船体振動起振力としてのプロペラBearing Forceの一推定法

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A study is made on the propeller bearing force that excites hull vibration of a single screw ship. The external vibratory excitation of the hull of a ship consists of six components, namely, vertical moment and force, horizontal moment and force, twisting moment (torque) and longitudinal force (thrust). It is to be noted that neither thrust variation nor torque variation contributes to the main vibratory excitation of the flexural hull vibration of a ship. On the other hand, the torsional vibration of the hull of a single screw ship will be induced by the excitation due to surface force. The present paper gives the calculation of the first four components of moment and force produced by the propeller blades mentioned above. These components of moment and force are computed by summing up those of the moment due to thrust and the tangential force with respect to each blade that encounters the flow of unequal wake at the propeller disk. The components of moment other than that mentioned above are accounted as that of the thrust eccentricity due to gravity of the propeller itself and also as the twisting moment of the blade induced by the peak of wake concentration. These two kinds of moments should be added to the moment due to thrust. For the sake of simplicity, however, these moments are ignored in the present study. By means of steady state consideration, the formulae for calculating components of the vibratory force and moment were obtained providing that the circumferential distribution of the wake fraction at 0.7R ring, for instance, is adopted and that of the corresponding effective thrust coefficient or torque coefficient is represented by the Fourier series. The formulae is shown with such a periodic function as having number of blades as variables and the Fourier coefficients, which depend on the number of blades of a given propeller as parameters. The vibratory exciting forces and moments have predominant blade frequency with statical force or moment respectively. The maximum amplitude of the variation of moment or force components is presented by a simple form, though it is definitely different from that of the thrust variation or torque variation. The numerical examples shown here treat of the three, four, five and six-bladed propellers, equal in diameter and nearly equivalent in advance coefficient, rotating in the typical ship wake of ordinary stern and Weser stern of a single screw ship. As the results, the propeller vibratory forces and moment exciting flexural hull vibrations in ordinary stern are less in the four-bladed propeller than that of the five-bladed propeller in the present example. The cause for this difference is clearly shown by the Fourier coefficients, which represent the wake pattern assumed in the present example.
社団法人日本船舶海洋工学会の論文
1962-03-30

船体振動起振力としてのプロペラBearing Forceの一推定法

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