形状不规则基础-地基的动力扭转相互作用

采用薄层元素法和有限单元法,研究了形状不规则基础-地基的扭转动力相互作用.对平面形状为"L"形和"C"形的箱形基础和刚性筏板基础的阻抗函数以及基础输入地动进行了比较分析.结果表明,随着凹进部分尺寸的增大,"L"形基础的扭转阻抗降低,它可以用相同扭转惯性矩的正方形基础进行近似等效;而凹进部分对"C"形基础的影响比较小,在凹进部分不太大且频率不太高的情况可以忽略不计.     

土-结构动力相互作用对隔震结构影响的模态分析方法

本文将频域模态分析方法推广到土－结构动力相互作用对基础事震结构的影响分析下。基于上部结构固定时具有正则型的假设下,推导了地震激励作用下,土－结构动力相互作用对基础隔震结构影响的频域模态分析的步骤。算例表明,采用低阶模态进行计算,得到较高精度的分析结果的同时,可以有效地减少计算时间。     

考虑桩-土-结构动力相互作用时高层建筑风致振动的响应计算

本文推导了考虑桩土结构动力相互作用时高层建筑在脉动风荷载作用下的运动方程。然后根据国家规范提供的参数及风洞试验得到的形状系数,推导出脉动风速及风压之间的关系,求出脉动风荷载的时程。利用该荷载对某超高层建筑的动力响应进行了计算。计算结果表明：桩土结构动力相互作用对高层建筑的风致振动响应的影响是明显的,应当引起重视。     

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.     

单向偏心结构的简化增量动力分析方法

增量动力分析方法(IDA)可以较为全面的评估结构的抗震性能,但需对结构进行大量的非线性时程分析,计算量巨大.该文将单向偏心结构的等效二自由度模型(EDDOF)应用于增量动力时程分析,提出了单向偏心结构的简化增量动力分析方法.然后选取20条实际地震记录和一栋5层偏心结构,基于等效二自由度模型和原型模型分别进行了增量动力时...     

考虑桩土耦合作用时桩基扭转振动特性研究

假设桩周土层为均质线性粘弹性体,土材料阻尼为粘性阻尼,桩为竖直弹性均匀圆形截面桩,从三维轴对称角度,对考虑桩土耦合作用时桩基扭转振动桩顶频域振动特性进行了理论研究。利用拉普拉斯变换,首先通过对土层进行求解得到其振动扭转角位移形式解,然后利用该解并以小应变条件下桩土接触界面位移连续来考虑桩土的耦合作用,来分析基桩的动力反应,研究得到了考虑桩土耦合作用时桩顶扭转频域响应函数的解析解。基于所得解对桩土系统的扭转振动特性进行了对比和分析,并重点探讨了桩侧土粘性阻尼对桩顶响应的特殊影响,校验了基于平面应变假定桩基扭转振动理论解的精确性。     

土-隔震结构相互作用体系动力特性参数的简化分析方法

基于集总参数SR(sway-rocking)模型,建立隔震结构考虑土-结构相互作用(SSI)影响的简化分析模型,并经严格推导得到了模型动力特性参数的计算公式,由此可将常规非隔震结构的简化分析方法延伸到隔震结构的相互作用分析。通过算例分析,与复模态分析方法进行了对比。对比结果表明,该文提出的计算公式对绝大多数工程场地都有很好的适用性,但是相比复模态方法该文方法更加简单实用。算例分析同时表明SSI对于高层隔震结构的影响比中低层结构大。该文提出的简化计算方法是隔震结构初步设计评估SSI效应的简便有效的工具,同时为隔震结构考虑SSI效应的基于反应谱理论的设计方法研究奠定基础。     

桩与粘性阻尼土耦合扭转振动时域响应研究

假设桩周土层为均质粘弹性体,土材料阻尼为粘性阻尼,从轴对称角度出发,对任意激振扭矩作用下弹性支承桩与土耦合扭转振动时的桩顶时域响应进行了理论研究,求得桩顶扭转角阻抗函数解析解,给出半正弦脉冲激振扭矩作用下桩顶速度时域响应半解析解.基于所得解对桩土系统的扭转振动特性进行了分析,讨论了桩土耦合扭转振动条件下长径比、波速比、桩底支承条件等因素对桩顶时域响应的影响,探讨了桩侧土粘性阻尼的特殊影响,得到若干新的结论.     

