采动区建筑物抗变形隔震装置的力学性能分析

介绍了采动区建筑物抗变形隔震装置的基本构成,并基于地震工程学和开采沉陷学的原理对抗变形隔震支座进行了理论分析,通过实验对采动区抗变形隔震支座在低周反复荷载作用下的滞回耗能特性进行了分析。结果显示,在低周循环荷载作用下采动区抗变形隔震支座的滞回耗能曲线饱满,表明其良好的自复位、耗能能力和变形能力大、稳定的滞回性能等特点,说明抗变形隔震支座的传力机制明确、构造比较合理。隔震支座充分利用了铅芯橡胶、粘滞阻尼器和蝶形弹簧三种不同的耗能材料和耗能机制,其适宜的水平隔震刚度和阻尼耗能性能、竖向能够抵抗不均匀沉降,充分体现了其良好的整体稳定性。该抗变形隔震支座有效的改善了采动区建筑抵抗煤矿采动损害和震害的能力,为采动区建筑物保护提供科学方法和依据。     

叠层橡胶隔震支座夹层受拉模型与分析：理论模型

为分析普通圆形叠层橡胶隔震支座的受拉性能,本文基于弹性力学理论,建立了叠层橡胶隔震支座橡胶夹层的受拉分析模型,根据橡胶层的约束边界条件及普通橡胶材料的不可压缩性质,推导了橡胶夹层的应力与位移分布简化计算公式。根据推导结果对橡胶夹层的应力分布与变形规律（如橡胶层内外自由边的变形形状）进行分析,并通过有限元数值模型进行了对比,结果表明,本文的分析模型与计算公式可以较好的分析不同形状系数的普通圆形叠层橡胶隔震支座橡胶夹层的应力分布与变形规律。     

地铁车站中柱减震效果的概率密度演化分析

本文旨在采用概率密度演化方法，对考虑土体随机性的地铁车站中柱减震效果进行概率密度演化分析．以一典型地铁车站地下工程为背景，基于土体剪切模量的对数正态分布模型，采用谱表现方法确定具有空间变异性的土体随机场分布，分别建立考虑土体随机性的土-地铁车站原型结构相互作用模型和土-地铁车站减震结构相互作用模型，进行地铁车站中柱减震效果的概率密度演化分析与对比研究．结果表明：地铁车站结构地震反应的概率密度演化过程是一种随时间变化的复杂随机过程；不同时刻下结构地震反应的概率密度函数形状有所不同，且某些时刻的概率密度函数具有双峰．在地铁车站中柱上端设置橡胶支座会降低结构中柱水平变形与截面内力的离散度，提高结构侧墙变形与内力的离散程度．同时，可以有效降低中柱水平变形与截面内力的地震反应值，降幅在25%～50%左右，而地铁车站的侧墙变形和内力有所提高．     

基于首次超越理论的高层隔震结构基础提离易损性分析

针对基础隔震的高层建筑,基于首次超越理论,计算了各个隔震支座在非平稳随机激励下发生基础提离破坏的易损性曲线。隔震结构采用三维有限元建模,隔震支座采用Bouc-Wen模型,经过等效线性化后,应用虚拟激励法求得结构的随机响应。讨论了隔震支座的阻尼比、屈服力以及地震动输入方向对隔震支座易损性曲线的影响。研究发现:增加隔震支座的阻尼比或是增加隔震支座的屈服力都会使得隔震支座发生基础提离的破坏概率增加,地震动的输入方向对隔震支座基础提离易损性曲线影响十分显著。     

叠层橡胶隔震支座夹层受拉模型与分析：开裂机理与试验

为了研究叠层橡胶隔震支座的受拉性能及开裂破坏机理,本文基于叠层橡胶隔震支座橡胶夹层的受拉分析模型及橡胶夹层的应力与位移分布计算公式,分析不同形状系数的橡胶支座橡胶夹层的应力分布与变形规律（如橡胶层内外自由边的变形形状）,并基于理论分析结果,采用开裂能理论研究橡胶夹层的开裂能密度及梯度分布,据此分析橡胶夹层的开裂发生与发展规律,揭示其开裂破坏机理。最后通过叠层橡胶隔震支座的受拉性能试验进一步分析对比,试验结果表明了采用开裂能密度与梯度分析橡胶夹层的开裂破坏机理的可行性与合理性。     

橡胶弹性支座动态承载特性及其影响因素分析

基于复刚度理论,采用正交实验法,对风力发电机橡胶弹性支座进行动态性能实验,研究载荷频率、载荷幅值、预载荷诸因素对弹性支座动态性能的影响规律. 实验结果表明,橡胶材料的动态性能与载荷频率和幅值具有显著的相关性. 频率增加,橡胶弹性元件的弹性刚度和阻尼因子明显增大;幅值增加,弹性刚度减小,阻尼因子却逐渐增大. 对实验数据进行方差分析,表明载荷频率对动态性能的影响最大,其次是载荷幅值,预加载因素影响非常有限.     

