Investigation on the Effects of Risers in the Dynamics of Floating Systems

This paper presents the experimental results obtained from the model tests performed at the IPT (State of Sa˜o Paulo Technological Research Institute) towing tank, located in Sa˜o Paulo, Brazil. The model used was the semi-submersible ITTC-SR192, at a scale 1:105. The main focus of this study is the analysis of the risers influence on the floating unit dynamics, taking into account damping effects caused by the lines. In order to establish basis of comparison the tests were performed with and without risers. These were modeled as a group of large diameter hoses that are able to provide a significant increment in the damping of the system. By such approach, it was possible to evaluate the changes on the dynamic behavior of the unit induced by the presence of risers. As an additional investigation tool, these results were analyzed with the aid of the software Numerical Offshore Tank (Tanque de Provas Nume´rico - TPN), which is a dynamic simulator of offshore systems based on parallel-processing developed by means of a partnership between the University of Sa˜o Paulo, Petrobras and other Brazilian research institutions. By means of the comparisons between the model tests results with and without risers and of the results from the numerical tool, TPN, the dynamic behavior of the floating unit was investigated in terms of the effects caused by the presence of risers, which is a very relevant subject as offshore industry walks towards ultra-depth waters.