Capability of a potential-flow solver to analyze articulated multibody offshore modules

Abstract

Within the EU-funded Space@Sea project, a standardized floating solution for offshore space was developed, and modularity was one of the key elements. Computational tools used to design and analyze such modules must be validated. The objective here was to critically examine the capability of a potential-flow solver to predict wave-induced motions and loads on offshore systems consisting of such articulated modules, as this kind of solver is often used to assess the safety and effectiveness of articulated multibody offshore structures. A frequency-domain analysis considered only the hydrodynamic interactions between two floating modules, by locking the motions of interacting structures. A time-domain analysis treated also the mechanical coupling effects between the two articulated floating modules. Comparative computations from a RANS-based solver and experimental model measurements were available to validate the results. Although the agreement was reasonable between numerical predictions and experimental measurements for the floating modules in wave frequencies far away from their natural frequencies, deviations were observed in waves at frequencies in the neighborhood of the module’s natural frequencies. Generally, the agreement between numerically predicted and experimentally measured hinge forces was favorable. The effects of incident wave angles on hinge forces revealed that numerically predicted hinge forces at all incident wave heading angles compared favorably to measurements. An accurate evaluation of wave-induced motions and loads on articulated floating structures was possible only by accounting also for nonlinearities associated with the connecting joints.