Experimental Assessments of the Added Mass of Flexible Cylinders in Water: The Role of Modal Shape Representation

A flexible vertical cylinder model, fixed at both ends, is tested experimentally immersed in water and then in air. Galerkin’s decomposition is applied to obtain a Reduced Order Model (ROM) from a continuum one. Two closed-form trial modal shapes are chosen for the modal decomposition process. Then, modal added mass is assessed using classical Fourier and Hilbert transform (HT) signal analyses, comparing the model eigenvalues with the frequency evaluated from the experimental signals. The choice of modal shape is shown to alter significantly added mass experimental assessment. Similarity to classic results with rigid cylinders is achieved by taking a sufficiently proper modal representation. Moreover, the first mode added mass coefficient attains the same value of that previously determined for a cantilevered flexible circular cylinder, by Pesce and Fujarra in (Pesce and Fujarra, Int J Offshore Polar Eng 10:26–33, 2000) [1].