scholarly journals A unified multiscale vision of behavioral crowds

2019 ◽  
Vol 30 (01) ◽  
pp. 1-22 ◽  
Author(s):  
Bouchra Aylaj ◽  
Nicola Bellomo ◽  
Livio Gibelli ◽  
Alessandro Reali
Keyword(s):  
Computational Model ◽  
Complex Interaction ◽  
Emotional States ◽  
Complex Environments ◽  
Flow Conditions ◽  
Unified Framework ◽  
Hydrodynamic Models ◽  
Local Flow ◽  
Microscopic Scale ◽  
Modeling Principles

This paper proposes a multiscale vision to human crowds which provides a consistent description at the three possible modeling scales, namely, microscopic, mesoscopic, and macroscopic. The proposed approach moves from interactions at the microscopic scale and shows how the same modeling principles lead to kinetic and hydrodynamic models. Hence, a unified framework is developed which permits to derive models at each scale using the same principles and similar parameters. This approach can be used to simulate crowd dynamics in complex environments composed of interconnected areas, where the most appropriate scale of description can be selected for each area. This offers a pathway to the development of a multiscale computational model which has the capability to optimize the granularity of the description depending on the pedestrian local flow conditions. An important feature of the modeling at each scale is that the complex interaction between emotional states of walkers and their motion is taken into account.

A numerical method for simulations of cohesive, porous sediments

2021 ◽  
Author(s):  
Alexander Metelkin ◽  
Bernhard Vowinckel
Keyword(s):  
Computational Model ◽  
Stokes Equations ◽  
Spatial Scales ◽  
Flow Characteristics ◽  
Hydrodynamic Forces ◽  
Cohesive Sediments ◽  
Flow Conditions ◽  
Mean Flow ◽  
Local Flow ◽  
Clay Particles

<p><span>The dynamics of cohesive sediments under various flow conditions </span><span>are </span><span>of special interest in the framework of aquatic ecosystems. Being one of the main sources of transport for minerals and organic matter, the constituents of cohesive sediments are the source of food for many aquatic organisms. Due to the additional complexity of physical mechanisms, there are only a few simulation techniques for cohesive sediments, which do not cover all spatial scales. The primary cohesive clay particles are platelets smaller than 2 μm, which is small enough to experience Brownian motion. Composed together under the influence of van der Waals forces, they shape rounded aggregates also known as microflocs that are rather stable. These microflocs can form fragile, larger macroflocs with complex shapes exceeding 100 μm in size. Owing to the huge difference in the spatial scales, it is almost impossible to simulate macroflocs as the assembly of primary clay particles in the context of cohesive sediment transport modeling. In contrast to separate sediment grains, microflocs represent porous aggregates. </span><span>T</span><span>o perform direct numerical simulations of microflocs transported in a viscous fluid flow, we are developing a computational model for immersed porous particles. The model resolves the flow outside and inside porous aggregates and accurately computes the hydrodynamic forces on the microflocs. The simulation of macroflocs is also attainable by employing </span><span>cohesive</span><span> forces between microflocs, which assembles them into bigger aggregates with the propensity of breaking up under high shear rates. Our computational model solves the system of Navier - Stokes equations directly with an additional Darcy term inside the porous aggregate. Using this approach, it becomes feasible to consider the influence of the flow inside porous media, so that we can study its impact on the mean flow characteristics depending on the properties of the porous flocs. The hydrodynamic forces are calculated implicitly based on the pressure and shear stress distribution. By comparison with methods that use Stokes-based drag coefficients, our approach allows estimating the influence of local flow conditions and the presence of neighboring aggregates on the resulting fluid force.</span></p><p><span> </span></p>

COMPUTATIONAL MODEL OF OBSESSIVE–COMPULSIVE DISORDER: A UNIFIED EXPLANATION OF THE TREATMENTS

2004 ◽  
Vol 14 (01) ◽  
pp. 263-277 ◽  
Author(s):  
SHIGERU KUBOTA ◽  
KAZUYUKI AIHARA
Keyword(s):  
Computational Model ◽  
Obsessive Compulsive Disorder ◽  
Common Property ◽  
Neural Network Modeling ◽  
Unified Framework ◽  
Obsessive Compulsive ◽  
Input Stimulus ◽  
Compulsive Disorder ◽  
The Stability ◽  
Stored Information

We propose a computational model explaining the pharmacological, behavioral, and neurosurgical treatments of obsessive–compulsive disorder (OCD) in a unified framework. On the basis of the concept that the striatum stores information linked to OCD symptoms, we analyze dynamical changes of a chaotic neural network modeling the striatum. The effect of pharmacological treatment is explained by the increase in refractoriness induced by the neurotransmitter serotonin. The effect of behavior therapy is explained by the time-variant input stimulus weakening neural interconnections according to the covariance rule concerning synaptic plasticity. The effect of neurosurgical treatment is explained by the lesions to the cortical-striatal-thalamic-cortical loop decreasing the feedback of the closed loop. These treatments have a common property that they decrease the stability of stored information in the striatum.

