车用发动机自动张紧器静态力学特性实测分析

自动张紧器是发动机前端附件驱动系统(front and accessory drive, FEAD)中,用于减小张紧轮两侧带段张力波动和带段横向振动位移的主要零部件之一. 张紧器的静态力学特性的评价参数包括张紧器的静刚度、初始扭矩和阻尼系数. 介绍了张紧器力-位移曲线的实验方法,以及张紧器扭矩-角位移曲线、性能评价参数的求解方法. 张紧器静态力学特性实测数据,为FEAD 系统静态、动态特性计算提供数据基础. 实验方法为类似旋转运动件的扭转静刚度测试提供参考.     

纵向力作用下无缝线路动态特性有限元分析

本文通过建立无缝线路有限元动力分析模型,研究了钢轨自振频率和温度力之间的关系.该动力模型包括钢轨模型,钢轨扣件模型,轨枕模型,考虑了钢轨断面特性,钢轨磨耗,轨下刚度以及扣件的弹性刚度和扭转刚度等因素对动力模型计算的影响.分别分析了钢轨磨耗,轨枕支承间距,扣件刚度,钢轨类型以及轨下刚度等参数改变的情况下,钢轨纵向力变化对钢轨振动特性的影响.对部分的计算数据与实际试验测得的数据进行比较分析后,发现通过有限元方法所建立分析模型的计算结果与现场测试结果对比有较好的吻合,采用所建立的计算模型可以更准确地分析无缝线路轨道结构中钢轨纵向力与振动特性的内在联系.     

不锈钢点焊车体性能仿真模型的有效性分析

依据点焊车体结构传力特点,提出点焊车体性能有限元仿真模型的创建方法;以某不锈钢点焊地铁车为研究对象,在BS EN12663-2010标准中静态载荷的作用下,对其车体结构进行刚度和静强度有限元分析与评价,并将仿真结果与测试结果进行对比分析.结果表明:车体各位移测点的测试值与计算值的相对误差最大为9.5％;各区域应力测点的测试值与计算值的变化趋势基本一致,96％的数值较大应力测点的相对误差百分比在0.3％～15％之间.该车体有限元分析模型能很好地反映车体结构的实际刚度和传力特性,其建模方法可以推广到其他点焊结构性能仿真中.     

高维非线性振动系统参数识别

将增量谐波平衡非线性识别推广到高维振动系统, 推导了基于增量谐波平衡的多自由度非线性系统的识别方程. 针对一个两自由度系统进行了数值模拟计算, 讨论了系统在单周期、倍周期和混沌运动状态下的参数识别, 以及噪声对识别结果的影响, 验证了增量谐波平衡非线性识别在多自由度系统中的有效性. 结果表明, 该方法具有较高的计算效率和识别精度, 以及良好的抗噪能力.      

反作用轮扰动特性测量及研究

反作用轮微振动是影响卫星姿态控制精度的重要因素.测量反作用轮扰动的目的是掌握其扰动规律,进而采取相应的控制方法和隔离技术.考虑到反作用轮的扰动与安装条件有关,使用"刚性六分量测试平台"和"柔性六分量测试平台"两种方法进行反作用轮扰动特性测量,并从三个方面对两种方法得到的结果进行比较.比较结果表明,不同测试条件下得到的谐波数是相同的;安装结构刚度降低会降低反作用轮的固有频率;柔性安装条件的减振作用会降低扰动峰值.试验结果可以为探讨卫星结构动态特性对扰动力的影响提供经验和指导.     

基于增量谐波平衡的参激系统非线性识别法

将增量谐波平衡法应用到非线性系统的建模和参数识别中,针对Mathieu-Duffing方程,推导了利用增量谐波平衡原理识别参数激励非线性系统参数的方法. 该方法改进了增量谐波平衡方法的推导过程,通过数值模拟对比研究了谐波平衡非线性识别(harmonic balance nonlinearity identification, HBNID)和增量谐波平衡非线性识别(incremental harmonic balance nonlinearity identification, IHBNID)的效果,验证了增量谐波平衡非线性识别的有效性. 结果表明,增量谐波平衡非线性识别的计算效率较高,计算精度和抗噪能力都优于谐波平衡非线性识别.      

正常使用极限状态下半刚性连接组合梁框架侧移的简化计算

对于无支撑半刚性连接框架而言,仅依靠梁柱本身的抗弯刚度为整个结构提供必需的水平抗侧移刚度,在满足正常使用要求的极限情况下,很有可能是框架的侧移控制设计而不是其承载力,为了充分理解半刚性连接组合梁框架在水平荷载下的侧移特性,本文采用等效刚度梁的概念,将半刚性连接的框架简化为等效的刚接框架,通过等效刚接框架与实际半刚性连接框架有限元分析结果的比较,表明采用等效刚接框架法能准确预测半刚性连接框架的侧移.半刚性连接组合梁框架中的有关参数对其侧移具有不同的影响,半刚性连接组合梁框架的侧移计算可用等效刚接框架进行简化计算,通过算例验证了建议的简化方法不仅可以使计算大大简化,而且具有工程设计可接受的精度.     

