Local Flows Research Articles

Effect of turning curvature on the single-file dynamics of pedestrian flow: An experimental study

Previous studies have shown considerable discrepancies in the characteristics of pedestrian flow obtained in different experiments. So far, the origin of these discrepancies is not well understood. Here we test a possible mechanism by studying the possible influence of geometry on pedestrian traffic by controlled experiments in different set-ups. By combining instantaneous and improved local measurements we find strong indications for an influence of curvature on the flow properties comparing local flows and densities for an oval set-up, which includes a straight part, and a circular set-up. In the jamming phase, the most efficient flow appears in the straight passage (curvature K=0) where the flow is about 20% higher than in the curved parts. We relate this reduction of flow in the curved part to the spatial distribution of pedestrians. Results for the headway distribution indicate that the curvature induces a more homogeneous distribution of pedestrians than the one observed for the straight part. The distribution on the straight part is more heterogeneous which seems to allow a more efficient use of the available space leading to larger flows.

Observation on sloshing flow and hydrodynamic pressures on cylindrical liquefied natural gas tank with swash bulkhead

In this study, a series of sloshing model tests were conducted for type-C tanks, particularly to observe the effects of the inner bulkhead and rings. In regular pitch motion, the internal flow by swash bulkhead and rings located inside the tank was observed. The frequency range near the resonance frequency was checked at filling heights of 70%, and sloshing-induced impact pressures were investigated. Through this study, the global flows inside the tank and local flows during impact occurrence at the hemispherical end of the tank were systematically observed, and the impact pressure pattern for each frequency ratio was compared. Due to the swash bulkhead located in the center of the tank, the flow does not move at once and the velocity of the flow is reduced by the inner rings. The flows passing through the swash bulkhead proceed with a time difference, overlapping with the first wave, generating various types of sloshing impact. The results of computational fluid dynamics calculation and the experiment were also compared for limited conditions.

The importance of local winds for the aerationof urban areas having hot and windless climatic conditions

Introduction. A city with its high-rise buildings, greenery and landscaping that prevent air motion aggravate windless conditions typical for climates in the cities located in the southern latitudes characterized by heat and lack of wind. Urban built-up areas have stagnant and overheated air that causes sultriness and significant air pollutions caused by anthropogenic sources. These factors require systematization of the local aerodynamics by means of local wind generation using solar energy.
 Materials and methods. Methods of theoretical research, large-scale field measurements involving the use of instruments, visual observations by means of smoke screening of the urban area’s structure were applied and laboratory research into thermal and wind processes using physical models of cities were applied to identify the role of insolation in the generation of local thermal winds that improve the local environment on the micro- and macroscale.
 Results. The author has found that if built-up urban areas have no general circulation wind fields, urban aeration systems develop local independent air flows due to the temperature difference between heat and cool islands. The temperature difference was applied as the source material for an urban wind model and it also helped to identify the dependence of the local wind velocity on the thermal contrast of urban islands. A classification of aeration models is developed at macro; meso-; micro- and nanoscales.
 Conclusions. The practical area of application of the theory of hot and windless processes was identified in respect of urban area planning. The aerodynamics of an urban environment was systematized due to the generation of local thermal winds. The process of local thermal wind generation was studied; the classification of natural aeration models was made for urban areas. Methods of using solar energy were applied to generate local winds, to develop the microclimate and to enhance the environment of urban areas and structures as a prerequisite for targeted urban planning actions, three-dimensional space-planning solutions that apply to urban structures, landscaping, architectural and structural concepts of buildings.
 Acknowledgments. The work was performed in accordance with the research schedule of Department of Design of Buildings and Structures, NRU MGSU, focused on “Function, Structure, Environment in the Architecture of Buildings and Towns”.

The politics of fiscal federalism: Building a stronger decentralization theorem

We explore how party structures can condition the benefits of decentralization in modern democracies. In particular, we study the interaction of two political institutions: democratic (de)centralization (whether a country has fiscally autonomous and elected local governments) and party (non)integration (whether power over local party leaders flows upwards through party institutions, which we model using control over candidate selection). We incorporate these institutions into our strong decentralization theorem, which expands on Oates (1972) to examine when the decentralized provision of public services will dominate centralized provision even in the presence of inter-jurisdictional spillovers. Our findings suggest that, when externalities are present, democratic decentralization will be beneficial only when parties are integrated. In countries with non-integrated parties, we find that the participation rules of primaries have implications for the expected gains from democratic decentralization. Under blanket primaries, Oates’ conventional decentralization theorem holds but our strong decentralization theorem does not. By contrast, when primaries are closed, not even Oates’ conventional decentralization theorem holds.

