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The effectiveness of virtual driving instruction can increase when techniques that automatically distinguish between violations and errors are available, two behaviours requiring different types of remediation. This study reports the analysis of the objectively measured performance of 520 participants completing a simulation-based training programme. Factor analysis of failure reasons showed that violations and errors were the primary underlying factors. Men committed more violations and women made more errors; the magnitude of sex differences corresponded to the factor loadings. Factor analysis of the mean task completion times yielded a factor that can be described as the extent to which motivation for speed resulted in quicker task execution. Quicker participants completed more tasks, committed more violations, but made fewer errors. Participants reduced errors during forced-paced driving and increased speed during self-paced driving. The authors would recommend exploiting the distinction between violations and errors by developing interfaces and feedback for both types of aberration.

Primary break‐up of liquid jets is often encountered in industrial processes and is scientifically challenging due to its complexity. An accurate description of the break‐up length and droplet sizes is critical for controlling the jet dynamics and hence the process performance. Despite the extensive research performed on jet break‐up, the existing correlations are not universally applicable to all encountered flow conditions. In this article, we perform Direct Numerical Simulation of a cylindrical liquid jet using the Local Front Reconstruction Method (LFRM) to track the liquid‐gas interface. Experiments are also carried out to validate the simulation results in the same range of Reynolds and Weber numbers. The LFRM method is able to accurately reproduce the experimental break‐up lengths and droplet diameters. The surface waves propagating along the jet are compared with the dominant wavelengths reported in literature. It can be concluded that LFRM can accurately describe the dynamics of laminar jets. [ABSTRACT FROM AUTHOR]

In biomass processing fluidized beds are used to process granular materials where particles typically possess elongated shapes. However, for simplicity, in computer simulations particles are often considered spherical, even though elongated particles experience more complex particle–particle interactions as well as different hydrodynamic forces. The exact effect of these more complex interactions in dense fluidized suspensions is still not well understood. In this study we use the magnetic particle tracking technique to compare the fluidization behavior of spherical particles to that of elongated particles. We found a considerable difference between fluidization behavior of spherical versus elongated particles in the time-averaged particle velocity field as well as in the time-averaged particle rotational velocity profile. Moreover, we studied the effect of fluid velocity and the particle's aspect ratio on the particle's preferred orientation in different parts of the bed, which provides new insight in the fluidization behavior of elongated particles. [ABSTRACT FROM AUTHOR]

In chemical industry, flows often occur in nontransparent equipment, for example in steel pipelines and vessels. Magnetic resonance imaging is a suitable approach to visualize the flow, which cannot be performed with classical optical techniques, and obtain quantitative data in such cases. It is therefore a unique tool to noninvasively study whole‐field porosity and velocity distributions in opaque single‐phase porous media flow. In this article, experimental results obtained with this technique, applied to the study of structure and hydrodynamics in packed beds of spherical particles, are shown and compared with detailed computational fluid dynamics simulations performed with an in‐house numerical code based on an immersed boundary method‐direct numerical simulation approach. Pressure drop and the radial profiles of porosity and axial velocity of the fluid for three packed beds of spheres with different sizes were evaluated, both experimentally and numerically, in order to compare the two approaches. © 2018 The Authors AIChE Journal published by Wiley Periodicals, Inc. on behalf of American Institute of Chemical Engineers AIChE J, 64: 1896–1907, 2018 [ABSTRACT FROM AUTHOR]

A complete knowledge of the effect of droplet viscosity on droplet-droplet collision outcomes is essential for industrial processes such as spray drying. When droplets with dispersed solids are dried, the apparent viscosity of the dispersed phase increases by many orders of magnitude, which drastically changes the outcome of a droplet-droplet collision. However, the effect of viscosity on the droplet collision regime boundaries demarcating coalescence and reflexive and stretching separation is still not entirely understood and a general model for collision outcome boundaries is not available. In this work, the effect of viscosity on the droplet-droplet collision outcome is studied using direct numerical simulations employing the volume of fluid method. The role of viscous energy dissipation is analysed in collisions of droplets with different sizes and different physical properties. From the simulations results, a general phenomenological model depending on the capillary number (Ca, accounting for viscosity), the impact parameter (B), theWeber number (We), and the size ratio (Δ) is proposed. [ABSTRACT FROM AUTHOR]

Direct numerical simulation results for gas flow through dynamic suspensions of spherical particles is reported. The simulations are performed using an immersed boundary method, with careful correction for the grid resolution effect. The flow systems we have studied vary with mean flow Reynolds number, solids volume fraction, as well as particle/gas density ratio. On the basis of the simulation results, the effect of particle mobility on the gas-solid drag force is analyzed and introduced into the existing drag correlation that was derived from simulations of stationary particles. This mobility effect is characterized by the granular temperature, which is a result of the particle velocity fluctuation. The modified drag correlation is considered so-far the most accurate expression for the interphase momentum exchange in computational fluid dynamics models, in which the gas-solid interactions are not directly resolved. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1958-1969, 2016 [ABSTRACT FROM AUTHOR]

