Uplift‐restraining Friction Pendulum seismic isolation system

This paper extends the scope of seismic isolation by introducing an innovative uplift‐restraining Friction Pendulum system. Termed the XY‐FP isolator, the new isolation device consists of two orthogonal opposing concave beams interconnected through a sliding mechanism that permits tension to develop in the bearing, thereby preventing uplift. Owing to its distinct configuration, the XY‐FP isolator possesses unique properties for a seismic isolator, including uplift restraint, decoupling of the bi‐directional motion along two orthogonal directions, and capability of providing independent stiffness and energy dissipation along the principal horizontal directions of the bearing. The study concentrates on introducing the concept and establishing the underlying principles of operation of the new XY‐FP isolator, formulating the mathematical model for the XY‐FP isolator, and presenting its mechanical behaviour through a displacement‐control testing program on a single XY‐FP isolator. Copyright © 2005 John Wiley & Sons, Ltd.     

改进型焦利氏秤与传统实验对比研究

针对高校教材《普通物理实验》中液体表面张力系数的测定实验存在的一些问题,进行了认真分析,指出传统实验前后所测量的一些物理量不是等精度测量,因而有必要对实验原理和公式进行修正。改进型焦利氏秤,在载物台下装有测量机构,实验测量方法有所改变,实验思路更加明确,并经实验比对,使用改进型焦利氏秤做此实验,不仅操作和计算简便,而且所得结果更接近公论值,取得了良好的效果。     

Relationships between volcanic patterns and neotectonics in Eastern Anatolia from analysis of satellite images and DEM

The late Neogene to Quaternary volcanism in Eastern Anatolia is related to the Arabia–Eurasia convergence but a clear deformation pattern has not yet been established in this region. We have used the distribution and shape of volcanoes and fault geometry as indicators of the tectonic regime. Volcanic edifices and related faults were analyzed in vertical view using SAR–ERS, Spot images and a Digital Elevation Model (DEM). In several places, adjacent volcanoes that form linear clusters or elongated volcanoes are clearly rooted on vertical tension fractures. These are compatible with horizontal σ₃ striking 90°N, associated with σ₁ horizontal (strike-slip regime) or vertical (extensional regime). We mapped the recent faults that are directly associated to volcanoes. Volcanic vents are related to tail-crack, horsetail or releasing bend structures. In this work, it has been possible to define the ESE-striking, 270-km-long Tutak–Hamur–Çaldiran fault that forms a releasing bend testifying to right-lateral motion. Extension is well documented for few places but no recent fold has been observed. Since 8 Ma, the tectonic system is principally strike-slip. Most of the tension fractures being 2 to 10 km in length, so we infer that they affect only part of the crust. Most strike-slip fault zones are of several tens to a few hundred kilometers long and thus not of lithospheric scale. Therefore, the channels used by the magma to reach the surface are crustal structures.     

基于环境振动的斜拉桥拉索基频识别

斜拉索是现代斜拉桥最重要的结构构件，索力在斜拉桥的施工控制和长期监测中起着重要作用。振动测试法是斜拉桥索力测定、监测和状态评估中应用最广泛的一种方法。振动法测索力的关键在于准确地识别出索的基频。本文使用自功率谱和倒频谱方法，基于MATLAB平台，开发出了斜拉桥拉索环境振动模态分析图形用户交互(GUI)工具箱，实现了斜拉索基频的快速自动识别。应用本文的方法，对福州青洲闽江主跨605m斜拉桥拉索的环境振动实测加速度数据进行了分析处理，斜拉索基频识别方便直观，结果可靠。     

Surface tension and friction coefficients in shallow,laminar overland flows through organic litter

