Novel Technique for SCR Porch Location Screening

For a spread moored FPSO, the determination of feasible SCR hangoff locations is usually performed considering numerous load combinations including different riser hangoff locations, vessel drafts, wave heights, periods and directions and current profiles. Due to the riser response sensitivity to the random waves multiple three hour random sea realizations are also typically used to capture the worst riser response. Thus, large numbers of load cases have to be performed. The amount of computational resources needed to obtain the results is substantial and sometimes prevents the work from completion in a timely manner. Furthermore, significant effort needs to be invested in organizing and understanding the results. This paper introduces the concept of developing Porch Location Envelopes (PLE) which considerably simplifies the understanding of all results, and recommends an approach that drastically reduces the time in obtaining those results. The PLE for a given SCR is defined as the limiting riser hangoff locations for a range of vessel motions. The PLE is determined using rigid body vessel motion transformation and relationships between porch motions and riser response characteristics. By utilizing the approach provided in this paper, the feasible SCR hangoff locations can be determined for each riser using only a limited number of riser strength analyses.