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In data opening and sharing, a trajectory privacy protection based on sensitive stay area replacement (SSAR) is proposed in order to improve the availability of protected trajectory while maintaining the same security. Firstly, the stay areas are extracted by analyzing the movement characteristics. Secondly, the sensitive stay areas are obtained according to the user-defined sensitive semantic positions. Then, the sensitive areas are constructed according to the user's privacy requirement needs to randomly select the substitution. Finally, part of the sampling positions in the sensitive area are reset. The parameter selection experiment and the comparison experiment with other schemes show that the trajectory similarity is improved by more than 35% in SSAR. That is to say, SSAR can greatly improve the availability of protected trajectory on the basis of ensuring the safety degree.

Titanium alloy (Ti) has been widely used in aerospace industry due to excellent mechanical properties and the demands of Ti parts with a high length-to-diameter ratio and a large diameter are increasing. However, deep hole drilling of large-diameter Ti holes is usually both time-consuming and cost-consuming due to a series of problems such as unfavorable chip removal, helical structure on the hole surface, poor hole precision and severe tool wear. This paper reports on the cutting mechanism and experimental results of low-frequency vibration-assisted single-lip drilling (LFVASLD) of large-diameter Ti holes (Ø17mm) for the first time. In this paper, a novel rotary low-frequency vibration device was developed and the vibration generation mechanism was analyzed. Thereafter, the material removal mechanism of LFVASLD was established. Then, the comparative experiments between LFVASLD and conventional single-lip drilling (CSLD) of Ti were conducted. The experimental results show that, compared with CSLD, LFVASLD can significantly prolong the drilling depth by 9 times due to reduced tool wear and alleviate helical structure on the hole surface due to the separated cutting mode. Furthermore, the influence of drilling parameters in LFVASLD on hole quality were also investigated. It is concluded that, the LFVASLD method is suitable for deep hole drilling of large-diameter titanium alloy and the developed rotary low-frequency vibration device can be used as a machine tool accessory to significantly improve the processing capacity in the industrial practice.