多层框架结构考虑土—结构相互作用的地震反应分析

本文提出了一个剪切振动连续体模型,将地基土、基础、上部结构视为一种性质分段均匀仅考虑剪切振动的连续体,将地基土的动力特性、阻抗直接引入动力方程中,利用质量、刚度、及阻尼对振型函数的正交性对动力方程解藕,以简化计算。算例结果显示此模型适用于以切振动为主的多层框架结构考虑土－结构相互作用的地震反应分析。     

多向地震耦合作用下高耸结构土-结构动力相互研究

研究了水平地震与竖向地震耦合作用下,考虑土-结构相互作用以及二阶效应对结构反应的影响。采用集总参数法,推导了结构在竖向地震和水平地震作用下的运动方程,对某高层建筑的地震反应进行了数值分析。结果表明:考虑土-结构相互作用使结构周期延长,变形增大;竖向地震作用使结构的地震反应有不同程度的增加;考虑二阶效应后结构的位移反应以及层间剪力增加。故在设计建筑在软土地基上的高层及高耸结构时,应该考虑结构的重力二阶效应,考虑其对结构的整体稳定性的不利影响。     

土-结构相互作用对储液结构动力反应的影响研究

在对大型工程结构进行地震反应分析时土-结构相互作用通常不可忽略,然而,结构本身巨大的体量及考虑土-结构相互作用后引入的大范围土域模型导致计算规模通常十分庞大,由此引起的计算效率低下问题已成为制约此类结构性能分析的关键因素。该文提出一种新型土-结相互作用分析方法,并基于此实现了大型结构考虑土-结构相互作用的高效地震反应分析,建立不同接触状态下的单元法向和剪切相对位移分解方法;采用三维无厚度Goodman接触面单元格式对土与结构的接触行为进行描述,并通过插值方法对单元非线性变形进行描述,推导出隔离非线性的接触面单元控制方程;在此基础上,建立了大型工程结构考虑土-结构相互作用的整体式计算模型和高效地震反应分析方法。由于该文方法在每次迭代求解过程采用Woodbury公式计算结构响应,其仅需对一个规模极小的局部非线性矩阵进行迭代更新,避免了传统方法所需的结构大规模整体刚度矩阵实时更新分解,因而能够大幅度提高结构地震反应分析效率,数值算例验证了该文方法的有效性及高效性。

     

Infinite boundary elements for the dynamic analysis of machine foundations

This paper describes an infinite boundary element technique for the dynamic analysis of three-dimensional machine foundations. The core region is modelled with quadratic elements while infinite boundary elements are used to discretize the unbounded far-field outside the immediate vicinity of the loaded area. The dynamic decay function assumed in the analysis is based on Rayleigh wave attenuation away from the centre of the foundation. Effective integration schemes for oscillatory integrals have been developed. Illustrative examples are presented in order to demonstrate the applicability and accuracy of the proposed infinite boundary element. © 1997 John Wiley & Sons, Ltd.     

