如何消除附加质量,刚度及阻尼对频响函数的影响

本文讨论了在实验中消除附加质量、刚度及阻尼对频响函数影响的方法,同时将该法做了进一步的发展,以用于结构修改与频响函数再分析与子结构综合的频响函数分析。文中附有算例,验证了此方法的有效性。     

基于RCSA的深孔内圆磨床主轴端点频响函数预测

基于响应耦合子结构分析法预测了深孔内圆磨床主轴端点的频响函数。首先对磨床主轴进行子结构划分,计算各子结构自由状态下的频响函数矩阵,然后顺序刚性耦合各子结构的频响函数矩阵,对轴承支撑点使用结构修改法修改轴承约束下的已耦合子结构频响函数矩阵,直至耦合到最后一个子结构,得到主轴端点的频响函数。以某深孔内圆磨床为研究对象,分别基于该方法和有限元法,对其主轴端点的频响函数进行预测,并对其进行实验测试。实验及分析结果表明：该方法预测精度高于有限元分析方法预测精度、计算速度快,便于深孔内圆磨床主轴系统的结构优化。     

一种改进的基于响应耦合子结构法的刀尖点频响函数预测方法

针对现有的基于响应耦合子结构法(RCSA)的刀尖点频响函数预测方法需要辨识主轴-刀柄、刀柄-刀具结合面参数以及需要自制刀柄模型等引起的预测误差和预测过程复杂等问题,提出一种改进的基于RCSA的铣刀刀尖点频响函数预测方法。该方法首先改进已有的子结构划分方法,将机床-主轴-刀柄-刀具系统划分为机床-主轴-刀柄-部分刀杆、剩余刀杆和刀齿三个子结构;然后改进主轴-刀柄处转动频响函数的计算方法,通过铣刀的模态锤击实验采用反向RCSA和有限差分法计算机床-主轴-刀柄-部分刀杆结构的转动频响函数,并基于Euler梁模型计算出剩余刀杆、刀齿子结构的频响函数;最后将三个子结构的频响函数耦合确定刀尖点的预测频响函数。以一立式加工中心为研究对象,应用所提出的方法对铣刀刀尖点的频响函数进行了预测,并与其实测频响函数进行对比。对比结果表明：刀尖点的预测频响函数与实测频响函数符合程度较高,其预测、实测前三阶固有频率之间的误差在6.9%以内,所提出的方法可行有效、简单方便,且可直接基于铣刀的模态实验计算主轴-刀柄的频响函数,避免了相关结合面参数的辨识和刀柄模型的制作。     

基于RCSA与GA的铣刀刀尖点频响函数预测

基于响应耦合子结构分析法建立了铣刀刀尖点的频响函数预测模型,针对其中主轴—刀柄基座系统频响函数矩阵难以理论计算和实验测试的问题,提出了基于实验模态测试与遗传算法寻优相结合的主轴—刀柄基座系统频响函数矩阵的优化拟合方法。以VMC850E型立式加工中心主轴系统为研究对象,基于上述方法对铣刀刀尖点频响函数进行了预测,并与其实测频响函数进行对比。结果表明:刀尖点的预测频响函数曲线与实测频响函数曲线符合较好,预测频响函数的固有频率与实测固有频率在0~4 000Hz范围内的相对误差小于4.37%。     

车削加工过程中轴类工件频响函数的快速预测

轴类工件在车削加工过程中由于材料去除,其动力学特性会实时变化。快速准确预测工件频响函数是构建车削稳定性极限图,防止车削颤振的关键环节。通过分析轴类工件连接界面的变形特性,发现刚性耦合条件下的频响耦合子结构法在预测轴类工件频响函数时具有局限性。在此基础上,考虑连接界面刚度影响因素,推导出连接界面刚度的计算方法,利用柔性耦合条件下的频响耦合子结构法建立了加工过程中轴类工件频响函数求解快速预测模型。试验与理论分析结果表明:柔性耦合模型能够快速准确地预测轴类工件随材料去除时的频响函数变化;与刚性耦合模型相比,柔性耦合模型对频响函数预测的准确性受工件尺寸变化影响较小,模型应用范围更广。     

基于近似似然的频响函数不确定性模型修正

贝叶斯模型修正框架下,以频响函数作为目标,提出了一种使用近似似然函数的不确定性模型修正方法。相比于模态参数,频响函数包含了结构更加充分的信息,用于结构动力学模型修正时有诸多优点,但现有的不确定性模型修正方法并不能很好地实现将频响函数作为目标进行修正。针对此问题,介绍了频响函数和贝叶斯框架下的不确定性模型修正理论,基于近似贝叶斯计算提出了一种近似似然函数,可适用于频响函数作为目标进行不确定性修正。将提出的似然函数应用到三自由度数值和H型非对称梁的有限元模型修正算例中,并结合DREAM算法对不确定性参数进行识别。研究结果表明：修正后参数的上、下限与目标值相差无几,修正后模型的频响函数与目标值几乎重合,在一定噪声水平下仍具有较好的修正效果,验证了所提方法的有效性。     

振动系统动力学模型修正方法比较研究

振动系统的动态特性主要取决于其模态参数.修正动力学模型可以提高分析模型与实际系统二者模态参数的一致性或其频响函数曲线间的相似度.这对于准确、可靠预测振动系统的动态特性或动态响应非常重要.文中概述了模型修正基本理论,并对不同模型修正方法进行比较分析.     

