Articulated Columnの波浪中の挙動解析(第2報) : 分数調波振動の発生に対する非線形流体抗力の効果

概要

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The hawser used to moor a floating structure to an articulated column generates nonlinear restoring force for the angular displacement of articulated column. The nonlinear restoring force causes an oscillation with a period of several times the period of oscillatory exciting force, that is to say, a subharmonic oscillation. The present report deals with the conditions necessary for the subharmonic oscillation to occur when an articulated column placed in regular waves is provided with nonlinear restoring force. As the result of numerical analysis, it is clarified that the magnitude of nonlinear hydrodynamic drag force coefficient as well as wave period, wave amplitude and nonlinear spring constant are deeply associated with the occurrence of subharmonic oscillation. In particular, the role of drag force coefficient is important ; as the drag force coefficient increases, the possibility of occurrence of subharmonic oscillation is reduced. Besides, the subharmonic oscillation does not occur in waves of an arbitrary period, but does occur in a particular range of wave period which is determined by the oscillatory characteristics of an articulated column.
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