车、路的相互作用下沥青路面动力学特性分析

文中采用二自由度四分之一汽车悬架模型模拟汽车系统,依据弹性层状体系理论,建立路面结构的三维有限元分析模型,考虑车路相互作用,采用ANSYS有限元分析软件对移动车辆荷载作用下路面各结构层中的位移、应力、应变进行了模拟。计算分析了行车速度、悬架刚度、悬架阻尼、轮胎刚度和轮胎阻尼五个参数对路面动力响应的影响。结果表明：沥青面层处于三向受压状态,层内切应力是引起其破坏的主要原因;最大水平拉应力和最大横向拉应力均发生在路面结构的基层和底基层结合处;车速对路面动态响应的影响规律很复杂,应考虑车辆模型和路面不平整度,并划分速度区间加以探讨;路面动态响应随轮胎刚度、悬架刚度和悬架阻尼的增大而减小。上述结论对于深入分析路面结构动力响应与疲劳损坏以及研究车辆与路面相互作用的机理有重要价值。     

任意形状板考虑初始荷载效应的动力特性有限元分析

基于板考虑初始荷载效应的动力控制微分方程,运用等参变换方法,提出了任意形状板考虑初始荷载效应影响的动力有限元分析方法,编制了相应程序。同时,为验证提出的有限元方法的正确性,分别运用伽辽金法、瑞利法求解了几种典型板考虑初始荷载效应的基频近似解和简支正方形板考虑初始荷载效应的前三阶频率近似解。对比验证说明了提出的基于等参变换的任意形状板考虑初始荷载效应的动力有限元分析方法和频率近似解正确、有效。并通过计算分析,讨论了初始荷载大小、板的厚度等因素对板自振频率的影响,结果表明:初始荷载的存在提高了板的自振频率,并主要与荷载大小,板的跨厚比和边界约束条件有关。计算分析中应重视初始荷载效应对板的结构行为产生的影响,以做到精确分析和合理结构设计。     

不同初始应力及变形对梁自振频率的影响

应用Hamilton原理,建立了同时考虑初始荷载产生的弯曲和轴向变形影响时梁的控制微分方程,利用Galerkin方法推导出了考虑两种初始变形影响时简支梁自振频率的解析表达式,讨论了初始荷载大小、梁自身刚度及约束情况等不同参数对这两种初始变形对梁动力反应影响的敏感度,采用产生相同变形能的方式,定量地比较了各种边界条件下两种初始变形对梁自振频率的影响。     

恒载效应对拱形梁自振频率的影响分析

应用Hamilton原理,推导了考虑恒载效应影响时拱形梁动力控制方程。根据所得方程,利用Galerkin方法讨论了恒载大小及结构自身刚度（矢高,跨度,惯性矩,惯性半径等）等不同因素在考虑恒载效应时对拱形梁动力特性的影响。结果表明,本文给出的方程对于曲直梁具有通用性,初始恒载的存在使拱形梁自振频率增大,这种影响与恒载的大小及结构自身的刚度有关,且在柔性结构及低阶频率中表现更为显著。     

冲击荷载作用下单层网壳结构动力稳定性研究

针对冲击荷载不同于地震作用,而常规动力稳定性判定准则不适用问题,阐述求解冲击问题的基本理论及冲击荷载取值;据冲击荷载特性提出适合冲击碰撞问题的单层网壳结构动力稳定性判定准则;选K6型单层网壳结构模型,利用非线性有限元软件ANSYS/LS-DYNA进行结构冲击作用下动力稳定性分析,通过大量算例,分析其在不同冲击物质量比及速度作用下全过程动力响应,结合动力响应模式获得冲击荷载作用下单层网壳动力失稳的临界能量区域,并从矢跨比、跨度、杆件截面三方面对结构进行参数分析。结果表明,基于网壳动力响应模式与冲击能量相结合方法对单层网壳进行动力稳定性判定合理;结构刚度越小,冲击作用下动力稳定性越差;加大主肋利于提高结构动力稳定性。     

