Siesmic Sloshing in Cylindrical Tanks with Flexible Baffles (original) (raw)
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Damping enhancement of seismic isolated cylindrical liquid storage tanks using baffles
Engineering Structures, 2007
The effect of baffles in reducing earthquake responses of seismically isolated cylindrical liquid storage tanks is investigated in this study. Seismic isolation is a well-known approach to reduce the earthquake effects on structures by lengthening their fundamental natural periods at the expense of larger displacements in the structural system. To reduce such effects in a system a higher damping ratio is required. In moving liquid containers, baffles play an important role in damping the liquid motion. Thus to study the effects of using baffles in seismically isolated tanks, in the first instance the velocity contours in a cylindrical tank are analysed to determine the most effective shape of baffle. Next, the damping coefficients are analytically determined for horizontal ring shape and vertical blade shape baffles. To estimate the sloshing height level and the damping ratio, a methodology, based on Tank Body Spectra, is developed in which the higher sloshing amplitude and the relative fluid velocity with respect to baffles in base isolated tanks are taken into consideration. A computer program is developed to put all these together and investigate the effect of baffles for different tank dimensions under the effect of four different earthquakes. The results show that the average damping ratio of sloshing mode due to ring baffle increases with a decrease in liquid height and highest damping may be achieved for height to radius ratios of between 1.0 and 1.5. In addition, for reasonable ring baffle dimensions, an average reduction of 6% in base displacement of base isolated tanks and an average reduction of more than 30% in the sloshing height of base isolated and fixed base tanks may be achieved. To study the effect of baffles on the distribution of hydrodynamic and tank body forces with height, a simple dynamic model is proposed. The results of analyses using this model indicate a constant reduction in sloshing forces and different reductions in moment and shear forces for different heights. This happens because contribution of the sloshing force to the total hydrodynamic force varies with height.
2011
Sloshing is a well-known phenomenon in liquid storage tanks subjected to base or body motions. In recent years the use of baffles for reducing the sloshing effects in tanks subjected to earthquake has been studied by some researchers. However, the use of multiple baffles has not been taken into consideration so much. On the other hand, although some of the existing computer programs are capable to model sloshing phenomenon by acceptable accuracy, the full dynamic analysis subjected to random excitations such as earthquake induced motions is very time consuming, particularly when there are vertical and horizontal baffles inside the tank, which postpone the convergence of response calculations. Therefore, a simplified method for evaluation of sloshing effects in baffled tanks is desired. In this paper a method is presented for this purpose based on conducting several dynamic analysis cases, by using a powerful Finite Element (FE) method for rectangular tanks with various dimensions, s...
Sloshing damping in cylindrical liquid storage tanks with baffles
Journal of Sound and Vibration, 2008
The potential of baffles in increasing the hydrodynamic damping of sloshing in circular-cylindrical storage tanks is investigated in this study. Based on the widespread use of baffles in moving liquid containers especially in space vehicles, the ability of baffles in reducing the sloshing effects in storage tanks that are especially broader than fuel containers was under question. Concerning horizontal ring and vertical blade baffles, an estimation of hydrodynamic damping ratio of liquid sloshing in baffled tanks undergoing horizontal excitation has been developed analytically using Laplace's differential equation solution. This method involves the assessment of dissipated fraction of total sloshing oscillation energy, which is caused by the flow separation around the baffles. A series of experiments employing a tank model on a shake-table has been carried out to validate the theoretically predicted damping ratio. A parametric study showed that the ring baffles are more effective in reducing the sloshing oscillations. r
Simplified Dynamic Analysis of Sloshing in Rectangular Tanks with Multiple Vertical Baffles
2013
Sloshing is a well-known phenomenon in liquid storage tanks subjected to base or body motions. Up to now the use of multiple vertical baffles for reducing the sloshing effects in tanks subjected to earthquake has not been taken into consideration so much. On the other hand, although some of the existing computer programs are able to model sloshing phenomenon with acceptable accuracy, the full dynamic analysis subjected to random excitations, such as earthquake induced motions, is very time consuming. In this paper a method is presented for reducing the analysis duration based on first, conducting several dynamic analysis cases by using ANSYS-CFX for rectangular tanks of various dimensions, subjected to seismic excitations, and then, using neural network to create simple relationships between the dominant frequency and amplitude of the base excitations and the maximum level of liquid in the tank during the sloshing. The numerical modeling has been verified by using some existing expe...
