Applied Mechanics and Materials Vol. 643

Abstract: The directional stability and control is crucial for the low-speed flight of a flying-wing aircraft. The split drag-rudders are well known devices used to provide directional stability and control in a flying-wing aircraft. As opposed to conventional rudders, the control efficiency of split drag-rudders is typically low for small deflection-angles and the influence on yawing moment is nonlinear. Such characteristics limit the control capability of split drag-rudders at low speed flight with large angle-of-attack. In this paper, a simple method is presented to improve the control efficiency of split drag-rudders at low speed flight with large angle-of-attack. The method is based on a strictly differential configuration of split drag-rudders which operates around a certain variable bias. The bias can be varied according to different flight conditions in order to achieve desired performance. The CFD simulation results are presented in support of this concept. Results also show that the proposed configuration has linearizing effects on yawing moment vs. deflection curves, which may prove helpful in control system design process. The possible control reversal in yaw at large angle of attack can also be avoided with this method.

Abstract: The next-generation semiconductor lithography equipment needs a suitable actuator to meet the requirement of high-speed, high-acceleration and high-precision. Reluctance actuator, which has a unique property of small volume, low current and can produce great force, is a very suitable choice. One of the major application challenges of reluctance actuator is the hysteresis of the force, which has a nonlinear relationship with respect to the current and is directly related to the final accuracy in the nanometer range. Therefore, it is necessary to study the control method for the hysteresis in reluctance force. This paper proposes a hysteresis control configuration for the current-driven variable reluctance actuator with hysteresis using the adaptive multilayer neural network (MNN), which is used as a learning machine of hysteresis. The simulation results show that the proposed method is effective in overcoming the hysteresis.

Abstract: Due to engine performance, fuel economy and emission performance are closely related with its transient air-fuel ratio, so the research of the engine air-fuel ratio control strategy is particularly important. The control strategies for neural network control, fuzzy control are introduced systemically, which can be well applied to the complicated nonlinear control system. The analysis compares the different control strategies in the role of air-fuel ratio control system, the transient air-fuel ratio control for the future to provide certain reference basis.

Abstract: This paper briefly introduced the concept and technology of MEMS. It analyzed the applications of MEMS units、MEMS sensors in the field of aerospace. The importance and unique advantages of MEMS technology play an irreplaceable role in high-tech industries. Finally, this paper discussed the development of MEMS and provided direction for further study of MEMS technology.

Abstract: To use C to build the simulation process in PSCAD, directing current control algorithm by using dq0 transform, the C language code of simulation can be directly applied to the actual SVG controller. The PI parameters can directly guide the field set, avoiding the complicated scene setting.

Abstract: In this paper, we study the stability properties of a general class of nonautonomous discrete-time switched nonlinear systems. The switched systems consist of stable and unstable subsystems. Based on Lyapunov functions, some sufficient conditions for uniform stability, uniform asymptotic stability and uniform exponential stability are established.

Abstract: In this paper, we study the strict practical stability for the discrete hybrid systems in terms of two measures. Using Lyapunov-like functions, we obtain some comparison theorems first and then by them get a sufficient condition on the strict practical stability of the hybrid system.

Abstract: In this paper, the process of the developments and changes of the network intrusion behaviors were analyzed. An improved epidemic spreading model was proposed to study the mechanisms of aggressive behaviors spreading, to predict the future course of an outbreak and to evaluate strategies to control a network epidemic. Based on Artificial Immune Systems, the concepts and formal definitions of immune cells were given. And in this paper, the forecasting algorithm based on Markov chain theory was proposed to improve the precision of network risk forecasting. The data of the Memory cells were analyzed directly and kinds of state-spaces were formed, which can be used to predict the risk of network situation by analyzing the cells status and the classification of optimal state. Experimental results show that the proposed model has the features of real-time processing for network situation awareness.

Abstract: Aiming at the situation where the double-threshold detection has been widely used without complete mathematical proof and condition of application, this paper proves its correctness under the circumstance of spectrum sensing, and circulates the condition where this method can work. The proof and simulation show that, comparing with traditional energy detection, this method can increase the probability of detection by 27% to 42% at most when the SNR is between-15dB and-2dB, while the probability of false alarm is increased by less than 2%.

Abstract: Applying Multiple-Input Multiple-Output (MIMO) technology in terrestrial wireless networks can obtain large capacity gain. Therefore, MIMO technology is widely applied in satellite communication system, in which orbital positions are increasingly crowded and frequency resources are of shortage. This paper attempts to research on channel capacity in 2×2 dual-polarized MIMO mobile satellite (DMMS) system and discovers that when XPD (Cross Polarization Discrimination) is above zero, the channel capacity increases approximately linearly with the XPD within certain range. Adding Ricean factor K in consideration of its special features, the system’s capacity increases with the Ricean factor K. Simulation results demonstrate that the application of MIMO technology in satellite mobile communication system can improve the channel capacity significantly, providing great support for the development of future satellite MIMO technology.