Evolution of a quasi-steady breaking wave

1995 ◽  
Vol 302 ◽  
pp. 29-44 ◽  
Author(s):  
J. C. Lin ◽  
D. Rockwell
Keyword(s):  
Free Surface ◽  
Froude Number ◽  
Large Scale ◽  
Mixing Layer ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Small Scale ◽  
Radius Of Curvature ◽  
Breaking Wave ◽  
Large Radius

The stages of evolution of a quast-steady breaker from the onest of a capillary pattern to a fully evolved breaking wave are cgaracterized using high-image-density particle image velocimetry, which provides instrantaneous representations of the free surface and the patterns of vorticity beneath it. The initial stage, which sets in at a low value of Froude number, involves a capillary pattern along each trough-crest surface of a quasi-stationary wave. The successive crests of the capillary pattern exhihit increasing scale and culminate in a single largest-scale crest of the free surface. Immediately upstream of the large-scale crest, the capillary pattern shows counterclockwise concentrations of vorticity at its troughs and regions of clockwise vorticity beneath its crests. The onset of the final, largest-scale crest exhihits two forms: one involving no flow sparation; and the other exhibiting a small-scale separaed mixing layer. At an intermediate value of Froude number, a breaker occurs and the acpillary pattern is replaced by large-scale distortions of the free surface. The onset of separation, which involves flow deceleration along a region of the free surface having a large radius of curvature, leads to formation of a long mixing layeer, which has substantial levels of vorticity. Downstream of this breaker, the long-wavelength wave pattern is suppressed. At the largest value of Froude number, the onset of flow sparation rapidly occurs in conjunction with an abrupt change in slope of the surface, giving rise to vorticity concentrationa in the mixing layer.

Numerical Simulations of Ship Bow and Shoulder Wave Breaking in Different Advancing Speeds

2018 ◽  
Author(s):  
Zhen Ren ◽  
Jianhua Wang ◽  
Decheng Wan
Keyword(s):  
Free Surface ◽  
Numerical Simulations ◽  
Wave Breaking ◽  
Wave Pattern ◽  
Breaking Wave ◽  
Wake Field ◽  
Bow Wave ◽  
Calm Water ◽  
Wave Phenomena ◽  
Good Agreement

The KCS model is employed for the numerical simulations to investigate the wave breaking phenomena of the bow and shoulder wave. RANS approach coupled with high resolution VOF technique is used to resolve the free surface. In order to study the speed effects on the phenomena of ship wave breaking, four different speeds, i.e. Fr = 0.26, 0.30, 0.32, 0.35, are investigated in calm water. Predicted resistance and wave patterns under Fr = 0.26 are validated with the available experiment data, and good agreement is achieved. For the Fr = 0.26 case, the wave pattern is steady, and the alternate variation of vorticity appear near the free surface is associated with the wake field. The breaking wave phenomena can be observed when the Froude number is over 0.32 and the Fr = 0.35 case shows most violent breaking bow wave. For the Fr = 0.35 case, the process of overturning and breaking of bow wave is observed clearly, and at the tail of bow wave, some breaking features of free surface are also captured. The reconnection of the initial plunger with the free surface results in a pair of counter-rotating vortex that is responsible for the second plunger and scar.

Mixing layer produced by a screen and its dependence on initial conditions

1984 ◽  
Vol 142 ◽  
pp. 217-231 ◽  
Author(s):  
Hakuro Oguchi ◽  
Osamu Inoue
Keyword(s):  
Large Scale ◽  
Initial Conditions ◽  
Mixing Layer ◽  
Mixing Layers ◽  
Laser Doppler Velocimeter ◽  
Small Scale ◽  
Wire Screen ◽  
Flow Features ◽  
Wire Method ◽  
Layer Flow

This paper aims to elucidate the structure of the turbulent mixing layers, especially, its dependence on initial disturbances. The mixing layers are produced by setting a woven-wire screen perpendicular to the freestream in the test section of a wind tunnel to obstruct part of the flow. Three kinds of model geometry are treated; these model screens produced mixing layers which may be regarded as the equivalents of the plane mixing layer and of two-dimensional and axisymmetric wakes issuing into ambient streams of higher velocity. The initial disturbances are imposed by installing thin rods of various sizes along the edge of the screen or at the origin of the mixing layer. Flow features are visualized by the smoke-wire method. Statistical quantities are measured by a laser-Doppler velocimeter. In all cases large-scale transverse vortices seem to persist, although comparatively small-scale vortices are superimposed on the flow field in the mixing layer. The mixing layers are in self-preserving state at least up to third-order moments, but the self-preserving state is different in each case. The growth rates of the mixing layer are shown to depend strongly on the initial disturbance imposed.

