A Stability Analysis of Risers Subjected to Dynamic Compression Coupled With Twisting

Risers anchored in a floating system and excited by a moderate sea state are often subjected to dynamic compression near the touchdown point, since the static tension in this region is usually very small. An analytical expression for the critical load of dynamically compressed risers was recently derived by Aranha et al. [1], whose results were compared with numerical simulations, showing a good agreement in several cases. This paper extends Aranha’s results by showing that the well-known Greenhill formula can be used to predict stability conditions in cables/risers having an initial curvature and subjected simultaneously to dynamic compression and twisting. This is done by extending Aranha’s reasoning, of a “local buckling length scale,” a little further, therefore creating a general procedure that enables one to obtain the buckling number $n$ appearing in the classical Greenhill formula. An application to rigid risers is presented and discussed.