刚性矩形基础阻抗矩阵的一种近似公式

给出了弹性半空间表面刚性矩形基础水平、竖向、摇摆和扭转方向阻抗函数一种近似公式。利用这种近似公式,可以得到已知长宽比和泊松比矩形基础的阻抗函数频域解,而且还可以直接得到阻抗函数的等效时域集中参数模型。     

地基-非线性结构相互作用体系的主共振与分叉

本文考虑上部结构的恢复力为双线型模型,地基上简化为集中参数模型,运用平均法研究相互作用体系的主共振,得到主共振的定数解并讨论其稳定性。文中导出相互作用体系的分叉方程,并根据厅异性理论给出开折参数平面下的分叉图和转迁集,讨论不同物理参数域内系统的振动行为并通过算例得到一些定性的结论。     

渤海地区地震参数的修定

本文介绍了一种横向不均匀介质中地震参数的修定方法。该方法以渤海及其邻区地壳、上地幔结构的最新成果为基础构造速度模型,集中起可利用的渤海周边地区的山东、河北,北京和辽宁等台网的资料,统一修定了近年来渤海及其邻区598个地震的震源参数。所有地震都给出了震源深度并且讨论了地震定位的精度。文中给出了近年来渤海内M_L≥4.0级的地震震源参数修定结果,讨论了该区震源深度分布的特征。     

基础隔震层钢螺旋弹簧软碰撞限位实验研究

设计制作了基础隔震软碰撞限位实验模型与3种类型的钢螺旋弹簧限位器，给出了实测的限位器力学特性参数。进行9种工况的振动台模型实验，分析实验数据得出了软碰撞限位器参数对结构反应的影响规律，优选出了适用于本隔震实验模型的软碰撞限位工况。     

用动力测量值确定基础－地基系统的频变参数

提出了基础－地基系统具有频变参数的质－弹－阻模型，在这个模型中，系统的刚度Ｋ＝Ｋ０－Ｋ１ω２和阻尼系数Ｃ＝Ｃ０＋Ｃ１ω随系统振动频率而变化。文章以竖向振动为例，给出了用稳态激振下的动力反应测量值确定系统参数Ｋ０、Ｋ１，Ｃ０，Ｃ１的方法；讨论了基础频变刚度系统与附加质量系统的等效范围和差别。     

岩石破裂电磁辐射频率与弹性参数的关系

为进一步研究岩石破裂电磁辐射特征,本文根据岩石破裂电磁辐射是由岩石破裂时产生带电粒子扰动引起的假说,通过断裂力学理论中的张开位移法计算岩石破裂过程中的裂纹宽度,由电磁辐射频率与破裂宽度之间的关系,研究电磁辐射频率与弹性参数之间的关系,并给出了它们之间的关系表达式.通过建立具有中心贯穿裂纹的无限大平板模型,根据破裂宽度计算了在该模型条件下几种岩石破裂过程中产生电磁辐射频率范围.理论模型计算出来的频率范围主要集中在实验观测的中高频段,并体现出频率随弹性参数的变化.     

地震危险性分析中贝叶斯模型的意义及其应用

本文重点讨论贝叶斯模型的推理结构及其在地震危险性分析中的意义。当历史记录较少时,用定值参数的常用模型(如,用确定平均发生率的泊松模型)不能给出危险性的合理估计。贝叶斯模型考虑了参数本身的不确定性,且能灵活地结合来自地震地质的信息,给出逻辑上一致的危险性估计。本文还提供了把地震地质证据和统计资料结合起来的具体力法,并附有简单列子作为说明。     

用动力测量值确定基础—地基系统的频变参数

提出了基础－地基系统具有频变参数的质－弹－阻模型，在这个模型中，系统的刚度Ｋ＝Ｋ０－Ｋ１ω＾２和阻尼系数Ｃ＝Ｃ０＋Ｃ１ω随系统振动频率而变化。文章以竖向振动为例，给出了用稳态激振下的动力反应测量值确定系统参数Ｋ０，Ｋ１，Ｃ０，Ｃ１的方法；讨论了基础频变刚度系统与附加质量系统的等效范围和差别。     

