An inverse-direct method for predicting the vortex-induced vibrations of cylinders in uniform and nonuniform flows

摘要

An inverse-direct method for predicting the vortex-induced vibrations of uniform and nonuniform cylinders in uniform and nonuniform flows is developed. In this method, the fluid force acting per unit length on a uniform cylinder in a uniform flow is found by using known experimental results and inverting the equation of motion of the cylinder. This force is a function of the response parameter (structural damping divided by the ratio of displaced fluid mass to structural mass) and the frequency ratio (the ratio of the intrinsic shedding frequency to the structural natural frequency). The dependence of the fluid force on the frequency ratio is shown to explain the modal coupling patterns found for taut cables and beams in uniform flows. For nonuniform flows or nonuniform cylinders, the force is applied locally and varies along the cylinder, depending on the local values of the response parameter and frequency ratio. The predictions of the inverse-direct method for the vortex-induced vibrations of uniform and tapered pivoted cylinders in uniform and linearly sheared flows are compared with experimental data. The general agreement between the predictions and the data is quite good.