基于最大熵原理的大坝安全监控组合预测模型研究

大坝性态受到内外多种不确定因素的影响,使得监测效应量在一定程度上呈现出随机和不确定性的特点,单一的安全监控预测模型不可避免地存在某些缺陷。采用最大熵原理建立大坝安全监控的组合预测模型,该模型以各单一模型的预测结果作为约束信息,利用最大熵原理得到预测结果的分布。实例分析表明该方法能够突出监测量变化的随机性特点,有效地提高了大坝安全监控模型的预测精度。     

刚体动力学初值问题的拟变分原理及其应用

随着科学技术的发展,对刚体动力学提出新的要求.应用变积方法,建立了刚体动力学初值问题的拟变分原理.推导出刚体动力学初值问题的拟变分原理的拟驻值条件.建立了刚体动力学初值问题的广义拟变分原理,说明了应用广义拟变分原理求得问题的解析解和数值解的途径.借助算例说明了应用变分方法来研究刚体动力学初值问题的优越性.     

A macro-meso constitutive law for concrete having imperfect interface and nonlinear matrix

The overall behavior of concrete depends on its meso structures such as aggregate shape, interface status, and mortar matrix property. The two key meso structure characters of concrete, bond status of interface and nonlinear property of matrix, are considered in focus. The variational structure principle is adopted to establish the macro-meso constitutive law of concrete. Specially, a linear reference composite material is selected to make its effective behavior approach the nonlinear overall behavior of concrete. And the overall property of linear reference composite can be estimated by classical estimation method such as self-consistent estimates method and Mori-Tanaka method. This variational structure method involves an optimum problem ultimately. Finally, the macro-meso constitutive law of concrete is established by optimizing the shear modulus of matrix of the linear reference composite. By analyzing the constitutive relation of concrete established, we find that the brittleness of concrete stems from the imperfect interface and the shear dilation property of concrete comes from the micro holes contained in concrete. Supported by the National Natural Science Foundation of China (Grant Nos. 50679022, 90510017, 50539090) and National Basic Research Program of China (Grant No. 2007CB714104)     

基于超声波原理的开孔参数标定系统研究

针对传统的人工丈量方法标定开孔方位角和倾斜角存在操作程序繁琐、稳钻时间长、精度低等问题,设计了基于超声波原理的钻孔开孔参数标定系统。该系统采用超声波渡越时间检测法测量参考点之间的距离,并由单片机解算出钻杆的方位角,选用微机械三轴加速度计测量倾斜角,实现了全自动化的实时跟踪测量及智能化的钻机姿态调整语音指导操作;在误差允许范围内,可快速标定所需开孔参数。该系统提高了开孔参数标定精度、标定效率及煤矿管理水平,降低了矿工劳动强度和煤矿管理成本。     

聚氨酯的阻尼性能与频率关系的研究

从时温等效原理出发,依据WLF方程和自由体积理论推导了一个较为简单的将高分子材料的温度谱转变为频率谱的方法。用该方法计算得到的损耗因子与实验数据吻合得很好。研究了所合成的聚氨酯材料在1～10000Hz范围内的特征阻尼频率.结果表明25℃下.含填料的H052的特征阻尼频率为5430Hz。     

HTTP-SoLDiER: An HTTP-flooding attack detection scheme with the large deviation principle

HTTP-flooding attack is a much stealthier distributed denial of service （DDoS） attack, challenging the survivability of the web services seriously. Observing the web access behavior, we find that the surfing preference of normal users is much more consistent with the webpage popularity than that of malicious users. Based on this observation, this paper proposes a novel detection scheme for HTTP-flooding （HTTP-SoLDiER）. Specifically, HTTP-SoLDiER first quantifies the consistency between web users surfing preference and the web- page popularity with large-deviation principle. Then HTTP-SoLDiER distinguishes the malicious users from normal ones according to the large-deviation probability. In practice, the webpage popularity plays a key role in attack detection of HTTP-SoLDiER. Due to the never-ending updating of the webpage content and the disturbance induced by attackers, the webpage popularity often varies over time. Thus, it is critical for HTTP-SoLDiER to dynamically update the webpage popularity. We design a reversible exponentially weighted moving average （EWMA） algorithm to solve the problem. Finally, we evaluate the effectiveness of this scheme in terms of true positive （TF） and false positive （FP） probabilities with NS-3 simulations. The simulation results show that HTTP-SoLDiER can detect all random HTTP-flooding attackers and most of the perfect-knowledge HTTP-flooding attackers at little false positive.     

液压阻尼器阀试验台电气控制系统

为了保证核电装置中液压阻尼器阀安全运行,设计一种液压阻尼器阀试验台,重点介绍其电气系统的设计.     

基于软分区的地区电网自动电压控制系统

介绍贵港地区电网基于软分区的三级自动电压控制（AVC）系统,并对该系统的三级控制原理及区域变电站的控制规则进行说明。     

导弹电动舵机控制系统设计

针对某型导弹现有电液伺服系统存在动态响应速度慢、结构复杂、可靠性差、使用维护困难等缺点,研究提出了一种以大功率无刷直流电机为控制对象的电流/位置/速度三闭环反馈控制系统设计方案;采用DSP和FPGA的组合工作模式,其中DSP内部主控制程序实现系统初始化、三闭环控制算法和产生PWM信号等功能,FPGA则实现各功能电路的时序逻辑控制;通过构建由模拟制导计算机、1553B总线通讯网络和舵机控制系统组成的测试系统,验证了三闭环电动舵机控制系统设计方案的可行性;实验结果表明,该导弹电动舵机控制系统最大负载扭矩为75N·m,满载角速度为200°/s,调节时间小于70 ms(±10°阶跃信号),动态相移小于5％(2°,1 Hz),具有输出力矩大、响应速度快、控制精度高、使用寿命长和可维护性好等优点.     

酸碱影响下砂岩流变参数识别方法及敏感度

根据长期暴露在自然环境中的砂质岩体易遭受水及可溶离子化学侵蚀作用的事实,通过对相同浓度不同pH值CaCl₂试剂浸泡处理过的砂岩试件进行三轴剪切试验,根据试验结果选取符合试验规律的二阶简化广义Kelvin流变模型,按照定泊松比假设将其变形为三项应力状态。基于搜索模式的最小二乘方法（LSMPS）获取模型参数最优解,以均方根误差评价模型对各参数变化的敏感性程度。采用延迟时间评价砂岩在不同化学环境中达到稳定蠕变过程所需时间。通过搜索模式识别的模型参数能够使模型计算值与加载试验获得的实测值比较接近,表明该模型及其参数识别方法在确定受化学因素干扰下的砂岩流变特征比较适用。