Entrainment and Transport in Idealized Three-Dimensional Gravity Current Simulation

2006 ◽  
Vol 23 (9) ◽  
pp. 1249-1269 ◽  
Author(s):  
Yu-Heng Tseng ◽  
David E. Dietrich
Keyword(s):  
Gravity Current ◽  
Vertical Mixing ◽  
Three Dimensional ◽  
Ocean Model ◽  
Numerical Dissipation ◽  
Good Convergence ◽  
Low Viscosity ◽  
Denmark Strait ◽  
Dimensional Gravity ◽  
Fine Resolution

Abstract A purely z-coordinate Dietrich/Center for Air Sea Technology (DieCAST) ocean model is applied to the Dynamics of Overflow Mixing and Entrainment (DOME) idealized bottom density current problem that is patterned after the Denmark Strait. The numerical results show that the background viscosity plays a more important role than the chosen coordinate system in the entrainment and mixing if the background viscosity is not small enough. Both higher horizontal viscosity and coarser resolution leads to slower along-slope propagation. Reducing vertical mixing parameterization also leads to slower along-slope propagation with thicker plume size vertically. The simulation gives consistent results for the moderate- and fine-resolution runs. At a very coarse grid the dense water descends more slowly and is mainly dominated by diffusion. Time-averaged downstream transport and entrainment are not very sensitive to viscosity after the flow reaches its quasi-steady status. However, more realistic eddies and flow structures are found in low-viscosity runs. The results show good convergence of the resolved flow as expected and clarify the effects of numerical dissipation/mixing on overflow modeling. Larger numerical dissipation is not required nor recommended in z-coordinate models.

scholarly journals A parameterization of local and remote tidal mixing

2020 ◽  
Author(s):  
Casimir de Lavergne ◽  
Clément Vic ◽  
Gurvan Madec ◽  
Fabien Roquet ◽  
Amy Waterhouse ◽  
...  
Keyword(s):  
Vertical Mixing ◽  
Three Dimensional ◽  
Internal Tide ◽  
Ocean Model ◽  
Internal Tides ◽  
Tidal Mixing ◽  
Global Ocean ◽  
Energy Conserving ◽  
Energy Constrained ◽  
Lagrangian Tracking

<p>Vertical mixing is often regarded as the Achilles’ heel of ocean models. In particular, few models include a comprehensive and energy-constrained parameterization of mixing by internal ocean tides. Here, we present an energy-conserving mixing scheme which accounts for the local breaking of high-mode internal tides and the distant dissipation of low-mode internal tides. The scheme relies on four static two-dimensional maps of internal tide dissipation, constructed using mode-by-mode Lagrangian tracking of energy beams from sources to sinks. Each map is associated with a distinct dissipative process and a corresponding vertical structure. Applied to an observational climatology of stratification, the scheme produces a global three-dimensional map of dissipation which compares well with available microstructure observations and with upper-ocean finestructure mixing estimates. Implemented in the NEMO global ocean model, the scheme improves the representation of deep water-mass transformation and obviates the need for a constant background diffusivity.</p>

Three-dimensional gravity-current flow within a subaqueous bend: Spatial evolution and force balance variations

Sedimentology ◽  
2013 ◽  
Vol 60 (7) ◽  
pp. 1668-1680 ◽  
Author(s):  
Taoyuan Wei ◽  
Jeff Peakall ◽  
Daniel R. Parsons ◽  
Zhongyuan Chen ◽  
Baocheng Zhao ◽  
...  
Keyword(s):  
Current Flow ◽  
Gravity Current ◽  
Three Dimensional ◽  
Force Balance ◽  
Spatial Evolution ◽  
Dimensional Gravity

scholarly journals Representation of the Denmark Strait Overflow in a z-coordinate eddying configuration of the NEMO (v3.6) ocean model: Resolution and parameter impacts

2020 ◽  
Author(s):  
Pedro Colombo ◽  
Bernard Barnier ◽  
Thierry Penduff ◽  
Jérôme Chanut ◽  
Julie Deshayes ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Mixing ◽  
Bottom Layer ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Fixed Number ◽  
Vertical Shear ◽  
Physical Parameters ◽  
Denmark Strait ◽  
The Impact