A model for interface cracks in layered orthotropic solids: Convergence of modal decomposition using the interaction integral method

The mode‐partitioning problem for bimaterial interfaces is still not resolved by the classical fracture mechanics approach in a satisfactory manner. Stress oscillations and overlapping crack faces are a direct consequence of the rigorous solution of the elastic boundary value problem, if the constitutive law changes discontinuously across the interface. Conversely, continuously varying material properties, also referred to as functionally graded materials (FGM), avoid these physically not admissible drawbacks. In this case the crack tip fields are of the same nature as those known from homogeneous materials. Therefore, the well‐established stress intensity factor concept can be used without any changes. Following this motivation an FGM‐interface model for delaminated composite beam structures was developed and its characteristics with respect to the modal decomposition of the crack tip fields were investigated. The considered beam structures consisted of two orthotropic layers, each of a different material. The spatial variation of the material properties in the interface region was modeled by a tanh ‐function introducing one transition parameter that controlled the FGM‐gradient. Four load cases were analyzed for each structural configuration: either a unit normal force or a unit bending moment was imposed on each end of the split beam. Thus, any load case can be simply reconstructed from the presented results by means of superposition. The stress intensity factors for modes I and II were then evaluated using an interaction integral method along with the finite element method. The corresponding results are given depending on the mesh density of the interface region, the integration domain and the transition parameter. In this manner, the influence of the transition parameter on the mode ratio and on the convergence behavior of the modal decomposition scheme with respect to its integration domain was identified. Finally, the ability of the FGM‐interface model to represent bimaterial interfaces while still maintaining the advantages of crack analysis in homogeneous materials was highlighted. Copyright © 2008 John Wiley & Sons, Ltd.     

Field-to-field coupled fluid structure interaction: A reduced order model study

The standard Fluid-Structure Interaction (fsi ) coupling, that uses as unknowns velocity and pressure for the fluid and displacements for the solid, is compared against two novel types of coupling, the first one a three-field coupling (velocity-pressure-stress/displacement-pressure-stress) introduced by the authors in a recent work, and a two-field coupling (velocity-pressure/displacement-pressure) introduced in this paper, in this way completing our set of Field to Field (f2f ) equations, all stabilized by means of the Variational Multi-Scale (vms ) method using dynamic and orthogonal subscales. The solid two-field fsi coupling formulation is benchmarked statically and dynamically. Proper Orthogonal Decomposition (pod ) is applied to all three fsi formulations to obtain reduced basis and asses their performance in a reduced space. Numerical tests are shown comparing all three formulations. By correctly resolving the Cauchy stress tensor, the three-field fsi coupling proves to provide more accurate results in both Full Order Model (fom ) and Reduced Order Model (rom ) spaces than its counterparts for a similar number of degrees of freedom, making it a reliable formulation. f2f pairing appears to be beneficial, providing more accurate results in all cases shown; mixed pairing with a three-field formulation in the solid appears to produce very precise results as well.     

结构-地基相互作用水平与扭转的超亚谐振动

基于多线性随动强化模型求得了基础和地基土之间的水平刚度与摇摆刚度，在此基础上建立了结构，地基非线性相互作用体系模型，利用能量法得到了结构水平侧移和扭转相耦合的振动方程，采用多尺度法研究了结构，地基相互作用体系的超谐和亚谐共振，比较了结构与地基非线性因素给体系反应带来的影响，揭示了发生超谐和亚谐振动时水平振动和扭转振动耦合的不同规律，为工程抗震提供了理论依据。     

Symmetric collocation BEM/FEM coupling procedure for 2-D dynamic structural–acoustic interaction problems

 This paper presents a symmetric collocation BEM (SCBEM)/FEM coupling procedure applicable to 2-D time domain structural–acoustic interaction problems. The use of symmetry for BEM not only saves memory storage but also enables the employment of efficient symmetric equation solvers, especially for BEM/FEM coupling procedure. Compared with symmetric Galerkin BEM (SGBEM) where double boundary integration should be carried out, SCBEM can reduce significantly the computing cost. Two numerical examples are included to illustrate the effectiveness and accuracy of the proposed method. Received: 2 November 2001 / Accepted: 27 May 2002     

A rigid surface boundary element for soil-structure interaction analysis in the direct time domain

