Collective motion can be observed in many systems at various length scales. Ranging from the interaction of microswimmers at the microscopic scale to the dynamics of people and flocking behaviours of birds at the macroscopic scale, the natural world is home to many examples of collective responses. The emergence of collective motion in systems has long fascinated the scientific community with the classical approach for their study based on experimental observation. However, the development of suitable computer algorithms has significantly supplemented and complemented these empirical studies while also motivating new research fields on collective behaviour. This chapter outlines methods for measuring collective motion and key algorithms for the simulation of collective responses in birds, fish, mammals and people.

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The aim of many industrial processes is to manipulate solid particle aggregates within gas suspensions. Prime examples of such processes include fluidised bed reactors, cyclone separators, and dust collectors. In recent years, fluidised bed reactors have been used in the gasification of biomass particles. When fluidised, these particles are subject to various hydrodynamic forces such as drag, lift and torque due to interactions with the fluid. Computational approaches, which can be used to replicate laboratory and industrial scale processes, offer a crucial method for the study of reactor design and for the formulation of optimal operating procedures. Until now, many computer models have assumed particles to be spherical whereas, in reality, biomass feedstocks typically consist of non-spherical particles. While lift and torque are of minimal importance for spherical particles, non-spherical particles experience varying lift force and torque conditions, depending on particle orientation relative to the direction of the fluid velocity. In this study, we present a numerical investigation on the effect of different lift force and torque correlations on fluidised spherocylindrical particles. We find that lift force has a significant influence on particle velocities parallel to the direction of gravity. On the other hand, particle orientation is dependent on hydrodynamic torque. Results from this numerical study provide new insight with regards to the dynamics of non-spherical particles that can be of paramount importance for industrial processes involving non-spherical particles.

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In this paper, we present a number of key numerical methods that can be used to study elongated particles in fluid flows, with a specific emphasis on fluidised beds. Fluidised beds are frequently used for the production of biofuels, bioenergy, and other products from biomass particles, which often have an approximate elongated shape. This raises numerous issues in a numerical approach such as particle-particle contact detection and the accurate description of the various hydrodynamic forces, such as drag, lift, and torque, that elongated particles experience when moving in a fluid flow. The modelling is further complicated by a separation of length scales where industrial flow structures that can extend for many metres evolve subject to solid-solid and solid-fluid interactions at the millimetre scale. As a result, it is impossible to simulate both length scales using the same numerical approach, and a multiscale approach is necessary. First, we outline the direct numerical simulation (DNS) approach that may be employed to estimate hydrodynamic force closures for elongated particles in a fluid flow. We then describe the key aspects of a CFD-DEM approach, which can be used to simulate laboratory scale fluidisation processes, that must be addressed to study elongated particles. Finally, we briefly consider how current industrial-scale models, which concretely assume particle sphericity, could be adapted for the simulation of large collections of elongated particles subject to fluidisation.

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The various radiation types that make up the electromagnetic (EM) spectrum are ubiquitous and highly significant in modern society. Detection of visible light by the eye facilitates sight, radio waves and microwaves are used in communication technologies, x-rays are used in medical imaging, and gamma rays are frequently employed in medical procedures. Although radiation plays a predominant role in daily life, many students have developed and retain misconceptions concerning EM radiation. These misconceptions could be addressed through the use of popular culture content such as superheroes in the classroom. In a number of superhero narratives, EM radiation plays a key role in the emergence or development of superpowers. In this paper, we outline three approaches for using superheroes to support the learning of the EM spectrum, and to potentially address key student misconceptions. In one approach we have designed a student worksheet based on Captain America and vita-rays, a fictional radiation type that plays a key role in his superpowers. The worksheet has been designed to instigate critical reflection on the part of the student, while allowing the student to apply their understanding of other forms of radiation.

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An updated mesoscopic model for transient forces between two star polymers is presented. Calculation of the transient forces is based on the response of a vectorial structure parameter between two star polymers and differs from previous models that used a scalar structure parameter. The update of the model is motivated by the occurrence of two distinct processes in previous small-scale simulations of two star polymers moving past each other. A simple model that takes these processes into account turns out to fit into an obvious generalization of the RaPiD model introduced by us some time ago. The model reproduces forces from the simulation quite well, and at the same time removes an unphysical feature of the RaPiD model used so far.@en

Communication of difficult concepts in the physics classroom can be negatively affected by the absence of a strong link between physics content and the experiences or interests of students. One possible method towards addressing this issue is to motivate physics content with reference to popular culture figures such as superheroes. We find ourselves in an age where superhero films are immensely popular with numerous superhero films scheduled for release over the coming years. With many students familiar with many of these characters and their superpowers, superheroes can facilitate a unique platform to aid in the dissemination of physics materials in the classroom. In this paper, we present three examples where superheroes can be used to motivate learning objectives in physics and, if desired, promote critical thinking on behalf of the student. We also reflect on how using the superhero genre in the classroom can be used to address underrepresentation of women, stereotyping, and diversity issues in physics.@en

The X-Men are an ensemble of superheroes whose powers are associated with the X-Gene, a mutant genetic factor. The powers exhibited by each character differ and are dependent on how the X-Gene has modified their individual genomes. For instance, Wolverine possesses regenerative healing, Storm can control local weather systems, and Colossus can create an impenetrable "organic steel" layer around his body. Thanks to the establishment of the superhero genre in modern cinema, audiences are familiar with Colossus from films such as X-Men: Days of Future Past and Deadpool. While attaining this power might be attractive to many people, there are innumerate scientific obstacles to be overcome to replicate this "organic steel" layer. Due to its unique combination of high strength and flexibility, a graphene-based layer might be a more realistic material for Colossus' impenetrable skin and would also address a number of physiological issues associated with an "organic steel" layer. The actualization of this layer would depend on complex processes associated with protein folding, protein self-assembly, and changing the structure of his skin. In the classroom, Colossus can foster a multidisciplinary learning environment where concepts in physiology can overlap with topics in physics, engineering, and materials science. Just like other superheroes, Colossus can also be used to promote scientific content in outreach for the general public.@en

