Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session L05: Free-surface Flows: Interaction with Structures |
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Chair: James Duncan, University of Maryland, College Park Room: Georgia World Congress Center B207 |
Monday, November 19, 2018 4:05PM - 4:18PM |
L05.00001: On the Spray Generated during the Vertical Impact of a Rigid Flat Plate on a Quiescent Water Surface James H Duncan, An Wang The spray generated as a rigid rectangular plate (122 cm by 38 cm) is driven with a controlled motion into a quiescent water surface is studied experimentally. The plate is oriented with its long edges horizontal and its short edges set at various angles between 10 and 25 degrees from horizontal. The velocity of the plate (W) remains constant (0.4 ≤ W ≤ 1.2 m/s) from initial impact until the upper long edge of the plate reaches the mean water level. A laser induced fluorescence technique is used to measure the evolution of the spray in a vertical plane at the center of the long edges of the plate. As the plate's lower edge reaches the water surface, a thin jet (defined as Type I spray) is generated and moves along the bottom surface of the plate at high speed. This jet connects to the rising water surface under the plate via a root point and breaks up into ligaments and droplets at its tip. As the root point reaches the horizontal position of the upper edge of the plate, a thin spray sheet (Type II spray) begins to form from the surrounding water surface. Various characteristics of both sprays are explored in detail. |
Monday, November 19, 2018 4:18PM - 4:31PM |
L05.00002: Surface wave energy absorption using elastic slender structures Clotilde Nové-Josserand, Benjamin Thiria, Ramiro Godoy-Diana Aquatic plants are known to protect coastlines and riverbeds from erosion by damping waves and fluid flow. These flexible structures absorb the fluid-borne energy of an incoming fluid by deforming mechanically. I will present our recent work on an experimental canopy model in a wave tank, where we focus on the mechanisms involved in these fluid-elasticity interactions, considering also their potential as a wave energy harvesting system. We study an array of flexible structures that are subjected to the action of a surface wave field, investigating the role of spacing between the elements of the array on the ability of our system to absorb energy from the flow. The energy absorption potential of the canopy model is examined using global wave height measurements for the wave field and local measurements of the elastic energy based on the kinematics of each element of the canopy. We study different canopy arrays and show in particular that flexibility improves wave damping by around 40%, for which half is potentially harvestable. |
Monday, November 19, 2018 4:31PM - 4:44PM |
L05.00003: The Oblique Impact of a Flexible Flat Plate on a Water Surface An Wang, Kit Pan Wong, Hyun-Tae Kim, Daniel Yang, Miao Yu, Kenneth Kiger, James H Duncan The impact of a flexible aluminum plate (122 cm by 38 cm by 0.79 cm) on a quiescent water surface is studied experimentally. The plate is installed with a roll angle of 10° and a pitch angle of 5° and approaches the water surface with three sets of horizontal (U) and vertical (W) velocity components, (U, W) = (5.0, 1.0), (4.0, 0.8), (3.0, 0.6) m/s. The surface profiles of the spray generated during the impact are measured with a laser induced fluorescence technique in a vertical plane perpendicular to the horizontal motion. The deformation of the plate is characterized by strain and out-of-plane deflection measurements at various locations on the top surface of the plate. The strains are measured with novel optical fiber Bragg grating sensors. Two types of spray are found and their behaviors vary significantly with impact speed. The location of maximum strain propagates from the trailing edge to the leading edge of the plate. The maximum deflection at the middle of the plate increases linearly with the impact speed. The spray measurements are compared to those from companion experiments with a rigid plate. |
Monday, November 19, 2018 4:44PM - 4:57PM |
