scholarly journals Influence of pycnocline on settling behaviour of non-spherical particle and wake evolution

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Magdalena M. Mrokowska
Keyword(s):  
Complex Dynamics ◽  
Stratified Fluid ◽  
Particle Orientation ◽  
Spherical Particles ◽  
Estimation Methods ◽  
Structure Evolution ◽  
Particle Settling ◽  
Faecal Pellets ◽  
Fluid Systems ◽  
Tightly Coupled

AbstractSettling of non-spherical particles in a stratified fluid exhibits complex dynamics in a low-to-moderate inertia regime. Although this process is involved in a wide variety of phenomena in natural fluid systems, its fundamental mechanisms are still unexplored. Understanding of particle settling in microscale is particularly important to explain challenging problems associated with ecological and biogeochemical processes in the ocean due to the delayed settling of particulate matter at pycnoclines. Here, I explore interactions between disk-shaped particles and a stratified fluid with a density transition. By laboratory experiments, I demonstrate that the settling dynamics of the disk crossing a density transition are tightly coupled with the wake structure evolution, and I observe for the first time in a two-layer ambient configuration a bell-shaped structure that forms on a jet after the wake has detached from the particle. Furthermore, I identify hydrodynamic conditions for the variations of settling velocity and particle orientation instabilities. These findings shed light on particle settling mechanisms necessary to explain dynamics of marine particles such as plankton, faecal pellets, and microplastics and may improve the estimation methods of sedimentation processes in various areas of earth sciences and engineering.

scholarly journals MOPSMAP v0.9: A versatile tool for modeling of aerosol optical properties

2018 ◽  
Author(s):  
Josef Gasteiger ◽  
Matthias Wiegner
Keyword(s):  
Remote Sensing ◽  
Optical Properties ◽  
Aerosol Particles ◽  
Particle Orientation ◽  
Spherical Particles ◽  
Refractive Indices ◽  
Hygroscopic Growth ◽  
Web Interface ◽  
Optical Modeling ◽  
Wide Range

Abstract. The spatiotemporal distribution and characterization of aerosol particles are usually determined by remote sensing and optical in-situ measurements. These measurements are indirect with respect to microphysical properties and thus inversion techniques are required to determine the aerosol microphysics. Scattering theory provides the link between microphysical and optical properties; it is not only needed for such inversions but also for radiative budget calculations and climate modeling. However, optical modeling can be very time consuming, in particular if non-spherical particles or complex ensembles are involved. In this paper we present the MOPSMAP package (modeled optical properties of ensembles of aerosol particles) which is computationally fast for optical modeling even in case of complex aerosols. The package consists of a data set of pre-calculated optical properties of single aerosol particles, a Fortran program to calculate the properties of user-defined aerosol ensembles, and a user-friendly web interface for online calculations. Spheres, spheroids, and a small set of irregular particle shapes are considered over a wide range of sizes and refractive indices. MOPSMAP provides the fundamental optical properties assuming random particle orientation, including the scattering matrix for the selected wavelengths. Moreover, the output includes tables of frequently used properties such as the single scattering albedo, the asymmetry parameter or the lidar ratio. To demonstrate the wide range of possible MOPSMAP applications a selection of examples is presented, e.g., dealing with hygroscopic growth, mixtures of absorbing and non-absorbing particles, the relevance of the size equivalence in case of non-spherical particles, and the variability of volcanic ash microphysics. The web interface is designed to be intuitive for expert and non-expert users. To support users a large set of default settings is available, e.g., several wavelength-dependent refractive indices, climatologically representative size distributions, and a parameterization of hygroscopic growth. Calculations are possible for single wavelengths or user-defined sets (e.g., of specific remote sensing application). For expert users more options for the microphysics are available. Plots for immediate visualization of the results are shown. The complete output can be downloaded for further applications. All input parameters and results are stored in the user’s personal folder so that calculations can easily be reproduced. The MOPSMAP package is available on request for offline calculations, e.g., when large numbers of different runs for sensitivity studies shall be made.

