Abstract

Normally, it is widely accepted that conventional FPSOs are not suitable for hosting Top-Tensioned Risers (TTRs) or Steel Catenary Risers (SCRs) in most environments due to their high motion response compared to those of TLPs and SPARs. Recently, an innovative FPSO design has been introduced to solve this limitation of conventional FPSOs. In this paper, this novel FPSO design marketed under the name of LM-FPSO; Low Motion FPSO, is analyzed in terms of its motion characteristics. LM-FPSO is basically a combination of displacement type hull structure and a Solid Ballast Tank (SBT) located certain distance below the hull keel and attached to the hull structure by using a number of short tendons. This paper aims to evaluate the heave motion response of the LM-FPSO. In order to evaluate the advantages of the SBT to the heave response, a potential flow solver by using higher order boundary element method is applied in motion analysis of LM-FPSO, while CFD analysis approach is utilized for prediction of the damping ratios of the SBT and hull. In the meantime, hydrodynamic characteristics of heave damping on the SBT with different tendon's stiffness are compared. It is noted that validation of the numerical results will be carried out in the near future through model testing, which will be presented appropriately.

Introduction

In general, FPSO (Floating Production Storage and Offloading) has a larger heave motion response compared to other offshore floaters such as TLP (Tension Leg Platform) and SPARs. The heave motion response and natural period affect not only performance and safety of floating systems, but also the type of risers that can be hosted on the floater as well as mooring system design and arrangement. Increasing of the heave natural period provides significant advantage of avoiding peak natural period of wave spectrum. In this course of development, a newly developed floating platform, titled " LM-FPSO" (Low Motion - FPSO) has been recently proposed in Mansour, Wu, Zuccolo and Azevedo (2015). They concluded that LM-FPSO can significantly increase the heave natural period when compared to conventional FPSOs, which can be realized by utilizing the concept of solid ballast tank (SBT) and tendons.

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