半空间饱和多孔介质中孔隙水压动力格林函数

该文引入三维饱和场地轴对称情况时的势函数,通过傅里叶积分变换,给出了三维饱和半空间中作用一孔隙水压力时的动力格林函数。首先在作用孔隙水压力处引入一辅助面,然后通过自由表面的边界条件以及辅助面处的连续条件,得到势函数系数,利用位移应力与势函数关系即可得到三维饱和半空间任一点的响应,也即格林函数。对于地表透水情况,该文考虑了地表的完全透水和完全不透水两种透水条件,该文进行了大量计算,分析了激励频率和孔隙率对位移和孔隙水压力的影响。     

埋置块式基础地基阻抗函数的简化计算方法研究

目前关于地基阻抗的分析和计算方法都比较繁琐,不易为工程设计人员所掌握.基于此,提出了埋置基础地基阻抗函数的简化计算方法.首先,采用锥体模型分析均质半空间内埋置圆盘一维振动波的传播过程,得到了平动和转动时的地基阻抗.在此基础上,利用埋置圆盘组来模拟埋置基础,分析得到了埋置基础地基阻抗函数.最后,通过算例表明此方法计算效率高,误差小,适用于工程计算.     

地基阻抗函数对地基土—结构相互作用分析的影响

本文选用八种不同的地基阻抗函数表达方法,研究地基阻抗选取对土－结构动力相互作用效应的影响,并给出选用建议。     

基于Boer多孔介质理论的饱和半空间上刚性圆板基础竖向振动特性研究

针对饱和黏弹性半空间地基上刚性圆板基础竖向振动问题,基于Boer多孔介质动力控制方程组,应用Hankel积分变换技术并结合基础与地基土接触面混合边值条件,推导求解相关方程得到了饱和黏弹性半空间地基上刚性圆板基础的竖向动力阻抗以及振幅放大系数公式。在此基础上进一步通过数值算例对比分析探讨了液固耦合系数、基础质量比、地基土黏滞阻尼系数对所得基础竖向动力阻抗及振幅放大系数的影响规律。解析推导得出的对应竖向动力阻抗三维精确解不但丰富了基础振动理论,还可为相关工程实践提供参考和理论支持。     

考虑土-结构相互作用大型动力机器基础三维有限元分析

本文提出了考虑土-结构相互作用计算大型机器基础动力反应的三维有限元方法.该方法将动力机器基础与周围地基作为一个完整的研究对象,将基础作为粘弹性体反映基础变形,建立粘-弹性人工边界模拟半无限地基的辐射阻尼和远场地球介质的弹性恢复性能,并通过构造等效弹簧实体元使这一人工边界在商业有限元程序中实现。文中进一步将上述方法用于分析燕化高压聚乙稀装置压缩机基础的动力反应，并通过数值试验定量讨论了影响大型机器基础动力反应的主要因素，得出了一些有用的结论。     

内水压作用下粘弹性饱和土-隧洞衬砌相互作用

混凝土衬砌既有粘弹性性质,又有渗透性。实际工程中内水压力值由衬砌和孔隙水共同承担,该文通过引入与孔隙流体体积分数有关的应力系数合理地分配了衬砌和孔隙水分别承担的内水压力值。根据衬砌和土体界面处衬砌中流体速度和土体中流体速度相等以及应力和位移连续性条件建立了部分透水边界条件。将衬砌和土体分别视为多孔粘弹性材料和液固两相介质,采用饱和多孔介质理论和粘弹性理论,在频率域内给出了内水压力作用下粘弹性饱和土-衬砌相互作用时饱和粘弹性土位移、应力和孔压和衬砌的位移和应力解析表达式。进行了参数研究,表明：应力系数以及衬砌和土体相对渗透系数对系统动力响应影响很大。另外,应力系数合理地确定了边界衬砌和孔隙水分别承担的内水压力值。     

