Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session G14: Free Surface Flows: Ships and Fluid-Solid Interactions |
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Chair: Fotis Sotiropoulos, Stony Brook University Room: C125-126 |
Monday, November 21, 2016 8:00AM - 8:13AM |
G14.00001: The Impact of a Deepwater Wave on a Wall with Finite Vertical Extent An Wang, James H. Duncan The impact of a dispersively focused 2D plunging breaker (average wave frequency 1.15 Hz) on a 2D wall that is 45~cm high and 30~cm thick is studied experimentally. The temporal evolution of the water surface profile upstream of the wall is measured with a cinematic LIF technique using frame rates up to 4,500~Hz. Impact pressures on the wall are measured simultaneously at sample rates up to 900~kHz. The wall is located horizontally 6.41~m from the wave maker in all cases and the submergence of the bottom surface of the wall is varied. It is found that the impact behavior varies dramatically with the wall submergence. When the bottom is submerged by 13.3~cm, a flip-through impact occurs. In this case, the impact evolves without wave breaking and a vertical jet is formed. When the wall is submerged by less than 4.5~cm, small-amplitude components in the wave packet interact with the bottom of the wall before the main crest arrives. Ripples reflected during this interaction modify the behavior of the incoming breaker significantly. When the bottom of the wall is located sufficiently high above the mean water level, the first interaction occurs when the undisturbed wave crest collides with the wall. The highest pressures are observed in this case. [Preview Abstract] |
Monday, November 21, 2016 8:13AM - 8:26AM |
G14.00002: Tsunami-induced force and surface pressure on multiple rectangular buildings in an unsteady free-surface channel flow Alireza Bahmanpour, Ian Eames We study the flow around multiple rectangular obstacles in an unsteady free-surface channel flow using a combination of mathematical models, computations and experiments. The unsteady flow is triggered by a dam-break. The total drag force and surface pressure distribution on the obstacles are examined. The height and length of the building are fixed; the influence of initial water height and blocking ratio $b/w$ is studied. The force scalings are confirmed from the computational analysis and found to be consistent with the experimental results. The effects of the additional buildings on the total drag force are noted and compared against the case of a single building. Increasing the number of buildings as well as the blocking ratio results in the water to inundate further onshore. The pressure distribution on the individual surfaces are analyzed and shown to vary linearly with height from the building base and dominated by the hydrostatic component. We summarize the results in terms of a new $Fr$ - $b/w$ regime diagram and explain how the force on buildings subject to an unsteady flow can be estimated from the upstream velocity and water height. [Preview Abstract] |
Monday, November 21, 2016 8:26AM - 8:39AM |
G14.00003: Computational simulations of the interaction of water waves with pitching flap-type ocean wave energy converters Ashish Pathak, Mehdi Raessi Using an in-house computational framework, we have studied the interaction of water waves with pitching flap-type ocean wave energy converters (WECs). The computational framework solves the full 3D Navier-Stokes equations and captures important effects, including the fluid-solid interaction, the nonlinear and viscous effects. The results of the computational tool, is first compared against the experimental data on the response of a flap-type WEC in a wave tank, and excellent agreement is demonstrated. Further simulations at the model and prototype scales are presented to assess the validity of the Froude scaling. The simulations are used to address some important questions, such as the validity range of common WEC modeling approaches that rely heavily on the Froude scaling and the inviscid potential flow theory. Additionally, the simulations examine the role of the Keulegan-Carpenter (KC) number, which is often used as a measure of relative importance of viscous drag on bodies exposed to oscillating flows. The performance of the flap-type WECs is investigated at various KC numbers to establish the relationship between the viscous drag and KC number for such geometry. That is of significant importance because such relationship only exists for simple geometries, e.g., a cylinder. [Preview Abstract] |
Monday, November 21, 2016 8:39AM - 8:52AM |
