单向耦合半导体激光器之间的混沌同步研究

研究了单向耦合半导体激光器之间的混沌同步。通过计算两个单向耦合的半导体激光器模型的Lyapunov指数,确定了耦合强度的取值范围。进一步设计了耦合控制器,使响应系统的状态变量精确同步于驱动系统。仿真模拟结果表明,该方法可快速有效地实现半导体激光器的混沌同步。     

小波极大模方法在旋转机械故障诊断中的应用研究

通过小波变换奇异性检测理论,利用连续小波变换提取极大模值线并求取Lipschitz指数,提取转子每转中Lipschitz指数的平均个数和全部Lipschitz指数的平均值作为转子故障振动信号的奇异性特征。通过BP神经网络对转子不平衡、不对中、油膜涡动、摩碰和无故障5种状态进行分类识别,取得了较好的效果。     

Effect of tempering temperature on strain hardening exponent and flow stress curve of 1000 MPa grade steel for construction machinery

To study the effect of tempering temperature on strain hardening exponent and flow stress curve, one kind of 1000 MPa grade low carbon bainitic steel for construction machinery was designed, and the standard uniaxial tensile tests were conducted at room temperature.A new flow stress model, which could predict the flow behavior of the tested steels at different tempering temperatures more efficient-ly, was established.The relationship between mobile dislocation density and strain hardening expo-nent was discussed based on the dislocation-stress relation.Arrhenius equation and an inverse propor-tional function were adopted to describe the mobile dislocation, and two mathematical models were established to describe the relationship between tempering temperature and strain hardening expo-nent.Nonlinear regression analysis was applied to the Arrhenius type model, hence, the activation energy was determined to be 37.6 kJ/mol.Moreover, the square of correlation coefficient was 0.985, which indicated a high reliability between the fitted curve and experimental data.By comparison with the Arrhenius type curve, the general trend of the inverse proportional fitting curve was coincided with the experimental data points except of some fitting errors.Thus, the Arrhenius type model can be adopted to predict the strain hardening exponent at different tempering temperatures.     

Stability of two-time scale linear stochastic hybrid systems

The problem of exponential mean-square stability of two-time scale, linear stochastic hybrid systems has been studied in this paper. To obtain the sufficient conditions of stability, two basic approaches of stability analysis: for one-time hybrid systems with a Markovian switching rule as well as switching rule and singularly perturbed nonhybrid systems, were combined. The Lyapunov techniques were used in both approaches.     

Hierarchical optimization of boiler–turbine unit using fuzzy stable model predictive control

This paper develops a hierarchical control system structure based on the Takagi–Sugeno fuzzy model to achieve an optimal control of a boiler–turbine unit. In the upper layer of the hierarchy, an optimal reference governor is designed to find the optimal operating point. A disturbance term is introduced to the fuzzy model to lump the modeling mismatch and unknown disturbance. Thus, the effect of plant behavior variation can be removed and the operating point found can be feasible to control. In the lower layer, a stable model predictive controller is developed to track the optimal set-points while guaranteeing the input-to-state stability of the system. Fuzzy Lyapunov function and appropriate slack and collection matrices are used to reduce the conservatism of stability design and improve the performance. Through the estimation of the disturbance term using an observer, the two layers in the hierarchy are coupled and the integrated system can realize a dynamic optimal control of the boiler–turbine unit, even in the case of severe plant behavior variations.     

Stabilization of nonlinear systems with a slowly varying parameter by a control Lyapunov function

Based on a control Lyapunov function (CLF) strategy, a novel approach for designing a controller for a slowly varying nonlinear system is proposed. The approach may be thought of as being in between the time-invariant and time-varying CLF techniques. If the time-invariant technique is used to control a slowly varying system, stability will not be guaranteed. On the other hand, the time-varying CLF technique, due to the control law, has complexity and needs to measure or estimate the derivative of system parameters. The advantage of the proposed method is its independence from the measurement or estimation of the derivatives of the system parameters. It is shown that the proposed control law can even be independent of the parameters of the system. In this paper, the conditions are derived that allow using the simple CLF formula that guarantees the stability of a slowly varying system. The efficiency of the approach is shown through some simulations.     

纳米碳酸盐催化剂对AP/Al/HTPB推进剂性能的影响

研究了纳米碳酸盐催化剂对AP/Al/HTPB推进剂的燃速压强指数、爆热和力学性能等的影响.结果表明:纳米催化剂对推进剂在高压强(10～18 MPa)和低压强(4～10 MPa)段的燃烧性能的影响差别较大,但压强指数都能降低到0.2以下,均达到平台推进剂水平; 而且随着纳米催化剂含量增多,推进剂的燃烧效率更充分,爆热也有一定程度的增加; 但是,纳米催化剂对推进剂的力学性能、工艺性能却有一定程度的影响.确定了纳米碳酸盐催化剂在推进剂中配比为0.5%～1%之间.     

景象匹配辅助导航在弹道导弹末制导中的应用

对景象匹配定位导航的工作原理进行了数学化描述,讨论SINS/SMNS组合导航系统的信息融合算法,重点研究了其中两种信息融合算法：外推法和Lyapunov自适应滤波算法.通过仿真实验表明,景象匹配可有效地减小组合导航系统的位置误差.     

State controllability computation technique for linear time‐varying systems by using Taylor series approximation

This article presents a technique to determine the controllability Grammian matrix (CGM) for linear time‐varying systems by using truncated Taylor polynomial vector and the operational matrix of integration. An important property of this algorithm is that it starts by integrating the Lyapunov differential matrix equation in terms of the CGM. However, the algorithm does not use the mathematical integration processes actually, but uses the truncated Taylor polynomial vector and the operational matrix of integration. Thus, the problem is reduced to solving a linear set of algebraic equations with constant coefficients consisting of the Taylor polynomial constant coefficients of each of the CGM elements. Numerical results and error curves are given to illustrate the improvements achieved by the proposed algorithm. Copyright © 2008 John Wiley & Sons, Ltd.     

Creep behavior of Mg–2 wt.%Nd binary alloy

A binary magnesium alloy, Mg–2 wt.%Nd, has been prepared. Under the condition of temperature between 150 and 250 °C and applied stress between 30 and 110 MPa, the alloy exhibits good creep resistance due to both solution-hardening and especially precipitation-hardening. Tiny precipitates forming dynamically during creep have been observed, which play an important role in restricting dislocation movements. When the creep tests are carried out at the temperature range between 150 and 250 °C, the stress exponents lie in the range of 4.5–7.1 at low stresses, which is consistent with the “five-power-law”. The values of stress exponent increase up to 9.8–29.5 at high stresses indicate power-law breakdown. When the creep tests are carried out under the applied stress between 30 and 90 MPa, the apparent activation energy values vary from 70.0 to 96.0 kJ/mol at low temperatures, but increase to 199.9–246.1 kJ/mol at high temperature range. Dislocations in basal plane are activated in the primary creep stage, but as creep goes on, they are observed in non-basal plane. The creep is mainly controlled by both dislocation-climb and cross-slip.