scholarly journals Bottom-trapped currents as statistical equilibrium states above topographic anomalies

2012 ◽  
Vol 699 ◽  
pp. 500-510 ◽  
Author(s):  
A. Venaille
Keyword(s):  
Velocity Field ◽  
Statistical Mechanics ◽  
Numerical Simulations ◽  
Potential Vorticity ◽  
Linear Relation ◽  
Direct Numerical Simulations ◽  
The Self ◽  
Self Organization ◽  
Probable Outcome ◽  
Geostrophic Turbulence

AbstractOceanic geostrophic turbulence is mostly forced at the surface, yet strong bottom-trapped flows are commonly observed along topographic anomalies. Here we consider the case of a freely evolving, initially surface-intensified velocity field above a topographic bump, and show that the self-organization into a bottom-trapped current can result from its turbulent dynamics. Using equilibrium statistical mechanics, we explain this phenomenon as the most probable outcome of turbulent stirring. We compute explicitly a class of solutions characterized by a linear relation between potential vorticity and streamfunction, and predict when the bottom intensification is expected. Using direct numerical simulations, we provide an illustration of this phenomenon that agrees qualitatively with theory, although the ergodicity hypothesis is not strictly fulfilled.

scholarly journals Molecular Recognition and Self-Organization in Life Phenomena Studied by a Statistical Mechanics of Molecular Liquids, the RISM/3D-RISM Theory

Molecules ◽  
2021 ◽  
Vol 26 (2) ◽  
pp. 271
Author(s):  
Masatake Sugita ◽  
Itaru Onishi ◽  
Masayuki Irisa ◽  
Norio Yoshida ◽  
Fumio Hirata
Keyword(s):  
Molecular Recognition ◽  
Statistical Mechanics ◽  
Self Assembly ◽  
The Self ◽  
Self Organization ◽  
Molecular Processes ◽  
Molecular Liquids ◽  
Organization Process ◽  
Structural Fluctuation ◽  
Life Phenomena

There are two molecular processes that are essential for living bodies to maintain their life: the molecular recognition, and the self-organization or self-assembly. Binding of a substrate by an enzyme is an example of the molecular recognition, while the protein folding is a good example of the self-organization process. The two processes are further governed by the other two physicochemical processes: solvation and the structural fluctuation. In the present article, the studies concerning the two molecular processes carried out by Hirata and his coworkers, based on the statistical mechanics of molecular liquids or the RISM/3D-RISM theory, are reviewed.

Miscible rectilinear displacements with gravity override. Part 2. Heterogeneous porous media

2000 ◽  
Vol 420 ◽  
pp. 259-276 ◽  
Author(s):  
EMMANUEL CAMHI ◽  
ECKART MEIBURG ◽  
MICHAEL RUITH
Keyword(s):  
Porous Media ◽  
Velocity Field ◽  
Numerical Simulations ◽  
Correlation Length ◽  
Resonant Interaction ◽  
Heterogeneous Porous Media ◽  
Direct Numerical Simulations ◽  
Buoyant Flows ◽  
Neutrally Buoyant ◽  
Strong Vorticity

The effects of permeability heterogeneities on rectilinear displacements with viscosity contrast and density variations are investigated computationally by means of direct numerical simulations. Physical interpretations are given in terms of mutual interactions among the three vorticity components related to viscous, density and permeability effects. In homogeneous environments the combined effect of the unfavourable viscosity gradient and the potential velocity field generated by the horizontal boundaries was seen to produce a focusing mechanism that resulted in the formation of a strong vorticity layer and the related growth of a dominant gravity tongue (Ruith & Meiburg 2000). The more randomly distributed vorticity associated with the heterogeneities tends to ‘defocus’ this interaction, thereby preventing the formation of the vorticity layer and the gravity tongue. When compared to neutrally buoyant flows, the level of heterogeneity affects the breakthrough recovery quite differently. For moderate heterogeneities, a gravity tongue still forms and leads to early breakthrough, whereas the same result is accomplished for large heterogeneities by channelling. At intermediate levels of heterogeneity, these tendencies partially cancel each other, so that the breakthrough recovery reaches a maximum. Similarly, the dependence of the breakthrough recovery on the correlation length is quite different in displacements with density contrasts compared to neutrally buoyant flows. For neutrally buoyant flows the resonant interaction between viscosity and permeability vorticities typically leads to a minimal recovery at intermediate values of the correlation length. In contrast, displacements with density contrast give rise to a gravity tongue for both very small and very large values of this length, so that the recovery reaches a maximum at intermediate values.

