Flexible and rigid risers hydrodynamic coefficients by model testing and finite element method

摘要

The Design of SCR (Steel Catenary Risers) has been requiring the processing of Finite Element Method Programs both time and frequency domain for extreme and fatigue conditions. These Programs require the knowledge of the drag (C_D) and mass (C_M) coefficients for each riser element. However, not as the vertically span supported conventional risers, the rigid (also the flexible) risers oscillate a greater amount about the static equilibrium configuration. For the former, the Coefficients are taken only as a function of the Reynolds number, but for the latter, the influence of the oscillations, regulated by the Keulegan-Carpenter number, has to be taken into consideration. This normally leads to an interactive process that is suggested by the present work. In order to gain experience with this property, reduced model tests have been performed at the IPT (Instituto de Pesquisas Tecnologicas) facilities in Sao Paulo, Brazil. A FEM program, the PETROBRAS' ANFLEX makes it possible to devise a methodology, for full scale application. Further model tests have been analyzed by the present work, evidencing also the influcence of the top connection trajectory.