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A three-dimensional, vehicle-track coupled dynamics model has been developed that accurately reflects the dynamic performance of a high speed train during operation. The model includes novel elements that allow detailed consideration of the transmission system and axle box bearings. Within these novel elements a number of nonlinear factors have been modelled, including gear time-varying mesh stiffness, bearing stiffness, bearing clearance, and wheel-rail contact. The model has facilitated a detailed analysis of the vibration and temperature environment of the critical axle box bearing of high speed trains. The proposed model was extensively validated by comparing the results of the simulation with those of experimental tests. The temperature characteristics of the axle box bearing of the motor car and the trailer were analyzed and the resultant mathematical model was subsequently validated through long-term experimental field tests. Additionally, the relationship between vibration and temperature was analyzed during operation. The results indicated that the loads acting on the axle box bearing closest to the gearbox of the motor car (bearing 1) are significantly higher than those distant to the gearbox (bearing 2), the cause being differences in structural stiffness, which also lead to higher local temperatures. Moreover, the roller-outer raceway contact force and temperature of Bearing 1 was also higher than that of bearing 2. Conversely, when considering the trailer car, the dynamic performance and hence vibration and temperature environment of bearing 1 and bearing 2 were almost identical, this being a result of similarities in their structure and mounting arrangement. In summary, the work demonstrates that the temperature and vibration characteristics of the axle box bearings and their assessment can be used to aid in the effective design and maintenance of high-speed trains, together with the development of remote condition based monitoring (RCM) systems.

Wildfires could pose a significant danger to electrical transmission lines and cause considerable losses to the power grids and residents nearby. Previous studies of preventing wildfire damages to electrical transmission lines mostly analyze wildfire and power system security independently due to their differences in disciplines and cannot satisfy the requirement of the power grid for active and timely responses. In this paper, we have designed an integrated wildfire early warning system framework for power grids, taking prediction of wildfires and early warning of line outage probability together. First, the proposed model simulates the spatiotemporal process of wildfires via a geography cellular automata model and predicts when and where wildfires initially get into the security buffer of an electrical transmission line. It is developed in the context of electrical transmission line operating with various situations of topography, vegetation, wind and, especially, multiple ignition points. Second, we have proposed a line outage model (LOM), based on wildfire prediction and breakdown mechanisms of the air gap, to predict the breakdown probability varying with time and the most vulnerable poles at the holistic line scale. Finally, to illustrate the validation and rationality of our proposed system, a case study for a 500-kV transmission line near Miyi county, China, is presented, and the results under various wildfire situations are studied and compared. By integrating wildfire prediction into the LOM and alarming the holistic line breakdown probability along time, this paper makes a significant contribution in the early warning system to prevent transmission lines to be damaged by wildfires, illustrating the related breakdown mechanisms at the line operation level rather than laboratory experiments only. Meanwhile, the implementation of cellular automata model under comprehensive environmental conditions and simulation of the breakdown probability for the 500-kV transmission line could serve as references for other studies in the community. INDEX TERMS Cellular automata, electrical transmission lines, earning warning, wildfire.

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