1 Proceedings of the 29 th International Conference on Ocean, Offshore and Artic Engineering OMAE 2011 June 19-24, 2011, Rotterdam, Netherland OMAE2011-50187 FURTHER INVESTIGATIONS ON VORTEX SELF INDUCED VIBRATION (VSIV) Antonio Carlos Fernandes LOC–COPPE–UFRJ Rio de Janeiro, Brazil acfernandes@peno.coppe.ufrj.br Sina Mirzaei Sefat LOC–COPPE–UFRJ Rio de Janeiro, Brazil Luis Victor Cascão LOC–COPPE–UFRJ Rio de Janeiro, Brazil Pedro Vilas Boas LOC–COPPE–UFRJ Rio de Janeiro, Brazil Ricardo Francis PETROBRAS Rio de Janeiro, Brazil ABSTRACT An experimental facility has been designed to study the transversal and response associated with vortex-induced vibration of a totally submerged horizontal cylinder hang on horizontally elastic support under the influence of vertical harmonic oscillating motion. The study aims to analyze the vortex self induced vibration (VSIV) phenomena, which occurs for instance with Steel Catenary Risers (SRCs) the deep offshore connected to floating platforms. These vibrations occur even in the absence of a current. The experiments were conducted in a tank at the LOC/COPPE/UFRJ (Laboratory of Waves and Current of COPPE, Federal University of Rio de Janeiro). The tests were carried out with Keulegan-Carpenter numbers equal to 10 and 20 and for several exciting frequencies. The vertical trajectories of the VSIV motion were then classified based on its different configurations such as oval- shape, eight-shape and etc. Different ranges of reduced velocities were also considered. The amplitude and frequency of transversal motion and also the forces calculated. INTRODUCTION The Steel Catenary Risers (SCRs) have an important role on exploring and production of oil and gas in both fixed and compliant offshore structures such as jackets, spars, tension leg platforms (TLPs) and semi-submersibles. The use of compliant ones has been improved in recent years due to their capability for deep water operation. On the other hand the SCR systems has becoming more practical in industry because of its simplicity and also lower cost in comparison with other systems such as flexible risers which are also limited in diameter and also weak against external forces in deeper waters. This study aims to understand the transversal motion of the SCRs due to oscillation of the platform, which may add to the fatigue of the SCRs. The Vortex Induced Vibration (VIV) of cylinders submitted to currents has been studied a lot by experiments, mathematical modeling and also by numerical simulations and its behavior has become better known [1]. But the vibrations which are induced by other kind of flows (current-less) are not so well known. The present research continues the research started by [2], [3] and [4] that proves the existence of transversal vibrations excited by the self oscillation of structure. These have been called Vortex Self-Induced Vibration (VSIV). Similarly, Sumer and Fredsoe [5] studied experimentally the response of a rigid cylinder but with an oscillatory regular flow (in the VSIV case, the body is moving, like the SCR connected to a floating platform). Other studies [6] tackled a particular cased called by them as HILM (Heave Induced Lateral Motion). The VSIV experiments were carried out for different combinations of spring stiffness and mass of cylinder, in Keulegan-Carpenter number range 5 to 100 and the range of reduced velocity is from 0 to 16. Their results show the response patterns of VSIV motion depends extensively on Keulegan- Carpenter as well on the reduced velocity. Regarding to the response of a cylindrical structure under conditions of irregular oscillatory flow, some results were published by Kozakiewicz et al.[7]. Some tests have been started on VSIV phenomenon with SCR (Steel Catenary Riser) models of the platform PETROBRAS 18 in IPT (Institute of Technological Research) in 1996, [2] which this research summarized in Fernandes et al. [8]. The condition of forced lateral oscillations on the top of the SCR was carried out and it was observed that the model responded with significant transverse vibrations. In the present new results of the VSIV phenomenon are presented due to the use of new apparatus with much less damping. The tests conducted for Keulegan-Carpenter of 10 and 20 and for various reduced velocities. The amplitude and frequency of transversal motion and also the loads coefficients calculated. Proceedings of the ASME 2011 30th International Conference on Ocean, Offshore and Arctic Engineering OMAE2011 June 19-24, 2011, Rotterdam, The Netherlands OMAE2011-50187 Copyright © 2011 by ASME