Dynamic Behavior of a Stepped Pipe-String with a Buffer at Its Lower End
Behavior of a pipe string in mining manganese nodules (4th Report)
1988 Volume 104 Issue 1205 Pages 443-448
Details
1988 Volume 104 Issue 1205 Pages 443-448
For the design and safety control of a mining system in the deep ocean, the dynamic behavior of a submerged, twostepped pipe string, which was hanging from a ship and equipped with a buffer at its lower end, was theoretically analysed, considering the effect of the ocean current.
The main results obtained are as follows:(1) The relative displacement of the stepped pipe-string to the ship continues to increase even in the towing period of a constant velocity, which follows the period of acceleration, and then it approaches to the steady-state value after a considerably long time, just in the same manner as the case of the pipe string with a uniform cross-section. However, the shape of deflection of the stepped string is convex at its lower part, while that of the other string is concave at the same part.
(2) The bending stress induced in the stepped pipe-string is much smaller than the maximum axial stress produced at the top of each part of the stepped string. Therefore, the bending stress does not play an important role in designing the above-mentioned mining system.
(3) When the other quantities are constant, the relative displacement of the string increases remarkably as the mass of the buffer decreases or as the constant towing velocity (the maximum towing velocity) increases. From the practical sense, however, the effect of size of the buffer on the displacement is comparatively small as compared with the effects of the above-mentioned two factors when the mass of the buffer is constant.
(4) The relative displacement of the string is considerably affected by the ocean current. Namely, the displacement in creases in case of the current whose direction is opposite to that of towing the string, and decreases in case of the current whose direction is the same as that of towing.
(5) The maximum tensile stress in the axial direction produced in the pipe string could be reduced by about 20% if the two-stepped pipe string designed in this study were used instead of the pipe string with a uniform cross-section.
