Studies on the Control Methods for Mining Systems in the Deep Sea

利用泵举系统从深海海底开采矿产资源，需要一根管柱将海面上的采矿船与海底的收集器连接起来，管柱的下端必须有缓冲器，中间必须有泵结核。然而，受船舶运动的影响，管柱容易产生纵向、横向和扭转振动。其中纵向振动的破坏性更大，为了保证上述系统的安全运行，必须尽可能控制纵向振动。1992年，为了减小纵向振动，研究了利用缓冲器的形状和附加在缓冲器上的动态减振器的被动控制方法。结果表明，采用该方法可使管柱纵向振动降低50%左右。1993年，研究了减少振动的主动控制方法，但由于难以确保大的输入控制功率和安装执行器的位置，这些方法被证明不适用于采矿系统。然后，根据矿用船舶的激励频率，通过改变吸振器中弹簧的刚度，研究了半主动控制方法。这种控制比被动控制更能减少振动。在本研究的最后一个会计年度（1994年），从可控性和经济性的角度对上述控制方法所获得的结果进行了比较，发现被动控制方法优于其他方法。然后，对缓冲器的最佳形状进行了研究，结果表明带圆盘的圆柱形缓冲器是最佳的。此外，通过找出长径比、圆盘与缓冲区直径比、圆盘间距与Keulegan-Carpenter数之间的关系，明确了最后一层缓冲的最佳条件。

For mining mineral resources from the deep-sea floor by pump-lift systems, a pipe-string is needed to connect a mining ship on the sea surface with a collector on the sea floor, and the string must be equipped with a buffer at the lower end and pupm nodules in between. However, the pipe string is apt to vibrate longitudinally, laterally and torsionally by the ship motions. Among the vibrations, the longitudinal vibration is more destructive and must be controlled as much as possible for the safe operation of the above systems.In 1992, the passive control methods by the shape of the buffer and the dynamic vibration-absorber attached to the buffer were studied in order to reduce the longitudinal vibration. It was found that the longitudinal vibration of the pipe string could be reduced by about 50% when the methods were applied.In 1993, active control methods were studied for reducing the vibration and proved to be inapplicable to the mining systems because of difficulties of securing a large input control-power and the position of installing an actuator for the power. Then, a semi-active control method was studied by changing the stiffness of the spring in the vibration absorber according to the excitation frequency of the mining ship. This control promised to reduce the vibration more than the passive control.In the final fiscal year (1994) of this research, the results obtained by the above control methods were compared with each other from the view points of controllability and economy, and the passive control methods were found to be advantageous over the other methods. Then, the optimum shape of the buffer was studied and the result indicated that the cylindrical buffer with disks was best. Moreover, the optimum conditions for the last buffer were clarified by finding the relationship among the aspect ratio, the diameter ratio of the disk to the buffer, the interval between disks and Keulegan-Carpenter number.