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

用泵举系统从深海海底开采矿物资源，需要一根管柱将海面上的采矿船与海底上的收集器连接起来，管柱下端必须装有缓冲器，中间必须装有泵举结核。然而，在船舶运动的作用下，管柱容易发生纵向、横向和扭转振动。在这些振动中，纵向振动的破坏性更大，为了保证上述系统的安全运行，必须尽可能地控制纵向振动，1992年，人们研究了通过缓冲器的形状和附加在缓冲器上的动力吸振器来减小纵向振动的被动控制方法。1993年，人们开始研究主动控制方法，但由于控制功率输入量大，且控制器安装位置不合适，不适用于采矿系统。研究了根据采矿船的激振频率改变减振器中弹簧刚度的半主动控制方法。在本研究的最后一个财政年度（1994年），从可控性和经济性的观点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最佳。通过对长径比、盘径比、盘间距与Keulegan-Carpenter数的关系的研究，确定了最后一个缓冲层的最佳制备条件。

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.