Hydroelastic Study of Elastic Beams with a Foil-Shaped Appendage

摘要

Equations of motion were derived for the free vibrations of an elastic beam representing a ship's hull with a foilshaped appendage, under the action of unsteady hydrodynamic loads. Hydrodynamic effects on the foil have been taken into account by two-dimensional unsteady flow theory applied in a stripwise fashion, whereas the hydrodynamic effects on the hull have been neglected, although corrections for added mass can be included. Computer programs were developed by which the decay rate and frequency of response in up to six degrees of freedom can be calculated for the hullappendage system. Thereby, the effect of forward speed is taken into account through the hydrodynamic damping force acting on the oscillating foil-shaped appendage. A cursory study of a two-degree-of-freedom system with hull bending and foil torsion showed that flutter of the hull-appendage system is possible even when hull damping is included. In addition, it is shown that the possibility of the occurrence of flutter can be minimized by a judicious choice of foil parameters, and furthermore that means can be found to insure that the unsteady loads acting on an appendage provide an energy-dissipation mechanism for hull vibrations, rather than an energy source. (Author)