2020 |
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Guillaume Duclos; Raymond Adkins; Debarghya Banerjee; Matthew S E Peterson; Minu Varghese; Itamar Kolvin; Arvind Baskaran; Robert A Pelcovits; Thomas R Powers; Aparna Baskaran; Federico Toschi; Michael F Hagan; Sebastian J Streichan; Vincenzo Vitelli; Daniel A Beller; Zvonimir Dogic Topological structure and dynamics of three-dimensional active nematics Journal Article Science, 367 (6482), pp. 1120–1124, 2020, ISSN: 0036-8075. Abstract | Links | BibTeX | Tags: @article{8fda6705603a42dc816f892c2a400490, title = {Topological structure and dynamics of three-dimensional active nematics}, author = {Guillaume Duclos and Raymond Adkins and Debarghya Banerjee and {Matthew S E } Peterson and Minu Varghese and Itamar Kolvin and Arvind Baskaran and {Robert A } Pelcovits and {Thomas R } Powers and Aparna Baskaran and Federico Toschi and {Michael F } Hagan and {Sebastian J } Streichan and Vincenzo Vitelli and {Daniel A } Beller and Zvonimir Dogic}, doi = {10.1126/science.aaz4547}, issn = {0036-8075}, year = {2020}, date = {2020-01-01}, journal = {Science}, volume = {367}, number = {6482}, pages = {1120--1124}, publisher = {American Association for the Advancement of Science (AAAS)}, abstract = {Topological structures are effective descriptors of the nonequilibrium dynamics of diverse many-body systems. For example, motile, point-like topological defects capture the salient features of two-dimensional active liquid crystals composed of energy-consuming anisotropic units. We dispersed force-generating microtubule bundles in a passive colloidal liquid crystal to form a three-dimensional active nematic. Light-sheet microscopy revealed the temporal evolution of the millimeter-scale structure of these active nematics with single-bundle resolution. The primary topological excitations are extended, charge-neutral disclination loops that undergo complex dynamics and recombination events. Our work suggests a framework for analyzing the nonequilibrium dynamics of bulk anisotropic systems as diverse as driven complex fluids, active metamaterials, biological tissues, and collections of robots or organisms.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Topological structures are effective descriptors of the nonequilibrium dynamics of diverse many-body systems. For example, motile, point-like topological defects capture the salient features of two-dimensional active liquid crystals composed of energy-consuming anisotropic units. We dispersed force-generating microtubule bundles in a passive colloidal liquid crystal to form a three-dimensional active nematic. Light-sheet microscopy revealed the temporal evolution of the millimeter-scale structure of these active nematics with single-bundle resolution. The primary topological excitations are extended, charge-neutral disclination loops that undergo complex dynamics and recombination events. Our work suggests a framework for analyzing the nonequilibrium dynamics of bulk anisotropic systems as diverse as driven complex fluids, active metamaterials, biological tissues, and collections of robots or organisms. | |
Michele Buzzicotti; Luca Biferale; Federico Toschi Statistical properties of turbulence in the presence of a smart small-scale control Journal Article Physical Review Letters, 124 (8), 2020, ISSN: 0031-9007. Abstract | Links | BibTeX | Tags: @article{efabf45ce9844b1d8f94506184714688, title = {Statistical properties of turbulence in the presence of a smart small-scale control}, author = {Michele Buzzicotti and Luca Biferale and Federico Toschi}, doi = {10.1103/PhysRevLett.124.084504}, issn = {0031-9007}, year = {2020}, date = {2020-01-01}, journal = {Physical Review Letters}, volume = {124}, number = {8}, publisher = {American Physical Society}, abstract = {By means of high-resolution numerical simulations, we compare the statistical properties of homogeneous and isotropic turbulence to those of the Navier-Stokes equation where small-scale vortex filaments are strongly depleted, thanks to a nonlinear extra viscosity acting preferentially on high vorticity regions. We show that the presence of such smart small-scale drag can strongly reduce intermittency and non-Gaussian fluctuations. Our results pave the way towards a deeper understanding on the fundamental role of degrees of freedom in turbulence as well as on the impact of (pseudo)coherent structures on the statistical small-scale properties. Our work can be seen as a first attempt to develop smart-Lagrangian forcing or drag mechanisms to control turbulence.}, keywords = {}, pubstate = {published}, tppubtype = {article} } By means of high-resolution numerical simulations, we compare the statistical properties of homogeneous and isotropic turbulence to those of the Navier-Stokes equation where small-scale vortex filaments are strongly depleted, thanks to a nonlinear extra viscosity acting preferentially on high vorticity regions. We show that the presence of such smart small-scale drag can strongly reduce intermittency and non-Gaussian fluctuations. Our results pave the way towards a deeper understanding on the fundamental role of degrees of freedom in turbulence as well as on the impact of (pseudo)coherent structures on the statistical small-scale properties. Our work can be seen as a first attempt to develop smart-Lagrangian forcing or drag mechanisms to control turbulence. | |
Pinaki Kumar; Evangelos Korkolis; Roberto Benzi; Dmitry Denisov; Andr é; Peter Schall; Federico Toschi; Jeannot Trampert On interevent time distributions of avalanche dynamics Journal Article Scientific Reports, 10 (1), 2020, ISSN: 2045-2322. Abstract | Links | BibTeX | Tags: @article{b37a36cda08840a4a249c0973eca6e25, title = {On interevent time distributions of avalanche dynamics}, author = {Pinaki Kumar and Evangelos Korkolis and Roberto Benzi and Dmitry Denisov and Andr é and Peter Schall and Federico Toschi and Jeannot Trampert}, doi = {10.1038/s41598-019-56764-6}, issn = {2045-2322}, year = {2020}, date = {2020-01-01}, journal = {Scientific Reports}, volume = {10}, number = {1}, publisher = {Nature Publishing Group}, abstract = {Physical systems characterized by stick-slip dynamics often display avalanches. Regardless of the diversity of their microscopic structure, these systems are governed by a power-law distribution of avalanche size and duration. Here we focus on the interevent times between avalanches and show that, unlike their distributions of size and duration, the interevent time distributions are able to distinguish different mechanical states of the system. We use experiments on granular systems and numerical simulations of emulsions to show that systems having the same probability distribution for avalanche size and duration can have different interevent time distributions. Remarkably, these interevent time distributions look similar to those for earthquakes and, if different from an exponential, are indirect evidence of non trivial space-time correlations among avalanches. Our results therefore indicate that interevent time statistics are essential to characterise the dynamics of avalanches.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Physical systems characterized by stick-slip dynamics often display avalanches. Regardless of the diversity of their microscopic structure, these systems are governed by a power-law distribution of avalanche size and duration. Here we focus on the interevent times between avalanches and show that, unlike their distributions of size and duration, the interevent time distributions are able to distinguish different mechanical states of the system. We use experiments on granular systems and numerical simulations of emulsions to show that systems having the same probability distribution for avalanche size and duration can have different interevent time distributions. Remarkably, these interevent time distributions look similar to those for earthquakes and, if different from an exponential, are indirect evidence of non trivial space-time correlations among avalanches. Our results therefore indicate that interevent time statistics are essential to characterise the dynamics of avalanches. | |
Joris Willems; Alessandro Corbetta; Vlado Menkovski; Federico Toschi Pedestrian orientation dynamics from high-fidelity measurements Journal Article arXiv, 2020. Abstract | BibTeX | Tags: cs.LG, physics.soc-ph @article{0c6a159182504960bcab1be66495fb3c, title = {Pedestrian orientation dynamics from high-fidelity measurements}, author = {Joris Willems and Alessandro Corbetta and Vlado Menkovski and Federico Toschi}, year = {2020}, date = {2020-01-01}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {We investigate in real-life conditions and with very high accuracy the dynamics of body rotation, or yawing, of walking pedestrians - an highly complex task due to the wide variety in shapes, postures and walking gestures. We propose a novel measurement method based on a deep neural architecture that we train on the basis of generic physical properties of the motion of pedestrians. Specifically, we leverage on the strong statistical correlation between individual velocity and body orientation: the velocity direction is typically orthogonal with respect to the shoulder line. We make the reasonable assumption that this approximation, although instantaneously slightly imperfect, is correct on average. This enables us to use velocity data as training labels for a highly-accurate point-estimator of individual orientation, that we can train with no dedicated annotation labor. We discuss the measurement accuracy and show the error scaling, both on synthetic and real-life data: we show that our method is capable of estimating orientation with an error as low as 7.5 degrees. This tool opens up new possibilities in the studies of human crowd dynamics where orientation is key. By analyzing the dynamics of body rotation in real-life conditions, we show that the instantaneous velocity direction can be described by the combination of orientation and a random delay, where randomness is provided by an Ornstein-Uhlenbeck process centered on an average delay of 100ms. Quantifying these dynamics could have only been possible thanks to a tool as precise as that proposed.}, keywords = {cs.LG, physics.soc-ph}, pubstate = {published}, tppubtype = {article} } We investigate in real-life conditions and with very high accuracy the dynamics of body rotation, or yawing, of walking pedestrians - an highly complex task due to the wide variety in shapes, postures and walking gestures. We propose a novel measurement method based on a deep neural architecture that we train on the basis of generic physical properties of the motion of pedestrians. Specifically, we leverage on the strong statistical correlation between individual velocity and body orientation: the velocity direction is typically orthogonal with respect to the shoulder line. We make the reasonable assumption that this approximation, although instantaneously slightly imperfect, is correct on average. This enables us to use velocity data as training labels for a highly-accurate point-estimator of individual orientation, that we can train with no dedicated annotation labor. We discuss the measurement accuracy and show the error scaling, both on synthetic and real-life data: we show that our method is capable of estimating orientation with an error as low as 7.5 degrees. This tool opens up new possibilities in the studies of human crowd dynamics where orientation is key. By analyzing the dynamics of body rotation in real-life conditions, we show that the instantaneous velocity direction can be described by the combination of orientation and a random delay, where randomness is provided by an Ornstein-Uhlenbeck process centered on an average delay of 100ms. Quantifying these dynamics could have only been possible thanks to a tool as precise as that proposed. | |
2019 |
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Roberto Benzi; Thibaut Divoux; Catherine Barentin; S é; Mauro Sbragaglia; Federico Toschi Unified theoretical and experimental view on transient shear banding Journal Article Physical Review Letters, 123 (24), 2019, ISSN: 0031-9007. Abstract | Links | BibTeX | Tags: @article{1e8ee0c6d37d40c886799ab8582ff9ee, title = {Unified theoretical and experimental view on transient shear banding}, author = {Roberto Benzi and Thibaut Divoux and Catherine Barentin and S é and Mauro Sbragaglia and Federico Toschi}, doi = {10.1103/PhysRevLett.123.248001}, issn = {0031-9007}, year = {2019}, date = {2019-01-01}, journal = {Physical Review Letters}, volume = {123}, number = {24}, publisher = {American Physical Society}, abstract = {Dense emulsions, colloidal gels, microgels, and foams all display a solidlike behavior at rest characterized by a yield stress, above which the material flows like a liquid. Such a fluidization transition often consists of long-lasting transient flows that involve shear-banded velocity profiles. The characteristic time for full fluidization τf has been reported to decay as a power law of the shear rate γ and of the shear stress σ with respective exponents α and β. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the Herschel-Bulkley law that describes the steady-state flow behavior of these complex fluids. Here we introduce a continuum model, based on the minimization of a "free energy," that captures quantitatively all the salient features associated with such transient shear banding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steady-state flow properties of yield stress fluids.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Dense emulsions, colloidal gels, microgels, and foams all display a solidlike behavior at rest characterized by a yield stress, above which the material flows like a liquid. Such a fluidization transition often consists of long-lasting transient flows that involve shear-banded velocity profiles. The characteristic time for full fluidization τf has been reported to decay as a power law of the shear rate γ and of the shear stress σ with respective exponents α and β. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the Herschel-Bulkley law that describes the steady-state flow behavior of these complex fluids. Here we introduce a continuum model, based on the minimization of a "free energy," that captures quantitatively all the salient features associated with such transient shear banding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steady-state flow properties of yield stress fluids. | |
