Ski jump trajectory with consideration of air resistance

In the case of the ski-jump type energy dissipation,the jet trajectory will be greatly affected by the air entrainment and the air resistance.It is necessary to consider those factors when estimating the trajectory of the jet flow.In this work,the effect of the air resistance on the jet trajectory is theoretically and experimentally investigated.A comprehensive resistance coefficient is proposed.To determine this coefficient,experiments of five models are conducted with the circular-shaped flip bucket placed at the point of the takeoff of ski jumps.It is shown that,this coefficient of the lower jet trajectory is only related to the approach flow Froude number,while that of the upper jet trajectory is dominated by both this Froude number and the deflection angle.Furthermore,the present methodology is validated by experimental data in this work and the maximum errors are not larger than 3.2%and 8.6%for the lower and upper jet trajectories,respectively.     

西南茶山村滑坡成因机制及稳定性分析

深入分析了滑坡的自身的结构特征:松散的滑坡堆积物,良好的临空条件。在人类不合理的活动、降雨、生活废水不合理的排放以及较差的排水条件等不利因素的共同作用下,最终滑坡发生。最后采用传递系数法分析了滑坡的整体稳定性。     

Optimal Control of Switching Times in Switched Stochastic Systems

In this paper, we solve an optimal control problem for switched stochastic systems using calculus of variations, where the objective is to minimize a cost functional defined on the state and the switching times are the sole control variables. In particular, we focus on the problem in which a pre‐specified sequence of active subsystems is given. For one switching time case, the derivative of the cost functional with respect to the switching time is derived, which has an especially simple form and can be directly used in gradient descent algorithms to locate the optimal switching instant. Then, we propose an approach to deal with the problem with multi‐switching times case. Finally, two numerical examples are given, highlighting the viability and advantages of the proposed methodology.     

Heuristic Dynamic Programming Using Echo State Network For Multivariable Tracking Control Of Wastewater Treatment Process

This paper proposes a heuristic dynamic programming (HDP) scheme to simultaneously control the dissolved oxygen concentration and the nitrate level in wastewater treatment processes (WWTP). Unlike traditional HDP schemes, the optimal control values are calculated in an analytical way by the proposed HDP controller. It can reduce the learning burden of the HDP controller to a great extent. The system model and the evaluation index J are approximated by two echo state networks (ESNs). Gradient‐based learning algorithms are employed to train both ESNs online, and the convergence of the training algorithm is investigated based on Lyapunov theory. The performance of the proposed ESN‐based HDP (E‐HDP) controller is tested and evaluated on a WWTP benchmark. Experimental results demonstrate that the proposed approach can achieve effective performance.     

一种基于Web日志和网站参数的入侵检测和风险评估模型的研究

随着网络技术的不断发展,网上冲浪变得并不像以前那么的安全,持续不断的网络漏洞导致越来越多的网站正面临着被入侵的风险。为了维护网站的安全性,人们提出了许多与入侵检测相关的研究方案。其中,基于实时系统的入侵检测方案在众多研究中占了绝大一部分,这种系统能在网站受到入侵时给出第一时间的警告和防护,但是一旦一个网站已经受到了入侵,那么这些检测手段将变得毫无作用。除此之外,另外一些学者还提出了一些非实时入侵检测方案,非实时入侵检测方法可以运用在系统受到入侵之后,它们的主要作用是对入侵行为进行溯源。但是由于每个网站的整体架构都不一样,这种检测方法并不能评估一个网站所面临的入侵风险的大小。文章在基于Web日志和网站参数的前提下,提出了一个用于非实时入侵检测的风险评估模型。这个模型可以根据不同的网站参数定义不同的评估策略,这种评估策略会为每种攻击方式分配一定的权重,通过这些权重和Web日志所匹配的攻击信息,模型可以计算出系统的风险模糊值从而评估系统所遭受攻击的风险程度。实验结果表明文章的研究能有效地检测出每个网站所面临的入侵风险,它将对保护网站安全以及防御黑客攻击起到很重要的作用。     

基于虚拟仪器的舵机综合测试系统设计

为了在实验室条件下模拟舵机系统实际飞行时所受的气动载荷,实现舵机部件和整机的动静态测试,设计了基于虚拟仪器的舵机综合测试系统;针对舵机测试系统自动化化和综合化需求,基于PXI架构和LabWindows/CVI平台,完成了测试系统的硬件设计和软件设计,采用异步定时器实现了实时数据采集,采用tdms数据流实现了大容量高速数据的记录,运用多线程实现了良好的人机交互与流畅的曲线显示,采用ActiveX技术调用Excel实现了测试报表的自动生成;使用和测试结果表明,该测试系统显著提高了舵机测试的效率和精确度以及自动化水平,使用方便,性能稳定,为舵机性能测试和设计优化提供了可靠保障.     

基于波变量补偿的阻抗匹配时延双边遥操作

通信时延是遥操作系统中固有的问题,它会严重影响遥操作的性能,降低系统的稳定性和跟踪性。基于无源理论的波变量法可以保证遥操作系统在任意时延下稳定,是解决时延问题的一个重要方法。然而,波变量法带来的波反射会阻扰有用信号的传输,降低了主从端信号的跟踪性,严重时甚至会导致整个系统振荡。针对这一问题,提出了一种基于波变量补偿的阻抗匹配双边遥操作系统结构,旨在减少波反射,提高操作者的临场感和系统的跟踪性。通过仿真实验,结果表明所提方法能够保证固定时延条件下遥操作系统的稳定性,并具有较好的跟踪性。     

基于模糊理论的信息系统安全防护有效性评估研究

论文基于信息保障技术框架(IATF)的核心思想,构建了定性指标与定量指标相结合的信息系统安全防护有效性评估指标体系.针对信息系统中部署实施安全防护措施的共性特征,基于模糊理论构建了信息系统安全防护有效性评估模型.最后,运用此模型对建设完成的信息系统进行了量化评估,验证了方法的可行性与实用性,为信息系统中安全措施部署实施方案的改进完善提供量化依据.     

基于特征点的图像拼接算法优缺点比较

该文主要详细讲解图像拼接技术中基于特征点的图像拼接算法,通过详细介绍几种常见的特征点提取算法,Harris算子,LOG算子,SUSAN算子,SIFT算法,并通过实验结果对这几种算法的优缺点进行比较,从而在实际的应用中,我们年应该根据需要选取合适的算法,从而更好的完成图像拼接工作。