Microforms in Gravel Bed Rivers: Formation, Disintegration, and Effects on Bedload Transport

This research aims to advance current knowledge on cluster formation and evolution by tackling some of the aspects associated with cluster microtopography and the effects of clusters on bedload transport. The specific objectives of the study are (1) to identify the bed shear stress range in which clusters form and disintegrate, (2) to quantitatively describe the spacing characteristics and orientation of clusters with respect to flow characteristics, (3) to quantify the effects clusters have on the mean bedload rate, and (4) to assess the effects of clusters on the pulsating nature of bedload. In order to meet the objectives of this study, two main experimental scenarios, namely, Test Series A and B (20 experiments overall) are considered in a laboratory flume under well-controlled conditions. Series A tests are performed to address objectives (1) and (2) while Series B is designed to meet objectives (3) and (4). Results show that cluster microforms develop in uniform sediment at 1.25 to 2 times the Shields parameter of an individual particle and start disintegrating at about 2.25 times the Shields parameter. It is found that during an unsteady flow event, effects of clusters on bedload transport rate can be classified in three different phases: a sink phase where clusters absorb incoming sediment, a neutral phase where clusters do not affect bedload, and a source phase where clusters release particles. Clusters also increase the magnitude of the fluctuations in bedload transport rate, showing that clusters amplify the unsteady nature of bedload transport. A fourth-order autoregressive, autoregressive integrated moving average model is employed to describe the time series of bedload and provide a predictive formula for predicting bedload at different periods. Finally, a change-point analysis enhanced with a binary segmentation procedure is performed to identify the abrupt changes in the bedload statistic characteristics due to the effects of clusters and detect the different phases in bedload time series using probability theory. The analysis verifies the experimental findings that three phases are detected in the bedload rate time series structure, namely, sink, neutral, and source.     

ТДГ3．15万kVA主变压器经济运行分析

根据电力变压器功率损耗的分析，找到ТДГ3．15万kVA2台主变压器的功率损耗与负荷率β的函数关系，并对该2台主变压器的经济运行进行了探讨，计算出了经济运行点。     

Repair of notched beam under dynamic load using piezoelectric patch

In this paper, the repair of a cracked beam under an external dynamic load employing the electro-mechanical characteristic of piezoelectric material to induce a local moment is presented. Conceptually, an external voltage is applied to actuate a piezoelectric patch bonded on the beam to effect closure of a crack so that the singularity at the crack tip under dynamic load may be decreased. Globally, this has the effect of altering the resonant frequency of the cracked beam towards that of the healthy beam, which is the criterion used for the repair. To demonstrate the repair methodology, a cantilever beam is used as an illustration, where the repair moment coefficient and the voltage required are mathematically derived. The relationship between repair moment coefficient, crack parameters and length of piezoelectric patch is investigated. The difference between the proposed repair criterion and an earlier published criterion for cracked beam under static load is also shown. A numerical example is used to study the effectiveness of the proposed repair methodology and its results are compared with those from 3-D finite element analyses using ABAQUS 6.4 as one means of verification.     

钻孔嵌岩灌注桩承载特性试验研究

钻孔嵌岩灌注桩已成为高层建筑较常用的基础形式之一．在南昌地区某工程中，通过对钻孔灌注桩进行静载试验，分析研究了钻孔嵌岩灌注桩的承载特性和荷载传递机理，对此类桩的侧摩阻力与端阻力的问题进行了探讨。     

不同轮压分布形式对半刚性路面结构力学响应的有限元分析

针对轮胎接地形状的不规则性和轮压分布的不均匀性,运用三维有限元方法分析了轮压在圆形均匀分布、矩形均匀分布和矩形非均匀分布3种轮载作用形式下半刚性路面结构的力学响应.计算表明,轮压作用于路面的形状和非均匀性均对沥青路面的力学响应有显著的影响,尤其是超载时,圆形均布假设和矩形均布假设均不能正确反应半刚性结构层内部的剪切指标,只有矩形非均布假设能够很好地反应.研究提出,欠载及标准轴载时,可以采用圆形均布假设进行路面结构力学响应的分析;超载时,鉴于剪切指标对轮压非均匀性分布的敏感性,建议采用矩形非均匀分布荷载形式进行路面结构力学响应的分析及模拟仿真.     

