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There is likely to be a demand to run high-speed trains in extreme cold weather conditions in the near future; therefore, it is important to study the change in the characteristics of the materials and components in an extreme cold environment and their effects on the vehicle system dynamics. Experimental research into the low temperature characteristics of a pantograph hydraulic damper was carried out in this study. The results show that low temperature causes an increase in damping forces, and when the temperature is above the boundary temperature range, most indices of the damping capability increase with the decrease of temperature; when the temperature is below the boundary temperature range, most indices decrease with the decrease of temperature. Key parameters are identified to obtain the theoretical description of low-temperature damping characteristics using a simplified-parametric damper model and the experimental data. A mathematical model of the pantograph–catenary system incorporating the pantograph damper model is then established to calculate the effect of the damper performance on the pantograph dynamics low temperatures. Simulation results show that the lowering performance of the pantograph deteriorates noticeably due to the unstable low-temperature damping characteristics, but the deterioration of the raising performance and contact quality of the pantograph due to the low-temperature characteristics of the damper are less obvious. The results obtained in this study are valuable for understanding the low-temperature characteristics of a hydraulic damper, and instructive in the optimal specification of the pantograph damper for high-speed trains running in cold weather conditions.

A new simplified parametric model, which is more suitable for pantograph–catenary dynamics simulation, is proposed to describe the nonlinear displacement-dependent damping characteristics of a pantograph hydraulic damper and validated by the experimental results in this study. Then, a full mathematical model of the pantograph–catenary system, which incorporates the new damper model, is established to simulate the effect of the damping characteristics on the pantograph dynamics. The simulation results show that large $$F_{\mathrm{const}}$$ (saturation damping force of the damper during compression) and $$C_{\mathrm{0}}$$ (initial damping coefficient of the damper during extension) in the pantograph damper model can improve both the raising performance and contact quality of the pantograph, whereas a large $$C_{\mathrm{0}}$$ has no obvious effect on the lowering time of the pantograph; the nonlinear displacement-dependent damping characteristics described by the second item in the new damper model have dominating effects on the total lowering time, maximum acceleration and maximum impact acceleration of the pantograph. Thus, within the constraint of total lowering time, increasing the nonlinear displacement-dependent damping coefficient of the damper will improve the lowering performance of the pantograph and reduce excessive impact between the pantograph and its base frame. In addition, damping performance of the new damper model would vary with the vehicle speeds, when operating beyond the nominal-speed range of the vehicle, the damping performance would deteriorate obviously. The proposed concise pantograph hydraulic damper model appears to be more adaptive to working conditions of the pantograph, and more complete and accurate than the previous single-parameter linear model, so it is more useful in the context of pantograph–catenary dynamics simulation and further parameter optimizations. The obtained simulation results are also valuable and instructive for further optimal specification of railway pantograph hydraulic dampers.

In order to collect energy from human activities, piezoelectric energy harvesters should have a flexible structure, low resonant frequency and wide frequency bandwidth. In this paper, the fabrication and characterization of a metal-based Pb(Zr,Ti)O3 (PZT) bimorph thick film energy harvester. PZT thick films were deposited on cantilever-shaped titanium (Ti) substrate via a dip-coating process. The electrical properties of the PZT films sintered at different temperatures were investigated. The nonlinear piezoelectric energy harvester has the following advantages: it is suitable for low frequency, weak vibration, and wide frequency bandwidth. The maximum open-circuit voltage of the piezoelectric energy harvester is 1.6 V and the output power is 0.85 μW with 150 kΩ load resistance at low resonant frequency of 17.6 Hz when the input vibration acceleration was 0.12 g. In addition, the frequency bandwidth is broadened from 0 to 8.4 Hz as the input acceleration increases from 0.05 g to 0.12 g. Keywords: Energy harvesting, PZT, Sintering temperature, Nonlinear vibration

Equivalent static wind loads (ESWLs) on cooling towers derived even by the refined multiple-mode dynamic algorithm such as the complete quadratic combination theory usually shows quite different types for various design targets. So, it is evitable to bring complex and burdensome calculation for structural design. To this problem, the improved multi-objectives ESWLs method was proposed by combining the wind vibration characteristics of large cooling towers itself. Through several numerical examples, the multi-objective ESWLs distribution characteristics were discussed, and its rationality of application in the cooling towers was also validated.

Interference factors (IFs) are commonly used to envelope various dynamic loading distributions due to wind-induced interference effects. However, those parameters are discrete in values for different evaluation criteria. Aiming at unifying cognitive distinction for series equivalent criteria about IFs, cooling tower groups with typical 6-towers arrangement were selected to conduct case studies by wind tunnel tests and numerical calculation, investigating interference effects among classical rectangular and rhombic arrangement. 25 kinds of IFs' definitions were totally compared basing on three index levels, namely loading, internal force and reinforcement ratio. Wind pressure measurements about 1:200 reduced-scale model were carried out in TJ-3 wind tunnel, corresponding 3D dynamic or static calculation were finished to analyse IFs. Main conclusions can be summarized, such as there are great distinctions about IFs’ value for different criteria, whose maximum may reach 42%, IFs’ variance coefficients in loading level would be the largest, and those in reinforcement level are the smallest, etc.