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Articoli di riviste sul tema "Stratification de densité"

Autore: Grafiati

Pubblicato: 26 ottobre 2024

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1

Bouterra, Mourad, Afif El Cafsi, Abdelfettah Belghith e Patrick Le Quere. "Etude de l'effet de la stratification thermique sur la dispersion d'un polluant autour d'un obstacle". Journal of Renewable Energies 6, n. 1 (30 giugno 2003): 53–68. http://dx.doi.org/10.54966/jreen.v6i1.961.

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L'étude numérique bidimensionnelle de la dispersion d'un polluant autour d'un obstacle soumis à un écoulement turbulent a été effectuée par la technique de Simulation des Grosses Structures L.E.S. Dans la première partie de ce travail, nous avons étudié la dispersion de polluant ayant la même densité que l'air ambiant. On montre que la dispersion de polluant est exclusivement tributaire des mouvements turbulents présents, le mécanisme dominant de la dispersion étant la convection. Dans la seconde partie, on s'est intéressé à l'étude de l'effet de la stratification thermique sur les mécanismes de dispersion de polluant. On montre que le polluant stagne au niveau de son point d'émission et pourra être émis dans la zone de mélange formé en aval de l'obstacle. Le polluant sera alors transporté par l'écoulement moyen, sur une thermocline entre les deux couches chaude et froide.

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De Oliveira-Verger, Christelle, e Angelo Di Caterino. "Sémiotique et anthropologie: un retour vers le futur?" Entornos 30, n. 1 (30 giugno 2017): 15. http://dx.doi.org/10.25054/01247905.1417.

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Cet article vise à rappeler les relations et le dialogue qu’entretiennent sémiotique et anthropologie depuis la théorie développée par Lévi-Strauss jusqu’au dialogue instauré récemment avec Descola. Nous nous attacherons à montrer comment interagissent ces deux disciplines, jusqu’à apparaître parfois telles les deux faces d’une même médaille. De plus, nous constaterons dans cette étude que les réflexions de Lévi-Strauss, Descola mais également de Geertz restent fondamentales pour des raisons qui confirment le lien entre anthropologie et sémiotique. La «bonne distance» ethnographique et la «bonne densité» analytique placeraient l’analyse entre Charybde et Scylla. La variété d’instruments à disposition servirait à éviter, d’un côté, le réductionnisme descriptif excessif à la faveur d’une stratification multi perspective et, de l’autre, elle réduirait le risque des dérives infinies au moyen d’une circonscription objectivante.

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Bournet, P. E., D. Dartus, B. Tassin e B. Vincon-Leite. "Ondes internes du lac du Bourget: analyse des observations par des modèles linéaires". Revue des sciences de l'eau 9, n. 2 (12 aprile 2005): 247–66. http://dx.doi.org/10.7202/705252ar.

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Deux campagnes de mesures effectuées sur le lac du Bourget en période de faible stratification (avril et décembre 1994) ont mis en évidence des oscillations de la thermocline de période comprise entre deux et trois jours. Ces oscillations atteignent 40 m d'amplitude pour une profondeur maximale de 145 m. Elles ont probablement un impact sur les processus biologiques et physico-chimiques qui gouvernent l'évolution de la qualité des eaux du lac. L'analyse des données brutes des températures révèle une corrélation étroite entre la génération des ondes internes et les événements de vents importants. Il apparaît en particulier que seuls les vents violents (< 8 m/s) affectent la stratification thermique de manière significative. Deux approches sont utilisées pour caractériser ces ondes : - une approche par traitement du signal qui donne accès aux périodes d'oscillations prédominantes ainsi qu'à la répartition de l'énergie dans la colonne d'eau en fonction de la fréquence. - une approche par modélisation mathématique au cours de laquelle les résultats obtenus par tjjois techniques distinctes utilisant plusieurs degrés de représentation de la bathymétrie du lac sont comparés. Ces modèles permettent de calculer les périodes d'oscillations ainsi que les déplacements de l'interface de densité et les vitesses dans chaque couche. A partir des valeurs des amplitudes d'oscillation obtenues expérimentalement, des vitesses maximales de l'ordre de 7 cm/s dans l'épîlîmnion et 3 cm/s dans l'hypolimnion ont pu être estimées pour les deux épisodes considérés. On montre que les modèles mathématiques et l'analyse spectrale corroborent les observations.

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4

Vincent, Grégoire, F. Caron, Damien Sabatier e Lilian Blanc. "L'imagerie LiDAR montre que les forêts les plus hautes comportent des tiges plus élancées". BOIS & FORETS DES TROPIQUES 314, n. 314 (1 dicembre 2012): 51. http://dx.doi.org/10.19182/bft2012.314.a20490.

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Une opération de balayage laser aéroporté à haute densité a permis de modéliser la hauteur du couvert forestier d'un site expérimental en forêt néotropicale (à Paracou en Guyane française). La hauteur des arbres individuels a été calculée par segmentation manuelle des houppiers sur le modèle numérique de canopée et extraction de la hauteur maximale locale du couvert forestier. Trois cent quatrevingt- seize estimations de hauteur d'arbres dominants ou émergents ont été mises en relation avec les données de terrain correspondantes pour les diamètres des tiges échantillonnées sur deux placettes de hauteur moyenne différente (28,1 m et 31,3 m). Les résultats montrent une corrélation positive et très significative entre l'élancement des tiges et la hauteur moyenne du couvert à l'échelle des placettes. La même corrélation apparaît à l'échelle des peuplements des trois essences suffisamment échantillonnées. Il est possible de conclure qu'une stratification selon la hauteur du couvert est à recommander dans le calcul de relations allométriques afin d'éviter les biais dans les estimations de biomasse aérienne.