Local characteristic of horizontal air–water two-phase flow by wire-mesh sensor

2016 ◽  
Vol 40 (3) ◽  
pp. 746-761 ◽  
Author(s):  
Weiling Liu ◽  
Chao Tan ◽  
Feng Dong
Keyword(s):  
Void Fraction ◽  
Transient Flow ◽  
Two Phase Flow ◽  
Wire Mesh ◽  
Local Characteristic ◽  
Phase Flow ◽  
Flow Conditions ◽  
Two Phase ◽  
Horizontal Pipe ◽  
Local Flow

Two-phase flow widely exists in many industries. Understanding local characteristics of two-phase flow under different flow conditions in piping systems is important to design and optimize the industrial process for higher productivity and lower cost. Air–water two-phase flow experiments were conducted with a 16×16 conductivity wire-mesh sensor (WMS) in a horizontal pipe of a multiphase flow facility. The cross-sectional void fraction time series was analysed by the probability density function (PDF), which described the void fraction fluctuation at different flow conditions. The changes and causes of PDFs during a flow regime transition were analysed. The local structure and flow behaviour were characterized by the local flow spectrum energy analysis and the local void fraction distribution (horizontal, vertical and radial direction) analysis. Finally, three-dimensional transient flow fluctuation energy evolution and characteristic scale distribution based on wavelet analysis of air–water two-phase flow were presented, which revealed the structural features of each phase in two-phase flow.

Three-Dimensional Computational Model of Left Heart Diastolic Function With Fluid–Structure Interaction

1999 ◽  
Vol 122 (2) ◽  
pp. 109-117 ◽  
Author(s):  
Jack D. Lemmon ◽  
Ajit P. Yoganathan
Keyword(s):  
Cardiac Function ◽  
Computational Model ◽  
Diastolic Function ◽  
Flow Fields ◽  
Momentum Conservation ◽  
Immersed Boundary ◽  
Left Heart ◽  
Flow Conditions ◽  
Heart Model ◽  
Tissue Properties

Aided by advancements in computer speed and modeling techniques, computational modeling of cardiac function has continued to develop over the past twenty years. The goal of the current study was to develop a computational model that provides blood–tissue interaction under physiologic flow conditions, and apply it to a thin-walled model of the left heart. To accomplish this goal, the Immersed Boundary Method was used to study the interaction of the tissue and blood in response to fluid forces and changes in tissue pathophysiology. The fluid mass and momentum conservation equations were solved using Patankar’s Semi-Implicit Method for Pressure Linked Equations (SIMPLE). A left heart model was developed to examine diastolic function, and consisted of the left ventricle, left atrium, and pulmonary flow. The input functions for the model included the pulmonary driving pressure and time-dependent relationship for changes in chamber tissue properties during the simulation. The results obtained from the left heart model were compared to clinically observed diastolic flow conditions for validation. The inflow velocities through the mitral valve corresponded with clinical values (E-wave=74.4 cm/s, A-wave=43 cm/s, and E/A=1.73). The pressure traces for the atrium and ventricle, and the appearance of the ventricular flow fields throughout filling, agreed with those observed in the heart. In addition, the atrial flow fields could be observed in this model and showed the conduit and pump functions that current theory suggests. The ability to examine atrial function in the present model is something not described previously in computational simulations of cardiac function. [S0148-0731(00)01302-9]

Analysis of Local Flow Structure and Global Compressor Performance During Rotating Stall

2004 ◽  
Author(s):  
Chiara Palomba
Keyword(s):  
Flow Field ◽  
Flow Structure ◽  
Rotational Speed ◽  
Axial Flow ◽  
Rotating Stall ◽  
Performance Parameters ◽  
Flow Conditions ◽  
Local Flow ◽  
Flow Parameters ◽  
Compressor Performance

Rotating stall is an instability phenomenon that arises in axial flow compressors when the flow is reduced at constant rotational speed. It is characterised by the onset of rotating perturbations in the flow field accompanied by either an abrupt or gradual decrease of performances. Although the flow field is unsteady and non axisymmetric, the global operating point is stable and a stalled branch of performance curve may be experimentally determined. The number, rotational speed, circumferential extension of the rotating perturbed flow regions named rotating cells may vary from one compressor to another and may depend on the throttle position. The present work focuses on the interaction between local flow parameters and global compressor performance parameters with the aim of reaching a better understanding of the phenomenon. Starting from the Day, Greitzer and Cumpsty [1] model the detailed flow conditions during rotating stall are studied and related to the global performance parameters. This is done both to verify if the compressor under examination fits to the model and if the detailed flow structure may highlight the physics that in the simple model may hide behind the correlation’s used.

scholarly journals A particle-based model for endothelial cell migration under flow conditions

2019 ◽  
Vol 19 (2) ◽  
pp. 681-692
Author(s):  
P. S. Zun ◽  
A. J. Narracott ◽  
P. C. Evans ◽  
B. J. M. van Rooij ◽  
A. G. Hoekstra
Keyword(s):  
Experimental Data ◽  
Cell Migration ◽  
Flow Direction ◽  
Healing Process ◽  
Endothelial Cell Migration ◽  
Bottom Surface ◽  
Flow Conditions ◽  
Directed Movement ◽  
Local Flow

