# Effect of the Anti-Yaw Damper on Carbody Vertical Vibration and Ride Comfort of Railway Vehicle
## 1 Introduction  
Duringtrain travel, passenger comfort can be affected by several factors, some due to the movement of the railway vehicle, such as vibrations and noise, while others coming from the environmentalconditions inside the vehicle--temperature, humidity and airspeed, lighting, or the interior fittings and decor (for instance, the shape and placement of chairs) [1; 2; 3]. Among all factors affecting the passengers' comfort, vibrations are paid special attention, as their effect upon the human body is very important [4; 5]. As a function of vibrations intensity, direction and frequency value they occur at, as well as the exposure time, vibrations can perturb the comfort and the ability of passengers to conduct certain sedentary activities and even their health condition. Generally, the vibrations of the railway vehicle are considered to be the main factor in determining the ride comfort [1; 2; 3; 6; 7; 8]. The railway vehicle vibrations are mainly caused by track irregularities [9; 10; 11; 12; 13]. The track geometric irregularities mainly come from construction imperfections, track exploitation, changes in infrastructure due to the action of environmental factors or soil movements [14] and also the irregularities in the rolling surfaces of railway rails. To these, the discontinuity of the rails are added--joints, switches and crossings. Rolling on a track with irregularities generates vibrations on the wheelsets that are transmitted to the bogies and further to the carbody, by means of the suspension and the connecting elements between the bogie and the carbody. To achieve good ride comfort, these vibrations have to be suppressed, aside comfort is negatively affected by high accelerations in the carbody [15]. The topic of reducing the vertical vibrations in the carbody [15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26] and the improvement of ride comfort [27; 28; 29; 30] is a research matter of high interest, especially for the lightweight carbody of the high-speed vehicles. A lighter weight of the carbody significantly contributes to a higher speed, lower energy consumption, reduction in the ground vibration, and construction-cost saving [31; 32]. The lighter the vehicle carbody, the higher its flexibility that will thus facilitate an easy excitation of the carbody structural vibrations to harm the ride comfort. Even though the carbody structural vibrations are rather complex, the greatest influence upon ride comfort comes from the first carbody vertical bending mode [33] whose frequency usually ranges from 6 to 11 Hz, an interval where the human body shows a higher sensitivity to vertical vibrations. The railway vehicle modelling is the starting point of all the theoretical research studies regarding the means to reduce the vertical vibrations of the carbody and to improve the ride comfort. In principle, the mechanical model of the railway vehicleis obtained by a simplified representation of the railway vehicle, while taking into account the important factors affecting the behavior of vibrations of the vehicle. One of these factors is the structural flexibility of the vehicle carbody, a reason for which the carbody is always represented by a \"flexible carbody\" [34; 35] type model. The \"flexible carbody\" type models vary from Euler-Bernoulli [11; 19; 23; 24] or Timoshenko [10; 36] beams, to structure-typetridimensional models [31], multi-body models [27], models based on the finite element method [33] or combinations of models based on multi-body systems and the finite element method [37]. Other elements that influence the vertical vibration behavior of the railway vehicle are the longitudinal connecting elements between the bogie and the carbody, such as traction devices and anti-yaw dampers, albeit more rarely included in the vehicle model. The authors of this paper have introduced the longitudinal traction system between the carbody and bogie in the vehicle model as a Kelvin-Voigt system in several pieces of researches.