Kamoi, Norriyuki (Kawasaki Heavy Industries, Ltd.) | Taniguchi, Tomokazu (Kawasaki Heavy Industries, Ltd.) | Kiso, Takashi (Kawasaki Heavy Industries, Ltd.) | Kada, Kazuo (Kawasaki Heavy Industries, Ltd.) | Motoi, Tatsuya (Kawasaki Heavy Industries, Ltd.) | Nakamura, Shinichi (Kawasaki Heavy Industries, Ltd.)
The present paper suggests a new lumped-mass method for a three dimensional quasi-static analysis of flexible riser. Solution of the fully non-linear governing equations based on the Krichhoff''s beam theory is numerically approached. The considered nonlinear terms are the geometric non-linearity, the hydrodynamic non-linear drag forces and the nonlinear effect of pipe flow. A continuous riser is discretized in a lumped-mass model, in which two neighbored lumped-mass points are connected with a straight massless beam element. The Diracdelta function is employed to solve the mathematically singular equations of the discrete numerical model. An incremental-iterative solving technique is chosen, in which the nonlinear differential equations are linearized by means of the Newton-method in an incremental way. The riser /seafloor interaction is dealt in a new way, in which the normal reaction forces at contact points are treated as a unknown state variable. The effect of bottom function is investigated with changing the loading speed of external forces on the riser.
With increasing deep-sea activities of flexible risers their roles m production of hydrocarbon or in ocean mining are of great Importance and interest. Flexible risers of a long, slender cylinder-type behave principally like a chain or a cable. The main structural restoring potential is axial tension forces. The capability of a riser to absorb the external loads from surrounding water and the drift and motion of surface unit depends mainly on system configuration. Buoyant modules are often employed for the purpose of an optimal configuration of riser system, i.e. the absorbance capability of external disturbances, the optimal distribution of tension forces and the exclusion of extreme local bendings. Mathematically, the theoretical global analysis of flexible risers is a complex fluid-structure interaction problem including strong geometric nonlinearity, nonlinear viscous drag force and pipe flow effects etc.(Hong 1992).