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Dessureault, Christian. "Parenté et stratification sociale dans une paroisse rurale de la vallée du Saint-Laurent au milieu du XIXe siècle1". Revue d'histoire de l'Amérique française 54, n. 3 (16 agosto 2004): 411–47. http://dx.doi.org/10.7202/005397ar.

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Résumé Les réseaux et les rapports de parenté représentent des vecteurs importants des recherches sur la société rurale du Québec. Cependant, nous n’avons encore aucune étude qui évalue de manière systématique l’importance des liens de parenté dans une paroisse rurale à un moment spécifique de l’histoire. Nous ne connaissons pas, de manière précise, la densité des liens familiaux entre les divers ménages d’une même paroisse, ni surtout le degré de variabilité de ces liens de parenté selon les familles, selon le genre et selon les groupes sociaux.Cette recherche vise à présenter une première mesure concernant l’étendue et les types des liens de parenté entre tous les chefs de ménage d’une vieille paroisse rurale de la vallée du Saint-Laurent en 1861: Saint-Antoine–de-Lavaltrie. L’un des principaux objectifs de cet article est de vérifier l’étendue, la sélectivité sociale et la différenciation selon le genre des réseaux de parenté dans un territoire donné où se vivent, au quotidien, les relations sociales. Cet article aide à mieux circonscrire le poids différencié des rapports de parenté dans les divers groupes au sein des communautés rurales. Cette recherche permet aussi de corroborer ou de nuancer, dans un contexte historique précis, certains constats de la sociologie, de l’anthropologie et de l’histoire sociale concernant l’importance et la structure des réseaux de parenté.

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6

Bosco, M., e P. Meunier. "Three-dimensional instabilities of a stratified cylinder wake". Journal of Fluid Mechanics 759 (20 ottobre 2014): 149–80. http://dx.doi.org/10.1017/jfm.2014.517.

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AbstractThis paper describes experimentally, numerically and theoretically how the three-dimensional instabilities of a cylinder wake are modified by the presence of a linear density stratification. The first part is focused on the case of a cylinder with a small tilt angle between the cylinder’s axis and the vertical. The classical mode A well-known for a homogeneous fluid is still present. It is more unstable for moderate stratifications but it is stabilized by a strong stratification. The second part treats the case of a moderate tilt angle. For moderate stratifications, a new unstable mode appears, mode S, characterized by undulated layers of strong density gradients and axial flow. These structures correspond to Kelvin–Helmholtz billows created by the strong shear present in the critical layer of each tilted von Kármán vortex. The last two parts deal with the case of a strongly tilted cylinder. For a weak stratification, an instability (mode RT) appears far from the cylinder, due to the overturning of the isopycnals by the von Kármán vortices. For a strong stratification, a short wavelength unstable mode (mode L) appears, even in the absence of von Kármán vortices. It is probably due to the strong shear created by the lee waves upstream of a secondary recirculation bubble. A map of the four different unstable modes is established in terms of the three parameters of the study: the Reynolds number, the Froude number (characterizing the stratification) and the tilt angle.

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7

Bessell, M. S., J. M. Brett, M. Scholz, Y. Takeda, R. Wehrse e P. R. Wood. "Photospheres of Mira Variables". International Astronomical Union Colloquium 108 (1988): 187–88. http://dx.doi.org/10.1017/s0252921100093763.

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Mira variables form an important subgroup of the red giant stars which are typical representatives of stars showing burnt material at their surfaces. Since the photospheres of Miras are not in hydrostatic equilibrium but are characterized by spherically very extended density stratifications, their properties and emitted spectra differ substantially from those of non-Miras, and any attempts to analyse Mira spectra by means of conventional techniques must fail. Non-hydrostatic models are needed for analysis work.We computed a small set of exploratory M type (solar abundances) Mira model photospheres whose density distributions were taken from an improved modification of a pulsation model proposed by wood (1979). Besides the fundamental model parameters, i.e. mass, luminosity and radius (or effective temperature), the parameters of the density stratification (e.g. the heights of the density discontinuities at the shock front positions, or the effective gravity acting between two successive shock fronts) must be treated as free parameters within certain limits, owing to insufficient knowledge of the velocity stratification entering the pulsation model. Typical density and temperature stratifications are shown in Fig. 1 of Scholz (1987). Both CO lines, measuring the outflow and infall velocities of matter between the shock fronts, and selected moleculer band features (colors) were found to react sensitively to adjustments of the model parameters. As an example, Fig.1 shows the differences between CO line profiles computed from the near-maximum model of Fig.1 of scholz (1987) (Fig.1a) and those computed from a model in which the effective gravity between the shock fronts was increased by a factor of 1.5 (Fig. 1b). The same velocity stratification was adopted in of monochromatic radii proves to be a powerful tool of diagnostics of Mira photospheres (Scholz and Takeda 1987; Bessell et al. 1987).

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8

Lam, W. K., L. Chan, H. Hasini e A. Ooi. "An Analysis of Two-Dimensional Stratified Gravity Current Flow using Open FOAM". International Journal of Engineering & Technology 7, n. 4.35 (30 novembre 2018): 589. http://dx.doi.org/10.14419/ijet.v7i4.35.22919.

