Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session J35: Free-Surface Flows: Waves I |
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Chair: Nimish Pujara, University of Wisconsin - Madison Room: 355 A |
Sunday, November 24, 2024 5:50PM - 6:03PM |
J35.00001: Wave-swash interactions: Collisions of breaking waves in shallow water Nimish Pujara, Claudio Meza-Valle On beaches, surface waves break and create a fast and shallow flow that climbs the sloping beach surface. This 'swash zone' flow, which controls the net import and export of sediment on the beach, is known to be well described by solutions to the non-linear shallow water equations. However, observations suggest that collisions of consecutive waves, known as wave-swash interactions, play an important role in suspending sediment in ways that are not well understood or modelled. We present results from a laboratory study on wave-swash interactions to improve upon existing knowledge of this phenomenon, which has only been described qualitatively in the past. We use consecutive solitary waves with different wave heights and separations to generate various wave-swash interactions and find that they can be quantitatively characterized in terms of two dimensionless parameters: (1) the ratio of wave heights and (2) the dimensionless time separation between consecutive wave crests. Using measurements of wall pressure and free-surface displacement, we also infer the total vertical acceleration. The peak vertical acceleration is upward-directed and can easily exceed gravity, even in very shallow water depths. These findings suggest that wave-swash interactions are capable of inducing large material suspension events of sediment or solutes in sediment pores. |
Sunday, November 24, 2024 6:03PM - 6:16PM |
J35.00002: Eliminating the Kelvin wake Jack Keeler, Mark Blyth Everyone has seen the v-shaped Kelvin wake-pattern visible in the wake of a moving object on the surface of water. These patterns are a rare example of a fluid dynamics phenomena well-known to scientists and layman alike. However, the wake is undesirable for a number of reasons; it can cause erosion to river banks and cause wave-drag, thus reducing the fuel efficiency. Therefore, the design of a moving body that can reduce or even eliminate these waves is important for sustainability. A typical approach is to model the boat by an imposed pressure distribution in the free-surface Bernoulli condition. In this talk we show, using a simple mathematical argument, that by a judicious choice of a pressure distribution, wave-free solutions are possible in the context of a model system; the forced Kadometsev-Petviashvili equation. Strikingly, we show that these solutions are stable, so they could potentially be visualised in a physical experiment. The answer of the question in the title is therefore; 'Yes', it is possible to eliminate Kelvin waves. |
Sunday, November 24, 2024 6:16PM - 6:29PM |
J35.00003: Turbulence below and along a free surface Filippo Coletti, Daniel Ruth, Yinghe Qi We investigate the flow below and along the non-wavy free surface of a volume of homogeneous turbulence. We leverage a two cubic meter water tank stirred by randomly actuated jets, where particle image velocimetry resolves from the dissipative to the integral scales below the surface. As the Reynolds number is increased, both the vertical and horizontal contributions to the turbulent kinetic energy approach the prediction of rapid distortion theory. At odds with the theory, however, the integral scale of the horizontal fluctuations grows as the surface is approached. Indeed, along horizontal separations, the direct cascade of horizontal energy is hindered, and an inverse cascade of vertical energy is established. This is connected to the balance of upwelling events (associated with extensional surface-parallel motions and vertical compression) and downwelling events (favoring horizontal compression and vertical stretching). This picture is reflected in the flow along the surface, where we resolve the dynamics of vorticity, strain-rate and divergence by tracking highly concentrated microscopic floating particles. We find that, in contrast with the three-dimensional flow, the compression of surface-attached vortices is as common and intense as their stretching, resulting in long-lived structures and a greatly reduced dissipation rate. |
Sunday, November 24, 2024 6:29PM - 6:42PM |
J35.00004: Designing Input Wave Signals to Achieve Desired Ship Responses Through Linear and Nonlinear Conditioning Dustin Keys, Hamid Sadat We present a new method for generating input wave signals for time-domain ship hydrodynamics simulations which are designed to achieve certain outcomes in ship responses, such as heave, pitch, or roll. By using conditional inputs, this method minimizes guesswork and reduces computation time, especially for predicting rare events. The developed model supports both linear and nonlinear (quadratic) conditioning of ship responses. Linear conditions allow for setting desired amplitude, derivative, and/or average response over a period, while quadratic conditions target specific envelopes and/or spectral moments. Although linear conditions on a Gaussian process preserve the Gaussian nature of the output, quadratic conditions do not, representing an advancement beyond traditional Gaussian approximations. The results demonstrate that the method effectively generates wave signals that meet the desired ship response criteria for both linear and nonlinear conditions. |
Sunday, November 24, 2024 6:42PM - 6:55PM |
J35.00005: Experimental exploration of free-surface turbulence Eirini I Florou, Philippe M Bardet Free surface flows are complex, multiphase and multiscale flow regimes with great interest for naval hydrodynamics (e.g., white water behind ships). Interfacial transport, mixing and bubble entrainment are some of the physical processes present in this environment that still need attention experimentally to validate Computational Fluid Dynamics (CFD) solvers and fill gaps or assumptions in existing models. Generating free-surface turbulence (FST) in a lab is not a trivial process, especially when needed to fulfill specific flow requirements and reach turbulence levels that up to date had been unexplored experimentally. In this study we discuss challenges and practices to generate homogeneous isotropic turbulence (HIT) in an open-box facility that can reach strong turbulence levels to capture bubble entrainment events. We will discuss turbulence statistics in a large region in the vicinity of the free surface to characterize the facility, and we will explore how turbulence levels can affect turbulence statistics to challenge the energy redistribution mechanism imposed by the kinematic boundary condition at the surface. Finally, we will discuss additional challenges that arise in strong FST and practices to tackle them during data acquisition. |
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