Remote identification of impact forces on loosely supported tubes: Part 2 - Complex vibro-impact motions

In a previous paper, techniques were presented, based on response measurements at remote locations, for the experimental identification of the flexural wave-guide propagation parameters and for recovering the impact forces. Numerical simulations and experiments were presented, for simple isolated impacts. Those basic results showed that such an inverse problem can be successfully attempted, and a good agreement was found between direct measurements and the remotely identified impact forces. However, when subject to flow-induced vibrations, the loosely supported tubes display very complex rattling motions-with the impact-generated primary waves completely immersed in countless wave reflections travelling between the tube boundaries. As a consequence, the multiple-impact patterns of tube-support interaction are much more difficult to identify than isolated force spikes. In this paper, the authors move a step further towards the identification of impacts for realistic tube vibrations. To deal with complex vibro-impact regimes, a signal-processing technique is presented for separating the multiple wave sources? which uses the information provided by a limited number of vibratory transducers. This technique can be applied to both non-dispersive and dispersive waves and is therefore useful for all kinds of beam motions. Such a method is instrumental in separating the primary impact-generated flexural waves from severe background contamination. This enables the straightforward identification of complex rattling forces at a loose support. Extensive results are given in order to assert the numerical conditioning of the technique used to identify the impact forces, the optimal location of the transducers used in the identification procedure, and the sensitivity of the identification method to noise contamination. Overall, results are quite satisfactory, as the complex identified impact forces compare favourably with direct measurements. (C) 1998 Academic Press.