考虑桩周饱和土扰动效应的楔形桩水平振动阻抗

为了计算考虑桩周土扰动效应下的楔形桩水平振动阻抗,将薄层饱和土径向离散,利用Biot波动理论建立饱和土的复刚度传递多圈层水平振动平面应变模型,计算径向非均质的桩周土对桩身的水平动反力;将楔形桩轴向离散,基于Timoshenko梁理论建立考虑桩身剪切振动效应的横向振动微分方程,利用传递矩阵法推导桩顶水平振动阻抗的半解析解。对考虑饱和土扰动效应下楔形桩水平振动阻抗的影响因素进行了参数化分析,研究表明：在低频激振下增大楔形角能提高桩顶的水平阻抗,且随着振动频率的提高,增大楔形角会增强阻抗的频率依赖性;在低频激振下桩周土弱化会降低楔形桩的水平阻抗,且随着振动频率的提高,弱化效应会提高阻抗的共振幅值;对于如砂砾、粗砂、细砂等渗透系数较大的饱和土应考虑土体中流体惯性效应对楔形水平振动阻抗的影响;对于桩身长径比小且高频振动的楔形桩,有必要采用可以考虑桩身转动惯量及剪切效应的Timoshenko梁模型描述桩身水平振动。     

地下水位对核电结构地震反应的影响分析

核电结构大多沿海或沿江、河而建,在地下水位以下,土体孔隙中的流体对土层的地震响应有较大影响,进而影响核电结构的响应。本文采用饱和多孔介质模型,考虑土-结相互作用效应,分析地下水位对核电结构地震反应的影响。通过传递矩阵方法,得到干土-饱和土水平成层场地的自由场,并结合透射人工边界,实现土-结相互作用分析的波动输入;采用土-结相互作用的分区并行计算方法,实现饱和土和结构相互作用分析。其中,含地下水位的场地土体采用广义饱和多孔介质模型描述,通过自编FORTRAN程序用集中质量显式有限元结合透射人工边界进行模拟,结构通过ANSYS中的隐式有限元进行分析。以某一核电结构为例,分析了0,-10,-20,-30,-40 m不同地下水位的五种场地上,土-基础-核电结构体系的动力响应。结果表明,地下水位对基础和结构的位移影响不大,对加速度的影响较大。     

竖向地震作用下饱和土-桩体系的耦合动力响应研究

为揭示竖向地震荷载作用下桩土系统的耦合动力特性,首先将基桩视为具有径向和竖向变形的三维轴对称杆件,采用Hamilton变分原理建立其运动方程,而桩周土体视为充满流体的三维多孔连续介质,采用Boer多孔弹性介质模型描述其动力学行为。在不引入势函数的情况下,先将土骨架的体积应变和孔隙流体压力作为中间变量处理土体运动方程,然后采用分离变量法求解土体和基桩的运动方程,进而结合桩-土系统的边界和连续条件,推导得到桩顶的运动放大系数和运动响应因子解析解。通过与相应有限元模型数值计算结果及已有解的比较,验证所提出解的正确性。最后分析桩土主要参数对桩土耦合系统动力特性的影响,得到了一些有意义的结论,可为相关工程实践提供参考。研究结果表明：当桩长径比较小时,基桩的径向变形对饱和土-桩系统的动力响应存在显著影响,忽略基桩的径向变形,将高估桩土系统的共振行为;对于单相土而言,在低频阶段,桩顶响应相对于自由场表面响应偏小,在高频阶段,其随着桩长径比的增大而偏大。桩土系统的共振行为发生于激振频率接近于土体自由场的自振频率。随着桩长径比的增大,桩土系统对基岩运动的放大效应呈增大趋势;对于饱和土而言,饱和土层表面的...     

