プロペラによって舵が受ける起振力について

抄録

As is well known, the vibratory forces by propeller can be divided into two groups, propeller bearing force and hull surface force. In the present investigation, however, a theoretical calculation on such vibratory forces that can be produced on a rudder by the induced velocity of a propeller which is not included in the above-mentioned groups, on the one hand, is carried out and the nature of a vibratory force working upon the rudder is, on the other, investigated by the experimental measurement of rudder's vibration as well as with the theoretical result. And such influences due to the gap between the propeller and the rudder, the number of propeller blades etc. are also described. The conclusions obtained in this investigation can be summarised as follows : (1) As for the vibratory force on a rudder caused by a propeller, the one due to the induced velocity of the propeller is remarkably higher than that due to the induced pressure. And the vibration of the induced velocity consists of two components, one of them being a periodicity caused by a finite number of propeller blades and another being that caused by the ununiformity of wake. In the case of odd numbered blades, the periodicity of a finite number of blades, which is symmetrical to the center of rudder, causes a lateral force, while that due to the ununiformity of wake results in a moment around the center of rudder. In the case of even numbered blades, on the contrary, both periodicities give moments around the center of rudder. This theoretical prediction obtains experimental support. (2) Although there exists theoretically such a distance between a rudder and a propeller that gives a minimum of vibratory forces are not so much different in magnitude for a practical range of distance, because of the levelling of a rudder's chord due to its finite dimension. (3) When a stream-line rudder and a reaction rudder are experimentally compared, the differences between vibratory forces due to a propeller are hardly observed.