DYNAMIC RESPONSE OF A STEEL CATENARY RISER AT THE TOUCHDOWN POINT BASED ON INTEGRATED ANALYSIS

This research’s purpose is to quantify the effect of different parameters on the dynamics of a SCR (Steel Catenary Riser) by incorporating floating-body inertia and the soil reaction force into the theoretical model of the dynamic equilibrium system. The dynamic response simulation of a SCR under oceanic environmental loads was carried out. The simulating method through which the riser-soil interaction is studied is based on an extensible curved beam with a large curvature and a beam on an elastic foundation. The sag-bend and the flow-line sections of the SCR are modeled by the extensible curve beam with a large curvature and the beam on an elastic foundation, respectively. Galerkin’s method was used to discretize the dynamic equations in space, resulting in a set of nonlinear 2nd-order ordinary differential equations in the time domain. Newmark-β method was employed for time-domain integration of the discretized equations. The hydrodynamic and inertial forces of the floating-body can be added to the dynamic equations by introducing a δ function. A 1800m floating-body and riser system of engineering is analyzed. Several test cases of top end harmonic excitations were performed, aiming to investigate the effect of the various dynamic parameters on the dynamic analysis at the key zone, such as hydrodynamic coefficient, internal fluid density, and seabed stiffness, etc. The results indicated that changing the hydrodynamic coefficient has an obvious effect on the amplitude of tension and bending moment at the TDP (Touchdown point), different internal densities will change the position of the TDP, and the changing soil stiffness has a great impact on the maximum variation of bending stress and on fatigue life. Fatigue damage at the TDP is mainly induced by bending stress rather than axial stress. Hence results have significance as a guideline for the design of SCR.