约束阻尼层合板的稳态响应

基于Reddy分层理论推导出约束阻尼层合板的稳态振动方程,得到了约束阻尼层合板的振动频率和损耗因子;分别分析了约束阻尼层合板的粘弹性夹层厚度、模量对固有频率和损耗因子的影响;得到了稳态振动时振幅和频率曲线以及横向应力与面内应力。数值计算结果表明所采用的算法是可靠的。     

黏弹夹芯板的有限元建模及实验研究

从有限元分析和数值模拟及实验验证的角度研究了黏弹夹芯板的频率依赖振动特性。夹芯板中间层为黏弹性材料，其刚度和阻尼的频率依赖性行为直接影响系统的模态频率和阻尼，并导致振动模式求解的复杂化。采用三阶七参数Biot模型描述黏弹性材料频率相关的黏弹性行为。开发了三层四节点28自由度的夹芯板单元，基于经典板理论和哈密顿原理建立了黏弹夹芯板的有限元动力学方程。通过引入辅助耗散坐标，将Biot模型和黏弹夹芯板的有限元动力学模型结合起来，并将其转化为常规二阶线性系统形式，极大简化了求解非线性振动特性的过程。对一边固定、另三边自由的黏弹夹芯板进行了前三阶固有频率和损耗因子的预测，并与实验结果对比。数值模拟结果和实验结果吻合良好，说明所提有限元方法是正确有效的。     

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。     

黏弹性地基上功能梯度材料板的振动分析

为研究黏弹性地基上功能梯度材料板的自由和强迫振动特性,基于Reddy高阶剪切变形理论以及由Shen导得的广义Karman型方程,用双重Fourier级数法推导了三参数黏弹性地基上四边简支功能梯度材料板自由振动和动力响应的解析解,计算了各模态自振频率和半波冲击载荷作用下的动力响应,讨论了材料组分指数、黏弹性地基参数、边厚比等因素对自由振动和动力响应的影响.结果表明,黏弹性地基的剪切和压缩刚度显著提升了功能梯度材料板的振动频率,减小了动力响应;另外,地基的黏性对振动频率和动力响应也有一定的影响.     

粘弹层合板的稳态振动和层间应力

应用混合分层理论和Ressiner混合变分原理，在板厚方向取二次位移插值函数和三次、四次横向应力插值函数推导出粘弹层合板的动力学方程，得出简支粘弹层合板稳态振动的解。不仅得出与三层弹性板精确的自振频率吻合良好的解，而且对于粘弹层合板，所计算的自振频率和结构损耗因子也与三维结果吻合较好。计算了自由阻尼层合板对应的低阶法向位移响应幅值和层问横向应力的幅值。结果表明，较高的层间横向正应力是低频稳态振动中引起粘弹层合板分层破坏的主要因素，采用适当模量和厚度的粘弹性材料将有效地降低粘弹层合板的层间横向正应力的幅值。     

复合纤维增强混凝土阻尼测试装置开发与试验研究

纤维与聚合物的掺入可以明显改善混凝土材料的阻尼性能。本文首先给出了正弦交变激励下粘弹性材料三点弯曲梁阻尼特性关系,其次首次自主开发了大尺寸材料的阻尼性能测试装置,然后利用开发的装置在频率(0.5~2.0Hz)条件下测定了6种不同配比复合纤维增强阻尼混凝土的损耗因子与储存模量,最后对纤维的阻尼增强机理进行了初步探讨。试验结果表明:复合纤维增强阻尼混凝土与素混凝土相比,提高了混凝土的损耗因子80%~200%。主要原因是聚合物分子在外力作用下的内耗增加了普通混凝土的阻尼能力,而纤维的阻尼增强机理在于纤维的掺入增加了纤维与水泥基材的界面摩擦力。     

黏弹性土层中单桩纵向振动的对比分析

在频率域内研究了黏弹性土层中端承桩纵向振动的动力特性.将土骨架视为具有分数阶导数本构关系的黏弹性体,基于黏弹性理论,采用平面应变模型给出了分数阶导数黏弹性土层的动力阻抗.考虑桩纵向振动时的横向惯性效应,将桩等效为Rayleigh-Love杆,得到了桩头动力复刚度和导纳的解析表达式.通过数值计算,分析了不同模型土条件下桩头动刚度因子和阻尼随激励频率的动力响应.同时,研究了Rayleigh-Love和Euler-Bernoulli两种模型桩动力特性的差异.分析了桩-土界面连续性模型和相对滑移模型对黏弹性土层中桩纵向振动的影响.结果表明:1随着阶数和材料参数比的增加,桩头刚度因子和阻尼明显减小;2对于大直径桩,随着外荷载激励频率的增加,桩横向效应对刚度因子和阻尼有显著影响.3连续性模型条件下桩头的刚度因子和阻尼在共振时的振幅小于相对滑移模型条件.     

