中红外固体激光器的振动可靠性

基于ANSYS建立了中红外固体激光器的有限元仿真计算模型，通过模态分析获取了固体激光器的各阶固有频率、振型等模态参数。结合非接触测振技术搭建了振动模态试验平台，通过试验与仿真对比，验证了模态仿真模型的可靠性。然后，在模态仿真的基础上，通过谐响应分析，重点研究了激光器光学晶体组件在车载正弦扫频振动下的振动特性，获得了等效应力、总机械应变以及位移与激振频率的关系。最后，分析了影响激光器振动可靠性的关键位置，为改进设计提供了有益的参考。结果表明，2 000 Hz以内，底面固定约束的中红外固体激光器共有4阶固有频率与振型，试验与模态仿真得到的振型描述一致，且固有频率误差小于8%，车载扫频振动条件下, 最大总机械应变和等效应力均出现在扩束器的输入镜边缘，沿光学晶体组件轴向的位移最大，其值约为0.14 mm。     

基于有限元的蜗轮蜗杆传动性能模态分析

针对蜗轮蜗杆传动，由于动载荷冲击引起振动变形和使用寿命等问题，文中提出基于有限元分析的蜗轮蜗杆传动性能模态分析研究，使用实验与仿真的方法，采用ANSYS Workbench软件进行蜗轮蜗杆传动性能模态分析，提取自由振动下的固有频率和振型，进行仿真分析与结果对比，实验表明，进行合理的蜗轮蜗杆传动性能模态分析，并且提取合理的模态分析参数，对于蜗轮蜗杆的可靠性研究具有重要性。     

An Investigation on the Coupled Thermal–Mechanical–Electrical Response of Automobile Thermoelectric Materials and Devices

Thermoelectric (TE) materials, which can directly convert heat to electrical energy, possess wide application potential for power generation from waste heat. As TE devices in vehicle exhaust power generation systems work in the long term in a service environment with coupled thermal–mechanical–electrical conditions, the reliability of their mechanical strength and conversion efficiency is an important issue for their commercial application. Based on semiconductor TE devices wih multiple p–n couples and the working environment of a vehicle exhaust power generation system, the service conditions of the TE devices are simulated by using the finite-element method. The working temperature on the hot side is set according to experimental measurements, and two cooling methods, i.e., an independent and shared water tank, are adopted on the cold side. The conversion efficiency and thermal stresses of the TE devices are calculated and discussed. Numerical results are obtained, and the mechanism of the influence on the conversion efficiency and mechanical properties of the TE materials is revealed, aiming to provide theoretical guidance for optimization of the design and commercial application of vehicle TE devices.     

Failure mechanism of FBGA solder joints in memory module subjected to harmonic excitation

This paper investigates the failure mechanism of Fine-pitch Ball Grid Array (FBGA) solder joints of memory modules due to harmonic excitation by the experiments and the finite element method. A finite element model of the memory module was developed, and the natural frequencies and modes were calculated and verified by experimental modal testing. Modal damping ratios are also obtained and used in the forced vibration analysis. The experimental setup was developed to monitor resistance variation of FBGA solder joints due to the harmonic excitation under Joint Electron Devices Engineering Council (JEDEC) standard service conditions. Experiments showed that the failure of the solder joints of the memory module under vibration mainly occurs due to resonance. Forced vibration analysis was performed to determine the solder joints having high stress concentration under harmonic excitation. It showed that failure occurs due to the relative displacement between PCB and package and solder joints are the most vulnerable part of the memory module under vibration. It also showed that cracked solder joints in the experiments match those in the simulations with the highest stress concentration.     

