scholarly journals The Velocity Field Underneath a Breaking Rogue Wave: Laboratory Experiments Versus Numerical Simulations

Fluids ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 68 ◽  
Author(s):  
Alberto Alberello ◽  
Alessandro Iafrati
Keyword(s):  
Velocity Field ◽  
Numerical Simulations ◽  
Wave Breaking ◽  
Ad Hoc ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Wave Crest ◽  
Driving Mechanisms ◽  
Image Velocimetry ◽  
Particle Image Velocimetry Method

Wave breaking is the most characteristic feature of the ocean surface. Physical investigations (in the field and at laboratory scale) and numerical simulations have studied the driving mechanisms that lead to wave breaking and its effects on hydrodynamic loads on marine structures. Despite computational advances, accurate numerical simulations of the complex breaking process remain challenging. Validation of numerical codes is routinely performed against experimental observations of the surface elevation. However, it is still uncertain whether simulations can accurately reproduce the velocity field under breaking waves due to the lack of ad-hoc measurements. In the present work, the velocity field recorded with a Particle Image Velocimetry method during experiments conducted in a unidirectional wave tank is directly compared to the results of a corresponding numerical simulation performed with a Navier–Stokes (NS) solver. It is found that simulations underpredict the velocity close to the wave crest compared to measurements. Higher resolutions seem necessary in order to capture the most relevant details of the flow.

scholarly journals VALIDATION OF A BUOYANCY-MODIFIED TURBULENCE MODEL BY NUMERICAL SIMULATIONS OF BREAKING WAVES OVER A FIXED BAR

2018 ◽  
pp. 71
Author(s):  
Brecht Devolder ◽  
Peter Troch ◽  
Pieter Rauwoens
Keyword(s):  
Numerical Simulations ◽  
Wave Breaking ◽  
Surf Zone ◽  
Breaking Waves ◽  
Navier Stokes ◽  
Two Phase ◽  
Numerical Wave Flume ◽  
Wave Flume ◽  
Nearshore Sediment Transport ◽  
Run Up

The surf zone dynamics are governed by important processes such as turbulence generation , nearshore sediment transport , wave run-up and wave overtopping at a coastal structure. During field observations , it is very challenging to measure and quantify wave breaking turbulence . Complementary to experimental laboratory studies in a more controlled environment , numerical simulations are highly suitable to understand and quantify surf zone processes more accurately. In this study, wave propagation and wave breaking over a fixed barred beach profile is investigated using a two­ phase Navier-Stokes flow solver. We show that accurate predictions of the turbulent two-phase flow field require special attention regarding turbulence modelling. The numerical wave flume is implemented in the open­ source OpenFOAM library. The computed results (surface elevations , velocity profiles and turbulence levels) are compared against experimental measurements in a wave flume (van der A et al., 2017) .

scholarly journals Assessment of Numerical Methods for Plunging Breaking Wave Predictions

2021 ◽  
Vol 9 (3) ◽  
pp. 264
Author(s):  
Shanti Bhushan ◽  
Oumnia El Fajri ◽  
Graham Hubbard ◽  
Bradley Chambers ◽  
Christopher Kees
Keyword(s):  
Solitary Wave ◽  
Wave Breaking ◽  
Large Scale ◽  
Turbulence Models ◽  
Navier Stokes ◽  
Wave Crest ◽  
Breaking Wave ◽  
Rans Turbulence Models ◽  
Run Up ◽  
Better Than

This study evaluates the capability of Navier–Stokes solvers in predicting forward and backward plunging breaking, including assessment of the effect of grid resolution, turbulence model, and VoF, CLSVoF interface models on predictions. For this purpose, 2D simulations are performed for four test cases: dam break, solitary wave run up on a slope, flow over a submerged bump, and solitary wave over a submerged rectangular obstacle. Plunging wave breaking involves high wave crest, plunger formation, and splash up, followed by second plunger, and chaotic water motions. Coarser grids reasonably predict the wave breaking features, but finer grids are required for accurate prediction of the splash up events. However, instabilities are triggered at the air–water interface (primarily for the air flow) on very fine grids, which induces surface peel-off or kinks and roll-up of the plunger tips. Reynolds averaged Navier–Stokes (RANS) turbulence models result in high eddy-viscosity in the air–water region which decays the fluid momentum and adversely affects the predictions. Both VoF and CLSVoF methods predict the large-scale plunging breaking characteristics well; however, they vary in the prediction of the finer details. The CLSVoF solver predicts the splash-up event and secondary plunger better than the VoF solver; however, the latter predicts the plunger shape better than the former for the solitary wave run-up on a slope case.

