The Effects Of Vibration Absorbers On The Longitudinal Vibration Of A Pipe String In The Deep Sea - Part 2: A Case Of Mining Manganese Nodules
- Authors
- K. Aso (Department of Mechanical Engineering, Mining College, Akita University) | K. Kan (Department of Mechanical Engineering, Mining College, Akita University) | H. Doki (Department of Mechanical Engineering, Mining College, Akita University) | T. Ohkoshi (Department of Mechanical Engineering, Mining College, Akita University)
- Document ID
- ISOPE-94-04-1-062
- Publisher
- International Society of Offshore and Polar Engineers
- Source
- International Journal of Offshore and Polar Engineering
- Volume
- 4
- Issue
- 01
- Publication Date
- March 1994
- Document Type
- Journal Paper
- Language
- English
- ISSN
- 1053-5381
- Copyright
- 1994. The International Society of Offshore and Polar Engineers
- Keywords
- amplitude, pump modules, buffer, Mining manganese nodules, vibration control by absorber, axial stress, pipe string, optimum condition of absorber, longitudinal vibration
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ABSTRACT:
In order to reduce the longitudinal vibration of the pipe string for mining manganese nodules in the deep sea, a vibration absorber, composed of a mass, springs and dampers, was attached to two pump modules as well as to the buffer. Then the effect of the absorber on the vibration was analyzed theoretically. The results indicate that the above-mentioned absorber attached only to the buffer could reduce the resonance amplitudes of the buffer and pump modules by almost 50% and the maximum axial stress produced at the top of the pipe string by about 17% in comparison with those pertaining to the buffer with no absorbers. There are the optimum values for the spring constant and mass of the absorber to minimize the axial stress as well as the vibration of the pipe string. Furthermore, the absorber attached to the buffer causes much greater effect on the vibration of the pipe string than that attached to the pump module.
INTRODUCTION
For mining manganese nodules from deep-sea bottoms, a pipe string is needed to connect the mining ship on the sea surface with the miner on the sea floor. Furthermore, in the pump-lift system, the string must be equipped with one or more pump modules for pumping the nodules up to the ship, and with a buffer for regulating the density of nodule-fluid mixture in the pipe string and for stabilizing the mechanical behavior of the string. The pipe string in this system is apt to vibrate longitudinally, laterally and torsionally due to the ship motions. As mentioned in the previous report (Aso et aI., 1991b), the longitudinal vibration is more destructive as far as the strength of the pipe string is concerned, and so it must be controlled as much as possible.
In order to reduce the longitudinal vibration of the pipe string for mining manganese nodules in the deep sea, a vibration absorber, composed of a mass, springs and dampers, was attached to two pump modules as well as to the buffer. Then the effect of the absorber on the vibration was analyzed theoretically. The results indicate that the above-mentioned absorber attached only to the buffer could reduce the resonance amplitudes of the buffer and pump modules by almost 50% and the maximum axial stress produced at the top of the pipe string by about 17% in comparison with those pertaining to the buffer with no absorbers. There are the optimum values for the spring constant and mass of the absorber to minimize the axial stress as well as the vibration of the pipe string. Furthermore, the absorber attached to the buffer causes much greater effect on the vibration of the pipe string than that attached to the pump module.
INTRODUCTION
For mining manganese nodules from deep-sea bottoms, a pipe string is needed to connect the mining ship on the sea surface with the miner on the sea floor. Furthermore, in the pump-lift system, the string must be equipped with one or more pump modules for pumping the nodules up to the ship, and with a buffer for regulating the density of nodule-fluid mixture in the pipe string and for stabilizing the mechanical behavior of the string. The pipe string in this system is apt to vibrate longitudinally, laterally and torsionally due to the ship motions. As mentioned in the previous report (Aso et aI., 1991b), the longitudinal vibration is more destructive as far as the strength of the pipe string is concerned, and so it must be controlled as much as possible.
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