Experiment and analysis of a leverage‐type stiffness‐controllable isolation system for seismic engineering

Owing to the fixed design parameters in traditional isolation systems, the optimal isolation performance may not always be achieved when a structure is subjected to a nondesign earthquake. At the same time, even though an active isolation system (AIS) can offer a better reduction for different seismic waves, in practice the control energy required still constrains its application. To solve this problem, a novel semi‐active isolation system called the Leverage‐type Stiffness Controllable Isolation System (LSCIS) is proposed in this paper. By utilizing a simple leverage mechanism, the isolation stiffness and the isolation period of the LSCIS can be easily controlled by adjusting the position of the pivot point of the leverage arm. The theoretical basis and the control law for the proposed system were first explained in this work, and then a shaking table test was conducted to verify the theory and the feasibility of the LSCIS. As shown in the experiment, the seismic behavior of the LSCIS can be successfully simulated by the theoretical model, and the isolation stiffness can be properly adjusted to reduce the seismic energy input in the LSCIS system. A comparison of the LSCIS with the other systems including passive isolation and AISs has demonstrated that based on the same limitation of base displacement, better acceleration reduction can be achieved by the LSCIS than by any of the other isolation systems. In addition, the control energy required by the LSCIS is lower than that for an AIS using the traditional LQR control algorithm. Copyright © 2010 John Wiley & Sons, Ltd.     

变径洞室超前支护开挖模拟与分析

变径洞室开挖稳定性是地下工程重要的研究课题之一。尤其在围岩软弱的情况下,从小截面向大截面洞室开挖的过程中,会给施工带来很多安全方面的难题。通过有限差分数值分析方法研究了变径洞室的开挖稳定性,分析了拱部小导管超前注浆支护与非超前支护两种施工方法对工程的影响。计算结果表明,由小截面向大截面洞室开挖,不稳定性因素增加,超前小导管注浆支护能够显著提高围岩的稳定性,明显减少了洞室的变形和塑性区,避免了软弱围岩开挖中塌方现象的产生。研究成果对洞室施工具有指导意义。     

基于内变量和张量函数表示定理的本构方程

针对各向同性材料,基于张量函数表示定理,建立了本构关系的张量不变性表示,其中,3个不可约基张量取决于应力的0～2次幂,且相互正交,3个系数由塑性应变增量和应力的不变量表示。基于塑性应变增量的不变量定义内变量,本构关系归结为确定内变量的演化。使用张量函数表示定理,给出了内变量演化方程的一般表达式,它取决于应力不变量的增量,因而与主轴旋转无关。讨论了如何根据试验资料和引入适当的假定,确定具体的演化方程。通过与塑性势理论和多重屈服面理论进行比较,表明所建模型是这些理论的最一般表示,且简捷直观、使用方便。     

基于区域化变量及RMR评价体系的金川III矿区矿岩质量评价

岩体质量的全面评价是自然崩落法矿山可行性研究和初步设计的重要前提和依据。RMR体系是通常采用的综合性评价方法,以钻孔或坑道的局部RMR评价值来表征整个区域的岩体质量具有片面性。因此,以金川III矿区1554水平以上的岩体质量调查数据为样品,首先对其空间结构性及变异性进行了分析,得出调查区RMR参数指标具有区域化变量特征的结论;其次,建立了评价范围内各类工程和岩性区段的三维表面模型,并对该模型用长方体单元进行了离散;然后,借助区域化变量最优无偏估值方法,对各离散单元块的RMR参数指标进行推估,建立了反映全局变化的矿岩质量三维可视化RMR评价模型;最后以RMR评价模型为基础,根据Laubscher崩落图对矿岩初始和持续崩落的水力半径进行了计算。结果表明：III矿区的RMR均值为39.8,矿岩可崩性属较好到很好。预测金川III矿区平均持续崩落水力半径为20.4 m。     

变精度粗糙集下的GIS面目标拓扑关系扩展研究

空间拓扑关系一直是GIS研究热点。本文在分析了GIS面目标拓扑关系的基础上,引入粗糙集概念。在Pawlak粗糙集中,把RCC模型中面目标看成粗糙集中的等价类划分,不考虑边界的模糊性和边界,RCC模型的关系表达模型不变。而在变精度粗糙集中,由于引入多数包含β因子,除PO(X,Y)和POI(X,Y)外,RCC模型其他关系表达模型也不会变化,并且这些关系属于β=0的特例。在PO(X,Y)模型中由于两个面目标存在公共相交部分,及X∩Y≠φ。因此,当C(X,Y)≤β,即X与Y中的公共元素的数目,大于X中元素数目的50%时,显然可以得到Y⊇^βX。因此,在变精度粗糙集中,我们认为两个面目标PO(X,Y)有两种集合表达形式Y⊇^βX和Y⊄^βX,并由此作出了POI(X,Y)和PO(X,Y)在变精度粗糙集下的面目标相交拓扑关系拓展图。     