The velocity field under breaking waves: coherent structures and turbulence

2002 ◽  
Vol 454 ◽  
pp. 203-233 ◽  
Author(s):  
W. KENDALL MELVILLE ◽  
FABRICE VERON ◽  
CHRISTOPHER J. WHITE
Keyword(s):  
Velocity Field ◽  
Kinetic Energy ◽  
Reynolds Stress ◽  
Particle Image ◽  
Early Stage ◽  
Breaking Waves ◽  
Video Frame ◽  
Turbulent Kinetic Energy Budget ◽  
Image Velocimetry ◽  
Coherent Vortex

Digital particle image velocimetry (DPIV) measurements of the velocity field under breaking waves in the laboratory are presented. The region of turbulent fluid directly generated by breaking is too large to be imaged in one video frame and so an ensemble-averaged representation of the flow is built up from a mosaic of image frames. It is found that breaking generates at least one coherent vortex that slowly propagates downstream at a speed consistent with the velocity induced by its image in the free surface. Both the kinetic energy of the flow and the vorticity decay approximately as t−1. The Reynolds stress of the turbulence also decays as t−1 and is, within the accuracy of the measurements, everywhere negative, consistent with downward transport of streamwise momentum. Estimates of the mometum flux from waves to currents based on the measurements of the Reynolds stress are consistent with earlier estimates. The implications of the measurements for breaking in the field are discussed. Based on geometrical optics and wave action conservation, we suggest that the presence of the breaking-induced vortex provides an explanation for the suppression of short waves by breaking. Finally, in Appendices, estimates of the majority of the terms in the turbulent kinetic energy budget are presented at an early stage in the evolution of the turbulence, and comparisons with independent acoustical measurements of breaking are presented.

Computational and Experimental Simulation of Nonbreaking and Breaking Waves for the Investigation of Structural Loads and Motions

2006 ◽  
Author(s):  
Gu¨nther F. Clauss ◽  
Robert Stu¨ck ◽  
Florian Stempinski ◽  
Christian E. Schmittner
Keyword(s):  
Data Transfer ◽  
Stokes Equations ◽  
Wave Structure ◽  
Breaking Waves ◽  
Experimental Simulation ◽  
Navier Stokes ◽  
Wave Crest ◽  
Breaking Wave ◽  
Simulation Code ◽  
Wave Trains

For the analysis of loads and motions of marine structures in harsh seaways precise information about the hydrodynamics of waves is required. While the surface motion of waves can easily be measured in physical wave tanks other critical characteristics such as the instantaneous particle velocity and acceleration as well as the pressure field, especially under the wave crest are difficult and time-consuming to obtain. Therefore a new method is presented to approximate the wave potential of a given instantaneous wave contour. Numerical methods — so called numerical wave tanks (NWTs) — are developed to provide the desired insight into wave hydrodynamics. A potential theory method based on the Finite Element method (Pot/FE), a RANSE (Reynolds-Averaged Navier-Stokes Equations) method applying VOF (Volume of Fluid) and a combination of both is utilized for the simulation of different model wave trains. The coupling of both CFD (computational fluid dynamics) solvers is a useful approach to benefit from the advantages of the two different methods: The Pot/FE solver WAVETUB (wave simulation code developed at Technical University Berlin) allows a very fast and accurate simulation of the propagation of nonbreaking waves while the RANSE/VOF solver has the capability of simulating breaking waves. Two different breaking criteria for the detection of wave breaking are implemented in WAVETUB for triggering the automated coupling process by data transfer at the interface. It is shown that an efficient method for the simulation of breaking wave trains including wave-structure interaction in 2D and 3D is established by the coupling of both CFD codes. All results are discussed in detail.

scholarly journals SERRE GREEN-NAGHDI MODELLING OF WAVE TRANSFORMATION BREAKING AND RUN-UP USING A HIGH-ORDER FINITE-VOLUME FINITE-DIFFERENCE SCHEME

2011 ◽  
Vol 1 (32) ◽  
pp. 13 ◽  
Author(s):  
Marion Tissier ◽  
Philippe Bonneton ◽  
Fabien Marche ◽  
Florent Chazel ◽  
David Lannes
Keyword(s):  
Energy Dissipation ◽  
Finite Difference ◽  
Finite Volume ◽  
Wave Breaking ◽  
Ad Hoc ◽  
Laboratory Data ◽  
Breaking Waves ◽  
Wave Transformation ◽  
Finite Volume Schemes ◽  
Boussinesq Model

