THE CHARACTERISATION OF WAVE PROPA GATION MECHANISMS USING TRANSIENT EXCITATION: CONTINUOUS SYSTEMS AND THE EFFECTS OF DISPERSION

摘要

This report forms the conclusion of a preliminary study of the wave propagation approach in the experimental characterisation of structural/acoustic systems. Continuous and dispersive systems are considered, flexural wave propagation being of particular interest, and it is shown that the measurement of time delays and attenuation factors by cross correlation offers a useful approach to system characterisation, in addition to the measurement of frequency response. It is further shown that although rapid frequency sweep excitation is suitable for measurements in continuous systems, the dispersion encountered in flexural wave propagation increases the difficulty in interpretation of correlation data. To overcome this problem, a second transient excitation function is developed which has essentially single frequency content but will yield clear correlation functions, thus permitting the direct measurement of group velocities. A wide range of model and practical experimental work is carried out in order to investigate the theoretical analyses and to demonstrate the use of the two excitation functions. Finally, tests on a built-up structure indicate the value of the wave propagation approach in practical tests in addition to displaying some of its limitations.