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Direct numerical simulations (DNSs) of two-dimensional stratified gravity-current are simulated using OpenFOAM. Three different aspect ratio, h0/l0 (where h0 is the height of the dense fluid and l0 is the length of the dense fluid) are simulated with stratification ranging from 0 (homogenous ambient) to 0.2 with a constant Reynolds number (Re) of 4000. The stratificationof the ambient air is determined by the density difference between the bottom and the top walls of the channel (ρb- ρ0, where ρb is the density at the bottom of the domain and ρ0 is the density at the top). The magnitude of the stratification (S=ԑb/ԑ) can be determined by calculating the reduced density differences of the bottom fluid with the ambient fluid (ԑb = (ρb- ρ0)/ ρ0) and the dense fluid with the ambient fluid (ԑ = (ρc-ρ0)/ ρ0, where ρc represents the density of the dense fluid). The configuration of the simulation is validated with a test case from Birman, Meiburg & Ungraish and the contour and front velocity (propagation speed) were in good agreement. The gravity current flow in the stratified ambient is analyzed qualitatively and compared with the gravity current in the homogenous ambient. Gravity current in homogenous ambient (S=0) and weak stratification (S=0.2) are supercritical flow where the flow is turbulent and Kelvin-Helmholtz (K-H) billow formed behind the gravity current head. The front location of the gravity is reduced as the stratification increase and denotes that the front velocity of the gravity current is reduced by the stratification.

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9

LAMB, KEVIN G. "A numerical investigation of solitary internal waves with trapped cores formed via shoaling". Journal of Fluid Mechanics 451 (25 gennaio 2002): 109–44. http://dx.doi.org/10.1017/s002211200100636x.

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The formation of solitary internal waves with trapped cores via shoaling is investigated numerically. For density fields for which the buoyancy frequency increases monotonically towards the surface, sufficiently large solitary waves break as they shoal and form solitary-like waves with trapped fluid cores. Properties of large-amplitude waves are shown to be sensitive to the near-surface stratification. For the monotonic stratifications considered, waves with open streamlines are limited in amplitude by the breaking limit (maximum horizontal velocity equals wave propagation speed). When an exponential density stratification is modified to include a thin surface mixed layer, wave amplitudes are limited by the conjugate flow limit, in which case waves become long and horizontally uniform in the centre. The maximum horizontal velocity in the limiting wave is much less than the wave's propagation speed and as a consequence, waves with trapped cores are not formed in the presence of the surface mixed layer.

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GOYAL, N., H. PICHLER e E. MEIBURG. "Variable-density miscible displacements in a vertical Hele-Shaw cell: linear stability". Journal of Fluid Mechanics 584 (25 luglio 2007): 357–72. http://dx.doi.org/10.1017/s0022112007006428.

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A computational study based on the Stokes equations is conducted to investigate the effects of gravitational forces on miscible displacements in vertical Hele-Shaw cells. Nonlinear simulations provide the quasi-steady displacement fronts in the gap of the cell, whose stability to spanwise perturbations is subsequently examined by means of a linear stability analysis. The two-dimensional simulations indicate a marked thickening (thinning) and slowing down (speeding up) of the displacement front for flows stabilized (destabilized) by gravity. For the range investigated, the tip velocity is found to vary linearly with the gravity parameter. Strongly stable density stratifications lead to the emergence of flow patterns with spreading fronts, and to the emergence of a secondary needle-shaped finger, similar to earlier observations for capillary tube flows. In order to investigate the transition between viscously driven and purely gravitational instabilities, a comparison is presented between displacement flows and gravity-driven flows without net displacements.The linear stability analysis shows that both the growth rate and the dominant wavenumber depend only weakly on the Péclet number. The growth rate varies strongly with the gravity parameter, so that even a moderately stable density stratification can stabilize the displacement. Both the growth rate and the dominant wavelength increase with the viscosity ratio. For unstable density stratifications, the dominant wavelength is nearly independent of the gravity parameter, while it increases strongly for stable density stratifications. Finally, the kinematic wave theory of Lajeunesse et al. (J. Fluid Mech. vol. 398, 1999, p. 299) is seen to capture the stability limit quite accurately, while the Darcy analysis misses important aspects of the instability.

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Ezhova, Ekaterina, Claudia Cenedese e Luca Brandt. "Dynamics of a Turbulent Buoyant Plume in a Stratified Fluid: An Idealized Model of Subglacial Discharge in Greenland Fjords". Journal of Physical Oceanography 47, n. 10 (ottobre 2017): 2611–30. http://dx.doi.org/10.1175/jpo-d-16-0259.1.

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AbstractThis study reports the results of large-eddy simulations of an axisymmetric turbulent buoyant plume in a stratified fluid. The configuration used is an idealized model of the plume generated by a subglacial discharge at the base of a tidewater glacier with an ambient stratification typical of Greenland fjords. The plume is discharged from a round source of various diameters and characteristic stratifications for summer and winter are considered. The classical theory for the integral parameters of a turbulent plume in a homogeneous fluid gives accurate predictions in the weakly stratified lower layer up to the pycnocline, and the plume dynamics are not sensitive to changes in the source diameter. In winter, when the stratification is similar to an idealized two-layer case, turbulent entrainment and generation of internal waves by the plume top are in agreement with the theoretical and numerical results obtained for turbulent jets in a two-layer stratification. In summer, instead, the stratification is more complex and turbulent entrainment by the plume top is significantly reduced. The subsurface layer in summer is characterized by a strong density gradient and the oscillating plume generates internal waves that might serve as an indicator of submerged plumes not penetrating to the surface.

