The increasing amount of solid waste, e.g., waste tyres from car industry and tailings from mine operations, causes substantial environmental and societal issues. The recycled tyre polymer fibre (RTPF) reinforced cemented tailings backfill (CTB) is a kind of composite that can treat waste tyres and tailings simultaneously and realize green mining, but its engineering properties have not been well understood. In this study, the rheology (i.e., static and dynamic yield stress, and structural build-up), strength (i.e., uniaxial and triaxial compressive, splitting tensile and flexural strengths), microstructure, and life cycle of RTPF reinforced CTB are comprehensively evaluated. For comparison, the engineering performance of the commonly used polypropylene fibre (PPF) reinforced CTB in mines is tested. The experimental results demonstrate that incorporating 0.6 wt% RTPF into CTB can achieve comparable fluidity and strength to the CTB reinforced with 0.3 wt% PPF at reduced cost and improved sustainability. A strength enhancement approach for RTPF reinforced CTB is also developed by adjusting the viscosity of suspending CTB before the addition of RTPF. With this approach, the splitting tensile strength increases by 68 %. The results obtained from this study pave the way for promoting the recycling of abandoned waste tyres and the safe design of backfill structures in mines.@en

Autonomous flight for UAVs relies on visual information for avoiding obstacles and ensuring safe collision-free flight. In addition to visual clues, safe UAVs often need connectivity with the ground station. In this article, we study the synergies between vision and communications for edge-computing-enabled UAV flight. By proposing a framework of edge computing assisted autonomous flight (ECAAF), we illustrate that vision and communications can interact with and assist each other with the aid of edge computing and offloading, and further speed up UAV mission completion. ECAAF consists of three functionalities that are discussed in detail: edge computing for 3D map acquisition, radio map construction from the 3D map, and online trajectory planning. During ECAAF, the interactions of communication capacity, video offloading, 3D map quality, and channel state of the trajectory form a positive feedback loop. Simulation results verify that the proposed method can improve mission performance by enhancing connectivity. Finally, we conclude with some future research directions.

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Recently, we have extended the kinetic theory of granular flow (KTGF) to include friction between the spherical particles and tested it in rectangular geometries. In this study, the extended KTGF implemented in cylindrical coordinates is used to model the more-commonly employed cylindrical bubbling fluidized beds. Special attention is paid to the anti-symmetric part of the velocity gradient in the solids stress tensor. For verification of the implementation, a comparison of the present model in the limit of zero friction with the original (frictionless) KTGF model was made. Subsequently, simulations of bubbling fluidized beds of inelastic particles were performed using our extended KTGF and an effective KTGF model for inelastic particles of Jenkins and Zhang. The simulation results show good agreement for the time-averaged solids volume fraction distribution and solids circulation patterns. Finally, our model is validated by predicting the individual bubble behavior in dense bubbling fluidized beds containing different granular materials in a comparison with experimental data from Verma et al. (2014). The extended KTGF leads to an improved agreement with experimental bubble data. Compared to previous work (Yang et al., 2016b, 2017c), and by introducing cylindrical coordinates, the current work demonstrates that the extended KTGF improves predictions for the temporal bubble behavior of cylindrical fluidized beds.@en

We derive new boundary conditions (BCs) for collisional granular flows of spheres at flat frictional walls. A new theory is proposed for the solids stress tensor, translational and rotational energy dissipation rate per unit area and fluxes of translational and rotational fluctuation energy. In the theory we distinguish between sliding and sticking collisions and include particle rotation. The predictions are compared with literature results obtained from a discrete particle model evaluated at a given ratio of rotational to translational granular temperature. We find that the new theory is in better agreement with the observed stress ratios and heat fluxes than previous kinetic theory predictions. Finally, we carry out two fluid model simulations of a bubbling fluidized bed with the new BCs, and compare the simulation results with those obtained from discrete particle simulations. The comparison reveals that the new BCs are better capable of predicting solids axial velocity profiles, solids distribution near the walls and granular temperatures.@en

The effect of normal restitution coefficient and friction coefficient on the hydrodynamics of a dense bubbling solid-gas fluidized bed is investigated using a two fluid model (TFM) based on our kinetic theory of granular flow (KTGF) for rotating frictional particles. A comparison between TFM simulations using the present KTGF model, and a simpler KTGF model for rapid flows of slightly frictional, nearly elastic spheres derived by Jenkins and Zhang [1], is carried out. The simulation results reveal that both the coefficient of normal restitution and friction coefficient play an important role in the homogeneity of the bubbling bed. The particle friction has a strong effect on the solids flow patterns and distribution, while the normal restitution coefficient has a relatively small effect on both. The present model also predicts a larger amount of energy dissipation caused by the inclusion of particle friction. The present KTGF model leads to better agreement with detailed discrete particle model (DPM) simulation results for the axial particle velocity profiles and solids volume fraction distribution@en

Cylindrical fluidized beds are mostly encountered in industry. This work involves a study of the hydrodynamics of large scale cylindrical fluidized beds. The Euler-Euler approach (two-fluid model) is considered to be the most effective for these larger scale applications. The challenge of this model incorporated with kinetic theory of granular flow (KTGF) is to establish an accurate hydrodynamic and rheological description of the solid phase. KTGF for frictional spheres developed by Yang et al. (2016) has been incorporated into our in-house two-fluid model (TFM) code for the modeling 3D cylindrical bubbling fluidized beds. For verification, a comparison of the present model in the limit of zero friction with the original (frictionless) KTGF model is made. Simulation results of both models agree well. Numerical tests on bubbling fluidized beds are carried out using present KTGF and the KTGF model from Jenkins and Zhang (2002). The simulation results show good agreement with the simulation results obtained from the KTGF model from Jenkins and Zhang for solids circulation pattern and solids volume fraction distribution. In addition, a comparative study has been performed to investigate the effects of inlet gas velocity on bubble behavior in fluidized beds.@en

Eulerian models incorporating kinetic theory of granular flow (KTGF) are widely used to simulate gassolids flow. The most widely used KTGF models have been derived for dilute flows of slightly inelastic, frictionless spheres. In reality, however, granular materials are mostly frictional. Attempts to quantify the friction effect have been somewhat limited. In this work, we focus on the validation of the KTGF model for rough spheres derived by Yang et al. (2016a, b) and the corresponding BCs from Yang et al. (2016c) for frictional walls. The present TFM simulations are validated by comparing with magnetic particle tracking (MPT) experimental data and results obtained from discrete particle model (DPM) simulations of a pseudo-2D bubbling fluidized bed. Numerical results are compared with respect to particle distribution, solids velocities, and energy balance in the bed. On comparison with a simple kinetic theory derived by Jenkins and Zhang (2002), we find that present model improves the predictions for particle axial velocity and flux upon simulation of inelastic rough particles. In conclusion, the current KTGF model obtains excellent agreement with experiment and discrete particle simulation for the time-averaged bed hydrodynamics.@en