Loop Formation in Catenary Risers on Installation Conditions: A Comparison of Statics and Dynamics

Loop formation may occur in cables, ropes, and also risers — flexible pipes or umbilical cables — used for offshore exploitation. The phenomenon occurs when there is enough torsion moment in the line and also a low tension condition or, even in the cases of cable slack (almost zero tension) with some torsion moment. Many references discuss about the loop formation prediction in different conditions, but mostly for the cases of an initial straight cable (rope or riser) which is usually represented by a beam. The problem of the loop formation in a catenary riser including the nonlinear contact with the seabed is very important, once during the riser installation in some conditions a low tension combined with torsion moment can lead to the loop formation, which is undesirable. There is a necessity of a better understanding of this theme. The present work explores the loop formation in catenary risers comparing the results of the static and the dynamic predictions, showing an asymptotic tendency from the dynamics to the statics. For that study, geometrically-exact nonlinear beam models were employed in the statics and in dynamics, leading to very realistic loop formation predictions.