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12

Shirane, M. "Stratification of Fabrics by Their Density". Sen'i Kikai Gakkaishi (Journal of the Textile Machinery Society of Japan) 38, n. 11 (1985): P482—P493,T201. http://dx.doi.org/10.4188/transjtmsj.38.11_p482.

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13

Shevtsova, V., D. Melnikov e J. C. Legros. "Unstable density stratification in binary mixture". Progress in Computational Fluid Dynamics, An International Journal 6, n. 6 (2006): 348. http://dx.doi.org/10.1504/pcfd.2006.010776.

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14

Korre, Lydia, e Nicholas A. Featherstone. "On the Dynamics of Overshooting Convection in Spherical Shells: Effect of Density Stratification and Rotation". Astrophysical Journal 923, n. 1 (1 dicembre 2021): 52. http://dx.doi.org/10.3847/1538-4357/ac2dea.

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Abstract Overshooting of turbulent motions from convective regions into adjacent stably stratified zones plays a significant role in stellar interior dynamics, as this process may lead to mixing of chemical species and contribute to the transport of angular momentum and magnetic fields. We present a series of fully nonlinear, three-dimensional (3D) anelastic simulations of overshooting convection in a spherical shell that are focused on the dependence of the overshooting dynamics on the density stratification and the rotation, both key ingredients in stars that however have not been studied systematically together via global simulations. We demonstrate that the overshoot lengthscale is not simply a monotonic function of the density stratification in the convective region, but instead it depends on the ratio of the density stratifications in the two zones. Additionally, we find that the overshoot lengthscale decreases with decreasing Rossby number Ro and scales as Ro0.23 while it also depends on latitude with higher Rossby cases leading to a weaker latitudinal variation. We examine the mean flows arising due to rotation and find that they extend beyond the base of the convection zone into the stable region. Our findings may provide a better understanding of the dynamical interaction between stellar convective and radiative regions, and motivate future studies particularly related to the solar tachocline and the implications of its overlapping with the overshoot region.

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15

Neuhart, Dan H., George C. Greene, Dale R. Satran e G. Thomas Holbrook. "Density stratification effects on wake vortex decay". Journal of Aircraft 23, n. 11 (novembre 1986): 820–24. http://dx.doi.org/10.2514/3.45387.

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16

RIAZ, AMIR, e ECKART MEIBURG. "Miscible, Porous Media Displacements with Density Stratification". Annals of the New York Academy of Sciences 1027, n. 1 (novembre 2004): 342–59. http://dx.doi.org/10.1196/annals.1324.029.

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Effler, Steven W., e Emmet M. Owens. "Density Stratification in Onondaga Lake: 1968–1994". Lake and Reservoir Management 12, n. 1 (marzo 1996): 25–33. http://dx.doi.org/10.1080/07438149609353994.

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18

Wright, Scott, e Gary Parker. "Density Stratification Effects in Sand-Bed Rivers". Journal of Hydraulic Engineering 130, n. 8 (agosto 2004): 783–95. http://dx.doi.org/10.1061/(asce)0733-9429(2004)130:8(783).

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Sha, Huyun, e J. M. Vanden-Broeck. "Internal solitary waves with stratification in density". Journal of the Australian Mathematical Society. Series B. Applied Mathematics 38, n. 4 (aprile 1997): 563–80. http://dx.doi.org/10.1017/s0334270000000862.

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AbstractLong periodic waves propagating in a closed channel are considered. The fluid consists of two layers of constant densities separated by a layer in which the density varies continuously. The numerical results of Vanden-Broeck and Turner [8] are extended. It is shown that their solutions are particular members of a family of solutions. Solutions are selected by requiring that the streamfunction takes values on the upper and lower walls which are consistent with a uniform stream far upstream. The new solutions are qualitatively similar to those of Vanden-Broeck and Turner [8]. In particular, there are periodic waves characterized by a train of ripples at their troughs. It is shown numerically that these waves approach solitary waves with oscillatory tails as their wavelength increases. Moreover special solutions for which the amplitude of the ripples is almost zero are identified. Such solutions without ripples were previously found for solitary waves with surface tension.

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Vladimirov, V. A. "Analogy between density stratification and rotation effects". Journal of Applied Mechanics and Technical Physics 26, n. 3 (1985): 353–62. http://dx.doi.org/10.1007/bf00910369.

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Ivey, G. N., K. B. Winters e J. R. Koseff. "Density Stratification, Turbulence, but How Much Mixing?" Annual Review of Fluid Mechanics 40, n. 1 (gennaio 2008): 169–84. http://dx.doi.org/10.1146/annurev.fluid.39.050905.110314.

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Dixit, Harish N., e Rama Govindarajan. "Effect of density stratification on vortex merger". Physics of Fluids 25, n. 1 (gennaio 2013): 016601. http://dx.doi.org/10.1063/1.4773445.

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Nandy, S., P. K. Joshi e K. K. Das. "Forest canopy density stratification using biophysical modeling". Journal of the Indian Society of Remote Sensing 31, n. 4 (dicembre 2003): 291–97. http://dx.doi.org/10.1007/bf03007349.

