Application of an SMA-based hybrid control device to 20-story nonlinear benchmark building

This paper investigates the seismic response control of a 20-story nonlinear benchmark building with a new recentering variable friction device (RVFD). The RVFD combines energy dissipation capabilities of a variable friction damper (VFD) with the recentering ability of shape memory alloy (SMA) wires. The VFD that is the first subcomponent of the hybrid device consists of a friction generation unit and piezoelectric actuators. The clamping force of the VFD can be adjusted according to the current level of ground motion by adjusting the voltage level of piezoelectric actuators. SMA wires that exhibit a unique hysteretic behavior and full shape recovery after experiencing large strains is the second subcomponent of the hybrid device. Numerical simulations of a seismically excited 20-story benchmark building are conducted to evaluate the performance of the hybrid device. A continuous hysteretic model is used to capture frictional behavior of the VFD and a neuro-fuzzy model is employed to describe highly nonlinear behavior of the SMA components of the hybrid device. A fuzzy logic controller is developed to adjust the voltage level of VFDs for favorable performance in an RVFD hybrid application. Results show that the RVFD modulated with a fuzzy logic control strategy can effectively reduce interstory drifts and permanent deformations without increasing acceleration response of the benchmark building for most cases. Copyright © 2012 John Wiley & Sons, Ltd.     

A revised approach to discriminating sediment transport histories in glacigenic sediments in a temperate alpine environment: a case study from Fox Glacier,New Zealand

Clast shape measurements have developed into a standard method for reconstructing the transport histories of sediments in glacial environments. The majority of studies use the ‘RA‐C₄₀’ covariance approach, with some researchers routinely including clasts of varying lithologies within their samples. The corollary is that variable lithological properties may control clast form and roundness, rather than debris‐transport mechanisms. Despite this, the role of lithology on clast shape in glacial environments has rarely been analysed. Furthermore, some studies have reported difficulties in using the RA‐C₄₀ co‐variance plot in discriminating clasts that have undergone subglacial transport, and clasts that have been modified by fluvial activity. Results from a glacierized valley in a temperate alpine setting indicate that detailed analysis of clast shape where samples are of uniform lithology, although time consuming, is a useful tool in the investigation of deposits in glaciated environments. Copyright © 2012 John Wiley & Sons, Ltd.     

Effects of hillslope geometry on spatial infiltration using the TOPMODEL and SCS-CN models

ABSTRACT

The estimation of infiltration is a main issue in runoff simulation. The geometry of hillslopes (plan shape and profile curvature) may affect the responses, as well as infiltration over the hillslopes. In this study, the equations of TOPMODEL (a topography-based model) were applied to complex hillslopes to develop the complex TOPMODEL. This model was coupled with the SCS-CN (Soil Conservation Service Curve Number) model to examine the effects of geometry on infiltration and derive a saturation excess-based curve number (CN). The effects of plan shape and profile curvature upon the spatial distribution of CN and infiltration were studied. The results show that convergent hillslopes have 15.4% less infiltration and divergent hillslopes have 7.8% more infiltration than parallel ones. The infiltration over concave hillslopes is 13.5% lower and infiltration over convex hillslopes 5.8% higher than for straight ones. The degree of convergence/divergence has a greater effect on the CN compared to that of profile curvature.     

Application of the parabolic bay shape equation to sand and gravel beaches on Mediterranean coasts

The equation most commonly used to describe the bay planform was proposed by Hsu and Evans (1989) and it was obtained through empirical analysis of sand beach planforms.In the last decade interest in gravel sediments increased owing to their greater stability on beaches, compared with sand sediments. Due to the differences between the morphodynamics of sand and gravel beaches, which is strictly influenced by their different hydraulic characteristics, it was necessary to create a predictive instrument for this beach type as well.Therefore, in this study the standard Hsu and Evans equation (1989) was modified in order to make it applicable not only to sand beaches but also to gravel beaches. The shoreline was computed according to a parabolic model in polar coordinates whose coefficients are considered linearly dependent on the wave direction and related to the beach type. The estimation of the free parameters of the model was performed according to a statistical analysis of a shorelines data set of Mediterranean sand and gravel embayed beaches.     

基于离散单元法的滑坡堆积及其涌浪计算

采用离散单元法对水库库岸边坡的动态破坏过程进行了研究,给出了计算流程并开发了相应的软件。介绍了离散单元法的基本原理,分析了常用的计算滑坡速度方法的不足及用离散单元法的优势,基于离散单元法提供的块体运动信息并结合波动方程模拟了滑坡体滑入水库时所激起的涌浪。此外,采用离散单元法研究了滑坡的堆积形状。通过算例验证了方法的可行性与程序的正确性。算例结果表明：块体在坡面上运动时,用离散单元法计算得到的块体的速度和能量法与潘家铮法一致,且更方便、更高效;由于涌浪的叠加,多个块体所激起的涌浪高度比单个块体的涌浪高一些,这表明在进行涌浪分析时,考虑多块体的涌浪叠加效应是至关重要的,滑坡的堆积形状为滑坡的灾害评估提供了依据。通过自行开发的离散单元法软件模拟了块体的滑动和涌浪的产生及其传播过程,其模拟结果为研究边坡的滑动破坏的启动、破坏过程及滑坡的风险评价提供了新的思路。     

