Three-Dimensional Dynamics of a Flexible Marine Riser Undergoing Large Elastic Deformations

The equations of the three dimensional motion of a marine riser undergoinglarge elastic deformations are formulated using Kane's formalism. The riseris modeled using lumped masses connected by extensional and rotationalsprings including structural damping. Surface waves are described by Stokes'second-order wave theory. Fluid-structure coupling is achieved byapplication of the hydrodynamic loads via Morison's equation and added-masscoefficients using the instantaneous relative velocities and accelerationsbetween the fluid field and the riser segments. In the same way, a model forincorporating the effects of vortex-induced lift forces is included. Theeffect of internal flow is included in the model. The detailed algorithm ispresented and the equations are solved using a robust implementation of theRunge–Kutta method provided in MATLAB. The mathematical model and associatedalgorithm are validated by comparing the steady-state equilibriumconfiguration of the riser with special cases of an elastic catenary mooringline and large deflection statics of a cantilever beam. The results ofsample simulations are presented.