Numerical Study on the Influence of Directional Natural Frequency on Flow Induced Vibrations

Abstract

A Two dimensional numerical analysis is done for varying directional natural frequency ratio for a cylinder which is mounted elastically and executes two-degrees of freedom vortex induced vibration (VIV). VIV of the cylindrical structure at subcritical Reynolds number (Re) of 3.8 x 104 is studied using a RANSE based CFD transient fluid structure interaction dynamic simulation model employing a user defined function for modeling the response. Analyses are carried out for three different values of directional natural frequency ratios in the range 0.5, 1 and 1.5. Cylindrical models corresponding to mass ratio 1.32 is investigated. Structural damping is neglected in the present study. The study leads to interesting observations with respect to the patterns of trajectories at certain values of frequency. The paper serves as additional guidelines in riser design and its trajectory predictions.