基于自适应最稀疏时频分析的钢筋混凝土梁非线性振动识别研究

研究了基于自适应最稀疏时频分析方法的弱非线性系统识别方法,并用于识别钢筋混凝土梁的非线性振动参数进而识别损伤。通过自适应最稀疏时频分析方法得到非线性系统自由振动响应的瞬时振幅和瞬时频率,进而识别其派生系统固有频率、阻尼系数、非线性系数。对一根钢筋混凝土简支梁进行分级加载破坏和不同损伤状态下的锤击激励测试,运用自适应最稀疏时频分析方法分解其加速度响应,识别梁的非线性振动参数。通过实验发现:钢筋混凝土梁的派生系统固有频率随着损伤的增大而减小,不受初始振幅大小的影响且离散性小,能够较好地识别损伤;阻尼系数和非线性系数仅在小损伤情况下随着损伤的增大而增大,可以识别小损伤。     

宇航级三浮陀螺仪三质量块隔振模型

从三浮陀螺仪的结构出发,考虑浮液和动压气体轴承的特点及隔振作用,运用振动理论和隔振技术,建立并论述了三浮陀螺仪三质量块振动模型。对该模型在受迫振动下的运动方程进行了分析,得到了运动方程的解。对该模型的参数进行了识别,对浮液阻尼特性进行了分析,用摄动法求解了阻尼系数c12;对波纹管弹性系数进行了推导计算,得到了弹性系数k12的表达式;对气体轴承的动态阻尼和刚度进行了分析说明,得到了阻尼系数c23和弹性系数k23的表达式。基于此模型,给出了力传递系数的求解方法以及表达式。对三浮陀螺仪振动传递研究有一定指导作用。     

橡胶隔振系统非线性振动参数识别与特性研究

建立单自由度非线性系统基础激励正弦扫描试验的数学模型,并针对多项式非线性阻尼与多项式非线性弹簧并联的橡胶隔振系统求解了数学模型.进而在此框架下通过正弦扫描振动试验,采用共振峰值法识别了橡胶隔振器的非线性阻尼与刚度系数,研究了不同振动量级下小型橡胶隔振器的振动特性.     

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基于结构动力学基本理论,系统地分析了路面材料阻尼系数的求解方法,以 及材料阻尼效应对路表动态弯沉的影响规律. 结果表明：利用第1,第2主振型的固有频率 计算阻尼系数的方法,能克服传统简化计算阻尼系数而带来的结果偏差;黏性阻尼系数几乎 对路表弯沉时程变化没有影响;土基阻尼效应是影响路表动态弯沉时程变化的关键因素,而 其它层材料的阻尼特征影响甚微. 研究结果为进行路面结构动力学分析时,材料阻尼参数的 计算以及合理取值提供了理论与实践依据.     

识别粘弹性材料力学参数的自由阻尼试件设计方法研究

工程上常用悬臂梁弯曲共振法识别粘弹性材料的力学参数,而自由阻尼试件是实验中常见的结构形式,因此试件设计的合理性直接关系到材料参数的测试精度。为了能够更好地指导试件设计,首先通过灵敏度分析法定义了影响系数的含义,并将其应用于分析试件的厚度比、共振频率比、密度比等参数的误差对材料参数测试精度的影响中,进而为试件的设计提出一些有重要工程价值的技术指标。其次,基于悬臂梁弯曲共振法实验,分析得出适合采用单边自由阻尼结构试件识别的粘弹性材料。最后,对弯曲共振法中两种不同的自由阻尼试件(单边自由阻尼试件和双边自由阻尼试件)对测试精度的影响进行了比较分析,为实验中这两种结构形式的选取提供了依据。     

基于数值分析的模态阻尼系数获取方法

结构模态阻尼系数是影响振动疲劳特性的主要因素,获取模态阻尼系数对于结构振动疲劳的分析和仿真计算有重要作用,对于揭示金属材料振动疲劳损伤形成机理有直接意义。本研究针对2024-O铝合金,进行了大量的元件级试件的振动疲劳仿真分析、试验研究以及数值分析计算,并提出了一种基于数值分析的快速获取结构模态阻尼系数的方法,适合于获取试验件振动疲劳试验过程中的模态阻尼系数变化趋势。研究表明:在不中断试件疲劳试验的情况下,本文方法可以快速准确地得到试验件在整个振动疲劳历程中的模态阻尼系数,固有频率的相对偏差小于0.06%,模态阻尼系数的相对偏差小于1%。为进一步揭示金属材料振动疲劳损伤的形成机理奠定了基础。     