Abstract. We investigate in this paper the sensitivity of the representation of the Denmark Strait overflow produced by a regional z-coordinate configuration of NEMO (version 3.6) to the horizontal and vertical grid resolutions and to various numerical and physical parameters. Three different horizontal resolutions, 1/12°, 1/36° and 1/60°, are used respectively with 46, 75, 150 and 300 vertical levels. Contrary to expectations, in the given numerical set-up, the increase of the vertical resolution did not bring improvement at eddy-permitting resolution (1/12°). We find a greater dilution of the overflow as the number of vertical level increases, and the worse solution is the one with 300 vertical levels. It is found that when the local slope of the grid is weaker than the slope of the topography the result is a more diluted vein. Such a grid enhances the dilution of the plume in the ambient fluid and produces its thickening. Although the greater number of levels allows for a better resolution of the ageostrophic Ekman flow in the bottom layer, the final result also depends on how the local grid slope matches the topographic slope. We also find that for a fixed number of levels, the representation of the overflow is improved when horizontal resolution is increased to 1/36° and 1/60°, the most drastic improvements being obtained with 150 levels. With such number of vertical levels, the enhanced vertical mixing associated with the step-like representation of the topography remains limited to a thin bottom layer representing a minor portion of the overflow. Two major additional players contribute to the sinking of the overflow, the breaking of the overflow into boluses of dense water which contribute to spread the overflow waters along the Greenland shelf and within the Irminger Basin, and the resolved vertical shear that results from the resolution of the bottom Ekman boundary layer dynamics. This improves the accuracy of the calculation of the entrainment by the turbulent kinetic energy mixing scheme (as it depends on the local shear), and improves the properties of the overflow waters such that they more favorably compare with observations. At 300 vertical levels the dilution is again increased for all horizontal resolutions. The impact on the overflow representation of many other numerical parameters were tested (momentum advection scheme, lateral friction, bottom boundary layer parameterisation, closure parameterisation, etc.) but none had a significant impact on the overflow representation.

scholarly journals Representation of the Denmark Strait overflow in a <i>z</i>-coordinate eddying configuration of the NEMO (v3.6) ocean model: resolution and parameter impacts

2020 ◽  
Vol 13 (7) ◽  
pp. 3347-3371 ◽  
Author(s):  
Pedro Colombo ◽  
Bernard Barnier ◽  
Thierry Penduff ◽  
Jérôme Chanut ◽  
Julie Deshayes ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Vertical Mixing ◽  
Bottom Layer ◽  
Horizontal Resolution ◽  
Ocean Model ◽  
Fixed Number ◽  
Vertical Shear ◽  
Physical Parameters ◽  
Denmark Strait ◽  
The Impact

Abstract. We investigate in this paper the sensitivity of the representation of the Denmark Strait overflow produced by a regional z-coordinate configuration of NEMO (version 3.6) to the horizontal and vertical grid resolutions and to various numerical and physical parameters. Three different horizontal resolutions, 1∕12, 1∕36, and 1/60∘, are respectively used with 46, 75, 150, and 300 vertical levels. In the given numerical set-up, the increase in the vertical resolution did not bring improvement at eddy-permitting resolution (1/12∘). We find a greater dilution of the overflow as the number of vertical level increases, and the worst solution is the one with 300 vertical levels. It is found that when the local slope of the grid is weaker than the slope of the topography the result is a more diluted vein. Such a grid enhances the dilution of the plume in the ambient fluid and produces its thickening. Although the greater number of levels allows for a better resolution of the ageostrophic Ekman flow in the bottom layer, the final result also depends on how the local grid slope matches the topographic slope. We also find that for a fixed number of levels, the representation of the overflow is improved when horizontal resolution is increased to 1∕36 and 1/60∘, with the most drastic improvements being obtained with 150 levels. With such a number of vertical levels, the enhanced vertical mixing associated with the step-like representation of the topography remains limited to a thin bottom layer representing a minor portion of the overflow. Two major additional players contribute to the sinking of the overflow: the breaking of the overflow into boluses of dense water which contribute to spreading the overflow waters along the Greenland shelf and within the Irminger Basin, and the resolved vertical shear that results from the resolution of the bottom Ekman boundary layer dynamics. This improves the accuracy of the calculation of the entrainment by the turbulent kinetic energy mixing scheme (as it depends on the local shear) and improves the properties of the overflow waters such that they more favourably compare with observations. At 300 vertical levels the dilution is again increased for all horizontal resolutions. The impact on the overflow representation of many other numerical parameters was tested (momentum advection scheme, lateral friction, bottom boundary layer parameterization, closure parameterization, etc.), but none had a significant impact on the overflow representation.

