2024A-OS10-2 The Axial Resonance on 4,000m-class Riser System For Deep Sea Mining

Abstract

The production system for deep sea mining requires a riser system. We believe that the drilling riser is an alternative for producing minerals from the seafloor because it is a field-proven technology. However, this type of riser is heavy. Thus, buoys must be attached along the riser to reduce the axial tension. This arrangement caused the first axial natural frequency around 7.0s, resulting in resonance. We combined the main tube's pipes with different thicknesses to address this resonance. The thickest pipe was used in the riser's top portion, and the thinner main tube's pipes were assembled in the lower portions. Thus, the axial tension was reduced, and fewer buoys were required. In this configuration, the first axial natural frequency was altered to about 6.0s, reducing the resonance effects on the effective tension.