薄板结构开裂特征声-振响应的实验研究

通过对薄板的振动及近场声场的测量探讨不同开裂特征对薄板结构的振动特性及近场声场响应的影响。首先对具有不同开裂形状、尺寸、位置的薄板结构进行了模态仿真计算,得到理论模态振型。然后通过激光测振仪进行振动实验,实验分析开裂薄板的结构模态,同时布置传声器列阵测量近场声压,通过近场声全息理论重构薄板表面声压分布。最后对比开裂薄板理论模态形状与实验测量结果,分析开裂特征对薄板结构的振动特性及近场声场响应的影响。分析结果表明开裂特征对薄板结构的固有频率和振型有明显影响,同时薄板的声响应跟薄板的振型密切相关。     

螺旋桨无人机三维流场数值模拟

采用流体动力学数值模拟方法对无人机及其螺旋桨发动机三维流场进行数值计算,获取了飞机的整体温度分布、螺旋桨发动机高温排气温度、浓度三维分布,为无人机红外辐射特性、空气动力学特性的计算与分析提供数据支撑.     

空调配管动态特性研究

以某空调样机的压缩机及其配管为研究对象,针对压缩机配管的振动与噪声问题。基于Ansys Workbench对其进行模态分析,得到其固有频率和振型。由于管路系统的6、7阶固有频率与压缩机工作频率接近,为避免共振对管路结构提出优化建议。分别基于压缩机内部转子旋转不平衡带来的激励,以及配管内气流脉动作为激励力对管路进行两次谐响应分析。并对两次谐响应仿真结果进行对比分析,根据分析结果提出了空调配管减振降噪措施。     

Analysis of Annular Thermoelectric Couples with Nonuniform Temperature Distribution by Means of 3-D Multiphysics Simulation

Thermoelectric (TE) modules with annular geometry are very attractive for waste heat recovery within the automotive world, especially when integrated as stacks into tubular heat exchangers. The required temperature difference is built up between the coolant, which flows inside an inner tube, and the exhaust gas, which flows around an outer tube. The flow pattern of the exhaust gas can be axial or circumferential, which can lead to higher heat transfer coefficients on the outer surface of the tube. However, this multidimensional construction in combination with a complex flow pattern can lead to a nonuniform heat flux. Additionally, the system experiences a nonuniform temperature distribution which consequently leads to complex conditions regarding the electrical potential. The relevant effects are investigated using a three-dimensional (3-D) numerical model implemented in the computational fluid dynamics (CFD) simulation environment Star-CCM+. The model supports temperature-dependent characteristics of the materials, contact resistances, and parasitic effects in the TE module. Furthermore, it involves techniques to quickly find the exact maximum power point of the TE module with the given boundary conditions. Using the validated model the influence of the nonuniform temperature distribution is investigated with emphasis on the electrical output and TE efficiency.     

基于小波变换的车门运行模态分析

高速列车车门是评价高速列车安全性的一个很重要的部件,它对高速列车的密封性及噪声控制有很关键的作用。模态分析是结构动态设计,振动和噪声控制及设备故障诊断的重要方法。传统的传递函数模态分析方法的特点是同时利用激励和响应信号进行参数识别,而基于环境激励下的模态参数识别方法仅根据系统的响应就可以进行参数识别。其中,基于小波变换的模态分析方法非常有前景,它利用其良好的时频分辨能力以及带通滤波性质可以使系统自动解耦,然后从自由振动信号的小波变换谱图的小波脊线出发识别模态参数。本文利用基于小波分析的运行模态分析方法,对高速列车车门进行模态参数识别,效果良好。     

Finite element modeling and modal analysis of the human spine vibration configuration

This study was designed to investigate the modal characteristics of the human spine. A 3-D finite element model of the spine T12-Pelvis segment was used to extract resonant frequencies and modal modes of the human spine. By finite element modal analysis and harmonic response analysis, several lower vibration modes in the flexion-extension, lateral bending, and vertical directions were obtained and its vibration configurations were shown in this paper. The results indicate that the lowest resonant frequency of the model is in the flexion-extension direction. The second-order resonant frequency is in the lateral bending direction and the third-order resonant frequency of the T12-Pelvis model is in the vertical direction. The results also show that lumbar spinal vertebrae conduct the rotation action during whole body vibration (WBV). The vibration configurations of the lumbar spine can explore the motion mechanism of different lumbar components under WBV and make us to understand the vibration-induced spine diseases. The findings in this study will be helpful to understand WBV-related injury of the spine in clinics and the ergonomics design and development of mechanical production to protect human spine safety.     