In this paper, a fully nonlinear Boussinesq model is presented and applied to the description of breaking waves and shoreline motions. It is based on Serre Green-Naghdi equations, solved using a time-splitting approach separating hyperbolic and dispersive parts of the equations. The hyperbolic part of the equations is solved using Finite-Volume schemes, whereas dispersive terms are solved using a Finite-Difference method. The idea is to switch locally in space and time to NSWE by skipping the dispersive step when the wave is ready to break, so as the energy dissipation due to wave breaking is predicted by the shock theory. This approach allows wave breaking to be handled naturally, without any ad-hoc parameterization for the energy dissipation. Extensive validations of the method are presented using laboratory data.

scholarly journals Breaking of Progressive Internal Gravity Waves: Convective Instability and Shear Instability*

2010 ◽  
Vol 40 (10) ◽  
pp. 2243-2263 ◽  
Author(s):  
Wei Liu ◽  
Francis P. Bretherton ◽  
Zhengyu Liu ◽  
Leslie Smith ◽  
Hao Lu ◽  
...  
Keyword(s):  
Numerical Simulations ◽  
Wave Energy ◽  
Wave Breaking ◽  
Convective Instability ◽  
Shear Instability ◽  
High Mode ◽  
Wave Crest ◽  
Linear Wave ◽  
Primary Wave ◽  
Wave Induced

Abstract The breaking of a monochromatic two-dimensional internal gravity wave is studied using a newly developed spectral/pseudospectral model. The model features vertical nonperiodic boundary conditions that ensure a realistic simulation of wave breaking during the wave propagation. Isopycnal overturning is induced at a local wave steepness of sc = 0.75–0.79, which is below the conventional threshold of s = 1. Isopycnal overturning is a sufficient condition for subsequent wave breaking by convective instability. When s = sc, little primary wave energy is being transferred to high-mode harmonics. Beyond s = 1, high-mode harmonics grow rapidly. Primary wave energy is more efficiently transferred by waves of lower frequency. A local gradient Richardson number is defined as Ri = −(g/ρ0)(dρ/dz)/ζ2 to isolate convective instability (Ri ≤ 0) and wave-induced shear instability (0 < Ri < 0.25), where dρ/dz is the local vertical density gradient and ζ is the horizontal vorticity. Consistent with linear wave theory, the probability density function (PDF) for occurrence of convective instability has a maximum at wave phase ϕ = π/2, where the wave-induced density perturbations to the background stratification are the greatest, whereas the wave-induced shear instability has maxima around ϕ = 0 (wave trough) and ϕ = π (wave crest). Nonlinearities in the wave-induced flow broaden the phase span in PDFs of both instabilities. Diapycnal mixing in numerical simulations may be compared with that in realistic oceanic flows in terms of the Cox number. In the numerical simulations, the Cox numbers increase from 1.5 (s = 0.78) to 21.5 (s = 1.1), and the latter is in the lower range of reported values for the ocean.

scholarly journals Numerical Simulations of Non-Breaking, Breaking and Broken Wave Interaction with Emerged Vegetation Using Navier-Stokes Equations

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2561 ◽  
Author(s):  
Xuefeng Zou ◽  
Liangsheng Zhu ◽  
Jun Zhao
Keyword(s):  
Wave Propagation ◽  
Wave Height ◽  
Wave Breaking ◽  
Surf Zone ◽  
Stokes Equations ◽  
Wave Interaction ◽  
Breaking Waves ◽  
Breaking Point ◽  
Navier Stokes ◽  
Inertia Force

Coastal plants can significantly dissipate water wave energy and services as a part of shoreline protection. Using plants as a natural buffer from wave impacts remains an attractive possibility. In this paper, we present a numerical investigation on the effects of the emerged vegetation on non-breaking, breaking and broken wave propagation through vegetation over flat and sloping beds using the Reynolds-average Navier-Stokes (RANS) equations coupled with a volume of fluid (VOF) surface capturing method. The multiphase two-equation k-ω SST turbulence model is adopted to simulate wave breaking and takes into account the effects enhanced by vegetation. The numerical model is validated with existing data from several laboratory experiments. The sensitivities of wave height evolution due to wave conditions and vegetation characteristics with variable bathymetry have been investigated. The results show good agreement with measured data. For non-breaking waves, the wave reflection due to the vegetation can increase wave height in front of the vegetation. For breaking waves, it is shown that the wave breaking behavior can be different when the vegetation is in the surf zone. The wave breaking point is slightly earlier and the wave height at the breaking point is smaller with the vegetation. For broken waves, the vegetation has little effect on the wave height before the breaking point. Meanwhile, the inertia force is important within denser vegetation and is intended to decrease the wave damping of the vegetation. Overall, the present model has good performance in simulating non-breaking, breaking and broken wave interaction with the emerged vegetation and can achieve a better understanding of wave propagation over the emerged vegetation.

