裂隙岩体在单轴加载过程中变形、破裂规律的PFC2D数值模拟研究

运用离散元软件PFC2D模拟裂隙岩体,建立一个包含不同倾角、不同组数,宽度5cm、厚度1mm裂隙的10cm×10cm模型,分析单轴加载情况下岩体的变形、破裂规律。结果显示,在单轴加载情况下,随着倾角的增加,岩体的单轴抗压强度出现先减后增的趋势,且裂纹不断增多;随着裂隙的增多,单轴抗压强度逐渐减小。岩体的破裂区集中在裂隙的尖端点部位,以翼裂纹、次生共面裂纹和次生倾斜斜纹为主。通过分析破裂后岩体的颗粒速度分布,从微观层面发现岩体破坏的主要形式及破裂原因。     

疲劳损伤RC梁氯离子腐蚀后疲劳性能和氯离子扩散性试验研究

对于沿海地区具有疲劳损伤的在役钢筋混凝土(RC)桥梁结构,其在氯腐蚀后的疲劳性能和氯离子扩散性对于结构耐久性设计和评估至关重要。为此,通过试验研究15根不同初始疲劳损伤程度RC梁在氯腐蚀后的疲劳性能和混凝土中氯离子含量,试验参数包括荷载水平(疲劳荷载上限与静载极限荷载之比,取0.2~0.5)、初始疲劳加载次数(1×104~120×104)、氯腐蚀时间(90、180d)和受拉纵筋配筋率(1.06%、1.59%和2.91%)。试验结果表明：疲劳损伤RC梁在氯腐蚀后进行疲劳加载时,梁挠度和混凝土应变等呈现典型的三阶段变化特征;荷载水平、初始疲劳加载次数、氯腐蚀时间和受拉纵筋配筋率均对其剩余疲劳寿命影响显著,荷载水平(不小于0.4)、初始疲劳加载次数(第一疲劳阶段)和氯腐蚀时间的增加均引起剩余疲劳寿命迅速降低,当配筋率增加到42%界限配筋率时,寿命有所增加;受拉混凝土氯离子扩散性的增加与RC梁剩余疲劳寿命的降低相关联,而受压混凝土的扩散性随荷载水平、初始疲劳加载次数和配筋率的增加而增加。     

高层框架-核心筒及衍生结构体系主要抗侧组件分析

为更加深入和系统地了解高层建筑中应用最广的框架-核心筒结构,基于构件的受力特点,首次提出了抗侧组件的概念,指出核心筒、腹板框架和翼缘框架为该种结构体系的三个主要抗侧组件。基于6栋普通框架-核心筒结构及衍生结构体系的高层塔楼,计算了主要抗侧组件所承担的倾覆力矩比例来衡量其抗侧能力,详尽剖析了抗侧组件的工作原理。通过量化各抗侧组件的抗侧效能,使框架-核心筒结构的抗侧体系设计更加明晰。结果表明:在普通框架-核心筒、筒中筒、带环桁架的框架-核心筒结构中,核心筒为关键抗侧组件;单独带巨撑或伸臂的框架-核心筒结构中,关键抗侧组件分别是腹板框架和翼缘框架。     

WGC特征描述的人脸表情识别

针对韦伯局部特征(WLD)仅计算中心像素与周围像素差异提取特征的不足,提出了一种韦伯梯度编码(WGC)特征描述的人脸表情识别算法。首先计算当前像素点周围水平、垂直和对角位置上的数值差与当前像素点的差异构成WGC特征的差动激励;然后进一步提出基于水平和对角线优先原则的WGC_HD特征;最后利用最佳分块方式得到行分块WGC_HD特征,采用自动优化参数的SVM分类器完成人脸表情识别。在公共人脸表情库JAFFE和CK库上进行交叉实验,平均识别率及平均特征提取时间分别为95.49%、12.30 ms和97.63%、31.54 ms。行分块WGC_HD特征考虑了不同梯度方向的像素差异,较好描述了表情图像的局部结构信息且具有较低的时间复杂度,与目前典型的表情识别算法结果对比也验证了算法具有较高的识别精度。     

Robust Direct Power Control Schemes of DFIGs Driven by Variable-speed Wind Turbines

Despite its several advantages, a classic direct power control (DPC) technique of doubly fed induction generators (DFIGs) driven by variable-speed wind turbines has some drawbacks such as high power ripples and variable switching frequency. In this paper, two robust controllers are designed to improve the classical DPC performance without complicating the overall scheme. First, an integral sliding mode controller (ISMC) is designed to regulate the stator active and reactive powers. Two integral switching functions are selected for controlling stator active and reactive powers. The idea of total sliding mode controller is selected to avoid reaching phase stability problem. Second, a diagonal recurrent neural network (DRNN) controller is designed and trained based on DPC. The DRNN has several advantages compared to the classical static neural networks such as recurrence and simple construction. Simple off-line back-propagation algorithm is proposed to train the proposed DRNN. The stability of the proposed ISMC and DRNN controller is proved using the Lyapunov stability theorem. The grid side converter is controlled based on the DPC principle to ensure both constant DC-link voltage and grid side reactive power. The feasibility of the proposed DPC schemes is validated by simulation studies on a 1.5-MW wind power generation system. The performance of the proposed schemes is compared with a conventional DPC scheme under different operating conditions.     

