When machining a small hole with high aspect ratio in EDM, it is hard for the flushing liquid entering the bottom gap and the debris could hardly be removed, which results in the accumulation of debris and affects the machining efficiency and machining accuracy. The assisted ultrasonic vibration can improve the removal of debris in the gap. Based on dynamics simulation software, Fluent, a three-dimensional (3D) model of debris movement in the gap flow field of EDM small hole machining assisted with side flushing and ultrasonic vibration is established in this paper. The laws of different amplitudes and frequencies and different aspect ratios on debris distribution and movement are quantitatively analyzed. The motion height of debris was observed under different conditions. The research results show that periodic ultrasonic vibration can promote the movement of debris, which is beneficial to the removal of debris in the machining gap. When compared to traditional small hole machining in EDM, the debris in the machining gap were greatly reduced, which ensures the stability of the machining process and improves the machining efficiency.

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A phase demodulation method specially developed for direct detection φ-OTDR is proposed and demonstrated. It is the only method to date that can be used for phase demodulation based on pure direct detection system. As a result, this method greatly simplifies the system configuration and lowers the cost. It works by firstly deriving a pair of orthogonal signals from the single-channel intensity and then realizing phase demodulation by means of IQ demodulation. Different forms of PZT induced vibration are applied to the fiber and the phase is correctly demodulated in each case. The experiment results show that this method can effectively perform phase demodulation with extremely simple system configuration.

In view of the braking process for the megawatt wind turbine brakes, considering the geometric and motion characteristics of brake pads and brake discs, a displacement gradient circulation method is put forward in this article, to resolve the deviation of coupling results caused by the difference of friction effect along the radial/circumferential direction of brake disc, and the thermal-structural coupling analysis of friction pair during the braking process is carried out. A three-dimensional model of transient heat transfer for brake friction pair is built based on the Abaqus software. The heat flow density is loaded by the displacement gradient circulation method, which is used to calculate the frictional heat flow during the braking process. The analysis results show that along the circumferential direction of the brake disc the temperature distribution in the friction zone is non-uniform and the temperature starting from the contact position of the brake disc and the brake pad decreases along the counterclockwise direction. The thermal stress caused by the temperature field during the braking process is the main factor causing the brake disc/pad failure. The effectiveness of the method and the model is verified by the designed inertia braking experiments. The analytical method proposed in this article provides a reference for simulating the friction braking process of large-size disc brakes.