Internal kinematics in a planar granular column collapse

2020 ◽  
Author(s):  
Miguel Angel Cabrera ◽  
Gustavo Pinzón
Keyword(s):  
Complex Dynamics ◽  
Industrial Applications ◽  
Mass Movements ◽  
System A ◽  
Column Collapse ◽  
Fluid Systems ◽  
Gravity Driven ◽  
Deformation Patterns ◽  
Granular Column ◽  
Fluid Interactions

<p>The granular column collapse is a simplified system of the complex dynamics observed in gravity-driven natural mass-movements (i.e., landslides, debris flows, rock avalanches) and industrial applications (i.e., pharmaceutics, concrete, and food industry). In this system, a granular column is built with an initial height and initial width and then is allowed to collapse by self-weight onto a horizontal plane, while observing the variation in runout as a function of its initial geometry. Despite its wide use in the study of mass-movements mobility, either dry or with a liquid, little is known on the internal physics during collapse and its variation when immersed in an ambient fluid. This work presents a planar setup that allows the study of fully and partially immersed granular columns, with little disturbance at release [1]. The use of a planar configuration allows the monitoring of the moving mass and its deformation patterns, providing a unique insight into the particle-fluid interactions at release and during collapse that were not possible before. These observations are of great importance for the understanding of particle-fluid interactions at a mesoscale and can shed light into larger processes like a submarine and subaerial landslides. This work addresses these interactions by varying the geometry and measuring the mobility in dry and immersed conditions. The associated deformation patterns are observed both at the column-scale and at the particle-scale, reflecting in the velocity scaling of a deformable and moving granular mass and the occasional ejection of particles at its surface. We observed that the area of the released portion decreases during collapse and converges toward an equivalent portion of surface particles with little influence by the initial column geometry. These observations validate the planar setup for the study of granular columns, provides a novel interpretation in the momentum transfer in particle-fluid systems, and sets a validation case for future numerical simulations.</p><p>[1] Pinzon & Cabrera, Planar collapse of a submerged granular column. Physics of fluids, v31, 2019.</p>

Dynamics and structure of an apolar active suspension in an annulus

2017 ◽  
Vol 835 ◽  
pp. 393-405 ◽  
Author(s):  
Sheng Chen ◽  
Peng Gao ◽  
Tong Gao
Keyword(s):  
Complex Dynamics ◽  
Travelling Waves ◽  
Travelling Wave ◽  
Coarse Grained ◽  
Structure Evolution ◽  
Concentrated Suspensions ◽  
Chaotic Flows ◽  
Active Particles ◽  
Crystal Model ◽  
Dilute Suspensions

We study the complex dynamics of a two-dimensional suspension comprising non-motile active particles confined in an annulus. A coarse-grained liquid crystal model is employed to describe the nematic structure evolution, and is hydrodynamically coupled with the Stokes equation to solve for the induced active flows in the annulus. For dilute suspensions, coherent structures are captured by varying the particle activity and gap width, including unidirectional circulations, travelling waves and chaotic flows. For concentrated suspensions, the internal collective dynamics features motile disclination defects and flows at finite gap widths. In particular, we observe an intriguing quasi-steady-state at certain gap widths during which $+1/2$-order defects oscillate around equilibrium positions accompanying travelling-wave flows that switch circulating directions periodically. We perform linear stability analyses to reveal the underlying physical mechanisms of pattern formation during a concatenation of instabilities.

Dynamic simulations of the inhomogeneous sedimentation of rigid fibres

2002 ◽  
Vol 468 ◽  
pp. 205-237 ◽  
Author(s):  
JASON E. BUTLER ◽  
ERIC S. G. SHAQFEH
Keyword(s):  
Sedimentation Rate ◽  
Particle Orientation ◽  
Hydrodynamic Interactions ◽  
Spherical Particles ◽  
Heterogeneous Structure ◽  
Mass Force ◽  
Dynamic Simulations ◽  
Slender Body Theory ◽  
A Value ◽  
Particle Force