Geometric Parameterization Technique for Continuation Power Flow Based on Quadratic Curve

The electricity sector, especially in emerging countries, has experienced several transformations, mainly resulting from the increase of electricity demand. This encourages more investment in the generation sector and causes increasing concerns with the development and improvement of tools for static voltage stability analysis of electrical power systems. This paper presents a new geometric parameterization technique for continuation power flow (CPF) that works based on the addition of a parabola that passes through three points in the plane formed by the variables of total real power losses and loading factor. This technique eliminates the Jacobian matrix singularity at the maximum loading point, which allows obtaining the solution trajectory (P–V curve) without any need to change the parameter, which is a very common procedure in the currently available CPFs. Intending to define a simple and efficient step size control procedure, the total real power losses values are normalized by its base case value. The results obtained by applying the proposed technique to the IEEE-300 bus system and two real large systems of 638 and 787 buses show its effectiveness.     

The impact of single-phase grid-connected distributed photovoltaic systems on the distribution network using P-Q and P-V models

The gradual emergence of photovoltaic (PV) systems as the most common distributed generation interconnected with the electric power system calls for a detailed power flow analysis with different models especially in the evolving unbalanced active distribution network. This paper is an extension of a previous study carried out on the performance evaluation of a 10 kWp grid-connected PV system deployed in a school, with the grid providing a virtual storage and access to upstream markets. For increased adoption of such systems in the unbalanced distribution network, it is pivotal to understand the mode of operation and the type of connection to the system. This article presents an impact analysis of such utility interactive single-phase PV systems distributed on all the single-phase load nodes of the traditional IEEE-13 bus distribution test feeder. The PV distributed generation (PV-DG) can be modelled as constant P-Q or P-V nodes with varied impacts in power flow studies for the unbalanced active distribution network. Results from these models are compared in terms of their impacts on voltage profiles at load buses, voltage unbalance, equipment loading, power losses and the total number of iterations for a converged power flow solution.     

徐深气田D区块气井积液诊断及水体规模

徐深气田D区块属于块状底水的火山岩气藏,准确识别气井出水、判断气井是否积液、计算水体规模成为急需解决的问题。通过理论计算与现场动态分析相结合,建立了一套适合D区块气井出水与积液诊断的方法。研究表明:气藏出地层水的水气比下限为0.2 m~3/10~4m~3,矿化度下限为8 000 mg/L,气井临界携液流量为(1.55～3.45)×10~4m~3/d,水体规模为(6.27～6.86)×10~8m~3;综合水气比和矿化度下限可以快速准确识别气井是否出水;气井是否积液,取决于油管直径、井筒温度和压力3种因素综合作用结果。在静态水体规模计算基础上,引入动态方法来验证,有利于减小静态法参数选取的不确定性,能够更准确计算水体规模大小。     

冲击载荷作用下压阻式微加速度计的动态力学响应研究

针对目前判断器件的可靠性实验中存在成本高、周期长的问题,对微型压阻式加速度计在冲击载荷作用下的动态力学响应特性进行研究,获得微加速度计在冲击载荷作用下的动态力学响应规律。以锥形头部弹体为例构建动力学模型,对典型的微加速度计和冲击载荷工况进行理论研究,分析压阻式微加速度计在冲击载荷作用下的动态力学响应特性。结果表明：压阻式微加速度计在冲击载荷下的响应由应力波的渡越时间、结构的本征振动周期及脉冲的持续时间这3个时间常数及其关系决定,可准确反应弹体所受冲击载荷的特性。     

高速板带轧机四列滚动轴承非均匀接触力学性能及修形优化研究

针对高速板带轧机四列滚子轴承在偏载运行下滚子-滚道非均匀接触力学性能及滚子修形优化进行研究。建立了滚子-滚道接触力学模型,模拟了其偏载运行下的接触力学性能。提出滚子接触应力均匀分布原则,采用非对称对数曲线对四列滚子母线修形优化。研究表明：偏载轧制导致四列滚子承载分布严重不均,以某冷轧机四列滚子轴承为例,载荷分布偏差较常规轧制增加20%,列间接触应力差接近200MPa,单列滚子轴线方向接触应力差接近60MPa。接触应力差随修形量k₃差值减小而减小,当k₃差值减小到一定程度时,接触应力差反而变大,最终修形曲线优化参数为k₁=1.3,k₂=1,k₃=0.014-0.011。研究为延长轴承使用寿命、保证轧机安全稳定运行提供理论依据,具有重要工程意义。