实验方法的研究和轮胎结构设计及车辆的动力性能分析提供指导。     

周期局域共振蜂窝板的弯曲振动特性研究

基于声子晶体局域共振原理,设计了周期附加局域振子的蜂窝夹层板结构,利用双协调自由界面模态综合法,计算了周期局域共振蜂窝夹层板弯曲振动的频响特性,并给出了蜂窝夹层板的振型图。分析了局域振子刚度、质量等参数对振动带隙的影响特性,得出了带隙变化的定性规律。研究表明在振动带隙频率范围内,弯曲振动在此蜂窝夹层板能得到有效的抑制,该研究有望为复杂板壳振动控制提供一条新的技术途径。     

客车排气系统振动特性分析及悬挂位置优化

排气系统的振动与噪声是影响整车NVH水平的重要因素,良好的排气系统悬挂点布置及刚度匹配能够有效的降低排气系统与车体之间的振动能量传递。采用Hyperworks软件对某增程式电动客车的排气系统进行有限元建模,同时依据有限元理论对此排气系统进行静平衡分析和模态分析;通过静平衡分析获得悬挂的变形量,通过模态分析得到排气系统的固有频率及振型,依据平均驱动自由度理论,获得排气系统悬挂点的理论最优布置方案,并对分析结果进行评估,为排气系统悬挂吊耳刚度及位置的选择提供技术依据。     

大型顶底复吹炼钢转炉振动特性的研究

本文提出了复吹转炉模型设计的相似理论，以及通过模型实测，确定系统的优势频带和振动型态，识别系统动态特性的方法。揭示了系统所受的是低频激励，以非线性复模态的形式作随机振动。这些成果对复吹技术的实际应用和转炉设计具有重要意义。     

Numerical analysis of wave generation and propagation in a focused surface acoustic wave device for potential microfluidics applications

We develop a 3-D finite element model of a focused surface acoustic wave (F-SAW) device based on LiNbO/sub 3/to analyze the wave generation and propagation characteristics for devices operating at MHz frequencies with varying applied input voltages. We compare the F-SAW device to a conventional SAW device with similar substrate dimensions and transducer finger periodicity. SAW devices with concentrically shaped focused interdigital transducer fingers (F-IDTs) are found to excite waves with high intensity and high beam-width compression ratio, confined to a small localized area. F-SAW devices are more sensitive to amplitude variations at regions close to the focal point than conventional SAW devices having uniform IDT configuration. We compute F-SAW induced streaming forces and velocity fields by applying a successive approximation technique to the Navier-Stokes equation (Nyborg's theory). The maximum streaming force obtained at the focal point varies as the square of the applied input voltage. Computed streaming velocities at the focal point in F-SAW devices are at least an order of magnitude higher than those in conventional SAW devices. Simulated frequency response indicates higher insertion losses in F-SAW devices than in conventional devices, reflecting their greater utility as actuators than as sensors. Our simulation findings suggest that F-SAW devices can be utilized effectively for actuation in microfluidic applications involving diffusion limited transport processes.     

圆柱结构声辐射估计中的振动传感器数目要求

使用近似Kirchhoff积分法估计点力源激励下圆柱壳体的辐射声压和声功率,研究壳体表面速度传感器均匀布放时传感器数目对估计精度的影响。单个场点声压估计和声功率估计误差给定的情况下,随着频率的升高,所需的传感器越来越多,但在场点声压级曲线或辐射声功率级曲线的峰值频率附近,需要的传感器数目会出现谷值;且激励源位置对单个场点声压估计时的传感器数目要求影响不大。进一步研究了全空间声压估计时的传感器数目需求,发现此时传感器需求数目曲线比单个场点声压估计时的传感器数目需求曲线平滑,不会在曲线峰值频率附近出现谷值。     

Effects of multi-scattering on the performance of a single-beam acoustic manipulation device

The effects of multiple scattering on acoustic manipulation of spherical particles using helicoidal Bessel-beams are discussed. A closed-form analytical solution is developed to calculate the acoustic radiation force resulting from a Besselbeam on an acoustically reflective sphere, in the presence of an adjacent spherical particle, immersed in an unbounded fluid medium. The solution is based on the standard Fourier decomposition method and the effect of multi-scattering is taken into account using the addition theorem for spherical coordinates. Of particular interest here is the investigation of the effects of multiple scattering on the emergence of negative axial forces. To investigate the effects, the radiation force applied on the target particle resulting from a helicoidal Bessel-beam of different azimuthal indexes (m = 1 to 4), at different conical angles, is computed. Results are presented for soft and rigid spheres of various sizes, separated by a finite distance. Results have shown that the emergence of negative force regions is very sensitive to the level of cross-scattering between the particles. It has also been shown that in multiple scattering media, the negative axial force may occur at much smaller conical angles than previously reported for single particles, and that acoustic manipulation of soft spheres in such media may also become possible.     

Vibration analysis and measurement of a rolling stay

Abstract

Rolling stay is a device that connects the main engine with the hull plates to reduce the rolling motion of the engine. Severe engine rolling may cause fatigue in bottom structures and base plates. A mathematical model is proposed to describe the motion of the rolling stay and the connecting structures. The rolling stay is modeled as a rod with damping, the hull structure and main engine on two ends of rolling stay are modeled as two sets of effective stiffness and mass, whose values are obtained from finite element analysis of the engine room. The mobility matrices of each subsystem are then used to construct the transfer functions between both ends of the rolling stay.

A set of vibration measurements from both ends of a rolling stay of a 43,000 DWT oil tanker has been taken during a sea trial. Using the scantlings from this ship, the effective stiffness and mass of the hull structure and main engine are obtained by performing finite element analysis. The transfer functions have been theoretically constructed between both ends of the stay and compared with the transfer function obtained from measurements. Results from the predictions and actual measurements show good agreements.     

复杂转子-轴承-汽封耦合系统的非线性振动分析

基于非线性动力学和转子动力学理论,综合考虑Muszynska非线性汽封力、非线性油膜力和转子不平衡量的耦合作用,建立了双叶轮-轴承交错布置的复杂转子-轴承-汽封系统动力学模型。采用有限元法（FEM）推导系统运动微分方程,编程计算了系统转速、圆盘偏心量、汽封长度和汽封间隙等参数对系统动力特性的影响,并利用分岔图、频谱图、相轨迹和Poincare映射图表征了系统的运动性态。研究表明：耦合系统具有高度非线性,随着参数的变化系统呈现出周期运动、倍周期运动、准周期运动和混沌运动等复杂动力学行为。通过减小圆盘偏心,增加系统汽封长度,选取合适的汽封间隙有利于提高转子-轴承-汽封系统的稳定性,改善系统的运动特性。     

水声传感器网络移动节点定位技术

针对水声传感器网络的移动节点定位问题,首先研究了基于距离测量值的多边定位方法(Multilateral Localization,ML);然后利用节点运动信息,提出采用扩展卡尔曼滤波(Extended Kalman Filter,EKF)进行跟踪的方法;最后针对水下移动节点的测量值不同步问题,提出了修正扩展卡尔曼滤波(Modified Extend Kalman Filter,MEKF)以改进EKF的精度。仿真分析结果表明,MEKF的定位精度要好于EKF,而EKF和MEKF由于其用到了节点的运动信息,因此其定位精度要远好于ML。