Storm Survival of a Tanker Based Floating Production System (FPSO) In a Realistic (Random) Seaway

Recent interest in tanker based FPSO's for the United States Gulf of Mexico (GOM) has occurred (MMS, 1997). The uniqueness of the GOM environment suggests that a totally new analysis methodology be considered in lieu of traditional ship static stability analysis. This is due to the occurrence of severe wind and waves from hurricanes and the resulting large amplitude dynamics response. As a result of nonlinearities inherent in extreme response, a dynamics based analysis procedure must be used. One approach is to solely use model testing or time domain simulation. However, an alternative to such tank or computer time intensive procedures is the application of analytic phase plane techniques. The dynamical systems techniques can be used in isolation or in conjunction with these other methodologies. The basis of the analytic phase plane technique is the identification of critical dynamics in terms of the important ship and environmental characteristics. Identification of such critical dynamics can provide a more focused model test or numerical simulation program. Moreover, recent advances in the dynamical systems techniques have allowed for the consideration of random excitation. These techniques will be described and a case study of a generic tanker based FPSO operating in the US GOM during an extreme weather event will then be undertaken. The case study results will then be analyzed in terms of suggestions for improved operating procedures and choosing a most favorable heading for minimization of dangerous extreme responses. In this work, our previously developed approach (Vishnubhotla, Falzarano and Vakakis, 1998) is applied to a tanker based FPSO. This approach makes use of a closed form analytic solution which is exact up to the first order of randomness, and takes into account the unperturbed (no forcing or damping) global dynamics.