In this paper we report the extension of an earlier reported DNS method (Deen et al., 2012; Deen and Kuipers, 2013) based on a novel Immersed Boundary Method (IBM) which incorporates the fluid-solid coupling at the level of the discrete field equations. The extended method is used to study coupled mass and heat transport in dense fluid-particle systems where the coupling arises as a consequence of an exothermal chemical reaction proceeding at the exterior surface of the particles. Following a detailed verification (using an independent numerical technique) and validation (using established empirical correlations) we apply our DNS technique to study coupled mass and heat transfer in a dense fluid-particle system. In addition a comparison is made with results obtained from a simple one-dimensional (1D) heterogeneous reactor model which uses empirical closures for the fluid-particle mass and heat transfer coefficients. The main features of the complex transient temperature profiles obtained from our DNS agree quite well with the corresponding profiles obtained from the 1D heterogeneous reactor model. [ABSTRACT FROM AUTHOR]

In this paper, a novel simulation technique is presentedto performdirect numerical simulation (DNS) of fluid flow and mass transferin dense fluid–particle systems. The fluid–solid couplingis achieved via direct (i.e., implicit) incorporation of the boundarycondition (with a second-order method) at the surface of the particlesat the level of the discrete momentum and species conservation equationsof the fluid. A fixed (Eulerian) grid is utilized to solve the Navier–Stokesequations for the entire computational domain. Dissipative particle–particleand/or particle–wall collisions are taken into account viaa hard-sphere discrete particle (DP) approach, using a three-parameterparticle–particle interaction model that accounts for normaland tangential restitution, as well as tangential friction. Followingthe verification of our method using well-known empirical expressionsfor the Sherwood number, we apply our method to study fluid–particlemass transfer in dense multiparticle systems involving random arraysof stationary particles. [ABSTRACT FROM AUTHOR]

The article presents the findings of a study on flow regimes seen during spout-fluid bed operation. The study involved a three-dimensional spout-fluid bed, which employed spectral analysis of pressure drop fluctuations and fast video recordings, and three-dimensional Euler-Lagrangian computations. The model was able to predict the appropriate regime, but overpredicted the frequency at which the largest power was found. The remaining differences between the simulated and the experimentally observed bed behavior were attributed to the representation of effective fluid-particle interaction in the model.

We investigate the dynamics of a liquid droplet in contact with a surface of a porous structure by means of the pore-scale level, fully resolved numerical simulations. The geometrical details of the solid porous matrix are resolved by a sharp interface immersed boundary method on a Cartesian computational grid, whereas the motion of the gas-liquid interface is tracked by a mass conservative volume of fluid method. The numerical simulations are performed considering a model porous structure that is approximated by a 3D cubical scaffold with cylindrical struts. The effect of the porosity and the equilibrium contact angle (between the gas-liquid interface and the solid struts) on the spreading behavior, liquid imbibition, and apparent contact angle (between the gas-liquid interface and the porous base) are studied. We also perform several simulations for droplet spreading on a flat surface as a reference case. Gas-liquid systems of the Laplace number, La = 45 and La = 144 × 103 are considered neglecting the effect of gravity. We report the time exponent (n) and pre-factor (C) of the power law describing the evolution of the spreading diameter (S = Ctn) for different equilibrium contact angles and porosity. Our simulations reveal that the apparent or macroscopic contact angle varies linearly with the equilibrium contact angle and increases with porosity. Not necessarily for all the wetting porous structures, a continuous capillary drainage occurs, and we find that the rate of the capillary drainage very much depends on the fluid inertia. At La = 144 × 103, numerically we capture the capillary wave induced pinch-off and daughter droplet ejection. We observe that on the porous structure the pinch-off is weak compared to that on a flat plate. [ABSTRACT FROM AUTHOR]

This paper reviews the use of direct numerical simulation (DNS) models for the study of mass, momentum and heat transfer phenomena prevailing in dense gas-solid flows. In particular, we consider the DNS models as the first important step in a multiscale modeling strategy. Both the merits and the limitations of different DNS methods are discussed, in particular for the field of fluidized bed modeling. The importance of the closures for interfacial transfer of mass, momentum and heat, obtained from DNS and applied in coarser scale models, is demonstrated with illustrative examples. Finally, we present our view on required future developments of DNS models for the investigation of various chemical engineering problems. [ABSTRACT FROM AUTHOR]