G14.00004: Computational modeling of pitching cylinder-type ocean wave energy converters using 3D MPI-parallel simulations Cole Freniere, Ashish Pathak, Mehdi Raessi Ocean Wave Energy Converters (WECs) are devices that convert energy from ocean waves into electricity. To aid in the design of WECs, an advanced computational framework has been developed which has advantages over conventional methods. The computational framework simulates the performance of WECs in a virtual wave tank by solving the full Navier-Stokes equations in 3D, capturing the fluid-structure interaction, nonlinear and viscous effects. In this work, we present simulations of the performance of pitching cylinder-type WECs and compare against experimental data. WECs are simulated at both model and full scales. The results are used to determine the role of the Keulegan-Carpenter (KC) number. The KC number is representative of viscous drag behavior on a bluff body in an oscillating flow, and is considered an important indicator of the dynamics of a WEC. Studying the effects of the KC number is important for determining the validity of the Froude scaling and the inviscid potential flow theory, which are heavily relied on in the conventional approaches to modeling WECs. [Preview Abstract] |
Monday, November 21, 2016 8:52AM - 9:05AM |
G14.00005: Fluid-structure interaction of complex bodies in two-phase flows on locally refined grids Dionysios Angelidis, Lian Shen, Fotis Sotiropoulos Many real-life flow problems in engineering applications involve fluid-structure interaction (FSI) of arbitrarily complex geometries interacting with free surface flows. Despite the recent significant computational advances, conventional numerical methods are inefficient to resolve the prevailing complex dynamics due to the inherent large disparity of spatial and temporal scales that emerge in the air/water phases of the flow and around rigid bodies. To this end, the new generation 3D, unsteady, unstructured Cartesian incompressible flow solver, developed at the Saint Anthony Falls Laboratory (SAFL), is integrated with a FSI immersed boundary method and is coupled with the level-set formulation. The predictive capabilities of our method to simulate non-linear free surface phenomena, with low computational cost, are significantly improved by locally refining the computational grid in the vicinity of solid boundaries and around the free surface interface. We simulate three-dimensional complex flows involving complex rigid bodies interacting with a free surface both with prescribed body motion and coupled FSI and we investigate breaking wave events. In all the cases, very good agreement with benchmark data is found. [Preview Abstract] |
Monday, November 21, 2016 9:05AM - 9:18AM |
G14.00006: Ship wave resistance on non-linear vertically sheared currents Benjamin Smeltzer, Yan Li, Simen Ellingsen Wave resistance is responsible for approximately one-third of the fuel consumption for large-size ships. We present calculations of this wave resistance force for a vessel traveling on a realistic background current of arbitrary depth-dependence. Previous theoretical work has considered currents that vary linearly with depth (constant shear), with results showing a dependence of the wave resistance forces on the shear strength as well as the direction of ship motion relative to the current profile. We extend these results to realistic measured profiles using a piecewise linear approximation to the current in the vertical direction. The background current is divided into layers each with a linear velocity profile. The method is applied to various measured current profiles, and wave resistance calculations are presented as a function of a number of system parameters such as ship Froude number, direction of motion relative to the surface current, and hull shape aspect ratio. For the profiles considered here, the wave resistance may vary up to a factor of two with direction of motion for low Froude numbers. [Preview Abstract] |
Monday, November 21, 2016 9:18AM - 9:31AM |
G14.00007: Free-surface turbulent wake of a surface-piercing slender body at various Froude numbers Jeonghwa Seo, Abdus Samad, Shin Hyung Rhee Free-surface effects on the near-wake around a surface-piercing slender body were investigated through flow field and wave elevation measurements. The near-wake flow field was measured by a towed underwater stereoscopic particle image velocimetry (SPIV) system. The measured flow field was analyzed to obtain coherent turbulence structures by using the Reynolds and proper orthogonal decomposition methods. Three different Froude numbers (Fr) - 0.126, 0.282, and 0.400 - were selected to represent mild, intermediate, and violent free-surface motions. At Fr = 0.126, the wave was hardly visible, although the turbulence strength and isotropy increased near the free-surface. At Fr = 0.282, though it was steady and smooth, wave-induced separation was clearly observed near the juncture of the free-surface and model trailing edge. At Fr = 0.400, wave breaking and the resulting bubbly free-surface were developed with an expanded wave-induced separation region. The wave-induced separation stimulated momentum transfer and turbulence dissipation, resulting in a significant change in the frequency of dominant free-surface motion in the downstream. [Preview Abstract] |