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Pham, Hieu T., e Sutanu Sarkar. "Ageostrophic Secondary Circulation at a Submesoscale Front and the Formation of Gravity Currents". Journal of Physical Oceanography 48, n. 10 (ottobre 2018): 2507–29. http://dx.doi.org/10.1175/jpo-d-17-0271.1.

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AbstractLarge-eddy simulations are performed to investigate the development of the ageostrophic secondary circulation (ASC) and associated transport in a submesoscale front. Based on the observations in the northern Bay of Bengal and in the Pacific cold tongue, the model front has a large cross-front density difference that is partially compensated with lateral temperature and salinity gradients. Vertical stratification is varied in different cases to explore its effect on the ASC. The evolution of the ASC differs with stratification. When the front is unstratified, shear instabilities, which develop from the geostrophic shear, cause the front to slump. Cold water from the light side propagates across the front on the surface, while warm water from the dense side spreads in the opposite direction at depth. In cases with stratifications, a shear layer driven by the cross-front pressure gradient forms at the surface to initiate the ASC. Shear-driven turbulence associated with the enhanced shear in the layer causes the front to slump, and the development of the ASC onward is similar to the unstratified case. Irrespective of the initial stratification of the strong fronts simulated here, the surface layer evolves into a gravity current. The ASC is composed of the surface gravity current and a countercurrent that are separated by a middle layer with enhanced stratification and a thermal inversion. Turbulent dissipation is enhanced at the nose of the gravity current and in a sheared region somewhat behind the leading edge of the countercurrent. The gravity current propagates at a speed proportional to the buoyancy difference across the front in the case with no stratification.

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BERON-VERA, F. J., e P. RIPA. "Free boundary effects on baroclinic instability". Journal of Fluid Mechanics 352 (10 dicembre 1997): 245–64. http://dx.doi.org/10.1017/s0022112097007222.

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The effects of a free boundary on the stability of a baroclinic parallel flow are investigated using a reduced-gravity model. The basic state has uniform density stratification and a parallel flow with uniform vertical shear in thermal-wind balance with the horizontal buoyancy gradient. A finite value of the velocity at the free (lower) boundary requires the interface to have a uniform slope in the direction transversal to that of the flow. Normal-mode perturbations with arbitrary vertical structure are studied in the limit of small Rossby number. This solution is restricted to neither a horizontal lower boundary nor a weak stratification in the basic state.In the limit of a very weak stratification and bottom slope there is a large separation between the first two deformation radii and hence short or long perturbations may be identified:(a) The short-perturbation limit corresponds to the well-known Eady problem in which case the layer bottom is effectively rigid and its slope in the basic state is immaterial.(b) In the long-perturbation limit the bottom is free to deform and the unstable wave solutions, which appear for any value of the Richardson number Ri, are sensible to its slope in the basic state. In fact, a sloped bottom is found to stabilize the basic flow.At stronger stratifications there is no distinction between short and long perturbations, and the bottom always behaves as a free boundary. Unstable wave solutions are found for Ri→∞ (unlike the case of long perturbations). The increase in stratification is found to stabilize the basic flow. At the maximum stratification compatible with static stability, the perturbation has a vanishing growth rate at all wavenumbers.Results in the long-perturbation limit corroborate those predicted by an approximate layer model that restricts the buoyancy perturbations to have a linear vertical structure. The approximate model is less successful in the short-perturbation limit since the constraint to a linear density profile does not allow the correct representation of the exponential trapping of the exact eigensolutions. With strong stratification, only the growth rate of long enough perturbations superimposed on basic states with gently sloped lower boundaries behaves similarly to that of the exact model. However, the stabilizing tendency on the basic flow as the stratification reaches its maximum is also found in the approximate model. Its partial success in this case is also attributed to the limited vertical structure allowed by the model.

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Wang, Xiuying, Wanli Cheng, Zihan Zhou, Dehe Yang, Jing Cui e Feng Guo. "Stratification observed by the in situ plasma density measurements from the Swarm satellites". Annales Geophysicae 38, n. 2 (20 aprile 2020): 517–26. http://dx.doi.org/10.5194/angeo-38-517-2020.

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Abstract. The stratification phenomenon is investigated using the simultaneous in situ plasma density measurements obtained by the Swarm satellites orbiting at different altitudes above the F2 peak. For the first time, the continuous distribution morphology and the exact locations are obtained for the nighttime stratification, which show that the stratification events are centered at the EIA (equatorial ionization anomaly) trough and extend towards the two EIA crests, with the most significant part being located at the EIA trough. Another new discovery is the stratification in southern mid-latitudes; stratification events in this region are located on a local plasma peak sandwiched by two lower density strips covering all the longitudes. The formation mechanism of the stratification for the two latitudinal regions is discussed, but the stratification mechanism in southern mid-latitudes remains an unsolved problem. Highlights. This paper addresses the following: first application of in situ plasma densities for the direct analysis of the stratification in F2 layer, refined features of the exact location and continuous morphology for the stratification phenomenon, a new discovery of stratification covering all longitudes in southern mid-latitudes.

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27

IWADE, Kotaro, e Masato AKAMATSU. "Disturbance of air-density stratification by magnetic force". Journal of the Visualization Society of Japan 29-1, n. 2 (2009): 1111. http://dx.doi.org/10.3154/jvs.29.1111.

