Pier settlement causes deformation of bridge structures, and further distorts the track structures placed on bridge decks, which may greatly affect the service life of the tracks and safe operation of trains. This study analyzes track stresses and vehicle dynamic responses in train–track–bridge system with pier settlement and determines the pier settlement safe value for high-speed railways with China Railway Track System (CRTS) II slab tracks. First, a detailed train–track–bridge dynamic model is established based on the train–track–bridge dynamic interaction theory. Verified with field experimental results, the model is utilized to calculate the dynamic responses of the vehicle–track–bridge system with different pier settlement values. Finally, the safe value of the pier settlement in the CRTS II slab track railway line is determined according to the limit of the vehicle dynamic indicators and the structural stresses of tracks. The results show that the vertical acceleration of the car body is more sensitive to pier settlement among all the vehicle dynamic indicators. Structural stresses of tracks caused by pier settlement appear at the positions of the pier with settlement and its two adjacent piers. The effect of train loads on the track stresses is much smaller than that of the pier settlement. It is important to adopt the structural stresses of tracks as the evaluation criteria of the pier settlement safe value than the vehicle dynamic indicators. Taking the effects of the bridge pier settlement, the vehicle load, the prestress effect, and the self-weight into consideration, the pier settlement safe value for the high-speed railway lines with the CRTS II slab track is 11.5 mm.

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In order to evaluate the nonlinear performance and the possible damage to rubber-bearings (RBs) during their normal operation or under strong earthquakes, a simplifi ed Bouc-Wen model is used to describe the nonlinear hysteretic behavior of RBs in this paper, which has the advantages of being smooth-varying and physically motivated. Further, based on the results from experimental tests performed by using a particular type of RB (GZN110) under different excitation scenarios, including white noise and several earthquakes, a new system identifi cation method, referred to as the sequential nonlinear leastsquare estimation (SNLSE), is introduced to identify the model parameters. It is shown that the proposed simplifi ed BoucWen model is capable of describing the nonlinear hysteretic behavior of RBs, and that the SNLSE approach is very effective in identifying the model parameters of RBs.

Electromagnetic railguns have an advantage over traditional chemical propulsion weapons, in that the projectile can be accelerated to extremely high speeds and effective damage can be achieved. However, during the launch from an electromagnetic railgun, the ammunition will be subject to a harsh environment, including very strong and violently changing electromagnetic fields, high-g acceleration impact, high temperatures, and so on; and thus, the reliability of the fuze is threatened, and the safety and damage effectiveness of the ammunition will be seriously degraded. In this paper, the harsh environment during the launch process is first reviewed, including the experimental data, the modeling, and simulation of the multiphysics fields. In particular, the coupling effect of these multiphysics fields are revealed, which aggravates the extreme environment. Furthermore, this paper reviews the protection of fuzes against strong magnetic fields and high-g impacts from three aspects, namely, materials, devices, and systems, and presents prospects for future research. This review will guide studies on the protection of fuzes and the stability of ammunition, as well as promote the effectiveness of electromagnetic railguns.INDEX TERMS Electromagnetic launching, fuze, reliability, harsh environment of multiphysics fields, electromagnetic shielding, anti-high-g impact technology.

Electromagnetic propulsion technology has important applications in military equipment such as electromagnetic rail guns. The extremely harsh multiphysics environment during electromagnetic propulsion is the key problem that now restricts its practical application. Most previous modeling studies have neglected or set overidealized approximations for the coupling effects between different physics fields, resulting in large deviations between simulated and actual results. In this paper, the multi-field coupling dynamic model of the electromagnetic propulsion process is established. Based on this model, the dynamic changes of the armature's speed, current distribution and temperature distribution during the electromagnetic propulsion process are effectively simulated, and some characteristics of these distributions are different from the previous uncoupled model. Furthermore, the physical mechanism behind these special distribution features is revealed, and the significance of the nonideal factors such as the piezoresistive effect of contact resistance and friction effect of the contact interface on the electromagnetic propulsion are analyzed. Therefore, a feasible path for the simplification of the multiphysics model and the relief of the extreme environment is revealed, which will greatly promote the practical application of electromagnetic propulsion technology. INDEX TERMS Current distribution, current skin effect, dynamic multi-field coupling model, electromagnetic propulsion, temperature distribution.