Automatic Dependent Surveillance - Broadcast (ADS-B), as the key component of next-generation air transportation system, becomes the replacement of secondary surveillance radar (SSR) since it will enhance air traffic control by requiring the aircraft periodically broadcast its geographical information. But the obstacle blocking the deployment of the promising ADS-B belongs to security concerns where ADS-B messages are all transmitted in the clear and can be forged and modified easily. The already proposals for ADS-B security refer to the privacy or integrity unilaterally, and all require the modification of existing ADS-B protocols. In this paper, we design ingeniously a solution for ADS-B security, by integrating carefully some recent specific crypto primitives, and then modifying properly them to adapt to ADS-B features. As opposed to previous methods, our solution is at the same time (1) lightweight for resource- constraint avionics devices and already congested data links, (2) highly-compatible to existing ADS-B protocols, (3) tolerating package loss for ADS-B broadcast data links. This makes our solution particularly practical and easy-deploying. Security analysis indicates that our solution can achieve confidentiality and integrity of ADS-B messages, and performance evaluation, based on the real-world ADS-B data, proves efficiency of our solution from cost of computation and communication. Furthermore, the deployment on a real airport environment demonstrates high compatibility of our solution.

Fatigue cracks caused by repetitive loads are one of the major threats to the structural integrity of civil infrastructure. Human inspection is the most common method for detecting fatigue cracks, but it is time-consuming, labor-intensive, and unreliable. In this paper, we propose a new vision-based fatigue crack detection and localization method that can detect the fatigue crack with marker-free and high precision using a consumer-grade digital camera. A motion tracking technology called optical flow algorithm is applied to the video for tracking the surface motion of the monitored structure under repetitive load. Then, a crack detection and localization algorithm based on optical flow information entropy are developed to search differential features at different video frames caused by the crack opening and closing. The proposed method’s precision is first validated by doing two experiments and then comparing its precision and efficiency to the existing crack detection methods, including image processing and digital image correlation. The results show that, when compared to the existing vision-based methods, the proposed method can accurately and efficiently identify the fatigue crack even when the crack is surrounded by other crack-like edges, covered by complex surface textures, or invisible to human eyes. In addition, based on the proposed methods, a practical application for calculating the stress intensity factor is given to track crack development.

The flow around wing 445.6 was modelled using Navier–Stokes equations and S-A model. The wing vibration and flow mesh deformation were computed using a fast dynamic mesh technology proposed by our own group. Wing 445.6 flutter was analysed through a strong coupling between the wing vibration and flow. The reduced flutter velocity was predicted and results are in good agreement with the experimental data. It is found that the subsonic flutter is mainly induced by the flow separation and the transonic and supersonic flutter are mainly caused by the oscillating shock wave and its induced flow separation. The positive aerodynamic work increases due to the oscillating shock wave when the subsonic flow becomes transonic reducing the flutter velocity. While the positive aerodynamic work induced by the oscillating shock wave decreases when the transonic flow becomes supersonic increasing the flutter velocity. That is why the transonic dip exists.

Damage can be identified using generalized flexibility matrix based methods, by using the first natural frequency and the corresponding mode shape. However, the first mode is not always appropriate to be used in damage detection. The contact interface of rod-fastened-rotor may be partially separated under bending moment which decreases the flexural stiffness of the rotor. The bending moment on the interface varies as rotating speed changes, so that the first- and second-modal parameters obtained are corresponding to different damage scenarios. In this paper, a structural damage detection method requiring single nonfirst mode is proposed. Firstly, the system is updated via restricting the first few mode shapes. The mass matrix, stiffness matrix, and modal parameters of the updated system are derived. Then, the generalized flexibility matrix of the updated system is obtained, and its changes and sensitivity to damage are derived. The changes and sensitivity are used to calculate the location and severity of damage. Finally, this method is tested through numerical means on a cantilever beam and a rod-fastened-rotor with different damage scenarios when only the second mode is available. The results indicate that the proposed method can effectively identify single, double, and multiple damage using single nonfirst mode.