PSI - Issue 37

Rogério Lopes et al. / Procedia Structural Integrity 37 (2022) 81–88 R. F. Lopes et al./ Structural Integrity Procedia 00 (2019) 000 – 000

82 2

power packs requires deeper design considerations. It demands further improvements in the natural modes of vibration that in classical design solutions (engine and power units under the vehicle floor platform) were not so prominent (An 2020). The low percentage of accidents registered in bus transportation can lead to a decreasing trend of the responsible entities. Subsequently, it is required to prevent any eventual accident which might be caused by human, such as meteorological or mechanical breakdowns, existing for this effect components that act actively on the vehicle or passively on the passenger (Cafiso, Di Graziano, and Pappalardo 2013). In this paper, the behavior of an articulated passenger vehicle is studied through numerical analysis using Finite Element Method (FEM) (Guosbeng 1997; Bertolini 1998). A modal analysis is undertaken to determine the dynamic behavior of the vibration frequency modes (Fu and He 2001). The structural dynamics of vehicles can be modelled by different types of degrees of freedom (DOF), integrated in extremely complex models, and employing equations with several DOF being time-integrated. Several authors have studied the modal parameters of the system by choosing the natural frequencies of the aforementioned system to obtain a more realistic approximation behavior. Some authors rely on experimental techniques in order to evaluate the system’s stiffness and damping characteristics (Oktav 2016; He and Fu 2001). Currently, there is a greater reliance on the numerical methods that allow the model simplification, and the insertion of a wide variety of parameters, both external and internal factors yielding fairly reliable results. It is possible to find some research works in the literature addressing the influence of vibrational dynamics by checking the response behaviour. Sun et al. (Sun et al. 2016) and Hosseini et al. (Hosseini et al. 2013) developed new trends in the vehicle structure design through computational studies on the natural vibrational frequencies in coupled analyses of body frame and chassis of railway vehicles and trucks. Saran et al. (Saran et al. 2017) used modal analysis, focused on the study of airplane wing damage in order to prevent it. Aiming the performance improvement of a vehicle, Haryanto et al. (Haryanto et al. 2018) studied a potential weight reduction using modal analysis. With this technique, they could achieve a reduction about 8%, without any significant modification on the vehicle characteristics. Furthermore, several studies have been performed in the field of modal analysis on the vehicles, c.f. (Rodrigues et al. 2015; Anderson and Mills 1972; Danielsson and Cocaña 2015). The resource of the vibration analysis theory is intended to study the effect of dynamic forces on vehicles for the most diversified types of transport. However, there are few associated studies linked to public transportation mainly buses, narrowing more the focus to articulated vehicles where the front body is the operating module with driver/powered unit, while the rear module is the load carrier trailer. Both modules are interconnected by an articulation with suitable mechanical features, that gives the bus ability to make sharp turns more easily than a single seater bus would with an equal length (Vasko et al. 2018). This type of transport includes a larger passenger capacity, which is very helpful for large densely populated cities. Szumilas et al. (Vasko et al. 2018) studied the dynamic behaviour of articulated vehicles. They analysed the behaviour of the damping action at the tractor/trailer connection joint. A hydraulic damping system was developed that could be monitored and controllable. As a result, the stability of the vehicle was severely affected by variations of the damping coefficient and the vehicle velocity. Zhang et al. (Zhang, Khajepour, and Huang 2018) proposed a model that could be applied to various types of buses with multiple axles linked by an articulation. It aimed at development a unified model allowing the study of different configurations, producing a research tool as crucial resource and usable potential. Therefore, it would be beneficial for the dynamics behaviour of these types of vehicles promoting a potential development of autonomous transports covering any multi-axle vehicle. Dang et al. (Dang and Kovanda 2014) carried out a study on a dynamic model of an articulated bus being linear. It used a set of simplifications in order to present the trajectory of the vehicle through Matlab-Simulink. Croccolo et al. (Croccolo, De Agostinis, and Vincenzi 2011) dealt with the study of the structural analysis of the articulated bus chassis using solid and shell FEM models. Their study included a broad spectrum of loading perspectives in order to predict the vehicle’s behaviour and to avoid potential damages. Variational fields regarding stress, deformation and displacement were obtained for the tractor and trailer unit. The outcome of this study provided a structural key factor for the bus frame manufacturers. As presented so far, several authors have carried out studies on the transport sector, in particular by means of modal analysis, either via numerical or analytical methods. From an analytical standpoint, it is a demanding process requiring technical details due to the large number of DOF. Nevertheless, this study contributed to numerically describe the modal behaviour of articulated urban buses under external conditions. Results are achieved for the passengers’ full and empty bus capacity, what induces different pressures on single-wheel buses with three axles and only one single joint. This work is still on going to carry out further research to constitute the application of this concept more