基于ANSYS的供球机构摆动轴静动态特性分析

供球机构摆动轴的静动态特性对稳定供球、提高供球成功率和提高植球良率有着重要意义。因此,有必要对摆动轴静动态特性进行仿真分析。通过建立简化的摆动轴力学模型,并应用有限元分析软件ANSYS对摆动轴摆动角0°中间位置和±45° QUOTE 极限位置进行了静态分析,得到了摆动轴在这些位置的应力、变形云图。对摆动轴进行模态分析,得到了摆动轴前6阶固有频率以及振形。分析结果表明,摆动轴的初步设计符合设计要求,同时判断出摆动角±45° QUOTE 位置是摆动轴危险位置,为植球机供球机构的下一步设计与优化提供了参考。     

Modal analysis of board-level electronic package

The reliability of board-level electronic package subjected to drop impact is one of the most concerned issues. After drop impact, the Printed Circuit Board (PCB) experiences free vibration which leads to the deformation of PCB, hence the failure of solder joints. The free vibration is dependent on the inherent parameters of PCB. So it is necessary to study the inherent parameters of board-level package. Modal analysis is a common way to characterize the inherent dynamic parameters of a system. By modal analysis, we can understand the inherent vibration features of board-level package system. In this paper, the theoretical vibration model of the JEDEC standard PCB assembled with three Chip Size Packages (CSPs) is performed. Then the results of theoretical analysis are validated by that of finite element analysis (FEA) and modal test. A series of modal parameters are obtained during the modal analysis such as the mode shapes, the natural frequencies and the damping ratios. These parameters are useful for studying the dynamic response of PCB and the strain rate of solder joints during drop test. The Modal Assurance Criterion (MAC) value is used to validate the correlation between two modal shapes obtained from two different modal parameters estimation methods during modal analysis. The MAC value is computed for the first two order mode shapes, indicating the high correlation between the experimental and predicted (including theoretical and FE results) mode shapes.     

Effect of geometric dimensions on thermoelectric and mechanical performance for Mg2Si-based thermoelectric unicouple

The generating efficiency of thermoelectric generation (TEG) depends not only on the thermoelectric (TE) performance of TE device, but also on its mechanical performance. And choosing suitable TE materials and geometric dimension can improve the working performance of TE device. Mg₂Si is one of the most promising TE materials in the medium temperature range, and Mg₂Si-based TE devices have broad application prospects. In this paper, a three-dimensional finite model of the Mg₂Si-based TE unicouple used for recovering vehicle exhaust waste heat is constructed for the performance analysis. The TE performance and mechanical performance of the Mg₂Si-based TE unicouple under the influence of different geometric dimensions are investigated, respectively. The curves of the output power, the power conversion efficiency and the thermal stress distribution varying with different geometric dimensions are discussed in detail. The calculated result would be helpful for further understanding of the TE and mechanical properties of the Mg₂Si-based TE unicouple, and it can also provide guidance for further strength check and optimum geometric design of TE unicouples in general.     

Design and Numerical Evaluation of Cascade-Type Thermoelectric Modules

Thermoelectric (TE) generation performance can be enhanced by stacking several TE modules (so-called cascade-type modules). This work presents a design method to optimize the cascade structure for maximum power output. A one-dimensional model was first analyzed to optimize the TE element dimensions by considering the heat balance including conductive heat transfer, Peltier heat, and Joule heat, assuming constant temperatures at all TE junctions. The number of p–n pairs was successively optimized to obtain maximum power. The power output increased by 1.24 times, from 12.7 W in a conventional model to 15.7 W in the optimized model. Secondly, a two-dimensional numerical calculation based on the finite-volume method was used to evaluate the temperature and electric potential distributions. Voltage–current characteristics were calculated, the maximum power output was evaluated, and the efficiencies of two possible models were compared to select the optimal design. The one-dimensional analytical approach is effective for a rough design, and multidimensional numerical calculation is effective for evaluating the dimensions and performance of cascade-type TE modules in detail.     

