Response control of FPSO using multiple tuned liquid dampers

Abstract

The Floating Production Storage and Off-loading (FPSO) vessels are being used widely in offshore industries. The motion of FPSO subjected extreme sea condition needs to be controlled in order to maintain the station keeping of the vessel. The crude oil containers of an FPSO can be utilized as passive dampers for controlling the response of FPSO. These containers can act as Tuned Liquid Damper (TLD) if the natural frequency of the liquid oscillation in containers is tuned to the natural frequency of FPSO. FPSO container (tank) can be divided into several tanks (Multiple Tuned Liquid Damper, MTLD) with different tank length and liquid depths. The natural frequencies of MTLD can be intelligently distributed over a range around the natural frequency of FPSO or over a band of excitation wave frequencies. Each TLD can be modelled by using an equivalent Tuned Mass Damper (TMD) analogy. The present study attempts to comprehend the response control of FPSO under surge motion only, and the vessel is modelled as a single degree of freedom system subjected to random waves. Both time domain and frequency domain analyses have been carried out to verify the response control. From the present study, it has been found that MTLD for FPSO will be effective if they are tuned to a range of wave excitation frequencies.