Transient 3D Simulation of the Turbulent Gas Solid Flow in Large Scale Risers Using a Density Based Solution Algorithm

2002 ◽  
Author(s):  
Asit K. Das ◽  
Gorik Van Engelandt ◽  
Guy B. Marin ◽  
Geraldine J. Heynderickx
Keyword(s):  
Large Scale ◽  
Cluster Formation ◽  
Large Diameter ◽  
Low Frequency ◽  
Solution Algorithm ◽  
3D Simulation ◽  
Small Scale ◽  
Two Phase ◽  
Solid Flow ◽  
Real Time Scale

Transient 3D simulation of the gas-solid flow in large diameter (> 0.3 m) risers is performed using a new density based solution algorithm. Unlike the conventional pressure based algorithm used so far for riser simulation, the density based solution method uses the pre-conditioning of time derivatives, does not have the internal pressure and velocity correction loop and hence provides a much faster convergence speed. The two phase flow is highly oscillatory with many small scale high frequency (10Hz) fluctuations and a few dominating low frequency (0.02 Hz) oscillations. The transient simulation of a case belonging to a fast fluidized regime with Geldart B particles, demonstrated the density inversion phenomena, experimentally observed before. Cluster formation is simulated on a real time scale for a dilute phase riser having solid fraction < 0.0007, although the time averaged flow fields still resemble a core-annular flow structure.

Effective rheology of a two-phase subduction shear zone: insights from numerical simple shear experiments and implications for subduction zone interfaces

2021 ◽  
Author(s):  
Paraskevi Io Ioannidi ◽  
Laetitia Le Pourhiet ◽  
Philippe Agard ◽  
Samuel Angiboust ◽  
Onno Oncken
Keyword(s):  
Simple Shear ◽  
Large Scale ◽  
Confining Pressure ◽  
Shear Zones ◽  
Dislocation Creep ◽  
Small Scale ◽  
Two Phase ◽  
Weak Phase ◽  
Pure Phases ◽  
Geodynamic Models

&lt;p&gt;Exhumed subduction shear zones often exhibit block-in-matrix structures comprising strong clasts within a weak matrix (m&amp;#233;langes). Inspired by such observations, we create synthetic models with different proportions of strong clasts and compare them to natural m&amp;#233;lange outcrops. We use 2D Finite Element visco-plastic numerical simulations in simple shear kinematic conditions and we determine the effective rheology of a m&amp;#233;lange with basaltic blocks embedded within a wet quartzitic matrix. Our models and their structures are scale-independent; this allows for upscaling published field geometries to km-scale models, compatible with large-scale far-field observations. By varying confining pressure, temperature and strain rate we evaluate effective rheological estimates for a natural subduction interface. Deformation and strain localization are affected by the block-in-matrix ratio. In models where both materials deform viscously, the effective dislocation creep parameters (A, n, and Q) vary between the values of the strong and the weak phase. Approaching the frictional-viscous transition, the m&amp;#233;lange bulk rheology is effectively viscous creep but in the small scale parts of the blocks are frictional, leading to higher stresses. This results in an effective value of the stress exponent, n, greater than that of both pure phases, as well as an effective viscosity lower than the weak phase. Our effective rheology parameters may be used in large scale geodynamic models, as a proxy for a heterogeneous subduction interface, if an appropriate evolution law for the block concentration of a m&amp;#233;lange is given.&lt;/p&gt;

scholarly journals Internal tide energy flux over a ridge measured by a co-located ocean glider and moored ADCP

2019 ◽  
Author(s):  
Rob Hall ◽  
Barbara Berx ◽  
Gillian Damerell
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Low Frequency ◽  
Internal Tide ◽  
Small Scale ◽  
Potential Density ◽  
The North ◽  
Model Study ◽  
Continental Shelves ◽  
Alternative Approach

Abstract. Internal tide energy flux is an important diagnostic for the study of energy pathways in the ocean, from large-scale input by the surface tide, to small-scale dissipation by turbulent mixing. Accurate calculation of energy flux requires repeated full-depth measurements of both potential density (ρ) and horizontal current velocity (u) over at least a tidal cycle and over several weeks to resolve the internal spring-neap cycle. Typically, these observations are made using full-depth oceanographic moorings that are vulnerable to being fished-out by commercial trawlers when deployed on continental shelves and slopes. Here we test an alternative approach to minimise these risks, with u measured by a low-frequency ADCP moored near the seabed and ρ measured by an autonomous ocean glider holding station by the ADCP. The method is used to measure the M2 internal tide radiating from the Wyville Thompson Ridge in the North Atlantic. The observed energy flux (4.2 ± 0.2 kW m−1) compares favourably with historic observations and a previous numerical model study. Error in the energy flux calculation due to imperfect co-location of the glider and ADCP is estimated by sub-sampling potential density in an idealised internal tide field along pseudorandomly distributed glider paths. The error is considered acceptable (

