scholarly journals High-resolution simulations of interactions between surface ocean dynamics and frazil ice

2020 ◽  
Vol 14 (11) ◽  
pp. 3707-3729
Author(s):  
Agnieszka Herman ◽  
Maciej Dojczman ◽  
Kamila Świszcz
Keyword(s):  
High Resolution ◽  
Vertical Velocity ◽  
Volume Fraction ◽  
Ocean Dynamics ◽  
Computational Domain ◽  
Water Mixture ◽  
Strong Wind ◽  
Surrounding Water ◽  
Frazil Ice ◽  
Ocean Atmosphere

Abstract. Frazil and grease ice forms in the ocean mixed layer (OML) during highly turbulent conditions (strong wind, large waves) accompanied by intense heat loss to the atmosphere. Three main velocity scales that shape the complex, three-dimensional (3D) OML dynamics under those conditions are the friction velocity u* at the ocean–atmosphere interface, the vertical velocity w* associated with convective motion, and the vertical velocity w*,L associated with Langmuir turbulence. The fate of buoyant particles, e.g., frazil crystals, in that dynamic environment depends primarily on their floatability, i.e., the ratio of their rising velocity wt to the characteristic vertical velocity, which is dependent on w* and w*,L. In this work, the dynamics of frazil ice is investigated numerically with the high-resolution, non-hydrostatic hydrodynamic model CROCO (Coastal and Regional Ocean COmmunity Model), extended to account for frazil transport and its interactions with surrounding water. An idealized model setup is used (a square computational domain with periodic lateral boundaries, spatially uniform atmospheric and wave forcing). The model reproduces the main features of buoyancy- and wave-forced OML circulation, including the preferential concentration of frazil particles in elongated patches at the sea surface. Two spatial patterns are identified in the distribution of frazil volume fraction at the surface: one related to individual surface convergence zones, very narrow, and oriented approximately parallel to the wind/wave direction and one in the form of wide streaks with a separation distance of a few hundred meters, oriented obliquely to the direction of the forcing. Several series of simulations are performed, differing in terms of the level of coupling between the frazil and hydrodynamic processes, from a situation when frazil has no influence on hydrodynamics (as in most models of material transport in the OML) to a situation in which frazil modifies the net density, effective viscosity, and transfer coefficients at the ocean–atmosphere interface and exerts a net drag force on the surrounding water. The role of each of those effects in shaping the bulk OML characteristics and frazil transport is assessed, and the density of the ice–water mixture is found to have the strongest influence on those characteristics.

scholarly journals High-resolution simulations of interactions between surface ocean dynamics and frazil ice

2020 ◽  
Author(s):  
Agnieszka Herman ◽  
Maciej Dojczman ◽  
Kamila Świszcz
Keyword(s):  
High Resolution ◽  
Vertical Velocity ◽  
Volume Fraction ◽  
Ocean Dynamics ◽  
Computational Domain ◽  
Water Mixture ◽  
Strong Wind ◽  
Surrounding Water ◽  
Frazil Ice ◽  
Ocean Atmosphere

Abstract. Frazil and grease ice forms in the ocean mixed layer (OML) during highly turbulent conditions (strong wind, large waves) accompanied by intense heat loss to the atmosphere. Three main velocity scales that shape the complex, three-dimensional OML dynamics under those conditions are: the friction velocity u* at the ocean--atmosphere interface, the vertical velocity w* associated with convective motion, and the vertical velocity w*,L associated with Langmuir turbulence. The fate of buoyant particles, e.g. frazil crystals, in that dynamic environment depends primarily on their floatability, i.e., the ratio of their rising velocity wt to the characteristic vertical velocity, dependent on w* and w*,L. In this work, dynamics of frazil ice is investigated numerically with a high-resolution, non-hydrostatic hydrodynamic model CROCO (Coastal and Regional Ocean COmmunity Model), extended to account for frazil transport and its interactions with surrounding water. An idealized model setup is used (a square computational domain with periodic lateral boundaries; spatially uniform atmospheric and wave forcing). The model reproduces the main features of buoyancy- and wave-forced OML circulation, including the preferential concentration of frazil particles in elongated patches at the sea surface. Two spatial patterns are identified in the distribution of frazil volume fraction at the surface, one related to individual surface convergence zones, very narrow and oriented approximately parallel to the wind/wave direction, and one in the form of wide streaks with separation distance of a few hundreds meters, oriented obliquely to the direction of the forcing. Several series of simulations are performed, differing in terms of the level of coupling between the frazil and hydrodynamic processes: from a situation when frazil has no influence on hydrodynamics (as in most models of material transport in the OML) to a situation when frazil modifies the net density, effective viscosity, transfer coefficients at the ocean--atmosphere interface and exerts a net drag force on the surrounding water. The role of each of those effects in shaping the bulk OML characteristics and frazil transport is assessed, and the density of the ice–water mixture is found to have the strongest influence on those characteristics.