Giorgia Guccione; Roberto Benzi; Abigail Plummer; Federico Toschi Discrete Eulerian model for population genetics and dynamics under flow Journal Article Physical Review E, 100 (6), 2019, ISSN: 2470-0045. Abstract | Links | BibTeX | Tags: @article{313daeaee9854121ab26a4b18b0ea997, title = {Discrete Eulerian model for population genetics and dynamics under flow}, author = {Giorgia Guccione and Roberto Benzi and Abigail Plummer and Federico Toschi}, doi = {10.1103/PhysRevE.100.062105}, issn = {2470-0045}, year = {2019}, date = {2019-01-01}, journal = {Physical Review E}, volume = {100}, number = {6}, publisher = {American Physical Society}, abstract = {Marine species reproduce and compete while being advected by turbulent flows. It is largely unknown, both theoretically and experimentally, how population dynamics and genetics are changed by the presence of fluid flows. Discrete agent-based simulations in continuous space allow for accurate treatment of advection and number fluctuations, but can be computationally expensive for even modest organism densities. In this report, we propose an algorithm to overcome some of these challenges. We first provide a thorough validation of the algorithm in one and two dimensions without flow. Next, we focus on the case of weakly compressible flows in two dimensions. This models organisms such as phytoplankton living at a specific depth in the three-dimensional, incompressible ocean experiencing upwelling and/or downwelling events. We show that organisms born at sources in a two-dimensional time-independent flow experience an increase in fixation probability.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Marine species reproduce and compete while being advected by turbulent flows. It is largely unknown, both theoretically and experimentally, how population dynamics and genetics are changed by the presence of fluid flows. Discrete agent-based simulations in continuous space allow for accurate treatment of advection and number fluctuations, but can be computationally expensive for even modest organism densities. In this report, we propose an algorithm to overcome some of these challenges. We first provide a thorough validation of the algorithm in one and two dimensions without flow. Next, we focus on the case of weakly compressible flows in two dimensions. This models organisms such as phytoplankton living at a specific depth in the three-dimensional, incompressible ocean experiencing upwelling and/or downwelling events. We show that organisms born at sources in a two-dimensional time-independent flow experience an increase in fixation probability. | |
Alessandro Corbetta; Vlado Menkovski; Roberto Benzi; Federico Toschi Deep learning velocity signals allows to quantify turbulence intensity Journal Article arXiv, 2019. Abstract | BibTeX | Tags: cond-mat.stat-mech, cs.AI, cs.LG, physics.flu-dyn @article{046d24a1bab542e983a477781595c64f, title = {Deep learning velocity signals allows to quantify turbulence intensity}, author = {Alessandro Corbetta and Vlado Menkovski and Roberto Benzi and Federico Toschi}, year = {2019}, date = {2019-01-01}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {Turbulence, the ubiquitous and chaotic state of fluid motions, is characterized by strong and statistically non-trivial fluctuations of the velocity field, over a wide range of length- and time-scales, and it can be quantitatively described only in terms of statistical averages. Strong non-stationarities hinder the possibility to achieve statistical convergence, making it impossible to define the turbulence intensity and, in particular, its basic dimensionless estimator, the Reynolds number. Here we show that by employing Deep Neural Networks (DNN) we can accurately estimate the Reynolds number within $15%$ accuracy, from a statistical sample as small as two large-scale eddy-turnover times. In contrast, physics-based statistical estimators are limited by the rate of convergence of the central limit theorem, and provide, for the same statistical sample, an error at least $100$ times larger. Our findings open up new perspectives in the possibility to quantitatively define and, therefore, study highly non-stationary turbulent flows as ordinarily found in nature as well as in industrial processes.}, keywords = {cond-mat.stat-mech, cs.AI, cs.LG, physics.flu-dyn}, pubstate = {published}, tppubtype = {article} } Turbulence, the ubiquitous and chaotic state of fluid motions, is characterized by strong and statistically non-trivial fluctuations of the velocity field, over a wide range of length- and time-scales, and it can be quantitatively described only in terms of statistical averages. Strong non-stationarities hinder the possibility to achieve statistical convergence, making it impossible to define the turbulence intensity and, in particular, its basic dimensionless estimator, the Reynolds number. Here we show that by employing Deep Neural Networks (DNN) we can accurately estimate the Reynolds number within $15%$ accuracy, from a statistical sample as small as two large-scale eddy-turnover times. In contrast, physics-based statistical estimators are limited by the rate of convergence of the central limit theorem, and provide, for the same statistical sample, an error at least $100$ times larger. Our findings open up new perspectives in the possibility to quantitatively define and, therefore, study highly non-stationary turbulent flows as ordinarily found in nature as well as in industrial processes. | |
Guillaume Duclos; Raymond Adkins; Debarghya Banerjee; Matthew S E Peterson; Minu Varghese; Itamar Kolvin; Arvind Baskaran; Robert A Pelcovits; Thomas R Powers; Aparna Baskaran; Federico Toschi; Michael F Hagan; Sebastian J Streichan; Vincenzo Vitelli; Daniel A Beller; Zvonimir Dogic Topological structure and dynamics of three dimensional active nematics Journal Article arXiv, 2019, (13 pages, 5 figures, plus Supplementary Information of 12 pages, 4 figures). Abstract | BibTeX | Tags: cond-mat.soft @article{e86486974c294689ad18cb25f012fe2e, title = {Topological structure and dynamics of three dimensional active nematics}, author = {Guillaume Duclos and Raymond Adkins and Debarghya Banerjee and {Matthew S E } Peterson and Minu Varghese and Itamar Kolvin and Arvind Baskaran and {Robert A } Pelcovits and {Thomas R } Powers and Aparna Baskaran and Federico Toschi and {Michael F } Hagan and {Sebastian J } Streichan and Vincenzo Vitelli and {Daniel A } Beller and Zvonimir Dogic}, year = {2019}, date = {2019-01-01}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {Point-like motile topological defects control the universal dynamics of diverse two-dimensional active nematics ranging from shaken granular rods to cellular monolayers. A comparable understanding in higher dimensions has yet to emerge. We report the creation of three-dimensional active nematics by dispersing extensile microtubule bundles in a passive colloidal liquid crystal. Light-sheet microscopy reveals the millimeter-scale structure of active nematics with a single bundle resolution and the temporal evolution of the associated nematic director field. The dominant excitations of three-dimensional active nematics are extended charge-neutral disclination loops that undergo complex dynamics and recombination events. These studies introduce a new class of non-equilibrium systems whose turbulent-like dynamics arises from the interplay between internally generated active stresses, the chaotic flows and the topological structure of the constituent defects.}, note = {13 pages, 5 figures, plus Supplementary Information of 12 pages, 4 figures}, keywords = {cond-mat.soft}, pubstate = {published}, tppubtype = {article} } Point-like motile topological defects control the universal dynamics of diverse two-dimensional active nematics ranging from shaken granular rods to cellular monolayers. A comparable understanding in higher dimensions has yet to emerge. We report the creation of three-dimensional active nematics by dispersing extensile microtubule bundles in a passive colloidal liquid crystal. Light-sheet microscopy reveals the millimeter-scale structure of active nematics with a single bundle resolution and the temporal evolution of the associated nematic director field. The dominant excitations of three-dimensional active nematics are extended charge-neutral disclination loops that undergo complex dynamics and recombination events. These studies introduce a new class of non-equilibrium systems whose turbulent-like dynamics arises from the interplay between internally generated active stresses, the chaotic flows and the topological structure of the constituent defects. | |
Kim Alards; Rudie Kunnen; Herman Clercx; Federico Toschi Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-Bénard convection Journal Article European Physical Journal E : Soft Matter, 42 (9), 2019, ISSN: 1292-8941. Abstract | Links | BibTeX | Tags: Problems and Applications, Topical issue: Flowing Matter @article{4008646d8f584ce7a26171d228d6b022, title = {Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-Bénard convection}, author = {Kim Alards and Rudie Kunnen and Herman Clercx and Federico Toschi}, doi = {10.1140/epje/i2019-11882-y}, issn = {1292-8941}, year = {2019}, date = {2019-01-01}, journal = {European Physical Journal E : Soft Matter}, volume = {42}, number = {9}, publisher = {Springer}, abstract = {Abstract.: The dynamics of inertial particles in Rayleigh-Bénard convection, where both particles and fluid exhibit thermal expansion, is studied using direct numerical simulations (DNS) in the soft-turbulence regime. We consider the effect of particles with a thermal expansion coefficient larger than that of the fluid, causing particles to become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. Because of the opposite directions of the net Archimedes’ force on particles and fluid, particles deposited at the plate now experience a relative force towards the bulk. The characteristic time for this motion towards the bulk to happen, quantified as the time particles spend inside the thermal boundary layers (BLs) at the plates, is shown to depend on the thermal response time, τ T, and the thermal expansion coefficient of particles relative to that of the flui}, keywords = {Problems and Applications, Topical issue: Flowing Matter}, pubstate = {published}, tppubtype = {article} } Abstract.: The dynamics of inertial particles in Rayleigh-Bénard convection, where both particles and fluid exhibit thermal expansion, is studied using direct numerical simulations (DNS) in the soft-turbulence regime. We consider the effect of particles with a thermal expansion coefficient larger than that of the fluid, causing particles to become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. Because of the opposite directions of the net Archimedes’ force on particles and fluid, particles deposited at the plate now experience a relative force towards the bulk. The characteristic time for this motion towards the bulk to happen, quantified as the time particles spend inside the thermal boundary layers (BLs) at the plates, is shown to depend on the thermal response time, τ T, and the thermal expansion coefficient of particles relative to that of the flui | |
Joost Visser; Alessandro Corbetta; Vlado Menkovski; Federico Toschi Stampnet: unsupervised multi-class object discovery Inproceedings 2019 IEEE International Conference on Image Processing, ICIP 2019 - Proceedings, pp. 2951–2955, Institute of Electrical and Electronics Engineers, United States, 2019. Abstract | Links | BibTeX | Tags: image clustering, image localization, object discovery, unsupervised learning @inproceedings{12bd62acd1b245cfbe20d6c70eabd531, title = {Stampnet: unsupervised multi-class object discovery}, author = {Joost Visser and Alessandro Corbetta and Vlado Menkovski and Federico Toschi}, doi = {10.1109/ICIP.2019.8803767}, year = {2019}, date = {2019-01-01}, booktitle = {2019 IEEE International Conference on Image Processing, ICIP 2019 - Proceedings}, pages = {2951--2955}, publisher = {Institute of Electrical and Electronics Engineers}, address = {United States}, abstract = {Unsupervised object discovery in images involves uncovering recurring patterns that define objects and discriminates them against the background. This is more challenging than image clustering as the size and the location of the objects are not known: this adds additional degrees of freedom and increases the problem complexity. In this work, we propose StampNet, a novel autoencoding neural network that localizes shapes (objects) over a simple background in images and categorizes them simultaneously. StampNet consists of a discrete latent space that is used to categorize objects and to determine the location of the objects. The object categories are formed during the training, resulting in the discovery of a fixed set of objects. We present a set of experiments that demonstrate that StampNet is able to localize and cluster multiple overlapping shapes with varying complexity including the digits from the MNIST dataset. We also present an application of StampNet in the localization of pedestrians in overhead depth-maps.}, keywords = {image clustering, image localization, object discovery, unsupervised learning}, pubstate = {published}, tppubtype = {inproceedings} } Unsupervised object discovery in images involves uncovering recurring patterns that define objects and discriminates them against the background. This is more challenging than image clustering as the size and the location of the objects are not known: this adds additional degrees of freedom and increases the problem complexity. In this work, we propose StampNet, a novel autoencoding neural network that localizes shapes (objects) over a simple background in images and categorizes them simultaneously. StampNet consists of a discrete latent space that is used to categorize objects and to determine the location of the objects. The object categories are formed during the training, resulting in the discovery of a fixed set of objects. We present a set of experiments that demonstrate that StampNet is able to localize and cluster multiple overlapping shapes with varying complexity including the digits from the MNIST dataset. We also present an application of StampNet in the localization of pedestrians in overhead depth-maps. | |
Xiao Xue; Luca Biferale; Mauro Sbragaglia; Federico Toschi Particle settling in a fluctuating multicomponent fluid under confinement Journal Article arXiv, 2019, (12pages, 7 figures). Abstract | BibTeX | Tags: cond-mat.soft, physics.comp-ph, physics.flu-dyn @article{d03238a0027f4132ad45a1d7327e35d7, title = {Particle settling in a fluctuating multicomponent fluid under confinement}, author = {Xiao Xue and Luca Biferale and Mauro Sbragaglia and Federico Toschi}, year = {2019}, date = {2019-01-01}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {We study the motion of a spherical particle driven by a constant volume force in a confined channel with a fixed square cross-section. The channel is filled with a mixture of two liquids under the effect of thermal fluctuations. We use the lattice Boltzmann method to simulate a fluctuating multicomponent fluid in the mixed-phase, and particle-fluid interactions are tuned to reproduce different wetting properties at the particle surface. The numerical set-up is first validated in the absence of thermal fluctuations; to this aim, we quantitatively compute the drift velocity at changing the particle radius and compare it with previous experimental and numerical data. In the presence of thermal fluctuations, we study the fluctuations in the particle's velocity at changing thermal energy, applied force, particle size, and particle wettability. The importance of fluctuations with respect to the mean drift velocity is quantitatively assessed, especially in comparison to unconfined situations. Results show that confinement strongly enhances the importance of velocity fluctuations, which can be one order of magnitude larger than what expected in unconfined domains. The observed findings underscore the versatility of the lattice Boltzmann simulations in concrete applications involving the motion of colloidal particles in a highly confined environment in the presence of thermal fluctuations.}, note = {12pages, 7 figures}, keywords = {cond-mat.soft, physics.comp-ph, physics.flu-dyn}, pubstate = {published}, tppubtype = {article} } We study the motion of a spherical particle driven by a constant volume force in a confined channel with a fixed square cross-section. The channel is filled with a mixture of two liquids under the effect of thermal fluctuations. We use the lattice Boltzmann method to simulate a fluctuating multicomponent fluid in the mixed-phase, and particle-fluid interactions are tuned to reproduce different wetting properties at the particle surface. The numerical set-up is first validated in the absence of thermal fluctuations; to this aim, we quantitatively compute the drift velocity at changing the particle radius and compare it with previous experimental and numerical data. In the presence of thermal fluctuations, we study the fluctuations in the particle's velocity at changing thermal energy, applied force, particle size, and particle wettability. The importance of fluctuations with respect to the mean drift velocity is quantitatively assessed, especially in comparison to unconfined situations. Results show that confinement strongly enhances the importance of velocity fluctuations, which can be one order of magnitude larger than what expected in unconfined domains. The observed findings underscore the versatility of the lattice Boltzmann simulations in concrete applications involving the motion of colloidal particles in a highly confined environment in the presence of thermal fluctuations. | |