力反馈式加速度计动态特性分析及重要参数选择

力反馈式微机械加速度计闭环系统的静电反馈力可以等效成一个与反馈电压成正比的负反馈力和一个与其平方成正比的负刚度,这使得加速度输入不同时,可以等效成不同参数的线性系统.首先,通过系统的等效开环数学模型的分析,提出静电反馈力的负刚度给整个系统带来的影响;然后在保证系统稳定性和其它性能的同时,以满足整个量程内的动态性能指标为目的,提出校正方案以及机械刚度的取值;接着对校验方案以及所选取参数进行了稳定性仿真和动态特性仿真;最后通过不同刚度和校正参数的两个加速度计的对比实验证明:适当提高系统机械刚度并合理选择校正参数能够在几乎不影响系统阈值的情况下提高系统的动态特性和稳定性.     

可倾瓦径向滑动轴承完整动特性系数的分析模型

基于可倾瓦径向滑动轴承瓦块的扰动特性,提出了计算轴承完整动力系数的数学解析模型。在由单块瓦和轴颈构成的子系统上建立局部动坐标参考系,全局广义位移向量可以通过简练的步骤转换为局部动坐标系下轴颈的位移向量,利用求解固定瓦轴承动力特性的方法求得的局部动坐标系下的油膜力又可以精确地转换为全局坐标系下的表达形式,全局坐标系下的油膜力向量关于广义位移和广义速度的Jocabian矩阵形成轴承的完整动力特性系数;利用Newton-Raphson方法同时求解瓦块和轴颈在给定的静态载荷下的平衡位置,其中所需用到的系数矩阵恰好为轴承油膜力关于广义位移的Jocabian矩阵的负值,在得到平衡位置的同时可以获得轴承完整的刚度和阻尼矩阵。数值算例证明了此方法的有效性。     

集簇式弹性连接组合梁桥的力学性能分析

基于二维弹性力学理论,将简支组合梁桥结构简化为层合的平面应力问题,用集中力替代集簇式弹性连接件提供的纵向作用力,根据桥梁表面的受力条件及界面处应力和位移的衔接条件,得到了组合梁桥的应力、位移分布函数。该计算方法收敛性较好且精度较高。参数化分析表明:桥梁跨中挠度和正应力随簇钉间距的增大而增大,但随簇钉刚度的增大而减小;当混凝土全部受压且钢梁全部受拉时簇钉承受的剪力值最大,建议簇钉刚度为104k N/mm,簇钉间距为0.5m~1.0m。计算结果为组合梁桥的科学设计提供了参考依据。     

Sequential non-linear least-square estimation for damage identification of structures

An early detection of structural damage is an important goal of any structural health monitoring system. In particular, the ability to detect damages on-line, based on vibration data measured from sensors, will ensure the reliability and safety of the structures. In this connection, innovative data analysis techniques for the on-line damage detection of structures have received considerable attentions recently, although the problem is quite challenging. In this paper, we proposed a new data analysis method, referred to as the sequential non-linear least-square (SNLSE) approach, for the on-line identification of structural parameters. This new approach has significant advantages over the extended Kalman filter (EKF) approach in terms of the stability and convergence of the solution as well as the computational efforts involved. Further, an adaptive tracking technique recently proposed has been implemented in the proposed SNLSE to identify the time-varying system parameters of the structure. The accuracy and effectiveness of the proposed approach have been demonstrated using the Phase I ASCE structural health monitoring benchmark building, a non-linear elastic structure and non-linear hysteretic structures. Simulation results indicate that the proposed approach is capable of tracking on-line the changes of structural parameters leading to the identification of structural damages.     

THEORETICAL MODEL AND NUMERICAL METHOD ON ONLINE IDENTIFICATION OF DYNAMICAL CHARACTERISTICS OF STRUCTURAL SYSTEM （Department of Engineering Mechanics, Southeast University, Nanjing 210096, P.R. China）

An online method of identification of dynamic characteristics only using measured ambient response of structural dynamic system is widely focused on. The Ibrahim and ARMA ( AutoRegressive Moving Average ) methods are basic identification methods. A model on dynamic system suffered by random ambient excitation was researched into, and a subspace decomposition methodwas introduced. Robustness and effectiveness of this approach on identification of vibration characteristics are demonstrated on numerical experiment.     

