FREQUENCY CONTROL OF THE RESPONSE OF COMPOSITE MATERIAL PANELS TO TURBULENT BOUNDARY LAYER EXCITATION

Most of the numerical and experimental analyses, performed in the last fifty years, on boundary layer exciting vibration and noise concern metallic structures. Little has been done for composite structures. This work is just focused on the study of the numerical and experimental responses of composite panels to turbulent boundary layer excitation and on the expected development of a passive control strategy based on material optimisation. A preliminary numerical analysis has been performed to analyse (i) the effect of fiber orientations on ideal single layer composite panels and (ii) the effect of fiber orientations and lamination sequence on multiple layer panels in the super-convective, convective and subconvective domains, respectively. To this aim, wall pressure fluctuations load is analytically represented in terms of cross-spectral densities using simple literature models. The experimental campaign is made in a towing tank by using a scaled ship model as test rig at different speed ranging between 3.3 and 5.3 m/s. In the ship portion selected for the experimental analysis, the hull surface is plane, local Reynolds numbers are significantly high, the boundary layer is fully developed and pressure gradient effects, most likely generated by the deformation of the free water surface, can be considered negligible. The structural responses are measured on three panels made of the same composite materials but with different lay-ups. Again, the main parameters investigated are the lamination sequence and fiber orientation. Due to the particular structural and flow conditions, the experimental analysis is representative of the sub-convective range only. Both the numerical and the experimental results shown that fiber orientation is fundamental for the control of the response of composite panels to turbulent boundary layer excitation in different frequency ranges.