PIN 3.2.3: Towing tank structural measurements and data analysis

An experimental campaign devoted to the vibro-acoustic characterization of turbulent boundary layer excitation has been performed in the CNR-INSEAN towing tank, using the Flame model. Different configurations have been tested varying structural geometry and material properties as well as flow conditions. In particular five panels have been considered: * a 5 mm thick aluminium bare panel; * a 3 mm thick aluminium panel ribbed by 3 stiffeners with an L section; * two 5 mm thick aluminium panels coated with two different kind of polyurethane; * a 5 mm thick aluminium panel coated with a foam. Acceleration and acoustic pressure have been acquired for tow speed ranging between 0.5 m/s and 5.1 m/s. Moreover, experimental modal analysis has been carried out to support the interpretation of the towing tank experimental data and to provide the information needed for the numerical structural and acoustical analysis. Most of the panel experimental vibration analysis is completed, in particular comparisons between different panel responses seem to be coherent with the panel characteristics. Moreover, dry and wet modal analysis performed experimentally and numerically on the bare aluminium panel gave satisfactory results in terms of identified natural frequencies. Dry modal parameters have been identified also for the composite panels, however, the possibility to perform a wet analysis and to design a numerical FEM model deserves some additional tests. In particular modal analysis with free boundary conditions is probably necessary to evaluate the exact material properties of the composites. The analysis of microphone signals has been performed only qualitatively, little is known "a priori" about the acoustic performance of these composite materials (aluminium + polyurethane and aluminium + foam) therefore, the possibility to perform acoustic measurements in an anechoic room for the evaluation of their properties is under consideration.