We have simulated the dynamics of suspensions of fibres sedimenting in the limit of zero Reynolds number. In these simulations, the dominant inter-particle force arises from hydrodynamic interactions between the rigid, non-Brownian fibres. The simulation algorithm uses slender-body theory to model the linear and rotational velocities of each fibre. To include far-field interactions between the fibres, the line distribution of force on each fibre is approximated by making a Legendre polynomial expansion of the disturbance velocity on the fibre, where only the first two terms of the expansion are retained in the calculation. Thus, the resulting linear force distribution can be specified completely by a centre-of-mass force, a couple, and a stresslet. Short-range interactions between particles are included using a lubrication approximation, and an infinite suspension is simulated by using periodic boundary conditions. Our numerical results confirm that the sedimentation of these non-spherical, orientable particles differs qualitatively from the sedimentation of spherical particles. The simulations demonstrate that an initially homogeneous, settling suspension develops clusters, or streamers, which are particle rich surrounded by clarified fluid. The instability which causes the heterogeneous structure arises solely from hydrodynamic interactions which couple the particle orientation and the sedimentation rate in particle clusters. Depending upon the concentration and aspect ratio, the formation of clusters of particles can enhance the sedimentation rate of the suspension to a value in excess of the maximum settling speed of an isolated particle. The suspension of fibres tends to orient with gravity during the sedimentation process. The average velocities and orientations, as well as their distributions, compare favourably with previous experimental measurements.

scholarly journals The ASKOS experiment for the validation of Aeolus L2A aerosol product 

2021 ◽  
Author(s):  
Eleni Marinou ◽  
Vasslis Amiridis ◽  
Ioanna Mavropoulou ◽  
Holger Baars ◽  
Stelios Kazadzis ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Microwave Radiometer ◽  
Dust Cloud ◽  
Cape Verde ◽  
Particle Orientation ◽  
Atmospheric Composition ◽  
Spherical Particles ◽  
Cloud Formation ◽  
In Situ Sensors

<p>For the in-orbit calibration and validation of the Aeolus products, ESA organized the Aeolus Tropical campaign, which will take place on June-July 2021 at Cape Verde region. During the campaign, Aeolus underfights will be performed with several aircrafts (by DLR, NASA, LATMOS, and the University of Nova Gorica (UNG)) and advanced ground-based instrumentation will be deployed in Mindelo island within ASKOS (https://askos.space.noa.gr/) experiment. ASKOS observations will provide an unprecedented dataset for the aerosol and wind conditions in the region, in order to provide reference values for the Cal/Val of the mission. Apart from the main aerosol Cal/Val objective of ASKOS, the foreseen synergistic activities will provide a wealth of information to address scientific questions posed by the participating groups on dust characterization, transportation and it’s impact of radiation and cloud formation.</p><p>Here, we report on the status of the ASKOS preparations for the evaluation of the aerosol and cloud product, focusing on the instrumentation requirements and availability, as well as the engagement of the scientific community so far. ASKOS will deploy advanced ground-based and airborne remote sensing and in-situ instrumentation, including the full ACTRIS aerosol and cloud remote sensing/in-situ facilities and airborne in-situ sensors to be operated on drones and/or aircrafts. The main ground-based remote sensing instrumentation in Cape Verde will consist of sophisticated lidar systems, including the EVE lidar, a circular polarization system that is tailored to mimic the Aeolus measurement from ground, the multi-wavelength Polly-XT and the WALL-E prototype for detecting particle orientation. The instrumentation will also include sun-photometers such as AERONET-CIMEL, but also polarimeters to advance microphysical retrievals for non-spherical particles such as dust. Cloud remote sensors including a cloud radar and a microwave radiometer will operate in parallel along with meteorological radiosondes. In-situ sensors at surface and onboard UAVs and light aircrafts will be available. ASKOS will be fully supported by several operational modeling simulations for meteorological and atmospheric composition forecasting. ASKOS will remain open to contributions from other communities and research groups and more synergies will be pursued in the future.</p><p> </p>

scholarly journals Taking the Complex Dynamics of Human–Environment–Technology Systems Seriously: A Case Study in Doctoral Education at the University of Luxembourg

2021 ◽  
Vol 2 ◽  
Author(s):  
Ariane König ◽  
Jerome Ravetz ◽  
Bo Raber ◽  
Jacek Stankiewicz ◽  
Ricardo Rojas-Aedo ◽  
...  
Keyword(s):  
Complex Dynamics ◽  
Knowledge Society ◽  
Change Agents ◽  
Human Environment ◽  
Transferable Skills ◽  
Tightly Coupled ◽  
Sustainability Challenges ◽  
The University ◽  
Technology Systems

