Abstract
The method of normal forms is applied to the nonlinear equations of the liquid motion hi a rectangular tank. In our previous study, analysis of O(1) was conducted. The excitation term in the original equations is regarded as O(ε^2). In this study, we derive the normal forms of O(ε^2) to investigate the forced oscillations. The equations of the stationary amplitudes are also obtained. These equations show that the response characteristics change from hardening-type to softening-type when the liquid depth is increasing. This transition coincides with the well-known results.