Roberto Benzi; Thibaut Divoux; Catherine Barentin; S é; Mauro Sbragaglia; Federico Toschi Unified theoretical and experimental view on transient shear banding Journal Article arXiv, 2019, (5 pages, 4 figures - supplemental 5 pages, 4 figures). Abstract | BibTeX | Tags: cond-mat.soft, cond-mat.stat-mech, physics.flu-dyn @article{67228bed5d894c6688f967ac3899f499, title = {Unified theoretical and experimental view on transient shear banding}, author = {Roberto Benzi and Thibaut Divoux and Catherine Barentin and S é and Mauro Sbragaglia and Federico Toschi}, year = {2019}, date = {2019-01-01}, journal = {arXiv}, publisher = {Cornell University Library}, abstract = {Dense emulsions, colloidal gels, microgels, and foams all display a solid-like behavior at rest characterized by a yield stress, above which the material flows like a liquid. Such a fluidization transition often consists of long-lasting transient flows that involve shear-banded velocity profiles. The characteristic time for full fluidization, $tau_textf$, has been reported to decay as a power-law of the shear rate $dot gamma$ and of the shear stress $sigma$ with respective exponents $alpha$ and $beta$. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the Herschel-Bulkley law that describes the steady-state flow behavior of these complex fluids. Here we introduce a continuum model based on the minimization of an out-of-equilibrium free energy that captures quantitatively all the salient features associated with such textittransient shear-banding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steady-state flow properties of yield stress fluids.}, note = {5 pages, 4 figures - supplemental 5 pages, 4 figures}, keywords = {cond-mat.soft, cond-mat.stat-mech, physics.flu-dyn}, pubstate = {published}, tppubtype = {article} } Dense emulsions, colloidal gels, microgels, and foams all display a solid-like behavior at rest characterized by a yield stress, above which the material flows like a liquid. Such a fluidization transition often consists of long-lasting transient flows that involve shear-banded velocity profiles. The characteristic time for full fluidization, $tau_textf$, has been reported to decay as a power-law of the shear rate $dot gamma$ and of the shear stress $sigma$ with respective exponents $alpha$ and $beta$. Strikingly, the ratio of these exponents was empirically observed to coincide with the exponent of the Herschel-Bulkley law that describes the steady-state flow behavior of these complex fluids. Here we introduce a continuum model based on the minimization of an out-of-equilibrium free energy that captures quantitatively all the salient features associated with such textittransient shear-banding. More generally, our results provide a unified theoretical framework for describing the yielding transition and the steady-state flow properties of yield stress fluids. | |
Kim Alards; Rudie Kunnen; R J A M Stevens; Detlef Lohse; Federico Toschi; Herman Clercx Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number Journal Article Physical Review Fluids, 4 (7), pp. 1–19, 2019, ISSN: 2469-990X, (16 pages, 9 Figures). Abstract | Links | BibTeX | Tags: @article{709efdea7c844697ad1b12ad5a26718c, title = {Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number}, author = {Kim Alards and Rudie Kunnen and R J A M Stevens and Detlef Lohse and Federico Toschi and Herman Clercx}, doi = {10.1103/PhysRevFluids.4.074601}, issn = {2469-990X}, year = {2019}, date = {2019-01-01}, journal = {Physical Review Fluids}, volume = {4}, number = {7}, pages = {1--19}, publisher = {American Physical Society}, abstract = {In Rayleigh–Bénard convection (RBC) for fluids with Prandtl number Pr≳1, rotation beyond a critical (small) rotation rate is known to cause a sudden enhancement of heat transfer, which can be explained by a change in the character of the boundary layer (BL) dynamics near the top and bottom plates of the convection cell. Namely, with increasing rotation rate, the BL signature suddenly changes from Prandtl–Blasius type to Ekman type. The transition from a constant heat transfer to an almost linearly increasing heat transfer with increasing rotation rate is known to be sharp and the critical Rossby number Roc occurs typically in the range 2.3≲Roc≲2.9 (for Rayleigh number Ra=1.3×10}, note = {16 pages, 9 Figures}, keywords = {}, pubstate = {published}, tppubtype = {article} } In Rayleigh–Bénard convection (RBC) for fluids with Prandtl number Pr≳1, rotation beyond a critical (small) rotation rate is known to cause a sudden enhancement of heat transfer, which can be explained by a change in the character of the boundary layer (BL) dynamics near the top and bottom plates of the convection cell. Namely, with increasing rotation rate, the BL signature suddenly changes from Prandtl–Blasius type to Ekman type. The transition from a constant heat transfer to an almost linearly increasing heat transfer with increasing rotation rate is known to be sharp and the critical Rossby number Roc occurs typically in the range 2.3≲Roc≲2.9 (for Rayleigh number Ra=1.3×10 | |
Enrico Ronchi; Alessandro Corbetta; Edwin R Galea; Max Kinateder; Erica Kuligowski; Denise Mcgrath; Adam Pel; Youssef Shiban; Peter Thompson; Federico Toschi New approaches to evacuation modelling for fire safety engineering applications Journal Article Fire Safety Journal, 106 , pp. 197–209, 2019, ISSN: 0379-7112. Abstract | Links | BibTeX | Tags: Egress, Emergency, Evacuation modelling, Exit choice, Fire safety, Human behaviour, Pedestrian dynamics, Pre-evacuation, Smoke @article{3bcafd866cbd49059b6ca109743cb862, title = {New approaches to evacuation modelling for fire safety engineering applications}, author = {Enrico Ronchi and Alessandro Corbetta and {Edwin R } Galea and Max Kinateder and Erica Kuligowski and Denise Mcgrath and Adam Pel and Youssef Shiban and Peter Thompson and Federico Toschi}, doi = {10.1016/j.firesaf.2019.05.002}, issn = {0379-7112}, year = {2019}, date = {2019-01-01}, journal = {Fire Safety Journal}, volume = {106}, pages = {197--209}, publisher = {Elsevier}, abstract = {This paper presents the findings of the workshop “New approaches to evacuation modelling”, which took place on the 11th of June 2017 in Lund (Sweden)within the Symposium of the International Association for Fire Safety Science (IAFSS). The workshop gathered international experts in the field of fire evacuation modelling from 19 different countries and was designed to build a dialogue between the fire evacuation modelling world and experts in areas outside of fire safety engineering. The contribution to fire evacuation modelling of five topics within research disciplines outside fire safety engineering (FSE)have been discussed during the workshop, namely 1)Psychology/Human Factors, 2)Sociology, 3)Applied Mathematics, 4)Transportation, 5)Dynamic Simulation and Biomechanics. The benefits of exchanging information between these two groups are highlighted here in light of the topic areas discussed and the feedback received by the evacuation modelling community during the workshop. This included the feasibility of development/application of modelling methods based on fields other than FSE as well as a discussion on their implementation strengths and limitations. Each subject area is here briefly presented and its links to fire evacuation modelling are discussed. The feedback received during the workshop is discussed through a set of insights which might be useful for the future developments of evacuation models for fire safety engineering.}, keywords = {Egress, Emergency, Evacuation modelling, Exit choice, Fire safety, Human behaviour, Pedestrian dynamics, Pre-evacuation, Smoke}, pubstate = {published}, tppubtype = {article} } This paper presents the findings of the workshop “New approaches to evacuation modelling”, which took place on the 11th of June 2017 in Lund (Sweden)within the Symposium of the International Association for Fire Safety Science (IAFSS). The workshop gathered international experts in the field of fire evacuation modelling from 19 different countries and was designed to build a dialogue between the fire evacuation modelling world and experts in areas outside of fire safety engineering. The contribution to fire evacuation modelling of five topics within research disciplines outside fire safety engineering (FSE)have been discussed during the workshop, namely 1)Psychology/Human Factors, 2)Sociology, 3)Applied Mathematics, 4)Transportation, 5)Dynamic Simulation and Biomechanics. The benefits of exchanging information between these two groups are highlighted here in light of the topic areas discussed and the feedback received by the evacuation modelling community during the workshop. This included the feasibility of development/application of modelling methods based on fields other than FSE as well as a discussion on their implementation strengths and limitations. Each subject area is here briefly presented and its links to fire evacuation modelling are discussed. The feedback received during the workshop is discussed through a set of insights which might be useful for the future developments of evacuation models for fire safety engineering. | |
Alessandro Corbetta; Federico Toschi Path-integral representation of diluted pedestrian dynamics Book Chapter Complexity science, pp. 329–346, World Scientific, United States, 2019, ISBN: 978-981-323-959-3. Abstract | Links | BibTeX | Tags: @inbook{36987199082c43c296efae95b7a222e6, title = {Path-integral representation of diluted pedestrian dynamics}, author = {Alessandro Corbetta and Federico Toschi}, doi = {10.1142/9789813239609_0010}, isbn = {978-981-323-959-3}, year = {2019}, date = {2019-01-01}, booktitle = {Complexity science}, pages = {329--346}, publisher = {World Scientific}, address = {United States}, abstract = {We frame the issue of pedestrian dynamics modeling in terms of path-integrals, a formalism originally introduced in quantum mechanics to account for the behavior of quantum particles, later extended to quantum field theories and to statistical physics. Path-integration enables a trajectory-centric representation of the pedestrian motion, directly providing the probability of observing a given trajectory. This appears as the most natural language to describe the statistical properties of pedestrian dynamics in generic settings. In a given venue, individual trajectories can belong to many possible usage patterns and, within each of them, they can display wide variability. We provide first a primer on path-integration, and we introduce and discuss the path-integral functional probability measure for pedestrian dynamics in the diluted limit. As an illustrative example, we connect the path-integral description to a Langevin model that we developed previously for a particular crowd flow condition (the flow in a narrow corridor). Building on our previous real-life measurements, we provide a quantitatively correct path-integral representation for this condition. Finally, we show how the path-integral formalism can be used to evaluate the probability of rare-events (in the case of the corridor, U-turns).}, keywords = {}, pubstate = {published}, tppubtype = {inbook} } We frame the issue of pedestrian dynamics modeling in terms of path-integrals, a formalism originally introduced in quantum mechanics to account for the behavior of quantum particles, later extended to quantum field theories and to statistical physics. Path-integration enables a trajectory-centric representation of the pedestrian motion, directly providing the probability of observing a given trajectory. This appears as the most natural language to describe the statistical properties of pedestrian dynamics in generic settings. In a given venue, individual trajectories can belong to many possible usage patterns and, within each of them, they can display wide variability. We provide first a primer on path-integration, and we introduce and discuss the path-integral functional probability measure for pedestrian dynamics in the diluted limit. As an illustrative example, we connect the path-integral description to a Langevin model that we developed previously for a particular crowd flow condition (the flow in a narrow corridor). Building on our previous real-life measurements, we provide a quantitatively correct path-integral representation for this condition. Finally, we show how the path-integral formalism can be used to evaluate the probability of rare-events (in the case of the corridor, U-turns). | |
Luca Biferale; Stefano Guido; Andrea Scagliarini; Federico Toschi Topical issue on fluids and structures: multi-scale coupling and modeling Journal Article European Physical Journal E : Soft Matter, 42 (3), pp. 28, 2019, ISSN: 1292-8941. Links | BibTeX | Tags: Topical issue: Fluids and Structures: Multi-scale coupling and modeling @article{6cd0288cc1244a8a9cf47d6884ae3f0b, title = {Topical issue on fluids and structures: multi-scale coupling and modeling}, author = {Luca Biferale and Stefano Guido and Andrea Scagliarini and Federico Toschi}, doi = {10.1140/epje/i2019-11808-9}, issn = {1292-8941}, year = {2019}, date = {2019-01-01}, journal = {European Physical Journal E : Soft Matter}, volume = {42}, number = {3}, pages = {28}, publisher = {Springer}, keywords = {Topical issue: Fluids and Structures: Multi-scale coupling and modeling}, pubstate = {published}, tppubtype = {article} } | |