群桩基础阻抗函数的集总参数模型研究

利用改进后的Chebyshev多项分式进行复数拟合,得到群桩基础阻抗函数可扩展精度的集总参数模型,以获取时域分析和非线性分析的群桩基础参数。基于薄层法求解得到半无限地基中群桩基础的阻抗函数,利用改进的Chebyshev多项式的比值表示地基的动力柔度函数,将改进的Chebyshev多项分式表示成部分分式的形式,最后将其等效为两种基本类型的集总参数模型。通过与薄层法求解得到的地基动力刚度阻抗函数进行比较,本文给出的集总参数模型能在很宽的频段上与弹性半空间解吻合良好,得到的集总参数可以直接运用到群桩地基-结构相互作用的时域分析和非线性分析中。     

Dynamic impedance of pile and caisson foundations

Abstract

The dynamic impedance of a pile or caisson foundation embedded in a homogeneous visco elastic half‐space was evaluated using the hybrid method. The soil‐foundation system is partitioned into a near‐field and a far‐field by choosing a cylindrical interface passing through the soil region very close to the foundation. The near‐field is modeled by the finite element method while the far‐field is characterized by a frequency‐dependent impedance matrix through the continuum approach. From the results presented, it is shown that the proposed method is very effective and can be widely used for parameter studies in engineering applications.     

Vibrations of a pipe on elastic foundations

A cantilevered pipe subjected to external transverse (or lateral) force is investigated. Two cases of elastic foundations are considered: rotational and both linear and rotational. The major findings are the variations in frequency with flow velocity and displacements at different points and times     

Influences of elastic foundations and boundary conditions on the buckling of laminated shell structures subjected to combined loads

This article presents to study the stability of laminated orthotropic cylindrical and truncated conical shells resting on elastic foundations and subjected to combined loads with the clamped and simply supported boundary conditions. Here, axial tensile loads separately applied to the small and large bases of a laminated truncated conical shell, respectively. The basic relations, the modified Donnell type stability and compatibility equations have been obtained for laminated orthotropic truncated conical shells on the Pasternak type elastic foundation. Applying Galerkin method, the critical combined loads of laminated orthotropic conical shells on the Pasternak type elastic foundation with different boundary conditions are obtained. The appropriate formulas for single-layer and laminated cylindrical shells on the Pasternak type elastic foundation made of orthotropic and isotropic materials are found as special cases. Finally, influences of the boundary conditions, the elastic foundation, the number and ordering of the layers and variations of the shell characteristics on the critical combined loads are investigated. The results are compared with their counterparts in the literature.     

基于传递矩阵法的分层饱和土中单桩扭转动力阻抗

以分层饱和土中单桩扭转振动为研究对象,将桩周土体视为分数阶黏弹性饱和土,借助分数阶黏弹性本构模型和土体运动平衡方程、应力位移关系建立分层分数阶黏弹性饱和土层扭转振动微分方程。以两层分数阶黏弹性饱和土为例,讨论主要桩土力学参数对扭转动力阻抗影响。结果表明：下上层土体本构模型阶数比对扭转动力阻抗随频率变化曲线峰值影响较大,下上层土体剪切波速比、土层厚度比和桩土模量比对扭转动力阻抗的影响与频率有关,下上层土体液固耦合系数较小时,其对扭转动力阻抗的影响很小。     

Influences of elastic foundations and shear deformations on the buckling behavior of functionally graded material truncated conical shells under axial compression

This article presents an investigation on the buckling of functionally graded (FG) truncated conical shells under an axial load resting on elastic foundations within the shear deformation theory (SDT). The governing equations are solved using the Galerkin method, and the closed-form solution of the axial buckling load for FG conical shells on elastic foundations within the SDT is obtained. Various numerical examples are presented and discussed to verify the accuracy of the closed-form solution in predicting dimensionless buckling loads for FG conical shells on the Winkler–Pasternak elastic foundations within the SDT.     

