Bulletin of the American Physical Society
72nd Annual Meeting of the APS Division of Fluid Dynamics
Volume 64, Number 13
Saturday–Tuesday, November 23–26, 2019; Seattle, Washington
Session A01: Free-Surface Flows: Interaction with Physical Structures I |
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Chair: Christine Gilbert, Virginia Polytechnic Institute and State University Room: 2A |
Saturday, November 23, 2019 3:00PM - 3:13PM |
A01.00001: Numerical Predictions of Spray Root Location, Hydrodynamic Pressure, and Structural Deformation of a Highly Flexible Deforming Wedge During Vertical Water Entry John Gilbert, Christine Gilbert Wave interactions with high-speed planing craft result in repeated slamming events that can lead to equipment failure and serious injury. Our earlier efforts investigated this problem through the use of wedge drop experiments and theoretical predictions, focusing on the effects of linear-elastic structural response on spray root propagation and hydrodynamic pressure. In the current work, predictions from a coupled, non-linear finite element - non-linear boundary value approach are used to extend our previous study to include the effects of large structural deformation. Observations from recent flexible wedge drop experiments conducted at the Virginia Tech Hydroelasticity Laboratory are used to inform the development of the solver. Numerical predictions for spray root location and hydrodynamic pressure as a function of time show good agreement with experiments, while predictions for the structural deformation show discrepancies. This work is part of a larger research effort aimed at understanding this fluid-structure interaction problem. [Preview Abstract] |
Saturday, November 23, 2019 3:13PM - 3:26PM |
A01.00002: Effect of convexity {\&} texture on the water entry of a cone; inspired by diving birds Wilson Llivichuzhca, Aman Agarwal, Yao Xiao, Zachary Otterpohl, Sunghwan Jung Previous studies on water entry of a projectile have been focused on the angle effect mostly. In this study, we tested and analyzed how the surface texture and convexity of a cone-shaped projectile also affect the magnitude of the force experienced by the object upon water impact and subsequently upon submersion. While testing cones of different shapes we observed, for instance, that a concaved cone experiences greater impact force than a convexed one; whereas the convexed cone has a shorter pinch off time than the concaved cone. Furthermore, we analyzed how the texture of the surface of this shape affects the impact and submersion forces that act on the cone. We chose the cone shape that experiences the least impact force (ellipsoid) and experimented different surface textures; we learned that an engraved spiral on the surface of the cone reduces the impact force whereas a feather like texture increases it but reduces pinch off forces significantly. [Preview Abstract] |
Saturday, November 23, 2019 3:26PM - 3:39PM |
A01.00003: Fluid-structure interaction (FSI) of Wedge Drop Slamming Lianxia Li, Mark Fenn, Maysam Mousaviraad, Christine Gilbert Fluid-structure interaction (FSI) problems are complex in nature, especially when the loading by the fluid is unpredictable and impulsive or when the material properties of the structure are nonlinear or otherwise complex. The purpose of this study is to investigate the water impact hydrodynamics/hydro-elasticity of flexible bodies through computational and experimental methods. Computational FSI capability is developed at University of Wyoming based on a two-way coupled approach. The flow is resolved by URANS CFD modeling and non-linear FEM equations are employed for structural dynamics. Slamming experiments are carried out at Virginia Tech for a 20\textdegree deadrise angle aluminum wedge with a bottom plate thickness of 3.175 mm and drop heights ranging from 0.9 to 38.1 cm. Measurements include time histories of vertical position, acceleration, pressure, and strain. Strain measurements are taken at single points using strain gauges as well as full-field measurements of all strain components and out-of-plane deflection using stereoscopic digital image correlation (S-DIC). Computational studies include validation and investigations of the physics involved in the interactions. Next step will extend to highly flexible structures where the two-way nonlinear interactions are more significant. [Preview Abstract] |
Saturday, November 23, 2019 3:39PM - 3:52PM |
