基础隔震结构抗震可靠度简化分析方法

选用胡聿贤平稳地震地面运动模型作为基础隔震结构的随机地震动输入,采用Bouc-Wen模型描述隔震结构的层间滞变位移,将滞变体系动力特性矩阵随机等效线性化,并建立等价线性状态方程。引入左右特征向量系,对振动微分方程进行解耦,推导了基础隔震结构随机地震响应的统计矩解析解。采用变形失效准则,定义了上部结构和隔震层的功能状态极限函数。在此基础上,采用首次超越破坏模型,基于Possion分布假设和串联系统可靠度模型,建立了从整体上评价基础隔震体系抗震可靠度的简化分析方法。最后,通过一个基础隔震框架结构计算实例,说明了这种方法的运用。     

结构地震反应的频域精细传递矩阵法

传统的传递矩阵法需要对控制微分方程进行求解,获得相应的传递矩阵。公式繁琐、复杂。文中提出将传递矩阵法与精细积分法中的指数矩阵运算技巧结合起来,在频域内对结构进行动力分析。与传统的传递矩阵法相比,无需对微分方程进行求解,只需按照迭代公式进行计算,就可以得到所需要的传递矩阵。这种方法公式简单,理论上可实现任意精度,而且计算效率较高,能够快速、高精度的进行结构的地震反应分析。算例显示了精细传递矩阵法的有效性。     

求解结构自振频率的精细传递矩阵法

将高精度的精细积分法和力学概念清晰的传递矩阵法结合起来,以微分方程和矩阵分析理论为基础,提出了一种新的精细传递矩阵形式,并用于求解结构自振频率.推导了该方法的计算公式.与传统的传递矩阵法相比,无需对微分方程进行求解,只需按照迭代公式进行计算,就可以得到所需要的传递矩阵.提出的方法虽然是条件稳定的,但是稳定性条件极易满足.算例表明本方法具有较高的精度和效率.可以对任意结构进行自振频率求解.     

曲线箱梁桥地震反应的频域精细传递矩阵法

本文将高精度的精细积分法和力学概念清晰的传递矩阵法结合起来,以微分方程和矩阵分析理论为基础,提出了一种新的精细传递矩阵形式,在频域内对曲线箱梁桥地震反应进行分析. 与传统的传递矩阵法相比,无需对微分方程进行求解,只需按照迭代公式进行计算,就可以得到所需要的传递矩阵.这种方法公式简单,理论上可实现任意精度要求,而且计算效率较高.能够快速、高精度地进行曲线梁桥的地震反应分析.算例显示了精细传递矩阵法的有效性..     

考虑楼板变形带转换层高层建筑结构简化计算

带转换层高层建筑属于复杂结构体系,其楼板变形问题较为突出,考虑楼板变形对带转换层高层建筑结构进行的地震反应简化计算研究非常必要.首先将带转换层的整体结构以转换层为界划分为若干个子结构部分;其次,对每个子结构内部的各类型竖向构件以轴线为单位运用超单元法进行简化等效,对其楼板和转换梁等水平构件则视为深梁,对所有构件考虑其类型、剪切变形、弯曲变形和轴向变形等因素的影响建立其单元刚度矩阵;最后,通过坐标变换和自由度缩减形成各子结构整体刚度矩阵,根据依次放松约束节点的计算思路完成整体结构的动力计算.算例结果表明,该简化计算法计算量小精度较高.     

频率波数域内层状地基动力柔度的精细求解

精细积分法既可得到在计算机精度意义下的精确解,又能够保持哈密顿体系的辛结构。其是求解一阶线性常微分方程组的精确数值方法,既可以用于时间域的初值问题,又可以应用于空间域的两点边值问题。运用精细积分法求解微层区段矩阵,并对微层区段矩阵合并得到整个层状地基的区段矩阵,最终得到层状地基的动力柔度值。运用数值算例验证了本文方法的计算精度。     