scholarly journals Lagrangian H/U3 Values Computed around Fronts Using a Fine-Resolution Numerical Model and Ferryboat-Monitored SST Dataset

2008 ◽  
Vol 38 (11) ◽  
pp. 2575-2586 ◽  
Author(s):  
Youn-Jong Sun ◽  
Atsuhiko Isobe
Keyword(s):  
Tidal Current ◽  
Vertical Mixing ◽  
Local Maximum ◽  
Accurate Estimate ◽  
Ocean Model ◽  
Efficiency Factor ◽  
Critical Values ◽  
Current Amplitude ◽  
The Seto Inland Sea ◽  
Fine Resolution

Abstract Front locations are identified as the local maximum of the sea surface temperature gradient revealed in the continuously ferryboat-monitored data in the Seto Inland Sea, Japan. In addition, Simpson and Hunter’s H/U3 values, where H is the water depth and U is the tidal-current amplitude, are computed at each cell using a fine-resolution, finite-volume ocean model to find the values at the fronts (i.e., Eulerian critical H/U3 values). Moreover, Lagrangian critical H/U3 values are computed using the same model in conjunction with particle-tracking experiments in which the particle’s H/U3 values saved along their trajectories are all averaged at each cell. In comparison with the Eulerian H/U3 values, it is revealed that the standard deviation of the Lagrangian critical values considerably reduces, especially for the fronts near straits. This accurate estimate of the critical H/U3 values shows that critical values depend on the tidal-current amplitude at the front locations. The dependency of critical H/U3 values on the tidal-current amplitude is likely due to dependency of the efficiency factor for vertical mixing in the original Simpson and Hunter formula on the amplitude. It is suggested that the efficiency factor for vertical mixing must be small (large) at locations with the large (small) tidal-current amplitude.

A study of three-dimensional gravity currents on a uniform slope

2002 ◽  
Vol 453 ◽  
pp. 239-261 ◽  
Author(s):  
ANDREW N. ROSS ◽  
P. F. LINDEN ◽  
STUART B. DALZIEL
Keyword(s):  
Laboratory Experiments ◽  
Gravity Current ◽  
Three Dimensional ◽  
Gravity Currents ◽  
Integral Model ◽  
Conductivity Measurements ◽  
Dense Fluid ◽  
Wedge Shape ◽  
Dimensional Gravity ◽  
Shallow Water Models

In many geophysical, environmental and industrial situations, a finite volume of fluid with a density different to the ambient is released on a sloping boundary. This leads to the formation of a gravity current travelling up, down and across the slope. We present novel laboratory experiments in which the dense fluid spreads both down-slope (and initially up-slope) and laterally across the slope. The position, shape and dilution of the current are determined through video and conductivity measurements for moderate slopes (5° to 20°). The entrainment coefficient for different slopes is calculated from the experimental results and is found to depend very little on the slope. The value agrees well with previously published values for entrainment into gravity currents on a horizontal surface. The experimental measurements are compared with previous shallow-water models and with a new wedge integral model developed and presented here. It is concluded that these simplified models do not capture all the significant features of the flow. In the models, the current takes the form of a wedge which travels down the slope, but the experiments show the formation of a more complicated current. It is found that the wedge integral model over-predicts the length and width of the gravity current but gives fair agreement with the measured densities in the head. The initial stages of the flow, during which time the wedge shape develops, are studied. It is found that although the influence of the slope is seen relatively quickly for moderate slopes, the time taken for the wedge to develop is much longer. The implications of these findings for safety analysis are briefly discussed.