单面碰撞TMD的减振性能分析与试验

根据质量块单面碰撞的特点,得到了SS-PTMD的动力特性;开展黏弹性材料自由碰撞试验,根据试验数据识别了碰撞力模型参数,验证了碰撞力模型的可靠性;设计了可改变频率的单自由度结构的试验模型,开展了减振试验。仿真分析表明:调谐时在自由振动阻尼比由0.1%增加到3.66%时,在简谐激励下的减振率达到95.1%;在频率失谐时(-11.6%)自由振动阻尼比可达到1.71%,在简谐激励下减振率达到94.6%。采用试验分析评估了结构在自由振动、简谐振动的控制效果,分析表明:调谐时在自由振动阻尼比由0.1%增加到3.52%,在简谐激励下的减振率达到95.6%;在频率失谐时(-11.6%)自由振动阻尼比可达到1.43%,在简谐激励下减振率达到95.3%。理论仿真分析和试验结果表明:SS-PTMD能够有效控制自由振动和简谐激励下结构的振动。     

一种利用复阻尼理论计算结构自由振动响应的数值方法

复阻尼理论的运动方程通解中包含有发散项,导致结构自由振动响应不能稳定收敛。在复阻尼理论的频域微分方程基础上,修正阻尼项,进而得到滞变阻尼理论表达式,可保证结构自由振动时程计算结果的稳定性。针对滞变阻尼理论的特点,本文依据正弦函数的希尔伯特变换,提出了相应的时程计算方法,可有效计算滞变阻尼理论下结构的自由振动响应。算例分析表明:基于滞变阻尼理论的结构自由振动响应是稳定收敛的,且与黏性阻尼理论计算结果近似相等;相比基于滞变阻尼理论的直接积分法,本文方法具有计算过程简单和计算量小的优点。     

高阻尼混凝土剪切阻尼性能的测试装置设计

高阻尼混凝土的阻尼性能与工作频率紧密相关, 以往测试材料阻尼性能的黏弹谱仪或 动态力学分析仪, 无法测试如混凝土之类大尺寸材料的剪切阻尼性能. 针对高阻尼素混凝土 剪切直杆, 采用复阻尼模型, 建立剪切振动方程, 通过振型分解法求得简谐荷载激励下杆端 稳态位移反应, 得到了混凝土材料剪切阻尼性能的测试公式, 并设计了相应的阻尼测试装置. 该测试装置为研究混凝土类大尺寸材料的剪切阻尼性能和阻尼机理奠定了重要基础.     

Structural vibration of flexural beams with thick unconstrained layer damping

In this paper, the dynamic behaviour of free layer damping beams with thick viscoelastic layer is analysed. A homogenised model for the flexural stiffness is formulated employing Reddy and Bickford’s quadratic shear in each layer, in contrast to the classical model of Oberst and Frankenfeld for thin beams, which does not take into account shear deformations. The results provided by these two models in free and forced vibration are compared by means of finite element procedures with those of a 2D model, which considers extensional and shear stress, and longitudinal, transverse and rotational inertias.The viscoelastic material is characterised by a fractional derivative model, which takes into consideration the variation of the complex modulus with frequency. To avoid the frequency dependence of the stiffness matrices, the extraction of the eigenvalues and eigenvectors is completed by a new iterative method developed by the authors. The frequency response to a harmonic force is deduced by the superposition of modal contribution functions.From these numerical applications it can be concluded that the model for thick beams provides sufficient accuracy for practical applications, able to reproduce the mechanical behaviour of free layer damping beams with thick viscoelastic layer, reducing the storage needs and computational time with respect to a 2D model.     

Analysis of frequency-domain vibration response of thin plate attached with viscoelastic free layer damping

To predict the vibration response of viscoelastic composite structure, two key issues need to be conducted, one is introducing the constitutive model of viscoelastic material into the analysis model and the other is describing the real damping behavior of viscoelastic composite structure. The emphasis of this study is to obtain the effects of frequency dependence on the vibration response of viscoelastic composite structure and the method of introducing two kinds of damping (viscoelastic material damping and remaining equivalent viscous damping). Vibration response analysis in frequency domain was investigated for viscoelastically damped plate. A cantilever plate attached with the ZN_1 viscoelastic free layer damping (FLD) was chosen to demonstrate the developed method. Frequency-domain response of the composite plate were solved and the obtained results were compared with the experimental values for the purpose of assessing the rationality of the proposed method. In addition, in order to obtain the effects of viscoelastic material parameters on vibration response of viscoelastic composite structure, a detailed parametric analysis was performed. This study shows that the frequency dependent characteristic of viscoelastic material has significant influence on the vibration response in the resonant region and acceptable results can be achieved in the non-resonant region if frequency dependent parameters are substituted by average values of the viscoelastic parameters reasonably in the analysis process.     

