AUTO-OSCILLATIONS OF ANCHORED VESSELS 

 UNDER THE ACTION OF WIND AND CURRENT 



A.V. Gerassimov, R. Y. Pershitz, N.N. Rakhmanin 

 Kryloff Ship Research Institute 

 Leningrad^ U. S. S. R. 



ABSTRACT 



Horizontal plane auto -oscillations of a vessel 

 laid at one anchor are investigated and condi- 

 tions under which auto -oscillations can be eli- 

 minated are established. Ship structure cha- 

 racteristics providing auto -oscillation elimi- 

 nation are considered. 



INTRODUCTION 



It is known from practice that in the presence of wind an 

 anchored vessel swings from side to side with respect to wind direc- 

 tion line. It performs angular (yaw) and translational (drift) oscilla- 

 tions in the horizontal plane. As is shown by full-scale observations, 

 the intensity of oscillations depends on the wind force, and their am- 

 plitude values may reach 90° to 100° for the yaw while for the drift 

 they may be equal to the depth at anchorage or even more than that. 

 The dependence of the oscillatory period on the wind force is weak. 

 When lying at anchor is a working condition for a vessel, such oscil- 

 lations may prove to be extremely undesirable. 



Yawing and drifting of anchored vessels are auto-oscillatory 

 in nature as they may be caused even by the wind of constant direction 

 and force. Such character of motion is due to nonlinear relationships 

 inherent in an oscillatory system formed by the anchored vessel. The 

 most significant of these manifest themselves in the nonlinear relation- 

 ship between the horizontal component of the anchor chain tension and 

 the shifting of the hawse-hole with respect to the sea bed, as well as 



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