瑞利波作用下考虑桩土相互作用的单桩竖向动力响应计算研究

在前人对瑞利波作用下考虑桩土相互作用的单桩动力响应简化算法研究的基础上,将采用Novak薄层法计算地基土动力阻抗的方法引入到该领域的研究中,得到了单桩竖向动力响应的计算公式。在此计算公式的基础上分析了长径比、桩土刚度比、地基土的泊松比对单桩竖向响应的影响,并与原简化公式的结果进行了对比。     

瑞利波作用下径向非匀质地基中的单桩竖向响应研究

在单桩动力响应简化算法研究的基础上，提出了一个用于计算瑞利波激励下的单桩竖向动力响应的简化解析方法，得到了桩底固支时单桩竖向动力位移分布的闭合解。采用考虑桩周土的非匀质性的Novak薄层法计算地基土动力阻抗的方法，获得桩底固支时单桩竖向动力响应的计算公式。分析结果表明非匀质区刚度与匀质区刚度比、非匀质区大小对单桩竖向动力位移响应有一定影响。     

分层土中群桩的竖向和摇摆动力阻抗计算

采用动力文克尔地基梁模型,在研究两桩竖向动力相互作用时,建立被动桩的运动方程,求得均匀土中竖向动力相互作用因子的解析解。在各分层土中建立单桩竖向振动微分方程,利用各分层土之间桩身的连续性条件和桩顶、桩底边界条件,求解单桩振动方程。采用三步法计算分层土中桩基竖向动力相互作用因子,结合单桩竖向动力阻抗和相互作用因子求解群桩竖向和摇摆动力阻抗。通过算例分析,得到一些有意义的结果和结论。     

分数导数微分算子描述的粘弹性土层中群桩的水平振动研究

将桩周土体视为粘弹性介质,利用分数导数粘弹性模型描述土体的力学特性,在Novak 平面应变假定的基础上,借助于势函数并考虑土体边界条件求得了分数导数微分算子描述的粘弹性土层水平位移的衰减函数以及分数导数粘弹性土层的刚度和阻尼系数。利用Winkler 动力弹簧-阻尼器模型模拟桩-土之间的动力相互作用,并在此基础上利用初始参数法求解了分数导数粘弹性土层中桩-桩水平动力相互作用和群桩的水平振动问题。以数值算例的形式讨论了分数导数微分算子的阶数和土体的模型参数对分数导数微分算子描述的粘弹性土层水平位移的衰减函数和群桩的水平动力阻抗的影响。研究表明:分数导数微分算子的阶数对土层水平位移的衰减函数的影响与桩间距和荷载方向角有关;分数导数粘弹性土中群桩的动力阻抗可以退化到经典粘弹性和弹性情况;分数导数微分算子的阶数和土体模型参数对群桩水平动力阻抗有较大影响。     

分数导数粘弹性土层模型中桩基竖向振动特性研究

粘弹土体的应力-应变关系利用分数导数粘弹性模型进行描述,建立了分数导数粘弹性土层的竖向振动控制方程。在考虑三维波动的条件下,利用势函数和分离变量的方法求解了分数导数粘弹性土层的竖向振动。考虑桩土边界条件和接触条件对分数导数粘弹性土中桩基的竖向振动进行了研究,分析了主要桩土力学参数对桩顶复刚度和导纳的影响规律。研究表明：...     

单桩竖向动力阻抗计算方法及其影响因素分析

运用土动力学和结构动力学原理，改进Winkler地基梁模型，考虑桩周土的弱化效应和桩-土界面的相对滑移效应，建立了竖向荷载作用下单桩动力阻抗函数的计算力学模型，运用数理方程方法分别求解单桩与桩周近场土域及远场土域的振动方程，确定了单桩的竖向动力阻抗函数。针对数值算例进行计算，将得到的单桩竖向动力阻抗随激振频率的变化关系与现有的数值计算和分析结果进行对比，验证了建议计算方法的合理性；并通过变动参数计算，对影响桩基振动特性的各相关因素进行了比较分析。     

饱和土中桩-桩竖向动力相互作用及群桩竖向振动

由于饱和土中孔隙水的流动特性以及桩基与土体的不同渗透率,饱和土与单相土中桩基的力学行为,尤其是动力学行为存在很大差异。运用Novak薄层法和引入势函数的方法,得到了饱和土层的竖向动力阻抗和自由场竖向位移衰减函数,在此基础上研究了饱和土中桩-桩的竖向动力相互作用及群桩的竖向动力阻抗问题。分析讨论了桩土力学参数对饱和土中群桩竖向动力阻抗的影响。研究表明:桩间距、液固耦合系数、桩土模量比等参数对桩-桩竖向相互作用和群桩竖向动力阻抗有影响,研究成果对于桩基动力检测和抗震设计具有较大的实际应用价值。     