This study investigates the contribution of surface tension forces to friction coefficients in shallow, laminar interrill flows. Friction coefficients in these flows are known to be increased greatly by organic litter and by stems. Fine litter provides extensive edges along which surface tension menisci can be drawn up, and evaluating the significance of this in the frictional retardation of flow was the primary objective of the experiments reported here. Using both standardized ‘litter particles’ (small wooden blocks of fixed dimensions) and natural plant litter, meniscus behaviour and the Darcy–Weisbach friction coefficient were evaluated in shallow flows on a laboratory sand board. For some tests, the surface tension of ordinary water was reduced by 40 per cent by the addition of a surfactant, and the friction coefficient redetermined. Results show that the presence of surface tension menisci flanking litter particles provides areas of deeper flow that are up to 7 mm in width and which can increase flow depths by 100–300 per cent. These zones support significantly higher flow speeds. Increased water depths within menisci are additionally associated with reduced depths beyond the menisci, so that an increase in the spatial variability of flow depths is a second consequence of meniscus formation. These modifications of flow depth by surface tension menisci are shown to reduce rather than increase the overall friction coefficient applicable to the flow. Consequently, additional frictional retardation does not arise within the menisci flanking litter particles and so cannot account for the greater drag arising from litter than from other surface features. Different factors, possibly the direct obstruction of flow paths, must therefore underlie the frictional drag. Copyright © 2002 John Wiley & Sons, Ltd.     

连续曲率张力样条方法参数选取

连续曲率张力样条方法在最小曲率格网化方程中引入张力参数,可以消除最小曲率拟合曲面在已知数据点之间的区域存在的较大波动和无关变形点,张力参数的取值在区间[0,1)。针对海面高数据,研究了张力参数取不同值的结果,得到了张力参数的最佳取值范围。     

An inverse problem methodology for multiple parameter estimation in bend stiffeners

The flexible riser top connection is a critical region for lifetime assessment due to large tension/curvature variations and modeling uncertainties. The bend stiffener polyurethane mechanical response not only presents a nonlinear loading rate and temperature dependency but is also subjected to weather ageing during operation, which may affect its mechanical behavior over time. The top tension, employed for riser local cross-section stress calculation, is usually obtained from global dynamic analyses performed under selected environmental conditions, if direct measurement is not available. As a consequence, both the bend stiffener effect on the curvature distribution and the top tension time series present inherent uncertainties for riser lifetime (re)assessment. In the present work, a proposed monitoring approach composed by gyrometers installed along flexible riser/bend stiffener top connection system length combined with an inverse problem methodology is numerically investigated to estimate the following parameters: (i) polyurethane hyperelastic response and (ii) effective top tension. The top connection system is modeled using a large deflection beam bending model and the parameters are estimated using a damped least-square minimization approach with the Levenberg–Marquardt algorithm. For the preliminary feasibility investigation, the gyrometer experimental data is numerically estimated through Monte Carlo simulations. A case study is carried out to investigate the influence that the number of sensors, sensors arrangement, loading conditions and top connection model have on the inverse parameters estimation. The results indicate that the proposed monitoring approach and inverse parameter estimation methodology may effectively reduce flexible riser lifetime calculation uncertainties.     

无筋砌体农居地震弹塑性有限元研究

利用ABAQUS软件对既有的砌体墙试验结果进行了数值模拟,验证了模型的正确性以及混凝土损伤塑性模型对模拟砌体结构受力性能的可用性。在此基础上,借助实地调查获得的结构参数和材料性能数据,以重庆典型农居建筑为例,建立了无筋砌体农居的三维有限元模型,对数值模型进行了动力特性分析和不同烈度下多遇及罕遇地震的动力弹塑性时程分析,并建议了无筋砌体结构农居在不同地震烈度破坏下墙体表面积受拉损伤率的临界值。最后,利用既有文献提出的层间位移角限值,分析了该农居的破坏程度,比较了墙体表面积受拉损伤率和层间位移角限值衡量砌体结构的破坏程度。分析结果表明:提出的墙体表面积受拉损伤率和层间位移角限值衡量砌体结构破坏程度吻合良好;当墙体表面积受拉损伤率小于1%时,结构轻微破坏;当位于1%~5%时,发生中等程度破坏;当位于5%~30%时,发生严重破坏;当大于30%时,结构倒塌。     

The stability of tension stars

By studying the cylindrically symmetric solution for matter in 2+1 space-time dimensions we arrive at stability criteria for such a configuration when the local energy density is proportional to the square of the tension (negative pressure). Our analysis demonstrates that to the post-Newtonian approximation that such a configuration is stable provided it does not shrink below a certain radius. We find our model provides a reason for how stars form from a two-dimensional configuration with both a maximum mass and a minimum radius.