计算近场地震作用下隔震结构支座破坏易损性曲线的概率凸集混合模型

用凸集模型模拟隔震结构参数的不确定性,而用随机模型模拟地震动输入的不确定性,提出了计算近场地震作用下在考虑双不确定性因素时隔震结构支座发生破坏的易损性曲线计算新方法;计算结果将给隔震支座力学参数的设计提供参考;通过计算对比可知,若不考虑结构参数不确定性将低估隔震支座破坏的地震易损性;对计算实例中基底最大位移敏感度分析发现,隔震支座的力学参数(如屈服力、屈服后刚度等)对基底最大位移影响较大,上部结构质量的影响次之,而上部结构的刚度对其影响不大;此外,本文的研究内容也为考虑结构参数和输入地震动双不确定性因素的情况下,计算各类结构地震易损性曲线提供了一种新的思路和途径。     

简谐荷载下橡胶隔震渡槽-水耦合体共振响应机理分析

采用计算流体力学（CFD）方法分析了在简谐激振作用下橡胶支座隔震渡槽槽-水耦合体的共振响应特性,并通过基于水体小幅晃动假设的槽水动力响应理论解进行了验证。结果表明：橡胶支座能将激振的高频分量隔离掉,使得槽-水耦合体不存在理论解所显示的高频共振问题;在接近水体一阶晃动频率的情况下容易发生共振响应;在以一阶水体自振频率的激振作用下,液面波高、动水压力、倾覆力、倾覆力矩均表现出随时间增长的共振放大现象,并且橡胶支座对耦合体的动力响应周期有一定的延长作用。本文对渡槽隔震设计选择隔震周期时,需要避开水体一阶晃动频率提供了参考依据。     

N330炭黑增强天然橡胶材料力学性能的实验研究

为了研究炭黑对橡胶材料力学性能的影响,对9种不同体积含量的炭黑填充橡胶材料进行了准静态力学实验研究。利用循环拉伸加卸载实验分析了炭黑对橡胶Mullins效应及能量损耗的影响,通过单轴拉伸实验研究了炭黑对橡胶材料刚度和起始模量的影响,采用多步松弛拉伸加卸载实验研究了炭黑对橡胶材料应力行为的应变历史相关性的影响。实验结果表明:炭黑填充量越高,橡胶材料的刚度越大,初始模量越大,Mullins效应也越明显;随着炭黑填充量的增加,橡胶在加卸载循环中所产生的迟滞损耗、Mullins效应相对能量损耗以及残余应变都呈现出非线性增长趋势;随着炭黑填充量的升高,橡胶在加卸载过程中的应力松弛现象越明显,其平衡态迟滞损耗以及与时间相关部分的迟滞损耗也越大。     

一般大气环境下锈蚀钢筋混凝土梁的时变可靠度分析

根据一般大气环境下锈蚀钢筋混凝土梁中的钢筋截面损失时变模型和抗剪、抗弯承载力退化模型,建立了考虑其随机性的极限状态方程。基于概率守恒原理分析得到满足该极限状态方程的概率密度演化方程,并引入吸收边界条件,提出了梁时变可靠度的计算方法。以受对称集中荷载的锈蚀钢筋混凝土简支梁为例,展示了目标函数的概率密度演化过程,并讨论了配置不同直径箍筋和不同厚度保护层时的时变可靠度。结果表明,在保证梁具有足够初始抗剪强度和抗弯强度的前提下,适当增大保护层厚度和箍筋直径(具有相同配箍率)能延缓混凝土构件力学性能的退化。通过和100万次蒙特卡洛模拟结果的对比可知,选用本文方法能在以付出较小计算代价的前提下,获得计算精度良好的分析结果。     

Influences of wear on dynamic characteristics of angular contact ball bearings

Wear between balls and races has significant effects on the dynamic characteristics of bearing, which is the main reason to cause bearing failure. Some existing contact stiffness models were established to study the dynamic characteristics of bearing. However, the wear of bearing has been rarely investigated due to the complexities of contact load and wear mechanism. This paper presents a new dynamic wear simulation model of angular contact ball bearings mounted in pairs to solve this problem. A final contact stiffness model is established based on the wear model. The effects of running distance, horizontal load, preload, initial contact angle, number and diameter of balls on wear performances are analyzed. A generalized time-varying and piecewise-nonlinear dynamic model of angular contact ball bearings is established to perform an accurate investigation on its dynamic characteristics, especially considering the coupling effects of wear and rolling contact. The effects of wear on the contact stiffness and nonlinear dynamic characteristics are analyzed according to the dynamic model. Additionally, the variations of the contact stiffnesses and frequency responses with different preloads are discussed and the results indicate that parameter selection has significant effects on the wear and nonlinear response.