Convection of a fluid with strongly temperature and pressure dependent viscosity

Plate tectonics on the Earth is a surface manifestation of convection within the Earth’s mantle, a subject which is as yet improperly understood, and it has motivated the study of various forms of buoyancy-driven thermal convection. The early success of the high Rayleigh number constant viscosity theory was later tempered by the absence of plate motion when the viscosity is more realistically strongly temperature dependent, and the process of subduction represents a continuing principal conundrum in the application of convection theory to the Earth. A similar problem appears to arise if the equally strong pressure dependence of viscosity is considered, since the classical isothermal core convection theory would then imply a strongly variable viscosity in the convective core, which is inconsistent with results from post-glacial rebound studies. In this paper we address the problem of determining the asymptotic structure of high Rayleigh number convection when the viscosity is strongly temperature and pressure dependent, i.e. thermobaroviscous. By a method akin to lid-stripping, we are able to extend numerical computations to extremely high viscosity contrasts, and we show that the convective cells take the form of narrow, vertically-oriented fingers. We are then able to determine the asymptotic structure of the solution, and it agrees well with the numerical results. Beneath a stagnant lid, there is a vigorous convection in the upper part of the cell, and a more sluggish, higher viscosity flow in the lower part of the cell. We then offer some comments on the possible meaning and interpretation of these results for planetary mantle convection.     

A review on evapotranspiration data assimilation based on hydrological models

Accurate estimation of evapotranspiration (ET), especially at the regional scale, is an extensively investigated topic in the field of water science. The ability to obtain a continuous time series of highly precise ET values is necessary for improving our knowledge of fundamental hydrological processes and for addressing various problems regarding the use of water. This objective can be achieved by means of ET data assimilation based on hydrological modeling. In this paper, a comprehensive review of ET data assimilation based on hydrological modeling is provided. The difficulties and bottlenecks of using ET, being a non-state variable, to construct data assimilation relationships are elaborated upon, with a discussion and analysis of the feasibility of assimilating ET into various hydrological models. Based on this, a new easy-to-operate ET assimilation scheme that includes a water circulation physical mechanism is proposed. The scheme was developed with an improved data assimilation system that uses a distributed time-variant gain model (DTVGM), and the ET-soil humidity nonlinear time response relationship of this model. Moreover, the ET mechanism in the DTVGM was improved to perfect the ET data assimilation system. The new scheme may provide the best spatial and temporal characteristics for hydrological states, and may be referenced for accurate estimation of regional evapotranspiration.     

改进的最优非负变权组合模型及其应用

根据GM(1,1) 、BP神经网络、卡尔曼滤波的特点,建立以灰色关联度最大为准则的最优非负变权组合预测模型,在一定程度上抑制了误差“放大”的效应。与以误差平方和最小为准则的变权组合模型、各最优加权组合模型、各单一模型进行对比分析,结果表明,本文模型预测精度最高。     

Protection of seismic structures using semi‐active friction TMD

Although the design and applications of linear tuned mass damper (TMD) systems are well developed, nonlinear TMD systems are still in the developing stage. Energy dissipation via friction mechanisms is an effective means for mitigating the vibration of seismic structures. A friction‐type TMD, i.e. a nonlinear TMD, has the advantages of energy dissipation via a friction mechanism without requiring additional damping devices. However, a passive‐friction TMD (PF‐TMD) has such disadvantages as a fixed and pre‐determined slip load and may lose its tuning and energy dissipation abilities when it is in the stick state. A novel semi‐active‐friction TMD (SAF‐TMD) is used to overcome these disadvantages. The proposed SAF‐TMD has the following features. (1) The frictional force of the SAF‐TMD can be regulated in accordance with system responses. (2) The frictional force can be amplified via a braking mechanism. (3) A large TMD stroke can be utilized to enhance control performance. A non‐sticking friction control law, which can keep the SAF‐TMD activated throughout an earthquake with an arbitrary intensity, was applied. The performance of the PF‐TMD and SAF‐TMD systems in protecting seismic structures was investigated numerically. The results demonstrate that the SAF‐TMD performs better than the PF‐TMD and can prevent a residual stroke that may occur in a PF‐TMD system. Copyright © 2009 John Wiley & Sons, Ltd.     

Theoretical and experimental research on a new system of semi-active structural control with variable stiffness and damping

In this paper, a new system of semi active structural control with active variable stiffness and damping (AVSD) is suggested. This new system amplifies the structural displacement to dissipate more energy, and in turn, effectively reduces the structural response in the case of relatively small story drifts, which occur during earthquakes. A predictive instantaneous optimal control algorithm is established for a SDOF structure equipped with an AVSD system Comparative shaking table tests of a 1/4 scale single story structural model with a full scale control device have been conducted. From the experimental and analytical results, it is shown that when compared to structures without control or with the active variable stiffness control alone, the suggested system exhibits higher efficiency in controlling the structural response, requires less energy input, operates with higher reliability, and can be manufactured at a lower cost and used in a wider range of engineering applications.