提高地铁车站结构抗震能力的理论及数值分析

1995年阪神地震中,地铁车站等地下结构遭受了严重的破坏,其中大开地铁车站破坏尤为严重,一半以上的中柱发生坍塌,为了提高地铁车站结构的抗震能力,本文基于第二类拉格朗日方程首先建立了地震荷载和轴力联合作用下柔性动边界梁动力响应的分析方法,并讨论了轴力和弹簧刚度与阻尼系数对动力响应的影响特点与规律,然后利用ABAQUS软件对阪神地震荷载作用下大开地铁车站在有无设置隔震器时进行了三维非线性动力分析。研究结果表明：)     

非同轴刚度偏心高层建筑平-扭耦合风振响应的研究

提出了分析非同轴刚度偏心结构风振响应的基本框架。第一，建立了两层6个自由度（6DOFs）非同轴刚度偏心结构的动力方程。第二，将建立的动力方程扩展至多层（大于两层）非同轴刚度偏心结构情况。第三，基于顺风向、横风向及扭转风荷载功率谱，并考虑横风向与扭转风荷载间相关性及模态响应间耦合，建立了非同轴刚度偏心结构风致平-扭耦合响应的分析方法。最后，以15DOFs结构为例，通过设置结构不同刚度偏心，数值研究了非同轴刚度偏心对结构风致平-扭耦合响应的影响。     

基于动力刚度法的体外预应力梁自振频率分析

用预应力梁-杆组合结构模拟体外预应力梁,以体外预应力简支梁为例,建立了预应力梁杆单元动力刚度矩阵。采用动力刚度法,进一步推导出预应力梁-杆组合结构的整体动力刚度矩阵,利用Williams-Wittrick算法求解频率。本文以理论推导为基础,引入了动力刚度法。最后通过算例,讨论了各种因素对梁横向的振动特性的影响,并与试验值比较。计算结果表明:动力刚度法能够精确有效的求解体外预应力混凝土梁的横向振动问题。     

大型地下厂房结构振动反应分析

建立锦屏一级水电站地下厂房结构三维有限元动力分析模型,计算结构自振特性,并复核结构共振。通过模型水力脉动试验,获得锦屏一级水电站流道脉动压力荷载特性,用动力法分析厂房结构在机组振动荷载与水力脉动荷载作用下的振动反应,并据国内外有关规程规范对振动反应进行评价。研究结果表明,地下厂房结构与各种振源频率相差较大,不存在共振的可能性。地下厂房结构整体刚度较大,在机组振动荷载及水力脉动荷载作用下,振动位移、应力、速度均较小,满足有关规程要求。     

基于有限振动信号的某移动天线有限元风荷载动力反应分析

提出了一种现场实测的有限振动信号与结构有限元模型模拟分析相结合的方法来获得结构（天线）在实际风荷载作用下的动力反应,即首先测试结构在脉动风荷载作用下的有限振动信号,如：加速度时程和频谱曲线,然后通过结构运动方程模拟出脉动风荷载时程并施加到结构有限元模型中,通过有限元计算求出模拟风荷载与实际风荷载之间的修正系数k,最后把修正后的风荷载时程再次施加到有限元模型中进而得出结构在实际脉动风荷载作用下的内力。通过比较,有限元分析结果与试验结果吻合较好,为结构在脉动风荷载作用下的全过程反应分析提供了一种简便方法。     

《薄壁Timoshenko梁弯扭耦合振动的动态有限元法》

通过直接求解单对称均匀薄壁Timoshenko梁单元弯扭耦合振动的运动微分方程,推导了其精确的动态刚度矩阵。在本文研究中考虑了弯扭耦合、翘曲刚度、转动惯量和剪切变形的影响。针对某弯扭耦合的薄壁梁算例,应用本文推导的动态刚度矩阵,采用自动Muller法和结合频率扫描法的二分法求解频率特征方程,计算了该薄壁梁的固有特性,并讨论了翘曲刚度、剪切变形和转动惯量对该弯扭耦合薄壁梁的固有频率和模态形状的影响。数值结果验证了本文方法的精确性和有效性,并指出随着模态阶次的增加,剪切变形、转动惯量和翘曲刚度对薄壁梁的固有特性的影响更加显著。     