Soft sediment deformation in dry pyroclastic deposits at Ubehebe Crater, Death Valley, California

Abstract Soft sediment deformation structures are common in fine-grained pyroclastic deposits and are often taken, along with other characteristics, to indicate that deposits were emplaced in a wet and cohesive state. At Ubehebe Crater (Death Valley, California, USA), deposits were emplaced by multiple explosions, both directly from pyroclastic surges and by rapid remobilization of fresh, fine-ash-rich deposits off steep slopes as local granular flows. With the exception of the soft sediment deformation structures themselves, there is no evidence of wet deposition. We conclude that deformation was a result of destabilization of fresh, fine-grained deposits with elevated pore-gas pressure and dry cohesive forces. Soft sediment deformation alone is not sufficient to determine whether parent pyroclastic surges contained liquid water and caused wet deposition of strata.

A Comparison Between the Nonlocal and the Classical Worlds: Minimal Surfaces, Phase Transitions, and Geometric Flows

The nonlocal world presents an abundance of surprises and wonders to discover. These special properties of the nonlocal world are usually the consequence of long-range interactions, which, especially in presence of geometric structures and nonlinear phenomena, end up producing a variety of novel patterns. We will briefly discuss some of these features, focusing on the case of (non)local minimal surfaces, (non)local phase coexistence models, and (non)local geometric flows.

A computational model applied to myocardial perfusion in the human heart: From large coronaries to microvasculature

In this paper we present a mathematical and numerical model for human cardiac perfusion which accounts for the different length scales of the vessels in the coronary tree. Epicardial vessels are represented with fully three-dimensional (3D) fluid-dynamics, whereas intramural vessels are modeled as a multi-compartment porous medium. The coupling of these models takes place through interface conditions based on the continuity of mass and momentum. Instead, is neglected in this first preliminary model the myocardium deformation. To estimate the physical parameters of the multi-compartment model, a virtual intramural vascular network is generated using a novel algorithm which works in non-convex domains. Modeling epicardial vessels with a 3D model and intramural ones with a porous medium approach makes it possible to apply the proposed strategy to patient-specific heart geometries reconstructed from clinical imaging data. We also address the derivation of numerical solvers for the coupled problem. In particular, we propose a splitting algorithm for the monolithic problem, with the corresponding convergence analysis performed in a simplified linearized case, and a suitable preconditioner for the multi-compartment porous sub-model. Finally, we test the computational framework in a realistic human heart, obtaining results that fall in the physiological range for both pressures and local myocardial flows.

Hydrogeochemical Study on Closed-Basin Lakes in Cold and Semi-Arid Climates of the Valley of the Gobi Lakes, Mongolia: Implications for Hydrology and Water Chemistry of Paleolakes on Mars

Previous studies suggested that, generally, the climate of early Mars would have been semi-arid when the surface temperatures were above freezing. On early Mars, closed-basin lakes would have been created; however, the hydrogeochemical cycles of the lake systems are poorly constrained. Here we report results of our field surveys to terrestrial analogs of closed-basin lake systems that developed in cold and semi-arid climates: The Valley of the Gobi Lakes of Mongolia. Our results show that groundwater plays a central role not only in hydrology, but also in geochemical cycles in the lake systems. We find that groundwater predominantly flows into the lakes through local seepage and regional flows in semi-arid climates. Through the interactions with calcite-containing soils, local groundwater seepage provides Ca2+ and HCO3− to the lakes. In the wetland located in between the lakes, high-salinity shallow pools would provide Cl− and Na+ to the groundwater through infiltration. If similar processes occurred on early Mars, local seepage of groundwater would have provided magnesium and alkalinity to the early Jezero lakes, possibly leading to authigenic precipitation of lacustrine carbonates. On early Mars, infiltration of surface brine may have transported salts and oxidants on the surface to lakes via regional groundwater flows. We suggest that inflows of multiple types of groundwater in semi-arid climates could have caused redox disequilibria in closed-basin lakes on early Mars.