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28

MIYATA, Yuichiro. "Periglacial involution-structure caused by reversed density stratification." Quaternary Research (Daiyonki-Kenkyu) 26, n. 4 (1988): 373–91. http://dx.doi.org/10.4116/jaqua.26.4_373.

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29

Davies, Geoffrey F. "Controls on density stratification in the early mantle". Geochemistry, Geophysics, Geosystems 8, n. 4 (aprile 2007): n/a. http://dx.doi.org/10.1029/2006gc001414.

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30

Renardy, Yuriko. "Viscosity and density stratification in vertical Poiseuille flow". Physics of Fluids 30, n. 6 (1987): 1638. http://dx.doi.org/10.1063/1.866228.

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31

TSUJIMURA, Shinji, Oaki IIDA e Yasutaka NAGANO. "Coherent Structure in Geostrophic Flow under Density Stratification." Transactions of the Japan Society of Mechanical Engineers Series B 64, n. 626 (1998): 3430–37. http://dx.doi.org/10.1299/kikaib.64.3430.

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32

SMITH, RONALD. "Stratification-induced lateral dispersion of a density anomaly". Journal of Fluid Mechanics 353 (25 dicembre 1997): 197–203. http://dx.doi.org/10.1017/s0022112097007325.

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When a small amount of marked solute is released into a stratified fluid, there is lateral dispersion of the marked solute and a larger lateral dispersion of any density anomaly. The method of moments is used to calculate the two dispersion coefficients. The excess dispersion for the density is shown to be proportional to the fractional density decrease from the bed to the free surface and to the cube of the water depth, and inversely proportional to the vertical mixing for lateral momentum. For weak turbulent mixing the stratification-induced lateral dispersion for the density anomaly can be several orders of magnitude greater than the lateral turbulent mixing for marked solute

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33

CAMASSA, R., e R. TIRON. "Optimal two-layer approximation for continuous density stratification". Journal of Fluid Mechanics 669 (5 gennaio 2011): 32–54. http://dx.doi.org/10.1017/s0022112010004891.

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Two-layer fluids of finite depth under gravity are the simplest configuration capable of supporting internal wave motion. The extent to which such systems can be used to provide quantitative information on smoothly stratified fluids, in configurations relevant for geophysical applications, is analysed and a model of practical interest derived. The model is based on long-wave asymptotic expansions and on first-principle criteria for an optimal choice of effective two-layer parameters for the incompressible, smoothly stratified Euler equations. The accuracy of the model is extensively tested, via fully resolved numerical computations, on the class of travelling wave solutions supported by smooth stratification systems. It is found that, despite the severe restrictions posed by the discrete two-layer density assumption, solitary wave solutions corresponding to experimentally realizable parametric values can be accurately predicted, in both wave and fluid parcel markers, such as phase speed and density fields, respectively. Thanks to this analysis, explicit closed-form solutions are available for all relevant physical quantities. The agreement between the simple, optimized two-layer model and the parent smooth-stratification Euler system persists up to extreme cases, such as that of internal fronts, and even up to thicknesses of the pycnocline comparable to that of the effective layers.

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34

Effler, Steven W., Emmet M. Owens e Keith A. Schimel. "Density stratification in ionically enriched Onondaga lake, U.S.A." Water, Air, & Soil Pollution 27, n. 3-4 (febbraio 1986): 247–58. http://dx.doi.org/10.1007/bf00649406.

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35

CAMASSA, ROBERTO, CLAUDIA FALCON, JOYCE LIN, RICHARD M. McLAUGHLIN e NICHOLAS MYKINS. "A first-principle predictive theory for a sphere falling through sharply stratified fluid at low Reynolds number". Journal of Fluid Mechanics 664 (12 ottobre 2010): 436–65. http://dx.doi.org/10.1017/s0022112010003800.

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A sphere exhibits a prolonged residence time when settling through a stable stratification of miscible fluids due to the deformation of the fluid-density field. Using a Green's function formulation, a first-principles numerically assisted theoretical model for the sphere–fluid coupled dynamics at low Reynolds number is derived. Predictions of the model, which uses no adjustable parameters, are compared with data from an experimental investigation with spheres of varying sizes and densities settling in stratified corn syrup. The velocity of the sphere as well as the deformation of the density field are tracked using time-lapse images, then compared with the theoretical predictions. A settling rate comparison with spheres in dense homogeneous fluid additionally quantifies the effect of the enhanced residence time. Analysis of our theory identifies parametric trends, which are also partially explored in the experiments, further confirming the predictive capability of the theoretical model. The limit of infinite fluid domain is considered, showing evidence that the Stokes paradox of infinite fluid volume dragged by a moving sphere can be regularized by density stratifications. Comparisons with other possible models under a hierarchy of additional simplifying assumptions are also presented.

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36

Haq, Fazal, Muzher Saleem e M. Ijaz Khan. "Investigation of mixed convection magnetized Casson nanomaterial flow with activation energy and gyrotactic microorganisms". Journal of Physics Communications 5, n. 12 (1 dicembre 2021): 125001. http://dx.doi.org/10.1088/2399-6528/ac3889.

