The primary purpose of the research is to study the effect of free surface nonlinearity in the overall slosh dynamics of base-isolated liquid tank by developing a nonlinear finite element model under different frequency content of earthquakes. Six natural earthquakes are considered, which are categorized under low-, intermediate-, and high-frequency contents. The mixed Eulerian and Lagrangian technique is adopted based on the potential flow theory for developing the fluid domain. The efficacy of the developed computational model is verified with the existing results. The potential constraints of linear responses are demonstrated alongside the dominance of nonlinear counterparts. The slosh amplitudes are underestimated in the linear model, which emphasizes the importance of the present nonlinear approach in adequately determining the freeboard to prevent loss of liquid due to spillage and unexpected roof failure. The laminated rubber bearing isolator played a crucial role in reducing the total and impulsive components of hydrodynamic pressure as well as base shear for both linear and nonlinear approaches. However, the effect of nonlinearity is significant in the contribution of the convective component of pressure and base shear, irrespective of the frequency content of earthquakes. Also, the nonlinear convective base shear is greater than the linear counterpart for non-isolated and base-isolated tanks, and such phenomenon is marginal for higher frequency content motions. Furthermore, resonant studies of both the tank systems are performed using a harmonic ground acceleration. The seismic parameters of the base-isolated tank are amplified when the excitation frequency is very close to its fundamental sloshing frequency rather than the natural frequency of the isolator.
