杜芬型滑移系统自由振动分析

研究了杜芬型滑移系统的自由振动特征.推导了系统自由振动停滞区和相轨线的解析表达式,计算分析了滑移振动停滞区长度、相轨线及残余滑移的变化规律.结果表明,停滞区长度随摩擦系数单调增加而随线性与非线性恢复力参数单调减小;振子最终停滞的位置具有随机性,残余滑移在整个停滞区间内呈均匀分布.     

渐硬恢复力滑移体系稳态随机响应的解析预测

研究了渐硬恢复力刚性滑移结构在水平和竖向高斯白噪声地面作用下稳态响应的概率分布问题。以等效线性恢复力刚性滑移结构代替原系统并利用等效非线性系统法推得了替代系统稳态响应的联合概率密度函数解析解;最后通过蒙特卡洛模拟结果说明了本文所提方法的适用性。     

金属橡胶消极减振系统复杂响应特性研究

对金属橡胶非线性消极减振系统的复杂响应特性进行了研究,基于减振器的双折线本构关系对隔振器的迟滞恢复力进行了线性等效,推导了减振系统的状态方程;对减振器进行了动态加载实验,利用实验数据识别得到了减振器的实际物理参数;利用辨识得到的有量纲的物理参数对系统进行数值仿真,绘制了系统随激励幅值和频率变化的分岔图,确定了系统产生混沌振动的参数区间,分析了金属橡胶减振系统的单频输入多频甚至宽频输出的复杂响应特性,并通过振动实验进行了验证。     

基于FPK方程的一类非线性问题辨识方法

一类受高斯白噪声激励的非线性动力学方程能通过求解对应的ＦＰＫ方程得到精确稳态解。本文基于这一结果导出非线性恢复力与系统位移输出的概率度的关系,将动力学系统中非线性（恢复力的非线性）结构参数的辨识问题论为求解系统的概率密度,是一种新的尝试,结果经数值仿真是可行的。但所研究系统限于自由度非线性恢复力系统,其中线性部分的参数已知,待辨识部分为非线性恢复力。     

二自由度不对称迟滞振动压实系统的响应计算

分析了振动压实过程中被压实材料的不对称迟滞特性,建立了一种分段线性的不对称迟滞模型。在一次近似的前提下,利用谐波线性化方法,将迟滞非线性恢复力转化为等效刚度和等效阻尼表示,用优化算法求解频响方程,得到了二自由度迟滞振动压实系统的幅频响应。通过数值算例分析了模型参数对系统动态响应的影响,发现由于迟滞非线性的存在,随着激励幅度的增大系统会出现软化的趋势。     

基于双剪统一强度理论应变退化模型的隧道结构稳定性分析

论文基于双剪统一强度准则应变软化模型对圆形隧道稳定性的分析,提出一种简单的数值计算方法来对围岩进行弹塑性分析。该文采用差分法,基于广义形式的双剪应力屈服准则,并采用相关联流动法则,建立本构方程。对于应变软化模型,该文选定塑性应变增量作为软化参数,并且假设强度参数随软化参数成线性函数关系。弹性区的解答引用拉梅解答,而求解塑性区的解答时,将塑性区分成很多微元圆环,并假设每个圆环的径向应力?r沿半径向内均匀递减;其次,建立每个微元圆环的平衡微分方程、本构方程、几何方程及相邻两微元之间的应力增量和应变增量的关系。从弹塑性交界面处的塑性区最外一个圆环开始,求解出每一个微元圆环的解答。并且利用MATLAB进行编程求解出最终的结果:应力场、应变场、径向位移场的数值解。此外还分析讨论了中间主应力影响系数b、软化参数临界值η*对解答的影响,并分析了影响塑性区半径的因素。     

滑移隔震支座的试验研究及力学模型

通过滑移隔震支座的试验研究,探讨了静摩擦系数、动摩擦系数的变化趋势及滑动摩擦系数的影响因素,研究滑移隔震支座的恢复力特性。试验研究表明:静摩擦系数和动摩擦系数都与竖向压力的大小有关,随着竖向压力的增大而逐渐减小;滑动摩擦系数随滑动速度的增大而增大;滑动摩擦系数与频率有关,总的趋势是随着激励频率的增大,摩擦系数增大;滑移隔震支座加硅脂润滑后摩擦系数明显降低;高频激励下摩擦滑移隔震支座的恢复力模型宜采用理想弹塑性模型,低频激励下宜采用刚塑性模型。最后,指出已有摩擦力模型存在的缺陷,并根据试验结果建议了一个新的摩擦力模型,分析表明该模型与试验数据拟合较好。     