Parametric identification of nonlinear systems using multiple trials

It is observed that the harmonic balance (HB) method of parametric identification of nonlinear system may not give right identification results for a single test data. A multiple-trial HB scheme is suggested to obtain improved results in the identification, compared with a single sample test. Several independent tests are conducted by subjecting the system to a range of harmonic excitations. The individual data sets are combined to obtain the matrix for inversion. This leads to the mean square error minimization of the entire set of periodic orbits. It is shown that the combination of independent test data gives correct results even in the case where the individual data sets give wrong results.     

基于子结构解耦的连接特性识别新方法

连接部件动态特性的准确辨识对预测装配式机械结构的动力学行为有重要意义. 针对传统基于子结构解耦的连接结构动力学特性识别方法难以直接利用可测量数据进行辨识及辨识结果受噪声影响显著等问题, 本文提出了一种新方法. 首先, 提取子结构解耦基本方程在测试自由度上的分量, 并经矩阵变换得到显含连接动刚度矩阵的形式, 而后由真实连接动刚度矩阵分解为已知的初始矩阵与待求的增量矩阵, 推导了具有收敛性质的增量型方程以增强界面自由度较多时辨识的数值稳定性, 并采用多项式拟合动刚度将其转化为了拟合系数的频域估计方程, 按给定准则选取合适的频率点联立方程后, 得到了只需装配体测试自由度上的频响函数来辨识连接特性的迭代公式. 最后, 以若干算例说明了算法的具体流程. 对10自由度弹簧?质量块系统进行了数值仿真, 验证了所提方法的正确性及抗噪性; 对包含一处胶接连接的T形梁结构和包含两处螺栓连接的L形梁结构进行了试验, 所辨识连接结构与残余结构重组的装配体有限元模型计算的频响函数与测量值在较宽频带内吻合较好, 表明了该方法能有效识别实际装配体结构中的连接特性.      

Identification and parameter estimation of a bilinear oscillator using Volterra series with harmonic probing

Identification of non-linear systems is mainly limited to polynomial form non-linearities. Among the non-polynomial forms, bilinear oscillator constitutes an important class of non-linear systems and it has been used for modeling of various physical systems, particularly for structural elements with a breathing crack. An identification procedure is presented here for the class of bilinear oscillator, using higher order FRFs derived from Volterra series under harmonic excitation. The procedure addresses the problem of both; identification of the non-linearity structure as well as estimation of the bilinear parameter, which can be correlated to the crack severity and structural degradation. The procedure is illustrated with numerical simulation and the estimation results indicate that even a weakly bilinear state introduced by a small crack size can be accurately identified and measured.     

Very large amplitude vibrations of flexible structures: Experimental identification and validation of a quadratic drag damping model

This article presents a theoretical, numerical and experimental study of resonant structures undergoing very large amplitude vibrations. The purpose of this work is to validate a model for the damping due to the action of the air on a structure’s single-mode response in the steady-state. Experiments are performed on cantilever beams and beam assemblies of various sizes, from centimetric to micrometric, under harmonic base excitation. Dimensionless linear and nonlinear modal damping coefficients are simultaneously identified by means of frequency-domain identification techniques. These measurements demonstrate the pertinence of the presented model.     

环境激励下Benchmark结构损伤识别的试验研究

针对结构健康监测中如何利用在线监测数据进行健康诊断的问题,基于时间序列分析提出了一种新的损伤识别方法.首先,获得结构健康状态的监测数据作为参考状态样本,对各数据样本建立ARMA模型并计算模型残差的方差.然后,将未知状态的监测数据作为待检状态样本,代入已建立的参考状态ARMA模型计算新的残差方差.计算发现,损伤前后两状态模型残差方差存在差异.因而,提出以残差方差之比作为损伤敏感特征,并建立基于F分布的假设检验来辨识结构的状态并预警损伤.最后,以Benchmark结构在环境激励下的试验为例,运用本文方法进行了损伤识别研究.结果表明,基于ARMA模型残差方差的损伤敏感特征可准确地区别结构的健康状态和损伤状态,具备结构在线实时损伤识别的应用价值.     

Nonlinear System Identification of Multi-Degree-of-Freedom Systems

A nonlinear system identification methodology based on theprinciple of harmonic balance is extended tomulti-degree-of-freedom systems. The methodology, called HarmonicBalance Nonlinearity IDentification (HBNID), is then used toidentify two theoretical two-degree-of-freedom models and anexperimental single-degree-of freedom system. The three modelsand experiments deal with self-excited motions of afluid-structure system with a subcritical Hopf bifurcation. Theperformance of HBNID in capturing the stable and unstable limitcycles in the global bifurcation behavior of these systems is alsostudied. It is found that if the model structure is well known,HBNID performs well in capturing the unknown parameters. If themodel structure is not well known, however, HBNID captures thestable limit cycle but not the unstable limit cycle.