Evolution of deepwater turbidite bedforms in the Huaguang channel–lobe transition zone revealed by 3D seismic data in the Qiongdongnan Basin, South China Sea

The theoretical model of turbidite bedform evolution has been verified based on laboratory tests and outcrop surveys. However, the evolution of the bedforms associated with flow regime variation within the channel–lobe transition zone (CLTZ) is poorly documented and generally extremely poorly understood. In this study, a combination of seismic sedimentological and topographic analyses, based on high-resolution 3D seismic data within the Qiongdongnan Basin of the South China Sea, was used. Continuous bedforms varied with the depositional elements within the CLTZ of the Huaguang leveed channel system along the flow direction. The depositional elements within the CLTZ change from the main channel to the distributary channels as well as to the sub-distributary channels. Numerous bifurcation and confluence points of gravity flows illustrated the complexity of the drainage network within the CLTZ. The average asymmetry index of the bedforms increased from 0.8 to 1.6, with the average wavelength increasing from 803 m to 1545 m along the thalweg of the channels. Crevasse splays at the starting reach of the CLTZ are likely to form the initial state of the new CLTZ in the future, because the slope gradient starting from the avulsion point was higher than that inside the channel. The deep scours at the bifurcation points and high steps at the confluence points demonstrate the critical roles of supercritical flows and hydraulic jumps in reworking the bedforms of the CLTZ. The high steps at confluence points were simultaneously formed along the margin and thalweg of the main channel. The acceleration mechanisms of flow velocity forming the high steps were the increase of the elevation difference along the internal slope of the main channel margin and promotion of discharge along the main channel thalweg. This paper presents newly completed deepwater observations of the present seafloor bedforms based on the turbidity currents within the CLTZ. These observations update the evolution model of local supercritical flows and hydraulic jumps under the global decreasing trend of the Froude numbers within CLTZs.

Effects of a Large Dust Storm in the Near‐Surface Atmosphere as Measured by InSight in Elysium Planitia, Mars. Comparison With Contemporaneous Measurements by Mars Science Laboratory

AbstractNASA's InSight landed in Elysium Planitia (~4.5°N,136°E) at Ls ~ 296° (November 2018), right after the decay of the 2018 Global Dust Storm (GDS) and before the onset of the 2019 Large Dust Storm (LDS) at Ls ~ 320° (January 2019). InSight's cameras observed a rise in the atmospheric opacities during the storm from ~0.7 to ~1.9, similarly to contemporaneous measurements by Curiosity in Gale crater. Pressure tides were strongly affected at the locations of InSight and Curiosity. In particular, the diurnal pressure mode experienced an abrupt increase during the onset of the LDS, similar to that measured by Curiosity, most likely due to longitudinally asymmetric dust loading. Later, the dust was redistributed around the planet and the semidiurnal mode evolved according to dust opacity in both missions. Before and after the onset of the storm, the observed wind patterns resulted from the interaction between regional and local slope flows induced by topography, which all produced a diurnal perturbation superimposed on a mean flow, dominated by the Hadley cell but with modifications due to channeling effects from the regional topography. However, the onset of the LDS modified this to a scenario consistent with enhanced tidal flows. The local air temperatures are strongly perturbed by the lander's thermal effects, and their retrieval significantly depends on wind patterns, which changed during the course of the dust storm. Observations suggest a decrease in convective vortices during the dust storm; however, vortex activity remained strong during the storm's onset due to the increase in wind speeds.

Fully Interactive and Refined Resolution Simulations of the Martian Dust Cycle by the MarsWRF Model

AbstractThe MarsWRF model is set up with fully interactive dust at 5° × 5° and 2° × 2 resolution. The latter allows for a better representation of topography and other surface properties. An infinite reservoir of surface dust is assumed for both resolutions. For 5° × 5°, surface dust lifting by wind stress takes place over broad areas, occurring in about 20% of the model's grid cells. For 2° × 2°, it is more spatially restricted, occurring in less than 5% of the grid cells, and somewhat reminiscent of the corridors Acidalia‐Chryse, Utopia‐Isidis, and Arcadia‐West of Tharsis. The onset times of major dust storms—large regional storms or global dust storm events (GDEs)—do not exhibit much interannual variability, typically occurring at around Ls 260°. However, their magnitude does show significant interannual variability—with only small regional storms in some years, large regional storms in others, and some years with GDEs—owing to the interaction between major dust lifting regions at low latitudes. The latter is consistent with observed GDEs having several active dust lifting centers. The agreement between the model's surface dust distribution and observation‐based dust cover index maps is potentially better for 2° × 2°. For the latter, there is also significant surface dust lifting by wind stress in the aphelion season that is largely confined to the Hellas basin. It has a recurring time pattern of 2–7 sols, possibly resulting from the interaction between midlatitude baroclinic systems and local downslope flows.

