Traveling waves in mode superposition

Abstract

Offshore marine risers are subject to Vortex Induced Vibrations (VIV) because of ocean currents. Response prediction techniques which accurately estimate the strain due to VIV are of help in deciding how to mitigate VIV, and also to predict the life of the structure. Experiments conducted in the Gulf Stream provided data about the way long flexible cylinders respond at high mode numbers. The data from these experiments showed that the response of long flexible cylinders is often in the form of traveling waves. Therefore, it was necessary to develop an excitation force model which has traveling wave characteristics. This idea has been implemented earlier using a Green's function approach. This work presents the idea of using mode superposition along with an excitation force model which has traveling wave characteristics. Examples of the implementation of this method are shown. Also, examples where a combination of standing and traveling wave excitation models are used is shown, and these agree well with the experimental data.