Design And Analysis Of Bellmouth In Flexible Riser

With the development of deep water oil and gas field, flexible risers have played an important part and the riser system is more complicated. In order to lower the load effects of flexible risers in the application process, the riser line must maintain a certain line. Riser attachment is an essential part in riser system which could maintain a certain line of riser and enhance the fatigue performance of the riser. Riser attachments mainly include: Bending Stiffener, Bending-restrictor, bellmouth and Buoyancy module. The design for the bellmouth and some analysis are discussed in this paper. The main works of this paper are:(1)The dynamic flexible riser attachments are described. The most commonly used attachments of the flexible riser are introduced based on flexible riser structure and the application environment.(2)Global analysis for catenary flexible risers is carried out using ABAQUS software to establish the overall model of the riser. Three cases are discussed in this paper: near point, far point and neutral point. Currents and wave loads as well as floating-body movement are considered in global analysis of the riser. The neutral point, at which the riser stress is relatively small, is very important layout for riser.(3)Simple design principles for bellmouth and general steps in the engineering design of bellmouth are described. Detailed derivation of the API proposed bellmouth of the linear form is carried out and the parameters in API proposed formula are simply introduced. Bellmouth installation on the platform is finally described.(4) Based on the global analysis of the riser, 4 different bellmouth forms are analysis and compared from four aspects: bellmouth weight, flexible riser stress, bellmouth stress, and contact stress. The conclusion is that the bellmouth which have the linear relationship between curvature and arc length, has a better overall performance.(5)Parameters in bellmouth whose curvature has a linear relationship with arc length are discussed. Bellmouth inner diameter has little effect on its performance; the bottom input curvature affects the bellmouth shape and weight: the greater the bottom input curvature is, the longer bellmouth length is, the heavier bellmouth weight is, and the smaller the stress range is. Bellmouth weight has a proportional relationship with the bottom input angle. Without affecting the bellmouth function, the bottom input angle should be minimized, to reduce the bellmouth arc length and bellmouth weight.(6)Global analysis of a riser equipped with bellmouth is carried out. It can be seen from the analysis: bellmouth greatly reduces the stress range of flexible riser at the top which has significant improvement for flexible riser top of the fatigue phenomenon.