A generalised nonlinear isolator-elastic beam interaction analysis for extremely low or high supporting frequency

Abstract

This paper presents an integrated analysis of a nonlinear isolator-elastic beam interaction system to obtain extremely low or high supporting frequency. The nonlinear suspension unit consists of two vertical inclined springs and two horizontal springs, of which the vertical ones are to generate nonlinear effect while the horizontal one to provide a physical mean for realising required horizontal forces in reported nonlinear isolation systems. The dynamic equations of the system are derived, based on which three reduced models are obtained by introducing the related conditions. The nonlinear dynamic behavour on equilibria and stablities of the system are investigated. The dynamic interaction mechanism between the nonlinear suspension system and the eleastic structures are revealed. It is investigated the two application cases: one for aircraft ground vibration tests requiring an extreme low suporting frequency and another involving structure dynamic tests in laboratory where a rigid supporting foundation is expected. High performance vibration isolators with very low or very high stiffness are widely required in engineering. For ground vibration tests (GVT) of aircrafts, the supporting frequency have to be lower than one third of its first elastic natural frequency for flutter analysis. The weight of a large aircraft is huge but its first elastic natural frequency is quite low so that the stiffness of suportor must have a big static stiffness to support the large weight and also a very low dynamic stiffness for a very low supporting frequency [1]. In laboratories, dynamic tests of structures are often expected to be fixed on a rigid foundation, for which the stiffenss of supportor must be extremelly high. Experiments show a quite “rigid” foundation for static tests could be very soft for high frequency dynamic tests. To design this type of supportors, one approach is using active feedback controls in passive systems to modify its dynamic stiffness [2-3], which requires energy supply, so that it is difficult if the required energy is huge. Another approach is useing nonlinear spring [1]. The investigations on nonlinear isolatorss were reported [4-6] and their behaviour on stabilities, birfurcations and chaos are also given [7-8]. Available publications seem not tackling nonlinear isolator-structure interactions. As for structure control interactions [9], the dynamic characteristics of both structures and control system are affected each other. To assess the efficiency of a nonlinear isolator, interactions analysis is necessary. This paper intends to discuss this problem

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ORCID for Yeping Xiong: orcid.org/0000-0002-0135-8464

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