平纹织物复合材料的振动能量耗散以及阻尼分析

平纹织物复合材料由于编织结构的特点，对于振动能量有一定的衰减作用．交织纤维束相互间的阻滞作用以及聚合物基体的粘弹性质都会耗损一部分振动能量．本文应用能量原理和阻尼分析的方法解决了平纹织物复合材料的复杂结构损耗因子的计算问题．     

DYNAMIC RESPONSES OF VISCOELASTIC AXIALLY MOVING BELT

Based on the Kelvin viscoelastic differential constitutive law and the motion equation of the axially moving belt, the nonlinear dynamic model of the viscoelastic axial moving belt was established. And then it was reduced to be a linear differential system which the analytical solutions with a constant transport velocity and with a harmonically varying transport velocity were obtained by applying Lie group transformations. According to the nonlinear dynamic model, the effects of material parameters and the steady-state velocity and the perturbed axial velocity of the belt on the dynamic responses of the belts were investigated by the research of digital simulation . The result shows:1) The nonlinear vibration frequency of the belt will become small when the relocity of the belt increases . 2) Increasing the value of viscosity or decreasing the value of elasticity leads to a deceasing in vibration frequencies. 3) The most effects of the transverse amplitudes come from the frequency of the perturbed veloc     

The use of pseudo-dynamic method in the evaluation of damping characteristics in reinforced concrete beams having variable bending stiffness

The objective of this work is to determine experimentally the damping properties of concrete reinforced beams under mechanical vibrations. This is a very important property in earthquake engineering once damping provides structure energy dissipation during moderate or strong earthquake motions. The experimental campaign used the pseudo-dynamic (PsD) method to analyse the beam dynamic behaviour. Essentially the PsD test method is a hybrid computer-driven testing procedure where a numerical algorithm and experimental step are used and combined on-line in order to solve a dynamic problem. The implementation of the method is not expensive and has the leading advantage of offering the operator a total control of any intermediate structure state during the test still keeping the realism of a real dynamic testing. In this analysis the dynamic model was assumed as single degree-of-freedom system (SDOF). For the calculation of the structural damping factor, the structure stiffness was determined prior the set-up of the time integration algorithm; thereafter a pseudo-dynamic process dealing with a free and a forced vibration scheme, where this last was achieved with an external harmonic load, led to the definition of the structure response where the dissipative effect of the damping properties of reinforced concrete beams was evidenced.     

DYNAMIC STABILITY OF A BEAM-MODEL VISCOELASTIC PIPE FOR CONVEYING PULSATIVE FLUID

The dynamic stability in transverse vibration of a viscoelastic pipe for conveying pulsative fluid is investigated for the simply-supported case.The material property of the beam- model pipe is described by the Kelvin-type viscoelastic constitutive relation.The axial fluid speed is characterized as simple harmonic variation about a constant mean speed.The method of mul- tiple scales is applied directly to the governing partial differential equation without discretization when the viscoelastic damping and the periodical excitation are considered small.The stability conditions are presented in the case of subharmonic and combination resonance.Numerical results show the effect of viscosity and mass ratio on instability regions.     

结构阻尼时域本构模型及其应用

阻尼合金作为一种新型结构功能材料在不少领域已获应用，由于其阻尼值较大且随频率呈复杂交化关系，传统的线性粘性阻尼理论或经典的非频变结构阻尼理论难以精确地描述其耗能行为。本文应用粘弹性阻尼理论，根据阻尼合金储能模量和损耗因子在频域的实测数据．应用最优化方法拟合出标准线性体模型中的本构参数；根据积分形式的三参量本构关系和变形体虚功原理，推导出了有限元形式的动力学方程；讨论了三参数初值的选取；对包含卷积积分的有限元动力学方程通过数学推导将其化为三阶线性微分方程组，再转化为标准状态变量方程，应用数值求解。数值计算实例证明了所提方法的正确和有效性。     

基于离散单元法的颗粒阻尼耗能减振特性研究

采用离散单元法并从能量耗散的角度研究颗粒阻尼对系统减振特性的影响。建立了颗粒介质细观下的法向、切向和滚动方向的粘弹性接触模型和能量耗散模型,通过冲击激励和简谐激励下系统振动响应的多参数能量耗散分析来研究颗粒阻尼的耗能机理和减振特性。数值试验表明,颗粒介质可以在一个较宽的振动幅值范围内有效的发挥其阻尼效应,其耗能具有阶梯状周期性的特点。填充率是影响颗粒阻尼耗能减振效果的主要工程可控参数并对系统共振频率产生重大影响,当填充率接近极值时,系统出现无阻尼共振及共振频率超出无颗粒系统固有频率的现象。系统在最优填充率下共振时,颗粒与箱体保持恒定相位差的超振幅稳态运动。较小粒径的颗粒可以提高能量耗散率并使振动系统更快趋向静平衡状态,而恢复系数和摩擦系数则对法向和切向耗能的比值有较大影响。