阻尼对空爆荷载等效静载动力系数的影响

为考查阻尼参数对空爆荷载等效静载动力系数的影响,理论推导了空爆荷载下结构等效单自由体系弹塑性位移解及延性比解,设计并计算了阻尼比0.000 1～0.1、延性比1～4的20种典型工况的动力系数,并与现行抗爆设计规范动力系数公式结果进行了对比。结果表明:阻尼比小于0.000 1时可基本代表无阻尼状态,阻尼比0.01的动力系数比无阻尼的最大降低幅度为2.08%,数值差异很小,因此阻尼比为0.01以内时,可忽略阻尼对动力系数的影响;阻尼比0.05的动力系数比无阻尼的降低幅度约9.92%,数值差异较大,认为阻尼比0.05以上时将具有明显的经济效益;现行设计规范动力系数更适用于柔性结构体系,运用于刚性结构抗爆设计时,计算误差较大,对阻尼比较小的结构设计更不利。     

静电悬浮微陀螺的压膜阻尼特性

空气阻尼对静电微陀螺系统的动态特性起着重要的影响。根据流体力学,构建了描述微陀螺内部气体压膜阻尼特性的线性Reynolds方程。将微陀螺内部气膜分成了13个分区,推导了转子在轴向振动、径向振动、径向摆动时的压膜阻尼系数。根据微陀螺的结构参数进行仿真,结果表明:轴向压膜阻尼系数对微陀螺支承系统的动态特性影响最大,而压膜阻尼系数与气体的温度,压强呈线性关系,与振动幅值呈抛物线型关系;在低频段系统呈现阻尼力,而到高频段,系统呈现弹性力。利用Simulink进行了微陀螺的系统建模,得出压膜阻尼系数Cz对PID参数的选取,尤其是Kd参数,起着重要作用,同时对系统的稳定性也有一定的影响。     

高速铁路连续箱型梁桥的动力响应与减振分析

根据列车具体的轴距和轴重,建立了和谐号动车组CRH380AL型列车简化模型;对高速铁路两跨连续梁桥采用多自由度欧拉伯努利梁单元进行主梁的模拟,并将液体黏滞阻尼器模拟为有限元阻尼单元;采用Newmark直接积分方法求解了高速列车作用下的连续梁桥运动方程,数值分析了列车车速以及液体黏滞阻尼器的阻尼系数对于高速铁路连续梁桥振动响应的影响。结果表明:黏滞阻尼器对于桥梁具有明显的减振效果,阻尼力不仅与阻尼系数有关还与列车时速有关;同一黏滞阻尼器条件下,桥梁的最大加速度并不随列车速度的增加而单调增加,而是在某些特定列车车速下桥梁的最大加速度出现了峰值,且随着黏滞阻尼器的阻尼系数增大,桥梁振动响应峰值处的最大加速度减幅不同;同一列车时速的条件下,桥梁的减振效果并不是随着阻尼系数的递增呈正比递增,而是随着阻尼系数的增大,阻尼器的减振效果增幅在减小。     

基于改进链码法的LuGre摩擦模型动态参数辨识

针对现有LuGre摩擦模型动态参数辨识方法辨识精度不高,收敛性难以保证及参数初值难以确定等不足,提出了一种基于改进链码特征识别法的参数辨识方法。首先,研究LuGre摩擦模型中两个动态参数-鬃毛刚度系数与阻尼系数之间的关系,以及鬃毛刚度系数与预滑动阶段位移-摩擦力曲线形状之间的对应关系;然后,改进现有Freeman链码的采样方式和码间距,利用改进的链码结合傅立叶描绘子提取位移-摩擦力曲线的形状特征并形成特征向量;最后,以加噪声原始位移-摩擦力曲线和仿真位移-摩擦力曲线的特征向量为参数建立度量两曲线相似程度的欧氏距离,寻优得到使欧氏距离满足给定误差的仿真位移-摩擦力曲线,该曲线对应的鬃毛刚度系数即为其辨识值,进一步可计算出阻尼系数。文末给出的辨识实例验证了提出方法的正确性和有效性。     

Identification of the damping properties of rigid isotropic materials by studying the damping flexural vibrations of test specimens

A technique for determining the damping properties of a rigid isotropic material from the experimental data on the damping capacity of elongated cantilever-fixed test specimens due to the internal and external aerodynamic damping is proposed. The following two methods for eliminating the aerodynamic damping component are considered: the extrapolation of the data on the damping capacity of a series of test specimens of different widths to the point corresponding to the zero width and the theoretical-experimental approach. The damping properties of the material are determined by the vibration logarithmic decrement depending on the amplitude of the linear deformation. This dependence is represented by a power polynomial. The polynomial coefficients are determined from the minimum condition of the goal function for the positive logarithmic decrement of the material vibrations. These coefficients are sought at the reference point by repeatedly solving the direct problem of determining the damping capacity of the test specimen from the given damping properties of the material. An example is considered to illustrate the identification of the damping properties of steel St.3.     