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Abstract Present article addresses mixed convection magnetohydrodynamic Casson nanomaterial flow by stretchable cylinder. The effects of thermal, solutal and motile density stratifications at the boundary of the surface are accounted. Flow governing expressions are acquired considering aspects of permeability, thermal radiation, chemical reaction, viscous dissipation and activation energy. The obtained flow model is made dimensionless through transformations and then tackled by NDsolve code in Mathematica. Physical impacts of sundry variables on nanomaterial velocity, temperature distribution, volume fraction of microorganisms and mass concentration is investigated through plots. Furthermore, quantities of engineering interest like surface drag force, heat transfer rate, density number and Sherwood number are computed and analyzed. We observed that fluid velocity diminishes for higher curvature variable, Casson fluid material variable, Hartmann number and permeability parameter. Fluid temperature has a direct relation with Eckert number, thermophoresis variable, Brownian dispersal parameter, Prandtl number and Hartmann number. Volume fraction of gyrotactic microorganisms is decreasing function of bioconvection Lewis number, stratification parameter and bioconvection Peclet number. Detailed observations are itemized at the end.

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37

Карьянский, Сергей Анатольевич, e Денис Николаевич Марьянов. "Adjustment of drilling slurry density during transportation by Platform Supply Vessels". Automation of ship technical facilities 27, n. 1 (25 novembre 2021): 52–62. http://dx.doi.org/10.31653/1819-3293-2021-1-27-52-62.

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Annotation – The issues of maintaining the drilling fluid density during its transportation from shore to the oil drilling platform by the Platform Supply Vessels were considered. The research was carried out on the vessel of 5650 deadweight tons, which made 2 ... 2.5 day voyages from port to drilling platform with possible waiting for direct approach to the platform for 1 ... 1.5 days. The drilling fluid was transported in four tanks of equal-size, arranged in pairs on each side of the vessel. It was found that during this period of time there is a latent stratification of drilling fluid along the depth of cargo tank, causing stratification of its density. The density of the drilling fluid was measured at depths corresponding to 10, 50 and 90 % of the total tank depth. The drilling fluid density stratification is defined as the relative density change in the upper (at 10 % depth) and lower (at 90 % depth) parts of the cargo tank. The hydrometer was used to measure density, allowing measurements in the range of 650 ... 1630 kg/m3 with an accuracy of 1 kg/m3 while controlling the temperature. Density measurements were taken at 6-hour intervals. It has been experimentally proved that during the 48-hour transportation of the drilling fluid with the density of 1295 kg/m3, the density value at the indicated depths is 1163 and 1524 kg/m3 respectively, while the density stratification reaches 31 %. It is offered to prevent the density stratification by creating a forced X-shaped circulation of the drilling fluid between cargo tanks which stand side by side. It is offered to regulate and maintain automatically the drilling fluid density in the range of 2 ... 7 % by using programmable controllers. When the density stratification reaches 7 %, the controller switches on the circulation pumps and circulates the drilling fluid between tanks which stand side by side. This increases the drilling fluid uniformity and helps to reduce the density stratification along the depth of the cargo tank. The process of additional circulation of the drilling fluid is rationally ensured until the density stratification reaches a value of 2 %. Fulfilment of the above-mentioned conditions will ensure that the drilling fluid maintains its operational properties and the energy consumption associated with the additional operation of the circulation pumps is minimised.

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38

Dandekar, Rajat, Vaseem A. Shaik e Arezoo M. Ardekani. "Swimming sheet in a density-stratified fluid". Journal of Fluid Mechanics 874 (4 luglio 2019): 210–34. http://dx.doi.org/10.1017/jfm.2019.445.

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In this work, we theoretically investigate the swimming velocity of a Taylor swimming sheet immersed in a linearly density-stratified fluid. We use a regular perturbation expansion approach to estimate the swimming velocity up to second order in wave amplitude. We divide our analysis into two regimes of low ($\ll O(1)$) and finite Reynolds numbers. We use our solution to understand the effect of stratification on the swimming behaviour of organisms. We find that stratification significantly influences motility characteristics of the swimmer such as the swimming speed, hydrodynamic power expenditure, swimming efficiency and the induced mixing, quantified by mixing efficiency and diapycnal eddy diffusivity. We explore this dependence in detail for both low and finite Reynolds number and elucidate the fundamental insights obtained. We expect our work to shed some light on the importance of stratification in the locomotion of organisms living in density-stratified aquatic environments.

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39

Zhu, Lei, Jiangchuan Sheng e Liwen Pang. "The Role of Tide and Wind in Modulating Density Stratification in the Pearl River Estuary during the Dry Season". Journal of Marine Science and Engineering 12, n. 8 (23 luglio 2024): 1241. http://dx.doi.org/10.3390/jmse12081241.

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Density stratification plays a crucial role in estuarine hydrodynamics and material transport. In this study, we utilized a well-calibrated numerical model to investigate the stratification processes and underlying mechanisms in the dynamically wide Pearl River Estuary (PRE). In the upper estuary, longitudinal straining governs stratification, enhancing it during ebb tide and reducing it during flood tide. The Coriolis force becomes significant in the lower estuary due to the increased basin width, causing seaward freshwater to be confined to the West Shoal, where a pronounced transverse salinity gradient forms. Interacting with lateral current shear, density stratification is most pronounced in this region. The prevailing northeasterly wind creates a mixed layer near the surface, shifting stratification to the middle layer of the water column in the upper estuary. Wind stirring reduces stratification throughout the estuary. Under the wind’s influence, the seaward outflow is confined to a narrower region and shifts westward, resulting in the most apparent stratification occurring on the West Shoal of the PRE due to lateral straining. These findings on the evolution of freshwater pathways and their role in modulating density stratification have significant implications for other wide estuaries, such as Delaware Bay and the La Plata-Parana estuary.

