Prediction of the vortex-induced vibrations for hang-off drilling risers via integral transform

When the marine environmental conditions exceed the safe operating limits of the marine riser, the riser must be separated from the blowout preventer (BOP) and enter a suspended state until the conditions improve. This paper establishes a nonlinear dynamic model to describe the dynamic behavior of the suspended riser under harsh conditions. The model system takes into account the influence of the axial variation of stiffness, mass, and hydrodynamic effects on the vortex-induced vibration (VIV) characteristics of the suspended riser system with attached LMRP mass in the shear flow field. The governing equations are solved using the generalized integral transformation technique (GITT), which combines semi-analytical form with error-controlled numerical integration to ensure efficient and stable computation. The accuracy of the model and method is verified by comparing with experimental data from the literature. Further parameter analysis shows that the LMRP mass and the suspension length have significant effects on the time history response, natural frequency, and mode shape of the riser. The research results can provide a theoretical basis for the design and safety assessment of suspended risers in complex marine environments.