非饱和地基中部分埋入桩的水平振动问题EI北大核心CSCD

本文研究非饱和土中部分埋入桩的水平振动问题,为模拟桥梁桩基的高承台桩的实际服役状态,考虑水平简谐荷载和竖向静载的组合作用,采用Timoshenko梁模型和三维连续介质建立了非饱和土⁃部分埋入桩的耦合振动理论模型,利用微分变换法和传递矩阵法求得了桩身水平动力响应解析解,将退化解与已有成果作比较,验证了本文解的合理性。基于建立的理论模型,探讨了竖向荷载、埋入比和饱和度对部分埋入桩水平动力特性的影响。研究结果表明:刚度因子随着竖向荷载的增大而迅速减小,但是阻尼因子略微减小;刚度因子和阻尼因子均随着埋入比的增加而减小;桩身水平位移、转角、弯矩和剪力幅值均随着埋入比的增大而增大,幅值位置逐渐向上移动;饱和度较低的对刚度因子的影响很小,但饱和度大于0.9时刚度因子随饱和度的增加而迅速增大,阻尼因子基本保持不变。     

黏弹性地基中基于虚土桩模型的桩顶纵向振动阻抗研究

基于虚土桩模型,对均质粘弹性地基中桩土纵向耦合振动问题进行了研究。首先,假定桩侧土为各向同性的线性粘弹性材料,并考虑土体的竖向波动效应,结合Euler-Bernoulli杆件理论,建立了桩土纵向耦合振动的定解问题;其次,采用分离变量法求解桩侧土纵向振动的控制方程,得到了桩侧土与桩身接触面上的剪切动刚度,将所得的剪切动刚度代入到桩身振动控制方程,采用Laplace变换技术,进一步求得了任意荷载作用下桩顶纵向振动阻抗的解析解。基于所得解,详细讨论了不同桩身设计参数时桩端土厚度对桩顶纵向振动阻抗的影响。最后,将虚土桩模型与其他桩端土支承模型进行了对比研究,结果表明,对虚土桩模型选用合适的材料参数和桩端土厚度,其得到的桩端支承复刚度值介于现有多种模型的计算值之间。     

饱和土中摩擦桩竖向振动解析解及应用

采用与频率相关的桩土接触面模型建立了三维轴对称条件下摩擦桩在饱和土中的竖向耦合振动模型,通过势函数分解法和分离变量法求解了饱和土动力固结方程,利用桩土耦合条件得到摩擦桩竖向振动解,对桩周剪应力分布、桩顶的频率和时域响应进行了参数研究.结果表明,桩底支承系数和桩土接触面动刚度对桩土荷载传递有明显影响,频率相关的阻尼系数可...     

高阻尼黏弹性阻尼器性能与力学模型研究

对2个高阻尼黏弹性阻尼器进行不同应变幅值、加载频率下的力学性能试验和疲劳性能试验,研究试件在不同工况下的最大剪应力、存储剪切模量、损耗剪切模量和等效黏滞阻尼比等力学性能及其变化规律,提出五单元模型模拟黏弹性阻尼器的滞回性能。研究结果表明：黏弹性阻尼器滞回曲线饱满、稳定,具有较高的等效黏滞阻尼比,表现出良好的变形性能和耗能能力;黏弹性阻尼器力学性能与应变幅值的相关性明显,与加载频率相关性较小,抗疲劳性能较好;五单元模型模拟的滞回曲线与试验滞回曲线吻合良好。     

Shear Modulus in Viscoelastic Solid 4He

The complex shear modulus of solid ⁴He exhibits an anomaly in the same temperature region where torsion oscillators show a change in period. We propose that the observed stiffening of the shear modulus with decreasing temperature can be well described by the response of glassy components inside of solid ⁴He. Since glass is an anelastic material, we utilize the viscoelastic approach to describe its dynamics. The viscoelastic component possesses an increasing relaxation as temperature decreases. The response functions thus derived are identical to those obtained for a glassy, time-delayed restoring back-action. By generalizing the viscoelastic equations for stress and strain to a multiphase system of constituents, composed of patches with different damping and relaxation properties, we predict that the maximum change of the magnitude of the shear modulus and the maximum height of the dissipation peak are independent of an applied external frequency. The same response expressions allow us to calculate the temperature dependence of the shear modulus?? amplitude and dissipation. Finally, we demonstrate that a Vogel-Fulcher-Tammann (VFT) relaxation time is in agreement with available experimental data.     

Optimal design and parameter estimation of frequency dependent viscoelastic laminated sandwich composite plates

Recent developments in optimization and parameter estimation of frequency dependent passive damping of sandwich structures with viscoelastic core are presented in this paper. A finite element model for anisotropic laminated plate structures with viscoelastic frequency dependent core and laminated anisotropic face layers has been formulated, using a mixed layerwise approach, by considering a higher order shear deformation theory (HSDT) to represent the displacement field of the viscoelastic core, and a first order shear deformation theory (FSDT) for the displacement fields of adjacent laminated face layers. The complex modulus approach is used for the viscoelastic material behaviour, and the dynamic problem is solved in the frequency domain, using viscoelastic material data for the core, assuming fractional derivative constitutive models. Constrained optimization of passive damping is conducted for the maximisation of modal loss factors, using the Feasible Arc Interior Point Algorithm (FAIPA). Identification of the frequency dependent material properties of the sandwich core is conducted by estimating the parameters that define the fractional derivative constitutive model. Optimal design and parameter estimation applications in sandwich structures are presented and discussed.     