L05.00004: Flexible V-Shaped Wedge Water Entry: When is One-Way Coupling Good Enough? Zhongshu Ren, M. Javad Javaherian, Christine Ikeda-Gilbert Slamming events occur very frequently in high-speed craft and reduce the operational envelope of a vessel. Vertical wedge drop tests simulating the vertical slamming of a ship cross-section give some fundamental insights into the physics of the fluid-structure interaction problem. In this work, a flexible wedge was vertically dropped into calm water. The structural deflection was measured using stereoscopic digital image correlation, and the pressure was resolved using an array of eight pressure sensors along the midline of one side of the wedge bottom. Other quantities measured include vertical position and acceleration of the wedge, and strains on the wedge bottom. A relationship between the nondimensional pressure coefficient and plate deflection will be proposed based on experimental results. Theoretically, there is a critical value of nondimensional deflection beyond which the pressure coefficient will be influenced by the structural response. A one-way coupling between Vorus’ theory and shear deformation plate theory was found to match well with experiments when the structural deflection was small. |
Monday, November 19, 2018 4:57PM - 5:10PM |
L05.00005: Prediction of Spray Root Location on a Deforming Wedge during Vertical Water Entry Christine Ikeda-Gilbert, Rohan Bardhan, Zhongshu Ren The phenomenon of slamming of ocean-going craft traveling at high-speed restricts the operating envelope of the vessel. The slamming (or impact) process is simulated using a wedge shape, that models a single section of the hull, vertically dropped into calm water. The model used in this study has a flexible bottom that deforms upon impact with the free surface. Much previous work done in this field assumes a rigid wedge. In the current study, Wagner’s method for 2-D water entry is extended to analyze a flexible wedge. The deformed shapes of the wedge at each timestep are taken from an experiment conducted in the lab. Second, third, and fourth order polynomial fits have been applied to deformation data to model the form of the bottom. The fourth order fit most accurately models the experiment and is used in calculating the location of the waterline. The calculated waterline locations are compared with the actual waterline location from the experiment, which is determined using image processing from high-speed cameras that film the impact process. The comparison agrees well, but discrepancies occur due to the linear assumptions in Wagner’s theory. |
Monday, November 19, 2018 5:10PM - 5:23PM |
L05.00006: Water Entry of a Flexible Wedge: The Correlation between Instantaneous Jet Root, Pressure History and Structural Response M. Javad Javaherian, Zhongshu Ren, Christine Ikeda-Gilbert Slamming plays a crucial role in the design process of high-speed craft. Using a vertically falling wedge drop experiment to model vertical impacts, the hydrodynamic loads and resulting structural response can be attributed to the loss in momentum of the penetrating body. As a result, a wave is formed, and the point of attachment to the hull is called the spray root. In this talk, a discussion of the results from the experimental investigation of water entry of a flexible wedge with a 20-degree deadrise angle will be presented. Hydrodynamic pressure and kinematic motions of the wedge are measured. The deflection of the thin bottom plate is measured using stereoscopic digital image correlation. High-speed cameras are used to capture the spray root. The instantaneous spray root positions on the flexible wedge are compared to its corresponding pressure distribution at each time increment. Results were compared with a rigid wedge drop experiment. Results show that evolution of spray root on a flexible wedge is slightly delayed compared to the rigid one. In fact, the jet has to travel additional distance on the wedge due to the curvature in flexible bottom that is caused by the fluid-structure interaction. |
Monday, November 19, 2018 5:23PM - 5:36PM |
L05.00007: Solution of Driven Thin Film Equations on Curved Substrates by the Helmholtz Minimum Dissipation Principle Chengzhe Zhou, Sandra Troian The dynamical behavior of thin viscous films on curved substrates is critically important to a range of processes fundamental to the coating industry, micro-lithography and biological flows. Substrate curvature can strongly affect film shape and stability, especially when the local film thickness couples to an external field. For thin viscous films on planar domains, accurate solutions can be obtained by exploiting the gradient flow structure of the governing equation and appealing to the Helmholtz minimum dissipation principle. Here we show how this minimization principle can be extended to include thin films on curved substrates in which the local film thickness is actively coupled to an external electric field and mitigated only by capillary forces. Accurate approximate solutions are obtained by invoking a variational principle and restricting trial solutions to polynomial functions in the direction normal to the substrate. We demonstrate this approach for a thin dielectric film coating a cylindrical conductor using a boundary/finite element method. We find that this solution method offers keen physical insight into allowable film configurations not accessible to planar geometries. |
