effect of baffles on sloshing mitigation in liquid storage...

Effect of Baffles on Sloshing Mitigation in Liquid Storage Tanks

Sung-Ho Yoon1 and Kee-Jin Park1,2

1 Department of Mechanical Engineering, Kumoh National Institute of Technology

61 Daehak-ro, Gumi, 730-701, Gyeongbuk, Korea Corresponding Author : [email protected]

2 Mechanical Robot Research Division, Daegu Mechatronics & Materials Institute 32 Seongseogongdan-ro, Dalseo-gu, Daegu, 704-240, Korea

[email protected]

Abstract. This study focused on the effect of baffles on sloshing mitigation in a liquid storage tanks. A vibration producing system was manufactured to apply a predetermined vibration to the tank. The sloshing force applied to the tank wall was measured when the tank vibrating the natural sloshing frequency was stopped instantaneously. The introduction of baffles was effective at mitigating the sloshing force on the tank wall.

Keywords: Liquid storage tank, Sloshing, Baffles

1 Introduction

Sloshing phenomenon can be observed in the liquid storage tanks of large vessels, aircrafts, and automobiles. When the vibrating frequency approaches the natural frequency of the stored liquid tank, the sloshing phenomenon becomes more pronounced. This, in turn, applies a force and moment to the tank wall, which causes serious consequences on the structural stability of the liquid storage tank [1-2]. Although the sloshing phenomena observed in liquid storage tanks have been analyzed, taking the factors associated with the damping mechanism into account, systematic studies of the sloshing problems in the liquid storage tanks have yet to be performed and are essential to the further development of liquid storage tanks [3-6].

For this study, a device that was capable of applying a wide range of vibration condition was manufactured to investigate the sloshing mitigation technique. The amount of liquid in the tank and the vibration conditions were used as experimental parameters. A method for measuring the sloshing force applied to the tank wall as a result of the sloshing is suggested.

2 Experimental Apparatus

Figure 1 shows the device used to produce vibrations. It consists of a DC motor, a connecting rod, a crank offset, and a controller. In an earlier version of this device, we

Advanced Science and Technology Letters Vol.108 (Mechanical Engineering 2015), pp.1-5

http://dx.doi.org/10.14257/astl.2015.108.01

ISSN: 2287-1233 ASTL Copyright © 2015 SERSC

used a stepper. Liquid storage tank with an internal diameter-to-length ratio of 1:3 was used. Baffles could be mounted at 1/4-way point, 1/2-way point and/or 3/4-way point from the right-hand end of the tank. When only one baffle was used, it was installed at 1/2-way point, and when two baffles were installed, they were placed at 1/4-way point and 3/4-way point.

Fig. 1. Vibration producing system

3 Sloshing Force Measurement

Figure 2 shows the apparatus used to measure the sloshing force on the liquid storage tank. A small-capacity load cell was mounted on the wall to measure the sloshing force. The liquid storage tank vibrating at the natural sloshing frequency must be stopped instantaneously such that any forces being generated are a result of the sloshing of the stored liquid only.

Fig. 2. Sloshing force measurement

Advanced Science and Technology Letters Vol.108 (Mechanical Engineering 2015)

2 Copyright © 2015 SERSC

Figure 3 shows the sloshing force signals measured from a load cell when the storage tank for 30%, 50%, and 70% full, is subject to an instantaneous stop. Figure 3 (a) shows the case of vibration at the first natural sloshing frequency, while (b) shows that for vibration at the second natural sloshing frequency. These results show that an instantaneous stop after vibrating at the first natural sloshing frequency produced larger force signals when the tank was 50% and 70% full than when it was only 30% full. While an instantaneous stop after vibrating at the second natural frequency produced larger force signals when the tank was 70% full than when it was either 30% or 50% full.

(a) (b)

Fig. 3. Sloshing force signals on the liquid storage tanks vibrating at (a) first natural frequency

and (b) second natural frequency.