SURFACE OCEAN RADIOCARBON FROM A PORITES CORAL RECORD IN THE GREAT BARRIER REEF: 1945–2017

Radiocarbon ◽  
2021 ◽  
pp. 1-11
Author(s):  
Yang Wu ◽  
Stewart J Fallon ◽  
Neal E Cantin ◽  
Janice M Lough
Keyword(s):  
High Resolution ◽  
Great Barrier Reef ◽  
Ocean Dynamics ◽  
Barrier Reef ◽  
Reference Series ◽  
Surface Ocean ◽  
Porites Coral ◽  
Subsurface Ocean ◽  
Ocean Atmosphere

ABSTRACT We present a high-resolution seawater radiocarbon (Δ14C) record from a Porites coral collected from Masthead Island in the southern Great Barrier Reef (GBR) covering the years 1945–2017. The Δ14C values from 1945–1953 (pre-bomb era) averaged –49‰. As a result of bomb-produced 14C in the atmosphere, Δ14C values started to rise rapidly from 1959, levelled off at ∼131‰ in the late 1970s and gradually decreased to ∼40.3‰ by 2017 due to the decrease in the air-sea 14C gradient and the overturning of the 14C ocean reservoir (i.e., surface ocean to subsurface ocean; atmosphere to surface ocean). The Masthead Island record is in agreement with previous 14C coral records from the southern GBR. A comparison between surface ocean and atmospheric Δ14C suggests that, since 2010, the main reservoir of bomb-derived 14C has shifted from the atmosphere to the surface ocean, potentially resulting in reversed 14C flux in regions where the CO2 gradient is favorable. The high-resolution Masthead coral Δ14C sheds light on long-term variability in air-sea exchange and GBR regional ocean dynamics associated with climate change and in conjunction with the previous records provides a robust seawater 14C reference series to date other carbonate samples.

scholarly journals SENSITIVITY OF UPPER OCEAN DYNAMICS IN HIGH-RESOLUTION TROPICAL INDIAN OCEAN MODEL TO DIFFERENT FLUX PARAMETERIZATION: CASE STUDY FOR THE BAY OF BENGAL (BOB)

2018 ◽  
Vol XLII-5 ◽  
pp. 839-847 ◽  
Author(s):  
S. K. Mallick ◽  
N. Agarwal ◽  
R. Sharma ◽  
K. V. S. R. Prasad
Keyword(s):  
High Resolution ◽  
Indian Ocean ◽  
Bay Of Bengal ◽  
Tropical Indian Ocean ◽  
Ocean Dynamics ◽  
Sea Surface ◽  
Upper Ocean ◽  
Wind Component ◽  
Strong Wind ◽  
Flux Parameterization

<p><strong>Abstract.</strong> Simulation experiments using a high-resolution ocean general circulation model (OGCM) of the tropical Indian Ocean (TIO) were carried out to assess the model’s sensitivity to different flux parameterization. The flux formulation proposed by Kara et al. (2000) is used in the control run (CR). One more experiment differing in the bulk fluxes formulation for the computation of momentum, freshwater and heat is carried out. In the first experiment (CR), actual wind is used for the computation of the exchange coefficient in air-sea bulk flux formulation. In the second experiment (E1), model surface current is used in the wind stress formulation to compute the turbulent air-sea fluxes for TIO region. The formulation used in E1 is the same as it is used in CR, instead of actual wind, relative wind component is used in flux formulas. Both experiments are carried out for the period 2014&amp;ndash;2016. The OGCM is forced using the daily fields of winds, radiation and freshwater fluxes obtained from ERA-Interim Reanalysis. In this study, we examine and quantify the performance of the above-mentioned experiments with respect to observations from ARGO, satellite-based sea surface temperature (SST) and sea surface salinity (SSS) for the year 2015. We observe that the upper ocean dynamics is significantly modulated by different flux algorithms. The errors in simulated SST is reduced by &amp;sim;8% to 10% in E1 compared to CR, respectively. The temperature errors in the top 20<span class="thinspace"></span>m depth are reduced by 8% in E1. It is found that this flux formulation using relative winds is effective in accurately simulating the upper ocean dynamics in strong wind regimes of the Bay of Bengal.</p>