Monday, November 19, 2018 5:36PM - 5:49PM |
L05.00008: Investigation of sloshing characteristics in the sloped bottom liquid container under periodic excitation. Amiya Pandit Sloshing can be defined as the formation of wave or oscillation of unrestrained free liquid surface under the influence of any kind of external excitation. Since the amount of liquid participates in sloshing depends on some crucial parameters, but here in this study, a slope bottom liquid container is addressed which dissipate the sloshing energy and minimize the hydrodynamic pressure distribution on the walls of the container. The concept of providing slope has come upon as the wave energy gets dissipated along the shores of the beach. So in this present study, a numerical approach based on Galerkin finite element method is adopted to analyze the liquid sloshing in the sloped bottom tank under periodic horizontal ground motion. The whole liquid domain is discretized as the combination of three node triangular element and four-node quadrilateral element. The efficiency of the present numerical formulation is verified by comparing the fundamental sloshing frequency with previously published experimental and analytical solution. The finite element code also capable of determining the slosh displacement from the free surface, base shear at tank bottom and pressure distribution along the walls of the container at a different instance of time. |
Monday, November 19, 2018 5:49PM - 6:02PM |
L05.00009: Analytical calculation of the added mass and the wave damping due to an oscillating horizontal circular cylinder using the bi-polar coordinate Gibbeum Lee, Yeunwoo Cho The added mass and the wave damping due to an oscillating horizontal circular cylinder are analytically calculated using the bi-polar coordinate. In the bi-polar coordinate, a point is uniquely defined by two orthogonal circles. These circles can be used to represent the mean surface of partially- and fully submerged oscillating circular cylinder along with the mean position of the free surface. By expressing boundary conditions on the surface of the cylinder and the free surface in terms of the bi-polar coordinate, the Laplace equation in terms of the velocity potential is analytically solved, and, thus, the added mass and the wave damping are analytically obtained. Both partially/fully submerged and heave/surge cases are considered. The analytical results are compared with existing numerical studies using the boundary element method. They agree with each other very well. |
Monday, November 19, 2018 6:02PM - 6:15PM |
L05.00010: Large-eddy simulation of solitary wave and bridge pier interaction: Model development and validation Elaheh Bagherizadeh, Ali Khosronejad |
Monday, November 19, 2018 6:15PM - 6:28PM |
L05.00011: Abstract Withdrawn A body in motion tends to stay in motion but is often slowed by friction. We investigate the friction experienced by centimeter-sized bodies sliding on water. We show that their motion is dominated by skin friction due to the boundary layer that forms in the fluid beneath the body. We develop a simple model that considers the boundary layer as quasi-steady, and is able to capture the experimental behaviour for a range of body sizes, masses, shapes and fluid viscosities. We define a dimensionless sliding number as the ratio between the fluid inertia and the body inertia, which allows us to assess the regime of validity of our model. Furthermore, we demonstrate that friction can be reduced by modification of the body's shape or bottom topography. Our results are significant for understanding natural and artificial bodies moving at the air-water interface, and can inform the design of aerial-aquatic microrobots for environmental exploration and monitoring. |
Monday, November 19, 2018 6:28PM - 6:41PM |
L05.00012: The liquid helix: Inertial-capillary adhesion of liquid jets around cylinders Etienne Jambon-Puillet, Wilco Bouwhuis, Jacco Snoeijer, Daniel Bonn From everyday experience, we all know that a solid edge can deflect a liquid flowing over it significantly, up to the point where the liquid completely sticks to the solid. Although important in pouring, printing and extrusion processes, there is no predictive model of this so-called ``teapot effect''. Here by grazing vertical cylinders with inclined capillary liquid jets, we use the teapot effect to attach the jet to the solid and form a helical rivulet: the liquid helix. We quantitatively predict the shape of the helix by modeling how rivulets relax toward their final velocity and the critical velocity for the helix formation follows from a parameter-free inertial-capillary adhesion model. |
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