Study of a Container Ship with Breaking Waves at High Froude Number Using URANS and DDES Methods

2019 ◽  
Author(s):  
Jianhua Wang ◽  
Zhen Ren ◽  
Decheng Wan
Keyword(s):  
Free Surface ◽  
Wave Breaking ◽  
High Speed ◽  
Hydrodynamic Performance ◽  
Small Scale ◽  
Breaking Wave ◽  
Container Ship ◽  
Ship Model ◽  
Bow Waves ◽  
Bow Wave

The KRISO container ship model is used for numerical simulations to investigate hydrodynamic performance under high speeds. Unsteady Reynolds-Averaged Navier-Stokes (URANS) and delayed detached eddy simulation (DDES) approaches are used to resolve the flow field around the ship model. High-resolution Volume of Fluid (VOF) technique in OpenFOAM is used to capture the free surface. The present work focuses on the wave-breaking phenomena of high-speed ships. To study the speed effects on the phenomenon of ship bow wave breaking, three different speeds, i.e., Fn = .26, .35, and .40, are investigated for a fixed ship model in calm water. Predicted resistance and wave patterns under Fn = .26 are validated with available experimental data, and a good agreement is achieved. The breaking wave phenomena can be observed from both URANS and DDES results for Froude numbers greater than .35. And the Fn = .40 case shows more violent breaking bow waves. The process of overturning and breaking of bow wave is more complex in the DDES results, and some small-scale free surface features are also captured. The predicted bow wave is compared with the experiment conducted at the China Ship Scientific Research Center. It shows that the DDES results are more accurate. Wave profiles and vorticity field at several cross sections are presented to illustrate the relationship between bow waves and vortices. It is found that the free surface vorticity dissipates quickly in the URANS simulation, which leads to the difference compared with the DDES results.

scholarly journals NUMERICAL MODELING OF TSUNAMI-INDUCED HYDRODYNAMIC FORCES ON ONSHORE STRUCTURES USING SPH

2012 ◽  
Vol 1 (33) ◽  
pp. 81 ◽  
Author(s):  
Philippe St-Germain ◽  
Ioan Nistor ◽  
Ronald Townsend
Keyword(s):  
Water Surface ◽  
Large Scale ◽  
Pressure Field ◽  
Hydrodynamic Forces ◽  
Small Scale ◽  
Breaking Wave ◽  
Total Force ◽  
Riemann Solver ◽  
Wave Impact ◽  
Time Histories

In this paper, the simulation of the violent impact of tsunami-like bores with a square column is performed using a single-phase, weakly compressible three-dimensional Smoothed Particle Hydrodynamics (SPH) model. In order to avoid large fluctuations in the pressure field and to obtain accurate simulations of the hydrodynamic forces, a Riemann solver-based formulation of the SPH method is utilized. Large-scale physical experiments conducted by the authors are reproduced using the numerical model. Time-histories of the water surface elevation as well as time-histories of the pressure distribution and net total force acting on the column are successfully compared. As observed in previous breaking wave impact studies, results show that the magnitude and duration of the impulsive force at initial bore impact depend on the degree of entrapped air in the bore-front. Although ensuring a stable pressure field, the Riemann solver-based SPH scheme is believed to induce excessive numerical diffusion, as sudden and large water surface deformations, such as splashing at initial bore impact, are marginally reproduced. To investigate this particular issue, the small-scale physical experiment of Kleefsman et al. (2005) is also considered and modeled.

scholarly journals Hypersensitivity of glacial temperatures in Siberia

2019 ◽  
Author(s):  
Pepijn Bakker ◽  
Irina Rogozhina ◽  
Ute Merkel ◽  
Matthias Prange
Keyword(s):  
Large Scale ◽  
Climate Model ◽  
Stationary Wave ◽  
Wave Pattern ◽  
Cold Climate ◽  
Ice Age ◽  
Geological Evidence ◽  
Model Experiments ◽  
Summer Temperatures ◽  
Glacial Periods

