Adel Shams

Experiments on the water entry of asymmetric wedges using particle image velocimetry

In this work, we experimentally characterize the water entry of an asymmetric wedge into a quiescent fluid through particle image velocimetry (PIV). The wedge enters the water surface with an orthogonal velocity falling from a fixed height. We systematically vary the heel angle to elucidate the effect of asymmetric impact on the flow physics and on the fluid-structure interaction. The pressure field in the fluid is reconstructed from PIV data by integrating the Poisson equation. We find that the impact configuration significantly influences both the velocity and the pressure field, ultimately, regulating the hydrodynamic loading on the wedge. Specifically, as the heel angle increases, the location of maximum velocity of the flow moves from the pile-up region to the keel. At the same time, the pressure field significantly decreases in the vicinity of the keel, reaching values smaller than the atmospheric pressure. The spatiotemporal evolution of the hydrodynamic loading is thus controlled by the heel angle, with larger heel angles resulting into more rapid and sustained impacts.

Fabrication and buckling analysis of ionic polymer metal composite pipes

In this paper, we study buckling of ionic polymer metal composite (IPMC) pipes under uniaxial compression. A novel methodology to fabricate shell-like IPMCs is developed by combining hot pressing and chemical reduction. In the compression tests, IPMC pipes of varying thickness are clamped at their ends through custom-made fixtures and both short-circuit current and deformation are recorded as a function of the applied load. Experimental results are interpreted using classical findings on the buckling of thin shells and finite element simulations. Our results demonstrate that IPMC buckling can be accurately sensed through the short-circuit current, which is nearly zero during the loading phase, before suddenly increasing at the onset of the elastic instability. The buckling patterns of the samples are largely non-axisymmetric with a number of lobes appearing along the axial and circumferential directions of the IPMC pipes.

Hydroelastic slamming of flexible wedges: Modeling and experiments from water entry to exit

Fluid-structure interactions during hull slamming are of great interest for the design of aircraft and marine vessels. The main objective of this paper is to establish a semi-analytical model to investigate the entire hydroelastic slamming of a wedge, from the entry to the exit phase. The structural dynamics is described through Euler-Bernoulli beam theory and the hydrodynamic loading is estimated using potential flow theory. A Galerkin method is used to obtain a reduced order modal model in closed-form, and a Newmark-type integration scheme is utilized to find an approximate solution. To benchmark the proposed semi-analytical solution, we experimentally investigate fluid-structure interactions through particle image velocimetry (PIV). PIV is used to estimate the velocity field, and the pressure is reconstructed by solving the incompressible Navier-Stokes equations from PIV data. Experimental results confirm that the flow physics and free-surface elevation during water exit are different from water entry....

Water Impact of Syntactic Foams

Syntactic foams are particulate composite materials that are extensively integrated in naval and aerospace structures as core materials for sandwich panels. While several studies have demonstrated the potential of syntactic foams as energy absorbing materials in impact tests, our understanding of their response to water impact remains elusive. In this work, we attempt a first characterization of the behavior of a vinyl ester/glass syntactic subject to slamming. High-speed imaging is leveraged to elucidate the physics of water impact of syntactic foam wedges in a free-fall drop tower. From the images, we simultaneously measure the deformation of the wedge and the hydrodynamic loading, thereby clarifying the central role of fluid–structure interaction during water impact. We study two different impact heights and microballoon density to assess the role of impact energy and syntactic foam composition on the slamming response. Our results demonstrate that both these factors have a critical role on the slamming response of syntactic foams. Reducing the density of microballoons might help to reduce the severity of the hydrodynamic loading experienced by the wedge, but this comes at the expense of a larger deformation. Such a larger deformation could ultimately lead to failure for large drop heights. These experimental results offer compelling evidence for the role of hydroelastic coupling in the slamming response of syntactic foams.

Buckling of an ionic polymer metal composite shell under uniaxial compression

In this paper, we analyze buckling of an ionic polymer metal composite (IPMC) shell subjected to uniaxial compression. A new technique is developed to fabricate tubular IPMCs using hot molding and a chemical reduction process. The short-circuit current and the mechanical deformation of the sample are recorded during the compression test. Experimental findings demonstrate that IPMC buckling can be accurately sensed via the short-circuit current, which is approximately zero during the loading phase, before exhibiting a sudden increase at the onset of the elastic instability.

Pressure reconstruction during water impact through particle image velocimetry: Methodology overview and applications to lightweight structures

Abstract As composite structures are increasingly integrated in marine vessels, the need for a thorough, physically based understanding of fluid-structure interactions during hull slamming becomes a compelling issue. During sea keeping and maneuvering, hull slamming is responsible for highly impulsive loading conditions, which may result into undesired vibrations, fatigue, and, potentially, failure. Despite significant progress in experimental mechanics, detailed measurements of the spatio-temporal evolution of the hydrodynamic loading during hull slamming are not currently available. Here, we summarize recent progress by our group on the use of particle image velocimetry toward an improved understanding of hull slamming. Our research puts forward a purely data-driven methodology to reconstruct the pressure field generated during hull slamming from the direct measurement of the velocity field in the fluid flow. Beside methodological aspects of our work, we detail the implementation of the approach to address few exemplary open problems in hull slamming research.