硬性结构面表面起伏形态测量及其尺寸效应研究

结构面表面形态与其力学性质密切相关,对结构面表面形态进行精细测量是研究结构面变形和强度等力学机理的基础。在分析国内外结构面测量仪器优缺点基础上,利用自主研制的新型便携式测量仪器———接触打孔器对硬性结构面进行机械化精细测量,应用效果表明:由接触打孔器获得的结构面粗糙度JRC值与结构面表面实际的JRC值十分接近。在此基础上,对硬性结构面进行尺寸效应分析,获得了结构面表面JRC值的统计方差随测量长度逐渐衰减的规律,并且计算分析了粗糙度对结构面剪切强度影响的极限长度,最后通过强风化粉砂岩节理、新鲜砂岩层面、泥岩层面进行了分析。结果表明,对于研究区强风化粉砂岩构造节理,当取样长度大于50cm时,可以消除剪切方向上起伏粗糙度尺寸效应;对于平直新鲜泥岩层面、平直的新鲜砂岩层面,当取样长度大于5cm时,可以消除剪切方向上起伏粗糙度尺寸效应。     

Solar wind influence on atmospheric processes in winter Antarctica

Galactic cosmic rays (GCRs) altered by solar wind are traditionally regarded as the most plausible agent of solar activity influence on the Earth's atmosphere. However, it is well known that severe reductions in the GCRs flux, known as Forbush decreases (FDs), are caused by solar wind of high speed and density, which sweeps away the GCRs on its way. Since the FD beginnings are registered at the Earth's orbit simultaneously with dramatic disturbances in the solar wind, the atmospheric effects, assigned to FDs, can be, in reality, the results of the solar wind influence on the atmospheric processes. This paper presents a summary of the experimental results demonstrating the strong influence of the interplanetary electric field on atmospheric processes in central Antarctica, where the large-scale system of vertical circulation is formed during winter seasons. The influence is realized through acceleration of the air masses, descending into the lower atmosphere from the troposphere, and the formation of cloudiness above the Antarctic Ridge, where the descending air masses enter the surface layer. The acceleration is followed by a sharp increase of the atmospheric pressure near-pole region, which gives rise to the katabatic wind strengthening above the entire Antarctica. The cloudiness formation results in the sudden warmings in the surface atmosphere, since the cloud layer efficiently backscatters the long wavelength radiation from the ice sheet, but does not affect the adiabatic warming process of the descending tropospheric air masses. When the drainage flow strengthening the circumpolar vortex around the periphery of the Antarctic continent decays, the surface easterlies typical of the coast stations during the winter season are replaced by southerlies and the cold Antarctic air masses flow out to the Southern ocean.     

一种放大位移型SMA阻尼器的减震控制分析

利用形状记忆合金(SMA)材料的超弹性,本文提出了一种放大位移型SMA阻尼器,建立了装有该阻尼器的框架有限元模型并对该框架的地震反应实施了模拟减震控制。分不安装阻尼器、安装不放大位移阻尼器和安装放大2倍层间位移阻尼器三种工况,输入El Centro和Taft地震动,对比研究了阻尼器的减震控制效果。分析结果表明:(1)放大位移型SMA阻尼器的控制效果优于不放大位移型SMA阻尼器;(2)该放大位移型SMA阻尼器对位移的控制效果优于对加速度的控制效果。     

夏季风期间长江流域的水汽输送状态及其年际变化

本文利用NCEP/NCAR再分析资料,分析了长江流域夏季风期间的水汽收支和循环,着重研究了不同月份与水汽收支的年际变化显著相关的大尺度水汽输送和环流异常.流域范围的西南夏季风水汽输送以6、7月最为强烈,经向输送在5～8月造成流域水汽辐合,9月造成辐散;纬向输送在5～7月造成流域水汽辐散,8、9月造成辐合.研究表明,在不同月份,流域的南北边界处的水汽输送在流域水汽收支的年际变化中起着不同的作用.这种变化与大气环流的异常密切相关.在夏季风相对较弱月份（5、8、9月）,流域水汽收支的年际变化极大地受到流域南边界南风水汽输入通道的影响,对应于水汽收入偏丰年,该3个月500 hPa高空在青藏高原东部都存在显著异常低压区,而且,8、9月在中南半岛及其以东洋面存在显著异常反气旋环流,与8月西太副高的向西向南异常伸展,以及9月副高的西伸较弱和南北范围较宽有关,这些异常环流均造成南边界的大量异常水汽输入.而在夏季风十分强盛的6、7月,流域北边界南风水汽输出极大增加,成为流域水汽收入年际变化的关键敏感通道,对应于水汽收入偏丰年,6月500 hPa高空主要受中纬度以黄海和东海为中心的异常低压系统和气旋性异常环流影响,与该区域副高偏南、偏弱有关,而7月则主要受中高纬以外兴安岭为中心的异常高压和反气旋性异常环流影响,应该是由于该区域大陆高压的频繁生成造成的,它们均造成流域北边界水汽输出的异常减少.