用于连续体的间隙非线性参数辨识方法

间隙在机械系统中是不可避免的,由间隙引起的接触非线性会严重影响系统的动态响应,使其偏离理想状态,进而降低机械系统的性能和使用寿命。若能利用系统的动态信息识别出间隙非线性参数,就能为机械系统的间隙控制提供依据。针对含间隙连续体系统,提出一种改进的恢复力-位移曲线和条件逆向路径法相结合的间隙非线性参数辨识方法。将哈密尔顿原理推导得到的微分方程简化为空间缩减模型,在获取系统输入和输出的基础上,使用改进的恢复力-位移曲线方法识别连续体系统的间隙值,再利用条件逆向路径法识别间隙接触刚度。整个识别过程在Matlab软件中进行仿真,并在设计的含间隙悬臂梁试验台上进行了参数辨识试验,仿真和试验结果均显示了较高的识别精度,验证了该方法的有效性。     

基于神经网络和子空间的非线性系统载荷识别

由于非线性描述函数选定困难,在不同激励水平下会导致时域非线性子空间辨识过程重复繁琐。针对此问题,基于不同激励水平下时域非线性子空间方法重构的非线性恢复力数据和测量的非线性位置响应数据训练神经网络模型,等效代替响应?非线性恢复力映射关系,使得辨识过程不再依赖系统模型,只需已知非线性位置的响应即可获取非线性恢复力,计算效率得以提高。针对非线性系统外载荷难以测量的问题,利用响应?非线性恢复力映射关系的神经网络模型预测非线性恢复力,进一步提出基于神经网络和子空间法的载荷识别方法,并通过间隙非线性结构的数值与实验研究验证了所提载荷识别方法的有效性和可行性。     

移动刚体激励悬臂梁的间隙模型与实验研究

利用理论建模与实验研究相结合的方法研究移动质量与悬臂梁导轨之间的动态间隙.利用二状态非线性弹簧-阻尼碰撞模型表征间隙铰,运用模态分析理论建立了含间隙作用移动刚体激励悬臂梁的时变横向振动分布参数模型,进行了数值计算.梁的动态响应与实验吻合较好验证了理论分析的正确性,间隙的时域曲线变化趋势基本相同,实验参数下计算的间隙一阶频率和实验一致.所建模型基本描述了系统的动态特性,为研究含间隙的机械系统提供了参考.     

金属橡胶迟滞环的广义恢复力模型

金属橡胶是一种具有非线性恢复力的材料。在对其进行基于位移加载的动态试验中,其恢复力-位移曲线为一迟滞环。本文用理论和试验相结合的手段研究金属橡胶弹性元件的动力学建模,提出了一种新的模型,即广义恢复力模型。将迟滞回线分解为广义弹性力和广义阻尼力,模型中的参数由实验数据辨识。用所建模型重构恢复力-位移迟滞回线,结果表明该模型能很好描述这类非线性振动系统的特性。     

基于Gauss—Newton法的含间隙动力系统的参数识别

运用适合非线性系统参数识别的Ｇａｕｓｓ－Ｎｅｗｔｏｎ方法,在对一含间隙的四自由度弹簧－质量振动系统做动力学分析的基础上,根据部分状态变量的观测值,进行了间隙和系统参数的评估。这些模拟用数据是计算机给模型化位移响应加“噪音”产生的。本文以具有良好收敛性的Ｇａｕｓｓ－Ｎｅｗｔｏｎ法评估动力系统中间隙的数值模拟过程,有好的实用性,并且对解决机械系统和结构中其余类的离散非线性现象的识别具有指导意义。     

一类迟滞非线性振动系统建模新方法

用理论和试验相结合的手段研究一类迟滞非线性振动系统的动力建模, 提出一种新的建模方法, 用此方法建立非线性模型用来描述这类系统的动态特性。该模型用非线性刚度和非线性阻尼机理构造, 刚度和阻尼机理由理论和试验推出, 模型中的参数由试验数据辨识。用所建模型重构恢复力——位移迟滞环, 结果表明, 该模型能很好描述这类非线性振动系统的特性, 模型中各参数的重要性得到展示, 提出的建模方法实用且有效。     

一种含间隙铰链接触分析方法及实验验证

提出一种含间隙铰链接触分析方法,该方法将间隙铰链衬套的几何廓线离散成点,通过判断离散点与铰链销轴几何中心的距离来确定铰链元素间的接触情况并获得最大接触深度,基于Lankarani-Nikravesh连续接触力模型和Ambrósio摩擦力模型计算铰链法向接触力和切向摩擦力。最后建立了含间隙铰链曲柄滑块机构动力学模型,分析了系统的动态响应并开展了相应的实验验证。研究表明,该方法能有效分析含间隙铰链机械系统的动力学特性。     

