Insulation failure is a crucial failure mode of traction motors. Insulation deteriorates under both fatigue load and shock. This paper focuses on proposing an optimal insulation condition-based maintenance strategy. By combining the information obtained from periodic inspections with historic life information, an integrated model of time-based maintenance and condition-based model is proposed, in which random shocks following Poisson process are also taken into account. In this model we define that insulation has three states: normal state, latent failure state, and functional failure state. Normal state and latent failure state differ in their operating cost, proneness to functional failure, and survival probability under extreme shocks. Preventive maintenance (PM) will be launched if an inspection result exceeds the threshold or if the operating time reaches the critical age. One operating cycle ends as soon as a preventive maintenance or a corrective maintenance is completed. Moreover, an optimization model is established, which takes minimal cost per unit time as the objective, and inspection interval and critical age as the optimization variables. Finally, a numerical example illustrates the analytic results.

This paper presents a combined dynamic parameter model (DPM) of a high speed train permanent magnet traction system using a dynamic reluctance mesh model and MATLAB Simulink. First, the dynamic reluctance model of the permanent magnet synchronous motor is introduced. Then the combined models of the traction system under i_d=0 and maximum torque per ampere control are built. Simulations using both constant parameter models and DPM models are carried out. The speed and torque characteristics are obtained. The results confirm that the DPM model provides higher accuracy without much sacrifice of time consumption or computation resource.

Overheating of permanent magnet (PM) machines has become a major technical challenge as it gives rise to magnet demagnetization, degradation of insulation materials, and loss of motor efficiency. This paper proposes a state-of-the-art cooling system for an axial flux permanent magnet (AFPM) machine with the focus on its structural optimization. A computational fluid dynamics (CFD) simulation with thermal consideration has been shown to be an efficient approach in the literature and is thus employed in this work. Meanwhile, a simplified numerical approach to the AFPM machine with complex configuration in 3D consisting of conduction, forced convection, and conjugate heat transfer is taken as a case study. Different simplification methods (including configuration and working conditions) and two optimized fans for forced convection cooling are designed and installed on the AFPM machine and compared to a natural convection cooling system. The results show that the proposed approach is effective for analyzing the thermal performance of a complex AFPM machine and strikes a balance between reasonable simplification, accuracy, and computational resource.

High strength and high conductivity Cu-based materials are key requirements in high-speed railway and high-field magnet systems. Cu-Fe alloys represent one of the most promising candidates due to the cheapness of Fe compared to Cu-Ag and Cu-Nb alloys. The high strength of Cu-Fe alloys primarily relies on the high density of the Cu/Fe phase interface, which is controlled by the co-deformation of the Cu matrix and Fe phase. In this study, our main attention was focused on the deformation behavior of the Fe phase using different scales. Cu-2.5% Fe-0.2% Cr (in weight) and Cu-6% Fe alloys were cast, annealed, and cold drawn into wires to investigate their microstructure and properties evolution. Cu-6% Fe contains Cu matrix and Fe, which become the primary particles in the micrometer scale after solution treatment. Cu-2.5% Fe-0.2% Cr contains Cu matrix and Fe precipitate particles in a nanometer scale after solution and aging treatment. The Fe primary particles were elongated and evolved into ribbons in a nanometer scale while the Fe precipitate particles were hardly deformed even at a drawing strain of 6. The reason for the unchanging characteristics of Fe precipitate particles is due to the size effect and incoherent phase interface of Cu matrix and Fe precipitate particles. The strength of both Cu-6% Fe and Cu-2.5% Fe-0.2% Cr alloys increases with the increase in the drawing strain. The electrical resistivity of Cu-6% Fe gradually increases and that of Cu-2.5% Fe-0.2% Cr keeps almost constant with the increase in the drawing strain.