Wavelet Analysis on Eddy Structure in Micro Bubble Two Phase Flow Using PIV

2004 ◽  
Author(s):  
Ling Zhen ◽  
Claudia del Carmen Gutierrez-Torres
Keyword(s):  
Boundary Layer ◽  
Turbulent Flow ◽  
Drag Reduction ◽  
Large Scale ◽  
Operating Conditions ◽  
Small Scale ◽  
Turbulent Structures ◽  
Two Phase ◽  
Multi Scale ◽  
Eddy Structures

The question of “where and how the turbulent drag arises” is one of the most fundamental problems unsolved in fluid mechanics. However, the physical mechanism responsible for the friction drag reduction is still not well understood. Over decades, it is found that the turbulence production and self-containment in a boundary layer are organized phenomena and not random processes as the turbulence looks like. The further study in the boundary layer should be able to help us know more about the mechanisms of drag reduction. The wavelet-based vector multi-resolution technique was proposed and applied to the two dimensional PIV velocities for identifying the multi-scale turbulent structures. The intermediate and small scale vortices embedded within the large-scale vortices were separated and visualized. By analyzing the fluctuating velocities at different scales, coherent eddy structures were obtained and this help us obtain the important information on the multi-scale flow structures in the turbulent flow. By comparing the eddy structures in different operating conditions, the mechanism to explain the drag reduction caused by micro bubbles in turbulent flow was proposed.

Unsteady Structure Measurement of Cloud Cavitation on a Foil Section Using Conditional Sampling Technique

1989 ◽  
Vol 111 (2) ◽  
pp. 204-210 ◽  
Author(s):  
A. Kubota ◽  
H. Kato ◽  
H. Yamaguchi ◽  
M. Maeda
Keyword(s):  
High Speed ◽  
Large Scale ◽  
Laser Doppler Anemometry ◽  
Low Frequency ◽  
Sampling Technique ◽  
Experimental Result ◽  
Small Scale ◽  
Conditional Sampling ◽  
Cloud Cavitation ◽  
Structure Of Flow

The structure of flow around unsteady cloud cavitation on a stationary two-dimensional hydrofoil was investigated experimentally using a conditional sampling technique. The unsteady flow velocity around the cloud cavitation was measured by a Laser Doppler Anemometry (LDA) and matched with the unsteady cavitation appearance photographed by a high-speed camera. This matching procedure was performed using data from pressure fluctuation measurements on the foil surface. The velocities were divided into two components using a digital filter, i.e., large-scale (low-frequency) and small-scale (high frequency) ones. The large-scale component corresponds with the large-scale unsteady cloud cavitation motion. In this manner, the unsteady structure of the cloud cavitation was successfully measured. The experimental result showed that the cloud cavitation observed at the present experiment had a vorticity extremum at its center and a cluster containing many small cavitation bubbles. The convection velocity of the cavitation cloud was much lower than the uniform velocity. The small-scale velocity fluctuation was not distributed uniformly in the cavitation cloud, but was concentrated near its boundary.

scholarly journals Cluster Assembly in Hierarchically Collapsing Clouds

2015 ◽  
Vol 12 (S316) ◽  
pp. 196-201
Author(s):  
Enrique Vázquez-Semadeni ◽  
Alejandro González-Samaniego ◽  
Manuel Zamora-Avilés ◽  
Pedro Colín
Keyword(s):  
Molecular Clouds ◽  
Large Scale ◽  
Fractal Structure ◽  
Cluster Formation ◽  
Formation Rate ◽  
Structural Features ◽  
Open Clusters ◽  
Small Scale ◽  
Cluster Assembly ◽  
Scale Free

