AE指数非线性预报的探讨

本文运用径向基函数法和邻点加权拟合法构造预测模型，利用ＡＢ指数对地磁活动的非线性预测的可能性进行了探讨。     

Effect of orthogonal inplane structural elements on inelastic torsional response

The elastic torsional stiffness of a structure has important influence on the seismic response of an asymmetric structure, both in the elastic and inelastic range. For elastic structures it is immaterial whether the stiffness is provided solely by structural elements in planes parallel to the direction of earthquake or by a combination of such elements in parallel and orthogonal planes. The issue of how the relative contribution of structural elements in orthogonal planes affects the torsional response of inelastic structures has been the subject of continuing study. Several researchers have noted that structural elements in orthogonal planes reduce the ductility demands in both the flexible and stiff edge elements parallel to the earthquake. Some have noted that the beneficial effect of structural elements in orthogonal planes is more pronounced when such elements remain elastic. These issues are further examined in this paper through analytical studies on the torsional response of single-storey building models. It is shown that, contrary to the findings of some previous studies, the torsional response of inelastic structures is affected primarily by the total torsional stiffness in the elastic range, and not so much by whether such stiffness is contributed solely by structural elements in parallel planes or by such elements in both parallel and orthogonal planes. Copyright © 1999 John Wiley & Sons, Ltd.     

橡胶座非线性弹性回转剪切特性的理论和试验研究

本文系统地研究分析了橡胶隔震支座(以下简称为橡胶座)回转、剪切相关的基础理论,提出了能够反映剪切应变特性的非线性回转刚度等概念。基于非线性回转刚度与Haringx弹性体计算模型,给出了计算橡胶座回转、压缩、剪切特性的计算理论。针对回转剪切计算理论采用天然橡胶和铅芯橡胶座原型试件进行了回转刚度试验,以及变动回转、变动压力等状态的剪切试验,结果表明建立的计算理论能够较理想地分析橡胶座回转剪切相关的力和弯矩等力学特性。     

低周反复扭矩下再生混凝土受扭构件抗震性能试验研究

通过对两根再生混凝土试件(再生骨料替代率为100%)在低周反复纯扭荷载作用下的抗震性能试验,对再生混凝土纯扭试件的破坏形态、滞回曲线、骨架曲线、延性、耗能能力等进行了分析。研究表明,再生混凝土受扭试件在低周反复扭矩作用下滞回环呈反S形,延性系数在3.67～4.14之间,具有良好的抗震性能。结合混凝土结构设计规范推导了抗扭承载力的计算公式,其计算值与试验值符合较好,具有一定的参考价值。     

The choice of the spherical radial basis functions in local gravity field modeling

The choice of the optimal spherical radial basis function (SRBF) in local gravity field modelling from terrestrial gravity data is investigated. Various types of SRBFs are considered: the point-mass kernel, radial multipoles, Poisson wavelets, and the Poisson kernel. The analytical expressions for the Poisson kernel, the point-mass kernel and the radial multipoles are well known, while for the Poisson wavelet new closed analytical expressions are derived for arbitrary orders using recursions. The performance of each SRBF in local gravity field modelling is analyzed using real data. A penalized least-squares technique is applied to estimate the gravity field parameters. As follows from the analysis, almost the same accuracy of gravity field modelling can be achieved for different types of the SRBFs, provided that the depth of the SRBFs is chosen properly. Generalized cross validation is shown to be a suitable technique for the choice of the depth. As a good alternative to generalized cross validation, we propose the minimization of the RMS differences between predicted and observed values at a set of control points. The optimal regularization parameter is determined using variance component estimation techniques. The relation between the depth and the correlation length of the SRBFs is established. It is shown that the optimal depth depends on the type of the SRBF. However, the gravity field solution does not change significantly if the depth is changed by several km. The size of the data area (which is always larger than the target area) depends on the type of the SRBF. The point-mass kernel requires the largest data area.     

The influence of interface geometry,stiffness, and crushing on the dynamic response of masonry collapse mechanisms

Failure of masonry structures generally occurs via specific collapse mechanisms which have been well documented. Using rocking dynamics, equations of motion have been derived for a number of different failure mechanisms ranging from the simple overturning of a single block to more complicated mechanisms. However, most of the equations of motion derived thus far assume that the structures can be modelled as rigid bodies rocking on rigid interfaces with an infinite compressive strength—which is not always the case. In fact, crushing of masonry—commonly observed in larger scale constructions and vertically restrained walls—can lead to a reduction in the dynamic capacity of these structures. This paper rederives the rocking equation of motion to account for the influence of flexible interfaces, characterized by a specific interface stiffness as well as finite compressive strength. The interface now includes a continually shifting rotation point, the location of which depends not only on the material properties of the interface but also on its geometry. Expressions have thus also been derived for interfaces of different geometries, and parametric studies conducted to gauge their influence on dynamic response. The new interface formulations are also implemented within a new analytical modelling tool that provides a novel approach to the dynamic analysis of masonry collapse mechanisms. Finally, this tool is exemplified, along with the importance of the interface formulation, by evaluating the collapse of the Dharahara Tower in Kathmandu, which was almost completely destroyed during the 2015 Gorkha earthquake.     

基于梯度径向夹角直方图的异源图像匹配

提出一种图像全局特征描述方法——梯度径向夹角金字塔直方图.该特征不受图像灰度级非线性变换和图像旋转的影响,具有较强的抗噪声能力.基于该特征的匹配算法能够对存在旋转变换的异源图像进行匹配.用SAR图像和可见光图像对匹配算法进行测试,结果表明基于梯度径向夹角金字塔直方图匹配方法的匹配成功率优于传统方法.由于对基准图进行离线...     

Nonlinear elastic and inelastic spectra with inherent and supplemental damping

During severe seismic events, structures designed according to current standards yield and develop inelastic deformations. While the acceleration responses are limited by the yielding strength, these structures develop permanent deformations (and possible damage) due to such yielding. Spectra developed for inelastic structures can help in determining the desired yield levels and the associated inelastic deformations. Some structures made of special materials or equipped with innovative structural systems may yield, but can recover the deformation upon unloading and, thus, may avoid permanent deformations. These structures are known as nonlinear elastic. Often the post yielding excursions are very large and may exceed their toughness (or deformability). By introducing damping in form of supplemental devices, it is possible to control such deformations and keep them within acceptable limits. Spectra for such nonlinear elastic structures and inelastic structures are developed herein, by considering both inherent and supplemental damping. The difference between the two types of damping is addressed both theoretically and numerically. Design examples of several simple structures using the newly developed spectra are presented, which illustrate the importance of lower strength and damping in these nonlinear elastic or inelastic systems. Copyright © 2013 John Wiley & Sons, Ltd.     

分析拟稳定流径向弥散试验数据的反函数法

将描述拟稳定流径向水动力弥散过程的近似解析解进行反函数变换。以变换后的表达式为基础,建立了具有c-t数据和c-r数据两种情况下的直线方程。该方程的因变量与自变量均为试验数据的函数,直线常数中含有待求弥散参数。经过适当的数据转化,就可以利用线性回归法或直接图解法求出直线常数,从而计算出含水层介质的纵向弥散度al和有效孔隙率n。算例表明,这种方法的计算结果精度令人满意。