     

永磁向心轴承承载能力与刚度的计算

目前，尽管磁浮轴承技术的研究与开发应用已经受到国内外学者的广泛重视，但在永磁向心轴承承载能力的研究方面，却还存在着两个尚待解决的问题：一是将环形磁体作为无限长条形磁体处理，二是只能对轴承承载能力进行估算。针对这种情况，根据等效磁荷理论，在圆环状态下对轴向控制的永磁向心轴承的承载能力和刚度进行了研究，建立了永磁向心轴承承载能力数学模型，并对其计算结果作了试验验证，同时还提出了利用刚度系数建立的可供工程设计应用的永磁轴承承载能力和刚度的计算公式。结果表明，承载能力的计算值与实测值相当吻合；在偏心距的实际应用范围内，永磁向心轴承的径向刚度是个常量；内外磁环的轴向位移对磁轴承的承载能力和刚度都有明显的影响．因此，为了最大限度地提高这种轴承的承载能力和刚度，就要在设计其结构的过程中注意尽力保证内外磁环轴向对齐。     

金属丝网橡胶压缩力学性能研究

对金属丝网橡胶进行了静态压缩试验。利用控制变量法研究了压缩量、相对密度、金属丝丝径、丝材和承压面积对金属丝网橡胶压缩力学性能的影响,并对平均刚度和能量耗散系数随压缩量和相对密度的变化关系进行了研究。试验结果表明:随着压缩量的增加,金属丝网橡胶非线性力学特性逐渐增强;相对密度越大,金属丝网橡胶承压能力越强;金属丝的丝径和丝材主要影响金属丝网橡胶非线性阶段的力学特性,丝径越大,丝材越硬,承压能力越强;承压面积越大,金属丝网橡胶的承压和耗能性能越好;随着压缩量的增加,平均刚度增大,承压能力增强,能量耗散系数减小,减震性能降低;随着相对密度的增加,平均刚度和能量耗散系数均增大,承压能力和减震性能均增强。     

Mechanical properties of isolation bearings identified by a viscoelastic model

The Haringx theory is usually employed to describe the mechanical behavior of rubber bearings subjected to a compressive axial load and a lateral shear deformation, but it does not consider the damping effect. In order to study the behavior of isolation bearings which possess an energy-dissipation capacity, the explicit formulas for the horizontal stiffness of viscoelastic columns and the corresponded height reduction are derived by the method of variable separation. These explicit formulas are then applied to develop an identification procedure to find the shear modulus and loss factor of the rubber using the cyclic shear tests of isolation bearings. Through this identification procedure, the empirical formulas for the shear modulus and the loss factor of rubber are established as functions of the strain amplitude and the excitation frequency.     

Periodic and Chaotic Motions of a Rotor-Active Magnetic Bearing with Quadratic and Cubic Terms and Time-Varying Stiffness

In this paper, we use the asymptotic perturbation method to investigate nonlinear oscillations and chaotic dynamics in a rotor-active magnetic bearings (AMB) system with 8-pole legs and the time-varying stiffness. The stiffness in the AMB is considered as the time varying in a periodic form. Because of considering the weight of the rotor, the formulation on the electromagnetic force resultants includes the quadratic and cubic nonlinearities. The resulting dimensionless equations of motion for the rotor-AMB system with the time-varying stiffness in the horizontal and vertical directions are a two-degree-of-freedom nonlinear system with quadratic and cubic nonlinearities and parametric excitation. The asymptotic perturbation method is used to obtain the averaged equations in the case of primary parametric resonance and 1/2 subharmonic resonance. It is found that there exist period-3, period-4, period-6, period-7, period-8, quasiperiodic and chaotic modulated amplitude oscillations in the rotor-AMB system with the time-varying stiffness. It is seen from the numerical results that there are the phenomena of the multiple solutions and the soft-spring type and the hardening-spring type in nonlinear frequency-response curves for the rotor-AMB system. The parametric excitation, or the time-varying stiffness produced by the PD controller is considered to be a controlling force which can control the chaotic response in the rotor-AMB system to a period n motion.     

