M.Sc Thesis


M.Sc StudentHazan Adva
SubjectExperimental Analysis on Liquid Sloshing in Rectangular
Containers
DepartmentDepartment of Mechanical Engineering
Supervisor PROFESSOR EMERITUS Pinhas Bar-Yoseph
Full Thesis textFull thesis text - English Version


Abstract


Liquid sloshing in containers is important in a wide range of engineering applications. For example, it can cause a loss of structural and dynamic stability in fuel tanks and structural failures in tanks that store toxic liquids. The investigation of the characteristic flow regimes - planar, swirling, chaotic - and the distinction of their limits as a function of the characteristic parameters of the problem, is of both academic and engineering interest. The sloshing phenomenon is determined by the fluid viscosity, the ratio of the initial fluid level height to the dimensions of the tank, the ratio of the excitation frequency to the natural frequency, the excitation amplitude and direction, and the tank shape.


This thesis presents an experimental approach that enables automated determination of the history of the liquid surface elevation during sloshing in containers with rectangular and round cross-sectional shapes. Experimental results are validated by comparing with computational simulations calculated for an ideal flow. Since fluid level is an essential measure in this comparison, a high total accuracy of the free surface level measurement is essential. However, since conventional experimental equipment for measuring water levels all along the tank is expensive, traditional methods typically sample a set of solitary points only. The drawback of this is that complexity of the rapidly changing surface of an advancing wave remains obscure. To enable automated continuous tracking of the motion of the free surface of the fluid along the tank instead of in isolated points, the waves were filmed using a fast camera and the levels determined offline via image processing.


A series of experiments were conducted using tanks subjected to longitudinal harmonic excitation. The fluid volume was kept constant, and the frequency and amplitude of excitations varied across experiments. Experimental results show both a qualitative and quantitative agreement of the flow regimes with the scientific literature. Signal decomposition was performed via Hilbert and Fourier transforms, demonstrating that the frequency spectrum correspond with the computational and experimental results reported in literature.


The automated determination of the water level throughout the container is obtained via a multi-step image processing technique, based in part on image segmentation. Image segmentation successfully identifies the liquid free surface in most images, but fails in some cases. For example, identification is not successful in instances in which the wave breaks or when parts of the free liquid surface are not evenly illuminated. Nonetheless, in images in which a good level-division is obtained, the water levels can be determined. Furthermore, image segmentation failures enable a better understanding of the conditions necessary for optimal operating conditions. As this experimental and image processing method enables determination of the full profile of the wave along the tank, this presents a significant advantage over other techniques. The thesis also investigates the effect of the width to length ratio on the decay rate of the resulting wave.


An interesting extension of this study is to improve the camera and digital image processing methodologies in order to investigate sloshing phenomena in 3D motion in cylindrical containers.