稳压器抗震分析简化力学模型探究

本文研究核电站稳压器抗震分析模型的建立方法。针对某堆型的稳压器，分析内部冷却剂的液面晃动效应及处理方法；对比分析节点个数、筒体壁厚、集中质量等因素对简化模型固有频率的影响，确定了稳压器抗震分析模型的简化原则。针对最终模型进行模态分析，并对计算结果进行评价。     

Bior1.5小波在路面不平度分析中的应用

文中介绍了一种基于小波变换的路面不平度分析方法.根据路面不平度样本值,运用AR（AotoRegressive）模型建立路面不平度时间序列,将路面不平度时间序列作为输入,用Bior1.5小波对路面不平度进行分析并得到各层小波功率谱.结果表明,将小波变换引入路面激励的分析中,可以清晰的了解信号的时频特性,更能充分揭示车辆的振动状况.     

基于Ansys的0-3型压电振子的有限元分析

0-3型压电复合材料以其柔软性,易加工成型和制备工艺简单等优点,具有广泛的应用前景.该文利用0-3型压电复合材料作为压电悬臂梁压电振子的压电体,利用Ansys软件对振子做有限元分析,包括静态和模态分析,得出压电振子各参数对其发电能力及谐振频率的影响:振子发电能力与外力及振子的长度成正比,与振子宽度成反比,存在最佳长度比和厚度比;振子的固有频率与长度及质量块的质量成反比,宽度对固有频率的影响较小.这些数据为压电悬臂梁的结构参数提供设计依据.     

压电驱动式疲劳试验系统动态特性分析

针对压电驱动式疲劳试验系统动态特性分析问题,根据振动力学理论,建立了压电疲劳试验系统的动力学模型,得出了系统固有频率和动载荷表达式,并通过Matlab仿真,分析了压电振子的刚度对系统固有频率和动载荷影响关系。最后进行了实验测试,测试结果表明,实验所得数据与理论分析在误差允许范围内吻合较好,验证了理论分析的正确性。为压电驱动式疲劳试验系统谐振频率跟踪与工作载荷精度控制提供了理论依据,同时也对压电驱动式疲劳试验系统的动态性能进行预测,具有一定的工程应用价值。     

Modal Characteristics of Crossed Rectangular Waveguides

The modal solution for the crossed rectangular waveguide is presented. Cutoff frequencies and modal fields are determined by formulating an integral eigenvalue equation which can be solved by application of the Ritz-Galerkin method. Field equations are given for both TE and TM modes. The calculated cutoff frequencies of several lower order modes agree very well with the available experimental results in the literature.     

Random vibration reliability of BGA lead-free solder joint

Solder joint fatigue failure under vibration loading has been a great concern in microelectronic industry. High-cycle fatigue failure of lead-free solder joints has not been adequately addressed, especially under random vibration loading. This study aims to understand the lead-free solder joint behavior of BGA packages under different random vibration loadings. At first, non-contact TV Laser holography technology was adopted to conduct experimental modal analysis of the test vehicle (printed circuit board assembly) in order to understand its dynamic characteristics. Then, its first order natural frequency was used as the center frequency and narrow-band random vibration fatigue tests with different kinds of acceleration power spectral density (PSD) amplitudes were respectively carried out. Electrical continuity through each BGA package is monitored during the vibration event in order to detect the failure of package-to-board interconnects. The typical dynamic voltage histories of failed solder joints were obtained simultaneously. Thirdly, failed solder joints were cross-sectioned and metallurgical analysis was applied to investigate the failure mechanisms of BGA lead-free solder joints under random vibration loading. The results show that the failure mechanisms of BGA lead-free solder joint vary as the acceleration PSD amplitude increases. Solder joint failure locations are changed from the solder bump body of the PCB side to the solder ball neck, finally to the Ni/intermetallic compound (IMC) interface of the package side. The corresponding failure modes are also converted from ductile fracture to brittle fracture with the increase of vibration intensity.