A study of fluid structure interactions in hydraulic piping of passive interconnected suspensions

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This thesis examines the fluid-induced high-frequency vibrations in the hydraulic pipelines of a recently invented vehicle suspension, namely Hydraulically Interconnected Suspension (HIS), which is applied to overcome the compromise between comfort and handling performance. The basic system of the suspension is a liquid-filled pipe-guided fluidic circuit, inside which the produced pressure changes often lead to vibrations of the whole pipeline and associated structures and hence become a source of noise. The results of this study can be extended to similar piping systems. The modelling approach proposed here is necessarily multidisciplinary, covering vibration theory and fluid dynamics. The one-dimensional wave theory is employed to formulate the equations of motions that govern the dynamics of the fluid-structural system. Piping sections are defined as continuous line elements and discontinuities between the sections as point elements. The Transfer Matrix Method (TMM) is applied to determine the relationships between individual components. The resulting sets of linear, frequency-dependent state-space equations, which govern the coupled dynamics of the system, are derived and then applied in a variety of ways. Key parameters that influence system dynamics are identified and analyses of their effects are presented. The theoretical model is validated by experimental investigations. Two piping systems are assembled and free vibration results acquired through both the systems agree well with those of the proposed linear models. The deviation is reasonable and possible impact factors are described. However, the results from a different system configuration reveal the limitations in terms of the linear modelling to precisely represent curved hoses. The methodology presented is found to be an effective and useful way of modelling liquid-filled pipe-guided piping systems, particularly in the frequency domain. The obtained results suggest possible improvements can be made in relation to decreasing the fluid induced vibration in the piping system and the surrounding structures. However, further investigation is needed. For example, the development of the precise hose bend model or the coupling between the piping system and the connected structures could provide the topic of future studies.
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