We have extended the semianalytic technique of Iyer and Will for computing the complex quasinormal frequencies of black holes, ω, by constructing the Padé approximants of the (formal) series for ω 2 . It is shown that for the (so far best documented) quasinormal frequencies of the Schwarzschild and Reissner-Nordström black holes the Padé transforms P 6 6 and P 6 7 are, within the domain of applicability, always in excellent agreement with the numerical results. We argue that the method may serve as the black box with the "potential" Q(x)as an input and the accurate quasinormal modes as the output. The generalizations and modifications of the method are briefly discussed as well as the preliminary results for other classes of the black holes.

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The article discusses the use of pivot bearing friction liners, made of selected materials, in railway freight wagons’ spherical centre bowls. Comparative studies on the effect of suspension dynamics on the equivalent stresses in the liner material were carried out using the finite element method and multibody simulation. The results show the magnitude and location of the highest stresses in the liner with varying input loads, friction coefficients and interacting materials. The analysis is a basis for a simulation method for predicting the fatigue life of the suspension friction liner placed in the centre bowl between the bogie frame and the vehicle body.

This paper investigates the influence of the models of dry friction suspension component used in the numerical simulation of freight car dynamics on the possible predictions related to safety against derailment. Moreover, the performance of the models is compared on the basis of simulation runtime. Three groups of static and dynamic models of friction are selected as three different approaches which are often utilized in popular multibody simulation tools. The models are used for the centre bowl friction joint between the car body and bogies. The friction torque in the centre bowl affects the rotational resistance of the bogie in motion relative to the car body and consequently influences the interaction forces between the wheels and rails. Simulation results of safety against derailment index obtained from the vehicle curving scenario suggest noticeable differences in predictions of the selected models of friction.