Abstract. Climate change in Siberia is currently receiving a lot of attention as large permafrost-covered areas could provide a strong positive feedback to global warming through the release of carbon that has been sequestered there on glacial-interglacial time scales. Geological evidence and climate model experiments show that the Siberian region also played an exceptional role during glacial periods. The region that is currently known for its harsh cold climate did not experience major glaciations during the last ice age, including its severest stages around the Last Glacial Maximum (LGM). On the contrary, it is thought that glacial summer temperatures were comparable to present-day. We combine LGM experiments from the second and third phases of the Paleoclimate Modelling Intercomparison Project (PMIP2 and PMIP3) with sensitivity experiments with the Community Earth System Model (CESM). Together these climate model experiments reveal that the intermodel spread in LGM summer temperatures in Siberia is much larger than in any other region of the globe and suggest that temperatures in Siberia are highly susceptible to changes in the imposed glacial boundary conditions, the included feedbacks and processes, and to the model physics of the different components of the climate model. We find that changes in the large-scale atmospheric stationary wave pattern and associated northward heat transport drive strong local snow and vegetation feedbacks and that this combination explains the susceptibility of LGM summer temperatures in Siberia. This suggests that a small difference between two glacial periods in terms of climate, ice buildup or their respective evolution towards maximum glacial conditions, can lead to strongly divergent summer temperatures in Siberia, that are sufficiently strong to allow for the buildup of an ice sheet during some glacial periods, while during others, above-freezing summer temperatures will preclude a multi-year snow-pack from forming.

Viscous Free-Surface Flow Past Twin Vertical Cylinders

2003 ◽  
Author(s):  
Tong Chen ◽  
Allen T. Chwang
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Circular Cylinders ◽  
Small Scale ◽  
The Finite Element Method ◽  
Suction Force ◽  
Large Scale Vortex ◽  
Vertical Cylinders

The laminar flow behaviors around two vertical circular cylinders (in a tandem arrangement) that pierce a free surface are investigated by the finite element method in this paper. The computational results exhibit two major free-surface effects: the presence of a free surface allows the occurrence of small-scale Kelvin-Helmholtz instabilities, but suppresses the onset of large-scale vortex alternating behavior. It is also found that the vorticity will expand in a necklace shape adjacent to the free surface. The second cylinder may experience a persisting suction force due to “trapped” vortices in the gap between the two cylinders, which may not happen in the absence of a free surface.

scholarly journals Restratification of Abyssal Mixing Layers by Submesoscale Baroclinic Eddies

2018 ◽  
Vol 48 (9) ◽  
pp. 1995-2010 ◽  
Author(s):  
Jörn Callies
Keyword(s):  
Large Scale ◽  
Water Mass ◽  
Mixing Layer ◽  
Mixing Layers ◽  
Small Scale ◽  
Surface Mixed Layer ◽  
Overturning Circulation ◽  
Topographic Slope ◽  
Abyssal Mixing ◽  
Water Mass Transformation

AbstractFor small-scale turbulence to achieve water mass transformation and thus affect the large-scale overturning circulation, it must occur in stratified water. Observations show that abyssal turbulence is strongly enhanced in the bottom few hundred meters in regions with rough topography, and it is thought that these abyssal mixing layers are crucial for closing and shaping the overturning circulation. If it were left unopposed, however, bottom-intensified turbulence would mix away the observed mixing-layer stratification over the course of a few years. It is proposed here that the homogenizing tendency of mixing may be balanced by baroclinic restratification. It is shown that bottom-intensified mixing, if it occurs on a large-scale topographic slope such as a midocean ridge flank, not only erodes stratification but also tilts isopycnals in the bottom few hundred meters. This tilting of isopycnals generates a reservoir of potential energy that can be tapped into by submesoscale baroclinic eddies. The eddies slide dense water under light water and thus restratify the mixing layer, similar to what happens in the surface mixed layer. This restratification is shown to be effective enough to balance the homogenizing tendency of mixing and to maintain the observed mixing-layer stratification. This suggests that submesoscale baroclinic eddies may play a crucial role in providing the stratification mixing can act on, thus allowing sustained water mass transformation. Through their restratification of abyssal mixing layers, submesoscale eddies may therefore directly affect the strength and structure of the abyssal overturning circulation.

Scale interactions in a mixing layer – the role of the large-scale gradients

2016 ◽  
Vol 791 ◽  
pp. 154-173 ◽  
Author(s):  
D. Fiscaletti ◽  
A. Attili ◽  
F. Bisetti ◽  
G. E. Elsinga
Keyword(s):  
Reynolds Number ◽  
High Speed ◽  
Large Scale ◽  
Mixing Layer ◽  
Physical Space ◽  
Small Scale ◽  
Velocity Fluctuations ◽  
Small Scales ◽  
Low Pass ◽  
Scale Characteristics