Abigail Plummer; Roberto Benzi; David R Nelson; Federico Toschi Fixation probabilities in weakly compressible fluid flows Journal Article Proceedings of the National Academy of Sciences of the United States of America (PNAS), 116 (2), pp. 373–378, 2019, ISSN: 0027-8424. Abstract | Links | BibTeX | Tags: Fisher wave, Population genetics, Selective advantage, Stochastic processes, Turbulence @article{adf67c42d6074f0fb2ad603537f6f3d1, title = {Fixation probabilities in weakly compressible fluid flows}, author = {Abigail Plummer and Roberto Benzi and {David R } Nelson and Federico Toschi}, doi = {10.1073/pnas.1812829116}, issn = {0027-8424}, year = {2019}, date = {2019-01-01}, journal = {Proceedings of the National Academy of Sciences of the United States of America (PNAS)}, volume = {116}, number = {2}, pages = {373--378}, abstract = {Competition between biological species in marine environments is affected by the motion of the surrounding fluid. An effective 2D compressibility can arise, for example, from the convergence and divergence of water masses at the depth at which passively traveling photosynthetic organisms are restricted to live. In this report, we seek to quantitatively study genetics under flow. To this end, we couple an off-lattice agent-based simulation of two populations in 1D to a weakly compressible velocity field—first a sine wave and then a shell model of turbulence. We find for both cases that even in a regime where the overall population structure is approximately unaltered, the flow can significantly diminish the effect of a selective advantage on fixation probabilities. We understand this effect in terms of the enhanced survival of organisms born at sources in the flow and the influence of Fisher genetic waves.}, keywords = {Fisher wave, Population genetics, Selective advantage, Stochastic processes, Turbulence}, pubstate = {published}, tppubtype = {article} } Competition between biological species in marine environments is affected by the motion of the surrounding fluid. An effective 2D compressibility can arise, for example, from the convergence and divergence of water masses at the depth at which passively traveling photosynthetic organisms are restricted to live. In this report, we seek to quantitatively study genetics under flow. To this end, we couple an off-lattice agent-based simulation of two populations in 1D to a weakly compressible velocity field—first a sine wave and then a shell model of turbulence. We find for both cases that even in a regime where the overall population structure is approximately unaltered, the flow can significantly diminish the effect of a selective advantage on fixation probabilities. We understand this effect in terms of the enhanced survival of organisms born at sources in the flow and the influence of Fisher genetic waves. | |
Juliane Adrian; Nikolai Bode; Martyn Amos; Mitra Baratchi; Mira Beermann; Maik Boltes; Alessandro Corbetta; Guillaume Dezecache; John Drury; Zhijian Fu; Roland Geraerts; Steve Gwynne; Gesine Hofinger; Aoife Hunt; Tinus Kanters; Angelika Kneidl; Krisztina Konya; Gerta K ö; Mira K ü; Georgios Michalareas; Fergus Neville; Evangelos Ntontis; Stephen Reicher; Enrico Ronchi; Andreas Schadschneider; Armin Seyfried; Alastair Shipman; Anna Sieben; Michael Spearpoint; Gavin Brent Sullivan; Anne Templeton; Federico Toschi; Zeynep Y ü; Francesco Zanlungo; Iker Zuriguel; Natalie van der Wal; Frank van Schadewijk; Cornelia von Krüchten; Nanda Wijermans A glossary for research on human crowd dynamics Journal Article Collective Dynamics, 4 , pp. 1–13, 2019, ISSN: 2366-8539. Abstract | Links | BibTeX | Tags: @article{88739111b7b14cfcb36893c00262541e, title = {A glossary for research on human crowd dynamics}, author = {Juliane Adrian and Nikolai Bode and Martyn Amos and Mitra Baratchi and Mira Beermann and Maik Boltes and Alessandro Corbetta and Guillaume Dezecache and John Drury and Zhijian Fu and Roland Geraerts and Steve Gwynne and Gesine Hofinger and Aoife Hunt and Tinus Kanters and Angelika Kneidl and Krisztina Konya and Gerta K ö and Mira K ü and Georgios Michalareas and Fergus Neville and Evangelos Ntontis and Stephen Reicher and Enrico Ronchi and Andreas Schadschneider and Armin Seyfried and Alastair Shipman and Anna Sieben and Michael Spearpoint and {Gavin Brent} Sullivan and Anne Templeton and Federico Toschi and Zeynep Y ü and Francesco Zanlungo and Iker Zuriguel and Natalie {van der Wal} and Frank {van Schadewijk} and Cornelia {von Krüchten} and Nanda Wijermans}, doi = {10.17815/CD.2019.19}, issn = {2366-8539}, year = {2019}, date = {2019-01-01}, journal = {Collective Dynamics}, volume = {4}, pages = {1--13}, publisher = {Forschungszentrum Jülich}, abstract = {This article presents a glossary of terms that are frequently used in research on human crowds. This topic is inherently multidisciplinary as it includes work in and across computer science, engineering, mathematics, physics, psychology and social science, for example. We do not view the glossary presented here as a collection of finalised and formal definitions. Instead, we suggest it is a snapshot of current views and the starting point of an ongoing process that we hope will be useful in providing some guidance on the use of terminology to develop a mutual understanding across disciplines. The glossary was developed collaboratively during a multidisciplinary meeting. We deliberately allow several definitions of terms, to reflect the confluence of disciplines in the field. This also reflects the fact not all contributors necessarily agree with all definitions in this glossary.}, keywords = {}, pubstate = {published}, tppubtype = {article} } This article presents a glossary of terms that are frequently used in research on human crowds. This topic is inherently multidisciplinary as it includes work in and across computer science, engineering, mathematics, physics, psychology and social science, for example. We do not view the glossary presented here as a collection of finalised and formal definitions. Instead, we suggest it is a snapshot of current views and the starting point of an ongoing process that we hope will be useful in providing some guidance on the use of terminology to develop a mutual understanding across disciplines. The glossary was developed collaboratively during a multidisciplinary meeting. We deliberately allow several definitions of terms, to reflect the confluence of disciplines in the field. This also reflects the fact not all contributors necessarily agree with all definitions in this glossary. | |
Federico Toschi; Marcello Sega (Ed.) Flowing matter Book Springer, Germany, 2019, ISBN: 978-3-030-23369-3. Abstract | Links | BibTeX | Tags: Complex fluids, Computational fluid dynamics, Flow dynamics, Lagrangian turbulence, Lattice Boltzmann methods, Open Access, Physical hydrodynamics, Thermal convection @book{ac9a870ba7d94b178e209d8f89cac388, title = {Flowing matter}, editor = {Federico Toschi and Marcello Sega}, doi = {10.1007/978-3-030-23370-9}, isbn = {978-3-030-23369-3}, year = {2019}, date = {2019-01-01}, publisher = {Springer}, address = {Germany}, series = {Soft and Biological Matter}, abstract = {This open access book, published in the Soft and Biological Matter series, presents an introduction to selected research topics in the broad field of flowing matter, including the dynamics of fluids with a complex internal structure -from nematic fluids to soft glasses- as well as active matter and turbulent phenomena.Flowing matter is a subject at the crossroads between physics, mathematics, chemistry, engineering, biology and earth sciences, and relies on a multidisciplinary approach to describe the emergence of the macroscopic behaviours in a system from the coordinated dynamics of its microscopic constituents.Depending on the microscopic interactions, an assembly of molecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elastically like a solid or behave in a complex manner. When the internal constituents are active, as for biological entities, one generally observes complex large-scale collective motions. Phenomenology is further complicated by the invariable tendency of fluids to display chaos at the large scales or when stirred strongly enough. This volume presents several research topics that address these phenomena encompassing the traditional micro-, meso-, and macro-scales descriptions, and contributes to our understanding of the fundamentals of flowing matter.This book is the legacy of the COST Action MP1305 “Flowing Matter”.}, keywords = {Complex fluids, Computational fluid dynamics, Flow dynamics, Lagrangian turbulence, Lattice Boltzmann methods, Open Access, Physical hydrodynamics, Thermal convection}, pubstate = {published}, tppubtype = {book} } This open access book, published in the Soft and Biological Matter series, presents an introduction to selected research topics in the broad field of flowing matter, including the dynamics of fluids with a complex internal structure -from nematic fluids to soft glasses- as well as active matter and turbulent phenomena.Flowing matter is a subject at the crossroads between physics, mathematics, chemistry, engineering, biology and earth sciences, and relies on a multidisciplinary approach to describe the emergence of the macroscopic behaviours in a system from the coordinated dynamics of its microscopic constituents.Depending on the microscopic interactions, an assembly of molecules or of mesoscopic particles can flow like a simple Newtonian fluid, deform elastically like a solid or behave in a complex manner. When the internal constituents are active, as for biological entities, one generally observes complex large-scale collective motions. Phenomenology is further complicated by the invariable tendency of fluids to display chaos at the large scales or when stirred strongly enough. This volume presents several research topics that address these phenomena encompassing the traditional micro-, meso-, and macro-scales descriptions, and contributes to our understanding of the fundamentals of flowing matter.This book is the legacy of the COST Action MP1305 “Flowing Matter”. | |
Kim Alards; Rudie Kunnen; Herman Clercx; Federico Toschi Thermally responsive particles in Rayleigh-Bénard convection Inproceedings M Gorokhovski; F S Godeferd (Ed.): Turbulent Cascades II, pp. 227–235, Springer, Germany, 2019, ISBN: 978-3-030-12546-2. Abstract | Links | BibTeX | Tags: @inproceedings{235ed1d2920e4893a97aae5bbdae2ffc, title = {Thermally responsive particles in Rayleigh-Bénard convection}, author = {Kim Alards and Rudie Kunnen and Herman Clercx and Federico Toschi}, editor = {M Gorokhovski and F S Godeferd}, doi = {10.1007/978-3-030-12547-9_24}, isbn = {978-3-030-12546-2}, year = {2019}, date = {2019-01-01}, booktitle = {Turbulent Cascades II}, pages = {227--235}, publisher = {Springer}, address = {Germany}, series = {ERCOFTAC Series}, abstract = {We track particles that experience both mechanical and thermal inertia in direct numerical simulations of Rayleigh-Bénard convection (RBC), a fluid layer heated from below and cooled from above. Both particles and fluid exhibit thermal expansion. The particles have a larger thermal expansion coefficient than the fluid, such that particles become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. First we investigate how the dynamics of thermal expansion affect the distribution of particles in the RBC cell. We find a regime of viscous and thermal response times where the concentration of particles at the plates is enhanced. A particle deposited on a plate re-suspends after a characteristic residence time, that depends on the thermal response time. Now that we found a mechanism driving particles towards the plates, while also enforcing a motion back to the bulk, we include mechanical and thermal two-way coupling and investigate how thermally responsive particles affect flow structures and heat transfer in RBC. Ultimately, we want to explore the possibility to enhance heat transfer using these thermally inertial particles.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } We track particles that experience both mechanical and thermal inertia in direct numerical simulations of Rayleigh-Bénard convection (RBC), a fluid layer heated from below and cooled from above. Both particles and fluid exhibit thermal expansion. The particles have a larger thermal expansion coefficient than the fluid, such that particles become lighter than the fluid near the hot bottom plate and heavier than the fluid near the cold top plate. First we investigate how the dynamics of thermal expansion affect the distribution of particles in the RBC cell. We find a regime of viscous and thermal response times where the concentration of particles at the plates is enhanced. A particle deposited on a plate re-suspends after a characteristic residence time, that depends on the thermal response time. Now that we found a mechanism driving particles towards the plates, while also enforcing a motion back to the bulk, we include mechanical and thermal two-way coupling and investigate how thermally responsive particles affect flow structures and heat transfer in RBC. Ultimately, we want to explore the possibility to enhance heat transfer using these thermally inertial particles. | |
2018 |
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A Corbetta; J A Meeusen; C Lee; Roberto Benzi; F Toschi Physics-based modeling and data representation of pairwise interactions among pedestrians Journal Article Physical Review E, 98 (6), 2018, ISSN: 2470-0045. Abstract | Links | BibTeX | Tags: @article{3ff9675dcc7a455a86c8e7c4decb19f6, title = {Physics-based modeling and data representation of pairwise interactions among pedestrians}, author = {A Corbetta and J A Meeusen and C Lee and Roberto Benzi and F Toschi}, doi = {10.1103/PhysRevE.98.062310}, issn = {2470-0045}, year = {2018}, date = {2018-01-01}, journal = {Physical Review E}, volume = {98}, number = {6}, publisher = {American Physical Society}, abstract = {In this work we study pedestrian-pedestrian interactions from observational experimental data in diluted pedestrian crowds. While in motion, pedestrians continuously adapt their walking paths trying to preserve mutual comfort distances and to avoid collisions. Leveraging on a high-quality, high-statistics data set, composed of several few millions real-life trajectories acquired from state-of-the-art observational experiments (about 6 months of high-resolution pedestrian tracks acquired in a train station), we develop a quantitative model capable of addressing interactions in the case of binary collision avoidance. We model interactions in terms of both long-range (sight based) and short-range (hard-contact avoidance) forces, which we superimpose on our Langevin model for noninteracting pedestrian motion [Corbetta, Phys. Rev. E 95, 032316 (2017)2470-004510.1103/PhysRevE.95.032316] (here further tested and extended). The model that we propose here features a Langevin dynamics with fast random velocity fluctuations that are superimposed on the slow dynamics of a hidden model variable: the intended walking path. In the case of interactions, social forces may act both on the intended path and on the actual walked path. The model is capable of reproducing quantitatively relevant statistics of the collision avoidance motion, such as the statistics of the side displacement and of the passing speed. Rare occurrences of actual bumping events are also recovered. Furthermore, comparing with large data sets of real-life tracks involves an additional computational challenge so far neglected: identifying automatically, within a database containing very heterogeneous conditions, only the relevant events corresponding to binary avoidance interactions. In order to tackle this challenge, we propose a general approach based on a graph representation of pedestrian trajectories, which allows us to effectively operate complexity reduction for efficient data classification and selection.}, keywords = {}, pubstate = {published}, tppubtype = {article} } In this work we study pedestrian-pedestrian interactions from observational experimental data in diluted pedestrian crowds. While in motion, pedestrians continuously adapt their walking paths trying to preserve mutual comfort distances and to avoid collisions. Leveraging on a high-quality, high-statistics data set, composed of several few millions real-life trajectories acquired from state-of-the-art observational experiments (about 6 months of high-resolution pedestrian tracks acquired in a train station), we develop a quantitative model capable of addressing interactions in the case of binary collision avoidance. We model interactions in terms of both long-range (sight based) and short-range (hard-contact avoidance) forces, which we superimpose on our Langevin model for noninteracting pedestrian motion [Corbetta, Phys. Rev. E 95, 032316 (2017)2470-004510.1103/PhysRevE.95.032316] (here further tested and extended). The model that we propose here features a Langevin dynamics with fast random velocity fluctuations that are superimposed on the slow dynamics of a hidden model variable: the intended walking path. In the case of interactions, social forces may act both on the intended path and on the actual walked path. The model is capable of reproducing quantitatively relevant statistics of the collision avoidance motion, such as the statistics of the side displacement and of the passing speed. Rare occurrences of actual bumping events are also recovered. Furthermore, comparing with large data sets of real-life tracks involves an additional computational challenge so far neglected: identifying automatically, within a database containing very heterogeneous conditions, only the relevant events corresponding to binary avoidance interactions. In order to tackle this challenge, we propose a general approach based on a graph representation of pedestrian trajectories, which allows us to effectively operate complexity reduction for efficient data classification and selection. | |