单斜面索拱支承曲梁人行桥人致振动控制研究

进行了一种单斜面索拱支承曲梁人行桥的人致振动控制研究。在人行桥的初始状态及静动力特性基础上,模拟了随机人群荷载作用下人行桥的振动响应,参数化地研究了调谐质量阻尼器(Tuned Mass Damper,TMD)的减振作用,考虑了TMD不同质量比、刚度、阻尼参数以及布置方式的影响。在TMD装置安装前后对人行桥进行实地动力测试,测试了结构减振前后的模态特性以及在单人、多人和人群荷载工况下的振动响应,讨论了TMD装置对该类型人行桥的减振效果。结果表明:减振后结构关键模态阻尼增大为减振前的4.14倍;单人步行和跑动工况下,通过设置TMD,结构加速度峰值下降31.1%～55.9%,加速度均方根下降36.4%～52.0%;多种人群步行工况下,结构竖向加速度峰值最大为0.41 m/s~2。研究结果表明单斜面索拱支承曲梁人行桥刚度较柔,TMD对控制该类型人行桥结构人致振动具有很好的效果。     

基于整体分析的钢悬链线立管触地点动力响应分析

在立管动力平衡系统的力学模型中考虑浮式平台的惯性作用和管-土相互作用,研究在不同参数激励下钢悬链线立管触地点动力响应。基于大挠度柔性索理论,分别采用具有弯曲刚度的大挠度细长梁、弹性地基梁模拟立管的悬垂段和流线段,考虑触地点处的大曲率,建立了立管的三维有限元模型,利用Galerkin方法对运动方程离散为一组非线性二阶常微分方程,运用Newmark-β法求解离散方程。通过在立管的动力方程中引入δ函数来体现浮式平台对立管的惯性和水动力影响,将悬链线立管与浮式平台作为一个整体进行动力分析,以工程中实际使用的1800m水深的钢悬链线立管为例,通过对立管顶部进行谐波激励,分别就水动力系数、管内流体密度和海床土体刚度对立管特征点动力分析的影响进行分析,研究表明:水动力系数的改变对立管触地点的动力响应的影响较为显著,主要体现在弯矩和张力幅值的增加;管内流体密度不同,触地点位置不同,表明立管在输送不同液体或气体可能发生疲劳破坏的位置也不同;而海床土刚度对立管触地点区域的弯曲应力影响较大,对轴向应力则影响不大,其结果对SCR设计具有重要的指导意义。     

Thrust bearing design for high-speed composite air spindles

The air spindles whose shafts are made of carbon fiber composite are appropriate for high-speed and high-precision machining such as small hole drilling of printed circuit board (PCB) or wafer cutting for manufacturing semiconductors because the carbon fiber composite shaft has low rotational inertia, high damping ratio and high fundamental natural frequency.

The axial load capability and stiffness of air spindles for drilling operation are dependent on thrust bearings that are composed of air supply part mounted on the housing and rotating part mounted on the rotating shaft of spindle.

Since the stresses induced in the rotating part of thrust bearing by centrifugal force are very high at high-speed rotation, the axial stiffness and load capability of an air spindle should be designed considering the stresses induced by the centrifugal force as well as the natural frequency of rotating shaft to avoid the resonant whip vibration of the spindle.

In this work, the air supply part of a thrust air bearing for a high-speed composite air spindle was designed considering its axial stiffness and load capability. The rotating part of the thin thrust bearing was designed through finite element analysis considering the static and dynamic characteristics under axial load and the centrifugal force during high-speed rotation.     

Spatial stability and free vibration of shear flexible thin-walled elastic beams. I: Analytical approach

An improved formulation for spatial stability and free vibration analysis of thin-walled elastic beams is presented by applying Hellinger–Reissner principle and introducing Vlasov's assumption. It includes shear deformation effects due to flexural shear and restrained warping stress, rotary inertia effects and bendirsg–torsional coupling effects due to unsymmetric cross sections. Closed-form solutions for determining flexural–torsional buckling loads and natural frequencies of unsymmetric simply supported beam-columns subjected to eccentric axial force are newiy derived and also, the tangent stiffness matrix and stability functions for symmetric thin-walled beam elements subjected to axial force are presented. In a companion paper,²⁶ these analytic solutions are compared with the finite element solutions according to the increase of shear deformation effects.     

