ロッドの横振動におよぼす周囲の水の減衰作用

海洋ボーリングロッドの振動について (第4報)

抄録

The model experiments were carried out in order to study the damping effects of surrounding water and air on the lateral vibrations of rods, and these experimental results enabled to estimate the damping effect of water in case of the lateral vibration of a full-scale boring rod.
The results obtained by these experiments were as follows:(1) The damping coefficient due to water was three to fifteen times greater than that due to air in the range covered by these experiments.
(2) The damping coefficient was greater in case of the rod with larger outer-diameter and with shorter span-length.
(3) The relationship between the damping coefficient, n (1/sec), and the Reynolds number, Re, derived from the average vibration-velocity of a rod, which was defined in this paper, was represented by the following equation.
n=0.54 log₁₀ Re-0.39
Furthermore, the above equation proved to be available for the estimation of the damping coefficient pertaining to a full-scale rod.
(4) The damping effect of surrounding water was not considered as viscous damping (linear damping) in the rigorous sense. However, the viscous damping could be assumed for the calculation of the lateral vibration of an off=shore boring rod without loss of precision in the practical sense if the size and property of the rod were constant.