Abstract: 

Liquid filled tanks can impose large hydrodynamic stresses on structures when exposed to seismic excitation. Accurately representing the dynamic behaviour of the fluid-structure system, including its sloshing frequencies, is paramount when designing safety critical structures with fluid filled tanks. For regularly shaped tanks, well established codes and standards are readily available to represent the impulsive and convective motion using springs and masses in finite element analysis (FEA). Depending on the complexity of the geometry, these codes and standards are unlikely to accurately predict the sloshing frequencies and hydrodynamic stresses of irregularly shaped tanks.

A study from literature, used an acoustic-structural approach to predict the sloshing modes in a complex shaped tank and validated using a physical model. This investigation replicates this acoustic-structural approach using Abaqus and uses a modified acoustic-structural approach, utilising Isight, and a Eulerian based FEA method, separately, to validate the sloshing frequencies.

The sloshing frequencies from the acoustic-structural eigenvalue extraction successfully replicate the sloshing frequencies from the literature. The modified acoustic-structural and the Eulerian methods both correctly predict the lower frequency modes, meaning both methods can be used to validate the sloshing frequencies from complex shaped tanks in the future.

To conclude, the acoustic method can accurately calculate the sloshing frequencies of a fluid-structure system and can be used to tune the spring-mass system representing the convective motion of the fluid.

Presenters: 

Ollie Bracher Engineer - AtkinsRéalis Ollie Bracher is engineer with an interest in solving problems with niche but reliable methods and is keen to share the knowledge from his early career to convert the non-believers to the powers of lesser-known FEA methods. Ollie has achieved degrees in both mechanical and biomedical engineering which introduced him to the world of FEA. Currently working as a stress engineer at Atkinsréalis in the nuclear civil structural sector, his jack-of-all-trades background has enabled him to apply the depths of Simulia’s toolbox to real world projects.