Bottom boundary mixing: The role of near-sediment density stratification

1998 ◽  
pp. 485-502 ◽  
Author(s):  
A. Wüest ◽  
M. Gloor
Keyword(s):  
Density Stratification ◽  
Bottom Boundary ◽  
Boundary Mixing

scholarly journals NUMERICAL MODELING OF A TURBULENT BOTTOM BOUNDARY LAYER UNDER SOLITARY WAVES ON A SMOOTH SURFACE

2018 ◽  
pp. 26
Author(s):  
Ahmad Sana ◽  
Hitoshi Tanaka
Keyword(s):  
Boundary Layer ◽  
Boundary Layers ◽  
Solitary Waves ◽  
Bottom Boundary Layer ◽  
Stream Velocity ◽  
Bottom Boundary ◽  
Sediment Movement ◽  
Bottom Boundary Layers ◽  
Turbulent Models

A number of studies on bottom boundary layers under sinusoidal and cnoidal waves were carried out in the past owing to the role of bottom shear stress on coastal sediment movement. In recent years, the bottom boundary layers under long waves have attracted considerable attention due to the occurrence of huge tsunamis and corresponding sediment movement. In the present study two-equation turbulent models proposed by Menter(1994) have been applied to a bottom boundary layer under solitary waves. A comparison has been made for cross-stream velocity profile and other turbulence properties in x-direction.

Physical limitations of dissolved methane fluxes: The role of bottom-boundary layer processes

2010 ◽  
Vol 272 (1-4) ◽  
pp. 209-222 ◽  
Author(s):  
Peter Linke ◽  
Stefan Sommer ◽  
Lorenzo Rovelli ◽  
Daniel F. McGinnis
Keyword(s):  
Boundary Layer ◽  
Bottom Boundary Layer ◽  
Dissolved Methane ◽  
Bottom Boundary ◽  
Boundary Layer Processes ◽  
Methane Fluxes ◽  
Physical Limitations

A numerical investigation of fine particle laden flow in an oscillatory channel: the role of particle-induced density stratification

2010 ◽  
Vol 665 ◽  
pp. 1-45 ◽  
Author(s):  
CELALETTIN E. OZDEMIR ◽  
TIAN-JIAN HSU ◽  
S. BALACHANDAR
Keyword(s):  
Boundary Layer ◽  
Particle Transport ◽  
Fine Particle ◽  
Richardson Number ◽  
Density Stratification ◽  
Shear Instability ◽  
Bulk Richardson Number ◽  
Turbulence Modulation ◽  
Oscillatory Boundary Layer

Studying particle-laden oscillatory channel flow constitutes an important step towards understanding practical application. This study aims to take a step forward in our understanding of the role of turbulence on fine-particle transport in an oscillatory channel and the back effect of fine particles on turbulence modulation using an Eulerian–Eulerian framework. In particular, simulations presented in this study are selected to investigate wave-induced fine sediment transport processes in a typical coastal setting. Our modelling framework is based on a simplified two-way coupled formulation that is accurate for particles of small Stokes number (St). As a first step, the instantaneous particle velocity is calculated as the superposition of the local fluid velocity and the particle settling velocity while the higher-order particle inertia effect neglected. Correspondingly, only the modulation of carrier flow is due to particle-induced density stratification quantified by the bulk Richardson number, Ri. In this paper, we fixed the Reynolds number to be ReΔ = 1000 and varied the bulk Richardson number over a range (Ri = 0, 1 × 10−4, 3 × 10−4 and 6 × 10−4). The simulation results reveal critical processes due to different degrees of the particle–turbulence interaction. Essentially, four different regimes of particle transport for the given ReΔ are observed: (i) the regime where virtually no turbulence modulation in the case of very dilute condition, i.e. Ri ~ 0; (ii) slightly modified regime where slight turbulence attenuation is observed near the top of the oscillatory boundary layer. However, in this regime a significant change can be observed in the concentration profile with the formation of a lutocline; (iii) regime where flow laminarization occurs during the peak flow, followed by shear instability during the flow reversal. A significant reduction in the oscillatory boundary layer thickness is also observed; (iv) complete laminarization due to strong particle-induced stable density stratification.

scholarly journals The Roles of Resuspension, Diffusion and Biogeochemical Processes on Oxygen Dynamics Offshore of the Rhone River, France: A Numerical Modeling Study

2016 ◽  
Author(s):  
Julia M. Moriarty ◽  
Courtney K. Harris ◽  
Christophe Rabouille ◽  
Katja Fennel ◽  
Marjorie A. M. Friedrichs ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Organic Matter ◽  
Oxygen Consumption ◽  
Water Column ◽  
Bottom Boundary Layer ◽  
Water Interface ◽  
Bottom Boundary ◽  
Rhône Delta ◽  
Oxygen Dynamics