FIRST-PASSAGE FAILURE OF PREISACH HYSTERETIC SYSTEMS

The first-passage failure of a single-degree-of-freedom hysteretic system with non- local memory is investigated. The hysteretic behavior is described through a Preisach model with excitation selected as Gaussian white noise. First, the equivalent nonlinear non-hysteretic sys- tem with amplitude-dependent damping and stiffness coefficients is derived through generalized harmonic balance technique. Then, equivalent damping and stiffness coefficients are expressed as functions of system energy by using the relation of amplitude to system energy. The stochastic aver- aging of energy envelope is adopted to accept the averaged It5 stochastic differential equation with respect to system energy. The establishing and solving of the associated backward Kolmogorov equation yields the reliability function and probability density of first-passage time. The effects of system parameters on first-passage failure are investigated concisely and validated through Monte Carlo simulation.     

Study of milling stability with Hertz contact stiffness of ball bearings

This present work examines the stability and nonlinear responses of a spindle milling system supported by ball bearings. A shaft finite element based on Timoshenko beam theory is employed to model the spindle, and modal reduction method is therefore adopted for saving the numerical calculating time. The issues of evaluating the effects of the ball bearing Hertz contact stiffness are consequently addressed. It is found that suitable constant bearing stiffness can be adopted to replace the nonlinear nonsmooth Hertz stiffness in prediction of the critical cutting depth of the milling system in certain bearing configuration conditions. For the constant bearing stiffness can be obtained by experiment, this replacement will undoubtedly simplify the spindle-bearing milling system. But with the increase in the bearing clearance, the spindle milling system will present obvious nonlinear behaviors, and the nonlinear Hertz contact bearing stiffness will take over. Isolated islands of chatter vibration, which are induced by the nonlinear nonsmooth bearing Hertz stiffness, can be found exist in milling processes in large bearing clearance conditions.     

基于阻抗法的矩形截面均压槽气浮支承静态性能分析

针对CFD仿真方法效率低下的状况,提出利用阻抗法来提升气浮支承承载性能的计算速度. 以矩形截面均压槽气浮支承为研究对象,研究了当均压槽高度、角度、数量、半径和供气压力变化对气浮支承承载性能的影响. 结果表明:与CFD仿真方法相比,阻抗法在保证计算结果精度的前提下可提高气浮支承承载力的计算速度. 当均压槽高度、角度、数量、半径和供气压力增大时,阻抗比会增加,气浮支承的承载力和刚度峰值对应的阻抗比也会增加. 当气膜厚度增加时,阻抗比会增加,但承载力会相应地减小. 本文作者通过阻抗法推导了气浮支承承载力简化计算公式,解决了气浮支承在均压槽方向上简化计算的难点,并为阻抗法在均压槽中的研究与应用提供了理论依据.      

弹性箔片动压径向气体轴承动特性的实验研究

建立了新型弹性箔片动压气体轴承性能测试实验台，在静载60N、转速9000r／min条件下进行轴承性能测试试验，通过中心插值法获得轴承中心的扰动速度和加速度，采用时域最小二乘法计算不同激振频率下的8个轴承动态线性刚度和阻尼系数，考察了激振频率对轴承动特性系数的影响．结果表明：轴颈中心扰动轨迹为椭圆形且振幅随动态激振频率增加而增大；刚度和阻尼系数的直接项随动态激振频率增加而减小；交叉刚度和阻尼相对激振频率的变化较小，且其值小于直接项；当激振频率与轴颈转动频率相同时，工频成分的影响较大，轴心扰动幅值明显增大，刚度和阻尼的直接项小于其它频率时的值．     

Deformation analysis of infinite-strip bearings of laminated elastic material interleaving with tension-only reinforcements

Bonding with fiber reinforcements can increase the stiffness of elastic layers only when the elastic layer is compressed. Fiber loses its rigidity when it is not stretched. The procedure to include this ‘tension-only’ nonlinearity in the deformation analysis of the fiber-reinforced bearing is developed. In the elastic layers bonded with tension-only reinforcements, the responses to the compression force and the bending moment are coupled unless the reinforcements are entirely in tension. The coupled relation, which is not linear, depends on the length of the tension zone in the reinforcement. Increasing the compression force on the bearings will extend the tension zone in the reinforcements and enhance the stiffness of the bearing, but the compression force may add more bending moment to the bearings and increase the lateral deformation. The vertical buckling load of the bearings with tension-only reinforcements varies with the lateral force and is smaller than the buckling load of the bearings with linear reinforcements.