离散网格中的弹性波动(Ⅲ)——时域离散化对波传播规律的影响

本文采用一维模型分析了时域离散化后有限元离散网格中波动的基本特征。文中讨论了时域离散化对波动的频散、截止频率及寄生振荡的影响,分析了由时域离散化引起的在频率域及由空间离散化引起的在波数域波动解的多重分支现象,并指出在研究中应取其基本分支。文中也给出了考虑时间步长影响的有限元离散化准则。研究结果表明,从模拟连续模型的精度上看,时域离散化使集中质最有限元法优于一致质量法,前者可取较大时间步长。从计算精度、容易程度及经济性各方面衡量,集中质量法均比一致质量法可取。本文的工作不但对波动有限元模拟的参数选取有指导意义,同时也是分析时域人工边界稳定性的基础工作之一。     

能量的集中消耗和摩擦效应

本文提出将结构中的地震能量进行集中控制和集中消耗。文中推导了使能量集中的最优控制参数,论述了摩擦在耗能的同时对最优控制过程的影响。利用两个模型的振动台实验和计算机模拟证实了这一设想。     

Material damping for lumped-parameter models of foundations

In foundation dynamics two mechanisms of energy dissipation exist, wave radiation and material damping. Elastic continuum models of the soil capture only the radiation effect. To incorporate material damping, use is made of the fact that the dynamic-stiffness relationships of all elastic foundations may be simulated by discrete assemblages of springs, dashpots and masses. (Such lumped-parameter models are exact for simple cone models of the soil and approximate for more involved cases.) By application of the correspondence principle directly to the discrete elements of the lumped-parameter model, it is possible to introduce Voigt viscoelasticity. Each original spring is augmented by a dashpot, and each original dashpot is augmented by a mass, attached in a special way. Going a step further, more realistic non-linear-hysteretic damping is represented by replacing the augmenting dashpots and masses by frictional elements. The analysis, which is effected solely in the time domain, is illustrated by an example from earthquake engineering.     

Lumped-parameter model and recursive evaluation of interaction forces of semi-infinite uniform fluid channel for time-domain dam-reservoir analysis

To calculate the hydrodynamic interaction forces of the reservoir directly in the time-domain, the dynamic stiffness of each mode of the semi-infinite uniform fluid channel is either represented by a lumped-parameter model with frequency-independent real coefficients of the springs, dashpots and masses and with only a few additional internal degrees of freedom, or the interaction forces are calculated recursively. For each mode characterized by its eigenvalue, the coefficients of the lumped-parameter model and the recursive coefficients are specified, which can be used directly in a practical application. The procedures exhibit many advantages: the only approximation (replacing the rigorous dynamic stiffness by a ratio of two polynomials) can be evaluated visibly. No unfamiliar discrete-time manipulations such as the z-transformation are used. The stiffness, damping and mass matrices corresponding to the lumped-parameter model are automatically symmetrical. Stability of the procedures is also guaranteed. Combining the lumped-parameter model of the semi-infinite uniform channel with the finite-element discretization of the irregular fluid region or calculating the interaction forces recursively allows a reservoir of arbitrary shape to be analysed directly in the time domain. Non-linearities in the dam can, thus, be taken into consideration in a seismic analysis.     

Simplified model for torsional foundation vibrations

A simplified model is presented to simulate unbounded soil for torsional foundation vibration problems. Based on the criterion of equivalent displacement response, a group of equivalent models are developed for a foundation-soil system. An optimal equivalent model is then determined to represent the best simplified model. The parameters of the optimal equivalent model may be obtained by a much easier and more efficient method than lengthy optimization techniques used by most existing lumped-parameter models. The dynamic torsional responses of the foundation-soil system using the optimal equivalent models are very consistent with those obtained by the half-space theory and by the existing models. With fewer parameters, the optimal equivalent model is also found to be as accurate as most existing models. This proposed method may be effectively applied to practical torsionally vibrating problems involving soil–structure interaction.     