Groundwater Controls on Wetland Vegetation of a Ridge-and-Swale Chronosequence in a Lake Michigan Embayment

A chronosequence of wetland swales between beach ridges in the Manistique/Thompson embayments of Lake Michigan contains plant communities that differ across the strandplain. We characterized vegetation in 33 swales and compared distribution with previously reported groundwater flow systems. Older swales near a groundwater divide created by the peak Nipissing ridge receive local flows and hold sedge/leatherleaf floating mats that transition to swamp. Farther lakeward, another groundwater divide is created by discharge of calcareous waters released by termination of an underlying clay confining layer, resulting in swales dominated by northern white cedar. Cedar swamp continues lakeward in swales having flow-through calcareous groundwater, but several swales are perched above those flows. Farther lakeward, a large amalgamated beach ridge creates another groundwater divide with discharges that again support cedar swamp. Calcareous discharge from the confined aquifer, with downslope flow-through waters, then supports more cedar swamp. Flow-through waters meet yet another calcareous discharge, resulting in ponding and development of floating mats. Finally, a deep regional aquifer discharges at the Lake Michigan shore and supports marsh/shoreline species. Our results have implications for assessing potential responses to climate change, interpretation of past climate changes in paleoecological studies, and management of wetlands facing future climate changes.

Modeling in food across the scales: towards a universal mass transfer simulator of small molecules in food

Multiscale modeling in food is the cutting-edge strategy to revisit food structure and food composition to meet specific targets such as bioavailability, oral perception, or to evaluate the contamination of food by chemicals. A special implementation of Langevin dynamics is proposed to describe mass transfer in structured food. The concepts of random walks over discrete times and physicochemical interactions are connected via an exact solution of the Fokker–Planck equation across interfaces. The methodology is illustrated on the calculation of effective diffusivities of small solutes in emulsions in relationship with their polydispersity, the volume fraction of dispersed phase d = [0.1, 0.4], the ratio of diffusion coefficients between the two phases, rD = [10−2, 102], and the partition coefficients between the continuous and disperse phases, K = [10−2, + ∞[. Simulated diffusion paths are detailed in 2D emulsions and the effective diffusivities compared with the core–shell model of Kalnin and Kotomin (J Phys A Math Gen 31(35):7227–7234, 1998). The same effects are finally tabulated for 3D emulsions covering the full range of food applications. The methodology is comprehensive enough to enable various extensions such as chemisorption, adsorption in the surfactant layer, local flows, flocculation/creaming.

A Markov chain model of particle deposition in the lung

Particle deposition in the lung during inhalation is of interest to a wide range of biomedical sciences due to the noninvasive therapeutic route to deliver drugs to the lung and other organs via the blood stream. Before reaching the alveoli, particles must transverse the bifurcating network of airways. Computational fluid mechanical studies are often used to estimate high-fidelity flow patterns through the large conducting airways, but there is a need for reduced-dimensional modeling that enables rapid parameter optimization while accommodating the complete airway network. Here, we introduce a Markov chain model with each state corresponding to an airway segment in which a particle may be located. The local flows and transition probabilities of the Markov chain, verified against computational fluid dynamics simulations, indicate that the independent effects of three fundamental forces (gravity, fluid drag, diffusion) provide a sufficient approximation of overall particle behavior. The model enables fast computation of how different inhalation strategies, called flow policies, determine total particle escape rates and local particle deposition. In a 3-dimensional airway tree model, the optimal flow policy minimizing the risk of deposition at each generation, compared to other inlet flow waveforms, predicted significantly higher probability of escape defined as the fraction of particles exiting the tree. The model also predicts a small influence of body orientation with respect to a gravitational field on total escape probability, but a significant effect of airway narrowing on regional deposition. In summary, this model provides insight into inhalation strategies for targeted drug delivery.

Spatial and non‐spatial proximity in university–industry collaboration: Mutual reinforcement and decreasing effects

AbstractThe role of geographical proximity in fostering innovation is widely recognized, and local flows of information and knowledge‐sharing play a critical role in interactive learning. The aim of this paper is to evaluate synergistic effects and non‐linearities in spatial and non‐spatial proximity in university–industry collaborations. Previous studies have evaluated this issue in scientific collaboration. Here, we examine the role of geographical and cognitive proximity in university‐industry collaboration using data from collaborative projects between academic research groups and firms in Brazil (4,342 collaborations involving 3,063 firms and 1,738 research groups in most scientific fields). Our results reveal synergistic effects that mutually reinforce the benefits of geographical and cognitive proximity and reveal non‐linearity in the impacts of geographical and cognitive proximity in university‐industry collaborations. The contribution of our research is its examination of synergistic effects and non‐linearities in university‐industry collaborations that include information exchange and knowledge‐sharing between firms and their academic partners.