scholarly journals A model of bubble-induced turbulence based on large-scale wake interactions

2013 ◽  
Vol 719 ◽  
pp. 362-387 ◽  
Author(s):  
Guillaume Riboux ◽  
Dominique Legendre ◽  
Frédéric Risso
Keyword(s):  
Probability Density ◽  
Vertical Velocity ◽  
Volume Fraction ◽  
Flow Instability ◽  
Vertical Direction ◽  
Small Scale ◽  
Computational Domain ◽  
Temporal Fluctuations ◽  
Spatial Fluctuations ◽  
Wake Interactions

AbstractNavier–Stokes simulations of the agitation generated by a homogeneous swarm of high-Reynolds-number rising bubbles are performed. The bubbles are modelled by fixed momentum sources of finite size randomly distributed in a uniform flow. The mesh grid is regular with a spacing close to the bubble size. This allows us to simulate a swarm of a few thousand bubbles in a computational domain of a hundred bubble diameters, which corresponds to a gas volume fraction $\alpha $ from 0.6 % to 4 %. The small-scale disturbances close to the bubbles are not resolved but the wakes are correctly described from a distance of a few diameters. This simple model reproduces well all the statistical properties of the vertical velocity fluctuations measured in previous experiments: scaling as ${\alpha }^{0. 4} $, self-similar probability density functions and power spectral density including a subrange evolving as the power $- 3$ of the wavenumber $k$. It can therefore be concluded that bubble-induced agitation mainly results from wake interactions. Considering the flow in a frame that is fixed relative to the bubbles, the combined use of both time and spatial averaging makes it possible to distinguish two contributions to the liquid fluctuations. The first is the spatial fluctuations that are the consequence of the bubble mean wakes. The second corresponds to the temporal fluctuations that are the result of the development of a flow instability. Note that the latter is not due to the destabilization of individual bubble wakes, since a computation with a single bubble leads to a steady flow. It is a collective instability of the randomly distributed bubble wakes. The spectrum of the time fluctuations shows a peak around a frequency ${f}_{cwi} $, which is independent of $\alpha $. From the present results it is possible to determine the origin of the overall properties of the total fluctuations observed in the experiments. The scaling of the velocity fluctuation as ${\alpha }^{0. 4} $ is a combination of the scalings of the spatial and temporal fluctuations, which are different from each other. As the time fluctuations are symmetric in the vertical direction, the asymmetry of the probability density function of the vertical velocity comes from that of the spatial fluctuations. Both contributions exhibit a ${k}^{- 3} $ spectral behaviour around the same range of wavenumbers, which explains why it is observed regardless of the nature of the dominant contribution.

scholarly journals Effect of the Preheated Oxidizer Temperature on Soot Formation and Flame Structure in Turbulent Methane-Air Diffusion Flames at 1 and 3 atm: A CFD Investigation

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3671
Author(s):  
Subrat Garnayak ◽  
Subhankar Mohapatra ◽  
Sukanta K. Dash ◽  
Bok Jik Lee ◽  
V. Mahendra Reddy
Keyword(s):  
Mole Fraction ◽  
Air Temperature ◽  
Reaction Rate ◽  
Volume Fraction ◽  
Diffusion Flames ◽  
Soot Formation ◽  
Flame Structure ◽  
Soot Volume Fraction ◽  
Computational Domain ◽  
Pressure Elevation

