Dynamics of Wave Propagation Across Solid–Fluid Movable Interface in Fluid–Structure Interaction

Abstract

A theoretical model for wave propagation across solid–fluid interfaces with fluid–structure interaction (FSI) was explored by conducting experiments. Although many studies have been conducted on solid–solid and fluid–fluid interfaces, the mechanism of wave propagation across solid–fluid interfaces has not been well examined. Consequently, our aim is to clarify the mechanism of wave propagation across a solid–fluid interface with the movement of the interface and develop a theoretical model to explain this phenomenon. In the experiments conducted, a free-falling steel projectile was used to impact a solid buffer placed immediately above the surface of water within a polycarbonate (PC) tube. Two different buffers (aluminum and polycarbonate) were used to examine the relation between wave propagation across the interface of the buffer and water and the interface movement. With the experimental results, we confirmed that the peak value of the interface pressure can be predicted via acoustic theory based on the assumption that projectile and buffer behave as an elastic body with local deformation by wave propagation. On the other hand, it was revealed that the average profile of the interface pressure can be predicted with the momentum conservation between the projectile and the buffer assumed to be rigid and momentum increase of fluid. The momentum transmitted to the fluid gradually increases as the wave propagates and causes a gradual decrease in the interface pressure. The amount of momentum was estimated via the wave speed in the fluid-filled tube by taking into account the coupling of the fluid and the tube.

Numerical analysis of wave propagation across Solid–Fluid interface with Fluid–Structure interaction in circular tube

“…1. This geometry was built with reference to the experiment conducted in our previous study (Kojima et al, 2017. The simulation model comprises two main parts: the cylindrical solid buffer and the water-filled circular tube.…”

Impulsive Motion in a Cylindrical Fluid-Filled Tube Terminated by a Converging Section

“…This is of course a simplifying assumption, and the reader should see Ref. [19] for a more detailed treatment of stress wave dynamics in the projectile and buffer.…”

Impulsively-Generated Pressure Transients and Strains in a Cylindrical Fluid-Filled Tube Terminated by a Converging Section

“…The idea that the motion of the projectile and the buffer is governed by rigid body mechanics has been validated through numerical simulations; making the buffer and the projectile rigid does not change the results other than producing a small increase of the peak pressures. This is of course a simplifying assumption, see [14] for a more detailed treatment of the wave dynamics in the projectile and buffer. The maximum pressure in the liquid below the buffer can be estimated using acoustic theory [15].…”