钢-混凝土组合梁收缩徐变分析的有限元方法

基于按龄期调整的有效模量法,提出了部分剪力连接钢-混凝土组合梁在长期荷载作用下收缩徐变分析的简化有限元模型,并通过建立特殊的剪力连接件单元刚度矩阵和利用Newton-Raphson迭代方法考虑滑移效应,同时考虑了负弯矩区混凝土板开裂对组合梁刚度和强度的影响。利用该模型计算了连续组合梁在长期荷载作用下的挠度、应力、滑移量,计算结果与已有的理论计算结果和实验结果吻合,证明本模型用于分析钢-混凝土组合梁收缩徐变是可靠的。     

Dynamic stability behavior of damped laminated beam subjected to uniformly distributed subtangential forces

The dynamic stability behavior of damped laminated beam with various boundary conditions subjected to the uniformly distributed subtangential forces is investigated using the finite element formulation. The formal engineering approach of the mechanics for the thin-walled laminated beam based on kinematic assumptions consistent with Vlasov beam theory is used. An extended Hamilton’s principle is employed to obtain the mass-, damping-, elastic stiffness-, geometric stiffness matrices, and the load correction stiffness matrix due to the subtangential forces, respectively. The method for the evaluation of critical values for divergence and flutter of the nonconservative systems is briefly introduced in case of considering and neglecting damping effects. Throughout numerical examples, the influence of various parameters on the dynamic stability behavior of the nonconservative laminated beam is newly investigated: (1) the variation of the divergence and flutter loads due to the nonconservativeness with respect to the fiber orientation, (2) the effect of boundary condition on the instability region of the divergence-flutter system, and (3) the influence of external and internal damping on the flutter load.     

On the free vibrations of grid-stiffened composite cylindrical shells

A unified analytical approach is applied for investigating the vibrational behavior of grid-stiffened composite cylindrical shells considering the flexural behavior of the ribs. A smeared method is employed to superimpose the stiffness contribution of the stiffeners with those of the shell in order to obtain the equivalent stiffness parameters of the whole panel. The stiffeners are modeled as a beam and considered to support shear loads and bending moments in addition to the axial loads. Therefore, the corresponding stiffness terms are taken into consideration while obtaining the stiffness matrices due to the stiffeners. Theoretical formulations are based on first-order shear deformation shell theory, which includes the effects of transverse shear deformation and rotary inertia. The modal forms are assumed to have the axial dependency in the form of Fourier series whose derivatives are legitimized using Stokes’ transformation. In order to validate the obtained results, a 3-D finite element model is also built using ABAQUS CAE software. Results obtained from two types of analyses are compared with each other, and good agreement has been achieved. Furthermore, the influence of variations in the shell thickness and changes of the boundary conditions on the shell frequencies is studied. The results obtained are novel and can be used as a benchmark for further studies.     

三点弯曲试样动应力强度因子求解的振动分析方法

采用振动分析方法,对冲击载荷作用下三点弯曲试样的动态响应进行了研究。通过对试样刚度的求解,把转动惯性和剪切变形的影响引入到动应力强度因子的计算中。动态有限元的分析结果表明,本文建立的动应力强度因子公式具有较好的计算精度。     

Flexural analysis of discontinuous tile core sandwich structure

Three-point flexure loading of sandwich beams with a core consisting of discrete ceramic tiles (DTSS) is considered. The tile gaps may be bonded or unbonded (open gaps). The analysis utilizes a layer-wise beam theory approach. The general formulation for the displacements and stresses in the face sheets, face/core adhesive layer, and core is derived. Solutions for stresses and displacements of the beam constituents are obtained from finite element formulation based on analytical solution of the face sheet/tile unit cell. The approach is verified by comparison to stress results obtained from ordinary finite element analysis where each layer is modeled discretely. Effects of load introduction and support conditions on the effective flexural stiffness are examined. It is demonstrated that the face sheets experience substantial stress concentrations at the tile joint locations, especially if the gaps are unfilled. Analysis of beam compliance reveals sensitivity to details of load introduction and support conditions, especially when the span length becomes comparable to the tile length.