A Phenomenological Model for Vortex-Induced Motions of the Monocolumn Platform and Comparison With Experiments

Vortex-Induced Motions (VIM) of floating structures is a very relevant subject for the design of mooring and riser systems. In the design phase, Spar VIM behavior as well as Semi Submersible and Tension Leg Platform (TLP) flow-induced motions are studied and evaluated. This paper discusses flow-induced behavior on the Monocolumn concept by presenting a phenomenological model and comparing its results with a set of experiments that took place in the IPT Towing Tank - Brazil (September 2008). The experimental results have shown some fundamental differences from previous VIM tests on other units such as Spars. This numerical model attempts to identify these disparities in order to better understand the mechanics of this phenomenon. The model is based on a time-domain, two degree-of-freedom structural model coupled with a van der Pol type wake oscillator. The comparison was performed in order to calibrate the model, to study and better understand the tests results, and finally to identify important aspects to investigate in further experiments.Copyright © 2009 by ASME