An Articulated Pipe System With Thrust Control For Deep-Ocean Mining

An articulated deep ocean pipe system with its bottom-end free is presented as part of the industry application phase of the ongoing cobalt-rich manganese research project. The articulation reduces the stringent requirements on the buffer-miner slant range during the miner" s maneuvering on the seafloor. 2-D deflection and 3-D motions of a 5486-m-long (18,000-ft) articulated pipe system and buffer can be controlled with elastic joints, axial dampers and the buffer at the bottom end of the pipe, and further with thrusters installed along the pipe, controlling the lateral deflection and reducing the axial motion and stress of a pipe. Using the 3-D nonlinear pipe code, 3DNLPIPE, the previous analysis (Cheng and Chung, 1996, 1997) showed design and operation principles following which arrangements of the axial vibration dampers at proper positions along the pipe, even without the joints, can effectively reduce the axial stress. Also, the joints with proper stiffness can be arranged along the pipe to be effective in reducing the axial stress is well as bending moments. Furthermore, the best combination of the multiple elastic joints and the axial dampers along the pipe can be achieved to control static, as well as mean dynamic, deflections, and to reduce the axial stress, bending moments and torsional deformation. The joints can make the biaxial and torsional vibrations reach steady state, while the axial dampers do not. The 5-s axial resonance period of the present 18,000-ft pipe is a very commonly encountered wave period in the ocean, and it can excite the axial pipe vibration.