SEISMIC IMPACT LOADING IN INELASTIC TENSION-ONLY CONCENTRICALLY BRACED STEEL FRAMES: MYTH OR REALITY?

Tension-Only Concentrically Braced Frames (TOCBF) exhibit deteriorating pinched hysteretic behaviour during strong earthquakes. Slender braces transit between an elastic buckling state, a restraightening state, in which they carry almost no load, an elastic tensile loading state as they are suddenly taut and, finally, a tensile yielding state. It has long been suspected that the sudden increase in tensile forces in the braces of TOCBSF creates detrimental impact loading on the connections and other structural elements. No experimental evidence, however, has been provided so far to confirm, or to quantify, this impact phenomenon. This paper addresses this issue through shake table tests of half scale, two-storey, TOCBF models. By normalizing the hysteresis loops of braces obtained from shake table tests to the yield strength of steel obtained from quasi-static tests, the increase in tensile forces in the braces was obtained. Results of dynamic tensile tests on steel coupons under similar strain rates as observed during the shake table tests showed that this increase in tensile forces is not the result of impact, but is rather caused by a yield strength increase of the steel under high strain rate. A procedure is proposed to estimate and account for this increase in tensile forces in the braces at the design stage.     

一种新的守时型原子钟综合时间尺度方法研究

在这篇文章中, 提出了一种基于改进的指数平滑和Vondrak_Cepek联合平滑的氢铯综合时间尺度产生方法. 以最小误差方法为理论基础, 动态估计氢原子钟频率漂移参数, 提升氢原子钟钟差预测准确度; 基于改进的二次指数平滑产生氢原子钟组时间尺度、加权平均方法产生铯原子钟时间尺度, 同时设计Vondrak_Cepek滤波器以结合两类时间尺度长短期稳定度优势, 提升综合时间尺度性能. 实验结果表明, 所提方法产生的氢铯综合时间尺度时稳可达1.60x10^-15,天稳可达3x10^-15,优于ALGOS、AT1和Kalman滤波3种经典方法产生的时间 尺度性能.     

随钻测量、随钻测井与录井工具

摆动阀泥浆脉冲器本身可以产生较高频率的载波,成为高速泥浆脉冲传输的较好选择。由于工作时负载力矩复杂,影响因素众多,为电机输出特性研究带来较大困难。利用在井下工作时的动力学平衡方程,通过水循环实验方式测量得到摆动阀电机在最大转矩比电流控制方式下的位置角度和输出电流数据,进而计算井下工作时电机输出转矩和输出功率,并对其影响因素进行综合分析。结果表明,受惯性转矩、弹性转矩和动态水力转矩的影响,电机输出转矩在不同工作频段表现为不同特征;低频段时,电机输出转矩的变化幅度随载波频率的增大而减小,输出功率随载波频率的增大而缓慢增大;中低频段时,电机输出转矩和输出功率在该频段幅度变化较小,相对比较稳定;高频段时,电机输出转矩和输出功率均随频率的增大而快速增大。可以通过增大扭杆刚度系数和降低摆动阀转子轴系转动惯量的方式降低电机在高频段的输出,以保证电机在额定转矩和额定功率下可以控制摆动阀在井下实现高频快速的摆动,产生稳定高载波频率下的泥浆脉冲压力波形,实现高频载波的目的,为随钻测井数据的高速传输提供了保障。

     

有限元强度折减法在边坡稳定性分析中的有效性及结果检验方法

有限元强度折减法的有效性及结果评价决定该方法是否能在工程上得到认可及推广的关键。本文基于有理论解的地基承载力问题和澳大利亚计算机应用协会（ACADS）边坡稳定性典型考题,通过计算值与理论解的对比以及塑性贯通区结果,对有限元强度折减法用于边坡稳定分析的有效性、失稳判据以及结果评价等问题进行了系统研究,提出了以塑性带宽度与长度之比检验计算结果的方法。结果发现,在足够且合理的网格密度下,有限元强度折减法分析边坡稳定性是有效的,不同类型的临界状态判据差异不大,而塑性区贯通判据最为客观;临界状态时塑性带的宽度与长度之比与安全系数的计算精度有很高的相关性,其值越小,精度越高,当塑性区相对宽度b/L小于0.05时,安全系数相对误差一般小于5%;对于强度折减法计算结果的精度评价,只要所得的等效塑性应变分布能确定滑动机制和大致的滑动面位置,其安全系数计算结果与更细密的网格的结果差异一般也在5%以内,精度就是足够的。     

A new theoretical solution of the effect of atmospheric pressure on water level

Based on the partial differential equation governing the effect of atmospheric pressure on water level of confined well, deriving the boundary condition and considering the seepage water between well and aquifer, the author obtained the analytical solution of water level change in time domain under the action of an atmospheric pressure history with the Laplace transform method. This solution is composed of two terms:stable and retarded terms. The stable term is the multiplication of barometric efficiency and simultaneous atmospheric pressure, and it implies the value of water level after infinite time when the atmospheric pressure is a constant from the time in question. The retarded term is the transient process due to the time lag of water exchange between well and aquifer. From the solution, it is obtained that the interference of atmospheric pressure on water level is the integral superimposition of the contribution of all atmospheric pressure changes before the time in question. So that, we further found out the response function of pulsive atmospheric pressure history. Calculation shows: (1) The pulsive response function starts from zero and tends to a steady value, which is proportional to the barometric efficiency, when the time tends to infinity; (2) The retarded time depends on the mechanical property of aquifer and the radius of well. The larger the seepage coefficient, the smaller the radius of well and the thicker the aquifer, then the shorter the retarded time gets. This solution can be used as the theoretical basis for further analysis of the atmospheric effect and practical correcting method in the future.     

多维动态GIS在海岛保护与利用管理中的应用

针对海岛空间信息的特点,分析了传统管理手段的缺陷,提出了利用多维动态GIS技术解决海岛及其周边海域三维特性和数据多源、多尺度、多时相以及海岛的历史变迁问题,并探讨了应用的关键技术,为海岛综合管理提供一个新的解决方案,提高了海岛管理的可视化、信息化、高效化和科学化.     

Approaches to analyse and model changes in impacts: reply to discussions of “How to improve attribution of changes in drought and flood impacts”*

ABSTRACT

We thank the authors, Brunella Bonaccorso and Karsten Arnbjerg-Nielsen for their constructive contributions to the discussion about the attribution of changes in drought and flood impacts. We appreciate that they support our opinion, but in particular their additional new ideas on how to better understand changes in impacts. It is great that they challenge us to think a step further on how to foster the collection of long time series of data and how to use these to model and project changes. Here, we elaborate on the possibility to collect time series of data on hazard, exposure, vulnerability and impacts and how these could be used to improve e.g. socio-hydrological models for the development of future risk scenarios.     

论环境流场切应变率对台风移动的作用

利用浅水波正压环境流场切应变率对台风移动的影响，得到的结果是：在环境流场切应变率空间不均匀条件下，正切应变率引起的台风偏差路径比负切应变率引起的偏差路径要长，特别在正切应变率的区域，正切应变率要比相对涡度梯度对台风移动有更大的影响。