高阶单步法控制MR智能隔震系统的试验研究

高阶单步法已成功地应用于结构非线性分析及考虑时滞的主动控制等，显示了它的稳定、精度高和计算迅速等特点。磁流变阻尼器是一种性能优良的智能阻尼器，它具有阻尼力可调范围宽、响应迅速且所需能量很少的特点。本文将磁流变（MR）阻尼器与普通橡胶隔震支座相结合，采用高阶单步算法和两种控制策略对结构进行振动控制。数值模拟分析与振动台试验结果表明：由MR阻尼器提供可调阻尼力的智能隔震控制系统能有效克服被动隔震最优控制频带窄的缺点，对较宽频域范围不同大小的地震激励均能提供最优控制。同时也表明该控制算法是一种能用于结构实际控制的变阻尼有效算法。     

Q estimation using multifrequency point average method based on the Taylor series expansion with a different order

The quality factor Q is an important parameter because it can reflect the reservoir attenuated features and can be used for inverse-Q filtering to compensate fo...     

弹性支承索拉力动力检测理论与试验研究

为了提高索力动力检测精度,考虑索的抗弯刚度、弹性嵌固和弹性支承等因素建立数学物理模型,推导出进行索力和边界条件动力检测的实用公式.该公式当弹性支承刚度趋于无穷时,收敛于不考虑弹性支承的索力动力检测公式.设计了三个试验验证索力和边界条件动力检测方法的有效性,试验结果表明:弹性支承刚度较小时,不考虑弹性支承对动力检测影响的...     

Assessment of uncertainty associated with the estimation of well catchments by moment equations

Non-local stochastic moment equations are used successfully to analyze groundwater flow in randomly heterogeneous media. Here we present a moment equations-based approach to quantify the uncertainty associated with the estimation of well catchments. Our approach is based on the development of a complete second order formalism which allows obtaining the first statistical moments of the trajectories of conservative solute particles advected in a generally non-uniform groundwater flow. Approximate equations of moments of particles’ trajectories are then derived on the basis of a second order expansion in terms of the standard deviation of the aquifer log hydraulic conductivity. Analytical expressions are then obtained for the predictors of locations of mean stagnation points, together with their associated uncertainties. We implement our approach on heterogeneous media in bounded two-dimensional domains, with and without including the effect of conditioning on hydraulic conductivity information. The impact of domain size, boundary conditions, heterogeneity and non-stationarity of hydraulic conductivity on the prediction of a well catchment is explored. The results are compared against Monte Carlo simulations and semi-analytical solutions available in the literature. The methodology is applicable to both infinite and bounded domains and is free of distributional assumptions (and so applies to both Gaussian and non-Gaussian log hydraulic conductivity fields) and formally includes the effect of conditioning on available information.     

Interaction of an axisymmetric body with obliquely incident seismic waves by global local finite elements

Asymmetric steady-state structure-media interaction due to obliquely incident body waves is investigated via a version of the global local finite element method. In the present version, a local region that houses an axisymmetric structure is modelled by conventional finite elements, while the behaviour in the remaining portion of the homogeneous semi-infinite medium is presented by the spherical harmonics that are the eigensolutions of the entire space problem. The solution scheme involves (1) full displacement and traction continuity along the boundary between the local and the exterior regions and (2) satisfaction of the traction-free requirement on the surface of the half-space beyond the discretized region by virtue of a sequence of integral constraints of the non-zero weighted surface tractions of the spherical harmonics. The numerical results presented are for a perfectly bonded rigid circular foundation resting on the surface of the half-space and subjected to obliquely incident body waves. Dependence of the displacement response of the footing upon incident angles and dimensionless wave numbers is thoroughly studied.     

Seismic performance and global ductility of RC frames rehabilitated with retrofitted joints by CFRP laminates

This paper presents a new FRP retrofi tting scheme to strengthen local beam-column joints in reinforced concrete(RC) frames.The new retrofi tting scheme was proposed following a preliminary study of four different existing retrofi tting schemes.A numerical simulation was conducted to evaluate the effectiveness of FRP-strengthened reinforced concrete frames by bridging behavior of local joints to the whole structure.Local confi nement effects due to varying retrofi tting schemes in the joints were simulated in the frame model.The seismic behavior factor was used to evaluate the seismic performance of the strengthened RC frames.The results demonstrated that the new proposed retrofi tting scheme was robust and promising,and fi nite element analysis appropriately captured the strength and global ductility of the frame due to upgrading of the local joints.     

