基于输出反馈滑模控制的分数阶超混沌系统同步

以具有更大秘钥空间的分数阶超混沌系统为驱动系统和响应系统,利用具有实际应用意义的输出反馈滑模控制实现两个系统的同步.通过对同步误差系统方程进行结构分解,在辅助系统的基础上设计具有输出反馈特性的滑模控制律.在分数阶系统稳定性理论基础上利用MATLAB YALMIP工具箱对滑模参数进行整定,并利用分数阶Lyapunov稳定性定理证明了滑模控制律和自适应滑模控制律的稳定性.最后,数值仿真表明了本文方法的有效性和可行性.     

利用空间矩提取亚象素角特征

A novel subpixel corner detection method based on spatial moment is developed in this paper. Firstly, the spatial-moment-generating function, gradient magnitude and variation of gradient-direction corner are used as the decision rule of corner detection by analyzing the mathematical formula of corner-model spatial moment. Then Non-max suppression technique is utilized to detect the vertex of feature corner. Finally, in order to improve its localization performance, subpixel corner detection is implemented by the bilinear interpolation and Newton iteration method. Experiments illustrate that the spatial moment corner detector has better robustness and localization performance than Kitchen detector and Harris detector.     

Sliding Mode Guidance Law Considering Missile Dynamic Characteristics and Impact Angle Constraints

In order to improve the precision of guidance for the missile intercepting maneuvering targets, this paper proposes a sliding mode guidance law with impact angle constraints based on the equation of the relative motion of the missile and the target in a 2D plane. Two finite-time convergent guidance laws are proposed based on the nonsingular terminal sliding mode, while, two exponential convergent guidance laws involving dynamic delay are developed through applying the higher-order nonsingular terminal sliding mode. The simulations denote that, in all the four scenarios of the target’s maneuvering, the guidance laws are able to inhibit the chattering phenomenon of the sliding modes effectively; and from an expected aspect angle, the missiles could attack the targets with high precision and fast speed.     

Adaptive Dynamic Surface Control for Spacecraft Terminal Safe Approach with Input Saturation Based on Tracking Differentiator

This thesis studies the spacecraft terminal safe approach control problem considering input saturation. Based on the spacecraft relative motion model and sphere collision avoidance potential function, an anti-saturation controller and an adaptive finite-time anti-saturation controller using dynamic surface control(DSC) are presented for the situations of known and unknown upper bound of external disturbances respectively, which can guarantee that no collisions happen in the tracking process. The second-order tracking differentiator is introduced to design the controllers, which avoids the differential of the virtual control signal and ensures the tracking performance of system output signals. Meanwhile, the auxiliary system is introduced to handle input saturation. Lyapunov stability theory is adopted to prove that the states of system under the designed controllers are uniformly ultimately bounded and practical finite-time stable respectively, and the chaser spacecraft can approach to the desired position without collision. The numerical simulation results demonstrate that the chaser spacecraft using the designed controllers can realize terminal safe approach to target spacecraft, which further illustrate the effectiveness of the proposed controllers.     

Fast terminal sliding mode tracking control of hypersonic vehicles based on non-homogeneous disturbance observer

The tracking control problem of hypersonic vehicles is studied and analyzed in this paper using terminal sliding mode control method (TSMC) and non-homogeneous disturbance observer(NHDO) considering parametric uncertainty and external disturbances. Non-singular terminal sliding mode controller is provided based on NHDO. The key idea is that the NHDO is adopted to estimate the aerodynamic uncertainties and external disturbances simultaneously, which can enhance the robustness of the system and lower the gain of the switch controller. Rigorous stability analysis for the closed-loop system is given via Lyapunov stability theory, which proves that the system states are always bounded even during the estimation process when the estimation error is not zero. The sliding manifold can be reached in finite time and the tracking errors can converge to zero asymptotically. Numerical simulations are conducted with the longitudinal nonlinear dynamic model of hypersonic vehicles to verify the effectiveness and robustness of the designed controller.     

