Bidaiari-trenen esekidura pneumatikoaren karakterizazio eta modelizazio dinamikoa

Abstract

An essential benefit of using virtual homologation in railway vehicles is the reduction of the high costs associated with on-track tests, which can be reached by analysing the performance of a railway vehicle under various operating conditions and, thus, by enhancing the vehicle’s design so as to optimise its performance under particular circumstances. In fact, as railway vehicle speed increases, the vehicle’s dynamic performance is affected. This demands the development of validated and accepted models that incorporate the influence of all vehicle components, including the wheel-rail contact, bogie frame, suspension elements, carbody, etc. In order to ensure comfortable trips the secondary suspension system aims to reduce and mitigate the vibration transmission. This suspension element is a complex component composed by a pressurized reinforced elastomeric bellows, which lies into a rubberlike emergency spring, connected though a pipeline or an orifice to a reservoir. In this thesis, the viability of the current secondary suspension models into higher frequencies and different working directions is investigated. Where necessary, new models are proposed to extend the frequency range up to 200 Hz (structural-borne vibration transmission frequency range) or incorporate existing non-linearities. Firstly, the available modelling techniques of air spring type pneumatic suspensions are evaluated according to the frequency range they cover, the component number included (bellows, pneumatic system, full secondary system) and the nonlinearities they can account for. FEM models arise as the most suitable modelling technique for the non-linear multidirectional and multiphysic and high frequency range replica of the secondary suspension system. After all, the suspension system is composed by several elements, including mainly a rubber-cord composite bellows, a rubberlike emergency spring and a moving air mass inside the pneumatic system, which results in a highly non-linear suspension element. One aspect that has been covered is the implementation into FEM models of non-linear behaviour of rubberlike elements (the nearly incompressible behaviour, non-linear elasticity, frequency and excitation-amplitude dependencies), the need of experimental characterization and model calibration. Secondly, the singularities of the bellows, the pneumatic system and the full secondary suspension are investigated separately. As far as the air spring is concerned, a bellows’s FEM model developed in ABAQUS is proposed, which is validated with experimental data. It incorporates the uniaxial reinforcements, the coupling between internal pressure and structural deformation, and the polytropic heat exchange definition between the inner air and the environment. Moreover, based on four surface response functions of the axial and transversal static stiffness and first axial and transversal vibration modes, which are function of seven construction parameters, a design tool is suggested. As an interesting outcome, the suspension system shows vibration modes bellow 200 Hz, in the frequency range which structure-borne vibration transmission takes place. Afterwards, the axial dynamic stiffness of the pneumatic suspension, more precisely of a single-lobe air spring connected to a reservoir via a pipeline is investigated, up to 400Hz. After carrying out an exhaustive experimental campaign, an enhanced FEM model is developed which incorporates the resonances due to the air flow between the bellows and the reservoir, the resonances due to the formation of standing waves in the pipeline and the resonances due to structural dynamics of the bellows. Up to date, available modelling techniques disregard the effect of the auxiliar volume (reservoir and pipeline) above 20 Hz. Nevertheless, this research shows, although that in a lesser extent, it modifies the dynamic performance of the suspension system. In addition, structural modes of the air spring can compromise the isolation above 20 Hz. Finally, a non-linear multiphysic FEM model of the full secondary suspension element, which incorporates the emergency spring to the pneumatic system is developed. Static and dynamic results up to 20 Hz of the FEM model are compared with available experimental data and afterwards, the model is extended up to 300 Hz. The dynamic performance of the suspension system in a pure axial, pure transversal or pure roll movements is predicted. In the three directions the model also predicts resonance frequencies below 200 Hz, which might compromise the isolation. As an application, based on the developed FEM model and with the advantage of avoiding any experimental test, the input parameters of the secondary suspension system model of multibody simulations are derived.