层状横观各向同性饱和土的非轴对称动力响应

通过方位角的Fourier变换,将圆柱坐标系下横观各向同性饱和土的Biot非轴对称波动方 程转化为一组一阶常微分方程组. 然后基于径向Hankel变换,建立问题的状态方程;求解状态方程后,得到传递矩阵. 进而利用传递矩阵,结合饱和层状地基的边界条件、排水条件及层间接触和连续条件,求解 了任意震源力作用下层状横观各向同性饱和地基频域动力响应问题. 时域解可通过频率的Fourier积分得到.     

地震波倾斜入射下两相饱和土层响应数值模拟

基于Biot两相饱和多孔介质理论建立了频域内饱和土层的刚度矩阵,对从基岩倾斜入射地震波下饱和土层的波动响应进行了数值研究,入射波采取修正的Kanai-Tajimi谱。通过土层地表面处的水平以及竖直放大系数研究了在不同工况条件下土层的波动响应,研究结果表明,土层的波动响应在入射角接近临界入射角时达到峰值;土层的波动响应随着基岩埋深基以及土层阻尼比的增大显著减小;而土层与基岩的波速比对土层的波动响应的影响存在临界波速比,使土层响应达到极值。对于含有夹层的地质环境,研究了波动响应沿深度的分布,通过与均质土层下响应对比,显示非均质夹层能显著减小土层地表处的波动响应,尤其软夹层能较好地阻止入射波向上的传播。     

Boundary conditions at the interface between fluid layer and fibrous medium

The flow through a channel partially filled with fibrous porous medium was analyzed to investigate the interfacial boundary conditions. The fibrous medium was modeled as a periodic array of circular cylinders, in a hexagonal arrangement, using the boundary element method. The area and volume average methods were applied to relate the pore scale to the representative elementary volume scale. The permeability of the modeled fibrous medium was calculated from the Darcy's law with the volume‐averaged Darcy velocity. The slip coefficient, interfacial velocity, effective viscosity and shear jump coefficients at the interface were obtained with the averaged velocities at various permeabilities or Darcy numbers. Copyright © 2008 John Wiley & Sons, Ltd.     

一种三维饱和土-基础-结构动力相互作用分析方法

地震波入射时土与结构动力相互作用分析是地震工程领域的重要问题.由于问题的复杂性,以往的研究大多考虑地基土为干土情形.而实际工程中,土体中经常充满孔隙水,土层往往是含水层或部分含水层.孔隙水对土层的地震反应影响较大,进而影响支撑于其上的基础和上部结构的响应.因此,有必要考虑饱和土-基础-结构动力相互作用问题.基于此,土体采用Biot模型,利用集中质量显式有限元方法并结合多次透射人工边界进行模拟;结构经有限元离散后,采用Newmark隐式时步积分方法进行分析,可通过ANSYS等有限元软件实现;基础假定为刚性,采用显式时步积分进行求解;土体和结构(及基础)可分别采用不同的时间步距;通过FORTRAN程序实现了三维饱和土-基础-结构系统在地震作用下的整体分析.从饱和多孔介质动力微分方程出发可知,干土是饱和土的特殊情形,通过将流体体积模量及孔隙率置为零,可将饱和土退化到干土,从而将干土统一到饱和土的计算框架中,通过土-结构相互作用算例对此进行了验证,进一步实现了干土与饱和土混合情形时的土-结构动力相互作用分析,使得问题的模拟更贴近实际工程(如考虑地下水位情形).通过算例对比了饱和土地基、干土地基、干土覆盖饱和土地基(考虑地下水位)情形时,土-结构相互作用对基础和结构响应的影响,结果表明地下水位对基础和结构响应的影响较大.     

Exact solutions to one-dimensional transient response of incompressible fluid-saturated single-layer porous media

Based on the Biot theory of porous media,the exact solutions to onedimensional transient response of incompressible saturated single-layer porous media under four types of boundary conditions are developed.In the procedure,a relation between the solid displacement u and the relative displacement w is derived,and the well-posed initial conditions and boundary conditions are proposed.The derivation of the solution for one type of boundary condition is then illustrated in detail.The exact solutions for the other three types of boundary conditions are given directly.The propagation of the compressional wave is investigated through numerical examples.It is verified that only one type of compressional wave exists in the incompressible saturated porous media.     

3-D DYNAMIC RESPONSE OF TRANSVERSELY ISOTROPIC SATURATED SOILS

Introduction Thedynamicanalysisofsaturatedporoelasticmediaisofbroadmeaninginmanyaspectssuchasseismology,earthquakeengineering,soilmechanicsandgeophysics,etc.Thetransverselyisotropicsaturatedsoilsissolid fluidcoupledtwophasemediainwhichthe soilskeletondisp…     

Axisymmetrical analytical solution for vertical vibration of end-bearing pile in saturated viscoelastic soil layer

Based on elasticity and the theory of saturated porous media, and regarding the pile and the soil as a single phase elastic and a saturated viscoelastic media, respectively, the dynamical behavior of vertical vibration of an end-bearing pile in a saturated viscoelastic soil layer is investigated in the frequency domain using the Helmholtz decomposition and variable separation method. The axisymmetrical analytical solutions for vertical vibrations of the pile in a saturated viscoelastic soil layer are obtained, and the analytical expression of the dynamical complex stiffness of the pile top is presented. Responses of dynamic stiffness factor and equivalent damping of pile top with respect to the frequency are shown in figures using a numerical method. Effects of the saturated soil parameters, modulus ratio of the pile to soil, slenderness ratio of pile and pile＇s Poisson ratio, etc. on the stiffness factor and damping are examined. It is shown that, due to the effect of the transversal deformation of the pile and the radial force of the saturated viscoelastic soil acting on the pile, the dynamic stiffness factor and the damping derived from the axisymmetrical solution are greatly different from those derived from the classical Euler-Bernoulli rod model, especially at some specific excitation frequencies. Therefore, there are limitations on applicability of the Euler-Bernoulli rod model in analyzing verticai vibration of the pile. More accurate analysis should be based on a three-dimensional model.     