International Journal of Engineering Research and
Liquid sloshing is generally caused by external container excitation, and often has significant influence on the response of the container. The liquid sloshing generates significant localized pressure on the tank walls and roof inflicting damage to the constituent parts and in the worst case scenario leads to the complete structural failure. Baffles are used effectively to reduce the sloshing response of liquid in the liquid storage containers by destroying the continuity of the pressure distribution on the wall along the vertical direction. In this study, the damping effect of the horizontal baffles inside a liquid storage tank is investigated. The horizontal ring baffle wall located at two heights equal to 0.8 and 0.9 of the water height was used for the study. A parametric study showed that the ring baffles are effective in reducing the sloshing oscillations.
Investigation of Sloshing Response in Rectangular Container with Flexible Baffle
2018
The commercial software ANSYS was used to simulate the sloshing response of liquid in the rectangularcontainer with bottom-mounted flexible baffle. To connect the numerical data between the fluid domain andstructural domain, the two-way FSI simulation is implemented. The free surface elevation and the sloshingfrequency with flexible baffle are compared with the results of tank with rigid baffle. Through the numericalexperiments performed by varying the height and thickness of the baffle, the hydrodynamic characteristics underhorizontal excitation are parametrically investigated. Figure 1 shows an example of the sloshing displacement atleft wall of the tank with various thicknesses of baffle. The baffle height is 0.5 d0, the exciting frequency is 1.1ω1, and exciting amplitude is a0 / L = 0.001, L is the tank width and the Young’s modulus of the baffle is1.51*106. According to the results of the present investigations, the sloshing response is significantly affected bythe size and loc...
Effects of baffles geometry on sloshing dynamics of a viscous liquid tank
Scientific Research and Essays, 2013
Baffles are used effectively to reduce the sloshing response of liquid in the liquid storage containers. In this paper, a brief equivalent method is proposed to model the influence of different baffle geometrical effects on liquid sloshing. It has been showed that the natural frequencies and the dynamic response of the liquid in the container are drastically changed if the free liquid surface in a cylindrical container is being covered with structural parts. The advantages of a partly covered free surface plane lies in the shifting of the natural propellant frequencies above and away from the control frequency of a space vehicle, and in the decrease of the sloshing masses participating in the dynamic motion of the system. The fundamental natural frequency of a viscous and incompressible liquid has been determined for different geometrical shape and width of an annular ring baffle attached to the tank wall. The response to translational and pitching excitation has also been evaluated and showed the shifting of the resonance margins to higher values. Simulation results showed the effectiveness of this procedure. The presented approach may be applied to the various arbitrary coverage of free liquid surface and different geometry of container.
Effect of Earthquake Frequency Content on 3D Sloshing in Rectangular Tanks
2019
Available online at: www.jseeonline.com Earthquake frequency content has a significant effect on sloshing wave amplitude and height in liquid storage tanks. In this paper, the finite element method had been used to obtain the three dimensional fluid-structure interaction response of the rectangular tanks to access the sloshing interference effects at the tank corners under various seismic input motions with different frequency contents. The flexibility of the tank wall as well as the structural and fluid damping have been taken into account to obtain more reliable and realistic results. It has also been shown that the 3D sloshing interference may increase the total wave height significantly at the corners of the tanks compared to the values presented in the design codes, which shows the maximum sloshing wave with much lower values and at a different location. It has been finally shown that the 3D sloshing effects relates to the ratio of the width and the length of the tank. Effect o...
Seismic Sloshing in a Horizontal Liquid Storage Tank
Structural Engineering International, 2014
A horizontal water storage tank was analyzed for seismic shaking at the ITER Tokamak Complex in France. The objectives were to (a) estimate the seismic forces in the tank; (b) calculate the sloshing response of the tank; (c) determine if baffles are needed to control sloshing; and (d) evaluate the possibility of using a single fixed support in the longitudinal direction to allow free thermal expansion of the tank. An approximate conservative analysis predicted very high sloshing waves and seismic forces in the tank. The fluid-structure interaction in the tank showed that only about 28% of the liquid moves with the tank wall and generates seismic forces in the longitudinal direction. The remaining 72% of the liquid sloshes near the free surface and does not generate significant seismic forces. The sloshing wave is not high enough in the longitudinal direction as the fundamental sloshing mode is not excited because of its very low natural frequency. Hence, baffles are not needed to control sloshing. The seismic force is low enough for a single fixed support to resist the entire seismic force in the longitudinal direction.