Design of experiments for Quick U-building method for building energy performance measurement

Quick U-building (QUB) is a method for short time measurement of energy performance of buildings, typically one night. It uses the indoor air temperature response to the power delivered to the indoor air by electric heaters. This paper introduces a method for estimating the expected measurement error as a function of the amplitude and the time duration of the input signal based on the decomposition of the time response of a state-space model into a sum of exponentials by using the eigenvalues of the state matrix. It is shown that the buildings have a group of dominant time constants, which gives an exponential response, and many very short and very large time constants, which have a small influence on the response. The analysis of the eigenvalues demonstrates that the QUB experiment may be done in a rather short time as compared with the largest time constant of the building.     

基于复特征值分析的某盘式制动器制动尖叫问题改进

以某车型出现2000 Hz制动尖叫问题的盘式制动器为研究对象,建立制动器的有限元模型。通过试验模态对有限元模型进行修正,应用复特征值分析技术,获取系统的复特征值和振型,并通过ODS测试确认与制动尖叫频率对应的不稳定模态。然后针对此不稳定模态,通过相关性分析量化制动器零件对系统不稳定模态的贡献,采用优化具有最大贡献量的零件几何结构来改善制动尖叫。最后通过SAE J2521台架试验验证此方法可行。     

SDN环境下基于BP神经网络的DDoS攻击检测方法*

软件定义网络是一种全新的网络架构,集中控制是其主要优势,但若受到DDoS 攻击则会造成信息不可达,也容易造成单点失效。为了有效的识别DDoS攻击,提出了一种SDN环境下基于BP神经网络的DDoS攻击检测方法：该方法获取OpenFlow交换机的流表项,分析SDN环境下DDoS攻击特性,提取出与攻击相关的流表匹配成功率、流表项速率等六个重要特征;通过分析六个相关特征值的变化,采用BP神经网络算法对训练样本进行分类,实现对DDoS攻击的检测。实验结果表明,该方法在有效提高识别率的同时,降低了检测时间。通过在软件定义网络环境中的部署,验证了该方法的有效性。     

两层双向加权星形网络的同步能力分析

[5]陆君安.从单层网络到多层网络——结构、动力学和功能[J].现代物理知识,2015,27 (4):3-8. [12]郭世泽,陆哲明.复杂网络基础理论[M].北京：科学出版社,2012. [14]傅晨波. 复杂网络同步若干问题研究[D]. 浙江大学,2013. [20]严洲.复杂网络随机稳定性和同步性研究[D].浙江大学,2012. [24]马腾.图拉普拉斯矩阵特征值优化及其应用[D].天津：天津大学,2013 [25]张晓转.基于超网络的超拉普拉斯矩阵研究[J].山东工业技术,2016,35(2):264.     

对求解对称三对角矩阵特征值区间分半法的探讨

研究了一种特殊的对称三对角矩阵,在其顺序主子阵的特征值不满足严格交织的条件下,证明了区间分半法仍适用于求解它的特征值。     

Lipschitz非线性系统观测器设计

运用微分方程方法,讨论了一类满足Ｌｉｐｓｃｈｉｔｚ条件的非线性系统观测器的设计,结论表明,稳定观测器的存在不仅与系统矩阵的特征值有关,而且与矩阵对距离不可观测性的大小有关,给出代数设计方法以条件数量小为目标准则,根据梯度下降法原理,用ＭＡＴＬＡＢ写代码,设计者只须提供初值,程序即自动完成观测器设计,文末咄了释例。     

Analytical study and numerical experiments for true and spurious eigensolutions of a circular cavity using the real‐part dual BEM