Influence of Bathymetry on the Performance of Regional Scale Model

2017 ◽  
Vol 68 (1) ◽  
pp. 104
Author(s):  
P. Anand ◽  
P.V. Hareesh Kumar
Keyword(s):  
Ocean Circulation ◽  
Regional Scale ◽  
Three Dimensional ◽  
Coastal Region ◽  
Circulation Model ◽  
Ocean Model ◽  
Scale Model ◽  
Princeton Ocean Model ◽  
Nearshore Processes ◽  
Fine Resolution

<p class="p1"><span class="Apple-converted-space"> </span>A three dimensional ocean circulation model (Princeton Ocean Model) is utilised to study the thermohaline variability of the eastern Arabian Sea associated with changes in the three input bathymetry data sets, viz. ETOPO5 (E5), Modified ETOPO5 (ME5) and ME5 further modified based on actual fine resolution data collected using Multibeam echo-sounder (MEN5). The temperature and salinity measurements made onboard INS Sagardhwani for the period July 2000 is utilised to validate the model. Simulations of temperature using Princeton Ocean Model show good improvement in the coastal region with MEN5 bathymetry data (RMS error of 0.71 °C and correlation coefficient of 0.98). The study highlights the choice of fine resolution bathymetry data in the simulation of nearshore processes, where bathymetry is very complex.</p>

Some quantitative applications of vascular corrosion casting

1992 ◽  
Vol 50 (1) ◽  
pp. 738-739
Author(s):  
Fred E. Hossler
Keyword(s):  
Blood Vessels ◽  
Nuclear Orientation ◽  
Three Dimensional ◽  
Surrounding Tissue ◽  
Confocal Laser ◽  
Corrosion Casting ◽  
Venous Valve ◽  
Casting Technique ◽  
Low Viscosity ◽  
Quantitative Measurements

Preparation of replicas of the complex arrangement of blood vessels in various organs and tissues has been accomplished by infusing low viscosity resins into the vasculature. Subsequent removal of the surrounding tissue by maceration leaves a model of the intricate three-dimensional anatomy of the blood vessels of the tissue not obtainable by any other procedure. When applied with care, the vascular corrosion casting technique can reveal fine details of the microvasculature including endothelial nuclear orientation and distribution (Fig. 1), locations of arteriolar sphincters (Fig. 2), venous valve anatomy (Fig. 3), and vessel size, density, and branching patterns. Because casts faithfully replicate tissue vasculature, they can be used for quantitative measurements of that vasculature. The purpose of this report is to summarize and highlight some quantitative applications of vascular corrosion casting. In each example, casts were prepared by infusing Mercox, a methyl-methacrylate resin, and macerating the tissue with 20% KOH. Casts were either mounted for conventional scanning electron microscopy, or sliced for viewing with a confocal laser microscope.

Modeling and Assessment of the Produced Water Discharges from Offshore Petroleum Platforms

2007 ◽  
Vol 42 (4) ◽  
pp. 303-310 ◽  
Author(s):  
Zhi Chen ◽  
Lin Zhao ◽  
Kenneth Lee ◽  
Charles Hannath
Keyword(s):  
Random Walk ◽  
Produced Water ◽  
Model Development ◽  
Three Dimensional ◽  
Monitoring Program ◽  
Ecological Monitoring ◽  
Numerical Approach ◽  
Ocean Model ◽  
Scale Model ◽  
Water Stream

Abstract There has been a growing interest in assessing the risks to the marine environment from produced water discharges. This study describes the development of a numerical approach, POM-RW, based on an integration of the Princeton Ocean Model (POM) and a Random Walk (RW) simulation of pollutant transport. Specifically, the POM is employed to simulate local ocean currents. It provides three-dimensional hydrodynamic input to a Random Walk model focused on the dispersion of toxic components within the produced water stream on a regional spatial scale. Model development and field validation of the predicted current field and pollutant concentrations were conducted in conjunction with a water quality and ecological monitoring program for an offshore facility located on the Grand Banks of Canada. Results indicate that the POM-RW approach is useful to address environmental risks associated with the produced water discharges.

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