用传递矩阵法求解多层层状弹性半空间轴对称动力问题的奇异解

本文利用laplace—Hankel联合变换及传递矩阵技术,导出了多层层状弹性半空间轴对称动力问题在层间完全接触情况下奇异解的一般解析表达式。本文方法概念清晰、公式简洁、易于应用。文中给出了计算实例,所得结果与文献的计算结果吻合较好。     

平面框架结构抗震易损性的简化分析方法

本文采用静力凝聚技术把平面框架结构简化为一维链状结构，从整体性能上估计结构的抗震易损性，引入状态向量，把结构运动微分方程化为状态方程的形式，地震地面加速度被模拟为均值为零的平稳过滤Ｇａｕｓｓ白噪声过程，在时域内导响应相关函数的解析表达式，通过求解协方差反应矩阵方程直接得到系统的均方响应，考虑变形极限状态，采用首次超越失效准则计算不同ＰＧＡ水平下的结构易损性。最后，用一座位于大庆市的九层框架结构的计     

黏滞阻尼器用于层间位移角超限的既有建筑的优化研究

在水平地震作用下,结构产生较大的层间变形或者结构底部地震剪力较大导致了很多建筑发生破坏。对于既有建筑,可采用安装黏滞阻尼器的加固方法减小其层间位移角,而结构层间位移角和基底剪力等均受阻尼器的位置与参数影响。因此,阻尼器的位置及参数优化的研究有重要意义。对于层间位移角超过现行规范限值的既有建筑结构,文中综合考虑结构变形与结构底部受剪两个目标,提出了黏滞阻尼器竖向位置优化目标函数;然后,设计了4种不同荷载分布情况的混凝土框架结构模型,对于目标函数中两个目标对应的权重系数,分别探讨了其确定方法,给出了简单快速得到权重系数取值的计算公式;最后,提出黏滞阻尼器阻尼系数的优化函数,给出了阻尼器的优化流程。分析数值算例结果说明本文提出的优化方法有效、经济,为黏滞阻尼器用于既有建筑的加固改造提供了有益的参考。     

海洋平台振动特性的传递矩阵法分析

本文继文献〔1〕后再次讨论结构振动计算中传递矩阵法的应用问题,目的是为海洋平台结构的振动特性分析引入一个简便、有效的方法。文中首先清理了与妥善地应用传递矩阵法有关的梁的端部支承条件与相应的边界状态向量的问题;接着给出了两个新的传递矩阵,使传递矩阵法能够处理包括一类海洋平台在内的更广泛的梁式结构的振动问题;最后结合一例多塔式重力平台的分析,介绍了一个特殊的边界状态向量以及与它有关的频率方程的形成方法,从而进一步扩大了传递矩阵法的应用范围。此外,文中亦补充讨论了应用传递矩阵法的其它一些优点。     

Effect of a forced harmonic vibration pile to its adjacent pile in layered elastic soil with double-shear model

A new model named double-shear model based on Pasternak foundation and Timoshenko beam theory is developed to evaluate the effect of a forced harmonic vibration pile to its adjacent pile in multilayered soil medium. The double-shear model takes into account the shear deformation and the rotational inertia of piles as well as the shear deformation of soil. The piles are simulated as Timoshenko beams, which are embedded in a layered Pasternak foundation. The differential equation of transverse vibration for a pile is solved by the initial parameter method. The dynamic interaction factors for the layered soil medium are obtained by the transfer matrix method. The formulation and the implementation have been verified by means of several examples. The individual shear effects of soil and piles on the interaction factors are evaluated through a parametric study. Compared to Winkler model with Euler beam, the present model gives much better results for the dynamic interaction of piles embedded in stiff soil with small slenderness ratios. Finally, the effect of a forced long pile to a short pile embedded in multilayered soil medium is studied in detail.     

欧拉梁动力反应初边值问题的微分求积解

动荷载作用下欧拉梁动响应的计算是一个初边值问题,通常很难得到解析解,传统数值方法一般是把空间和时间分别离散进行求解,计算相对复杂,效率也不高.针对分布动荷载作用下欧拉梁的振动偏微分方程,采用传统微分求积法,在空间和时间上同时进行离散;对于所有非0阶的初/边值条件,采用嵌入法在权系数计算中予以考虑.算例的数值结果与精确解的对比证明采用传统微分求积法处理此问题是可行的,而且是高效的.对于实际工程中的其他类似问题,该方法同样适用.     

