Axial-Stress Control of Pipe String for Mining Manganese Nodules in Deep Sea by Using Multi-Stepped Pipe

摘要

In order to reduce the axial stress produced in the pipe string, multi-stepped pipe strings are taken into consideration. Then, their longitudinal vibrations as well as axial stresses caused by the ship's heave-motion are theoretically analyzed. The results obtained are compared with those of the uniform and exponential pipe strings with the same mass. Furthermore, the optimum configuration of the multi-stepped pipe string is found in various cases by equalizing the maximum axial stress in every part of the string, and this procedure leads to minimization of the axial stress produced in the string. Then, it is found that the multi-stepped pipe string with larger diameter at the upper part could reduce the axial stress induced in the pipe string by almost 22 ～ 31% as compared with that of the uniform pipe string.