In order to reduce the maximum axial stress produced in the pipe string for mining manganese nodules from deep-sea floors by a pump-lift system, the string is assumed to be a two-stepped pipe string with larger diameter in the upper part. Moreover, a buffer and two pump-modules attached to the string are assumed to be equipped with a vibration absorber. Then, the longitudinal vibration and axial stress caused in the string by the heave-motion of the mining ship are analyzed theoretically for practical cases. The result shows that the maximum axial stress in the optimum stepped pipe-string with the buffer having the optimum vibration absorber is found to be smaller by about 42 percent than the one produced in the uniform pipe string with the same mass and no vibration absorbers.

Issue Section:
Research Papers
Topics:
Mining, Pipes, Stress, String, Vibration absorbers, Polishing equipment, Pumps, Seas, Ships, Vibration
1.
Aso
K.
,
Kan
K.
,
Doki
H.
, and
Mori
M.
,
1991
a, “
The Shape-Effect of Buffer on the Longitudinal Vibration of a Pipe String in the Deep Sea
,”
Int. Journal of Offshore and Polar Engineering
, Vol.
1
, No.
2
, pp.
154
–
160
.
2.
Aso
K.
,
Kan
K.
,
Doki
H.
, and
Mori
M.
,
1991
b, “
The Drag and Added-Mass Coefficients of Buffers Vibrating Axially in Water
,”
ASME Journal of Energy Resources Technology
, Vol.
113
, pp.
80
–
86
.
3.
Aso
K.
,
Kan
K.
,
Doki
H.
, and
Iwato
K.
,
1992
, “
The Effects of Vibration Absorbers on the Longitudinal Vibration of a Pipe String in the Deep Sea—Part 1: In Case of Mining Cobalt Crusts
,”
Int. Journal of Offshore and Polar Engineering
, Vol.
2
, No.
4
, pp.
309
–
317
.
4.
Aso, K., Kan, K., Doki, H., Ohkoshi, T., and Natori, T., 1993, “Vibration-Control of a Pipe String for Mining Manganese Nodules by the Shape of Buffer,” Proc. 3rd Int. Offshore & Polar Eng. Conference, Singapore, Vol. I, pp. 143–148.
5.
Aso
K.
,
Kan
K.
,
Doki
H.
, and
Ohkoshi
T.
,
1994
a, “
The Effects of Vibration Absorbers on the Longitudinal Vibration of a Pipe String in the Deep Sea—Part 2: A Case for Mining Manganese Nodules
,”
Int. Journal of Offshore and Polar Engineering
, Vol.
4
, No.
1
, pp.
62
–
67
.
6.
Aso, K., Kan, K., Doki, H., and Maeda, T., 1996, “The Optimum Design of a Stepped Pipe String for Mining Manganese Nodules, with Consideration for Reducing Its Maximum Axial Stress,” Proceedings, 6th Int. Offshore & Polar Engineering Conference, Los Angeles, USA, Vol. I, pp. 29–36.
7.
Cheng, B.-R., Chung, J. S., and Zheng, Z.-C, 1995, “Effects of Flexible Joints on the 3-D Nonlinear Coupled Responses of a Long Vertical Pipe,” Proc, 5th Int. Offshore & Polar Eng. Conference, The Hague, The Netherlands, Vol. 11, pp. 236–243.
8.
Chung, J. S., and Whitney, A. K., 1981, 1983, “Axial Stretching Oscillation of an 18,000-Ft Vertical Pipe in the Ocean,” Proc, Offshore Tech. Conf, Houston, and ASME Journal of Energy Resources Technology, Vol. 105, pp. 195–200.
9.
Chung
J. S.
,
Cheng
B.
, and
Huttelmaier
H.-P.
,
1994
a, “
Three-Dimensional Coupled Responses of a Vertical Deep-Ocean Pipes: Part I. Excitation at Pipe Ends and External Torsion
,”
Int. Journal of Offshore and Polar Engineering
, Vol.
4
, No.
4
, pp.
320
–
330
.
10.
Chung
J. S.
,
Cheng
B.
, and
Huttelmaier
H.-P.
,
1994
b, “
Three-Dimensional Coupled Responses of a Vertical Deep-Ocean Pipes: Part II. Excitation at Pipe Top and External Torsion
,”
Int. Journal of Offshore and Polar Engineering
, Vol.
4
, No.
4
, pp.
331
–
339
.
11.
Morison
J. R.
,
O’Brien
M. P.
,
Johnson
J. W.
, and
Schaaf
S. A.
,
1950
, “
The Force Exerted by Surface Waves on Piles
,”
Petroleum Transactions of AIME
, Vol.
189
, pp.
149
–
154
.
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