On the Vortex-Induced Oscillation of Long Structural Elements

Previous solutions to the vortex-induced vibration of structures have been primarily based on modal analysis, using a one or two-mode approximation. Such an analysis is generally meaningful only when the vortex shedding frequency is locked onto a natural frequency of the structure. In very large structures, typical of those found in some ocean engineering applications, modes are closely spaced, and it is not reasonable to assume total spanwise correlation in the fluid forces or response. The approach used herein avoids the limitations associated with the modal solution of such problems by implementing a solution based on the traveling wave nature of the response. Results presented indicate that the amplitude of response of a long cable is smaller than is predicted by a conventional modal analysis. The drag forces on such a structure may therefore be overestimated by current design approaches.