The influence of preform on the modes of vibrating beams

A theoretical analysis is presented of a vibratory system in which it is possible to eliminate an unwanted mode of vibration by using that mode as an initial deformation of the system. The analysis shows that this is possible in straight beams with end restraints in axial deformation. The mathematical problem leads to an eigenvalue problem of a type not normally encountered. In the paper examples are given for the changes in eigenfrequency and mode shape produced by the initial preformed shape of the beam for cases where the preform is proportional to a mode of the straight beam and when the preform is unrelated to any mode. The analysis shows that, while elimination of a mode in the strict sense is not achieved, the results can be interpreted for practical purposes in this way.     

曲线桥抗震传递矩阵法

本文考虑曲线梁桥在竖直方向的弯扭耦合以及水平方向的弯曲、轴向变形,导出了曲线梁单元竖直方向和水平方向的传递矩阵.给出了用传递矩阵法计算曲线梁桥竖直方向和水平方向的振动频率、振型、地震内力和变形的计算公式和步骤,并运用传递矩阵法对单跨简支桥进行了地震反应分析.算例表明,本文方法简单、具有较高精度和效率,可用于曲线梁桥抗震设计.     

A method of directly extracting multiwave angle-domain common-image gathers

Angle-domain common-image gathers (ADCIGs) can provide an effective way for migration velocity analysis and amplitude versus angle analysis in oil–gas seismic exploration. On the basis of multi-component Gaussian beam prestack depth migration (GB-PSDM), an alternative method of directly extracting multiwave ADCIGs is presented in this paper. We first introduce multi-component GB-PSDM, where a wavefield separation is proceeded to obtain the separated PP- and PS-wave seismic records before migration imaging for multiwave seismic data. Then, the principle of extracting PP- and PS-ADCIGs using GB-PSDM is presented. The propagation angle can be obtained using the real-value travel time of Gaussian beam in the course of GB-PSDM, which can be used to calculate the incidence and reflection angles. Two kinds of ADCIGs can be extracted for the PS-wave, one of which is P-wave incidence ADCIGs and the other one is S-wave reflection ADCIGs. In this paper, we use the incident angle to plot the ADCIGs for both PP- and PS-waves. Finally, tests of synthetic examples show that the method introduced here is accurate and effective.     

A NEW APPROXIMATE METHOD FOR DIRECTLY INTERPRETING GRAVITY ANOMALY PROFILES CAUSED BY SURFACE GEOLOGIC STRUCTURES*

For outcropping bodies an approximate direct interpretation of the associated gravity anomaly is generally obtained with the flat plate formula. Results can be significantly improved if the causative body is approximated by a bell shape instead of a flat plate. A set of parameter curves allows the conversion to depth data. The validity of the method is borne out by synthetic models and by field examples in a Nevada valley with Tertiary and in the Los Angeles Basin. The method provides structural definition more accurate than can be obtained with the flat plate formula, particularly in the case of narrow anomalies.     

基于离散时间传递矩阵法的变截面梁地震时程分析方法研究

为提高变截面梁地震动力求解的计算效率,提出了基于离散时间传递矩阵法的时程分析方法。首先,从欧拉梁的偏微分振动方程出发,基于逐步时间积分法的线性化方法并结合张量变换原理,建立了变截面梁的动力时程计算方法;其次,考虑地震动激励的非一致输入效应,采用数值迭代求解的方式建立了变截面梁地震动力时程分析的离散时间传递矩阵算法;最后,编制了数值仿真计算程序,并结合具体算例进行了算法的有效性和高效性验证。算例结果表明:在采用相同计算模型的前提下,离散时间传递矩阵法不仅能够在计算精度方面与有限元法保持一致,同时还拥有更高的计算效率。     