杜芬型滑移系统振动非线性评估

以叠加原理为判别准则,通过计算杜芬型滑移系统对双频简谐激励作用的动力响应,分析系统的振动非线性及其影响因素。结果表明,恢复力非线性与阻尼非线性存在相互作用机制,一定条件下摩擦阻尼的增加可以抑制恢复力非线性的发挥,系统整体振动的非线性并非两者效应的简单累加。外部激励的影响体现在其幅值和频率两个方面,双频激励强度均较大时会激发系统的振动非线性。     

DMPA含量对具有软段结晶性水性聚氨酯性能的影响

采用预聚体分散法,以DMPA作为亲水性单体,合成了一系列具有软段结晶性水性聚氨酯乳液(WPU)。通过FT-IR、粒径测量仪、接触角测量仪、XRD等对乳液性能和涂膜性能进行了表征。实验结果表明:乳液的粒径随DMPA含量的增加而减小,zeta电位和黏度随之增大;涂膜的接触角和断裂伸长率随DMPA含量的增加而减小,拉伸强度随DMPA含量的增加而增加;软段微区的结晶性能随着DMPA含量的增加而减小,当DMPA质量分数增加至5.6%时,软段微区表现出非晶态。     

金属橡胶材料迟滞特性力学模型研究

受成型与制备工艺参数影响,金属橡胶有记忆型恢复力模型数学表达式复杂,特别是在对非线性迟滞特性参数进行识别时存在困难。根据金属橡胶微元体理论,研究干摩擦力对迟滞特性力学模型的影响。应用材料细观结构特征构造金属丝微元体力学模型,描述了金属丝滑移接触过程中干摩擦产生机理,结合金属橡胶制备工艺计算处于滑移状态的微元体数目,建立金属橡胶干摩擦阻尼力数学表达式。利用静态激励试验系统进行试验研究,并结合MATLAB软件对该理论模型进行参数识别。通过理论与试验结果对比,验证了模型的正确性。结果表明:含干摩擦分量的有记忆恢复力模型适用性强,表达式简单,特别是在参数识别时具有较好的精度。     

基础滑移隔震房屋结构设计与工程应用的理论研究

本文进行了隔震体系限位耗能元件的弹塑性分析，利用多层砖房的足尺结构进行了滑移结构动力特性试验。通过对隔震房屋有限位装置的恢复力特性的研究，提出了多层砖房隔震结构的恢复力计算模型，编制了隔震结构的分析程序，提出了基础滑移隔震房屋结构设计的构造措施和减震效果试推检验方法。实际工程算例表明，滑移隔震结构较基础固定结构有较好的抗震性能，在设计中可降低设计烈度二度进行隔震设计。     

非线性系统参数识别的能量法

本文提出了由能量积分来分批识别非线性系统参数的新思想。文中把构成系统力学模型的元件区分为耗能类和保守类;利用在相等变形之间任意变形历史中保守类元件不耗能,可以建立仅含耗能类元件参数的线性识别方程;以此为基础再利用能量积分又可建立仅含保守类元件参数的线性识别方程。仿真试验表明:这种分批线性识别技巧简便有效,可用于识别含间隙、弹塑性等多种非线性因素的系统参数,还特别适合于解决弱阻尼型的非线性系统参数识别难题。     

Incremental harmonic balance method with multiple time variables for dynamical systems with cubic non‐linearities

The incremental harmonic balance method with multiple time variables is developed for analysis of almost periodic oscillations in multi‐degree‐of‐freedom dynamical systems with cubic non‐linearities, subjected to the external multi‐tone excitation. The method is formulated to treat non‐autonomous as well as autonomous dynamical systems. The almost periodic oscillations, which coexist with periodic oscillations in a rotating system model with cubic restoring force and an electromagnetic eddy‐current damper are analysed. The closed form solutions based on generalized Fourier series containing two incommensurate frequencies are obtained in the case of small non‐dimensional stiffness ratio. Almost periodic oscillations of a rotating system model in dependence on variable parameters are also analysed, where solutions are computed through an augmentation process including a greater number of harmonics and combination frequencies involved. Copyright © 2003 John Wiley & Sons, Ltd.     

Numerically consistent regularization of force‐based frame elements

Recent advances in the literature regularize the strain‐softening response of force‐based frame elements by either modifying the constitutive parameters or scaling selected integration weights. Although the former case maintains numerical accuracy for strain‐hardening behavior, the regularization requires a tight coupling of the element constitutive properties and the numerical integration method. In the latter case, objectivity is maintained for strain‐softening problems; however, there is a lack of convergence for strain‐hardening response. To resolve the dichotomy between strain‐hardening and strain‐softening solutions, a numerically consistent regularization technique is developed for force‐based frame elements using interpolatory quadrature with two integration points of prescribed characteristic lengths at the element ends. Owing to manipulation of the integration weights at the element ends, the solution of a Vandermonde system of equations ensures numerical accuracy in the linear‐elastic range of response. Comparison of closed‐form solutions and published experimental results of reinforced concrete columns demonstrates the effect of the regularization approach on simulating the response of structural members. Copyright © 2008 John Wiley & Sons, Ltd.     