Our existential sustainability challenges involve human–environment–technology systems that are complex, dynamic and tightly coupled. But at Universities, knowledge, in teaching and research, is mostly organized into discrete parcels, the disciplines. These are further divided into the categories of natural sciences, social science and the humanities. This paper addresses the question of how in their training of researchers, universities can equip them to better understand their roles and also to act as change agents. It describes a doctoral school course in transferable skills that is offered across faculties. The unique aim of the course is to provide a space for reflection on different research paradigms and the way they differ in their framing the role of a scientific researcher in pluralist societies that face existential challenges. The pedagogical framework and approach of the course encourages questioning one's own ontological and epistemological assumptions about the constitution of our world and how we might better understand it in dialogues with participants who come from diverse disciplinary backgrounds. The course includes discussions of: what is a discipline, and how disciplines differ in their understandings of the world and of the role of science within it; how tools and representations can shape or breach disciplinary paradigms; how instrumental science and interdisciplinarity can raise the dilemma of rigor or relevance; how complexity, contradictions and values are embraced in responsible research design, and last but not least we discuss the relation of science, progress and open futures. The course introduces diverse more recent approaches to scientific inquiry that harness the potential of democratizing science in our networked knowledge society, including critical interdisciplinarity, post-normal science, citizen science and transformative sustainability science, that complement normal disciplinary research practices.

Numerical Simulation and Modelling of the Forces Acting on Single and Multiple Non-Spherical Particles

2014 ◽  
Author(s):  
Rafik Ouchene ◽  
Amine Chadil ◽  
Pascal Fede ◽  
Mohammed Khalij ◽  
Anne Tanière ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Drag Coefficient ◽  
Turbulent Flows ◽  
Large Range ◽  
Direct Numerical Simulations ◽  
Particle Orientation ◽  
Spherical Particles ◽  
Ellipsoidal Particle ◽  
Particle Shapes

The paper deals with gas-solid turbulent flows carrying non-spherical particles. The main objective of the present paper is to compute the hydrodynamics forces on non-spherical particles as a function of the particle orientation, for different particle shapes and a large range of particle Reynolds number. Two Direct Numerical Simulations at the scale of the particle are used, i.e. a body-fitted approach and a viscous penalty approach, in the case of a uniform flow with a single ellipsoidal particle. Results are compared with several correlations from the literature and a new proposal for the drag coefficient is given. The study is then extended to the case of a lattice of non-spherical particles to measure the pressure drop and to connect it with the drag coefficient.

scholarly journals Population Studies of Deer (Odocoileus virginianus, Mazama americana) in Southern Yucatán, Mexico

2021 ◽  
pp. 38-51
Author(s):  
Montes-Perez Ruben ◽  
Lopez-Coba Ermilo ◽  
Pacheco-Sierra Gualberto ◽  
May-Cruz Christian ◽  
Sierra-Gomez Andrés III
Keyword(s):  
Habitat Use ◽  
Tropical Forest ◽  
Estimation Methods ◽  
Sustainable Harvest ◽  
Population Densities ◽  
Faecal Pellets ◽  
A Value ◽  
Statistical Precision ◽  
Deer Harvest ◽  
Harvest Model

