Natural Frequency Of Fluid Research Articles

Experimental study of sloshing characteristics in a rectangular tank with elastic baffles

A series of laboratory experiments are conducted to investigate liquid sloshing in a rectangular tank with a vertical baffle of varying elasticity under horizontal excitations. Image processing techniques are introduced to track baffle displacement, as well as to identify the free surface and the bubble. Dye visualization is employed to reveal the vortex behavior around the baffle. The air entrainment mechanism, including jet impinging, air cavity formation and deformation, and turbulent mixing, is analyzed. Moreover, the study investigates the effect of baffles with different stiffness on suppressing liquid sloshing across a wide range of excitation frequencies. The results show that the peak frequencies of the maximum free surface elevation-frequency curves correspond to the first natural frequency of fluid, the sub-resonance frequency, and the wet natural frequency of the elastic baffle. It is also found that the elastic baffle can effectively reduce liquid sloshing within a certain frequency range and balance the slamming impact both on the wall and the baffle, providing promising prospects for its practical applications.

Numerical Study on the Characteristics of Boger Type Viscoelastic Fluid Flow in a Micro Cross-Slot under Sinusoidal Stimulation.

The cross-slot geometry plays an important role in the study of nonlinear effects of viscoelastic fluids. The flow of viscoelastic fluid in a micro cross-slot with a high channel aspect ratio (AR, the ratio of channel depth to width) can be divided into three types, which are symmetric flow, steady-state asymmetric flow and time-dependent flow under the inlet condition with a constant velocity. However, the flow pattern of a viscoelastic fluid in the cross-slot when a stimulation is applied at inlets has been rarely reported. In this paper, the response of cross-slot flow under an external sinusoidal stimulation is studied by numerical simulations of a two-dimensional model representing the geometry with a maximum limit of AR. For the cases under constant inlet velocity conditions, three different flow patterns occur successively with the increase of Weissenberg number (Wi). For the cases under sinusoidal varying inlet velocity conditions, when the stimulation frequency is far away from the natural frequency of a viscoelastic fluid, the frequency spectrum of velocity fluctuation field shows the characteristics of a fundamental frequency and several harmonics. However, the harmonic frequency disappears when the stimulation frequency is close to the natural frequency of the viscoelastic fluid. Besides, the flow pattern shows spatial symmetry and changes with time. In conclusion, the external stimulation has an effect on the flow pattern of viscoelastic fluid in the 2D micro cross-slot channel, and a resonance occurs when the stimulation frequency is close to the natural frequency of the fluid.

大型浮体を構成する浮体要素間の微小間隙内における流体共振特性とその発生条件

This study presents an appearance condition of resonant phenomena in a narrow gap between two modules of very large floating structure under waves. We apply a theoretical method for an estimation of natural frequency of fluid in a U-tube with different diameters to a theoretical development for the appearance condition. A natural frequency of fluid in the gap which is composed of a geometrical condition of floating structure, a gap width, a length of module, a draft and a water depth, is derived by energy conservation around a module on the side of incident wave. Then, the appearance condition is derived by substituting a dispersion relation of incident wave into the natural frequency of fluid in the gap as kl tanh kh=1 (k: incident wave number, l: geometrical condition of floating structure, h: water depth). A laboratory experiment is also conducted in order to understand characteristics of fluid resonance in the gap, and the validity of the appearance condition is verified by the arrangement of experimental results using kl tanh kh and l/λ(λ: wave length).