A FINITE ELEMENT APPROACH FOR EVALUATION OF THE MOMENT–CURVATURE RESPONSE OF FLEXIBLE RISERS

Resumo

Flexible risers are critical components employed in the offshore oil and gas industry, designed to withstand significant loads arising from their self-weight, environmental actions (such as ocean currents and wave loads), and the dynamic motions imposed by floating production platforms. These systems are engineered to exhibit high axial tensile stiffness while maintaining low bending stiffness — a fundamental characteristic for operations in dynamic environments. This anisotropic mechanical response is enabled by a multilayered architecture, composed of alternating structural and sealing elements with varying levels of interlayer adhesion. Helically wound metallic layers provide structural reinforcement and resistance to both tensile forces and internal/external pressures, whereas polymeric layers ensure fluid tightness throughout the system. This configuration allows flexible risers to operate under considerably smaller bending radii compared to metallic pipes of equivalent pressure capacity, making them particularly suitable for scenarios requiring high flexibility without compromising structural integrity. Due to their intricate construction, the global mechanical behavior of flexible risers is inherently nonlinear and strongly influenced by interlayer interactions. Under bending loads, this behavior becomes even more complex, as relative sliding between layers induces hysteresis effects in the moment-curvature response, thereby necessitating advanced modeling techniques for accurate representation. In this context, the present work proposes a methodology for estimating the moment-curvature behavior of flexible risers. To this end, various analytical formulations available in the technical literature were reviewed and compared, forming the foundation for the proposed procedure. The approach includes numerical modeling using the finite element method (FEM) implemented in the Abaqus software, with particular attention given to the interlayer interaction and sliding mechanisms between layers. The methodology was validated through comparison with experimental data and reference models reported in the literature. The proposed model was able to capture the moment-curvature response, including the unloading path hysteresis. The bending stiffnesses obtained through this methodology showed good agreement with the values reported in previous studies, demonstrating its effectiveness.