Aims: Estimate the population density of deer in the municipality of Tzucacab, Yucatán in the periods of 2003-2004, 2007-2008 and 2008-2009, determine the use of the habitat by these populations and the sustainability of the deer harvest from the estimated population densities. Study Design: A descriptive and vertical free-living deer population study was carried out in southern Yucatan, Mexico over a three-year period. Methodology: The map of the municipality of Tuzcacab was zoned in quadrants of 36 km2, completing a total of 36 quadrants; Unrestricted random sampling was applied to select seven quadrants in the period from 2003 to 2004 and 18 in each annual period between 2007 and 2009. Population samplings were carried out by applying three population estimation methods: direct sighting in a linear transect of 5 km in length, count of tracks in transect except period 2003-2004 and faecal pellets group count in plots. The evaluation of the use of habitat was carried out using the Bonferroni intervals, from the data of faecal pellets count. The evaluation of the deer harvest was carried out using the sustainable harvest model. Results: The population densities were different in each method, the density by the excreta count was 4.63 ± 2.49 deer / km2 in 2003-2004, 0.294 ± 0.198 deer / km2 in 2007-2008, and in the year 2008-2009 was 0.419 ± 0.0000085 deer / km2. Habitat use in 2007-08 and 2008-2009 was higher in the tropical forest, lower in agriculture and similar to that expected in secondary succession forest (acahual). The values of sustainable harvest, taking as a value the density per count of excreta in the plot because it showed the highest statistical precision, in the period 2003-04 it is sustainable, but in the period from 2007 to 2009 it is not sustainable. Conclusion: The population densities of deer (O. virginianus and M. americana) in Tuzcacab by means of the excreta count method, have decreased significantly. The habitat use preference is the tropical forest. The deer harvest in the period from 2007 to 2009 is not sustainable.

Settling Velocity of Particles in Viscoelastic Fluids: A Comparison of the Shear-Viscosity and Elasticity Effects

SPE Journal ◽  
2018 ◽  
Vol 23 (05) ◽  
pp. 1689-1705 ◽  
Author(s):  
Sumanth Kumar Arnipally ◽  
Ergun Kuru
Keyword(s):  
Elastic Properties ◽  
Shear Viscosity ◽  
Settling Velocity ◽  
Particle Diameter ◽  
Viscoelastic Fluids ◽  
Spherical Particles ◽  
High Shear ◽  
Fluid Shear ◽  
Particle Settling ◽  
Fluid Elasticity

Summary The objective of this paper is to determine how fluid shear viscosity and elasticity might influence the particle-settling velocity, and even more so to answer the question of which one of these two rheological properties is more dominant in controlling the particle-settling velocity when viscoelastic drilling fluids are used. The settling velocities of spherical particles (diameters: 1.18, 1.5, 2, and 3 mm) in partially hydrolyzed polyacrylamide (HPAM) polymer fluids were measured using the particle-image-shadow graph (PIS) technique. Two sets of test fluids were formulated by mixing three different grades of HPAM (molecular weights of 500,000, 8 million, and 20 million g/g mol) at polymer concentrations of 0.09, 0.05, and 0.03 wt%. The shear-viscosity and elasticity characteristics of test fluids were determined by performing shear-viscosity and frequency-sweep oscillatory measurements, respectively. The first set of fluids had almost identical shear-viscosity characteristics while showing significantly different elastic properties (quantified in terms of relaxation time). The second set of fluids had similar elastic properties but different shear-viscosity characteristics. In addition, the effect of the particle size on the settling velocities in these test fluids was also investigated. The experimentally measured settling velocities were compared with the values calculated from the Shah et al. (2007) model developed for predicting the settling velocity of spherical particles in power-law (viscoinelastic) fluids as well as the values calculated from the Malhotra and Sharma (2012) correlation developed for settling velocity in shear-thinning viscoelastic fluids in unconfined media. Experimental results showed the following: When the fluids with similar shear-viscosity profiles were used, the settling velocity of spherical particles decreased significantly with the increasing fluid elasticity. The settling-velocity values can be 14 to 50 times overestimated if the effect of the elasticity is not considered. At constant elasticity, the settling velocity of spherical particles also decreased significantly when the fluid shear viscosity was increased. The spherical particle-settling velocity increased pronouncedly as particle diameter increased from 1.18 to 3 mm. However, the magnitude of the increase in settling velocity with the increasing particle diameter is less for the samples with higher elasticity and similar shear-viscosity characteristics. The fluid shear viscosity and the elasticity both seem to have significant effect on the particle-settling velocity. However, from the field operational point of view, fluids with high shear-viscosity values are not always practical to use because the high shear viscosity increases parasitic pressure losses and potentially has a negative effect on the drilling rate. Hence, in such cases increasing the fluid elasticity can help to reduce the particle-settling velocity even at lower shear-viscosity values. By conducting experiments under controlled conditions, we were able to quantify the individual effects of fluid shear viscosity and elasticity on the particle-settling velocity for the first time in drilling literature.

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