Abstract
The Deep Sea Mining will require a vertical riser system to convey a slurry composed of the ore and seawater from the seafloor up to the floating platform. Then a second pipe shall be necessary to return this seawater to be discharged above the seafloor.
We carried out numerical simulation in the time domain, assuming a 4,000 m riser system composed of two rigid pipes with the same diameter and thickness. The numerical model has two separate pipes in side-by-side and tandem configurations regarding the platform’s forward motion. These two pipes are attached in the way they shall bend together. We assumed a current profile, irregular waves, and floating platform motion as external loads. Besides, we considered the three different boundary conditions for the bottom end of the riser, namely, (i) no equipment, (ii) 300-ton submerged pump, and (iii) 500-ton submerged pump attached to the bottom end.
We observed the Mathieu Instability in both configurations with no pump. For the cases with pumps attached to the bottom end, the Mathieu Instability did not occur because the pump’s wet weight kept the pipes tensioned throughout the whole simulation. Finally, the set of pipes in tandem configuration with a 300-ton pump had the best dynamic response among the cases studied in this article.
