Axial Stretching Oscillation of an 18,000-Ft Vertical Pipe in the Ocean

Abstract

For a long pipe in deep ocean with the equipment attached to its free bottom end, the bottom end oscillation can be amplified near resonance several times the top end oscillation amplitude. This can become a unique design and operation problem of the deepsea mining or drilling system equipment. Accounting for the added mass and damping of the bottom end equipment, the solution is obtained through numerical iteration for an 18,000-ft long vertical pipe with the bottom equipment, which is handled from a 300,000-t mining ship. It shows significantly large oscillatory pipe stretching near the resonance. The same trend of stretching is measured by the at-sea test with the Glomar Explorer test-mining operation. Near resonance, the bottom end motion is out of phase with the top end motion, thus increasing the net pipe stretching. The pipe response characteristics can be significantly altered by the pipe weight distribution, wall thickness, and length. These transfer functions, spectral analysis results and parametric analyses are presented. The stretching oscillation can impose stringent requirements on the design and operation of the equipment hardware at the bottom end. The analysis method also applies to the OTEC cold water pipe, to the re-entry operation of deepsea drilling, and to the submarine pipelines/laying.