基于近似似然的频响函数不确定性模型修正

贝叶斯模型修正框架下,以频响函数作为目标,提出了一种使用近似似然函数的不确定性模型修正方法。相比于模态参数,频响函数包含了结构更加充分的信息,用于结构动力学模型修正时有诸多优点,但现有的不确定性模型修正方法并不能很好地实现将频响函数作为目标进行修正。针对此问题,介绍了频响函数和贝叶斯框架下的不确定性模型修正理论,基于近似贝叶斯计算提出了一种近似似然函数,可适用于频响函数作为目标进行不确定性修正。将提出的似然函数应用到三自由度数值和H型非对称梁的有限元模型修正算例中,并结合DREAM算法对不确定性参数进行识别。研究结果表明:修正后参数的上、下限与目标值相差无几,修正后模型的频响函数与目标值几乎重合,在一定噪声水平下仍具有较好的修正效果,验证了所提方法的有效性。     

基于阻抗耦合子结构法的电主轴固有特性求解

根据阻抗耦合子结构法的基本原理,提出基于阻抗耦合子结构法求解电主轴固有特性的流程,包括电主轴轴段的划分、根据Timoshenko梁理论求解各轴段固有频率和各轴段频响函数、电主轴的阻抗耦合、结果分析等步骤。以某立式加工中心电主轴为研究对象,应用所提出的方法,对该电主轴的固有特性进行求解,并与有限元分析结果对比,证明了该方法的有效性。     

一种新的预测铣刀刀尖频响函数的方法

为准确快速地预测铣刀刀尖点频响函数,提出一种基于逆响应耦合子结构分析（IRCSA）法辨识刀柄-刀具结合面参数的刀尖点频响函数预测方法。该方法通过建立计算刀柄末端频响函数矩阵和刀尖点频响函数矩阵的数学模型,利用逆响应耦合子结构分析法求取随频率变化的刀柄-刀具结合面参数。通过Cuckoo search算法及有限元分析确定刀尖点频响函数中对刀柄-刀具结合面复刚度矩阵变化最为敏感的固有频率,取该频率对应的结合面参数为刀柄-刀具结合面复刚度矩阵的辨识结果,由此计算出刀尖点频响函数。通过硬质合金圆柱棒、2刃铣刀和4刃铣刀进行验证,对比了所提预测方法、Cuckoo search优化算法预测的刀尖点频响函数与实测值三者之间的差异,实验结果表明该预测方法预测的刀尖点频响函数的固有频率和实测固有频率的误差在5%以内,所用时间约为Cuckoo search优化算法的1%,达到了较高的预测精度,并且更加省时、简便。     

Vibration characteristics investigation of mistuned blisks with receptance substructure component modal synthesis method

To improve the simulation efficiency of mistuned blisk, a method called receptance substructure component modal synthesis method (RSCMSM) is proposed to reduce its degrees of freedom (DOFs). The advantage of this method is that only the interface DOFs need to be solved, which observably enhances the computational efficiency. The modal frequencies, maximum modal shape and frequency response function are calculated via RSCMSM. It is seen that the smooth frequency band is governed by blade vibration and the steep frequency band is governed by disk or bladed-disk coupling vibration. In addition, a peak is observed for the tuned blisk but many peaks appear for the mistuned blisk and many small wave crests are observed near the peak. To verify validity of this method, the computational time of RSCMSM is compared with high fidelity finite element method (HFFEM) and classical substructure component modal synthesis method (CSCMSM), which manifests that the computational efficiency increases by 32.19 %–80.82 % than that of HFFEM when the mistuned level is 0 %~5 %. Moreover, computational efficiency of RSCMSM is increased by 0.85 %–7.56 % than that of CSCMSM. The validity of RSCMSM is verified for calculating the complex mechanical structure.

