地震作用下水-结构-土动力相互作用分析

该文基于ABAQUS建立了地震作用下水-结构-土系统数值模型,分析了地震动水平和竖向作用时在不同水深条件下水-结构、水-土相互作用对结构、土体和水体响应的影响.结果表明,水平地震动作用下水-土相互作用对系统响应的影响远小于水-结构相互作用,且对水、土、结构响应的影响较小,可忽略不计.竖向地震动作用下水-结构相互作用对系...     

考虑桩-土相互作用的多年冻土区多跨简支梁桥地震响应分析

为分析青藏铁路多年冻土区多跨简支梁桥地震响应情况,建立了一座10×32m箱形多跨简支梁桥三维全桥模型,以等效基础弹簧考虑桩-土相互作用;以具有初始间隙的并联弹簧-阻尼单元模拟伸缩缝两端结构的碰撞,研究了冻土融化深度、行波效应及碰撞效应对多跨简支桥梁结构地震响应的影响。结果表明：随着融土下限加深,等效基础弹簧刚度明显减小,在强地震动作用下,桥梁结构易发生落梁、桥墩倾覆等震害;当相邻碰撞体的相向位移超过伸缩缝宽度时两者发生碰撞,碰撞次数及碰撞力随地震动视波速及行进距离不同而不同,在行波波速较低且行进距离较小时碰撞效果明显,对桥梁地震响应影响较大,极易导致落梁;此外桥台对结构地震响应亦有显著影响。在对多年冻土区多跨简支梁桥抗震性能进行评估时,应特别重视夏季地震动低速行波时可能发生的震害。     

地震作用下水-轴对称柱体相互作用的子结构分析方法

针对水-轴对称柱体动力相互作用问题,提出了一种地震作用下水-结构相互作用的时域子结构分析方法.基于三维不可压缩水体的波动方程和边界条件,利用分离变量法将其转换为环向解析、竖向和径向数值的二维模型;基于比例边界有限元推导了截断边界处无限域水体的动力刚度方程,并将水体内域有限元方程和人工边界处的动水压力进行耦合,从而得到结...     

高层或高耸结构考虑土—结构相互作用的地震反应分析

本文提出了一个变曲振动连续体模型,将地基土、基础、上部结构视为一种性质分段均匀的连续体,将地基土的动力特性、阻抗直接引入动力方程中,即可体现结构的变化、土的分层、又简化了计算。算例结构表明此法适用于高层或高耸结构考虑土－结构相互作用的地震反应分析。     

土-结构相互作用下网架结构动力性能研究

采用整体有限元法分析土-结构动力相互作用(SSDI)下网架的动力性能。以大型有限元软件ABAQUS为平台,结合FORTRAN程序实现粘弹性动力人工边界精确施加、土体自重应力平衡及粘弹性边界条件下地震动输入,并通过算例验证有限元计算过程的有效性与合理性;建立地基土-支承体系-网架屋盖相互作用的三维整体模型,分析SSDI对网架结构动力性能影响。研究表明,SSDI使网架结构自振周期较刚性地基下延长且地基土越软周期越长,网架结构自振频率随地基土变软更密集;SSDI使基础底面峰值加速度较自由场地表峰值加速度增大5%~30%,且地基土越软增大幅度越大;SSDI效应可增大网架结构节点加速度及节点水平相对位移,且使网架结构节点水平相对位移随地基土的变软逐渐增大。     

考虑土-结构相互作用的大跨度连续刚构桥振动台阵试验研究

土-结构相互作用(SSI)对软土地基上桥梁结构地震响应的影响不可忽略, 研究SSI效应对提高桥梁结构抗震安全性十分重要。通过对一座1∶10比例的三跨连续刚构桥模型的振动台阵试验, 系统分析了SSI效应对大跨度连续刚构桥地震响应的影响规律。研究表明：SSI效应使振动台台面地震动的峰值和频谱特性发生较大变化;剪切波速和上覆土层厚度是影响SSI效应的重要因素;SSI效应会增大桥梁结构的位移和应变响应, 其影响程度与地震动的频谱特性和桥梁结构-地基体系的固有特性密切相关;实时耦联动力子结构试验技术是进行桥梁结构考虑SSI效应的振动台试验的有效方法。     