It has been found recently that the multiple reciprocity method (MRM) (Chen and Wong. Engng. Anal. Boundary Elements 1997; 20 (1):25–33; Chen. Processings of the Fourth World Congress on Computational Mechanics, Onate E, Idelsohn SR (eds). Argentina, 1998; 106; Chen and Wong. J. Sound Vibration 1998; 217 (1): 75–95.) or real‐part BEM (Liou, Chen and Chen. J. Chinese Inst. Civil Hydraulics 1999; 11 (2):299–310 (in Chinese)). results in spurious eigenvalues for eigenproblems if only the singular (UT) or hypersingular (LM) integral equation is used. In this paper, a circular cavity is considered as a demonstrative example for an analytical study. Based on the framework of the real‐part dual BEM, the true and spurious eigenvalues can be separated by using singular value decomposition (SVD). To understand why spurious eigenvalues occur, analytical derivation by discretizing the circular boundary into a finite degree‐of‐freedom system is employed, resulting in circulants for influence matrices. Based on the properties of the circulants, we find that the singular integral equation of the real‐part BEM for a circular domain results in spurious eigenvalues which are the zeros of the Bessel functions of the second kind, Y (kρ), while the hypersingular integral equation of the real‐part BEM results in spurious eigenvalues which are the zeros of the derivative of the Bessel functions of the second kind, Y_n′(kρ). It is found that spurious eigenvalues exist in the real‐part BEM, and that they depend on the integral representation one uses (singular or hypersingular; single layer or double layer) no matter what the given types of boundary conditions for the interior problem are. Furthermore, spurious modes are proved to be trivial in the circular cavity through analytical derivations. Numerically, they appear to have the same nodal lines of the true modes after normalization with respect to a very small nonzero value. Two examples with a circular domain, including the Neumann and Dirichlet problems, are presented. The numerical results for true and spurious eigensolutions match very well with the theoretical prediction. Copyright © 2000 John Wiley & Sons, Ltd.     

On the eigenvalues of a uniform cantilever beam carrying any number of spring–damper–mass systems

The eigenvalues of a uniform cantilever beam carrying any number of spring–damper–mass systems with arbitrary magnitudes and locations were determined by means of the analytical‐and‐numerical‐combined method (ANCM). First of all, each spring–damper–mass system was replaced by a massless effective spring with spring constant k_eff, which is the main point that the ANCM is available for the present problem. Next, the equation of motion for the ‘constrained’ beam (with spring–damper–mass systems attached) was derived by using the natural frequencies and normal mode shapes of the ‘unconstrained’ beam (without carrying any attachments) incorporated with the expansion theorem. Finally, the equation of motion for the ‘constrained’ beam in ‘complex form’ is separated into the real and the imaginary parts. From either part, a set of simultaneous equations were obtained. Since the simultaneous equations are in ‘real form’, the eigenvalues of the ‘constrained’ beam were determined with the conventional numerical methods. To confirm the reliability of the presented theory, all the numerical results obtained from the ANCM were compared with the corresponding ones obtained from the conventional finite element method (FEM) and good agreement was achieved. Because the order of the property matrices for the equation of motion derived by using the ANCM is much lower than that by using the conventional FEM, the storing memory and the CPU time required by the ANCM are much less than those required by the FEM. Besides, the solution of the equation of motion derived from the ANCM can always be obtained with the general personal computers, but that from the FEM can sometimes be obtained only with the computers of workstations or main frames when the total degrees of freedom exceeding a certain limit. Copyright © 1999 John Wiley & Sons, Ltd.     

基于相干性的多聚焦图像融合算法

为提高多聚焦图像的融合效果,提出一种基于相干性的融合算法。该算法对源图像进行离散小波变换,利用高频小波系数构造结构张量矩阵,通过矩阵特征值定义反映局部几何信息的相干性并建立融合策略。实验结果表明,该算法得到的融合图像在主观视觉效果和客观量化指标方面均有良好的表现,提高了融合的视觉效果。     

Application of ICCG Method to Numerical Solutions of Few-Group Neutron Diffusion Equations

Emergency core cooling (ECC) mater is carried up to the upper plenum and falls down again into the core during the reflood phase in PWR-LOCA. Therefore the quench front also propagates downward from the top of the core. The effect of upward steam flow rate on the top-down quench propagation was experimentally investigated. It was found that top-down quench velocity was delayed by upward steam flow. This effect is more significant when rod surface temperature is low and the falling water flow rate is small.

The effect of the flow rate and the rod temperature on the quench velocity was correlated based on the experimental results under the conditions of atmospheric pressure, saturation temperature for water and steam, rod surface temperature of 350–600°C, down-ward water velocity of 0.01–0.1 m/s and upward steam velocity of 0–20 m/s.