Bending Flutter and Torsional Flutter of Flexible Hydrofoil Struts

A large body of experimental and theoretical flutter results for hydrofoil struts were analyzed to determine significant characteristics. Flutter was found to occur in two different structural mode shapes, corresponding to a predominantly bending mode and a predominantly torsional mode, respectively. The flutter mode shape was related to the vibration mode shapes and the generalized mass ratio of the strut at zero speed. The behavior of the hydroelastic modes of typical struts as a function of speed was investigated by using a strip theory with three-dimensional loading modifications. Flutter predictions for struts which underwent, flutter in the torsional mode were usually conservative and predicted the correct mode shape. However, flutter predictions for struts which underwent flutter in the bending mode were unreliable in predicting the mcae of flutter because of an extreme sensitivity to the loading modification used. Strut-foil systems of the inverted-T configuration typical of full-scale hydrofoil craft appear to undergo either bending flutter or torsional flutter, depending on pod and foil characteristics. ADMINISTRATIVE INFORMATION This work was authorized and funded und^r the Hydrofoil Development Program of the Naval Ship Systems Command, Subproject S4606, Task 1703. This report is a verbatim reproduction of a paper presented at the Ninth Syrmosium on Naval Hydrodynamics, 20-25 August 1972, Paris, France.