The dynamic spin modes observed in magnetic vortex structures are shown to depend strongly on the nature of the initial excitation by a transient pulse field. In submicrometer-sized Permalloy disks, when a uniform perpendicular transient field is used to perturb the magnetization, radial standing-wave modes are excited; whereas if an in-plane transient field is used, angular or azimuthal modes are formed. The existence of the vortex core is responsible for a frequency splitting of the azimuthal modes, as demonstrated through comparison to micromagnetic simulations of a ring geometry

2015): Nonlinear modelling of high-speed catenary based on analytical expressions of cable and truss elements, Vehicle System Dynamics: International Journal of Vehicle Mechanics and Mobility,Due to the intrinsic nonlinear characteristics and complex structure of the high-speed catenary system, a modelling method is proposed based on the analytical expressions of nonlinear cable and truss elements. The calculation procedure for solving the initial equilibrium state is proposed based on the Newton-Raphson iteration method. The deformed configuration of the catenary system as well as the initial length of each wire can be calculated. Its accuracy and validity of computing the initial equilibrium state are verified by comparison with the separate model method, absolute nodal coordinate formulation and other methods in the previous literatures. Then, the proposed model is combined with a lumped pantograph model and a dynamic simulation procedure is proposed. The accuracy is guaranteed by the multiple iterative calculations in each time step. The dynamic performance of the proposed model is validated by comparison with EN 50318, the results of the finite element method software and SIEMENS simulation report, respectively. At last, the influence of the catenary design parameters (such as the reserved sag and pre-tension) on the dynamic performance is preliminarily analysed by using the proposed model.

In most previous works, liquid hold-ups were studied by using a cold model of a fixed bed soaked prior to experiments. However, they did not consider that the dripping zone of a blast furnace is saturated with liquids or with evenly distributed droplets. In the present study, the characteristics of liquid hold-ups and liquid flow were investigated by using a one-dimensional cold model of a fixed bed soaked and unsoaked prior to experiments (initially soaked and unsoaked beds). Packed balls were five kinds, the diameters (D p ) of which ranged from 5.4 to 30 mm. Tap water was used as liquid. Contact angles (q) for these particle/liquid systems were about 70°and 10°for fluorine-coated particles and non-coated particles, respectively.Although, under bad wettability condition (q Լ 70°), total and static hold-ups for initially unsoaked bed packed with small balls are remarkably smaller than those for initially soaked bed, the difference in their hold-ups between initially unsoaked and soaked beds decreases with increasing ball size in the bed. In initially soaked bed, total and static hold-ups increase monotonically as ball size decreases, which means the specific surface area increases. On the other hand, in initially unsoaked bed, total and static hold-ups under bad wettability condition indicate maximum values at about D p ϭ10 mm and decrease abruptly in proportion to a decrease in particle size, despite an increase in the specific surface area. Only restricted liquid droplets and/or liquid rivulets are formed within the packed bed with good wettability condition (qԼ 10°) for initially unsoaked bed, nevertheless liquid is easy to spread out on the solid surface. The influence of the initial bed condition, soaked or unsoaked bed, on liquid hold-ups is great under bad wettability condition.KEY WORDS: ironmaking; blast furnace; dripping zone; fixed bed; liquid hold-ups; particle/liquid wettability; initially soaked and unsoaked beds.

Due to its long-span structure and large flexibility, an electrified railway catenary is very sensitive to environmental wind load, especially the time-varying stochastic wind, which may lead to a strong forced vibration of contact line and deteriorate the current collection quality of the pantograph–catenary system. In this paper, in order to study the wind-induced vibration behavior of railway catenary, a nonlinear finite element procedure is implemented to construct the model of catenary, which can properly describe the large nonlinear deformation and the nonsmooth nonlinearity of dropper. The spatial stochastic wind field is developed considering the fluctuating winds in along-wind, vertical-wind, and cross-wind directions. Using the empirical spectra suggested by Kaimal, Panofsky, and Tieleman, the fluctuating wind velocities in three directions are generated considering the temporal and spatial correlations. Based on fluid-induced vibration theory, the model of fluctuating forces acting on catenary are developed considering the spatial characteristics of catenary. The time- and frequency-domain analyses are conducted to study the wind-induced vibration behavior with different angles of wind deflection, different angles of attack, as well as different geometries of catenary. The effect of spatial wind load on contact force of pantograph–catenary system is also investigated.

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With the rapid development of high-speed railways, fault detection and diagnosis for traction transformers are more and more important, and the detection method with high accuracy is the key to assure the normal operation of the traction power supply system. A method based on kernel principal component analysis (KPCA) and random forest (RF) is proposed to diagnose the traction transformer faults in this study. In this method, KPCA can obtain more fault characteristics in high-dimensional space through the non-linear transformation of the original data with dissolved gas analysis, and RF can utilise these characteristics to construct the classifier group. The experimental results show that the combination of KPCA and RF can effectively extract more characteristics of traction transformer faults to construct the classifiers with better performance, which contributes to the higher accuracy in traction transformer fault diagnosis and gets better anti-jamming performance.

In high-speed rail operations, the irregularity of the overhead system is a typical disturbance that affects the pantograph-catenary interaction performance. The existing methods, which treat the contact wire irregularities as hard spots, overestimate the negative effect of the irregularities on the contact force, leading to conservative results. In this work, a more accurate methodology aiming to include the effect of contact wire irregularities in the assessment of the pantographcatenary dynamic performance is proposed. Measured contact wire irregularity data, collected from the Chinese high-speed network, is added to the initial configuration of the catenary model, through a developed Target Configuration Under Dead-loads (TCUD) method. This approach is used here to investigate the effect of the contact wire irregularities on the contact forces. The results indicate that the catenary imperfections have a direct impact on the pantograph-catenary interaction, leading to an increment of the contact forces amplitude, an increase of their standard deviation and an expansion of the contact forces range. A frequency analysis of the results shows that the contact wire irregularity increases the Power Spectral Density (PSD) peaks of the contact force at specific frequencies relevant to the span length and to the dropper spacing.

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