Small-Scale Tests on the Dynamic Compression of Lazy-Wave Risers: Experimental Design Methodology

The study of the dynamic compression phenomenon in risers subjected to harmonic motions from FPSOs is important to ensure structural safety during operation. On this topic, theoretical predictions for the critical loads have been developed for risers in free hanging catenary configurations and have been experimentally and numerically validated. For risers in lazy-wave configurations, however, the validity of these theoretical predictions is not yet fully understood. In the present work, a methodology to design small-scale experiments focusing on the dynamic compression of lazy-wave risers subjected to a harmonic and vertical excitation at the top is presented. The test facility and the designed experimental arrangement are described, and the main aspects regarding its construction methodology are discussed. Stability analyses for both in-plane and out-of-plane buckling are compared with dynamic simulations, and it is shown that both types of instability may occur under the same excitation conditions for the designed small-scale model. Finally, by comparing the critical top-motion conditions (i.e. under which the occurrence of buckling is theoretically predicted) with the capabilities of an in-house actuator, the feasible range of frequencies to be used in the experiments is determined.