A Gupta; H J H Clercx; F Toschi Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow Journal Article European Physical Journal E : Soft Matter, 41 (10), 2018, ISSN: 1292-8941. Abstract | Links | BibTeX | Tags: Problems and Applications, Topical issue: Flowing Matter @article{e5b00c30eb0a4b9296c91a4696acba91, title = {Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow}, author = {A Gupta and {H J H } Clercx and F Toschi}, doi = {10.1140/epje/i2018-11724-6}, issn = {1292-8941}, year = {2018}, date = {2018-01-01}, journal = {European Physical Journal E : Soft Matter}, volume = {41}, number = {10}, publisher = {Springer}, abstract = {Anisotropic particles are present in many natural and industrial flows. Here we perform direct numerical simulation (DNS) of turbulent pipe flows with dispersed finite-size prolate spheroids simulated by means of the lattice Boltzmann method (LBM). We consider three different particle shapes: spheroidal (aspect ratio 2 and 3) and spherical. These three simulations are complemented with a reference simulation of a single-phase flow. For the sake of comparison, all simulations, laden or unladen have the same energy input. The flow geometry used is a straight pipe with length eight times its radius where the fluid is randomly seeded with 256 finite-size particles. The volume fraction of particles in the flow has been kept fixed at 0.48% by varying the major and minor axis of each particle such that their volume remains the same. We studied the effect of different particle shapes on particle dynamics and orientation, as well as on the flow modulation. We show that the local accumulation of spheres close to the wall decreases for spheroids with increasing aspect ratio. These spheroidal particles rotate slower than spheres near to the wall and tend to stay with their major axes aligned to the flow streamwise direction. Despite the lower rotation rates, a higher intermittency in the rotational rates was observed for spheroids and this increase at increasing the aspect ratio. The drag reduction observed for particles with higher aspect ratio have also been investigated using the one-dimensional energy and dissipation spectra. These results point to the relevance of particle shapes on their dynamics and their influence on the turbulent flow.}, keywords = {Problems and Applications, Topical issue: Flowing Matter}, pubstate = {published}, tppubtype = {article} } Anisotropic particles are present in many natural and industrial flows. Here we perform direct numerical simulation (DNS) of turbulent pipe flows with dispersed finite-size prolate spheroids simulated by means of the lattice Boltzmann method (LBM). We consider three different particle shapes: spheroidal (aspect ratio 2 and 3) and spherical. These three simulations are complemented with a reference simulation of a single-phase flow. For the sake of comparison, all simulations, laden or unladen have the same energy input. The flow geometry used is a straight pipe with length eight times its radius where the fluid is randomly seeded with 256 finite-size particles. The volume fraction of particles in the flow has been kept fixed at 0.48% by varying the major and minor axis of each particle such that their volume remains the same. We studied the effect of different particle shapes on particle dynamics and orientation, as well as on the flow modulation. We show that the local accumulation of spheres close to the wall decreases for spheroids with increasing aspect ratio. These spheroidal particles rotate slower than spheres near to the wall and tend to stay with their major axes aligned to the flow streamwise direction. Despite the lower rotation rates, a higher intermittency in the rotational rates was observed for spheroids and this increase at increasing the aspect ratio. The drag reduction observed for particles with higher aspect ratio have also been investigated using the one-dimensional energy and dissipation spectra. These results point to the relevance of particle shapes on their dynamics and their influence on the turbulent flow. | |
Daniel A Beller; Kim M J Alards; Francesca Tesser; Ricardo A Mosna; Federico Toschi; Wolfram M ö Evolution of populations expanding on curved surfaces Journal Article EPL, 123 (5), 2018, ISSN: 0295-5075. Abstract | Links | BibTeX | Tags: @article{d3f9ebd509d54075b1c4f2049e7689c4, title = {Evolution of populations expanding on curved surfaces}, author = {{Daniel A } Beller and {Kim M J } Alards and Francesca Tesser and {Ricardo A } Mosna and Federico Toschi and Wolfram M ö}, doi = {10.1209/0295-5075/123/58005}, issn = {0295-5075}, year = {2018}, date = {2018-01-01}, journal = {EPL}, volume = {123}, number = {5}, publisher = {Institute of Physics}, abstract = {The expansion of a population into new habitat is a transient process that leaves its footprints in the genetic composition of the expanding population. How the structure of the environment shapes the population front and the evolutionary dynamics during such a range expansion is little understood. Here, we investigate the evolutionary dynamics of populations consisting of many selectively neutral genotypes expanding on curved surfaces. Using a combination of individual-based off-lattice simulations, geometrical arguments, and lattice-based stepping-stone simulations, we characterise the effect of individual bumps on an otherwise flat surface. Compared to the case of a range expansion on a flat surface, we observe a transient relative increase, followed by a decrease, in neutral genetic diversity at the population front. In addition, we find that individuals at the sides of the bump have a dramatically increased expected number of descendants, while their neighbours closer to the bump's centre are far less lucky. Both observations can be explained using an analytical description of straight paths (geodesics) on the curved surface. Complementing previous studies of heterogeneous flat environments, the findings here build our understanding of how complex environments shape the evolutionary dynamics of expanding populations.}, keywords = {}, pubstate = {published}, tppubtype = {article} } The expansion of a population into new habitat is a transient process that leaves its footprints in the genetic composition of the expanding population. How the structure of the environment shapes the population front and the evolutionary dynamics during such a range expansion is little understood. Here, we investigate the evolutionary dynamics of populations consisting of many selectively neutral genotypes expanding on curved surfaces. Using a combination of individual-based off-lattice simulations, geometrical arguments, and lattice-based stepping-stone simulations, we characterise the effect of individual bumps on an otherwise flat surface. Compared to the case of a range expansion on a flat surface, we observe a transient relative increase, followed by a decrease, in neutral genetic diversity at the population front. In addition, we find that individuals at the sides of the bump have a dramatically increased expected number of descendants, while their neighbours closer to the bump's centre are far less lucky. Both observations can be explained using an analytical description of straight paths (geodesics) on the curved surface. Complementing previous studies of heterogeneous flat environments, the findings here build our understanding of how complex environments shape the evolutionary dynamics of expanding populations. | |
Guillaume Tauzin; Luca Biferale; Mauro Sbragaglia; Abhineet Gupta; Federico Toschi; Andreas Bartel; Matthias Ehrhardt A numerical tool for the study of the hydrodynamic recovery of the Lattice Boltzmann Method Journal Article Computers & Fluids, 172 , pp. 241–250, 2018, ISSN: 0045-7930. Abstract | Links | BibTeX | Tags: Hydrodynamics, Lattice Boltzmann Method, Turbulence modeling @article{181b79e7a9204995b79fc0c169fde21f, title = {A numerical tool for the study of the hydrodynamic recovery of the Lattice Boltzmann Method}, author = {Guillaume Tauzin and Luca Biferale and Mauro Sbragaglia and Abhineet Gupta and Federico Toschi and Andreas Bartel and Matthias Ehrhardt}, doi = {10.1016/j.compfluid.2018.05.031}, issn = {0045-7930}, year = {2018}, date = {2018-01-01}, journal = {Computers & Fluids}, volume = {172}, pages = {241--250}, publisher = {Elsevier}, abstract = {We investigate the hydrodynamic recovery of Lattice Boltzmann Method (LBM) by analyzing exact balance relations for energy and enstrophy derived from averaging the equations of motion on sub-volumes of different sizes. In the context of 2D isotropic homogeneous turbulence, we first validate this approach on decaying turbulence by comparing the hydrodynamic recovery of an ensemble of LBM simulations against the one of an ensemble of Pseudo-Spectral (PS) simulations. We then conduct a benchmark of LBM simulations of forced turbulence with increasing Reynolds number by varying the input relaxation times of LBM. This approach can be extended to the study of implicit subgrid-scale (SGS) models, thus offering a promising route to quantify the implicit SGS models implied by existing stabilization techniques within the LBM framework.}, keywords = {Hydrodynamics, Lattice Boltzmann Method, Turbulence modeling}, pubstate = {published}, tppubtype = {article} } We investigate the hydrodynamic recovery of Lattice Boltzmann Method (LBM) by analyzing exact balance relations for energy and enstrophy derived from averaging the equations of motion on sub-volumes of different sizes. In the context of 2D isotropic homogeneous turbulence, we first validate this approach on decaying turbulence by comparing the hydrodynamic recovery of an ensemble of LBM simulations against the one of an ensemble of Pseudo-Spectral (PS) simulations. We then conduct a benchmark of LBM simulations of forced turbulence with increasing Reynolds number by varying the input relaxation times of LBM. This approach can be extended to the study of implicit subgrid-scale (SGS) models, thus offering a promising route to quantify the implicit SGS models implied by existing stabilization techniques within the LBM framework. | |
G Di Staso; S Srivastava; E Arlemark; H J H Clercx; F Toschi Hybrid lattice Boltzmann-direct simulation Monte Carlo approach for flows in three-dimensional geometries Journal Article Computers & Fluids, 172 , pp. 492–509, 2018, ISSN: 0045-7930. Abstract | Links | BibTeX | Tags: Direct simulation Monte Carlo, Hybrid method, Kinetic theory, Lattice Boltzmann Method, Rarefied gas flows @article{c9750f5f458f48c999fa8f07e9f76c72, title = {Hybrid lattice Boltzmann-direct simulation Monte Carlo approach for flows in three-dimensional geometries}, author = {G {Di Staso} and S Srivastava and E Arlemark and {H J H } Clercx and F Toschi}, doi = {10.1016/j.compfluid.2018.03.043}, issn = {0045-7930}, year = {2018}, date = {2018-01-01}, journal = {Computers & Fluids}, volume = {172}, pages = {492--509}, publisher = {Elsevier}, abstract = {We present the results of a comparative study performed with three numerical methods applied to a flow in a three-dimensional geometry characterized by weak compressibility and large rarefaction effects. The employed methods, all based on the kinetic theory of gases, are the Lattice Boltzmann Method (LBM) in a regularized formulation, the Direct Simulation Monte Carlo (DSMC) approach and a hybrid method coupling the LBM and the DSMC recently developed by Di Staso et al., in this contribution extended to the case of simulations involving many particles and three-dimensional geometries. Owing to the common kinetic nature shared by the employed methods and to their implementation in a single code infrastructure, a detailed comparison of the results can be performed on a quantitative ground. The numerical results permit to determine, for the studied flow problem, the range of applicability in terms of a geometry-based Knudsen number for the present LBM formulation. The need to employ the hybrid method is justified by the very large computational cost of the DSMC simulation. Limitations of the current hybrid method formulation in treating thermal and large compressibility effects are underlined and possible strategies to overcome them are delineated. Finally, good scalability properties of the parallel algorithms, as well as the large computational cost reduction guaranteed by the hybrid method, while providing an accurate solution, are demonstrated.}, keywords = {Direct simulation Monte Carlo, Hybrid method, Kinetic theory, Lattice Boltzmann Method, Rarefied gas flows}, pubstate = {published}, tppubtype = {article} } We present the results of a comparative study performed with three numerical methods applied to a flow in a three-dimensional geometry characterized by weak compressibility and large rarefaction effects. The employed methods, all based on the kinetic theory of gases, are the Lattice Boltzmann Method (LBM) in a regularized formulation, the Direct Simulation Monte Carlo (DSMC) approach and a hybrid method coupling the LBM and the DSMC recently developed by Di Staso et al., in this contribution extended to the case of simulations involving many particles and three-dimensional geometries. Owing to the common kinetic nature shared by the employed methods and to their implementation in a single code infrastructure, a detailed comparison of the results can be performed on a quantitative ground. The numerical results permit to determine, for the studied flow problem, the range of applicability in terms of a geometry-based Knudsen number for the present LBM formulation. The need to employ the hybrid method is justified by the very large computational cost of the DSMC simulation. Limitations of the current hybrid method formulation in treating thermal and large compressibility effects are underlined and possible strategies to overcome them are delineated. Finally, good scalability properties of the parallel algorithms, as well as the large computational cost reduction guaranteed by the hybrid method, while providing an accurate solution, are demonstrated. | |