AbstractWe discuss the mechanism of cluster formation in hierarchically collapsing molecular clouds. Recent evidence, both observational and numerical, suggests that molecular clouds (MCs) may be undergoing global, hierarchical gravitational collapse. The “hierarchical” regime consists of small-scale collapses within larger-scale ones. The latter implies that the star formation rate increases systematically during the early stages of evolution, and occurs via filamentary flows onto “hubs” of higher density, mass, and velocity dispersion, and culminates a few Myr after than the small-scale collapses have started to form stars. In turn, the small-scale collapses occur in clumps embedded in the filaments, and are themselves falling into the larger potential well of the still-ongoing large-scale collapse. The stars formed in the early, small-scale collapses share the infall motion of their parent clumps towards the larger potential trough, so that the filaments feed both gaseous and stellar material to the hubs. This leads to the presence of older stars in a region where new protostars are still forming, to a scale-free or fractal structure of the clusters, in which each unit is composed of smaller-scale ones, and to the eventual merging of the subunits, explaining the observed structural features of open clusters.

A model for the spreading and compaction of two-phase viscous gravity currents

2009 ◽  
Vol 630 ◽  
pp. 299-329 ◽  
Author(s):  
CHLOÉ MICHAUT ◽  
DAVID BERCOVICI
Keyword(s):  
Large Scale ◽  
Gravity Current ◽  
Fluid Phase ◽  
Gravity Currents ◽  
Small Scale ◽  
Fluid Loss ◽  
Large Area ◽  
Finite Radius ◽  
Two Phase ◽  
Mixture Density

Two-phase viscous gravity current theory has numerous applications in the natural sciences, from small-scale lava, sedimentary and glacial flows, to large-scale flows of partially molten mantle. We develop the general equations for two-phase viscous gravity currents composed of a high viscosity matrix and low viscosity fluid for both constant volume and constant flux conditions. A loss of fluid phase is taken into account at the current's upper boundary and corresponds to the degassing of a lava flow or loss of water in sedimentary flows. As the current spreads, its surface increases and fluid loss is facilitated, which modifies the mixture density and viscosity and thus the current's shape; hence spreading of the flow affects fluid loss and vice-versa. Our results show that two-phase gravity currents retain and transport the fluid out to large distances, but the fluid is almost entirely lost within a region of finite radius. This ‘loss radius’ depends on the flow's volume or flux, fluid and matrix properties as well as on the size of fluid parcels or matrix permeability. Application to lava flows shows that degassing occurs over a large area, which affects gas release and transport in the atmosphere.

Asian Summer Precipitation over the Past 544 Years Reconstructed by Merging Tree Rings and Historical Documentary Records

2018 ◽  
Vol 31 (19) ◽  
pp. 7845-7861 ◽  
Author(s):  
Hui Shi ◽  
Bin Wang ◽  
Edward R. Cook ◽  
Jian Liu ◽  
Fei Liu
Keyword(s):  
El Niño ◽  
Large Scale ◽  
El Nino ◽  
Rainfall Variability ◽  
Low Frequency ◽  
Summer Precipitation ◽  
Small Scale ◽  
Central Pacific El Niño ◽  
Asian Summer ◽  
Mode A

Sparse long-term Asian monsoon (AM) records have limited our ability to understand and accurately model low-frequency AM variability. Here we present a gridded 544-yr (from 1470 to 2013) reconstructed Asian summer precipitation (RAP) dataset by weighted merging of two complementary proxies including 453 tree-ring-width chronologies and 71 historical documentary records. The RAP dataset provides substantially improved data quality when compared with single-proxy-type reconstructions. Skillful reconstructions are obtained in East and North China, northern India and Pakistan, the Indochina Peninsula, midlatitude Asia, the Maritime Continent, and southern Japan. The RAP faithfully illustrates large-scale regional rainfall variability but has more uncertainties in representing small-scale local rainfall anomalies. The RAP reproduces a realistic climatology and captures well the year-to-year rainfall variability averaged over monsoon Asia, arid central Asia, and all of Asia during the twentieth century. It also shows a general agreement with other proxies (speleothems and ice cores) during the period of 1470–1920. The RAP captures the remarkably abrupt change during the 1600s recorded in the upwelling proxy over the Arabian Sea. Four major modes of variability of the Asian summer precipitation are identified with the long record of the RAP, including a biennial El Niño–Southern Oscillation (ENSO) mode, a low-frequency ENSO mode, a central Pacific El Niño–like decadal mode, and an interdecadal mode. In sum, the RAP provides a valuable dataset for study of the large-scale Asian summer precipitation variability, especially the decadal–centennial variability that is caused by external forcing and internal feedback processes within the Earth climate system.