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。     

动力荷载作用下水-桩-土相互作用简化分析研究EI北大核心CSCD

针对近海结构单桩基础在动力荷载作用下发生复杂的水-桩-土相互作用问题,建立了三维水-桩-土全耦合动力有限元分析模型。土体、桩和水体分别采用实体单元和声学单元模拟,土体截断边界采用滚轴边界条件、水体截断边界采用无反射吸收边界条件,并确定了合理的截断边界位置;以全耦合分析模型计算结果为参考解,系统研究了四种动荷载作用下水-桩不耦合(两者界面自由)和水-土不耦合(两者界面自由)对桩体和海床表面位移和动水压力响应的影响,揭示了不同水深和桩体半径变化下不考虑两种相互作用的影响规律。     

考虑桩-土-结构相互作用的结构振动控制研究

在Penzien模型的基础上,建立了考虑桩-土-结构相互作用(PSSI)的计算模型,推导了其主动控制方程,分析了PSSI对结构控制的影响,以及土与结构各种主要参数对控制效果的影响。分析结果表明:考虑PSSI,结构地震响应有所加大,控制效果有所降低,最大控制力增大;在一定范围内,土的剪切波速、桩的截面惯性矩以及上部结构的基本周期对结构的主动控制有着显著的影响。     

考虑土-结构相互作用的高层建筑横风向振动分析

用由风洞试验得出的横风向荷载功率谱密度公式,推导出考虑结构-土相互作用(SSI)的横风向荷载功率谱密度和结构的频率响应函数矩阵公式,得到结构横风向风振响应计算公式.对超高层建筑横风向振动算例说明,考虑SSI后,房屋高度、土层的剪切波速和结构阻尼比的变化,对结构顶层的弹性位移、总位移和总加速度响应有不同影响,并指出不考虑SSI,高层建筑的横风向风振响应可能偏于不安全,因而对不同的响应类型,给出了不需考虑SSI的结构阻尼比取值范围的建议值.     

Plastic buckling analysis of a circular cylinder considering plastic compressibility

In this study the plastic buckling analysis of a circular cylinder under axial compression is carried out considering plastic compressibility. For the stability analysis, the linearized finite element equation is derived and the general elastic-plastic constitutive equation is formulated. The Drucker-Prager plastic potential is used to describe the plastic compressible yielding and the strength-differential effect. The influence of plastic compressibility on the buckling load is investigated for a circular cylinder.     

考虑流固耦合的弹性圆柱体涡激振动研究

利用CFX软件对质量比为7和3.24时圆柱体两向自由度涡激振动进行数值模拟,捕捉到了"锁定区"、"拍"和"相位开关"等现象,探讨了质量比对涡激振动的影响。最终通过研究表明:流固耦合在圆柱体涡激振动分析中应予以考虑;质量比为3.24时的锁定区范围、最大横向振幅以及达到锁定时的流速要比质量比为7时的大;质量比为7时顺流向频率一直为横向频率的2倍,但当质量比为3.24时,顺流向频率在较低约化速度(Ur≤4)下为横向频率的2倍,在较高约化速度下有两个值,一个为横向频率的2倍,另一个与横向频率接近。     

Oblique wave scattering by a circular cylinder submerged beneath an ice-cover

When a train of small-amplitude surface water waves is normally incident on a very long horizontal circular cylinder fully submerged in deep water with a free surface, it is well known that it passes over and below the cylinder with a change of phase without experiencing any reflection. However the cylinder does experience reflection for oblique incidence of the surface wave train. It is shown here that the same phenomenon also holds good when the deep water has an ice-cover instead of a free surface, the ice-cover being modelled as a thin elastic plate. Here, for oblique incidence, the reflection and transmission coefficients are obtained approximately and depicted graphically against the wave number in a number of figures.     

Acoustic scattering of an incident cylindrical wave by an infinite circular cylinder

Exact scattered acoustic fields generated by an infinite circular cylinder in the presence of an incident cylindrical wave are derived for fluid media. Equations are given for the scattered field outside the cylinder and for the total field within.     

