THEORY OF SHIP AND STRUCTURAL MECHANICS

The article considers the definition of second-order nonlinear forces and the corresponding amplitudes of the second harmonics of various types of ship's motions based on the application of three-dimensional potential theory. The calculations of the amplitude-frequency characteristics of the second order are compared with the calculations by the two-dimensional method. In most cases, there was good agreement between the results. A study was made of the influence of a change in relative depth on the amplitudes of the second order and on the total amplitudes of motions. Their significant increase in the low-frequency zone with decreasing relative depth is shown. The results of calculations of the amplitudes of the second harmonics at different heading angles are presented. It is shown that the largest amplitudes of the second harmonics of the transverse types of ship's motions occur when the ship is in beam waves, and longitudinal motions occur at oblique angles or in head waves. A study was made of the influence of ship velocity on the amplitudes of the second harmonics in shallow water conditions. A significant decrease in the roll amplitudes in the superharmonic resonance zone with an increase in velocity is shown.