Abstract Endothelial cells (ECs) play a major role in the healing process following angioplasty to inhibit excessive neointima. This makes the process of EC healing after injury, in particular EC migration in a stented vessel, important for recovery of normal vessel function. In that context, we present a novel particle-based model of EC migration and validate it against in vitro experimental data. We have developed a particle-based model of EC migration under flow conditions in an in vitro vessel with obstacles. Cell movement in the model is a combination of random walks and directed movement along the local flow velocity vector. For model calibration, a set of experimental data for cell migration in a similarly shaped channel has been used. We have calibrated the model for a baseline case of a channel with no obstacles and then applied it to the case of a channel with ridges on the bottom surface, representative of stent strut geometry. We were able to closely reproduce the cell migration speed and angular distribution of their movement relative to the flow direction reported in vitro. The model also reproduces qualitative aspects of EC migration, such as entrapment of cells downstream from the flow-disturbing ridge. The model has the potential, after more extensive in vitro validation, to study the effect of variation in strut spacing and shape, through modification of the local flow, on EC migration. The results of this study support the hypothesis that EC migration is strongly affected by the direction and magnitude of local wall shear stress.

Update on covered endovascular reconstruction of the aortic bifurcation

Vascular ◽  
2020 ◽  
Vol 28 (3) ◽  
pp. 225-232
Author(s):  
Michel MPJ Reijnen
Keyword(s):  
Initial Data ◽  
Treatment Algorithm ◽  
Occlusive Disease ◽  
Surgical Reconstruction ◽  
Aortic Bifurcation ◽  
Flow Conditions ◽  
Local Flow ◽  
Current Review ◽  
Comparative Trials

Objective The covered endovascular reconstruction of the aortic bifurcation (CERAB) technique was introduced in 2009 in order to provide an anatomically and physiologically optimal endovascular reconstruction of the aortic bifurcation. Method In the current review, all available evidence on this technique was summarized. Results In vitro studies have shown a more favorable geometry of CERAB compared to kissing stents, leading to better local flow conditions. The results of CERAB are at least as good as those achieved with kissing stents in a more complex group of treated patients. The mid-term patency rates approach those of surgical reconstruction. Initial data show that the technique can also be used in combination with chimney grafts in order to preserve side branches. Conclusion CERAB has proven to be the most optimal endovascular treatment option for aorto-iliac occlusive disease with regard to geometry and flow and is related to promising clinical outcomes. Prospective and comparative trials are necessary to elucidate the most optimal treatment algorithm for patients with aorto-iliac occlusive disease.

scholarly journals Calibration of hydrological models for ecologically relevant streamflow predictions: a trade-off between fitting well to data and estimating consistent parameter sets?

2020 ◽  
Vol 24 (3) ◽  
pp. 1031-1054 ◽  
Author(s):  
Thibault Hallouin ◽  
Michael Bruen ◽  
Fiachra E. O'Loughlin
Keyword(s):  
Flow Regime ◽  
River Flow ◽  
Freshwater Ecosystems ◽  
Living Environment ◽  
Rate Of Change ◽  
Low Flow ◽  
Hydrological Models ◽  
Flow Conditions ◽  
Local Flow ◽  
Trade Off

Abstract. The ecological integrity of freshwater ecosystems is intimately linked to natural fluctuations in the river flow regime. In catchments with little human-induced alterations of the flow regime (e.g. abstractions and regulations), existing hydrological models can be used to predict changes in the local flow regime to assess any changes in its rivers' living environment for endemic species. However, hydrological models are traditionally calibrated to give a good general fit to observed hydrographs, e.g. using criteria such as the Nash–Sutcliffe efficiency (NSE) or the Kling–Gupta efficiency (KGE). Much ecological research has shown that aquatic species respond to a range of specific characteristics of the hydrograph, including magnitude, frequency, duration, timing, and the rate of change of flow events. This study investigates the performance of specially developed and tailored criteria formed from combinations of those specific streamflow characteristics (SFCs) found to be ecologically relevant in previous ecohydrological studies. These are compared with the more traditional Kling–Gupta criterion for 33 Irish catchments. A split-sample test with a rolling window is applied to reduce the influence on the conclusions of differences between the calibration and evaluation periods. These tailored criteria are shown to be marginally better suited to predicting the targeted streamflow characteristics; however, traditional criteria are more robust and produce more consistent behavioural parameter sets, suggesting a trade-off between model performance and model parameter consistency when predicting specific streamflow characteristics. Analysis of the fitting to each of 165 streamflow characteristics revealed a general lack of versatility for criteria with a strong focus on low-flow conditions, especially in predicting high-flow conditions. On the other hand, the Kling–Gupta efficiency applied to the square root of flow values performs as well as two sets of tailored criteria across the 165 streamflow characteristics. These findings suggest that traditional composite criteria such as the Kling–Gupta efficiency may still be preferable over tailored criteria for the prediction of streamflow characteristics, when robustness and consistency are important.

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