ABSTRACT The equations of motion for a marine riser undergoing large deflections and rotations are derived using a modal discretization approach Shear effects based on nonlinear elastic theory are included In the formulation. The dynamic response of a typical marine riser system to the excitations of ocean waves and currents IS studied The hydrodynamic loading on the riser is represented In general terms using the Monson equation.
INTRODUCTION A marine-riser is an Important subsystem of offshore structures mining, hydro-thermal energy, oil and gas recovery are only a few of the engineering applications developed since the 1940's. Depending on the application, a marine-riser can be a production or a drilling-riser A marine-riser is a slender, flexible structure connecting a wellhead at the seabed to a fixed or floating platform, or to a vessel. In the case of a production-riser, the riser is essentially a pipe conveying internal flow during production. One of the restrictlons in earlier formulations of the marine-riser was the exclusion of shear effects which follows from the assumption Inherent In the Euler beam theory (Brouwers, 1982, Chakrabarti et. aI., 1982, Chung et. ai, 1981, Finn, 1972, Hall, 1980, Irani, 1989, Nordgren, 1982, O"Bnen et al, 1987). Another restriction was that the Internal flow was not taken Into account (e.g., Brouwers, 1982). However, in recent studies, Internal flow is included in the formulations (Chakrabarti, 1982). In this paper, a marine riser IS modeled as a slender, flexible structure conveying Internal flow, and is connected to a platform as depicted In Figure 1. It is assumed that during production, the Internal flow In the pipe, e.g. oil and gas, is transported simultaneously from the platform to a vessel so that the mass of the platform remains constant In spite of the Internal flow from the seabed.