Finite Element Dynamic Analysis of Laminated Viscoelastic Structures

This work is concerned with the dynamic behavior of laminated beam, plate and shell structures consisting of a viscoelastic damping layer constrained between two structural layers. Finite element models for modal, harmonic and transient analyses are developed. The dynamic interlaminar shear stresses are determined and presented under harmonic and transient loads. The effect of the damping ratio of the viscoelastic material is investigated. It is found that the viscoelastic material damping reduces the interlaminar stresses. The results also show the dependency of the viscoelastic material on frequency, hence, the effect of the viscoelastic material appears significantly under harmonic loading. In transient analysis, the importance of the viscoelastic material is observed in absorbing the impact and returning the structure to its original configuration.     

Finite Element Dynamic Analysis of Laminated Viscoelastic Structures

This work is concerned with the dynamic behavior of laminated beam, plate and shell structures consisting of a viscoelastic damping layer constrained between two structural layers. Finite element models for modal, harmonic and transient analyses are developed. The dynamic interlaminar shear stresses are determined and presented under harmonic and transient loads. The effect of the damping ratio of the viscoelastic material is investigated. It is found that the viscoelastic material damping reduces the interlaminar stresses. The results also show the dependency of the viscoelastic material on frequency, hence, the effect of the viscoelastic material appears significantly under harmonic loading. In transient analysis, the importance of the viscoelastic material is observed in absorbing the impact and returning the structure to its original configuration.     

阻尼层合板中波传播性能研究

最近许多约束阻尼复合结构的研究中,阻尼层一般都选用粘弹性材料,由于粘弹性材料的刚度一般远小于约束层和基层的刚度,所以大部分研究都在计算和建模时,忽略粘弹材料的弯曲刚度,而不考虑阻尼层的外延和弯曲变形的影响。应用高阶理论研究了敷设具有一定刚度的蜂房型粘弹性材料的约束阻尼层合板结构动力学方程,探讨了复合层合板梁在振动情况时材料的弯曲刚度,剪切刚度对弯曲波在复合梁中传播的能量损耗影响,以及各层厚对层合板梁的阻尼性能的影响。     

高聚物材料动态模量测量与分析

高聚物材料具有良好的阻尼结构特性,因此在减振降噪中发挥很大作用。高聚物材料的模量是复数,并且随着系统的频率和环境温度呈非线性变化。将某高聚物材料在动态热机械分析仪上进行动态力学行为实验,并对实验结果采用分数导数维模型进行拟合。结果表明,分数导数维Maxwell模型可以同时精确的拟合高聚物材料的存储模量和损耗模量随频率变化的曲线,而且其形式简单,统一,计算所需参数较少,研究结果为实际应用提供了参考依据。     

A hyper-viscoelastic constitutive model for polyurea

This letter presents a new constitutive model for polyurea by superposing the hyperelastic and viscoelastic behaviors of polyurea. The Ogden model is used for the hyperelastic part and its parameters are determined from curve fitting of quasi-static test data. A nonlinear viscoelastic model is employed for describing the viscoelastic behavior and its relaxation time is obtained based on the test data of shear relaxation modulus. A special form of Zapas kernel for the damping function is found to be very effective to capture the viscoelastic behavior of polyurea subjected to wide ranges of strain rate. Both the versatility and accuracy of the model are examined via virtual testing.     

新型高阻尼黏弹性阻尼器性能试验研究

设计制作3个高阻尼黏弹性阻尼器,对其进行变形相关性和频率相关性的性能试验、疲劳性能试验及老化性能试验,以最大剪应力、存储剪切模量和等效黏滞阻尼比为指标研究阻尼器的性能规律,采用通用Bouc-Wen计算模型模拟其滞回曲线,并对比模拟结果和试验结果。研究结果表明:该阻尼器滞回曲线饱满、力学性能稳定,具有较强的耗能性能和大变形能力,抗疲劳性能和抗老化性能良好。变形对该新型高阻尼黏弹性阻尼器力学性能指标的影响明显,加载频率对其影响较小。Bouc-Wen模型的模拟结果与试验结果吻合良好。     

定频变温下粘弹材料动力学特性数据拟合分析

本文研究了粘弹性阻尼材料的耗能机理和动态阻尼特性,采用分数导数模型,并与温频等效原理相结合,得到了粘弹性阻尼材料的复模量、损耗因子与温度关系的参数化数学模型;并结合粘弹性阻尼材料的DMA测试实验数据对模型参量进行了拟合。实验结果和误差分析表明拟合的数学模型能够准确反映粘弹性材料在定频率变温度条件下的动力学特性的变化情况。