Homogeneity of turbulence generated by static-grid structures

2010 ◽  
Vol 654 ◽  
pp. 473-500 ◽  
Author(s):  
Ö. ERTUNÇ ◽  
N. ÖZYILMAZ ◽  
H. LIENHART ◽  
F. DURST ◽  
K. BERONOV
Keyword(s):  
Reynolds Number ◽  
Velocity Field ◽  
Numerical Simulations ◽  
Direct Numerical Simulations ◽  
Uniform Grid ◽  
Reynolds Stresses ◽  
Hot Wire ◽  
Mean Velocity ◽  
Wide Range ◽  
The Mean

Homogeneity of turbulence generated by static grids is investigated with the help of hot-wire measurements in a wind-tunnel and direct numerical simulations based on the Lattice Bolztmann method. It is shown experimentally that Reynolds stresses and their anisotropy do not become homogeneous downstream of the grid, independent of the mesh Reynolds number for a grid porosity of 64%, which is higher than the lowest porosities suggested in the literature to realize homogeneous turbulence downstream of the grid. In order to validate the experimental observations and elucidate possible reasons for the inhomogeneity, direct numerical simulations have been performed over a wide range of grid porosity at a constant mesh Reynolds number. It is found from the simulations that the turbulence wake behind the symmetric grids is only homogeneous in its mean velocity but is inhomogeneous when turbulence quantities are considered, whereas the mean velocity field becomes inhomogeneous in the wake of a slightly non-uniform grid. The simulations are further analysed by evaluating the terms in the transport equation of the kinetic energy of turbulence to provide an explanation for the persistence of the inhomogeneity of Reynolds stresses far downstream of the grid. It is shown that the early homogenization of the mean velocity field hinders the homogenization of the turbulence field.

Non-geostrophic instabilities of an equilibrium baroclinic state

2013 ◽  
Vol 734 ◽  
pp. 535-566 ◽  
Author(s):  
Alexandre B. Pieri ◽  
F. S. Godeferd ◽  
C. Cambon ◽  
A. Salhi
Keyword(s):  
Numerical Simulations ◽  
Potential Vorticity ◽  
Baroclinic Instability ◽  
Direct Numerical Simulations ◽  
Vertical Shear ◽  
Dimensionless Numbers ◽  
Stability Bound ◽  
Simultaneous Existence ◽  
The Stability ◽  
Symmetric Instability

AbstractWe consider non-geostrophic homogeneous baroclinic turbulence without solid boundaries, and we focus on its energetics and dynamics. The homogeneous turbulent flow is therefore submitted to both uniform vertical shear $S$ and stable vertical stratification, parametrized by the Brunt–Väisälä frequency $N$, and placed in a rotating frame with Coriolis frequency $f$. Direct numerical simulations show that the threshold of baroclinic instability growth depends mostly on two dimensionless numbers, the gradient Richardson number $\mathit{Ri}= {N}^{2} / {S}^{2} $ and the Rossby number $\mathit{Ro}= S/ f$, whereas linear theory predicts a threshold that depends only on $\mathit{Ri}$. At high Rossby numbers the nonlinear limit is found to be $\mathit{Ri}= 0. 2$, while in the limit of low $\mathit{Ro}$ the linear stability bound $\mathit{Ri}= 1$ is recovered. We also express the stability results in terms of background potential vorticity, which is an important quantity in baroclinic flows. We show that the linear symmetric instability occurs from the presence of negative background potential vorticity. The possibility of simultaneous existence of symmetric and baroclinic instabilities is also investigated. The dominance of symmetric instability over baroclinic instability for $\mathit{Ri}\ll 1$ is confirmed by our direct numerical simulations, and we provide an improved understanding of the dynamics of the flow by exploring the details of energy transfers for moderate Richardson numbers.

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