k-ary n-cube网络中跨区域适应性路由算法

针对k-ary,n-cube网络,提出一种无死锁、元活锁、负载均衡的跨区域路由算法(Quadrant Crossing Routing,QCR).算法按照分组源目的节点相对位置将网络划分路由区域,并给予这些区域不同的权重,同时设定跨区域规则,允许分组根据网络负载状态跨区域路由,这样就使得网络的流量分布更均衡.网络的负载程度由输出端口等待分组请求的时间间隔的大小决定.最后,利用OPNET对所提算法在不同流量模式下进行仿真.结果表明:相比已有的同类算法,如维序路由算法(Dimension Order Routing,DOR),Duato及GAL等,QCR表现出较好的时延、吞吐性能.     

WEB应用系统性能测试的实现

对WEB应用系统进行合理的性能测试是保证系统质量的一个重要过程。以某远程教学系统为案例,借助于测试工具Load Runner,从负载反应层面对系统性能进行验证,并对测试结果进行分析,以保证系统的合理优化。     

网络等值与互联电网潮流分析

基于互联电网解合环潮流分析的现实需求。开发了一个应用软件。它采用潮流网络等值算法进行电网解合环分析。介绍了该算法的基本思路。并以实际算例阐明其计算精度高。具有普遍应用意义。在等值模式的选择中,通过分析端口模式和局部网络模式的优缺点。认为在可获得较多主网数据的情况下应优先采用局部网络模式。同时还指出。在软件的实现中应注意操作界面的图形化、数据对接的自动化和数据传送的信息化等问题。     

计及数据不平衡的RUSBoost-LightGBM 短期负荷预测方法

随着人工智能技术的发展,负荷预测的准确度显著提高,但仍有一些负荷曲线预测精度较低。造成这种现象的原因 在于训练集中这类负荷曲线属于少数类,导致数据不平衡,模型无法充分学习,从而影响了预测的精度。为解决电力负荷数 据不平衡问题导致的预测精度降低的问题,提出了一种先分类后预测的解决方法。通过改进的K-Mediods 方法把具有高相 似性的历史负荷曲线进行聚类,并构造分类标签与电力负荷的特征集;然后根据预测时间的特征进行分类,通过RUSBoost 算 法很好的优化了分类过程中数据不平衡问题;最后在每类中使用LightGBM算法进行负荷预测。在公开数据集上的实验表 明,所提出方法对少数类负荷的预测效果显著,其平均绝对百分比误差(MAPE) 为2.95%,均方根误差(RMSE) 为 175.71 MW;对于常规负荷的预测,MAPE为3 .52%,RMSE为195.84 MW,相对其他方法也具有较好的预测效果。     

基于粒子群优化的电力负荷灰色预测模型

通过对dt^-dx^（1）＋ax^（1）=u的通解x^^（1）=ce^-ak＋a^-u的参数a、u、c直接求解,避免了灰微分方程参数辨识时选取合理背景值的问题,构建了适应性更强的不需构造GM（1,1）模型的背詈值而直接求解灰微分方程参数的模型,并且在求解这些参数的过程中,应用了在求解非线性问题中具有全局寻优能力的粒子群算法（PSO）。提出了基于粒子群算法优化的电力负荷灰色预测模型PSOGM（1,1,a,u,c）,通过在电力负荷实例中的应用并与传统的GM（1,1）预测模型进行了效果比较,验证了基于粒子群算法优化的电力负荷GM（1,1）模型具有很好的预测精度和适用性。