基于最优控制时变非线性参数模糊辨识

运动状态下结构连接处的时变物理参数对研究结构动态特性与工程实际应用具有重要价值,由此提出了一种结构连接处时变非线性物理参数辨识方法。该方法利用每个子结构的动力学模型,将结构连接处的非线性恢复力作为模型的输入,利用最优控制理论与模糊数学的方法辨识出结构连接处的非线性恢复力,并应用子结构法计算出结构连接处的响应,最后利用最小二乘法拟和了非线性恢复力．计算出非线性恢复力的时变系数。仿真算例表明了该方法用来计算连接结构物理参数精度较高。且结果稳定,避免了迭代发散的现象。     

间隙误差条件下辊轧机传动系统动态特性分析

基于齿轮系统动力学及非线性系统动力学理论,建立了考虑时变啮合刚度、综合啮合误差以及齿侧间隙等因素的叶片辊轧机传动系统的非线性动力学模型。采用数值积分方法对含间隙非线性微分方程组进行了求解,研究了齿侧间隙对辊轧机传动系统的动态特性影响。研究表明:齿侧间隙增大使系统由简谐振动进入混沌振动;传动系统啮合状态由双边冲击转为单边冲击,且间隙的增加对上轧辊一级齿轮-齿条以及二级齿轮-齿条啮合动态响应影响较大,对下轧辊齿轮-齿条啮合动态响应影响较小。     

基于位移加载控制的金属橡胶弹性元件试验建模研究

基于电液材料试验机精确的位移加载控制,对圆环形金属橡胶弹性元件进行了动态力学试验,结果表明,金属橡胶材料具有明显的迟滞非线性性质,其阻尼由多种成分组成。根据动态试验结果建立迟滞回线拟和分解的高次弹性复合阻尼模型,该模型用非线性刚度和非线性复合阻尼机理构造,模型中的参数由试验数据辨识。用所建模型重构恢复力一位移迟滞回线．结果表明,该模型能很好描述这类非线性振动系统的特性,为进一步理论分析提供了依据。     

Effects of joint on dynamics of space deployable structure

Joints are necessary components in large space deployable truss structures which have significant effects on dynamic behavior of these joint dominated structures.Previous researches usually analyzed effects of one or fewer joint characters on dynamics of jointed structures.Effects of joint stiffness,damping,location,number,clearance and contact stiffness on dynamics of jointed structures are systematically analyzed.Cantilever beam model containing linear joints is developed based on finite element method,influence of joint on natural frequencies and mode shapes of the jointed system are analyzed.Analytical results show that frequencies of jointed system decrease dramatically when peak mode shapes occur at joint locations,and there are cusp shapes present in mode shapes.System frequencies increase with joint damping increasing,there are different joint damping to achieve maximum system damping for different joint stiffness.Joint nonlinear force-displacement is described by describing function method,one-DOF model containing nonlinear joints is established to analyze joints freeplay and hysteresis nonlinearities.Analysis results show that nonlinear effects of freeplay and hysteresis make dynamic responses switch from one resonance frequency to another frequency when amplitude exceed demarcation values.Joint contact stiffness determine degree of system nonlinearity,while exciting force level,clearance and slipping force affect amplitude of dynamic response.Dynamic responses of joint dominated deployable truss structure under different sinusoidal exciting force levels are tested.The test results show obvious nonlinear behaviors contributed by joints,dynamic response shifts to lower frequency and higher amplitude as exciting force increasing.The test results are further compared with analytical results,and joint nonlinearity tested is coincident with hysteresis nonlinearity.Analysis method of joint effects on dynamic characteristics of jointed system is proposed,which can be used in optimal design of joint parameters     

Dynamic behaviour analysis of planar mechanical systems with clearance in revolute joints using a new hybrid contact force model

In this study, the dynamic behaviour of planar mechanical systems including revolute joints with clearance is investigated using a computational methodology. The contact model in revolute joint clearance is established using a new nonlinear continuous contact force model, which is a hybrid contact force model, and the friction effect is considered using modified Coulomb friction model. And then, the dynamic characteristics of planar mechanical system with revolute joint clearance are analysed based on the new contact model. Numerical results for two simple planar mechanisms with revolute clearance joints are presented and discussed. The correctness and validity of the new contact force model of revolute joint clearance is verified through the demonstrative application examples. Clearance size and friction effect are analysed separately. The numerical simulation results show that the proposed contact force model is a new method to predict the dynamic behaviour of planar mechanical system with clearance in revolute joints.     

Investigation of the milling stability based on modified variable cutting force coefficients

The cutting force signal distortion is caused by the dynamic characteristics of cutting force testing system. In order to handle this issue, we propose two improvements in the traditional inverse filtering technology. Firstly, we use three-spline interpolation method instead of the curve fitting method to fit the frequency response function of the test system which basically improves the accuracy of fitting. Secondly, the low-pass filter is added before the inverse filter to eliminate the influence of the high-frequency noise signal on the cutting force signal. We choose the cavity-free surface of outer covering parts of mold of automobile as research objects. The inverse filter dynamic compensation technology has been used to remove the influence of the dynamic characteristics of the test system and the high-frequency noise on the cutting force signal. The effectiveness of the proposed method is verified by relative milling experiments. Based on the experimentally measured forces after dynamic compensation, the modified cutting force coefficients are obtained using the average milling force method. The variation law of the cutting force coefficients with the axial depth, the radial width, and the feed rate is examined. Based on the modified variable cutting force coefficients, the 3D stability of the ball end milling cutter surface has been obtained using full-discretization approach. Combining the results from the cutting experiment and the nonlinear method, the stability prediction based on the modified variable cutting force coefficient can improve the prediction accuracy. The results provide theoretical support for the optimization of the machining process of the cavity-free surface of outer covering parts of mold of automobile.     