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40

Мар’янов, Д. М. "IMPROVEMENT OF THE STORAGE SYSTEM AND CIRCULATION OF DRILLING SUSPENSION ON TYPE VESSELS PLATFORM SUPPLY VESSEL". SHIP POWER PLANTS 43, n. 1 (7 settembre 2021): 54–68. http://dx.doi.org/10.31653/smf343.2021.54-68.

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The system of storage and circulation of drilling fluid on Platform Supply Vessel class vessels is considered. It was experimentally established that for the transport time of 6 … 36 hours the stratification of the density of the drilling fluid by the depth of the cargo tank is 3.04 … 32.04 %. As a method that ensures minimal stratification of the density of the drilling fluid during its transportation, it is proposed to use additional X-shaped circulation of the drill slurry in the volume of adjacent cargo tanks. Studies have confirmed that the density stratification for the time period of 6 … 36 hours decreases to the range of 2.30 … 9.01 %. The integrated use of additional X-shaped circulation and simultaneous air supply to the bottom of the cargo tank provides a value of density stratification of 0.73 … 2.93 %.

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41

Jung, Ju-Hun, e In-Cheol Bang. "Investigation of Stratification Instability in the Density Lock for Inherent Safety Features of Nuclear Reactors without Control Rods". KSFM Journal of Fluid Machinery 26, n. 6 (31 dicembre 2023): 50–56. http://dx.doi.org/10.5293/kfma.2023.26.6.050.

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42

Er-raiy, Aimad, Radouan Boukharfane e Matteo Parsani. "Effects of Composition Heterogeneities on Flame Kernel Propagation: A DNS Study". Fluids 5, n. 3 (4 settembre 2020): 152. http://dx.doi.org/10.3390/fluids5030152.

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In this study, a new set of direct numerical simulations is generated and used to examine the influence of mixture composition heterogeneities on the propagation of a premixed iso-octane/air spherical turbulent flame, with a representative chemical description. The dynamic effects of both turbulence and combustion heterogeneities are considered, and their competition is assessed. The results of the turbulent homogeneous case are compared with those of heterogeneous cases which are characterized by multiple stratification length scales and segregation rates in the regime of a wrinkled flame. The comparison reveals that stratification does not alter turbulent flame behaviors such as the preferential alignment of the convex flame front with the direction of the compression. However, we find that the overall flame front propagation is slower in the presence of heterogeneities because of the differential on speed propagation. Furthermore, analysis of different displacement speed components is performed by taking multi-species formalism into account. This analysis shows that the global flame propagation front slows down due to the heterogeneities caused by the reaction mechanism and the differential diffusion accompanied by flame surface density variations. Quantification of the effects of each of these mechanisms shows that their intensity increases with the increase in stratification’s length scale and segregation rate.

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43

INAGAKI, Yuki, e Oaki IIDA. "Homogenization of horizontally inhomogeneous turbulence under stable density stratification". Proceedings of Mechanical Engineering Congress, Japan 2020 (2020): S05431. http://dx.doi.org/10.1299/jsmemecj.2020.s05431.

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44

Boehrer, Bertram, Peter Herzsprung, Martin Schultze e Frank J. Millero. "Calculating density of water in geochemical lake stratification models". Limnology and Oceanography: Methods 8, n. 11 (novembre 2010): 567–74. http://dx.doi.org/10.4319/lom.2010.8.0567.

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45

KITANO, Yoshikazu, Tomohito J. YAMADA e Norihiro IZUMI. "The Development of disturbance on the atmospheric density stratification". Journal of Japan Society of Civil Engineers, Ser. G (Environmental Research) 68, n. 5 (2012): I_205—I_210. http://dx.doi.org/10.2208/jscejer.68.i_205.

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46

Oh, Chan-Sung, e Jung-Hoon Choi. "Consideration on Changes of Density Stratification in Saemangeum Reservoir". Journal of the Korean Society for Marine Environment & Energy 18, n. 2 (25 maggio 2015): 81–93. http://dx.doi.org/10.7846/jkosmee.2015.18.2.81.

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47

MICHIOKU, Kohji. "Density Stratification and Thermal Cycle in Temperature Zone Lakes". PROCEEDINGS OF HYDRAULIC ENGINEERING 37 (1993): 337–42. http://dx.doi.org/10.2208/prohe.37.337.

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48

Inagaki, Yuki, e Oaki Iida. "Homogenization of horizontally inhomogeneous turbulence under stable density stratification". Proceedings of Conference of Tokai Branch 2020.69 (2020): 511. http://dx.doi.org/10.1299/jsmetokai.2020.69.511.

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49

Verso, Lilly, Maarten van Reeuwijk e Alexander Liberzon. "Transient stratification force on particles crossing a density interface". International Journal of Multiphase Flow 121 (dicembre 2019): 103109. http://dx.doi.org/10.1016/j.ijmultiphaseflow.2019.103109.

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50

Srinivasan, J. "Convection suppression in horizontal solar collectors using density stratification". Solar Energy 48, n. 5 (1992): 287–89. http://dx.doi.org/10.1016/0038-092x(92)90056-g.

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