The interaction between the large and the small scales of turbulence is investigated in a mixing layer, at a Reynolds number based on the Taylor microscale ($Re_{{\it\lambda}}$) of $250$, via direct numerical simulations. The analysis is performed in physical space, and the local vorticity root-mean-square (r.m.s.) is taken as a measure of the small-scale activity. It is found that positive large-scale velocity fluctuations correspond to large vorticity r.m.s. on the low-speed side of the mixing layer, whereas, they correspond to low vorticity r.m.s. on the high-speed side. The relationship between large and small scales thus depends on position if the vorticity r.m.s. is correlated with the large-scale velocity fluctuations. On the contrary, the correlation coefficient is nearly constant throughout the mixing layer and close to unity if the vorticity r.m.s. is correlated with the large-scale velocity gradients. Therefore, the small-scale activity appears closely related to large-scale gradients, while the correlation between the small-scale activity and the large-scale velocity fluctuations is shown to reflect a property of the large scales. Furthermore, the vorticity from unfiltered (small scales) and from low pass filtered (large scales) velocity fields tend to be aligned when examined within vortical tubes. These results provide evidence for the so-called ‘scale invariance’ (Meneveau & Katz, Annu. Rev. Fluid Mech., vol. 32, 2000, pp. 1–32), and suggest that some of the large-scale characteristics are not lost at the small scales, at least at the Reynolds number achieved in the present simulation.

Vorticity and mixing in Rayleigh–Taylor Boussinesq turbulence

2016 ◽  
Vol 802 ◽  
pp. 395-436 ◽  
Author(s):  
Nicolas Schneider ◽  
Serge Gauthier
Keyword(s):  
Large Scale ◽  
Mixing Layer ◽  
Boussinesq Approximation ◽  
The Self ◽  
Small Scale ◽  
Nonlinear Growth ◽  
Small Scales ◽  
Self Similar ◽  
Order Quantities ◽  
Non Gaussian

The Rayleigh–Taylor instability induced turbulence is studied under the Boussinesq approximation focusing on vorticity and mixing. A direct numerical simulation has been carried out with an auto-adaptive multidomain Chebyshev–Fourier–Fourier numerical method. The spatial resolution is increased up to $(24\times 40)\times 940^{2}=848\,M$ collocation points. The Taylor Reynolds number is $\mathit{Re}_{\unicode[STIX]{x1D706}_{zz}}\approx 142$ and a short inertial range is observed. The nonlinear growth rate of the turbulent mixing layer is found to be close to $\unicode[STIX]{x1D6FC}_{b}=0.021$. Our conclusions may be summarized as follows.(i) The simulation data are in agreement with the scalings for the pressure ($k^{-7/3}$) and the vertical mass flux ($k^{-7/3}$).(ii) Mean quantities have a self-similar behaviour, but some inhomogeneity is still present. For higher-order quantities the self-similar regime is not fully achieved.(iii) In the self-similar regime, the mean dissipation rate and the enstrophy behave as $\langle \overline{\unicode[STIX]{x1D700}}\rangle \propto t$ and $\langle \overline{\unicode[STIX]{x1D714}_{i}\,\unicode[STIX]{x1D714}_{i}}^{1/2}\rangle \propto t^{1/2}$, respectively.(iv) The large-scale velocity fluctuation probability density function (PDF) is Gaussian, while vorticity and dissipation PDFs show large departures from Gaussianity.(v) The pressure PDF exhibits strong departures from Gaussianity and is skewed. This is related to vortex coherent structures.(vi) The intermediate scales of the mixing are isotropic, while small scales remain anisotropic. This leaves open the possibility of a small-scale buoyancy. Velocity intermediate scales are also isotropic, while small scales remain anisotropic. Mixing and dynamics are therefore consistent.(vii) Properties and behaviours of vorticity and enstrophy are detailed. In particular, equations for these quantities are written down under the Boussinesq approximation.(viii) The concentration PDF is quasi-Gaussian. The vertical concentration gradient is both non-Gaussian and strongly skewed.

DYNAMIC SIMILARITY IN GROUNDWATER FLOW WITH A FREE SURFACE

1963 ◽  
Vol 41 (1) ◽  
pp. 90-94
Author(s):  
A. E. Scheidegger
Keyword(s):  
Free Surface ◽  
Groundwater Flow ◽  
Large Scale ◽  
Small Error ◽  
Small Scale ◽  
Drainage Ditches ◽  
Scaling Relationships ◽  
Large Length ◽  
River Valleys ◽  
Laboratory Models

The scaling relationships applicable for the construction of laboratory models representing groundwater flow with a free surface are deduced. It is found that, for large length reductions, these scaling relationships are very difficult to satisfy. The scaling relationships, however, can generally be used for transferring results from small-scale systems (such as drainage ditches) to large-scale systems (such as river valleys). However, if one is willing to allow a small error by assuming that the boundary conditions may be correctly scaled if the pressure at the free surface in the prototype and in the model is taken as zero, much simpler scaling relationships can be obtained, which can be easily satisfied in practice.

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