Modelling of pipe/soil interactions in flexible risers : Proc BOSS'88, Trondheim, June 1988 V1, P279–293. Publ Trondheim: Tapir, 1988

Abstract

Various flexible riser configurations include a part laying on the seabed. The length of that part varies during the motions of the support vessel and of the riser. Taking into account this variable contact with the seabed is fairly easy and currently done in programs such as FLEXCAN-C. However, such programs generally assume that there is no friction between the pipe and the seabed, which greatly simplifies the numerical problem. This assumption is often acceptable but may be too conservative when studying the problem of interactions between two neighbouring lines or between a flexible riser and a TLP tendon or a mooring line. In both cases, a realistic modelling of the pipe/soil interaction is fairly important. For this reason, the above mentioned computer program has been modified in order to account for soil friction during the static analysis with current. Based on experimental evidences, the soil/pipe friction is assumed to be of Coulomb type, proportional to the weight of the pipe. Assuming furthermore, that the mechanical behaviour at the soil/pipe interface is perfectly plastic, the behaviour of a catenary element partly laying on the seafloor is modelled and incorporated in the general finite element program. Applications of this model to some practical cases are presented. It should be noted that this program is also useful when defining the shafting area of the mooring lines of semisubmersibles or loading buoys.