Information Entropy Analysis of a PIV Image Based on Wavelet Decomposition and Reconstruction.

In particle image velocimetry (PIV) experiments, background noise inevitably exists in the particle images when a particle image is being captured or transmitted, which blurs the particle image, reduces the information entropy of the image, and finally makes the obtained flow field inaccurate. Taking a low-quality original particle image as the research object in this research, a frequency domain processing method based on wavelet decomposition and reconstruction was applied to perform particle image pre-processing. Information entropy analysis was used to evaluate the effect of image processing. The results showed that useful high-frequency particle information representing particle image details in the original particle image was effectively extracted and enhanced, and the image background noise was significantly weakened. Then, information entropy analysis of the image revealed that compared with the unprocessed original particle image, the reconstructed particle image contained more effective details of the particles with higher information entropy. Based on reconstructed particle images, a more accurate flow field can be obtained within a lower error range.

Dual-terminal decentralized event-triggered control for switched systems with cyber attacks and quantization.

This article concerns dual-terminal event-triggered communication and decentralized control of switched systems that are the target of cyber attacks. Due to different properties of physical system, this system uses decentralized communication channels to transmit feedback data. In order to make efficient use of communication resources in each channel, the information sent by the sub-system needs to meet the given event-triggering conditions before it can be released. Moreover, the quantization is employed in both sides of the controller to further improve the data transmission efficiency. Then, considering that the triggered and quantified data are affected by dual-terminal cyber attacks, the event-triggered closed-loop switched (CLS) systems under attacks are derived. Furthermore, by utilizing average dwell time (ADT) technique and piecewise Lyapunov function (LF) method, sufficient conditions are given to ensure that the event-triggered CLS systems subject to dual-terminal cyber attacks are globally exponentially stable (GES). Accordingly, the design conditions for the gains of event-triggered dynamic output feedback (DOF) controllers and the parameters of decentralized event-triggering mechanisms (DETMs) are presented. Finally, simulations for verifying the system stability with and without cyber attacks are given.