Numerical Study on Slosh Reduction using Air-Trapping Mechanism and Sloshing Behavior in a Tank

Abstract

Sloshing is an important phenomenon, that is studied in the fields of sea transport, land transport, air transport, storage tanks and areas such as civil, chemical, mechanical and nuclear fields. Sloshing causes structural integrity and stability problems to the tanks/containers due to the high impact forces at localized areas of the tank, such as tank roofs, walls, and corners. In this study, a 2D rectangular tank, subjected to horizontal excitations, was used to analyze the sloshing effects. The tank was fitted with horizontal baffles on either side, in order to suppress the slosh dynamics using air-trapping mechanism. The Volume of Fluid (VOF) method was adopted to perform multi-phase analysis of sloshing phenomena. Five cases were used to analyze the sloshing effects, namely a tank with no baffles (Case 1) and a tank with baffles of four different length variations. Four cases of baffle lengths, namely 0.01, 0.02, 0.03 and 0.04 and five cases of baffle gaps, namely 0.017, 0.025, 0.033, 0.042 and 0.005 were used to analyze the effects of baffles and air trapping mechanism in reducing the sloshing impact loads at the tank wall. First, the effects of baffle lengths were used to analyze the slosh reduction. For this purpose, the lengths of the baffles were varied from 0.01, 0.02, 0.03 and 0.04 and the distance between the baffles was fixed at 0.025. Eight measure points were used to measure the sloshing pressure loads at the tank wall near the free surface. The peak pressure values of Cases 2 to 5 were compared with that of Case 1 to estimate the amount of slosh reduction. Results show that 63.6% of slosh suppression is reported for Case 4 at measure point 5 due to the presence of baffles and the air-trapping regions in between them. Also, the results of sloshing behavior inside the tank with and without baffles at different time periods are presented visually. Secondly, three cases of tank variations were used to analyze the effects of baffle gaps in reducing the sloshing inside the tank. For this purpose, the baffle lengths were kept fixed at 0.02 and 0.03 and the distance between the baffles are allowed to vary from 0.017, 0.025, 0.033, 0.042 and 0.005. The peak pressure values of Cases 3 and 4 were compared with that of Case 1 to estimate the amount of slosh reduction. The results indicate that 81.3% of slosh suppression is reported for Case 4 with the gap of 0.005 due to air-trapping. Also, the results of sloshing behavior in the tank are presented visually. Thirdly, the sloshing impact loads in a prismatic tank under forced horizontal motions were studied using numerical techniques. The VOF method was adopted to model the sloshing flow. Six cases were used to compare the effects of natural frequencies of a simple rectangular and prismatic tank, with impact pressure on the prismatic tank wall. This study also discusses the variable pressure loads and sloshing phenomena in the prismatic tank when the frequencies are changed. The results show that the average peak pressure value for ω′1= 4.24 is 22% higher than that of ω1= 4.6.