Dynamic behavior of steel catenary riser at the TDZ considering soil stiffness degeneration and trench development. (15th April 2022) - Chen, Jiaming
Abstract: This work is focused on developing a riser-soil interaction model with soil stiffness degradation and trench formation, herein named the weakening model, for steel catenary riser (SCR) touchdown zone (TDZ) fatigue damage assessment. At present the riser-soil interaction models mainly include the linear, non-linear hysteretic and P - y curve behaviors. However, there are still some drawbacks in the existing models, such as the soil stiffness degradation is not considered in the P - y curve, and the trench development is not described in the hysteretic curve. The new procedure for global analysis of SCRs is obtained based on the weakening model and implemented in the program CABLE3D RSI. Results show that the soil strength gradually degenerates in the cyclic riser-soil interaction weakening model when compared with the P - y curve model. The ultimate soil strength values were selected for comparison of fatigue analysis for a typical case study, and the fatigue life is increased compared with the case without the strength degradation with the increase of the weakening factor. The results of this study can provide an effective and convenient method considering degradation of soil strength and trench development for predicting the response and fatigue life of SCRs. Highlights: A mathematical model employed to analyses the global dynamics of a Steel Catenary Riser (SCR) taking into account the degeneration seabed soil is established. The solutions for static and dynamic problem computed by different interaction model, the new model in this paper which is considered both the weakening of seabed stiffness and the influence of trench. The trench development tends to follow a slow process rather than quickly reaching a final stable state after a few cycles without the degradation of soil stiffness, so the program can effectively improve calculation speed and reducing the number of elements required for the whole riser. The fatigue damage at the SCR TDZ is proportional to the seabed stiffness, and the inversely proportional to the weakening parameters γ.