Sloshing Behavior in Rigid and Flexible Propellant Tanks: Computations and Experimental Validation

Liquid-propellant slosh occurrence in spacecraft continues to introduce instability-induced failures. Current mechanical models are insufficient in predicting differences in slosh frequencies for varying tank structure flexibilities. This paper is focused on 3-D high-fidelity computational simulation of sloshing in liquid-filled tanks under dynamic loads using the arbitrary Lagrangian-Eulerian method and their experimental validation. Varying fill levels and tank thicknesses that represent flexibility were studied. The computational results were compared with in-house experiments for the same fill levels and thicknesses. Fast Fourier transform analysis was performed on the acceleration data to determine the natural frequencies due to slosh. Comparisons were also made between experiments and simulations in terms of wave height and resonance observed in acceleration time histories. It was found that the natural frequency values after the first mode compared well between simulation and experiment. The computational simulation was capable of predicting the differences in frequency values due to the tank-thickness-induced flexibility and varying fill levels. It is concluded that a high-fidelity computational model is capable of capturing these differences and is necessary to accurately characterize the nonlinear behavior of propellant slosh in flexible tanks as opposed to the mechanical models in use.