Flow Intensity Parameter in Pier Scour Experiments

Technical note discusses a detailed approach to dimensional analysis for the bridge pier scour phenomenon and the introduction of flow intensity. It demonstrates the dependence of critical upstream velocity on the rest of the parameters describing the process and its implications on dimensional analysis. Assuming that the viscous effects are negligible in the local scour phenomenon, it is concluded that the flow intensity of the approaching undisturbed flow is not an adequate parameter to describe the process in usual laboratory conditions. A new proposal is established.     

Combined Continua and Lumped Parameter Modeling for Nonlinear Response of Structural Frames to Impulsive Ground Shock

The response of a beam-column frame to impulsive ground shock, such as those induced by an underground explosion, has characteristics of both impact and natural earthquake responses. The critical effects may be governed by the dynamic response of individual elements as continuous mass systems, while to a certain extent the global vibration (as of lumped-mass systems) may also be involved. To incorporate both dynamic features, the present study proposes a combined continua and lumped parameter (CCLP) model, which consists of the basic beam-column element with distributed stiffness and mass, along with concentrated mass-springs at element ends to form the reduced dynamic system. To take into account of the shear deformation and rotary inertia which become important in the impulsive response, the governing equations are formulated based on the Timoshenko beam theory. The nonlinearities are described through three mechanisms, namely the distributed nonlinear flexural and diagonal shear behavior, and the direct sliding shear at the member ends. A generic restoring force model is adopted to describe the hysteretic behavior. Comparison with a scaled model test demonstrates that the CCLP model is capable of representing the primary dynamic features in a frame structure under impulsive ground shock. Extended parametric studies indicate that, with increase of the ground shock frequency, the failure tends to become shear dominant. For ground shocks of frequency at 20–30?Hz and above, the failure in a reinforced concrete column will require a peak ground velocity (PGV) on the order of 3?m/s, whereas failure in a beam would occur at PGV of about 1.5?m/s.     

无绳提升系统模糊自整定PID位置控制

由于垂直运动永磁直线同步电动机的特殊结构及特殊的边端效应,其精确的数学模型不容易建立。针对永磁直线同步电动机驱动的无绳提升系统,用常规PID调节器很难满足位置伺服系统快速、无超调的响应特性的要求,提出了模糊自整定PID位置控制策略,并通过模糊规则在线调整PID控制的参数。仿真结果表明,和传统的PID控制比较,模糊PID控制系统具有良好的稳定性和自适应能力。     

Optimization of Welding Process Parameters for 9Cr-1Mo Steel Using RSM and GA

Optimization of A-TIG welding process parameters for 9Cr-1Mo steel has been carried out using response surface methodology (RSM) and genetic algorithm (GA). RSM has been used to obtain the design matrix for generating data on the influence of process parameters on the response variables. A second-order response surface model was developed for predicting the response for the set of given input variables. Then, numerical and graphical optimization was performed using RSM to obtain the target depth of penetration (DOP) and heat-affected zone (HAZ) width using desirability approach. Multiple regression models were developed based on the generated data, and then the models were used in GA to determine the optimum process parameters for achieving the target DOP and HAZ width. GA-based models employed two different selection processes. Both the RSM- and GA-based models suggested a number of solutions in terms of process parameters, and the identified solutions were validated by experiments. GA-based model employing tournament selection has been found to be a more accurate method for determining the optimum A-TIG welding process parameters.     

Determination of Material Parameters of Welded Tube via Digital Image Correlation and Reverse Engineering Technology

Material characteristics play an important role in tube hydroforming (THF). A method, based on digital image correlation (DIC) and reverse engineering (RE) technology, is proposed to determine the material parameters of a welded tube in hydroforming with a single tubular blank. The material parameters of the weld and parent metal are determined by applying membrane theory and the force equilibrium equations, as well as the deformation data which are obtained by DIC and RE technology in the THF process. Finite element simulations of welded THF are performed with these material parameters and the maximum bulge radii and axial profiles of the weld and parent the metal obtained from the simulations are compared with those obtained from the hydroforming experiments to verify the reliability of the proposed method. The results show that the material parameters of the weld are lower than those of the parent metal. With the material parameters adopted in FE simulation there is a good agreement between the simulation and the experiment as for the maximum bulge radii and axial profiles of the weld and parent metal. This verifies that the proposed method is acceptable for determining material parameters of a welded tube.     

发电机励磁系统参数辨识的仿真研究

研究发电机励磁系统参数辩识问题,由于励磁系统是一个非线性系统,造成电力系统不稳定.传统时域或频域辩识方法不能辩识其非线性环节,导致励磁系统辩识的精度低.为了提高发电机励磁系统的辩识精度,提出一种神经网络的发电机励磁系统参数非线性辨识方法.以发电机励磁系统实际输入作为神经网络的输入,以实际励磁系统输出与神经网络输出之间的最小误差作为目标函数,通过不断调整神经网络的权值对神经网络模型进行优化,最后得到满足系统误差要求的发电机励磁系统参数.仿真结果表明,改进方法解决了传统辩识方法无法准确辩识励磁系统非线性环节的难题,有效提高了励磁系统的辨识精度.     

组态王在烟气脱硝中的应用

随着国内经济发展,火电厂锅炉烟气排放指标控制越加严格,火电厂烟气污染物的排放越来越受到国家和社会的广泛关注。锅炉烟气脱硫技术已经在国内全面普及,作为脱硝还原剂液氨的运用由于受到安全、地域等因素的限制,尿素热解制氨技术逐渐受到青睐。本文重点介绍介绍组态王6.53在尿素烟气脱硝监控系统中的应用。     

基于参数优化SVM融合的网络异常检测

网络异常检测技术是入侵检测系统中不可或缺的部分。然而目前的入侵检测系统普遍存在检测率不高,误报率过高等问题,从而难以在实际的企业中大规模采用。针对之前的检测技术检测效果不佳的问题,提出基于SVM回归和改进D-S证据理论的入侵检测方法。该方法是将支持向量机回归的分类融合应用到网络异常行为分析中,在SVM参数选择时采用交叉验证和深度优先搜索算法进行优化选择,并通过融合证据理论,建立网络异常检测模型。通过仿真实验表明,该模型能够有效地提高入侵检测性能,缩短检测时间。     

基于IHS_RELM的网络安全态势预测方法

针对网络安全态势感知中的态势预测问题,提出一种基于IHS_RELM的网络安全态势预测方法。对和声搜索算法的原理进行了研究,在此基础上提出一种改进的和声搜索算法。将正则极速学习机(RELM)嵌入到改进的和声搜索算法(IHS)的目标函数计算过程中,利用IHS算法的全局搜索能力来优化选取RELM的输入权值和隐含层阈值,在一定程度上提升了RLLM的学习能力和泛化能力。仿真实验表明,与已有的其他预测方法相比,该方法具有更好的预测效果。     

Evaluating the Sensitivity of Attic Radiant Barrier Performance to Climate Parameters

By employing a calibrated and tested computer model, simulations of ceiling heat transfer in typical residential attics located in 12 locations across the United States were obtained to study the sensitivity of attic radiant barrier performance to local climate parameters. For each location, the net ceiling heat flux over the summer cooling season was computed for an attic with and for an attic without an installed radiant barrier. The net reduction of heat flux induced by the radiant barrier was computed and then related to climate variables. Among the local environmental parameters, the local ambient air temperature, local ambient humidity, and latitude had significant effects on the performance of radiant barriers. It was concluded that the installation of radiant barriers would be most beneficial in regions with high outdoor air temperatures and high relative humidity.