Low-gravity liquid nonlinear sloshing analysis in a tank under pitching excitation

Under pitch excitation, the sloshing of liquid in circular cylindrical tank includes planar motion, rotary motion and rotary motion inside planar motion. The boundaries between stable motion and unstable motion depend on the radius of the tank, the liquid height, the gravitational intension, the surface tensor and the sloshing damping. In this article, the differential equations of nonlinear sloshing are built first. And by variational principle, the Lagrange function of liquid pressure is constructed in volume integration form. Then the velocity potential function is expanded in series by wave height function at the free surface. The nonlinear equations with kinematics and dynamics free surface boundary conditions through variation are derived. At last, these equations are solved by multiple-scales method. The influence of Bond number on the global stable response of nonlinear liquid sloshing in circular cylinder tank is analyzed in detail. The result indicates that the systemʹs amplitude–frequency response changes from a ‘soft-spring’ to a ‘hard-spring’ in the planar motion with the decreasing of the Bond number, while it changes from a ‘hard-spring’ to a ‘soft-spring’ in the rotary motion. At the same time, jump, lag and other nonlinear phenomena of liquid sloshing are discovered.