WIT Press

Response Of Free Standing Flexible Cylinders To Waves


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D. D. K. Anbiah & J. M. Roesset


The effects of the surrounding water on the dynamic response of flexible, free standing, cylinders fixed at their base, is studied using linear diffraction theory and two different solution approaches. The first one uses a consistent transmitting boundary to reproduce the water, while the second expresses analytically the solution in terms of the natural modes of vibration of the water and of the structure. This approach, used first by Liaw and Chopra (Report EERC 73-25, University of California, 1973) proves to be very efficient and accurate. Results are presented in terms of change in the effective natural period of the cylinder due to the presence of the water, and the effective damping, considering both an incompressible and a compressible fluid. The same formulation is used next to determine the dynamic response of these cylinders to wave action. The results (base shear and overturning moment) for the flexible cylinders are compared to those that would be obtained assuming a rigid cylinder (only diffraction forces). Keywords: hydrodynamics, diffraction forces, flexible cylinders. 1 Introduction The dynamic response of a flexible vertical cylinder fixed at its base and surrounded by water has been a problem of interest in relation to the design of some harbor structures subjected to wave action, impact forces or earthquake excitation. It was investigated in this work considering the cylinder subjected to a harmonic force applied at its top and under the action of waves. Solutions were obtained for both an incompressible and a compressible fluid, using linear diffraction theory and the equivalent of Morison’s equation and comparing the numerical predictions. In the former case two different formulations were used


hydrodynamics, diffraction forces, flexible cylinders.