Dynamic behavior of flexible rectangular fluid containers with time varying fluid

With fuel consumption, the fuel container system vibrates with decreasing mass, which is a typical variable mass system. This paper investigates the dynamic characteristics of flexible rectangular fluid containers with decreasing liquid. The dynamic equations of the container with time varying liquid are derived by combining finite element method (FEM) and virtual mass method (VMM). Free vibration states of the variable mass system are mainly investigated. The vibration signals are decomposed using Choi-Walliam Distribution, and the energy density spectrum is given by time frequency analysis. Results show that decrease of the liquid of the system induces increase of the vibration frequencies of the system, and generates an additional negative damping causing the vibration decay slowly. It is found that the additional damping is proportional to rate of mass change. The additional negative damping can cause the system vibrate with increasing amplitudes while the negative damping plays the dominant role rather than the structural damping.