Abstract
The exploitation of polymetallic nodules will require the use of riser systems longer than 4,000 m. The main issue of such riser systems is that the effective tension increases linearly with length and overcomes the riser material’s yield strength at its top portion. Thus, buoys must be attached along the riser to reduce this effective tension. In this article, we apply a classic Genetic Algorithm to optimize the number and position of these buoys. The algorithm was set to minimize the failure criterion defined in a standard of riser pipes. This failure criterion considers the effective tension and bending moment. The evaluation function was calculated using only the static result of the riser simulation. However, the Genetic Algorithm minimized the failure criterion by reducing the riser’s effective tension with attached buoys. The dynamic simulation results show that this reduced effective tension raised other issues, such as large amplitudes of the effective tension and bending moment; even axial compression was observed. A large effective tension variation may result in the Mathieu Instability. The large bending moment variation may result in cumulative fatigue damage. At the same time, axial compression may cause the riser to buckle.
