Three different mathematical models are formulated which predict the two-dimensional response of cylinders in unidirectional oscillatory flow. The first two models both use the relative velocity formulation of the Morison equation for the force inline with the flow, however each use different expressions for the transverse force. The equations of motion for these models are uncoupled. In contrast, the third model considers the drag and lift force components in directions parallel and perpendicular to the direction of instantaneous relative velocity between the cylinder and the flow, which results in coupled equations of motion. The usefulness and limitations of each of the models are assessed by comparison with experiments of the response of a flexibly mounted rigid cylinder subjected to oscillatory flow in a V-tube. In general, the simple models used here are able to predict the cylinder response in a satisfactory fashion even though the interaction between the response of the cylinder and the flow is very complicated.


For the safe and efficient design of an offshore structure in deep water, it is important to be able to predict both the forces acting on the structure as well as the response of the structure. A numerical solution of the time dependent NavierStokes equations coupled with the response of the structure would provide the complete solution for this problem, however such an undertaking is not currently feasible due to the prohibitive computational power required. Previous investigators have studied various aspects of steady and oscillatory flow about fixed and flexible structures, and the knowledge aquired to date can be used to formulate simple mathematical models which predict the twodimensional response of a flexible structure. These models are necessarily approximate, and must be evaluated by comparison with experiment to determine their usefulness and limitations.

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