The ability of a highly coarse-grained polymer model is explored to simulate the impact of carbon black (CB) filler concentration on the rheological properties of unvulcanized styrene–butadiene melts—an intermediate stage in the production of styrene–butadiene rubber (SBR) commonly used in tyres. Responsive particle dynamics (RaPiD), previously used to study dilute polymeric systems, models entire polymers as single particles interacting through a combination of conservative interactions and transient entanglement-mimicking forces. The simulation parameters are tuned to the linear rheology of the unfilled melt, as measured using a rubber process analyzer (RPA). For the filled compounds, only the interaction between the polymers and fillers is varied. On top of excluded volume interactions, a slight attraction (≈0.1 kBT) between polymers and fillers is required to attain agreement with RPA measurements. The physical origins of the small strength of this interaction are discussed. This method offers potential for future numerical investigations of filled melts.@en

In industry we encounter many processes that rely on equipment in which particles are suspended by a gas flow, such as pneumatic conveyors, CFB gasifiers, combustors and fluidized bed reactors. In numerical models of these processes, particles have traditionally been represented as spheres, thus limiting complexities associated with drag or lift forces. However, spherical particles are not representative of the entities encountered in real systems. For example, non-spherical biomass particles of varying aspect ratios are used in the production of biomass fuels. Thus far literature is quite limited when it comes to hydrodynamic forces experienced by non-spherical particles under fluidized conditions. In fluidized beds, particles will experience varying lift force conditions dependent on the orientation of the particle relative to the direction of the flow. In this study, we investigate numerically the effect of different lift force coefficient correlations on fluidization of spherocylindrical particles. We employ correlations derived from previous simulations on non-spherical particles and aerofoil dynamics in simulations. We also look into the effect of the Di Felice approximation, in this case applied to take into account the effect of surrounding particles on the lift force. Particle interactions are modelled using the Open Source engine CFDEM, which uses the OpenFOAM computational fluid dynamics (CFD) solver to describe the fluid component and LIGGGHTS to implement discrete element method (DEM) calculations. We investigate the importance of lift forces on non-spherical particles under dense fluidised conditions and compare results to the case of spherical particles where lift forces are often neglected.@en

We present results from a new variant of a diffusion hopping model, the convective diffusive lattice model, to describe the behavior of a particulate flux around bluff obstacles. Particle interactions are constrained to an underlying square lattice where particles are subject to excluded volume conditions. In an extension to previous models, we impose a real continuous velocity field upon the lattice such that particles have an associated velocity vector. We use this velocity field to mediate the position update of the particles through the use of a convective update after which particles also undergo diffusion. We demonstrate the emergence of an expected wake behind a square obstacle which increases in size with increasing object size. For larger objects we observe the presence of recirculation zones marked by the presence of symmetric vortices in qualitative agreement with experiment and previous simulations.@en

Multiphase (gas-solid) flows are encountered in numerous industrial applications such as pharmaceutical, food, agricultural processing and energy generation. A coupled computational fluid dynamics (CFD) and discrete element method (DEM) approach is a popular way to study such flows at a particle scale. However, most of these studies deal with spherical particles while in reality, the particles are rarely spherical. The particle shape can have significant effect on hydrodynamics in a fluidized bed. Moreover, most studies in literature use inaccurate drag laws because accurate laws are not readily available. The drag force acting on a non-spherical particle can vary considerably with particle shape, orientation with the flow, Reynolds number and packing fraction. In this work, the CFD-DEM approach is extended to model a laboratory scale fluidized bed of spherocylinder (rod-like) particles. These rod-like particles can be classified as Geldart D particles and have an aspect ratio of 4. Experiments are performed to study the particle flow behavior in a quasi-2D fluidized bed. Numerically obtained results for pressure drop and bed height are compared with experiments. The capability of CFD-DEM approach to efficiently describe the global bed dynamics for fluidized bed of rod-like particles is demonstrated.

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Particle aggregates are frequently processed in industrial apparatus such as pneumatic conveyors, bed gasifiers and fluidised bed reactors. In numerical models of these processes, particles have traditionally been represented as spheres, thus limiting complexities associated with drag or lift forces. However, spherical particles are not representative of the entities encountered in real systems. For example, non-spherical biomass particles of varying aspect ratios are used in the production of biomass fuels. Thus far, there is limited literature in relation to hydrodynamic forces experienced by non-spherical particles under fluidised conditions. In fluidised beds, particles will experience varying lift force conditions dependent on the orientation of the particle relative to the direction of the fluid velocity. In this study, we investigate numerically the effect of differing lift force coefficient correlations on spherocylindrical particles of varying aspect ratios. We employ correlations derived from previous simulations on non-spherical particles [1] and aerofoil dynamics [2] in simulations. Particle interactions are modelled using the Open Source engine CFDEM, which uses the OpenFOAM computational fluid dynamics (CFD) solver to describe the fluid component and LIGGGHTS to implement discrete element method (DEM) calculations [3]. We investigate the importance of lift forces on non-spherical particles under dense fluidised conditions and compare results to the case of spherical particles where lift forces are often neglected.@en