The present entire pipe system consists of a very long vertical pipe with elastic joints, pin-joining the buffer (mass) at the pipe's bottom end to a much shorter horizontal pipe. The opposite end of the horizontal pipe is pin-joined to a vehicle maneuvering in the planar (x, y) seafloor. The seafloor vehicle can restrain the motion of the horizontal pipe. This requires more elaborate computational modeling of the entire pipe system than for the vertical pipe alone. The joints on the entire pipe were modeled previously in Part I by 2 methods:
the mass-spring elements (MSE) and
finite elements (FEM). Because the entire pipe system has one zero eigenvalue associated with the rigid-body mode, the zero-eigenvalue problem is solved with the sh02 technique. The weight, generating the internal axial force of the vertical pipe, influences the eigenvalues of the entire system. Based on both the present static analysis and eigenvalue analysis, it can be stated that MSE is simpler and gives better computational accuracy, than FEM. The accuracy and advantages of the MSE modeling over FEM are clearer for the entire pipe system than for the vertical pipe system alone.
In developing deep-ocean mining pipe systems, a self-propelled, seafloor vehicle - the miner - has been a preferred system for its operation at the 800~6000-m depth (Chung and Chung et al., 1980–1997). The miner is capable of maneuvering independently of the pipe behavior within the slant range or the miner-to-pipe link length, and is equipped with a collector device. For such a system the designers have developed a 3-D pipe response model coupled with pipe torsion. Dynamic axial stress of a very long vertical pipe is one of the primary concerns for designers and operators, as was first pointed out by Chung and Whitney (1981). The present 3-D FEM model was successfully coupled with torsion: code 3DNI_PIPE. For the solution the numerical stability is very sensitive to the timestep size, and more sensitive when coupled with torsion. Installation of elastic joints along the pipe, making for articulation, was successfully modeled.