Abstract. Observations indicate that seabed resuspension of organic material and the associated entrainment of porewater into the overlying water can alter biogeochemical fluxes in some environments, but measuring the role of sediment processes on oxygen and nutrient dynamics is challenging. A modeling approach offers a means of quantifying these fluxes for a range of conditions, but models have typically relied on simplifying assumptions regarding seabed-water column interactions. Thus, to evaluate the role of resuspension on biogeochemical dynamics, we developed a coupled hydrodynamic, sediment transport, and biogeochemical model (HydroBioSed) within the Regional Ocean Modeling System (ROMS). This coupled model accounts for processes including the storage of particulate organic matter (POM) and dissolved nutrients within the seabed; entrainment of this material into the water column via resuspension and diffusion at the sediment-water interface; and biogeochemical reactions within the seabed. A one-dimensional version of HydroBioSed was then implemented for the Rhone Delta, France. To isolate the role of resuspension on biogeochemical dynamics, this model implementation was run for a two-month period that included three resuspension events; also, the supply of organic matter, oxygen and nutrients to the water column was held constant in time. Consistent with time-series observations from the Rhone Delta, model results showed that resuspension increased the diffusive flux of oxygen into the seabed by increasing the vertical gradient of oxygen at the seabed-water interface. This enhanced supply of oxygen to the seabed allowed seabed oxygen consumption to increase, primarily through nitrification. Resuspension of POM into the water column, and the associated increase in remineralization, also increased oxygen consumption in the bottom boundary layer. During these resuspension events, modeled rates of oxygen consumption increased by up to factors of ~ 2 and ~ 8 in the seabed and bottom boundary layer, respectively. When averaged over two months, the intermittent cycles of erosion and deposition led to a 20 % increase of oxygen consumption in the seabed, as well as a larger increase of ~ 200 % in the bottom boundary layer. These results imply that observations collected during quiescent periods, and biogeochemical models that neglect resuspension or use typical parameterizations for resuspension, may underestimate net oxygen consumption at sites like the Rhone Subaqueous Delta. Local resuspension likely has the most pronounced effect on oxygen dynamics at study sites with a high oxygen concentration in the bottom boundary layer, only a thin seabed oxic layer, and abundant labile organic matter.

A Study of the Bottom Boundary Layer of the Florida Current

1972 ◽  
Vol 2 (1) ◽  
pp. 54-72 ◽  
Author(s):  
Georges L. Weatherly
Keyword(s):  
Boundary Layer ◽  
Current System ◽  
Bottom Boundary Layer ◽  
Bottom Current ◽  
Frictional Stress ◽  
Florida Current ◽  
Bottom Boundary ◽  
Straits Of Florida ◽  
Logarithmic Layer

This is a report of an experiment designed to study the bottom boundary layer of the Florida Current at a representative site in the Straits of Florida. The objectives of the experiment were 1) to determine the bottom frictional stress τ0, and 2) to determine whether the bottom boundary layer is a turbulent Ekman layer. A typical value of the bottom stress τ0 was found to be ~0.2 dyn cm−2. A mean veering of ~10° in the correct sense was observed in the logarithmic layer. No mean veering was observed above the logarithmic layer; this is believed to be a consequence of the strong modulation of the bottom current by the diurnal tide. The implication of τ0≈0.2 dyn cm−2 is considered in a simplified model of the Gulf Stream current system; this analysis suggests that, dynamically, the role of bottom friction is rather small.

scholarly journals Dipole collapse in rotating stratified dynamos

2019 ◽  
Vol 82 ◽  
pp. 357-363
Author(s):  
L. Petitdemange ◽  
R. Raynaud
Keyword(s):  
Numerical Modelling ◽  
Outer Surface ◽  
Boussinesq Approximation ◽  
Force Balance ◽  
Density Stratification ◽  
Ekman Number ◽  
Background Density ◽  
The Common ◽  
The Stability

Numerical modelling of convection driven dynamos in the Boussinesq approximation revealed fundamental characteristics of the dynamo-generated magnetic fields, but the relevance of these results remains to be assessed for highly stratified systems, like gas planets and stars. The common approach is then to rely on the anelastic approximation to model the background density stratification. A conclusion from different anelastic studies is that dipolar solutions seem more difficult to obtain in presence of a substantial density contrast. We review some important results obtained by Raynaud et al. (2015), who investigated the influence of the density stratification on the stability of dipolar dynamos. This study indicates that the loss of the dipolar branch does not ensue from a specific modification of the dynamo mechanisms related to the background stratification, but could instead result from a bias as our observations naturally favour a certain domain in the parameter space characterized by moderate values of the Ekman number. In strongly stratified systems, the force balance may vary with depth, and a local increase of inertia close to the outer surface can explain the loss of the dipolar branch, while volume-averaged measures may underestimate the role of inertia on the field topology.

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