In applying external forces or thrust vectors to the elastic joints along a vertical deep-ocean pipe, the joints are modeled in Part I of this paper (Chung and Cheng, 1997) by finite elements (FEM) as well as mass-spring elements (MSE). The MSE can provide greater accuracy for a pipe with a joint and for the application of thrust vector to that joint. The MSE is simpler and more precise than the FEM in the modeling accuracy of the elastic joint, and the accuracy of prediction depends on the configuration and size and mass of the joints. The responses predicted by the FEM for the present examples of joints on an 18,000-ft-long pipe are generally close to the MSE predictions. When the mass and mass moment of inertia of the joints made with nonrigid transverse (x) stiffness are accounted for, however, there are noticeable differences between the MSE and the FEM in the predicted pipe responses and eigenvalues. The differences are pronounced in dynamic biaxial bending (y) and torsional (θz) responses, even though both models predict nearly identical static responses. The effects of the thrust vector on pipe responses are more obvious in dynamic than static responses. The thrust activation increases the torsional amplitudes, θz, though very small, and can change the bending (x) response periods. The thrust vectors reduce the amplitudes of the axial stress and combined axial and bending stresses. The advantages of the MSE, such as the accuracy of the response predictions, over FEM can be more pronounced for complex pipe systems with larger size and mass of joints.
Recently, new researchers in developing deep-ocean mining pipe systems tend to prefer a self-propelled, seafloor miner (or collector) to operate at 4,000~6000-m depth, that is similar to those of Chung and Chung et al. (1980–1997).