A model for the constant-density boundary layer surrounding fire whirls

Abstract

Current vortices in aromatic carbon molecules

The local current flow through three small aromatic carbon molecules, namely benzene, naphthalene and anthracene, is studied. Applying density functional theory and the non-equilibrium Green's function method for transport, we demonstrate that pronounced current vortices exist at certain electron energies for these molecules. The intensity of these circular currents, which appear not only at the anti-resonances of the transmission but also in vicinity of its maxima, can exceed the total current flowing through the molecular junction and generate considerable magnetic fields. The $\pi$ electron system of the molecular junctions is emulated experimentally by a network of macroscopic microwave resonators. The local current flows in these experiments confirm the existence of current vortices as a robust property of ring structures. The circular currents can be understood in terms of a simple nearest-neighbor tight-binding H\"uckel model. Current vortices are caused by the interplay of the complex eigenstates of the open system which have energies close-by the considered electron energy. Degeneracies, as observed in benzene and anthracene, can thus generate strong circular currents, but also non-degenerate systems like naphthalene exhibit current vortices. Small imperfections and perturbations can couple otherwise uncoupled states and induce circular currents.

Explosion-driven interfacial instabilities of granular media

This paper investigates the evolution of a Richtmyer–Meshkov (RM)-like instability on the internal surface of particle rings impinged by divergent blast waves. Despite the signature spike–bubble instability structure analogous to the hydrodynamic RM instability, the growth of the perturbation amplitude in granular media undergoes an exponential phase followed by a linear phase, markedly differing from the hydrodynamic RM instability and indicating a fundamentally different mechanism. The granular RM-like instability arises from the incipient transverse granular flows induced by hydrodynamic effects upon the shock interaction. Substantial perturbation growth is initiated by the ensuing rarefaction dilation when the hydrodynamic effects are small. It is found that the interplay between the localized transverse and radial granular flows sustains the persistent perturbation growth and drives the corresponding morphological changes in the instability pattern.

Microgrid Energy Management Systems Design by Computational Intelligence Techniques

With the capillary spread of multi-energy systems such as microgrids, nanogrids, smart homes and hybrid electric vehicles, the design of a suitable Energy Management System (EMS) able to schedule the local energy flows in real time has a key role for the development of Renewable Energy Sources (RESs) and for reducing pollutant emissions. In the literature, most EMSs proposed are based on the implementation of energy systems prediction which enable to run a specific optimization algorithm. Such strategy, known as Rolling Time Horizon (RTH), demonstrated very effective when the supporting prediction system performs well. However, it is featured by high operational times. In this work, different lightweight EMS models synthesized through machine learning algorithms have been compared considering six different simulation scenarios. Results shows that an RTH-based EMS owns the best overall performances. However, in some case studies, also other EMSs show competitive results, especially those based on Adaptive Neuro Fuzzy Inference Systems (ANFIS) trained by clustering, which in one case outperform RTH EMSs, and in other 3 cases (out of 6) yields performances close to RTH EMSs within 5%. A second contribution concerns the RTH EMS implementation on a small micro-controller, highlighting the high computational effort which can range in the order of minutes. Conversely, the ANFIS EMS shows always almost negligible computational costs (less than one second) and therefore can be used in realistic scenarios on cheap devices at run time. The paper also proposed a novel graphic tool to better represent, observe and analyze microgrid energy flows in each time slot or along the overall considered dataset.

Stress-Induced Dinoflagellate Bioluminescence at the Single Cell Level.

One of the characteristic features of many marine dinoflagellates is their bioluminescence, which lights up nighttime breaking waves or seawater sliced by a ship's prow. While the internal biochemistry of light production by these microorganisms is well established, the manner by which fluid shear or mechanical forces trigger bioluminescence is still poorly understood. We report controlled measurements of the relation between mechanical stress and light production at the single cell level, using high-speed imaging of micropipette-held cells of the marine dinoflagellate Pyrocystis lunula subjected to localized fluid flows or direct indentation. We find a viscoelastic response in which light intensity depends on both the amplitude and rate of deformation, consistent with the action of stretch-activated ion channels. A phenomenological model captures the experimental observations.