Non-stationary spatial covariance structure estimation in oversampled domains by cluster differences scaling with spatial constraints

In the analysis of spatiotemporal processes underlying environmental studies, the estimation of the non-stationary spatial covariance structure is a well known issue in which multidimensional scaling (MDS) provides an important methodological approach (Sampson and Guttorp in J Am Stat Assoc 87:108–119, 1992). It is also well known that approximating dispersion by a non-metric MDS procedure offers, in general, low precision when accurate differences in spatial dispersion are needed for interpolation purposes, specially if a low dimensional configuration is employed besides a high number of stations in oversampled domains. This paper presents a modification, consisting of including geographical spatial constraints, of Heiser and Groenen’s (Psychometrika 62:63–83, 1997) cluster differences scaling algorithm by which not the original stations but the cluster centres can be represented, while the stations and clusters retain their spatial relationships. A decomposition of the sum of squared dissimilarities into contributions from several sources of variation can be employed for an exploratory diagnosis of the model. Real data are analyzed and differences between several cluster-MDS strategies are discussed.     

考虑发射波形的瞬变电磁三维模型降阶快速正演算法

瞬变电磁响应受到发射波形的影响,正演计算中需考虑发射波形.基于位移逆Krylov子空间投影的模型降阶算法能够精确模拟三维全波形瞬变电磁正演响应,但该算法计算精确的on-time响应非常耗时.目前实际工作中多数情况下都是对off-time时间段的数据进行处理解释,因此可以将正演问题简化为精确模拟考虑发射波形的off-time时间段的响应.

本文实现了一种改进的基于位移逆Krylov子空间投影的模型降阶算法,能够实现任意发射波形的瞬变电磁off-time时间段的响应的三维快速正演.基于频谱分析理论实现了一种定量化的评价on-time采样波形精度的方法,能够在保证off-time响应精度的同时,极大的减少on-time波形采样点的数量,从而显著的减少正演计算时间.典型的半正弦波、梯形波和复杂的VTEM波的模型的正演结果表明,相比密集采样的正演结果,本文算法在保证off-time响应精度的同时,能够实现5倍以上的正演加速.

     

An experimental study of water table recharge by seepage losses from a ditch with intermittent flow

Farmed catchments in the Mediterranean area often exhibit dense networks of ditches which are also preferential zones of water table recharge, and thereby of groundwater contamination. This study presents an experimental analysis of seepage losses and related groundwater recharge patterns during a typical Mediterranean runoff event at the scale of a ditch located above a shallow water table. The objectives were (i) to evaluate the patterns of water table recharge by seepage in a ditch, (ii) to study the main flow processes occurring during recharge, and (iii) to estimate solute propagation in case of contaminated flow in the ditch. The field observation indicated three major points. Firstly, they showed that seepage losses during a runoff event in a ditch can rapidly lead to a significant recharge of a shallow water table. Secondly, the recharge induces a groundwater mound much larger than the event plume. The infiltrated water and the accompanying solutes remained in the vicinity of the ditch. The patterns of groundwater recharge and contamination appeared very different. Lastly, both unsaturated and saturated‐piston flow processes were observed which suggests that a variably‐saturated flow modelling approach ought to be used to simulate the ditch‐water shallow table interaction. Finally, the study indicates that the patterns of water table recharge and contamination in Mediterranean catchments with dense ditches network vary largely in space and time, and will require dense monitoring networks to estimate the evolution of the average contamination levels. Copyright © 2008 John Wiley & Sons, Ltd.     

替换阻尼杆件的双层柱面网壳被动控制振动台试验研究

本文在拟动力装置上对自行设计的孔隙式粘滞阻尼杆件进行了性能测试，并用其替换双层柱面网壳的部分下弦杆进行了被动减震控制的振动台试验，输人了多种能级的不同地震动，针对替换不同位置和数量的阻尼杆件进行了多种工况下的试验研究。试验结果表明减震效果明显，与理论分析结果吻合较好。