Asymptotic analysis of the torsional modes of wave propagation in a piezoelectric solid circular cylinder of (622) class

An asymptotic method due to “Achenbach” is used to analyze the torsional modes of wave propagation in a solid circular cylinder of piezoelectric material of (622) crystal class. Information obtained in this method is useful for the frequency spectrum at long wavelengths. In this method, the field variables and the frequency are expressed as power series of the dimensionless wavenumber, $\text{? = 2π × R/W}$. Substituting these expansions in the field equations and the boundary conditions, a system of coupled second order inhomogeneous ordinary differential equations with the radial coordinate as independent variable is obtained by collecting the terms of same order $\text{?}{}^{\mathrm{m}}$. Integration of such systems of differential equations yield the various terms in the series expansions for the above modes and for the whole range of frequencies, when the real-valued dimensionless wavenumber less than unity ($\text{0<?<1}$). To test the correctness of the present scheme, the roots of the exact frequency equation are computed in double precision and the results thus obtained are compared with the results obtained in the present analysis. The results agree upto five decimal places.     

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。     

Scattering of antiplane shear wave by a piezoelectric circular cylinder with an imperfect interface

Summary We present analytical solutions for the scattering of an antiplane shear wave by a piezoelectric circular cylinder with an imperfect interface. We first consider the simple case in which the imperfection is homogeneous along the interface. Two typical imperfect interfaces are addressed: 1) mechanically compliant and dielectrically weakly conducting interface, and 2) mechanically compliant and dielectrically highly conducting interface. The expressions for the directivity pattern and scattering cross-section of the scattered shear waves are derived. We then investigate the more difficult problem in which the imperfection is circumferentially inhomogeneous along the interface. A concise expression for an inhomogeneously compliant and weakly conducting interface is derived by means of matrix notation. Numerical examples are presented to demonstrate the effect of the imperfection and the circumferential inhomogeneity of the interface on the directivity patterns and scattering cross-sections of the scattered shear wave. The circumferentially inhomogeneous interface is also utilized to model the interface where an arbitrary number of cracks exist. Results show that when every part of the interface is rather compliant, large low-frequency peaks of the scattered cross-sections, which correspond to the resonance scattering, can be observed no matter if the interface is homogeneous or inhomogeneous. The appearance of large low-frequency peaks can be well explained by estimating the natural frequency of the corresponding reduced mass-spring system where the cylinder is assumed as a rigid body. Peaks of the scattered cross-sections spanning from low frequencies to high frequencies can be observed for a cylinder with a partially debonded interface.     

Exterior caustics produced in scattering of a diagonally incident plane wave by a circular cylinder: semiclassical scattering theory analysis

We use the semiclassical limit of electromagnetic wave scattering theory to determine the properties of the exterior caustics of a diagonally incident plane wave scattered by an infinitely long homogeneous dielectric circular cylinder in both the near zone and the far zone. The transmission caustic has an exterior/interior cusp transition as the tilt angle of the incident beam is increased, and each of the rainbow caustics has a farzone rainbow/exterior cusp transition and an exterior/interior cusp transition as the incident beam tilt angle is increased. We experimentally observe and analyze both transitions of the first-order rainbow. We also compare the predictions of the semiclassical approximation with those of ray theory and exact electromagnetic wave scattering theory.     

Wave scattering by a circular cylinder half-immersed in water with an ice-cover

The problem of scattering of water waves obliquely incident on a fixed long circular cylinder half-immersed in deep water with an ice-cover is investigated here. The ice-cover is modelled as an elastic plate of very small thickness. The problem is formulated using the method of multipoles. This leads to an infinite system of linear equations which are solved numerically by truncation. The reflection and transmission coefficients are obtained and depicted graphically against the wave number for various values of the angle of incidence and flexural rigidity of the ice-cover to show the effect of the presence of ice-cover on these quantities. The effect of ice-cover is seen to increase the reflection coefficient and to decrease the transmission coefficient.     

结构-土相互作用体系的地震作用取值——基于规范地震动模型的复模态时域法

对多自由度结构-土相互作用体系基于规范地震动模型的复模态时域法的地震响应问题进行了系统研究。首先建立了结构运动方程，针对所得运动方程为非对称质量与非经典阻尼矩阵的情况，用复模态法解耦，然后采用与新抗震规范地震动参数一致的Clough-Penzien非平稳随机地震动模型进行随机地震响应分析，获得了体系相对位移方差的时域解。从而可得等效平稳化方差及其峰值，由此便可以得到结构的地震作用取值。晟后，通过一个例子来说明结构-土相互作用体系的地震响应和地震作用取值的计算方法，同时给出了由规范的反应谱法得到的基础固定结构的各质点位移和地震作用取值。