基于分离式建模的砖石古塔动力性能与响应分析

为研究砖石古塔的动力特性及地震响应机制,以渭南慧照寺塔为对象,采用块体-灰浆分区离散方法,分别建立刚性地基条件与考虑地基-结构相互作用条件下古塔的数值模型,计算比较了塔体的动力特性;并分别按9度小震、中震和大震输入El-Centro波、Taft波和兰州人工波,计算了结构的位移和加速度反应,与相互作用系统进行比较。结果表明,考虑土-结构相互作用后,古塔结构的一阶自振频率降低5.7%,二阶频率降低45%;El-Centro波和Taft波作用下,位移和加速度响应显著增大,大震作用时,与不考虑土-结构相互作用对比,主拉应力峰值显著增加,古塔从灰浆开裂发展为砖与灰浆同时开裂;兰州人工波作用下,考虑土-结构相互作用后,主拉应力和结构开裂变形反而降低。研究结果可为古塔抗震计算与性能评估提供参考。     

Dynamic torsional response of pre-strained end bearing pile embedded in pre-strained isotropic saturated soil medium

The influence of initial strain state on the dynamic response of an end bearing pile embedded in isotropic saturated soil is investigated through the linearized theory of small elastic perturbation superposed on largely stressed bodies. The governing equations for soil, based on Blot＇s poroelasticity theory, are derived in the cylindrical coordinates, and the pile is modeled by using the one-dimensional elastic theory. The analytical solutions of pile impedance, frequency response of both twist angle and time history of velocity response are obtained by using of separation of variables technique. Finally, a parametric study of the influence of initial strains on the torsional impedance, twist angle, and velocity response at the top of the pile is carried out.     

充液系统液体-多体耦合动力响应分析

提出了充液系统的液体-多体耦合力学模型，基于ALE有限元法和多体系统动力学理论，发展了液体-多体耦合动力响应分析的一种有效方法. 对于液体子系统，将其运动分解为随同贮箱的大位移运动和相对贮箱的大幅晃动，引入贮箱固连参考系中的任意拉格朗日-欧拉(ALE)运动学描述，建立了贮箱固连非惯性参考系中液体的ALE有限元方程，对液体有限元方程的缩聚大大减少了液体子系统的计算规模. 为了计及液体阻尼的影响，引入了液体修正的Rayleigh阻尼，避免了伪阻尼力的出现. 对于多体子系统，应用多体系统动力学理论建立动力学方程. 在此基础上详细导出了液体-多体耦合动力学方程，并采用预估-多重校正算法(PMA)和时间步长控制算法进行迭代求解，既保证了迭代收敛，又提高了计算效率. 所给算例成功求解了液体运输车辆系统的液体-多体耦合动力响应，深入分析了有关参数对系统动力响应的影响，获得了一些结论.     

Dynamic response of a rotating disk submerged and confined. Influence of the axial gap

In this paper, the natural frequencies and mode shapes of a rotating disk submerged and totally confined inside a rigid casing, have been obtained. These have been calculated analytically, numerically and experimentally for different axial gaps disk-casing. A simplified analytical model to analyse the dynamic response of a rotating disk submerged and confined, that has been used and validated in previous researches, is used in this case, generalised for arbitrary axial gaps disk-casing. To use this model, it is necessary to know the averaged rotating speed of the flow with respect to the disk. This parameter is obtained after an analytical discussion of the motion of the flow inside the casing where the disk rotates, and by means of CFD simulations for different axial positions of the disk. The natural frequencies of the rotating disk for the different axial confinements can be calculated following this method. A Finite Element Model has been built up to obtain the natural frequencies by means of computational simulation. The relative velocity of the flow with respect to the disk is also introduced in the simulation model in order to estimate the natural frequencies of the rotating disk. Experimental tests have been performed with a rotating disk test rig. A thin stainless steel disk (thickness of 8 mm, (h/r<5%) and mass of 7.6 kg) rotates inside a rigid casing. The position of the disk can be adjusted at several axial gaps disk-casing. A piezoelectric patch (PZT) attached on the rotating disk is used to excite the structure. Several miniature and submergible accelerometers have measured the response from the rotating frame. Excitation and measured signals are transmitted from the rotating to the stationary frame through a slip ring system. Experimental results are contrasted with the results obtained by the analytical and numerical model. Thereby, the influence of the axial gap disk-casing on the natural frequencies of a rotating disk totally confined and surrounded by a heavy fluid is determined.     

移动荷载作用下非局部地基梁动力响应分析的有限元法Dynamic response of beams with nonlocal foundations subjected to moving loads using finite element method

基于非局部地基理论,推导了移动荷载作用下非局部地基梁动力响应问题的有限元解,分别讨论了地基的非局部参数、刚度、阻尼系数以及移动荷载速度对非局部地基梁动力响应的影响,并比较了非局部结果与局部结果的差异。结果表明,地基的非局部参数、刚度和阻尼是地基梁的动力响应的主要影响参数,地基梁最大响应及其发生的时刻与移动荷载速度有关。研究成果可为轨道地基系统设计提供参考。