A new and simple approach is presented to analyze the time effect in the settlement of single pile and the distributions of pile shaft resistance and pile axial force. First, the viscosity of soil is considered by using a linear damper, and the nonlinear elasticity of pile lateral soil and pile end soil are simulated by using a hyperbola model and idealized elastoplastic model, respectively. Then, the settlement of the pile head, shaft resistance, and axial force along the pile are derived by virtue of a wave equation analysis program based on traveling wave decomposition. Based on the solutions, a parametric study has been undertaken to investigate the influences of the parameters of a pile-soil system on the settlement behavior of a single pile. Finally, the calculated results are compared with the measured results to demonstrate the effectiveness and accuracy of the proposed approach. Note that the presented solution allows for a good prediction of the settlement behavior of a single pile and can provide a reference for the preliminary design of a pile foundation.

It is difficult to establish a constitutive model of damage for rock materials due to the complex meso-mechanism of the rock deterioration process. In this paper, by analysis of the damage mechanism, the reason for the existence of a rock damage threshold is explained and we conclude that damaged rock elements of micro scale can still bear stress. The correlation between damaged and undamaged elements is examined in relation to stress distribution. Rocks under different initial conditions can be defined as undamaged materials with different properties, to avoid the issue of the solution of the undamaged condition and to simplify the damage model. On the basis of the Mohr-Coulomb criterion and theories of continuum damage and statistical mechanics, a constitutive model of rock materials affected by the load-bearing capacity of damaged elements under triaxial compression is established. Compared with previous experimental data and theoretical results, we show that this model can reflect the stress-strain relationship of the whole process of rock failure. In particular, the description of the strain softening stage after peak strength is proved to be more reasonable. Programming of the constitutive model applied to stability analysis of the Qingdao subway station is achieved by secondary development of FLAC^3D. The computing results compare very well with field monitoring data, indicating that the constitutive model of damaged rock can reflect the deterioration effect of weathered rock at the site. This constitutive model of rock damage may provide a useful reference for practical application.

The aero-elastic instability mechanism of a tensioned membrane structure is studied in this paper. The response and wind velocities above two closed-type saddle-shaped tensioned membrane structures, with the same shape but different pre-tension levels, were measured in uniform flow and analyzed. The results indicate that, for most wind directions, several vibration modes are excited and the amplitude and damping ratio of the roof slowly increase with the on-coming flow velocity. However, for particular wind directions, only one vibration mode is excited, and the amplitude and damping ratio of the vibration mode increase slowly with the on-coming flow velocity. The aero-elastic instability is caused by vortex-induced resonance. On exceeding a certain wind speed, the amplitude of the roof vibration increases sharply and the damping ratio of the vibration mode decreases quickly to near zero; the frequency of the vortex above the roof is locked in by the vibration within a certain wind velocity range; the amplitudes of the roof in these wind directions reach 2–4 times the amplitudes for other wind directions. The reduced critical wind speeds for the aero-elastic instability of saddle-shaped membrane structures at the first two modes are around 0.8–1.0.

Porous polymers are very suitable materials for the adsorption of organic pollutants due to their abundant pores and organic frameworks in aqueous solution. However, their recovery from treated pollutant is difficult, and thus, their application is limited. A facile strategy to synthesize reusable magnetic porous microspheres (MPMS) of Fe₃O₄/poly(methylmethacrylate (MMA)-co-divinylbenzene (DVB)) is described in this paper. The magnetic microspheres were synthesized by suspension copolymerization. MMA was used as a monomer, DVB was used as a crosslinker, and the magnetic fluid was added to the organic phase. The morphology of MPMS was observed by scanning electron microscope (SEM) and other properties were tested by superconducting quantum interference device, Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and nitrogen sorption-desorption techniques. The synthesized MPMS possessed a high specific surface area using toluene as a porogen. It was further found that the ratio of DVB to MMA, the ratio of porogen to monomer, and the type of porogen all affected the specific surface area and the morphology of the microspheres. Furthermore, the microspheres were applied to remove Rhodamine B from its aqueous solution. The results showed that the microspheres possessed good adsorption capacity for Rhodamine B. This result was due to the porous structure, polar groups, and superparamagnetic characteristic of the synthesized microspheres.

The original version of this article unfortunately contained two mistakes.