GA-fuzzy control of smart base isolated benchmark building using supervisory control technique

The effectiveness of a supervisory fuzzy control technique for reduction of seismic response of a smart base isolation system is investigated in this study. To this end, a first generation, base isolated, benchmark building is employed for numerical simulation. The benchmark structure under consideration has eight stories and an irregular plan. Furthermore it is equipped with low damping elastomeric bearings and magnetorheological (MR) dampers for seismic protection. The proposed control technique employs a hierarchical structure of fuzzy logic controllers (FLC) consisting of two lower-level controllers (sub-FLC) and a higher-level supervisory controller. One sub-FLC has been optimized for near-fault earthquakes and the other sub-FLC is well-suited for far-fault earthquakes. These sub-FLCs are optimized by use of a multi-objective genetic algorithm. Four objectives, i.e. reduction of peak superstructure acceleration, peak isolation system deformation, RMS superstructure acceleration and RMS isolation system deformation are used in a multi-objective optimization process. When an earthquake is applied to the benchmark building, each of the sub-FLCs provides different command voltages for the semi-active controllers and the supervisory fuzzy controller appropriately combines the two command voltages based on a fuzzy inference system in real time. Results from numerical simulations demonstrate that isolation system deformation as well as superstructure responses can be effectively reduced using the proposed supervisory fuzzy control technique in comparison with a sample clipped optimal controller.     

Fairness of traffic controls for inelastic flows in the Internet

In best-effort networks, fairness has been used as a criterion to guide the design of traffic controls. The notion of fairness has evolved over time, from simple equality to a form of equality modulated by the user’s need (e.g. max–min and proportional fairness). However, fairness has always been defined on a per-user basis for a deterministic workload. In this paper, we argue that we must redefine the notion of fairness when we study traffic controls for the co-existence of elastic and inelastic traffics. Our results indicate that subjecting inelastic flows to fairness congestion control on a per-flow basis does not necessarily maximize the network’s utility. Instead, inelastic flows may follow their own form of traffic control, such as admission control (without congestion control). At the aggregate level, our results indicate that it still makes sense to maintain a balance between elastic and inelastic traffic. In order to support our arguments, we develop a methodology for comparing different traffic controls for given utility functions and different workloads, both deterministic and stochastic.     

基于紧支径向基函数的局部径向点插值方法

文章对紧支径向基函数进行完备性修正,利用完备性修正的紧支径向基函数,并结合局部残差的思想,建立了局部径向点插值方法.由于该方法中的插值函数满足Delta函数性质,因此本质边界条件可以像传统的有限元方法一样容易施加,在计算过程中不需要积分网格,是一种"纯无网格方法".将该方法用于二维弹性静力问题的求解,导出其相应的离散方程.数值算例初步验证了该方法的有效性与合理性.     

结构性对软土压缩特性的影响

针对同一地段的50个原状土样的试验数据进行统计分析,得出孔隙比、含水量、密度、干密度是影响软土压缩特性的重要因素。通过原状土和重塑土一维固结压缩试验,对固结系数、压缩系数、压缩模量进行分析,得出结构性对软土压缩特性有较大的影响。同时给出了压缩特性的微观行为。     

冻融疲劳作用下LHFRC损伤演变规律

为了研究层布式混杂纤维混凝土（LHFRC）在冻融疲劳作用下的损伤演变规律，提出了混凝土抗冻劣化的损伤演变数学模型，同时进行了普通混凝土（OC）与层布式混杂纤维混凝土的冻融试验，并在试验的基础上，回归出它们的冻融损伤演变方程。结果表明，LHFRC和OC的初劣点值相同，且在劣化初始阶段具体相同的损伤演变方程；在劣化扩展阶段，LHFRC和OC均具有幂函数形式的损伤演变方程，但LHFRF损伤变量小于同期的OC，钢纤维和聚丙烯纤维有效地抑制了其内部损伤发展。     

基于变形控制的逆作法超大深基坑的数值模拟

基于变形控制和环境安全的要求，对天津某项目超大深基坑进行了施工过程的数值模拟。考虑地下室施工采用楼板作为内支撑的楼板逆作工法以及基坑围护结构应力应变的复杂性，采用通用有限元程序ANSYS建立了三维空间模型进行计算。试算得到安全可靠的深基坑设计方案，并对方案控制工况施工状态基坑围护结构以及水平楼板的内力和变形进行了分析，同时还对楼面板作用进行了分析。     

反映物态变化的砂土状态参数本构模型

基于状态参数Ψ、峰值应力比、相态转换应力比、依赖于状态的剪胀方程和一个双曲线的应力应变关系,建立了一个静力条件下能统一反映密度和压力对砂土变形特性影响的本构模型。该模型具有8个材料参数,都能从常规三轴试验中确定,模型能很好的模拟不同密度和不同固结压力下砂土的这些变形特性,通过数值试验初步验证了模型的合理性。     

Matsuoka-Nakai破坏准则的拓展应用

Matsuoka-Nakai破坏准则有两个缺点：一是没有考虑岩土类材料的内聚力对材料的强度贡献,二是它与子午面的交线是直线,基于此,提出了一个拓展的Matsuoka-Nakai破坏准则.该准则在保持Matsuoka-Nakai破坏准则优点的基础上,考虑了岩土类材料的内聚力对其破坏强度的影响,且在子午面上呈现为外凸的曲线形状,因而能更合理地模拟岩土类材料的强度特性.红砂岩的真三轴试验资料检测了该拓展的Matsuoka-Nakai破坏准则的有效性.最后借助该拓展的破坏准则,通过寻求试验强度与预测强度之间的误差函数最小值的方法,提出了一个评估试验中难以测准的岩土类材料抗拉强度的计算方法.     

屈曲约束支撑滞回性能的影响因素

为检验不同连接方式及构造方式对屈曲约束支撑滞回性能的影响，设计了螺栓连接和铰接2种连接方式，“十”字形、“T”形及“一”字形3种芯材截面形式，端部焊接型及中部切削型2种芯材制作方式，沿芯材纵向全长焊接及仅在工作段焊接2种组合方式共7个屈曲约束支撑试件。通过拟静力加载试验，分析了屈曲约束支撑的承载力、割线刚度、耗能系数及延性等变化规律。结果表明：7个试件的滞回曲线饱满稳定、耗能能力强；承载力、耗能系数及延性均随加载位移的增大而增大，割线刚度随加载位移的增大而降低，恢复力模型具有典型的双线性特征；连接方式及构造特性对屈曲约束支撑的滞回性能不产生明显影响，芯材材料性能、宽厚比、间隙与芯材厚度的比值是影响其滞回性能的主要因素。结果表明，两角钢具有协同的工作性能；提高焊接质量、增大限位卡附近过渡圆弧的曲率半径分别是增强两种类型屈曲约束支撑稳定滞回的主要工艺及构造措施。     

超声波振动仪器在采用沉降法进行粘性泥沙粒径分析中的应用

本文提出在粘性泥沙粒径颗粒分析中使用超声波振动仪器进行细颗粒泥沙分散的方法,使用基于沉降法原理的TZC-4粒度分析仪,采用三种不同的颗粒粒径测量工艺分别对乐清湾港区、阳澄湖、奉贤边滩、上海闵行河道四种不同的泥样进行了颗粒粒径分析,并与现有规范规定的测量工艺所得结果进行了对比。实验分析表明,该方法能够有效地测量泥沙的基本粒径,泥沙颗粒越细,该方法的优越性越为突出。