This article presents the results of computations on pilot-based turbulent methane/air co-flow diffusion flames under the influence of the preheated oxidizer temperature ranging from 293 to 723 K at two operating pressures of 1 and 3 atm. The focus is on investigating the soot formation and flame structure under the influence of both the preheated air and combustor pressure. The computations were conducted in a 2D axisymmetric computational domain by solving the Favre averaged governing equation using the finite volume-based CFD code Ansys Fluent 19.2. A steady laminar flamelet model in combination with GRI Mech 3.0 was considered for combustion modeling. A semi-empirical acetylene-based soot model proposed by Brookes and Moss was adopted to predict soot. A careful validation was initially carried out with the measurements by Brookes and Moss at 1 and 3 atm with the temperature of both fuel and air at 290 K before carrying out further simulation using preheated air. The results by the present computation demonstrated that the flame peak temperature increased with air temperature for both 1 and 3 atm, while it reduced with pressure elevation. The OH mole fraction, signifying reaction rate, increased with a rise in the oxidizer temperature at the two operating pressures of 1 and 3 atm. However, a reduced value of OH mole fraction was observed at 3 atm when compared with 1 atm. The soot volume fraction increased with air temperature as well as pressure. The reaction rate by soot surface growth, soot mass-nucleation, and soot-oxidation rate increased with an increase in both air temperature and pressure. Finally, the fuel consumption rate showed a decreasing trend with air temperature and an increasing trend with pressure elevation.

Dynamics of Interdecadal Climate Variability: A Historical Perspective*

2012 ◽  
Vol 25 (6) ◽  
pp. 1963-1995 ◽  
Author(s):  
Zhengyu Liu
Keyword(s):  
Climate Variability ◽  
Time Scale ◽  
Ocean Dynamics ◽  
Interdecadal Variability ◽  
Driving Mechanism ◽  
Stochastic Forcing ◽  
The Pacific ◽  
Ocean Atmosphere ◽  
Almost All ◽  
Interdecadal Climate Variability

Abstract The emerging interest in decadal climate prediction highlights the importance of understanding the mechanisms of decadal to interdecadal climate variability. The purpose of this paper is to provide a review of our understanding of interdecadal climate variability in the Pacific and Atlantic Oceans. In particular, the dynamics of interdecadal variability in both oceans will be discussed in a unified framework and in light of historical development. General mechanisms responsible for interdecadal variability, including the role of ocean dynamics, are reviewed first. A hierarchy of increasingly complex paradigms is used to explain variability. This hierarchy ranges from a simple red noise model to a complex stochastically driven coupled ocean–atmosphere mode. The review suggests that stochastic forcing is the major driving mechanism for almost all interdecadal variability, while ocean–atmosphere feedback plays a relatively minor role. Interdecadal variability can be generated independently in the tropics or extratropics, and in the Pacific or Atlantic. In the Pacific, decadal–interdecadal variability is associated with changes in the wind-driven upper-ocean circulation. In the North Atlantic, some of the multidecadal variability is associated with changes in the Atlantic meridional overturning circulation (AMOC). In both the Pacific and Atlantic, the time scale of interdecadal variability seems to be determined mainly by Rossby wave propagation in the extratropics; in the Atlantic, the time scale could also be determined by the advection of the returning branch of AMOC in the Atlantic. One significant advancement of the last two decades is the recognition of the stochastic forcing as the dominant generation mechanism for almost all interdecadal variability. Finally, outstanding issues regarding the cause of interdecadal climate variability are discussed. The mechanism that determines the time scale of each interdecadal mode remains one of the key issues not understood. It is suggested that much further understanding can be gained in the future by performing specifically designed sensitivity experiments in coupled ocean–atmosphere general circulation models, by further analysis of observations and cross-model comparisons, and by combining mechanistic studies with decadal prediction studies.