     

代理模型在结构动力学优化设计中的应用研究

在结构动力学优化设计中,使用代理模型是提高计算效率的主要方法。研究实现了代理模型中常用的几种近似方法,以典型函数算例和结构动力学优化为例,建立了对应的代理模型,并就不同代理模型精度进行了对比。研究表明,一些代理模型具有更高的精度和更广泛的适用性,并针对结构动力学优化中的问题,给出选用代理模型的一些建议。     

Comprehensive Overview on Computational Intelligence Techniques for Machinery Condition Monitoring and Fault Diagnosis

Computational intelligence is one of the most powerful data processing tools to solve complex nonlinear problems, and thus plays a significant role in intelligent fault diagnosis and prediction. However, only few comprehensive reviews have summarized the ongoing efforts of computational intelligence in machinery condition monitoring and fault diagnosis. The recent research and development of computational intelligence techniques in fault diagnosis, prediction and optimal sensor placement are reviewed. The advantages and limitations of computational intelligence techniques in practical applications are discussed. The characteristics of different algorithms are compared, and application situations of these methods are summarized. Computational intelligence methods need to be further studied in deep understanding algorithm mechanism, improving algorithm efficiency and enhancing engineering application. This review may be considered as a useful guidance for researchers in selecting a suitable method for a specific situation and pointing out potential research directions.     

Dynamic analysis of harmonically excited non-linear structure system using harmonic balance method

An analytical method is presented for evaluation of the steady state periodic behavior of nonlinear structural systems. This method is based on the substructure synthesis formulation and a harmonic balance procedure, which is applied to the analysis of nonlinear responses. A complex nonlinear system is divided into substructures, of which equations are approximately transformed to modal coordinates including nonlinear term under the reasonable procedure. Then, the equations are synthesized into the overall system and the nonlinear solution for the system is obtained. Based on the harmonic balance method, the proposed procedure reduces the size of large degrees-of-freedom problem in the solving nonlinear equations. Feasibility and advantages of the proposed method are illustrated using the study of the nonlinear rotating machine system as a large mechanical structure system. Results obtained are reported to be an efficient approach with respect to nonlinear response prediction when compared with other conventional methods.     

具有某阶频率约束的试验架设计

为了避开试验架的加载设备的激振频率与试验架的某一阶固有频率耦合，提高试验系统工作的可靠性、安全性和动态性能，针对试验架的结构特点，对试验架建立了具有某阶固有频率约束、以重量最小化为目标函数的优化模型。通过有限元建模、灵敏度分析和采用逐次线性规划求解优化问题，对试验架的主要构件的截面参数进行了优化。结果表明，该方法具有简单、收敛快，具有一定的工程价值。     

削片机进给机构随动系统仿真分析

为提高削片机的工作效率，保证作业的安全性，解决随动系统跟踪过程中响应慢、稳定性不足等问题。以削片机进给机构液压随动系统为研究对象，基于工作原理进一步分析系统中双喷嘴挡板二级电液伺服阀和四通阀控非对称液压缸2个主要部件的结构特性，并建立相应的数学模型。根据系统原理框图,推导随动系统的开环传递函数，采用MATLAB仿真软件搭建系统Simulink仿真框图，通过PID控制器校正系统，对比分析校正前后的仿真结果。结果表明，系统截止频率由86.3 rad/s降为25.8 rad/s，响应时间由0.679 s缩短至0.302 s，幅值裕度提高至为6.09 dB，校正后系统稳定性增强。     

Structural response reconstruction with transmissibility concept in frequency domain

This paper presents a method for structural response reconstruction in the full structure or in a substructure, using the generalized transmissibility concept in frequency domain. The response reconstruction is based on transforming the measured responses into responses at other selected locations with the transmissibility matrix. The use of transmissibility concept in a substructure for response reconstruction is introduced by taking the interface forces at the interface degrees-of-freedom as input excitations. The First-Order-Hold input approximation is used in the forward response calculation to improve the accuracy of the dynamic response analysis. Numerical studies on a seven-storey plane frame structure are conducted to investigate the accuracy and efficiency of the proposed method and the effects of influencing parameters, such as the system sampling duration, sampling rate, sensor numbers and measurement noise are studied. Accurate reconstruction is achieved in all studies when there is significant vibration in the measured responses.     

Isolation of vibrations due to speakers in audio-visual electronic devices without deteriorating vibration of speaker cone

As audio-visual electronic devices such as TV and laptop computer get thinner, vibrations due to speakers bring about sometimes deteriorations in the audio-visual performance. When visco-elastic isolators are installed between speakers and device structures in order to reduce the structural vibration just based on the transmissibility of a single-degree of freedom system, other by-product problems may occur, such as the structural vibration noise inside the devices or the decrease of read/write speed in a hard disk drive system. In this paper, how to isolate speakers is presented so as to reduce the structural vibration of audio-visual electronic devices without reducing the vibration of the cone in speakers. An electro-mechanical vibration model for the whole system, which includes a loud speaker, vibration isolators and a device structure, is derived based on the substructure synthesis method. A dynamic model is derived mathematically for the loud speaker, isolators are treated as lumped springs and damping elements and the device structure is characterized experimentally in terms of compliance. Subsequently, they are coupled using frequency response functions at the connection points. It is claimed that, through simulations on modification of the isolator stiffness and loss factor, a realistically ‘good’ isolator can be designed before making a prototype so that the vibration of the structure may be the minimum, yet without reducing the key performance of a loud speaker in terms of vibration of speaker cone.