Prasad Patnaik B S V

The dynamics of slosh induced wave systems in shallow water tanks is analyzed for various excitation conditions. Shake table experiments have been systematically performed to understand the complex interaction of multi-wave system under harmonic excitation. From the experiments, it was observed that, for relatively large excitation amplitudes, the hydraulic jumps emanated around the resonance region. The hydraulic jump phenomenon is further explored for different tank aspect ratios, i.e, 2.5 ≤L∕B≤ 4.038. To establish the frequency bounds for hydraulic jumps, excitation amplitude and frequency are demarcated over the range of 0.841 ≤β≤ 1.628 and liquid depth range of 0.034 ≤h∕L≤0.069. The experimental bounds are juxtaposed with the theoretical bounds to analyze the margins present in hydraulic jumps. Although, the theoretical bound is independent of liquid depth, experimental observations clearly indicate a strong dependency.

Present study explores liquid sloshing in a three-dimensional (3D) rectangular tank subjected to surge and coupled surge, sway and heave excitations. A number of applications of practical interest in nuclear systems such as, spent fuel storage tanks, fast reactor vessels, pool type coolant etc will be benefited from such analysis. Effect of harmonic excitation is investigated emphasizing finite liquid depth when the internal resonance condition 1:1 is satisfied between the natural frequencies of dominant modes (1,0), (0,1) and (0,2). The numerical model was validated against available in–house experimental shake table studies. Temporal snapshots of velocity magnitudes and free surface time history at different locations are presented when the tank is excited under two different loading conditions. The amplification of diagonal slosh modes were observed under planar excitation. This analysis assumes significance, as the attendant hydrodynamic forces could eventually cause fatigue failure of the tank structure. Non-linear square-like, swirling and wave breaking features were observed, when the tank was subjected to earthquake excitation.

An experimental study is conducted to investigate the frequency dependent decay of free-surface water waves in a sloshing tank with partially-submerged floating plastic balls on the free-surface. The present study is motivated by the need to understand the possible mechanisms for ocean wave decay in the marginal ice zone. Laboratory experiments are performed to estimate the wave decay rate due to floating balls representing ice floes. The decay rates with the balls are sufficiently greater than the decay rates without the balls and we assume the effect of the balls dominates the decay. The temporal decay rates of the free-surface wave amplitudes are measured for a small excitation amplitude and different water-depths. The decay rates for the first and third modes of sloshing are extracted, even when these two modes are combined. It is shown that the decay rates obtained from the present study match with the exponent three power-law dependence on wave frequency as observed for the decay rates in the marginal ice zone. This matching of exponent suggests that the same mechanism may be responsible for both types of decay.

Understanding violent sloshing is of practical concern to a wide range of applications as it may compromise safety in a number of engineering applications. The present study investigates violent sloshing in a 2D tank. In particular, the evolution and influence of an air pocket and the impact pressure on tank walls are numerically studied. Since the problem involves multi-phase flows, standard dam-break problem is used for validations. The liquid depth and amplitude of excitation are systematically varied to assess the impact pressures on walls and roof of the tank. Non-linear effects are captured qualitatively and the distribution of impact pressures on the tank walls is examined. The entrainment of an air pocket by a standing wave at the tank roof is delineated. The violent sloshing wave motion causes the formation of air pockets that arise for a range of forcing amplitudes and a variety of liquid depths. Gradual decay in the impact pressure due to the generation of these air pockets is significant on overall sloshing dynamics. The maximum peak pressure predicted on the tank roof is about 10 times the static pressure, which is also about twice the peak pressure obtained on the side wall. Furthermore, the distribution of average impact-pressure profiles on the tank walls and roof is presented for different loading conditions vis-á-vis global impact characteristics of sloshing wave motion.

Spent nuclear liquid waste is often kept in partially filled storage tanks. When such storage tanks are subjected to wind and/or earthquake induced excitations, this could lead to detrimental conditions. Therefore, storage tank designers should ensure safe design margins and develop methodologies to overcome a wide range of possible scenarios. In the present study, systematic numerical simulations are carried out to investigate the sloshing dynamics of liquid in a storage tank, subjected to seismic excitation. As a precursor, the influence of resonant harmonic excitation on the free surface displacement, pressure distribution, slosh forces etc. is studied. To suppress the free surface fluctuations and the associated slosh force, two types of baffles viz., ring and vertical baffle are examined. Based on the response to an imposed harmonic excitation, the vertical baffle plate in the middle of the tank, was found to be effective and its dimensions are systematically optimized. This baffle geometry was tested for a well known seismic excitation (El Centro) and it was observed to effectively suppress free surface fluctuations and the slosh forces.