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.     

时域自适应算法求解移动荷载下梁的多宗量反问题

通过一种时域自适应算法,建立了求解变速移动荷载下梁的多宗量反问题的数值模型,可同时识别移动荷载和梁的物性参数.正问题采用时域自适应算法和FEM建模,并可由此方便地推导敏度公式;在反问题求解中采用Levenberg-Marquardt法,计算表明该方法具有较好的抗不适定性.通过两个算例,对所提算法进行了数值验证,并探讨了噪声和测点的变化对反演结果的影响,结果令人满意.     

求解Rayleigh阻尼系数的加权最小二乘法

在地震反应分析过程中,提出了一种优化方法以解决Rayleigh阻尼系数计算时选择两阶合理参考频率的难题。该方法是以反应谱理论为基础,以结构位移峰值误差最小为目标函数。将位移反应谱用一阶Taylor级数近似计算,从而将目标函数简化为加权最小二乘法的方程。随后以框架结构为例,讨论了模态个数和阻尼比模型对Rayleigh阻尼系数计算的影响,并与传统方法、最小二乘法及基于多参考振型的加权最小二乘法进行比较。计算结果表明,最小二乘法由于忽略了模态贡献的影响,不是计算Rayleigh阻尼系数的合理方法。当模态个数所包含的累积振型参与质量达90%以上,本文方法所得Rayleigh阻尼系数计算结果稳定,结构动力反应的计算精度高。     

Structural damping identification method using normal FRFs

All structures exhibit some form of damping, but despite a large literature on the damping, it still remains one of the least well-understood aspects of general vibration analysis. The synthesis of damping in structural systems and machines is extremely important if a model is to be used in predicting vibration levels, transient responses, transmissibility, decay times or other characteristics in design and analysis that are dominated by energy dissipation. In this paper, new structural damping identification method using normal frequency response functions (NFRFs) which are obtained experimentally is proposed and tested with the objective that the damped finite element model is able to predict the measured FRFs accurately. The proposed structural damping identification is a direct method. In the proposed method, normal FRFs are estimated from the complex FRFs, which are obtained experimentally of the structure. The estimated normal FRFs are subsequently used for identification of general structural damping. The effectiveness of the proposed structural damping identification method is demonstrated by two numerical simulated examples and one real experimental data. Firstly, a study is performed using a lumped mass system. The lumped mass system study is followed by case involving numerical simulation of fixed–fixed beam. The effect of coordinate incompleteness and robustness of method under presence of noise is investigated. The performance of the proposed structural damping identification method is investigated for cases of light, medium, heavily and non-proportional damped structures. The numerical studies are followed by a case involving actual measured data for the case of a cantilever beam structure. The results have shown that the proposed damping identification method can be used to derive an accurate general structural damping model of the system. This is illustrated by matching the damped identified FRFs with the experimentally obtained FRFs.     

Melnikov analysis for a ship with a general roll-damping model

In the framework of a general roll-damping model, we study the influence of different damping models on the nonlinear roll dynamics of ships through a detailed Melnikov analysis. We introduce the concept of the Melnikov equivalent damping and use phase-plane concepts to obtain simple expressions for what we call the Melnikov damping coefficients. We also study the sensitivity of these coefficients to parameter variations. As an application, we consider the equivalence of the linear-plus-cubic and linear-plus-quadratic damping models, and we derive a condition under which the two models yields the same Melnikov predictions. The free- and forced-oscillation behaviors of the models satisfying this condition are also compared.     

Non-linear Damping and Frequency Identification in a Progressively Damaged R.C. Element

This paper describes the non-linear identification of a progressively damaged reinforced concrete beam-column node. The aims are the detection and identification of the different sources of damping and their dependence from the damage level. To this end a specially formulated non-linear identification method is proposed, based on a time-varying polynomial approximation of the system dynamics, suitable for use in the presence of excitations of any form. A minimum condition imposed to the identified dissipated energy leads to the distinction of the linear viscous component from the other damping mechanisms. The estimated values obtained from the experimental tests show a significant influence of the damage level on the linear viscous damping coefficient. This suggests that, in a non-linear dynamic time-history analysis, the use of Rayleigh damping model with proportionality to the initial stiffness is basically in contrast with experimental evidence and more refined viscous damping models are needed for prediction purposes.     

非线性系统参数辩识的一种频域模型

本文基于对非线性系统的可分离性假设，将非线性弹性力和阻尼力分别分解为物理坐标下各点间相对位移和相对速度的幂级数函数，导出了一般多自由度非线性系统在恒幅激励下的广义频率响应函数与输入输出之间的迭代关系式，提出了非线性系统中基本线性部分的概念，进而了一种在实验条件下的系统物理参数辩识方法。