钢丝绳隔振系统的神经网络杂交建模

提出一种基于神经网络的杂交建模方法,并对某电子设备的钢丝绳隔振系统滞后恢复力进行建模研究。利用周期载荷试验数据,通过参数识别确定系统非线性滞后恢复力的骨架模型。采用神经网络对系统恢复力中难以参数建模的特性进行学习训练,从而得到系统恢复力的神经网络杂交模型。利用得到的杂交模型对隔振系统在周期载荷和宽频随机载荷下的响应进行预测分析与比较,结果显示杂交模型具有较好的预测精度。     

用于电容式传感器的静电激振台的研究

提出了用静电力激振法确定电容式加速度传感器的动态特性，并分析了其静电力的非线性、频率误差及补偿传感器本身寄生电容的方法。给出的静电振动台结构简单、经济实用，具有很宽的低频测量范围(可达1Hz)和较低的静电力非线性系数，输出端具有较高的信噪比，可广泛用于电容式传感器频率特性的测试及结构优化。本文给出了传感器在静电振动台上的测试结果。结果表明：传感器可动系统的几何参数直接影响频率特性曲线，随着传感器平均空气间隙的减小，可动系统的阻尼比增加。     

Dynamic analysis of planar mechanical systems with clearance joints using a new nonlinear contact force model

We investigated the dynamic behavior of planar mechanical systems with clearance joints. First, the contact effect in clearance joint was studied using a new nonlinear contact force model, and the rationality of this model was verified by the results of numerical simulations, which are based on a journal and bearing contact model. Then, the dynamic characteristics of a planar slider-crank mechanism with clearance were analyzed based on the new nonlinear contact force model, and the friction effect of clearance joint was also considered using modified Coulomb friction model. Finally, the numerical results of the influence of clearance size on the acceleration of slider are presented, and compared with the published experimental results. The numerical and experimental results show that the new nonlinear contact force model presented in this paper is an effective method to predict the dynamic behavior of planar mechanical system with clearance joints, and appears to be suitable for a wide range of impact situations, especially with low coefficient of restitution.     

机器人动力学参数辨识方法的研究

在不解体情况下,采用ＣＡＤ方法计算各动力学参数值,基于多体系统动力学模型及ＰＵＭＡ机器人单关节运动试验结果修正相应动力学参数,并考虑各关节摩擦与阻尼特性。通过ＰＵＭＡ机器人各臂联动试验验证辨识参数的正确性。     

滚动轴承-转子系统非线性参数、强迫联合振动

建立考虑非线性轴承力、径向游隙、变柔度等非线性因素和不平衡力的滚动轴承-转子系统动力学方程,并用自适应Runge-Kutta-Felhberg算法对其求解,利用分岔图、Poincaré映射图和频谱图,分析参数、强迫联合激励的滚动轴承-转子系统的响应、分岔和混沌等非线性动力特性.结果表明,滚动轴承-转子系统有多种周期和混沌响应形式,其振动频率不仅有参数振动频率成分和强迫振动频率成分,而且有二者的倍频成分和组合频率成分;随着径向游隙的增大,转子系统的非线性特性增强;不平衡力较小时,系统中参数振动占主导地位,增大不平衡力有利于抑制转子系统的不稳定振动.随不平衡力的增大,强迫振动逐渐增强,大的不平衡力会诱发系统产生混沌振动;转子系统进入混沌的主要途径是倍周期分岔.     

Effects of restitution coefficient and material characteristics on dynamic response of planar multi-body systems with revolute clearance joint

To study the effects of restitution coefficient and material parameters on the dynamic characteristics of planar multi-body systems with revolute clearance joints, a comprehensive methodology for clearance revolute joints in a planar multibody system is presented and analyzed. A new nonlinear contact force model, which accounts for the axial length of bearing and has a wide suitable range of impact situation, is presented to evaluate the contact force between journal and bearing. Furthermore, a modified Coulomb friction force model also presented to consider the effect of friction in clearance joint. Then, a typical journal-bearing model and a planar slider-crank mechanism has revolute clearance joint are used as examples. From the main numerical results under the different restitution coefficient and material parameters, it can be concluded that coefficient of restitution has significant effects on dynamic response of multi-body systems with revolute clearance joint. Additionally, materials of journal and bearing with smaller Young’s modulus will cause obvious delay on dynamic response of multi-body systems.