scholarly journals Stochastic modeling of the oceanic mesoscale eddies

2021 ◽  
Author(s):  
Long Li ◽  
Bruno Deremble ◽  
Noé Lahaye ◽  
Etienne Mémin
Keyword(s):  
Large Scale ◽  
Mesoscale Eddy ◽  
Low Frequency ◽  
Stochastic Approach ◽  
Coarse Grained ◽  
Small Scale ◽  
Oceanic Circulation ◽  
Stochastic Representation ◽  
Stochastic Framework ◽  
Gyre Circulation

&lt;p&gt;In this work, a stochastic representation [Bauer2020a, Bauer2020b] based on a physical transport principle is proposed to account for mesoscale eddy effects on the the large-scale oceanic circulation. This stochastic framework [M&amp;#233;min2014] arises from a decomposition of the Lagrangian velocity into a time-smooth component and a highly oscillating noise term. One important characteristic of this random model is that it conserves the energy of any transported tracer. Such an energy-preserving representation has been successfully implemented in a well established multi-layered quasi-geostrophic dynamical core (http://www.q-gcm.org). The empirical spatial correlation of the small-scale noise is estimated from the eddy-resolving simulation data. In particular, a sub-grid correction drift has been introduced in the noise due to the bias ensuing from the coarse-grained procedure. This non intuitive term seems quite important in reproducing on a coarse mesh the meandering jet of the wind-driven double-gyre circulation. In addition, a new projection method has been proposed to constrain the noise living along the iso-surfaces of the vertical stratification. The resulting noise enables us to improve the intrinsic low-frequency variability of the large-scale current. From some statistical studies and energy transfers analysis, this improvement is well demonstrated.&lt;/p&gt;&lt;ul&gt;&lt;li&gt;&lt;span&gt;[&lt;/span&gt;Bauer2020a] W. Bauer, P. Chandramouli, B. Chapron, L. Li, and E. M&amp;#233;min. Deciphering the role&amp;#160;of small-scale inhomogeneity on geophysical flow structuration: a stochastic approach. Journal of Physical Oceanography, 50(4):983-1003, 2020a.&lt;span&gt;&amp;#160; &amp;#160; &amp;#160; &amp;#160;&lt;/span&gt;&lt;/li&gt; &lt;li&gt;&lt;span&gt;[&lt;/span&gt;Bauer2020b] W. Bauer, P. Chandramouli, L. Li, and E. M&amp;#233;min. Stochastic representation of mesoscale&amp;#160;eddy effects in coarse-resolution barotropic models. Ocean Modelling, 151:101646 (2020b). &lt;span&gt;&amp;#160; &amp;#160;&lt;/span&gt;&lt;/li&gt; &lt;li&gt;[M&amp;#233;min2014] E. M&amp;#233;min. Fluid flow dynamics under location uncertainty. Geophysical &amp; Astrophysical Fluid Dynamics, 108(2):119-146, 2014.&lt;span&gt;&amp;#160; &amp;#160; &amp;#160;&lt;/span&gt;&lt;/li&gt; &lt;/ul&gt;

Influence of non-monochromaticity on zonal-flow generation by magnetized Rossby waves in the ionospheric E-layer

2009 ◽  
Vol 75 (3) ◽  
pp. 345-357 ◽  
Author(s):  
T. D. KALADZE ◽  
H. A. SHAH ◽  
G. MURTAZA ◽  
L. V. TSAMALASHVILI ◽  
M. SHAD ◽  
...  
Keyword(s):  
Large Scale ◽  
Laboratory Experiments ◽  
Low Frequency ◽  
Zonal Flow ◽  
Present Theory ◽  
Resonant Interaction ◽  
Finite Amplitude ◽  
Small Scale ◽  
Zonal Flows ◽  
Flow Generation

AbstractThe influence of non-monochromaticity on low-frequency, large-scale zonal-flow nonlinear generation by small-scale magnetized Rossby (MR) waves in the Earth's ionospheric E-layer is considered. The modified parametric approach is used with an arbitrary spectrum of primary modes. It is shown that the broadening of the wave packet spectrum of pump MR waves leads to a resonant interaction with a growth rate of the order of the monochromatic case. In the case when zonal-flow generation by MR modes is prohibited by the Lighthill stability criterion, the so-called two-stream-like mechanism for the generation of sheared zonal flows by finite-amplitude MR waves in the ionospheric E-layer is possible. The growth rates of zonal-flow instabilities and the conditions for driving them are determined. The present theory can be used for the interpretation of the observations of Rossby-type waves in the Earth's ionosphere and in laboratory experiments.

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