一种改善Tent混沌序列随机性的方法

Tent混沌映射具有良好的遍历性和均匀性,但其随机性不理想。为此,提出一种改善Tent混沌序列随机性的方法。通过将Tent混沌映射变换为分段混沌映射,增大Lyapunov指数,改善相关系数和功率谱特性。对序列进行NIST随机性测试,结果表明,该分段Tent映射的序列具有较好的随机性,适用于通信与信息安全领域。     

四维混沌系统及其在图像加密中的应用

传统基于低维混沌系统的图像加密算法往往具有密钥空间较小、安全性较差的问题。针对这些问题,首先提出了一类新的平衡点不稳定的四维离散混沌系统,通过数值仿真对该类系统进行了动力学行为分析,正的Lyapunov指数的个数可以达到三个。同时并基于该类混沌系统设计了一个新的图像加密方案,并进一步对明密文的分布直方图、相关系数、信息熵以及加密方案对参数的敏感性进行了分析。分析结果表明,该加密方案抵抗外来攻击的能力强,密钥空间可达2996△,具有较高的安全性。     

T-S模糊离散多时滞系统的H∞控制

提出了一种新型非二次型Lyapunov函数, 在非并行分布补偿控制策略框架下, 研究了一类基于T-S模糊模型的离散多时滞系统的H∞控制. 通过引入一个矩阵变换, 所得控制律均以线性矩阵不等式的形式给出. 现有的并行分布补偿控制律可视作该新方法在某些条件下的特例. 仿真算例显示, 该函数方法保守性较低, 系统控制性能良好.     

Contribution to the decoupled control of large-scale mechanical systems

This paper presents the concept of decomposition as applied to the control synthesis of multivariable mechanical systems, in which the coupling among the subsystems can be very strong. The system class considered contains subsystems with powered degrees of freedom, as well as subsystems without their own actuators. Global control is introduced to diminish the influence of coupling on the stability of the whole system. The procedure is illustrated by simulation of two examples, one in robotics, the other in biomechanics.     

Asymptotic stability of nonlinear multiparameter singularly perturbed systems

Sufficient conditions are derived to guarantee the asymptotic stability of a class of nonlinear singularly perturbed systems with several perturbation parameters of the same order. Estimates of the region of attraction and bounds on the small parameters are obtained.     

典型电力系统模型的双参数分岔分析

针对一个典型的电力系统模型,综合考虑了负荷节点的有功和无功率荷对电压稳定的影响,对模型进行了双参数分岔分析,求得到了参数空间中的鞍节点分岔曲线和霍普夫分岔曲线。结果表明,在有功负荷水平较低时,系统在达到ＳＮＢ点之前会首先遇到ＨＢ点,因此系统会出现振荡失稳;随有功负荷的增国ＨＢ曲线将达到极限点;如果有功负荷继续增加,则ＨＢ点将会消失,电压骨溃将发生在ＳＮＢ点处。并且通过计算Ｌｙａｐｕｎｏｖ指数到了系     

基于空间栅格法的最大Lyapunov指数算法研究

最大Lyapunov指数是判断时间序列是否为混沌的一个重要判据,但传统方法求解的计算量很大,所需时间较长,导致在工程实际应用中受到限制,本文提出了基于空间栅格法的最大Lyapunov指数的改进算法,该方法将重构后的整个相空间进行分割,形成多个小空间,搜索邻近点时只需在其子空间内进行搜索,可以大大提高搜索速度.仿真实验表明改进的邻近点搜索方法无论在有噪声情况下还是在无噪声情况下都具有良好的鲁棒性,可以快速而有效地实现参考点邻域的搜索,极大的缩短了计算时间,且易于编程实现,使混沌信号特征指数的在线提取成为了可能.     

Chaotic mixing performance and mass transfer enhanced by rigid-flexible impeller with pulse jet

Conventional stirred reactors generally use rigid impeller for mechanical stirring, which leads to the easy creation of isolation mixing regions in the reactor and reduces the efficiency of fluid mixing. The use of multi-flow field coupling to induce chaos and promote more fluids into a chaotic state is one of the effective ways to improve fluid mixing efficiency. In this work, the largest Lyapunov exponent(LLE) and multi-scale entropy(MSE) are investigated with the Matlab compile pressure pulsation signals. The effects of duty ratio, paddle type, flexible paddle thickness, paddle height from the bottom and pulsed air jet flow rate on the chaotic mixing of fluids in a stirred reactor under different pulse periods are explored. In addition, the effects of different impeller types, jet types and air jet flow rate on the volume oxygen mass transfer coefficient K_La are compared and analyzed. When T=0.4 s and D=80%, the results show that the LLE of the rigid-flexible RT impeller compared with the rigid RT impeller increases 11.58% and the MSE of the rigid-flexible RT impeller is also larger than that of rigid RT impeller. It was showed that the pulsed jet rigid-flexible impeller system can better enhance fluid chaos, increase the fluid mixing efficiency and homogenize the system energy distribution. In addition, pulse jet coupling RF-RT impeller system enhances the turbulent characteristics of the fluid, promotes the reduction of the thickness of the liquid film, strengthens the mass transfer and increases the K_La value of the system. When power consumption per unit volume is 360 W/m³, the K_La of the PJ-RF-RT system compared with the PT-R-RT system increases 13.46%, and the K_La of the PJ-R-RT system compared with the SJ-R-RT system increases 11.86%.     

Extended dissipativity-based non-fragile control for multi-area power systems with actuator fault

This paper addresses the issue of reliable load frequency control design of an uncertain multi-area power system with constant time delays and disturbances via non-fragile sampled-data control approach. In particular, the parameter uncertainties are assumed to be randomly occurring which are described by the Bernoulli distributed sequences. By constructing a suitable Lyapunov–Krasovskii functional together with Wirtinger-based inequality, a new set of sufficient conditions in terms of linear matrix inequalities is obtained to ensure the asymptotic stability and extended dissipativity of the multi-area power system not only when all actuators are operational, but also in case of some actuator failures. Finally, simulation results are conducted to validate the effectiveness of the proposed control design technique.     

Note on flash and distillation systems

Flash and distillation systems evolving on the equilibrium manifold possess stable steady states when the molar flows and the boundary conditions are fixed and a vapor and liquid phase is present at all times. The results extend the range of validity of a local stability theorem for linear, constant molar overflow systems due to Acrivos and Amundson. The approach to stability analysis is motivated by the tangent plane method developed by Gibbs to open systems as it takes advantage of the negative curvature of the entropy surface to construct a Lyapunov function. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3322–3332, 2013