## 1 Introduction
However, each of the assessment methods above has different formulations, and the ride comfort assessment parameters to be derived depend on how the acceleration data are measured and processed. It is, consequently, problematic to build a correlation among different ride comfort assessment methods, which is why research in this direction is scarce [1; 10; 13; 28; 29]. A reference paper, belonging to [PERSON] et al. [1], examines the relations among several evaluation methods--[PERSON]'s method, the statistical method according to the UIC 513 leaflet and the r.m.s. acceleration-based method as per ISO 2631. For this, a vibration model resulting from the frequency analysis and the statistical analysis of acceleration measurements in the railway vehicles is used. [PERSON] et al. [10] compared the level of ride comfort via two methods, namely the method based on the standard EN 12299 and [PERSON]'s method. The former method is used to evaluate the ride comfort in two positions, sitting and standing, and the latter to validate and compare the derived data. [PERSON] and [PERSON] [13] have set up a correlation among the comfort indices at the vertical vibrations corresponding to EN 12299 and [PERSON]'s method, based on the connection between the comfort sensation and the values of these indices. The strengths and limitations of the continuous comfort indices, mean comfort indices and the Sperling's index in three directions are examined in [PERSON] et al. 's paper [28]. Based on the experimental results, similarities and benefits among these ride comfort methods are examined and discussed. [PERSON] et al. [29] have studied and compared three methods for evaluating the ride comfort--equivalent level of vibrations, [PERSON] ride index, and several other methods included in EN 12299, based on the vibration data recorded by using an inservice tram--to find an optimum procedure for the tramway comfort evaluation. With the exception of reference [13], all the research presented above is based on experimental results. However, in the literature of review there are numerous researches developed on the basis of the ride comfort evaluation methods that use results obtained through numerical simulations. For instance, such studies concern the influence of the suspension [30; 31; 32; 33] of the carbody flexibility [34; 35], the suspended equipment [36; 37] or of the track [38; 39] upon the ride comfort, as well as the studies regarding the possibilities to improve the ride comfort of the railway vehicles [32; 33; 40; 41; 42; 43; 44; 45; 46]. In this paper, we analyzed two methods of evaluating ride comfort in the vertical direction, namely themean comfort method (according to standard EN 12299) and [PERSON]'s method, in an original manner, using the results of numerical simulations. The most important difference between the two methods lies in the frequency weighting function which takes into account the higher sensitivity of the human body to vertical vibrations. The ride comfort assessment based on results from numerical simulations involves the representation of the railway vehicle through an equivalent mechanical model, which will consider the important factors affecting the behavior of vibrations of the vehicle in the vertical plan. One of these factors is the structural flexibility of the vehicle carbody. For the high-speed trains, the ride comfort can be strongly influenced by the resonance phenomenon of the flexible vibration modes in the carbody--mainly the first vertical bending mode, which is more pronounced in the center of the carbody [47; 48]. Therefore, to assess the ride comfort performance of the railway vehicles, it is consequently necessary to adopt a 'flexible carbody' type model. Another important element, which affects the behavior of vibrations in the vertical plan of the railway vehicle carbody, is the longitudinal traction system between the carbody and the bogie, through which the pitch vibrations of the bogie are conveyed to the carbody to excite its first vertical bending mode.