不同拉压特性结构振动分析的双线性近似方法

对拉压特性不同的双模量结构的非线性自由振动进行了研究。给出了恢复力-位移曲线由三段斜率不 同的直线构成的单自由度系统自由振动频率的精确解。应用双线性近似方法讨论了有间隙双模量结构和无间隙双模量 结构非线性自由振动频率的近似求解问题。结果表明,不管恢复力-位移表达式多么复杂,应用双线性近似方法都可以 方便地求得结构的等效线性刚度,进而获得结构固有频率的近似解。通过近似计算结果与精确解之间的比较,验证了双 线性近似方法对于工程中大量存在的一类具有不同拉压特性的结构进行振动分析的实用性。     

The oscillatory damped behaviour of incommensurate double-walled carbon nanotubes

The mechanical properties of sliding carbon nanotubes have been investigated by classical molecular dynamics simulations in the canonical ensemble. In particular we have studied damped oscillations in the separation between the centres of mass of the inner and outer tubes of double-walled carbon nanotubes (DWCN). Incommensurate DWCNs forming (7, 0)@(9, 9) structures were simulated for systems at 298.15?K with axial lengths from 12.21 to 98.24?nm. The oscillations exhibited frequencies in the range of gigahertz with the frequency decreasing as the length of the system increases. The time until oscillations become negligible exhibited a nearly linear dependence on the length of the system. Two macroscopic models were developed in order to understand the forces involved in terms of macroscopic properties like friction and shear. The first model considered constant restoring forces during the whole event, while in the second the value of these constant restoring forces depended on the initial conditions of each oscillation. Both models reproduced the oscillations quite well, while the second model allows us to predict the dynamic shear strength in terms of the axial length of the system for tubes with the same diameters. The calculated dynamic shear strength exhibited monotonic behaviour with an inverse dependence on the length of the system. For systems with unequal axial lengths, the restoring force, which drives the oscillation, is reduced compared to the system with equal lengths, regardless of whether the outer nanotube is longer or shorter.     

自复位变阻尼耗能支撑的力学原理与性能研究

为解决现有自复位支撑起滑力大的问题,提出了一种新型自复位变阻尼耗能支撑。支撑采用组合碟簧提供复位能力,通过构造设计实现磁流变液变阻尼耗能。对其变阻尼特性进行了分析,建立了描述其滞回特性的恢复力模型,提出了基于性能需求的支撑设计边界条件。对支撑整体和阻尼耗能装置磁场进行了模拟,结果表明,支撑具有饱满的类旗型滞回曲线,起滑力小、无残余变形、拉压对称,能够兼顾不同振动强度下的性能需求,有效控制结构振动响应。分析了支撑设计参数对滞回性能的影响,为提高复位与耗能能力,设计时组合碟簧预压力应略大于初始阻尼力,同时应增大组合碟簧刚度、提高最大阻尼力、减小变阻尼区间。与现有自复位支撑相比,起滑力大幅降低、起滑刚度比增加,在相同自复位装置设计下等效粘滞阻尼比与最大承载力也有较大提高。     

Data based model free hysteresis identification for a nonlinear structure

In the last two decades, the damage detection for civil engineering structures has been widely treated as a modal analysis problem and most of the currently available vibration-based system identification approaches are based on modal parameters, namely the natural frequencies, mode shapes and damping ratios, and/or their derivations, which are suitable for linear systems. Nonlinearity is generic in engineering structures. For example, the initiation and development of cracks in civil engineering structures as typical structural damages are nonlinear process. One of the major challenges in damage detection, early warning and damage prognosis is to obtain reasonably accurate identification of nonlinear performance such as hysteresis which is the direct indicator of damage initiation and development under dynamic excitations. In this study, a general data-based identification approach for hysteretic performance in form of nonlinear restoring force using structural dynamic responses and complete and incomplete excitation measurement time series was proposed and validated with a 4-story frame structure equipped with smart devices of magneto-rheological (MR) damper to simulate nonlinear performance. Firstly, as an optimization method, the least-squares technique was employed to identify the system matrices of an equivalent linear system of the nonlinear structure model basing on the excitation force and the corresponding vibration measurements with impact test when complete and incomplete excitations; and secondly, the nonlinear restoring force of the structure was identified and compared with the test measurements finally. Results show that the proposed data-based approach is capable of identifying the nonlinear behavior of engineering structures and can be employed to evaluate the damage initiation and development of different structure under dynamic loads.