Many soil-structure interaction problems involve studies of single or multiple rigid bodies of arbitrary shape and soil media. The commonly used boundary element methods implement the equations of the rigid body in a form that depends on the particulars of the geometry and requires partitioning and condensation of the associated algebraic system of equations. The present work employs the direct time domain B-Spline BEM for 3D elastodynamic analysis and presents an efficient implementation of rigid bodies of arbitrary shape in contact with, or embedded in, elastic media. The formulation of a rigid surface boundary element introduced herein is suitable for direct superposition in the BEM system of algebraic equations. Consequently, solutions are computed in a single analysis step, eliminating, thus, the need for partitioning of the system of equations. Computational efficiency is also achieved due to the extremely sparse form of the associated coefficient matrices. The proposed element can be used for the modeling of single or multiple rigid bodies of arbitrary shape within the framework of the BEM method. The efficiency and general nature of the proposed element is demonstrated through applications related to the dynamic analysis of rigid surface and embedded foundations and their interaction with embedded rigid bodies of arbitrary shape. Received 17 December 1999     

A simplified recursive formulation for the dynamic analysis of planar mechanisms

Summary In the present paper, a numerical method for generating the equations of motion of planar mechanisms with only revolute joints is presented. The method rests upon the idea of replacing the rigid body by a dynamically equivalent constrained system of particles. For the open loop case, the equations of motion are generated recursively along the open chains. Geometric constraints that fix the distance between the particles are introduced. For the closed loop case, the system is transformed to open loops by cutting suitable kinematic joints with the addition of kinematic constraints. The method is conceptually easy and suitable for computer implementation. It eliminates the necessity of distributing the external forces and moments over the particles and uses the concepts of linear and angular momentums to generate the rigid body equations of motion without introducing any rotational coordinates. An example with closed loops is chosen to demonstrate the generality and simplicity of the proposed method.     

地震波斜入射下考虑局部地形影响和土结动力相互作用的多跨桥动力响应分析

不规则地形条件下斜入射地震波场求解难度较大,以往的方法在计算精度和适用范围方面仍有不足。该文结合解析推导和有限元模拟,提出了一种基于波场分离技术的不规则地形条件下地震波输入方法,将地震P波和SV波在不同边界下进行波场分离：垂直入射时在侧面边界上分离为自由波场和散射波场,底部边界上分离为入射波场和边界外行场;斜入射时将输入侧对面的边界改为分离成入射波场和边界外行场;并充分考虑局部地形条件的影响,还基于改进的波动方法以便捷地输入节点力。同时对比了多组不同地震入射角度下规则场地和不规则场地的振动反应。结果表明：该方法在多类地形条件下计算精度与效率均较高,适用范围广且易于推广至复杂场地条件,并发现地震波入射角度和局部场地条件对地表位移响应影响较大。该研究可为不规则地形条件下的振动响应分析提供有效的手段。     

燃气轮机拉杆转子考虑接触效应的扭转振动模态分析

燃气轮机转子一般是由多个层叠的轮盘通过拉杆组合而成,各轮盘接触面由磨削加工形成。粗糙度测试结果表明磨削加工的实验拉杆转子轮盘面具有两个不同分形结构的区域。利用结构函数法计算了这种双重分形面的轮廓曲线的分形维数D1、D2和分形粗糙度参数G1、G2 。采用双重分形几何描述接触表面的拓扑结构,并根据赫兹接触理论导出接触微凸体的切向接触刚度。弹塑性双重分形面的切向接触刚度等于所有微观弹性接触点的切向接触刚度的总和。粗糙层是由相接触的微凸体所构成的,其抗扭刚度模化为接触转子轮盘间的一个抗扭弹簧。通过三维有限元模态分析和实验模态分析得到了拉杆转子在不同预紧力下的扭振模态频率。通过上述计算和实验结果识别了粗糙层的抗扭刚度,实验测试结果和理论计算结果相一致,这表明上述接触层抗扭刚度的双重分形模型实合理的,可以有效地考虑接触效应对拉杆转子扭转振动模态频率的影响。