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This paper addresses the issue of the effect of structural load on structural dynamic behavior, and how an understanding of this behaviour can be used beneficially to reduce the amplitude of response. The processes discussed lead to a new method of adaptively retuning structures through the introduction of known loads, with particular reference to helicopter response suppression. In many applications it is desirable to reduce the response of a structure without the use of damping. This has been the subject of much research with regard to helicopter design. Passive methods exist but do not allow for multiple excitation frequencies, shifting frequencies or structural alterations arising from different flight configurations and loading. Active systems have the advantage that they can respond quickly and continuously to changes in system configuration but they require significant power and higher levels of maintenance than passive systems. Adaptive passive or semi-active systems are able to adapt to flight conditions while using far less power than fully active systems. They generally involve similar techniques to passive methods with some mechanism for tuning the parameters of the vibration absorber. In this paper, numerical and experimental techniques are used to investigate the effect of loading on structural response with a view to implementing a structural load based adaptive passive device. To set the scene for this proposal, a case study of structural loading on a helicopter tailboom is presented, illustrating the extent to which the dynamic response can be affected by loading. Finite element techniques are investigated and the results compared with experimental data. The difficulties in modelling the changes in dynamic performance are discussed with refence to a case study on joint parameterization. It is found that parameters updated for one load case may not apply across an entire loading regime. A preliminary study is then carried out to assess the feasibility of the proposal, and it is demonstrated that such a system can provide improved response with low power requirements across a range of narrow band excitation frequencies. This important result provides a starting point for further research into automated adaptive techniques for response suppression, and critical areas for new work to be focused on are identified.

Adaptive Passive Control of Dynamic Response Through Structural Loading