Three-dimensional analysis of transient slosh within a partly-filled tank equipped with baffles

Abstract

The directional dynamic analyses of partly-filled tank vehicles have been limited to quasi-static fluid motion due to computational complexities associated with dynamic fluid slosh analyses. The dynamic fluid slosh causes significantly higher magnitudes of slosh forces and moments in the transient state that cannot be characterized through quasi-static approach, which provides reasonably good estimates of the mean responses. In this study, a three-dimensional nonlinear model of a partly-filled cylindrical tank with and without baffles is developed to investigate the significance of resulting destabilizing forces and moments caused by the transient fluid slosh, and the effects of baffles. The baffles and the end caps are modeled with curved shapes. The analyses are performed under varying magnitudes of steady lateral, longitudinal and combinations of lateral and longitudinal accelerations of the tank, and two different fill volumes using the FLUENT software. The results of the study are presented in terms of mean and peak slosh forces and moments, and variations in the mass moments of inertia of the fluid cargo within a clean bore and a baffled tank, for two different fill volumes and different magnitudes of acceleration excitations. The ratios of transient responses to the mean responses, termed as amplification factors, are further described to emphasize the significance of dynamic fluid slosh on the forces and moments induced on the vehicle. The results in general suggest that the mean responses attained from dynamic fluid slosh analyses correlate well with those attained from the quasi-static analyses for a clean bore tank. The amplification ratios of the resulting forces and moments could approach as high as 2. The results clearly show that the presence of baffles helps to suppress the peak as well as mean slosh forces and moments significantly.

An Analysis of Baffles Designs for Limiting Fluid Slosh in Partly Filled Tank Trucks~!2009-10-29~!2010-04-21~!2010-07-23~!

“…A quasi-static slosh model, however, is limited to fluid slosh in the steady state, and cannot be applied to study effects of baffles, particularly the forces and moments arising from the transient slosh. Moreover, the fundamental slosh frequencies in a full size cleanbore tank occur in the 0.16-0.26 Hz range in the longitudinal mode, and in 0.56-0.74 Hz in the lateral mode, depending upon the fill volume and tank size [6,[8][9][10]. These frequencies may lie in the vicinity of the steering frequency and the rotational modes of the sprung mass, and could lead to resonant oscillations.…”

“…The tank trucks generally employ transverse baffles with a large central orifice and a nearly semi-circular equalizer opening at the bottom. The effects of such baffles on the longitudinal and lateral fluid slosh have been investigated in only a few experimental and analytical studies [4,6,[18][19][20][21]. These have shown that presence of transverse baffles could limit slosh only in the longitudinal direction.…”

“…These frequencies may lie in the vicinity of the steering frequency and the rotational modes of the sprung mass, and could lead to resonant oscillations. It has been further shown that the magnitudes of destabilizing forces and moments during the transient slosh are significantly higher than those attributed to steady-state or quasi-static slosh [4,6,11].…”

“…Only limited applications of the CFD methods, however, could be found for three-dimensional slosh analyses of baffled highway tanks. Modaressi-Tehrani et al [6] and Yan et al [4] studied the forces due to transient 3-D fluid slosh in a full size cylindrical and an optimal baffled tank, proposed in [3], using the CFD methods, and showed that the peak longitudinal slosh force is strongly dependent upon the baffle design.…”

“…Reported studies on dynamics of partly filled tank vehicle combinations have invariably shown that the roll dynamics and braking properties of such vehicles are strongly influenced by fluid slosh in an adverse manner [e.g., [1][2][3]. It has been shown that the free surface oscillations of low viscosity fluids in partly-filled tank trucks persist over long durations, and can lead to significantly lower roll stability limits and braking performance [4][5][6]. The magnitudes of dynamic load shift, slosh forces and moments are strongly dependent upon the fill volume and the tank geometry.…”