Laboratory studies of Lagrangian transport by breaking surface waves

2019 ◽  
Vol 876 ◽  
Author(s):  
Luc Lenain ◽  
Nick Pizzo ◽  
W. Kendall Melville
Keyword(s):  
Numerical Simulations ◽  
Wave Breaking ◽  
Linear Prediction ◽  
Critical Role ◽  
Breaking Waves ◽  
Direct Numerical Simulations ◽  
Laboratory Studies ◽  
Maximum Slope ◽  
Lagrangian Transport ◽  
Surface Transport

While it has long been recognized that Lagrangian drift at the ocean surface plays a critical role in the kinematics and dynamics of upper ocean processes, only recently has the contribution of wave breaking to this drift begun to be investigated through direct numerical simulations (Deike et al., J. Fluid Mech., vol. 829, 2017, pp. 364–391; Pizzo et al., J. Phys. Oceanogr., vol. 49(4), 2019, pp. 983–992). In this work, laboratory measurements of the surface Lagrangian transport due to focusing deep-water non-breaking and breaking waves are presented. It is found that wave breaking greatly enhances mass transport, compared to non-breaking focusing wave packets. These results are in agreement with the direct numerical simulations of Deike et al. (J. Fluid Mech., vol. 829, 2017, pp. 364–391), and the increased transport due to breaking agrees with their scaling argument. In particular, the transport at the surface scales with $S$, the linear prediction of the maximum slope at focusing, while the surface transport due to non-breaking waves scales with $S^{2}$, in agreement with the classical Stokes prediction.

Kinetic, Dynamic and Energy Characteristics of Vortex Evolution on Bragg Scattering of Water Waves

2010 ◽  
Author(s):  
Tai-Wen Hsu ◽  
Shan-Hwei Ou ◽  
Chin-Yen Tsai ◽  
Jian-Feng Lin
Keyword(s):  
Velocity Field ◽  
Water Waves ◽  
Wave Reflection ◽  
Wave Theory ◽  
Navier Stokes ◽  
Linear Wave ◽  
Bragg Scattering ◽  
Energy Characteristics ◽  
Linear Wave Theory ◽  
Image Velocimetry

The vortex generation and dissipation under Bragg scattering of water wave propagation over a series of submerged rectangular breakwaters are investigated both numerically and experimentally. A Reynolds Averaged Navier-Stokes (RANS) model combined with a k–ε turbulence closure is applied to simulate the entire vortex evolution process as water waves pass over a series of artificial rectangular bars. The Particle Image Velocimetry (PIV) is also used to measure the velocity field in the vicinity of the obstacles. The numerical model is validated through the comparisons of water surface elevations and velocity field with the measurements. The mechanism of vortex evolution and its influence on the interaction of water waves with submerged structures for both cases of resonance and non-resonance were studied. Wave reflection coefficients for both resonant and non-resonant cases were calculated and compared with experiments and solutions based on the linear wave theory. It is also found that the calculated vortex intensity at the last bar is only one third of that at the leading bar for the near-resonant case. The local kinetic energy is also found to attain its minimum value at a place where potential energy became larger in Bragg scattering of water waves.

The Velocity Field Underneath Linear and Nonlinear Breaking Rogue Waves

2016 ◽  
Author(s):  
Alberto Alberello ◽  
Amin Chabchoub ◽  
Alexander V. Babanin ◽  
Jason P. Monty ◽  
John Elsnab ◽  
...  
Keyword(s):  
Velocity Field ◽  
Field Experiments ◽  
Dynamical Evolution ◽  
Wave Theory ◽  
Rogue Waves ◽  
Breaking Waves ◽  
New Wave ◽  
Image Velocimetry ◽  
Surface Measurements ◽  
The University

During the past decades, a large number of waves of extreme height and abnormal shape, also known as freak or rogue waves, have been recorded in the ocean. Velocities and related forces can be enormous and jeopardise the safety of marine structures. Here, we present an experimental study devoted to investigate the velocity field underneath a breaking rogue wave. The latter is replicated in the laboratory by means of dispersive focussing methods such as the New Wave Theory and nonlinear focussing techniques based on the Nonlinear Schrödinger equation. While the former is basically a liner method, the nonlinear focussing fully accounts for the dynamical evolution of the wave field. Experiments were carried out in the Extreme Air-Sea Interaction flume of the University of Melbourne using a Particle Image Velocimetry (PIV) system to measure the velocity field below the water surface. Measurements show that the mechanism of generation affects the shape of the breaking waves as well as the kinematic field and associated hydrodynamic forces. Particularly, the New Wave Theory leads to higher velocities and a more energetic breaker than the nonlinear focussing.

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