X Xue; M Sbragaglia; L Biferale; F Toschi Effects of thermal fluctuations in the fragmentation of a nanoligament Journal Article Physical Review E, 98 (1), 2018, ISSN: 2470-0045. Abstract | Links | BibTeX | Tags: @article{2091e326523f46f9b40375248ab42774, title = {Effects of thermal fluctuations in the fragmentation of a nanoligament}, author = {X Xue and M Sbragaglia and L Biferale and F Toschi}, doi = {10.1103/PhysRevE.98.012802}, issn = {2470-0045}, year = {2018}, date = {2018-01-01}, journal = {Physical Review E}, volume = {98}, number = {1}, publisher = {American Physical Society}, abstract = {We study the effects of thermally induced capillary waves in the fragmentation of a liquid ligament into multiple nanodroplets. Our numerical implementation is based on a fluctuating lattice Boltzmann (LB) model for nonideal multicomponent fluids, including nonequilibrium stochastic fluxes mimicking the effects of molecular forces at the nanoscales. We quantitatively analyze the statistical distribution of the breakup times and the droplet volumes after the fragmentation process at changing the two relevant length scales of the problem, i.e., the thermal length scale and the ligament size. The robustness of the observed findings is also corroborated by quantitative comparisons with the predictions of sharp interface hydrodynamics. Beyond the practical importance of our findings for nanofluidic engineering devices, our study also explores a novel application of LB in the realm of nanofluidic phenomena.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We study the effects of thermally induced capillary waves in the fragmentation of a liquid ligament into multiple nanodroplets. Our numerical implementation is based on a fluctuating lattice Boltzmann (LB) model for nonideal multicomponent fluids, including nonequilibrium stochastic fluxes mimicking the effects of molecular forces at the nanoscales. We quantitatively analyze the statistical distribution of the breakup times and the droplet volumes after the fragmentation process at changing the two relevant length scales of the problem, i.e., the thermal length scale and the ligament size. The robustness of the observed findings is also corroborated by quantitative comparisons with the predictions of sharp interface hydrodynamics. Beyond the practical importance of our findings for nanofluidic engineering devices, our study also explores a novel application of LB in the realm of nanofluidic phenomena. | |
Alessandro Corbetta; Werner Kroneman; Maurice Donners; Antal Haans; Philip Ross; Marius Trouwborst; Sander van de Wijdeven; Martijn Hultermans; Dragan Sekulovski; Fedosja van der Heijden; Sjoerd Mentink; Federico Toschi A large-scale real-life crowd steering experiment via arrow-like stimuli Inproceedings Proceedings of Pedestrian and Evacuation Dynamics 2018, 2018. BibTeX | Tags: @inproceedings{8c563d077c6548dd8e8c49b4ee39952a, title = {A large-scale real-life crowd steering experiment via arrow-like stimuli}, author = {Alessandro Corbetta and Werner Kroneman and Maurice Donners and Antal Haans and Philip Ross and Marius Trouwborst and Sander {van de Wijdeven} and Martijn Hultermans and Dragan Sekulovski and Fedosja {van der Heijden} and Sjoerd Mentink and Federico Toschi}, year = {2018}, date = {2018-01-01}, booktitle = {Proceedings of Pedestrian and Evacuation Dynamics 2018}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } | |
A Gupta; H J H Clercx; F Toschi Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow Journal Article European Physical Journal E, 41 (3), 2018. BibTeX | Tags: @article{RID:0801180259191-202, title = {Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow}, author = {A Gupta and H J H Clercx and F Toschi}, year = {2018}, date = {2018-01-01}, journal = {European Physical Journal E}, volume = {41}, number = {3}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
K M J Alards; H Rajaei; R P J Kunnen; F Toschi; H J H Clercx Directional change of tracer trajectories in rotating Rayleigh-Benard convection Journal Article Physical Review E, 97 (6), 2018. BibTeX | Tags: @article{RID:0801180259191-291, title = {Directional change of tracer trajectories in rotating Rayleigh-Benard convection}, author = {K M J Alards and H Rajaei and R P J Kunnen and F Toschi and H J H Clercx}, year = {2018}, date = {2018-01-01}, journal = {Physical Review E}, volume = {97}, number = {6}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
G Di Staso; S Srivastava; E Arlemark; H J H Clercx; F Toschi Hybrid lattice Boltzmann-Direct Simulation Monte Carlo approach for non-equilibrium flows in complex geometries Inproceedings Proceedings of the 5th European Conference on Microfluidics - mFlu18 & 3rd European Conference on Non-Equilibrium Gas Flows - NEGF18, February 28-March 2, 2018, Strasbourg, France, pp. 1–4, 2018. BibTeX | Tags: @inproceedings{735b15fe550244e59bc92cfe94563943, title = {Hybrid lattice Boltzmann-Direct Simulation Monte Carlo approach for non-equilibrium flows in complex geometries}, author = {G {Di Staso} and S Srivastava and E Arlemark and H J H Clercx and F Toschi}, year = {2018}, date = {2018-01-01}, booktitle = {Proceedings of the 5th European Conference on Microfluidics - mFlu18 & 3rd European Conference on Non-Equilibrium Gas Flows - NEGF18, February 28-March 2, 2018, Strasbourg, France}, pages = {1--4}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } | |
F Milan; M Sbragaglia; L Biferale; F Toschi Lattice Boltzmann simulations of droplet dynamics in time-dependent flows Journal Article European Physical Journal E, 41 (1), 2018. BibTeX | Tags: @article{RID:0801180259191-183, title = {Lattice Boltzmann simulations of droplet dynamics in time-dependent flows}, author = {F Milan and M Sbragaglia and L Biferale and F Toschi}, year = {2018}, date = {2018-01-01}, journal = {European Physical Journal E}, volume = {41}, number = {1}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
A Scagliarini; E Calzavarini; Daniela Mansutti; F Toschi Modelling sea ice and melt ponds evolution: sensitivity to microscale heat transfer mechanisms Journal Article arXiv, 2018 , 2018. @article{05a494845f7c4dcbbca95ca054bffb5b, title = {Modelling sea ice and melt ponds evolution: sensitivity to microscale heat transfer mechanisms}, author = {A Scagliarini and E Calzavarini and Daniela Mansutti and F Toschi}, year = {2018}, date = {2018-01-01}, journal = {arXiv}, volume = {2018}, publisher = {Cornell University Library}, abstract = {We present a mathematical model describing the evolution of sea ice and meltwater during summer. The system is described by two coupled partial differential equations for the ice thickness h and pond depth w fields. We test the sensitivity of the model to variations of parameters controlling fluid-dynamic processes at the pond level, namely the variation of turbulent heat flux with pond depth and the lateral melting of ice enclosing a pond. We observe that different heat flux scalings determine different rates of total surface ablations, while the system is relatively robust for what concerns the statistical distributions of pond surface areas, which are extracted by means of cluster analysis. Finally, we study pond morphology in terms of fractal dimensions, showing that the role of lateral melting is minor, whereas there is evidence of an impact from the initial sea ice topography.}, keywords = {}, pubstate = {published}, tppubtype = {article} } We present a mathematical model describing the evolution of sea ice and meltwater during summer. The system is described by two coupled partial differential equations for the ice thickness h and pond depth w fields. We test the sensitivity of the model to variations of parameters controlling fluid-dynamic processes at the pond level, namely the variation of turbulent heat flux with pond depth and the lateral melting of ice enclosing a pond. We observe that different heat flux scalings determine different rates of total surface ablations, while the system is relatively robust for what concerns the statistical distributions of pond surface areas, which are extracted by means of cluster analysis. Finally, we study pond morphology in terms of fractal dimensions, showing that the role of lateral melting is minor, whereas there is evidence of an impact from the initial sea ice topography. | |
A Gupta; H J H Clercx; F Toschi Simulation of Finite-Size Particles in Turbulent Flows Using the Lattice Boltzmann Method Journal Article Communications in Computational Physics, 23 (3), pp. 665-684, 2018. BibTeX | Tags: @article{RID:0801180259191-257, title = {Simulation of Finite-Size Particles in Turbulent Flows Using the Lattice Boltzmann Method}, author = {A Gupta and H J H Clercx and F Toschi}, year = {2018}, date = {2018-01-01}, journal = {Communications in Computational Physics}, volume = {23}, number = {3}, pages = {665-684}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
2017 |
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A Corbetta; V Menkovski; F Toschi Weakly supervised training of deep convolutional neural networks for overhead pedestrian localization in depth fields Inproceedings 2017 14th IEEE International Conference on Advanced Video and Signal Based Surveillance, AVSS 2017, pp. 1–6, Institute of Electrical and Electronics Engineers, United States, 2017, ISBN: 978-1-5386-2940-6. Abstract | Links | BibTeX | Tags: @inproceedings{3920d05b3db34a7fadde93466f695348, title = {Weakly supervised training of deep convolutional neural networks for overhead pedestrian localization in depth fields}, author = {A Corbetta and V Menkovski and F Toschi}, doi = {10.1109/AVSS.2017.8078490}, isbn = {978-1-5386-2940-6}, year = {2017}, date = {2017-01-01}, booktitle = {2017 14th IEEE International Conference on Advanced Video and Signal Based Surveillance, AVSS 2017}, pages = {1--6}, publisher = {Institute of Electrical and Electronics Engineers}, address = {United States}, abstract = {Overhead depth map measurements capture sufficient amount of information to enable human experts to track pedestrians accurately. However, fully automating this process using image analysis algorithms can be challenging. Even though hand-crafted image analysis algorithms are successful in many common cases, they fail frequently when there are complex interactions of multiple objects in the image. Many of the assumptions underpinning the hand-crafted solutions do not hold in these cases and the multitude of exceptions are hard to model precisely. Deep Learning (DL) algorithms, on the other hand, do not require hand crafted solutions and are the current state-of-the-art in object localization in images. However, they require exceeding amount of annotations to produce successful models. In the case of object localization, these annotations are difficult and time consuming to produce. In this work we present an approach for developing pedestrian localization models using DL algorithms with efficient weak supervision from an expert. We circumvent the need for annotation of large corpus of data by annotating only small amount of patches and relying on synthetic data augmentation as a vehicle for injecting expert knowledge in the model training. This approach of weak supervision through expert selection of representative patches, suitable transformations and synthetic data augmentations enables us to successfully develop DL models for pedestrian localization efficiently.}, keywords = {}, pubstate = {published}, tppubtype = {inproceedings} } Overhead depth map measurements capture sufficient amount of information to enable human experts to track pedestrians accurately. However, fully automating this process using image analysis algorithms can be challenging. Even though hand-crafted image analysis algorithms are successful in many common cases, they fail frequently when there are complex interactions of multiple objects in the image. Many of the assumptions underpinning the hand-crafted solutions do not hold in these cases and the multitude of exceptions are hard to model precisely. Deep Learning (DL) algorithms, on the other hand, do not require hand crafted solutions and are the current state-of-the-art in object localization in images. However, they require exceeding amount of annotations to produce successful models. In the case of object localization, these annotations are difficult and time consuming to produce. In this work we present an approach for developing pedestrian localization models using DL algorithms with efficient weak supervision from an expert. We circumvent the need for annotation of large corpus of data by annotating only small amount of patches and relying on synthetic data augmentation as a vehicle for injecting expert knowledge in the model training. This approach of weak supervision through expert selection of representative patches, suitable transformations and synthetic data augmentations enables us to successfully develop DL models for pedestrian localization efficiently. | |
A Corbetta; C -M Lee; A Muntean; F Toschi Frame vs. trajectory analyses of pedestrian dynamics asymmetries in a staircase landing Journal Article Collective Dynamics, 1 (A10), pp. 1–26, 2017, ISSN: 2366-8539. Abstract | Links | BibTeX | Tags: @article{c9d76a1b63fb406b81daaf598f6126a6, title = {Frame vs. trajectory analyses of pedestrian dynamics asymmetries in a staircase landing}, author = {A Corbetta and C -M Lee and A Muntean and F Toschi}, doi = {10.17815/CD.2017.10}, issn = {2366-8539}, year = {2017}, date = {2017-01-01}, journal = {Collective Dynamics}, volume = {1}, number = {A10}, pages = {1--26}, publisher = {Forschungszentrum Jülich}, abstract = {Real-life, out-of-laboratory, measurements of pedestrian walking dynamics allow extensive and fully-resolved statistical analyses. However, data acquisition in real-life is subjected to the randomness and heterogeneity that characterizes crowd flows over time. In a typical real-life location, disparate flow conditions follow one another in random order: for instance, a low density pedestrian co-flow dynamics may suddenly turn into a high density counter-flow scenario and then back again. Isolating occurrences of similar flow conditions within the acquired data is a paramount first step in the analyses in order to avoid spurious statistics and to enable qualitative comparisons.In this paper we extend our previous investigation on the asymmetric pedestrian dynamics on a staircase landing, where we collected a large statistical database of measurements from ad hoc continuous recordings. This contribution has a two-fold aim: first, method-wise, we discuss an analysis workflow to consider large-scale experimental measurements, suggesting two querying approaches to automatically extract occurrences of similar flow scenarios out of datasets. These pursue aggregation of similar scenarios on either a frame or a trajectory basis. Second, we employ these two different perspectives to further explore asymmetries in the pedestrian dynamics in our measurement site. We report cross-comparisons of statistics of pedestrian positions, velocities and accelerations vs. flow conditions as well as vs. querying approach.}, keywords = {}, pubstate = {published}, tppubtype = {article} } Real-life, out-of-laboratory, measurements of pedestrian walking dynamics allow extensive and fully-resolved statistical analyses. However, data acquisition in real-life is subjected to the randomness and heterogeneity that characterizes crowd flows over time. In a typical real-life location, disparate flow conditions follow one another in random order: for instance, a low density pedestrian co-flow dynamics may suddenly turn into a high density counter-flow scenario and then back again. Isolating occurrences of similar flow conditions within the acquired data is a paramount first step in the analyses in order to avoid spurious statistics and to enable qualitative comparisons.In this paper we extend our previous investigation on the asymmetric pedestrian dynamics on a staircase landing, where we collected a large statistical database of measurements from ad hoc continuous recordings. This contribution has a two-fold aim: first, method-wise, we discuss an analysis workflow to consider large-scale experimental measurements, suggesting two querying approaches to automatically extract occurrences of similar flow scenarios out of datasets. These pursue aggregation of similar scenarios on either a frame or a trajectory basis. Second, we employ these two different perspectives to further explore asymmetries in the pedestrian dynamics in our measurement site. We report cross-comparisons of statistics of pedestrian positions, velocities and accelerations vs. flow conditions as well as vs. querying approach. | |