Lumped-parameter model for a rigid cylindrical foundation embedded in a soil layer on rigid rock

To represent a cylindrical rigid foundation vibrating in horizontal, vertical, rocking or torsional motions embedded in a soil layer resting on rigid rock, a lumped-parameter model is described. The coupling between the horizontal and rocking degrees of freedom is considered. For each degree of freedom eight frequency-independent real coefficients determine the springs, dashpots and the mass of the lumped-parameter model with two internal degrees of freedom. These coefficients are specified for various ratios of the radius of the foundation to the depth of the layer and lateral contact ratios. To derive the mechanical properties of the lumped-parameter model a systematic procedure of curvefitting of the dynamic-stiffness coefficient up to, in general, twice the fundamental frequency of the layer is applied, capturing the fact that below the (horizontal) fundamental frequency (cutoff frequency) no radiation of energy occurs. The lumped-parameter model can be used to represent the soil in a standard finite-element program for structural dynamics working in the time domain, whereby the structure can exhibit non-linear behaviour. Stability of the unbounded soil-layer model and of the total system is guaranteed. A hammer foundation with partial uplift of the anvil is analysed for illustration.     

Consistent lumped-parameter models for unbounded soil: Physical representation

A systematic procedure to develop a consistent lumped-parameter model with real frequency-independent coefficients to represent the unbounded soil is developed. Each (modelled) dynamic-stiffness coefficient in the frequency domain is approximated as a ratio of two polynomials, which is then formulated as a partial-fraction expansion. Each of these terms is represented by a discrete model, which is the building block of the lumped-parameter model. A second-order term, for example, leads to a discrete model with springs and dampers with two internal degrees of freedom, corresponding to two first-order differential equations, or, alternatively, results in a discrete model with springs, dampers and a mass with one internal degree of freedom, corresponding to one second-order differential equation. The lumped-parameter model can easily be incorporated in a general-purpose structural dynamics program working in the time domain, whereby the structure can even be non-linear. A thorough evaluation shows that highly accurate results are achieved, even for dynamic systems with a cutoff frequency.     

Consistent lumped-parameter models for unbounded soil: Frequency-independent stiffness,damping and mass matrices

A systematic procedure to develop consistent (symmetric) stiffness, damping and mass matrices with real coefficients to represent any unbounded soil is developed. These property matrices are based on the lumped-parameter models of Reference 1. Either stiffness and damping matrices corresponding to first-order differential equations involving the internal degrees of freedom and those on the structure-soil interface result or, alternatively, in addition mass matrices are introduced, corresponding to second-order differential equations, which reduce the number of internal degrees of freedom by a factor 2. The stiffness, damping and mass matrices can easily be incorporated in a general-purpose structural dynamics program working in the time domain, whereby the structure can even be non-linear.     

桩土相互作用分析中的动力Winkler模型研究评述

Winkler地基梁集中参数模型在桩一土动力相互作用分析中得到了普遍应用,在现有研究成果的基础上,对桩一土相互作用分析中的动力Winkler模型进行了较全面的综述,指出了各种模型的优缺点,并对有待于深入探讨的问题及发展动向进行了简要评述,为今后深入研究提供了基础。     

A new lumped-parameter model for flow in unsaturated dual-porosity media

A new lumped-parameter approach to simulating unsaturated flow processes in dual-porosity media such as fractured rocks or aggregated soils is presented. Fluid flow between the fracture network and the matrix blocks is described by a non-linear equation that relates the imbibition rate of the local difference in liquid-phase pressure between the fractures and the matrix blocks. Unlike a Warren-Root-type equation, this equation is accurate in both the early and late time regimes. The fracture/matrix interflow equation has been incorporated into an existing unsaturated flow simulator, to serve as a source/sink term for fracture gridblocks. Flow processes are then simulated using only fracture gridblocks in the computational grid. This new lumped-parameter approach has been tested on two problems involving transient flow in fractured/porous media, and compared with simulations performed using explicit discretisation of the matrix blocks. The new procedure seems to accurately simulate flow processes in unsaturated fractured rocks, and typically requires an order of magnitude less computational time than do simulations using fully-discretised matrix blocks.