4 Sloshing Mitigation Effect

Baffles were installed to mitigate the sloshing of the liquid storage tank. Figure 4 shows the four types of baffles used in this study. Type 1 is a hollow baffle with an external diameter of 244 mm and an internal diameter of 122 mm. Type 2 is a Type 1 hollow baffle with twelve 20-mm holes. The Type 3 and Type 4 baffles have sixteen 30-mm holes and twenty-nine 22-mm holes, respectively.


Copyright © 2015 SERSC 3

Fig. 4. Sloshing force measurement

Figure 5 shows the sloshing force signals measured from the load cell when the tank, with one or two baffles, was stopped instantaneously. The tank was 50% full, the vibration amplitude was 40 mm, and the vibration frequency was 0.461 Hz of the first natural sloshing frequency. The experimental conditions were as follows: (1) no baffle, (2) Type 1 baffle, (3) Type 2 baffle, (4) Type 3 baffle, and (5) Type 4 baffle. The presence of a baffle played a significant role in mitigating the sloshing force on the tank wall. In (a), using one baffle, the degree of sloshing mitigation varied depending on the baffle type being used; the Type 3 and 4 baffles mitigated the sloshing more effectively than Types 1 and 2. In particular, the Type 4 baffle reduced the sloshing force being applied to the tank wall to a greater extent than Type 3. In (b), using two baffles, the degree of sloshing mitigation was similar to (a). However, when the tank was stopped instantaneously, the sloshing force on the tank wall decreased rapidly. In the same way as in (a), the Type 3 and 4 baffles mitigated the sloshing more effectively than Types 1 and 2, while the Type 4 baffle reduced the sloshing force on the tank wall more than Type 3.

5 Conclusions

To observe the sloshing of a liquid stored inside a tank, a vibration producing system was manufactured. The sloshing force applied to the tank wall was measured when the tank vibrating at the natural sloshing frequency is stopped instantaneously. The baffles have a significant influence on the mitigation of the sloshing force on the tank wall. Among the hollow baffle types with the same surface area, those with more holes of smaller diameters are more effective at reducing the sloshing force.

Acknowledgments. This work was supported by the research fund, Kumoh National Institute of Technology.


4 Copyright © 2015 SERSC

(a) (b)

Fig. 5. Sloshing force signals at different types and numbers of baffles:

(a) use of one baffle and (b) use of two baffles

References

1. Smith, Jr. C. C., “The Effect of Fuel Sloshing on the Lateral Stability of a Free-flying Airplane Model,” NACA RM-L8C16, 1948.

2. Silveira, M. A., Stephens, D. G., Leonard, H. W., “An Experimental Investigation of the Damping of Liquid Oscillations in Cylindrical Tanks,” NASA TN D-715, 1961.

3. Abramson, H. N. and Ransleben, Jr. G., “Wall Pressure Distributions During Sloshing in Rigid Tanks,” ARS Journal, Vol. 31, No. 4, pp. 545-547, 1961.

4. Shibata, H., Tokuda, N., Sakurai, T., “Sloshing Test of a Cylindrical Tank with an Eccentric Core Barrel,” Proceedings of the ASME Pressure Vessels and Piping Conference, Fluid-Structure Interaction and Structural Mechanics, Vol. 310, pp. 55-61, 1995.

5. Ibrahim, E. R., Pilipchu,k V. N., Ikeda, T., “Recent Advances in Liquid Sloshing Dynamics,” Applied Mechanics Reviews, Vol. 54, No. 2, pp. 133-199, 2001.

6. Panigrahy, P. K., Saha, U. K., Maity, D., “Experimental Studies on Sloshing Behavior due to Horizontal Movement of Liquids in Baffled Tanks,” Ocean Engineering, Vol. 36, No. 3-4, pp. 213-222, 2009.


Copyright © 2015 SERSC 5

effect of baffles on sloshing mitigation in liquid storage...

Documents