H Ardeshiri; F G Schmitt; S Souissi; F Toschi; E Calzavarini Copepods encounter rates from a model of escape jump behaviour in turbulence Journal Article Journal of Plankton Research, 39 (6), pp. 878-890, 2017. BibTeX | Tags: @article{RID:0801180259191-299, title = {Copepods encounter rates from a model of escape jump behaviour in turbulence}, author = {H Ardeshiri and F G Schmitt and S Souissi and F Toschi and E Calzavarini}, year = {2017}, date = {2017-01-01}, journal = {Journal of Plankton Research}, volume = {39}, number = {6}, pages = {878-890}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
M A T van Hinsberg; H J H Clercx; F Toschi Enhanced settling of nonheavy inertial particles in homogeneous isotropic turbulence: The role of the pressure gradient and the Basset history force Journal Article Physical Review E, 95 (2), 2017. BibTeX | Tags: @article{RID:0801180259191-171, title = {Enhanced settling of nonheavy inertial particles in homogeneous isotropic turbulence: The role of the pressure gradient and the Basset history force}, author = {M A T van Hinsberg and H J H Clercx and F Toschi}, year = {2017}, date = {2017-01-01}, journal = {Physical Review E}, volume = {95}, number = {2}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
F Tesser; J C H Zeegers; H J H Clercx; L Brunsveld; F Toschi Finite-size effects on bacterial population expansion under controlled flow conditions Journal Article Scientific Reports, 7 , 2017. BibTeX | Tags: @article{RID:0801180259191-155, title = {Finite-size effects on bacterial population expansion under controlled flow conditions}, author = {F Tesser and J C H Zeegers and H J H Clercx and L Brunsveld and F Toschi}, year = {2017}, date = {2017-01-01}, journal = {Scientific Reports}, volume = {7}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
L Campo-Deano; N Araujo; I P Mora; F Toschi Flowing Matter 2017 Journal Article Applied Rheology, 27 (3), pp. 47-49, 2017. BibTeX | Tags: @article{RID:0801180259192-336, title = {Flowing Matter 2017}, author = {L Campo-Deano and N Araujo and I P Mora and F Toschi}, year = {2017}, date = {2017-01-01}, journal = {Applied Rheology}, volume = {27}, number = {3}, pages = {47-49}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
A Corbetta; C M Lee; R Benzi; A Muntean; F Toschi Fluctuations around mean walking behaviors in diluted pedestrian flows Journal Article Physical Review E, 95 (3), 2017. BibTeX | Tags: @article{RID:0801180259192-292, title = {Fluctuations around mean walking behaviors in diluted pedestrian flows}, author = {A Corbetta and C M Lee and R Benzi and A Muntean and F Toschi}, year = {2017}, date = {2017-01-01}, journal = {Physical Review E}, volume = {95}, number = {3}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
K M J Alards; H Rajaei; L Del Castello; R P J Kunnen; F Toschi; H J H Clercx Geometry of tracer trajectories in rotating turbulent flows Journal Article Physical Review Fluids, 2 (4), 2017. BibTeX | Tags: @article{RID:0801180259192-249, title = {Geometry of tracer trajectories in rotating turbulent flows}, author = {K M J Alards and H Rajaei and L Del Castello and R P J Kunnen and F Toschi and H J H Clercx}, year = {2017}, date = {2017-01-01}, journal = {Physical Review Fluids}, volume = {2}, number = {4}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
A Haans; A Corbetta; P P Kumar; F Toschi 2017, (2017 International Conference on Environmental Psychology (ICEP 2017), August 30- September 1, 2017, Coru~na, Spain, ICEP 2017 ; Conference date: 30-08-2017 Through 01-09-2017). @conference{36c926c51fa041358d345f909ee37e97, title = {Measuring the effect of dynamic lighting on pedestrian speed by means of overhead kinectTM sensors and continuous pedestrian tracking algorithms}, author = {A Haans and A Corbetta and P P Kumar and F Toschi}, url = {http://www.icep2017.org/}, year = {2017}, date = {2017-01-01}, pages = {219--219}, note = {2017 International Conference on Environmental Psychology (ICEP 2017), August 30- September 1, 2017, Coru~na, Spain, ICEP 2017 ; Conference date: 30-08-2017 Through 01-09-2017}, keywords = {}, pubstate = {published}, tppubtype = {conference} } | |
K P Iyer; F Bonaccorso; L Biferale; F Toschi Multiscale anisotropic fluctuations in sheared turbulence with multiple states Journal Article Physical Review Fluids, 2 (5), 2017. BibTeX | Tags: @article{RID:0801180259192-264, title = {Multiscale anisotropic fluctuations in sheared turbulence with multiple states}, author = {K P Iyer and F Bonaccorso and L Biferale and F Toschi}, year = {2017}, date = {2017-01-01}, journal = {Physical Review Fluids}, volume = {2}, number = {5}, keywords = {}, pubstate = {published}, tppubtype = {article} } | |
R Benzi; L Biferale; F Bonaccorso; H J H Clercx; A Corbetta; W Mobius; F Toschi; F Salvadore; C Cacciari; G Erbacci TurBase: a software platform for research in experimental and numerical fluid dynamics Book 2017. BibTeX | Tags: @book{RID:0801180259192-328, title = {TurBase: a software platform for research in experimental and numerical fluid dynamics}, author = {R Benzi and L Biferale and F Bonaccorso and H J H Clercx and A Corbetta and W Mobius and F Toschi and F Salvadore and C Cacciari and G Erbacci}, editor = {W W Smari}, year = {2017}, date = {2017-01-01}, pages = {51-57}, series = {2017 International Conference on High Performance Computing & Simulation}, keywords = {}, pubstate = {published}, tppubtype = {book} } | |
A Corbetta; V Menkovski; F Toschi; Ieee Weakly supervised training of deep convolutional neural networks for overhead pedestrian localization in depth fields Book 2017. BibTeX | Tags: @book{RID:0801180259192-345, title = {Weakly supervised training of deep convolutional neural networks for overhead pedestrian localization in depth fields}, author = {A Corbetta and V Menkovski and F Toschi and Ieee}, year = {2017}, date = {2017-01-01}, series = {2017 14th Ieee International Conference on Advanced Video and Signal Based Surveillance}, keywords = {}, pubstate = {published}, tppubtype = {book} } | |
2016 |
|
A Corbetta; C -M Lee; R Benzi; A Muntean; F Toschi Fluctuations around mean walking behaviours in diluted pedestrian flows Journal Article arXiv.org, e-Print Archive, Physics, (1610.07429v1), pp. 1–10, 2016. Abstract | BibTeX | Tags: physics.data-an, physics.soc-ph @article{ba1dbdb0ddd24f03bd2313cde67ca761, title = {Fluctuations around mean walking behaviours in diluted pedestrian flows}, author = {A Corbetta and C -M Lee and R Benzi and A Muntean and F Toschi}, year = {2016}, date = {2016-01-01}, journal = {arXiv.org, e-Print Archive, Physics}, number = {1610.07429v1}, pages = {1--10}, abstract = {Understanding and modeling the dynamics of pedestrian crowds can help with designing and increasing the safety of civil facilities. A key feature of crowds is its intrinsic stochasticity, appearing even under very diluted conditions, due to the variability in individual behaviours. Individual stochasticity becomes even more important under densely crowded conditions, since it can be nonlinearly magnified and may lead to potentially dangerous collective behaviours. To understand quantitatively crowd stochasticity, we study the real-life dynamics of a large ensemble of pedestrians walking undisturbed, and we perform a statistical analysis of the fully-resolved pedestrian trajectories obtained by a year-long high-resolution measurement campaign. Our measurements have been carried out in a corridor of the Eindhoven University of Technology via a combination of Microsoft Kinect 3D-range sensor and automatic head-tracking algorithms. The temporal homogeneity of our large database of trajectories allows us to robustly define and separate average walking behaviours from fluctuations parallel and orthogonal with respect to the average walking path. Fluctuations include rare events when individuals suddenly change their minds and invert their walking direction. Such tendency to invert direction has been poorly studied so far even if it may have important implications on the functioning and safety of facilities. We propose a novel model for the dynamics of undisturbed pedestrians, based on stochastic differential equations, that provides a good agreement with our experimental observations, including the occurrence of rare events.}, keywords = {physics.data-an, physics.soc-ph}, pubstate = {published}, tppubtype = {article} } Understanding and modeling the dynamics of pedestrian crowds can help with designing and increasing the safety of civil facilities. A key feature of crowds is its intrinsic stochasticity, appearing even under very diluted conditions, due to the variability in individual behaviours. Individual stochasticity becomes even more important under densely crowded conditions, since it can be nonlinearly magnified and may lead to potentially dangerous collective behaviours. To understand quantitatively crowd stochasticity, we study the real-life dynamics of a large ensemble of pedestrians walking undisturbed, and we perform a statistical analysis of the fully-resolved pedestrian trajectories obtained by a year-long high-resolution measurement campaign. Our measurements have been carried out in a corridor of the Eindhoven University of Technology via a combination of Microsoft Kinect 3D-range sensor and automatic head-tracking algorithms. The temporal homogeneity of our large database of trajectories allows us to robustly define and separate average walking behaviours from fluctuations parallel and orthogonal with respect to the average walking path. Fluctuations include rare events when individuals suddenly change their minds and invert their walking direction. Such tendency to invert direction has been poorly studied so far even if it may have important implications on the functioning and safety of facilities. We propose a novel model for the dynamics of undisturbed pedestrians, based on stochastic differential equations, that provides a good agreement with our experimental observations, including the occurrence of rare events. | |
A Corbetta; J A Meeusen; C -M Lee; F Toschi Continuous measurements of real-life bidirectional pedestrian flows on a wide walkway Journal Article arXiv, pp. 1–9, 2016, (9 pages, 7 figures). Abstract | BibTeX | Tags: physics.data-an, physics.soc-ph @article{68dcea056c30443eaa8e4cafce542089, title = {Continuous measurements of real-life bidirectional pedestrian flows on a wide walkway}, author = {A Corbetta and J A Meeusen and C -M Lee and F Toschi}, year = {2016}, date = {2016-01-01}, journal = {arXiv}, pages = {1--9}, publisher = {Cornell University Library}, abstract = {Employing partially overlapping overhead kinectTMS sensors and automatic pedestrian tracking algorithms we recorded the crowd traffic in a rectilinear section of the main walkway of Eindhoven train station on a 24/7 basis. Beside giving access to the train platforms (it passes underneath the railways), the walkway plays an important connection role in the city. Several crowding scenarios occur during the day, including high- and low-density dynamics in uni- and bi-directional regimes. In this paper we discuss our recording technique and we illustrate preliminary data analyses. Via fundamental diagrams-like representations we report pedestrian velocities and fluxes vs. pedestrian density. Considering the density range $0$ - $1.1,$ped/m$^2$, we find that at densities lower than $0.8,$ped/m$^2$ pedestrians in unidirectional flows walk faster than in bidirectional regimes. On the opposite, velocities and fluxes for even bidirectional flows are higher above $0.8,$ped/m$^2$.}, note = {9 pages, 7 figures}, keywords = {physics.data-an, physics.soc-ph}, pubstate = {published}, tppubtype = {article} } Employing partially overlapping overhead kinectTMS sensors and automatic pedestrian tracking algorithms we recorded the crowd traffic in a rectilinear section of the main walkway of Eindhoven train station on a 24/7 basis. Beside giving access to the train platforms (it passes underneath the railways), the walkway plays an important connection role in the city. Several crowding scenarios occur during the day, including high- and low-density dynamics in uni- and bi-directional regimes. In this paper we discuss our recording technique and we illustrate preliminary data analyses. Via fundamental diagrams-like representations we report pedestrian velocities and fluxes vs. pedestrian density. Considering the density range $0$ - $1.1,$ped/m$^2$, we find that at densities lower than $0.8,$ped/m$^2$ pedestrians in unidirectional flows walk faster than in bidirectional regimes. On the opposite, velocities and fluxes for even bidirectional flows are higher above $0.8,$ped/m$^2$. | |