Monday, November 21, 2016 9:31AM - 9:44AM |
G14.00008: Modified Contact Line Dynamics about a Surface-Piercing Hydrofoil Morgane Grivel, David Jeon, Morteza Gharib The contact line around a surface-piercing hydrofoil is modified by introducing alternating hydrophobic and hydrophilic bands along one side of the body. These bands are either aligned perpendicular or parallel to the flow direction. The other side of the hydrofoil is un-patterned and retains its original, uniformly hydrophilic properties. The hydrofoil is mounted onto air bearings, such that it can freely move side-to-side in the water tunnel. A force sensor is attached to the setup via a universal joint in order to measure the forces acting on the body for several Reynolds numbers (ranging from 10$^{\mathrm{4}}$ to 10$^{\mathrm{5}})$ and angles of attack (ranging from -10$^{\mathrm{o}}$ to 10$^{\mathrm{o}})$. Cameras are also used to record the resulting flow structures and free surface elevation. The generation of wave trains and an altered free-surface elevation (also associated with the generation of surface waves) are observed over a wide range flow conditions. Force measurements elucidate how introducing these flow features impacts the forces acting on the hydrofoil, specifically with regards to the generation of lateral forces due to the asymmetric wetting conditions on either side of the hydrofoil. [Preview Abstract] |
Monday, November 21, 2016 9:44AM - 9:57AM |
G14.00009: Hydrodynamic interaction between rigid surfaces planing on water. Ghazi Bari, Konstantin Matveev This study addresses hydrodynamic interaction of multi-surface planing hulls in the linearized, inviscid, steady flow approximation. A potential-flow-based hydrodynamic sources are distributed on the water surface to model water flow around three-dimensional hulls at finite Froude numbers. The pressure distribution on the hull surfaces are calculated as a part of the solution, and then the lift force and center of pressure are determined. For validation, numerical results are compared with an available analytical solution, experimental results, and empirical correlation equations. Parametric calculations are carried out for different hull designs in variable speed regimes, hull aspect ratios, deadrise angles and hull spacings. Results are presented for the lift coefficient, drag components, lift-drag ratio, center of pressure, and some illustrations are given for the water surface elevations. Obtained results can assist naval architects in improving design of high speed marine vehicles. [Preview Abstract] |
Monday, November 21, 2016 9:57AM - 10:10AM |
G14.00010: Turbulent mass flux closure modeling for variable density turbulence in the wake of an air-entraining transom stern Kelli Hendrickson, Dick Yue This work presents the development and \emph{a priori} testing of closure models for the incompressible highly-variable density turbulent (IHVDT) flow in the near wake region of a transom stern. This complex, three-dimensional flow includes three regions with distinctly different flow behavior: (i) the convergent corner waves that originate from the body and collide on the ship center plane; (ii) the ``rooster tail" that forms from the collision; and (iii) the diverging wave train. The characteristics of these regions involve violent free-surface flows and breaking waves with significant turbulent mass flux (TMF) at Atwood number $At=(\rho_{2} - \rho_{1})/(\rho_{2} + \rho_{1})\approx 1$ for which there is little guidance in turbulence closure modeling for the momentum and scalar transport along the wake. Utilizing datasets from high-resolution simulations of the near wake of a canonical three-dimensional transom stern using conservative Volume-of-Fluid (cVOF), implicit Large Eddy Simulation (iLES), and Boundary Data Immersion Method (BDIM), we develop explicit algebraic turbulent mass flux closure models that incorporate the most relevant physical processes. Performance of these models in predicting the turbulent mass flux in all three regions of the wake will be presented. [Preview Abstract] |
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