Analysis and prediction of shock-induced near-field acoustics from an exhaust pipe

In this study an acoustic problem of a single shock wave moving through a circular pipe instead of a real pulsating flow with blast waves is considered. Due to the failure of a linear acoustic theory for the problem of interest, the method of computational fluid dynamics is employed to analyze the present problem. For this purpose, the axisymmetric Euler equations are solved by a high-resolution method which consists of a fifth-order weighted essential non-oscillation scheme for spatial discretization and a fourth-order Runge–Kutta method for time integration. In order to reduce the large computational time on a single computer, parallel computation with seven personal computers has been conducted. The detailed flow and sound pressure fields inside and downstream of the pipe are studied. The near-field sound pressure level downstream of the pipe was computed. The sound lobe and its orientation are investigated. In particular, an interesting phenomenon of spatial variation of velocity components associated with the sound lobe is reported. It is found that the spatial variations of the streamwise velocity component and pressure are in phase. However, the spatial variations of the radial velocity component and pressure are out of phase. Moreover, the generation mechanism of acoustics is attributed to the fact of the back-and-forth reflections of upstream-moving expansion waves generated at the pipe wall corner when the shock wave diffracts around the corner. The back-and-forth wave reflections result in the formation of interlacing high- and low-pressure regions that change with time.     

Improving product based on affordance with fuzzy theory for product development strategy

This paper presents a design strategy which combines both conceptual and mental design information to quantitative degrees of affordance using a fuzzy scale that provides user-to-designer information. The traditional communication channel has been hidden. In the past, design concepts were not a result of direct communication between designers and users. This study found that, based on users’ mental models, users can reflectively modify product characteristics to improve the convenience of usage. These insights offer a hidden communication channel for designers and are defined as generalised affordance within the context of this research. This study proposed a novel method to semi-quantify affordance using a fuzzy linguistic modelling technique to establish a fuzzy scale table that quantifies degrees of affordance. An affordance fuzzy matrix (AFM) was created to assess the effects of affordance of each task necessary to utilise each product component. The overall results of the AFM indicate the generalised affordance of a particular product. Hidden messages are the characteristic of a product improved by the user itself because of his habit, which incurs additional product features, symbols and words, and will help product designers for further design strategy and improvements. In this study, generalised affordance is applied to an electric oven as an example.     

氧化铝粉末系统微结构对θ到α相转换温度的影响

以一平均晶径15.2 nm的θ-氧化铝粉末,通过(1)原取得(as received)粉末,(2)利用机械搅拌调制均匀分散粉料,(3)将均匀分散粉料制成高密度坯体(单轴压500 MPa)三种方式,改变其粒体间的距离及其均质度,了解氧化铝粉末θ-到α-相转换温度的下降现象.研究系通过DTA曲线,配合等温试验,由晶粒成长速率式计算θ-晶粒成长活化能,来进行三系统的相变观察.结果显示,提高均质程度,及缩短晶粒间的距离,均有助于相变发生温度的下降及时间的缩短,而θ-晶粒所需成长活化能也减少.后者经计算,经均质化并拉近粒体间距离可致该活化能减半,由原需300kJ/mol降至150 kJ/mo1.     

Robust Finite-time Attitude Tracking Control of Rigid Spacecraft Under Actuator Saturation

This paper investigates the robust finite-time attitude tracking control problem for rigid spacecraft considering the modeling uncertainty, external disturbance and actuator saturation. An auxiliary system is proposed to directly compensate for the saturated control input. First, the basic controller is formulated based on the fast nonsingular terminal sliding mode surface (FNTSMS), the fast-TSM-type reaching law and the auxiliary system in the presence of upper bounded external disturbance. Then, when facing system uncertainty which consists of both modeling uncertainty and external disturbance and has upper bounded first derivative, the extended state observer (ESO) is associated with the first controller to improve the robustness of control system. Furthermore, to handle more general system uncertainty which is upper bounded by a polynomial function of the closed-loop system states, a continuous adaptive controller is designed to compensate for the total system uncertainty on line. The proposed controllers are able to deal with system uncertainty, input singularity and actuator saturation, while simultaneously providing fast finite-time convergence speed for the control system. And the problems of complex parameters selection process and repeated differentiations of nonlinear functions can be avoided. Rigorous stability analyses are given via the Lyapunov stability theory and digital simulations are conducted to illustrate the effectiveness of the proposed controllers.