Electroacoustic Study of n-Hexadecane/Water Emulsions

2001 ◽  
Vol 54 (8) ◽  
pp. 503 ◽  
Author(s):  
Linggen Kong ◽  
James K. Beattie ◽  
Robert J. Hunter
Keyword(s):  
Particle Size ◽  
Zeta Potential ◽  
Volume Fraction ◽  
Sodium Dodecyl ◽  
Surfactant Solution ◽  
Minimum Size ◽  
Water Mixture ◽  
Concentrated Suspensions ◽  
Minimum Concentration ◽  
Median Diameter

n-Hexadecane-in-water emulsions were investigated by electroacoustics using a prototype of an AcoustoSizer-II apparatus. The emulsions were formed by passing the stirred oil/water mixture through a homogenizer in the presence of sodium dodecyl sulfate (SDS) at natural pH (6–7). With increasing oil-volume fraction, the particle size increased linearly after 5 and also after 20 passages through the homogenizer, suggesting that surface energy was determining particle size. For systems in which the surfactant concentration was limited, the particle size after 20 passages approached the value dictated by the SDS concentration. With ample surfactant present, the median diameter was a linear function of the inverse of the total energy input as measured by the number of passes. There was, however, a limit to the amount of size reduction that could be achieved in the homogenizer, and the minimum size was smaller at smaller volume fractions. Dilution of the emulsion with a surfactant solution of the same composition as the water phase had a negligible effect on the particle size and changed the zeta potential only slightly. This confirms results from previous work and validates the equations used to determine the particle size and zeta potential in concentrated suspensions. The minimum concentration of SDS that could prevent the emulsion from coalescing for the system with 6% by volume oil was 3 mM. For this dilute emulsion, the particle size decreased regularly with an increase in SDS concentration, but the magnitude of the zeta potential went through a strong maximum at intermediate surfactant concentrations.

scholarly journals Simulation of the Effect of Oil Volume Fractions in an Oil-Water Flows Along a Circular Pipe: A Finite Element Approach

2018 ◽  
Vol 10 (5) ◽  
pp. 19
Author(s):  
Ferdusee Akter ◽  
Md. Bhuyan ◽  
Ujjwal Deb
Keyword(s):  
Finite Element ◽  
Volume Fraction ◽  
Fluid Velocity ◽  
Galerkin Approximation ◽  
Computational Domain ◽  
Two Phase Flows ◽  
Two Phase ◽  
Volume Fractions ◽  
Oil In Water ◽  
Element Approach

Two phase flows in pipelines are very common in industries for the oil transportations. The aim of our work is to observe the effect of oil volume fraction in the oil in water two phase flows. The study has been accomplished using a computational model which is based on a Finite Element Method (FEM) named Galerkin approximation. The velocity profiles and volume fractions are performed by numerical simulations and we have considered the COMSOL Multiphysics Software version 4.2a for our simulation. The computational domain is 8m in length and 0.05m in radius. The results show that the velocity of the mixture decreases as the oil volume fraction increases. It should be noted that if we gradually increase the volume fractions of oil, the fluid velocity also changes and the saturated level of the volume fraction is 22.3%.

scholarly journals Conductivity Study of DTAB in Water and Ethanol-Water Mixture in the Presence and Absence of ZnSO4

2020 ◽  
Vol 17 (4) ◽  
pp. 1207
Author(s):  
Sangita Acharya ◽  
Tulasi Niraula ◽  
Ajaya Bhattarai
Keyword(s):  
Free Energy ◽  
Critical Micelle Concentration ◽  
Volume Fraction ◽  
Standard Free Energy ◽  
Water Mixture ◽  
Dodecyltrimethylammonium Bromide ◽  
Degree Of Dissociation ◽  
Ethanol Content ◽  
Presence And Absence ◽  
Free Energy Of Micellization

The physicochemical behaviour of dodecyltrimethylammonium bromide (DTAB) in water and ethanol-water mixture in the presence and absence of ZnSO4 were studied by measuring the conductivity at 298.15 K. The pre-micellar (S1) and post-micellar slopes (S2) were obtained and calculated the degree of dissociation (α) and the critical micelle concentration (cmc). With an increase in ethanol content, the cmc and α of DTAB increased whereas, in the presence of ZnSO4, the cmc and α decreased. By using cmc and α, thermodynamic properties as the standard free energy of micellization ( ) were evaluated. With an increase in ethanol content, the negative values of  are decreased indicating less spontaneous in the micellization which makes micellization less favourable. The correlation of the pre-micellar and post-micellar slopes with the volume fraction of ethanol were discussed. DTAB micellization was tested in contexts of specific solvent parameters and solvophobic parameter.

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