A Corbetta; C -M Lee; A Muntean; F Toschi Eulerian vs. Lagrangian analyses of pedestrian dynamics asymmetries in a staircase landing Book arXiv.org, 2016. Abstract | BibTeX | Tags: physics.data-an, physics.soc-ph @book{48dcd3f0eced41bcb82e21e2bf27e727, title = {Eulerian vs. Lagrangian analyses of pedestrian dynamics asymmetries in a staircase landing}, author = {A Corbetta and C -M Lee and A Muntean and F Toschi}, year = {2016}, date = {2016-01-01}, publisher = {arXiv.org}, abstract = {Real-life, out-of-laboratory, measurements of pedestrian movements allow extensive and fully-resolved statistical analyses. However, data acquisition in real-life is subjected to the wide heterogeneity that characterizes crowd flows over time. Disparate flow conditions, such as co-flows and counter-flows at low and at high pedestrian densities, typically follow randomly one another. When analysing the data in order to study the dynamics and behaviour of pedestrians it is crucial to be able disentangle and to properly select (query) data from statistically homogeneous flow conditions in order to avoid spurious statistics and to enable qualitative comparisons. In this paper we extend our previous analysis on the asymmetric pedestrian dynamics on a staircase landing, where we collected a large statistical database of measurements from ad hoc continuous recordings. This contribution has a two-fold aim: first, method-wise, we discuss two possible approaches to query experimental datasets for homogeneous flow conditions. For given flow conditions, we can either agglomerate measurements on a time-frame basis (Eulerian queries) or on a trajectory basis (Lagrangian queries). Second, we employ these two different perspectives to further explore asymmetries in the pedestrian dynamics in our measurement site. We report cross-comparisons of statistics of pedestrian positions, velocities and accelerations vs. flow conditions as well as vs. Eulerian or Lagrangian approach.}, keywords = {physics.data-an, physics.soc-ph}, pubstate = {published}, tppubtype = {book} } Real-life, out-of-laboratory, measurements of pedestrian movements allow extensive and fully-resolved statistical analyses. However, data acquisition in real-life is subjected to the wide heterogeneity that characterizes crowd flows over time. Disparate flow conditions, such as co-flows and counter-flows at low and at high pedestrian densities, typically follow randomly one another. When analysing the data in order to study the dynamics and behaviour of pedestrians it is crucial to be able disentangle and to properly select (query) data from statistically homogeneous flow conditions in order to avoid spurious statistics and to enable qualitative comparisons. In this paper we extend our previous analysis on the asymmetric pedestrian dynamics on a staircase landing, where we collected a large statistical database of measurements from ad hoc continuous recordings. This contribution has a two-fold aim: first, method-wise, we discuss two possible approaches to query experimental datasets for homogeneous flow conditions. For given flow conditions, we can either agglomerate measurements on a time-frame basis (Eulerian queries) or on a trajectory basis (Lagrangian queries). Second, we employ these two different perspectives to further explore asymmetries in the pedestrian dynamics in our measurement site. We report cross-comparisons of statistics of pedestrian positions, velocities and accelerations vs. flow conditions as well as vs. Eulerian or Lagrangian approach. | |
S Kramel; G A Voth; S Tympel; F Toschi Preferential rotation of chiral dipoles in isotropic turbulence Journal Article arXiv.org, e-Print Archive, Physics, 2016. Abstract | BibTeX | Tags: physics.flu-dyn @article{05679cb42abe4f178b839c71697fa9f8, title = {Preferential rotation of chiral dipoles in isotropic turbulence}, author = {S Kramel and G A Voth and S Tympel and F Toschi}, year = {2016}, date = {2016-01-01}, journal = {arXiv.org, e-Print Archive, Physics}, abstract = {Particles in the shape of chiral dipoles show a preferential rotation in three dimensional homogeneous isotropic turbulence. A chiral dipole consists of a rod with two helices of opposite handedness, one at each end. We can use 3d printing to fabricate these particles with length in the inertial range and track their rotations in a turbulent flow between oscillating grids. High aspect ratio chiral dipoles will align with the extensional eigenvectors of the strain rate tensor and the helical ends will respond to the strain field by spinning around its long axis. The mean of the measured spinning rate is non-zero and reflects the average stretching the particles experience. We use Stokesian dynamics simulations of chiral dipoles in pure strain flow to quantify the dependence of spinning on particle shape. Based on the known response to pure strain, we build a model that gives the spinning rate of small chiral dipoles using Lagrangian velocity gradients from high resolution direct numerical simulations. The statistics of chiral dipole spinning determined with this model show surprisingly good agreement with the measured spinning of much larger chiral dipoles in the experiments.}, keywords = {physics.flu-dyn}, pubstate = {published}, tppubtype = {article} } Particles in the shape of chiral dipoles show a preferential rotation in three dimensional homogeneous isotropic turbulence. A chiral dipole consists of a rod with two helices of opposite handedness, one at each end. We can use 3d printing to fabricate these particles with length in the inertial range and track their rotations in a turbulent flow between oscillating grids. High aspect ratio chiral dipoles will align with the extensional eigenvectors of the strain rate tensor and the helical ends will respond to the strain field by spinning around its long axis. The mean of the measured spinning rate is non-zero and reflects the average stretching the particles experience. We use Stokesian dynamics simulations of chiral dipoles in pure strain flow to quantify the dependence of spinning on particle shape. Based on the known response to pure strain, we build a model that gives the spinning rate of small chiral dipoles using Lagrangian velocity gradients from high resolution direct numerical simulations. The statistics of chiral dipole spinning determined with this model show surprisingly good agreement with the measured spinning of much larger chiral dipoles in the experiments. | |
A Corbetta; C -M Lee; A Muntean; F Toschi Asymmetric pedestrian dynamics on a staircase landing from continuous measurements Book Chapter V L Knoop; W Daamen (Ed.): Traffic and Granular Flow '15, pp. 49–56, Springer, Germany, 2016, ISBN: 978-3-319-33481-3, (8 pages). Abstract | Links | BibTeX | Tags: physics.soc-ph @inbook{f2810bf56d4e4f15a67ed06087ee40df, title = {Asymmetric pedestrian dynamics on a staircase landing from continuous measurements}, author = {A Corbetta and C -M Lee and A Muntean and F Toschi}, editor = {V L Knoop and W Daamen}, doi = {10.1007/978-3-319-33482-0_7}, isbn = {978-3-319-33481-3}, year = {2016}, date = {2016-01-01}, booktitle = {Traffic and Granular Flow '15}, pages = {49--56}, publisher = {Springer}, address = {Germany}, abstract = {We investigate via extensive experimental data the dynamics of pedestrians walking in a corridor-shaped landing in a building at Eindhoven University of Technology. With year-long automatic measurements employing a Microsoft KinectTM 3D-range sensor and ad hoc tracking techniques, we acquired few hundreds of thousands pedestrian trajectories in real-life conditions. Here we discuss the asymmetric features of the dynamics in the two walking directions with respect to the flights of stairs (i.e. ascending or descending). We provide a detailed analysis of position and speed fields for the cases of pedestrians walking alone undisturbed and for couple of pedestrians in counter-flow. Then, we show average walking velocities exploring all the observed combinations in terms of numbers of pedestrians and walking directions.}, note = {8 pages}, keywords = {physics.soc-ph}, pubstate = {published}, tppubtype = {inbook} } We investigate via extensive experimental data the dynamics of pedestrians walking in a corridor-shaped landing in a building at Eindhoven University of Technology. With year-long automatic measurements employing a Microsoft KinectTM 3D-range sensor and ad hoc tracking techniques, we acquired few hundreds of thousands pedestrian trajectories in real-life conditions. Here we discuss the asymmetric features of the dynamics in the two walking directions with respect to the flights of stairs (i.e. ascending or descending). We provide a detailed analysis of position and speed fields for the cases of pedestrians walking alone undisturbed and for couple of pedestrians in counter-flow. Then, we show average walking velocities exploring all the observed combinations in terms of numbers of pedestrians and walking directions. | |
publications
2020 |
|
Topological structure and dynamics of three-dimensional active nematics Journal Article Science, 367 (6482), pp. 1120–1124, 2020, ISSN: 0036-8075. | |
Statistical properties of turbulence in the presence of a smart small-scale control Journal Article Physical Review Letters, 124 (8), 2020, ISSN: 0031-9007. | |
On interevent time distributions of avalanche dynamics Journal Article Scientific Reports, 10 (1), 2020, ISSN: 2045-2322. | |
Pedestrian orientation dynamics from high-fidelity measurements Journal Article arXiv, 2020. | |
2019 |
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Unified theoretical and experimental view on transient shear banding Journal Article Physical Review Letters, 123 (24), 2019, ISSN: 0031-9007. | |
Discrete Eulerian model for population genetics and dynamics under flow Journal Article Physical Review E, 100 (6), 2019, ISSN: 2470-0045. | |
Deep learning velocity signals allows to quantify turbulence intensity Journal Article arXiv, 2019. | |
Topological structure and dynamics of three dimensional active nematics Journal Article arXiv, 2019, (13 pages, 5 figures, plus Supplementary Information of 12 pages, 4 figures). | |
Statistical properties of thermally expandable particles in soft-turbulence Rayleigh-Bénard convection Journal Article European Physical Journal E : Soft Matter, 42 (9), 2019, ISSN: 1292-8941. | |
Stampnet: unsupervised multi-class object discovery Inproceedings 2019 IEEE International Conference on Image Processing, ICIP 2019 - Proceedings, pp. 2951–2955, Institute of Electrical and Electronics Engineers, United States, 2019. | |
Particle settling in a fluctuating multicomponent fluid under confinement Journal Article arXiv, 2019, (12pages, 7 figures). | |
Unified theoretical and experimental view on transient shear banding Journal Article arXiv, 2019, (5 pages, 4 figures - supplemental 5 pages, 4 figures). | |
Sharp transitions in rotating turbulent convection: Lagrangian acceleration statistics reveal a second critical Rossby number Journal Article Physical Review Fluids, 4 (7), pp. 1–19, 2019, ISSN: 2469-990X, (16 pages, 9 Figures). | |
New approaches to evacuation modelling for fire safety engineering applications Journal Article Fire Safety Journal, 106 , pp. 197–209, 2019, ISSN: 0379-7112. | |
Path-integral representation of diluted pedestrian dynamics Book Chapter Complexity science, pp. 329–346, World Scientific, United States, 2019, ISBN: 978-981-323-959-3. | |
Topical issue on fluids and structures: multi-scale coupling and modeling Journal Article European Physical Journal E : Soft Matter, 42 (3), pp. 28, 2019, ISSN: 1292-8941. | |
Fixation probabilities in weakly compressible fluid flows Journal Article Proceedings of the National Academy of Sciences of the United States of America (PNAS), 116 (2), pp. 373–378, 2019, ISSN: 0027-8424. | |
A glossary for research on human crowd dynamics Journal Article Collective Dynamics, 4 , pp. 1–13, 2019, ISSN: 2366-8539. | |
Flowing matter Book Springer, Germany, 2019, ISBN: 978-3-030-23369-3. | |
Thermally responsive particles in Rayleigh-Bénard convection Inproceedings M Gorokhovski; F S Godeferd (Ed.): Turbulent Cascades II, pp. 227–235, Springer, Germany, 2019, ISBN: 978-3-030-12546-2. | |
2018 |
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Physics-based modeling and data representation of pairwise interactions among pedestrians Journal Article Physical Review E, 98 (6), 2018, ISSN: 2470-0045. | |
Effect of particle shape on fluid statistics and particle dynamics in turbulent pipe flow Journal Article European Physical Journal E : Soft Matter, 41 (10), 2018, ISSN: 1292-8941. | |
Evolution of populations expanding on curved surfaces Journal Article EPL, 123 (5), 2018, ISSN: 0295-5075. | |
A numerical tool for the study of the hydrodynamic recovery of the Lattice Boltzmann Method Journal Article Computers & Fluids, 172 , pp. 241–250, 2018, ISSN: 0045-7930. | |
Hybrid lattice Boltzmann-direct simulation Monte Carlo approach for flows in three-dimensional geometries Journal Article Computers & Fluids, 172 , pp. 492–509, 2018, ISSN: 0045-7930. | |
Effects of thermal fluctuations in the fragmentation of a nanoligament Journal Article Physical Review E, 98 (1), 2018, ISSN: 2470-0045. | |
A large-scale real-life crowd steering experiment via arrow-like stimuli Inproceedings Proceedings of Pedestrian and Evacuation Dynamics 2018, 2018. | |
Computational study of radial particle migration and stresslet distributions in particle-laden turbulent pipe flow Journal Article European Physical Journal E, 41 (3), 2018. | |
Directional change of tracer trajectories in rotating Rayleigh-Benard convection Journal Article Physical Review E, 97 (6), 2018. | |
Hybrid lattice Boltzmann-Direct Simulation Monte Carlo approach for non-equilibrium flows in complex geometries Inproceedings Proceedings of the 5th European Conference on Microfluidics - mFlu18 & 3rd European Conference on Non-Equilibrium Gas Flows - NEGF18, February 28-March 2, 2018, Strasbourg, France, pp. 1–4, 2018. | |
Lattice Boltzmann simulations of droplet dynamics in time-dependent flows Journal Article European Physical Journal E, 41 (1), 2018. | |
Modelling sea ice and melt ponds evolution: sensitivity to microscale heat transfer mechanisms Journal Article arXiv, 2018 , 2018. | |
Simulation of Finite-Size Particles in Turbulent Flows Using the Lattice Boltzmann Method Journal Article Communications in Computational Physics, 23 (3), pp. 665-684, 2018. | |
2017 |
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Weakly supervised training of deep convolutional neural networks for overhead pedestrian localization in depth fields Inproceedings 2017 14th IEEE International Conference on Advanced Video and Signal Based Surveillance, AVSS 2017, pp. 1–6, Institute of Electrical and Electronics Engineers, United States, 2017, ISBN: 978-1-5386-2940-6. | |
Frame vs. trajectory analyses of pedestrian dynamics asymmetries in a staircase landing Journal Article Collective Dynamics, 1 (A10), pp. 1–26, 2017, ISSN: 2366-8539. | |
Copepods encounter rates from a model of escape jump behaviour in turbulence Journal Article Journal of Plankton Research, 39 (6), pp. 878-890, 2017. | |
Enhanced settling of nonheavy inertial particles in homogeneous isotropic turbulence: The role of the pressure gradient and the Basset history force Journal Article Physical Review E, 95 (2), 2017. | |
Finite-size effects on bacterial population expansion under controlled flow conditions Journal Article Scientific Reports, 7 , 2017. | |
Flowing Matter 2017 Journal Article Applied Rheology, 27 (3), pp. 47-49, 2017. | |
Fluctuations around mean walking behaviors in diluted pedestrian flows Journal Article Physical Review E, 95 (3), 2017. | |
Geometry of tracer trajectories in rotating turbulent flows Journal Article Physical Review Fluids, 2 (4), 2017. | |
2017, (2017 International Conference on Environmental Psychology (ICEP 2017), August 30- September 1, 2017, Coru~na, Spain, ICEP 2017 ; Conference date: 30-08-2017 Through 01-09-2017). | |
Multiscale anisotropic fluctuations in sheared turbulence with multiple states Journal Article Physical Review Fluids, 2 (5), 2017. | |
TurBase: a software platform for research in experimental and numerical fluid dynamics Book 2017. | |
Weakly supervised training of deep convolutional neural networks for overhead pedestrian localization in depth fields Book 2017. | |
2016 |
|
Fluctuations around mean walking behaviours in diluted pedestrian flows Journal Article arXiv.org, e-Print Archive, Physics, (1610.07429v1), pp. 1–10, 2016. | |
Continuous measurements of real-life bidirectional pedestrian flows on a wide walkway Journal Article arXiv, pp. 1–9, 2016, (9 pages, 7 figures). | |
Eulerian vs. Lagrangian analyses of pedestrian dynamics asymmetries in a staircase landing Book arXiv.org, 2016. | |
Preferential rotation of chiral dipoles in isotropic turbulence Journal Article arXiv.org, e-Print Archive, Physics, 2016. | |
Asymmetric pedestrian dynamics on a staircase landing from continuous measurements Book Chapter V L Knoop; W Daamen (Ed.): Traffic and Granular Flow '15, pp. 49–56, Springer, Germany, 2016, ISBN: 978-3-319-33481-3, (8 pages). | |