Gabor‐frame‐based Gaussian packet migration

We present a Gaussian packet migration method based on Gabor frame decomposition and asymptotic propagation of Gaussian packets. A Gaussian packet has both Gaussian‐shaped time–frequency localization and space–direction localization. Its evolution can be obtained by ray tracing and dynamic ray tracing. In this paper, we first briefly review the concept of Gaussian packets. After discussing how initial parameters affect the shape of a Gaussian packet, we then propose two Gabor‐frame‐based Gaussian packet decomposition methods that can sparsely and accurately represent seismic data. One method is the dreamlet–Gaussian packet method. Dreamlets are physical wavelets defined on an observation plane and can represent seismic data efficiently in the local time–frequency space–wavenumber domain. After decomposition, dreamlet coefficients can be easily converted to the corresponding Gaussian packet coefficients. The other method is the Gabor‐frame Gaussian beam method. In this method, a local slant stack, which is widely used in Gaussian beam migration, is combined with the Gabor frame decomposition to obtain uniform sampled horizontal slowness for each local frequency. Based on these decomposition methods, we derive a poststack depth migration method through the summation of the backpropagated Gaussian packets and the application of the imaging condition. To demonstrate the Gaussian packet evolution and migration/imaging in complex models, we show several numerical examples. We first use the evolution of a single Gaussian packet in media with different complexities to show the accuracy of Gaussian packet propagation. Then we test the point source responses in smoothed varying velocity models to show the accuracy of Gaussian packet summation. Finally, using poststack synthetic data sets of a four‐layer model and the two‐dimensional SEG/EAGE model, we demonstrate the validity and accuracy of the migration method. Compared with the more accurate but more time‐consuming one‐way wave‐equation‐based migration, such as beamlet migration, the Gaussian packet method proposed in this paper can correctly image the major structures of the complex model, especially in subsalt areas, with much higher efficiency. This shows the application potential of Gaussian packet migration in complicated areas.     

Winkler弹性地基板梁的自由振动分析

中短型轨道板的几何构型介于梁、板之间,属于宽梁结构。从Mindlin板理论出发,退化得到适用于宽梁的Mindlin板梁控制方程;引入Winkler地基刚度系数,推导得到位移和转角的模态函数表达式。考虑两端简支的边界条件,得到弹性地基板梁的自由振动特征方程。通过无量纲数值算例求解出弹性地基板梁的自振频率,并与Timoshenko梁理论和Mindlin板理论进行对比。研究高跨比、泊松比和弹性地基刚度等参数对结构自振特性的影响,总结出弹性地基板梁方程的特点及适用范围,即宽度效应显著且泊松比较大的宽梁结构。     

Effect of fracture pressure depletion regimes on the dual-porosity shape factor for flow of compressible fluids in fractured porous media

A precise value of the matrix-fracture transfer shape factor is essential for modeling fluid flow in fractured porous media by a dual-porosity approach. The slightly compressible fluid shape factor has been widely investigated in the literature. In a recent study, we have developed a transfer function for flow of a compressible fluid using a constant fracture pressure boundary condition [Ranjbar E, Hassanzadeh H, Matrix-fracture transfer shape factor for modeling flow of a compressible fluid in dual-porosity media. Adv Water Res 2011;34(5):627-39. doi:10.1016/j.advwatres.2011.02.012]. However, for a compressible fluid, the consequence of a pressure depletion boundary condition on the shape factor has not been investigated in the previous studies. The main purpose of this paper is, therefore, to investigate the effect of the fracture pressure depletion regime on the shape factor for single-phase flow of a compressible fluid. In the current study, a model for evaluation of the shape factor is derived using solutions of a nonlinear diffusivity equation subject to different pressure depletion regimes. A combination of the heat integral method, the method of moments and Duhamel’s theorem is used to solve this nonlinear equation. The developed solution is validated by fine-grid numerical simulations. The presented model can recover the shape factor of slightly compressible fluids reported in the literature. This study demonstrates that in the case of a single-phase flow of compressible fluid, the shape factor is a function of the imposed boundary condition in the fracture and its variability with time. It is shown that such dependence can be described by an exponentially declining fracture pressure with different decline exponents. These findings improve our understanding of fluid flow in fractured porous media.