Ship-Pipe Interaction during Laying Operations

Recent offshore activities are continuously moving towards deeper and deeper waters with increased problems for all the related above and underwater support activities. This general trend will not change in the near future and it is foreseeable that it will challenge the capabilities of the existing technologies to positively answer to the demand. For the development of the new ones a better understanding of the design constraints due to ultra-deep water scenario is therefore mandatory. The pipe laying operations are certainly one the most challenging aspects of the ultra-deep water activities and several new vessels are now under constructions. Such a design requires the optimization of seakeeping behavior of the vessel with the aim of reducing the motions of the stinger and thus increasing the operability in storm conditions. The related J-Lay tower design is affected by the induced dynamic accelerations and the increased tension demand coming from the pipe during laying operations. Unfortunately, a theoretical model able to manage both the vessel and pipe dynamics simultaneously is yet not sufficiently developed and in addition it has not been thoroughly investigated. The availability of a prediction tool able to highlight the effects of the ship-pipe interaction at the design stage will facilitate the selection of alternative technological solutions and rationally support final technical decisions. The theoretical model developed by the authors for a cable laying vessel has been recently enhanced and suitably adapted for simulating the pipe laying operations in deep water conditions. The model allows one to analyze all the significant quantities of the pipe as for example the local curvature, stress and maximum tension at stinger. The dynamics of the ship-pipe interaction is explicitly considered and the effect on the ship motion evaluated. It has been shown that for large pipe diameters and increased water depth this effect cannot be neglected. The results of the experience gained during the design of a pipelay vessel is here presented.