Highlights• A coupled two beam system with non-linearity from impact and asymmetry is used to improve the energy harvested.• The influence of different system parameters, such as contact stiffness, clearance and asymmetry on the energy harvested was identified.• The power generated depends on the number of close modes within the bandwidth of excitation of the non-linear impact.• The asymmetry of the close mode shapes and the frequency spacing alters the power generated. AbstractEnergy harvesting has many potential applications for structures with broadband excitation, such as aircraft noise and low frequency vibrations from human motion.The advantage with a vibro-impacting system is the capability of converting low frequency response to high frequencies. A coupled beam system is base excited and the influence of different system parameters are studied. Exciting the system at a single resonant frequency highlights the influence of clearance and base excitation amplitude on the beam responses. The frequency sweep study shows the sensitivity of the power generated to the contact stiffness, damping and clearance between the beams. The power generated by the coupled system from the non-linear impact is sensitive to the thickness ratio of the beams and the clearance. The variation in thickness ratio alters the spacing of the natural frequencies of the system which causes modes to interact. This study shows that higher power is produced than the linear system, depending on the dissimilarity in the mode shapes of the interacting close modes.

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A major concern within the oil drilling industry remains the high risk associated with the drilling bit and tool failure from the build-up of damaging vibrations. Effective understanding of the drillstring dynamics is essential for efficient drilling operation. Complex dynamic behaviour is often observed in the drillstring due to friction, impact, unbalance eccentricity and energy exchange between different modes of vibrations. The interaction between the drillstring and borehole wall involves nonlinearities in the form of friction and contact. Initially a two discs model was developed to analyse the behaviour of the system. The theoretical model was tuned by altering the phase of the eccentric mass. This excites each lateral modes of the system in isolation. The effects of impact, friction and mass unbalance are included in the model. The drillstring borehole interaction induces whirling behaviour of the drillstring causing forward whirl, backward whirl or intermittent bouncing behaviour depending on the system parameters. A critical steady state behaviour within the system is the backward whirling of the drillstring, which reduces the fatigue life of the drillstring. For the tuned system the backward whirl behaviour was analysed by carrying out a rotor speed sweep spanning the lateral natural frequencies. The influence of rotor speed on the system dynamics is explored using a run up and run down and is analysed using a waterfall plot. The waterfall plot indicated the frequency of maximum response corresponding to each

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