Pt/YSZ电极结构老化特性的复阻抗研究

借助于交流复阻抗测试技术和电子扫描电镜设备,对以YzO3稳定ZrO2固体氧离子导体(YSZ)为基体的Pt／YSZ电极结构电学性能和电极形貌随时间的老化变化特性进行了研究;根据作者提出了一种有关Pt／YSZ电极结构电极界面的形貌模型,对不同老化时间下的电极Pt／空气／YSZ三相界面的长度进行了定量计算。实验测试和模型计算等结果都表明：Pt／YSz电极结构的电学性能和电极形貌均随老化时间出现了明显的变化。     

Free vibrations of anisotropic doubly-curved shells and panels of revolution with a free-form meridian resting on Winkler–Pasternak elastic foundations

The Generalized Differential Quadrature (GDQ) method is applied to study the dynamic behavior of anisotropic doubly-curved shells and panels of revolution with a free-form meridian resting on Winkler–Pasternak elastic foundations. The First-order Shear Deformation Theory (FSDT) is used to analyze the above mentioned moderately thick structural elements. In order to include the effect of the initial curvature from the beginning of the theory formulation a generalization of the kinematical model is adopted for the Reissner–Mindlin and Toorani–Lakis theory. By so doing a generalization of the theory of anisotropic doubly-curved shells and panels of revolution is proposed. Simple Rational Bézier curves are used to define the meridian curve of the revolution structures. The Differential Quadrature (DQ) rule is introduced to determine the geometric parameters of the structures with a free-form meridian. Results are obtained taking the meridional and circumferential co-ordinates into account, without using the Fourier modal expansion methodology. Comparisons between the general formulation and the Classical Reissner–Mindlin and Classical Toorani–Lakis theory are presented. New results are presented in order to investigate the effects of the Winkler modulus, the Pasternak modulus and the inertia of the elastic foundation on the free vibrations of anisotropic shells of revolution with a free-form meridian.     

等待时距与系统响应度对语音交互等待体验及学习效果的影响

目的 本研究模拟用户向教育人工智能提问英文单词释义的情境,以词汇学习为主要任务,探究语音交互系统的系统反应时间以及系统响应度对词汇学习效果以及主观体验的影响.方法 采取2(等待时距:500 ms、2450 ms)×2(系统响应度:有提示音、无提示音)被试内设计.结果 最佳等待时距下的主观体验及学习效果优于较慢等待时距,...     

长周期地面运动和SSI效应对风机动力响应的影响

针对建设在软土地基上的大功率风机结构,需要同时考虑长周期地面运动和土-结构相互作用(SSI)的影响.为了全面研究长周期地面运动和SSI效应对风机塔筒结构动力响应的影响,首先基于某1.25 MW变桨距风机结构建立了包含叶片、机舱、塔筒和基础的结构整体有限元模型,并进行了模态分析.其次在世界地震记录数据库中选择了1条普通波...     

An efficient parallel computation of unsteady incompressible viscous flow with elastic moving and compliant boundaries on unstructured grids

This paper presents the development and validation of a parallel unstructured‐grid fluid–structure interaction (FSI) solver for the simulation of unsteady incompressible viscous flow with long elastic moving and compliant boundaries. The Navier–Stokes solver on unstructured moving grid using the arbitrary Lagrangian Eulerian formulation is based on the artificial compressibility approach and a high‐order characteristics‐based finite‐volume scheme. Both unsteady flow and FSI are calculated with a matrix‐free implicit dual time‐stepping scheme. A membrane model has been formulated to study fluid flow in a channel with an elastic membrane wall and their interactions. This model can be employed to calculate arbitrary wall movement and variable tension along the membrane, together with a dynamic mesh method for large deformation of the flow field. The parallelization of the fluid–structure solver is achieved using the single program multiple data programming paradigm and message passing interface for communication of data. The parallel solver is used to simulate fluid flow in a two‐dimensional channel with and without moving membrane for validation and performance evaluation purposes. The speedups and parallel efficiencies obtained by this method are excellent, using up to 16 processors on a SGI Origin 2000 parallel computer. A maximum speedup of 23.14 could be achieved on 16 processors taking advantage of an improved handling of the membrane solver. The parallel results obtained are compared with those using serial code and they are found to be identical. Copyright © 2005 John Wiley & Sons, Ltd.