A01.00004: How air deforms the free surface just before disk impact on a liquid bath Devaraj Van Der Meer, Utkarsh Jain, Anais Gauthier, Detlef Lohse When a flat disk impacts onto a liquid bath, a layer of air is trapped between the disk and the free surface, a phenomenon known as air cushioning. The air layer is pushed out radially at increasing speeds, causing the water surface to be lifted up towards the approaching disk. This qualitative observation is traditionally ascribed to Bernoulli suction occurring in the low-pressure region created by the large air velocities in the gap. Here, by means of a novel high-speed imaging technique that uses the free surface as a mirror, we quantitatively measure the time evolution of the free surface profile. The predicted elevation of the free surface below the disk is observed to be followed by an unanticipated depression just outside the disk's edge. Although this depression starts growing at a later point in time, its magnitude eventually surpasses that of the elevation. We show that the results are inconsistent with Bernoulli suction and that instead, the deformation appears to be initiated by a Kelvin-Helmholtz instability occuring under the edge of the approaching disk. [Preview Abstract] |
Saturday, November 23, 2019 3:52PM - 4:05PM |
A01.00005: Passive Cavity Deflation after Water Entry Emma Fraley, Rafsan Rabbi, Kelli Hendrickson, Tadd Truscott Under specific impact conditions, objects form cavities when they enter a quiescent surface and persist for an extended time. The ability to quickly deflate or remove the cavity is important for naval, acoustic and marine applications. Herein, we propose a passive cavity deflation mechanism made of a hollow tube attached to a sphere with radial holes near the base, called the Kiara tube. We perform a series of experiments varying tube length, radial hole area and drop height to assess what factors influence cavity deflation and utilize high-speed cameras and image processing to quantify the cavity deflation. In general, tube lengths less than a critical length provide no deflation while larger tube lengths provide a consistent deflation rate. We will also discuss the effects of additional factors such as drop height, radial hole area, surface coatings, and forces as they relate to the cavity deflation rate. [Preview Abstract] |
Saturday, November 23, 2019 4:05PM - 4:18PM |
A01.00006: The effect of bending stiffness on the impact of flexible plates on a water surface An Wang, Kit Pan Wong, Miao Yu, Kenneth T. Kiger, James H. Duncan The controlled oblique impact of a series of flexible/rigid rectangular plates (length 108~cm, width 41~cm, pitch angle 10$^\circ$) on a quiescent water surface is studied experimentally. The flexible plates, which are made of 6061 aluminum, have various thicknesses while the rigid plate structure is made of two aluminum plates stiffened by a light-weight frame glued between them. The mounting structure allows each end of the plate to rotate about a transverse horizontal axis located slightly above the plate. For each plate, the motion trajectory and the impact speed are varied. The plate thickness and impact speed are chosen so that the impact time scale is on the same order of the wet natural period of the plate. The spray formation, the transient impact force, the moment about a horizontal transverse axis, the deflection along the plate's center line and the impact pressure on the plate's lower surface are measured with various techniques. For the same plate, it is found the maximum impact force/moment scale with the square of the component of the impact velocity normal to the undeformed plate. The temporal evolution of impact force and moment arm each have two distinct slopes. The relationship of this behavior to the plate's deformation is explored. [Preview Abstract] |
Saturday, November 23, 2019 4:18PM - 4:31PM |
A01.00007: Tuning the restitution coefficient of closed containers partially filled with water Pablo Gutierrez, Gustavo Castillo, Vicente Salinas, Francisco Olea, Leonardo Gordillo It is well known that when open containers partially filled with water fall, a strong jet emerges after they hit the ground (Milgram, JFM, 1969). Surprisingly Antkowiak et al. (JFM, 2007) showed that if the water surface of the flow remains perfectly flat during the fall, no jet forms at all. In this work, we show how the shape of the water surface just before the impact not only has an effect on the presence of the jet but also on the rebound of the overall system (container$+$water). We focus in closed containers and study the influence of the filling fraction, which has been shown to be a relevant ingredient in the bouncing of spheres partially filled with grains and liquids on surfaces (Killian, Klaus, and Truscott, PoF, 2012; Pacheco-V\'{a}zquez and Dorbolo, Scientific Reports, 2013). Our analysis allow us to couple water-surface shape and filling fraction to estimate the momentum transfer and energy loss due to the internal motion of the liquid and link it with the restitution coefficient of the overall system. The understanding of this effect allow us to tune the coefficient restitution of the system before its release. [Preview Abstract] |
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